Geology of the Chang 7 Member oil ... - Petroleum Geoscience · Northwest Branch of Research...

Geology of the Chang 7 Member oil shale of the YanchangFormation of the Ordos Basin in central north China

Bai Yunlai amp Ma Yuhu

Northwest Branch of Research Institute of Petroleum Exploration and Development (NWGI) PetroChina Lanzhou 730020Gansu ChinaCorrespondence 782352398qqcom

Abstract We present a review of the Chang 7 Member oil shale which occurs in the middlendashlate Triassic YanchangFormation of the Ordos Basin in central north China The oil shale has a thickness of 28 m (average) an area of around30 000 km2 and a Ladinian age It is mainly brown-black to black in colour with a laminar structure It is characterized byaverage values of 18 wt TOC (total organic carbon) 8 wt oil yield a 835 MJ kgminus1 calorific value 400 kg tminus1 hydrocarbonproductivity and kerogen of type IndashII1 showing a medium quality On average it comprises 49 clay minerals 29 quartz16 feldspar and some iron oxides which is close to the averagemineral composition of global shale The total SiO2 and Al2O3

comprise 6369 wt of the whole rock indicating a medium ash type The SrBa is 033 the VNi is 78 the UTh is 48 and theFeOFe2O3 is 05 indicating formation in a strongly reducing freshwater or low-salinity sedimentary environmentMultilayered intermediate-acid tuff is developed in the basin which may have promoted the formation of the oil shaleThe Ordos Basin was formed during the northwards subduction of the Qinling oceanic plate during the LadinianndashNorian in aback-arc basin context The oil shale of the Ordos Basin has a large potential for hydrocarbon generation

SupplementarymaterialTables of oil-shale geochemical composition proximate and organic matter analyses from the Chang7 Member oil shale the Ordos Basin Central north China are available at httpsdoiorg106084m9figsharec4411703

Received 28 July 2018 revised 23 December 2018 accepted 17 February 2019

In addition to oil natural gas coal coal-seam gas uranium andgroundwater resources a large tonnage of oil shale is also present inthe Ordos Basin (Fig 1) which is one of the largest oil- and gas-bearing basins ranked second in oil and gas resources and first inannual production in China (Pan 1934 Yang 1991 2002 Wanget al 1992 Guan et al 1995 Zhang et al 1995 Yang amp Pei 1996Li 2000 Chen 2002 Liu amp Liu 2005 Lu et al 2006 Yang et al2006 2016a b Bai et al 2006 2009 2010a b 2011 Liu et al2009 Qian 2009Wang et al 2016 Deng et al 2017) The oil shalehas attracted considerable interest in recent years in the context ofglobal oil depletion and the search for unconventional energyresources The commercial potential of the oil shale has beenassessed and the resource may become more important as otherenergy reserves decline Recent research undertaken by theNorthwest Branch of the Research Institute of PetroleumExploration and Development (NWGI) PetroChina and othershas shown that the Ordos Basin contains more than 2000 times108 tonnes (t) of lsquoshale oilrsquo predicted resources of which the Chang7 Member shale oil comprises more than 1000 times 108 t that is 50of that occurring at depths of 0ndash2000 m in the entire basin TheChang 7Member oil shale also called lsquothe Zhangjiatan shalersquo in thenorthern Ordos Basin has an area of around 30 000 km2 an averagethickness of 28 m and an average oil yield of 8 wt It is both ahigh-quality source rock and an oil shale with a high residualorganic matter content and is the most important oil-shale seam inthe basin (Yang 2002 Duan et al 2004 Bai et al 2006 Yang et al2006 2016a b Zhang et al 2008b) It is located in the YanchangFormation (Fig 2) which was originally deposited over an areaof c 400 000 km2 during the middlendashlate Triassic with a currentarea of 250 000 km2 and current thicknesses of 184ndash2060 m(Yang 2002 Bai et al 2009)

The Yanchang Formation is a well-documented lithostratigraphicunit first discovered in the northern Shaanxi in 1926 byML Fullerand FG Clapp who described it as a set of stratigraphic units

including grey or green sandstone and shale (Fuller amp Clapp 1926Pan 1934 Yang 2002) Its reservoirs produce 90 of the oil in theOrdos Basin It is a group of terrestrial sequences of middlendashlateTriassic age and is composed of fluvial delta plain and lake faciesThe overlying strata of theYanchang Formation are the WayaobaoFormation which was a set of coal-bearing strata that originallybelonged to the upper Yanchang Formation but was later separatedfrom the Yanchang FormationThey contain 10 reservoir memberseach including both reservoir sands and (oil) shales (Fig 2) Theunits are numbered 1ndash10 from the top of theWayaobao Formation tothe bottom of the Yanchang Formation (ie opposite to the normalgeological convention) Chang 1 is now contained in the WayaobaoFormation but it is still called Chang 1 rather than the customarylsquoWa1rsquo Among them the Chang 6 and 8 members are the two mainoil reservoirs

The Chang 7 Member oil shale is a high-quality source rockwhich supplies oil for the reservoirs of the Yanchang Formationespecially the Chang 6 Member and Chang 8 Member reservoirsand it even supplies oil to reservoirs of the younger middle JurassicYanan Formation (Fig 2) Yang et al (2016a b) discovered that theoil derived from the Chang 7 Member oil shale also fills internalnano-sized pores and pore throats to form lsquoshale oilrsquo equivalent totight oil occurring naturally in oil-bearing shales which is isdifferent to lsquooil-shale-derived oilsrsquo (lsquooil shalersquo is an organic-richfine-grained sedimentary rock containing immature kerogen a solidmixture of organic chemical compounds from which liquidhydrocarbons can be produced by low-temperature pyrolysis)The Chang 7 Member oil shale and its host stratum the YanchangFormation have been investigated by the drilling of at least 57boreholes in the basin interior (Fig 1) Early in the last centuryoutcrops of the Chang 7 Member oil shale were investigated by PanZhongxiang (Pan 1934) who studied its distribution occurrenceand quality In the 1960s the Shaanxi Industrial Bureaucommenced open-cast mining of the oil shale which outcrops in

copy 2019 The Author(s) This is an Open Access article distributed under the terms of the Creative Commons Attribution 40 License (httpcreativecommonsorglicensesby40) Published by The Geological Society of London for GSL and EAGE Publishing disclaimer wwwgeolsocorgukpub_ethics

Review article Petroleum Geoscience

Published Online First httpsdoiorg101144petgeo2018-091

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Fig 1 (a) Location map showing two cross-sections through the Ordos Basin XndashX and YndashY together with outcrops of the middlendashlate Triassic and the oilshale (i) Location map of the Ordos Basin in China and (ii) the location map for Figure 5 (b) Cross-sections XndashX and (c) YndashY through the Ordos Basinshowing the spatial distribution of the Chang 7 Member oil shale and its host strata (modified and supplemented after Bai et al 2009 2010a b) Key QQuaternary System N Neogene System E Paleogene System Mz Mesozoic K Cretaceous System J Jurassic System T Triassic System C-PCarboniferousndashPermian systems isin-O CambrianndashOrdovician systems Pt Proterozoic Ar Archean

Y L Bai amp Y H Ma


the Tongchuan area in the southern margin of the basin Theyrefined the oil shale using a cracking process but the annual shale oilproduction was only 80ndash90 t and production was terminatedbecause of water shortages and technological shortcomings (Baiet al 2009) During 2000ndash08 several private enterprises attempted

to initiate oil shale production using the Fushun Furnace a smalllow-temperature pyrolysis furnace but all of them failed Since2005 given the heightened imperative for seeking alternativeenergy sources outcrops and drilling data for the oil shales inthe region were reinvestigated (Liu amp Liu 2005 Lu et al 2006

Fig 2 Strtigraphic chart summarizing the history of the Ordos Basin which is divided into five phases including the Meso-Neo Proterozoic the earlyPaleozoic the late Paleozoic the middlendashlate Triassic and the Jurassicndashearly Cretaceous (modified and supplemented after Bai et al 2009 2010b)(The width of the bars in the far-right column represents the importance of the resource)

Ordos oil shale


Liu et al 2006 2009 Qian 2009 Shu 2012 Bai et al 2009 2010ab 2011) Supported by PetroChina Professor Bai Yunlai conducteda high-quality study (Bai et al 2010b) However in generalresearch on the oil shale of the region remains sporadic andunsystematic This has hindered further exploration and exploitationof the oil shale resource moreover most of the research has beenpublished in Chinese making comparisons with comparabledeposits elsewhere more difficult

Previous research focused primarily on the characteristics of theoil shale especially its occurrence volume and quality Howeverlittle research has been conducted to address such key questions asHow and when did the oil shale form Is it Triassic or middlendashlateTriassic in age How did the basin accumulate such abundant oiland oil shale resources What was the tectonic settingWhat are theproperties of the basin Is it marine Is it an intracratonic basin or aforeland basin (Li 2000 Yang 2002 Yang amp Zhang 2005 Bai et al2006 Wang et al 2017) The present review seeks to address thesequestions

The structure of the present study is to summarize pre-existingresearch describe the characteristics of the Chang 7 Member oilshale and to discuss the environment and processes of formationThe overall aim is to provide a basis for future investigations of theOrdos Basin oil shale and to facilitate comparisons with similardeposits elsewhere

Geological context

Tectonic setting

The Ordos Lakewas located in the SW part of the North China Plateand at the northern edge of the Qinling orogenic belt (Figs 1 and 3)(Yang 1991 2002 Zhang et al 1995 Yang amp Pei 1996 Bai et al2006 Yang et al 2006 James 2012) The Qinling Ocean Platesubducted beneath the North China Plate in the middlendashlate

Triassic forming a volcanicndashmagmatic arc and back-arc basin onthe northern side of the volcanicndashmagmatic arc (Fig 3) (Wan 2004Chen 2010) Thick piedmont facies (up to 2400 m) are distributed inthe SW Ordos Basin and are called the Kongtongshan conglom-erates (the lower left part of Fig 1 highlights their location) Theyare regarded as the remnants of the foredeep deposits of the back-arcforeland basin most of which were destroyed subsequently Thesesuggest that the Ordos Lake environment was in fact a back-arcforeland basin with a similar structural mechanism to the KarooBasin in South Africa (Smith 1990)

Sedimentary fill

TheOrdosBasin has a sedimentary fill with amaximum thickness ofabout 12 800 m which has accumulated in varying tectonic settingsand different climatic regimes since the Proterozoic era (Fig 2)Broadly the Ordos area has experienced five sedimentary cyclesincluding (1) theMeso-Neo Proterozoic (2) the early Paleozoic (3)the late Paleozoic (4) the middlendashlate Triassic and (5) the Jurassicndashearly Cretaceous and in only the last three phases was the oil shaleformed In the Meso-Neo Proterozoic and the early Paleozoicthe marine facies carbonate sedimentary rocks accumulated on theOrdos area In the late Paleozoic 600ndash1400 m-thick deltaic andfluvial facies sandstone mudstone and coal and oil-shale seamsformed in a paralic environment at first under humid and later underdry and hot conditions (Fig 2) From the middle Triassic to theJurassic fluvial deltaic and lacustrine facies sandstone mudstoneand oil shale accumulated in terrestrial environments in a damp hotphase in general attaining 20ndash3000 m in thickness in the middlendashlate Triassic and 184ndash2060 m in the Jurassic There is also anunconformable blanket of Cretaceous sandstone and mudstone(terrestrial facies) that covers the entire basin varying from 600 to3000 m in thickness (Fig 2) Present day the southern Ordos area iscovered by nearly 100 m of Quaternary loess and the northern area is

Fig 3 Tectonic profiles and background during the middlendashlate Triassic (LadinianndashNorian) in the Ordos areas The top sketch shows a back-arc forelandbasin resulting from subduction of the Qinling oceanic plate and the bottom sketch shows the location of the Ordos Basin in the regional structure (afterWan 2004 Chen 2010 James 2012)

Y L Bai amp Y H Ma


beneath the Mu Us Desert (Fig 2) (Liu 1986 Bureau of Geology ampMineral Resources of Shaanxi Province (BGMRSP) 1989 1998Yang 1991 2002 Yang amp Pei 1996 Zhang et al 2005 Yang ampZhang 2005 Bai et al 2006 2013 2014 Yang amp Liu 2006 Yanget al 2006 2016a b) Based on analyses of previous works onvitrinite reflectance fluid inclusions and apatite fission tracks in thebasin Ren (1991) reconstructed the thermal history of the OrdosBasin depicting a temperature gradient of 22ndash30degC100 m fromthe Paleozoic to the early Mesozoic which increased to 33ndash45degC100 m in the late Mesozoic gradually decreasing to 28degC100 mduring the Cenozoic Research on the relationship between thethermal history and oil-gas accumulation of the Ordos Basinsuggests that (1) the low temperature gradient and low thermalmaturation of gas resource rockswere favourable for the preservationof organic matter from the Paleozoic to the early Mesozoic (2) thehigher temperature gradient in the Cretaceous (150minus125 Ma) wasresponsible for generating andmigrating gas from the Paleozoic coalseries and carbonates (Jia et al 2006) (3) the higher temperaturegradient during the Cretaceous was also responsible for maturingand migrating Triassic and Jurassic oils and (4) the decrease intemperature gradient during the Cenozoic was favourable to thepreservation of oil-gas fields Both the late generation ofhydrocarbons and the lack of faults in the Ordos Basin are keyfactors in preserving the hydrocarbon accumulations

Burial history analysis show that the strongest uplift and erosionevent took place at the end of the later Cretaceous and three weakeruplift and erosion events took place at the end of the late Triassic themiddle Jurassic and the late Jurassic (Chen et al 2006)

Characteristics of the oil shales and shale in different stratain the Ordos Basin

Since the late Paleozoic multiple oil-shale (shale) seams developedin different strata of the Ordos Basin in the late CarboniferousndashearlyPermian Taiyuan Formation the middlendashlate Triassic (LadinianndashNorian) Yanchang Formation the late Triassic (Rhaetian)Wayaobao Formation the middle Jurassic (AalenianndashBajocian)Yanan Formation and the middle Jurassic (BathonianndashCallovian)Anding Formation (Bai et al 2009 2010b)

The oil shales of the Taiyuan Formation were formed in a paralicenvironment Because of deep burial it is mature to overmaturewith the vitrinite reflectance of the shale verying from 09ndash25 Romost of the kerogen was converted to gasThe oil shales and coalsmainly crop out along the edge of the basin with a burial depthgreater than 600 m in the eastern part near Hancheng and attain amaximum burial depth of c 3000 m in the mid-western part(Qingshen-2 well) (Fig 1) The oil shale generally has a low oilyield (only 28 wt) and thin seams (c 2 m) forming a relativelylow-grade resource (Bai et al 2009)

The Jurassic oil-shale seams were mainly formed in a lake-deltaenvironment and are interbedded with coal seams The oil-shaleseams are thin and local and therefore are of low economic value(Bai et al 2009)

The Chang 9 7 4 + 5 and 1 Member oil shale (shale) occurred inthe Yanchang Formation and the Wayaobao Formation

The Chang 9Member oil shale also called lsquothe Lijiapan shalersquo inthe Ordos Basin is present at the top of the Chang 9 Member of theYanchang Formation The oil shale is mainly distributed in thenorth-central basin in Yanan Zhidan and Ansai counties It has anarea of 4336 km2 about one-seventh of the Chang 7 Member oilshale with a limited thickness of about 6 m It is characterized by arelatively large burial depth and a relatively low abundance oforganic matter (c 45 wt on average) (Zhang et al 2008a Zhouet al 2008) Its organic matter type is different to that of the Chang 7Member oil shale the sapropel content of the former is less than inthe latter A deep or semi-deep lake was formed during the interval

of accumulation of the Chang 9 Member which was supplied withlarge amounts of terrigenous material and a small amount of algalparent material The framboidal pyrite content is low Althoughindicating an overall euxinic environment the low framboidal pyritecontent in the Chang 9 Member oil shale indicates a weaklyoxidizingndashreducing environment

The Chang 7Member oil shale is widely distributed in the regionwith an area of around 30 000 km2 and a thickness of 28 m (averagethickness) It developed in an anoxic deep-lake environment (about60 m depth Yang et al 2016a) and is rich in framboidal pyritethere is a relatively small amount of clay minerals and abundantalgal material (Ji et al 2007) Although some of the oil from the oilshales have been migrated into oil reservoirs of the oilfields theresidual organic matter content is still very high about 18 wt TOC(see below) and the in situ oil shale resources account for more than50 of the total oil shale resources of the basin (Wang et al 1992Guan et al 1995 Liu amp Liu 2005 Liu et al 2006 2009 Lu et al2006 Bai et al 2009 2010a b 2011)

In addition to the Chang 7 and 9 Member oil shales a shale seamis present in the Chang 4 + 5 Member of the Yanchang Formationwith a wide distribution and a distinct response in wireline logs andis known as the lsquothin neck sectionrsquo forming a regional marker Itwas deposited in a shallow lake-delta environment and there is nokerogen in the shales and therefore lacks the basic conditions forforming oil shale or hydrocarbon source rocks (Fu et al 2012)

A thin oil-shale seam is present in the Chang 1 Member of theWayaobao Formation formed in the limnic and delta environmentand interbedded with coal seams it covers a limited area and is thin(Wang et al 2007) The oil shale with coal had been mined mainlyused as fuel In summary the Chang 7 Member oil shale has a realsignificance for exploration and is quite different to the others

The Yanchang Formation host rock of the Chang 7Member oil shale

The middlendashlate Triassic Yanchang Formation (Ty) mainlycomprises carnation and celadon finendashcoarse grain arkose withinterbeds of black shale oil shale and andesitic to dacitic tuff(Fig 4) It is an important oil-bearing formation

The lower part of the Yanchang Formation consists of carnationand celadon mediumndashcoarse grain arkose fine sandstone sand-wiched with siltite argillaceous siltite mudstone oil shale (Chang 9Member oil shale) and tuff followed by oil shale (Change 7Member oil shale) black shale interbeded with argillaceous siltiteand tuff (Fig 4)

The upper part of the Yanchang Formation is grey celadon finendashmedium grain arkose black shale mudstone siltite and interbed-ding of celadon sandstone and black silty mudstone (Fig 4)

The Yanchang Formation has conformable contacts with theoverlying stratum (the Wayaobao Formation) and underlyingstratum (the Ermaying Formation) and can be readily distinguishedby its celadon grey black colour The base of the YanchangFormation is marked by the disappearance of the crimson mudstonewhich located the top of the Ermaying Formation also known as theZhifang Formation (T2) The top of the Yanchang Formation or thebase of the Wayaobo Formation is marked by the occurrence ofrhythmic layers of sandstone and mudstone containing coal seamsor very thin coal seams (Fig 4)

The Yanchang Formation contains abundant fossils (egphytoliths palynoflora estheria bivalves insect acritarchs andfish) and framboidal pyrite (Liu 1986 Bai et al 2006) and formedin fluviatile delta lake facies during the middlendashlate Triassic(BGMRSP 1998 Bai et al 2006 2009 Deng et al 2017) The ageof the Yanchang Formation which was regarded as Late Triassic(Yang 2002 Bai et al 2006 Wang et al 2017) has recently beendetermined to be middlendashlate Triassic (Deng et al 2017)

Ordos oil shale


The Yanchang Formation is a lithostratigraphic unit Accordingto the formal definition it lacks coals The coal-bearing section ofthe Chang 1 Member is therefore assigned to the WayaobaoFormation (BGMRSP 1998)

The Yanchang Formation experienced three lake transgressionscorresponding respectively to the Chang 9 Chang 7 and Chang 4+ 5 members (in terms of sedimentary cycles Ty1 Ty2 Ty3respectively) (Figs 2 and 4)

In the Chang 10 Member deposition comprised alluvial plaindeltaic plain and shallow lake facies The lake facies covers arelatively small area During deposition of the Chang 9Member thelacustrine area was significantly enlarged with development ofshallow lake and delta facies while in some regions a deeper lakefacies formed The alluvial plain and alluvial fan facies becamerestricted The Chang 9 Member represents the first laketransgression in the area In the Chang 8 Member although thelake area was wide it was narrower and shallower than that of theChang 9Member The deltaic sandstone deposited during this stageis one of the main reservoirs in the basin This completes the firstlake transgressivendashregressive cycle (Ty1) (Deng et al 2011)

In the Chang 7 Member lacustrine facies dominated and thedeeper lake facies reached its maximum extent of c 30 000 km2 andpossible water depth of about 60 m representing a major lacustrinetransgression This was fellowed by the Chang 6Member where thelake shallowed and deltaic sand bodies developed to form anothermain reservoir This represents the second lake transgressivendashregressive cycle (Ty2) (Deng et al 2011)

In the early stages of Chang 4 + 5 Member the lake began tonarrow considerably but was extended again in the middle of theinterval A mudstone-rich lake facies developed that formedthe regional cap rocks Subsequently deltaic plain sand bodies

developed again In the Chang 3 and Chang 2 Member sedimentaryintervals the lake remained narrow and the deeper lake facies beganto disappear This represents the third lake transgressivendashregressivecycle (Ty3) (Deng et al 2011)

In the Wayaobao Formation or the Chang 1 Member the lakedisappeared completely and there was extensive swamp develop-ment with the deposition of some coal seams some interbedding ofoil shale large amounts of charcoal debris and numerous plant fossils

Geological and geochemical characteristics of the Chang7 Member oil shale

Spatial distribution

The Chang 7 Member oil shale is present on a large scale with analmost northndashsouth-orientated asymmetrical syncline (Figs 1 and 5)

The oil shales with the Yanchang Formation have been upliftedand eroded in the eastern southern and western parts (arcdistribution) and have subsided in the mid-western parts (includingthe Qingshen-2 well Huangxian Huachi and Qingyang countiesand Xifeng city Figs 1 and 5) The deepest burial is in HuanxianCounty in Gansu Province (Fig 5) In the western part of the OrdosBasin (including the Tiantan-1 well west Huanxian CountyZhenyuan County and the Qingshen-2 well) (Figs 1 and 5) theoil-shale seams and its host rock are steeply uplifted and dip to theeast while in the eastern part (including Zhidan Fuxian andYanchang counties and Yanan city) is gently uplifted and dips tothe west (Figs 1 and 5) The structural contours in Figure 5 indicatethe burial depth of the oil shales which also reflects the structuralcharacteristics of the oil-shale layers Outcrops of both the oil shaleand strata are mainly distributed in the east and south in Yijun

Fig 4 Stratigraphic column indicating the position of the oil-shale-rich seams within the Triassic section

Y L Bai amp Y H Ma


County Tongchuan city Yaoqu town and Binxian County innorthern Shaanxi (Fig 1)

Basic sequence of the Chang 7 Member

The basic sequence of the Chang 7 Member consists of three parts(1) oil shale shale and mudstone (2) sandstone and siltite and (3)tuff (Fig 4) The lower part of the Chang 7 Member consists of oilshale and tuff with interbeded fine sandstone and siltite The upperpart consists of mudstone shale and tuff sandwiched with siltiteand fine sandstone The stratigraphic characteristics of the oil shalesare clearly resolved in a well wireline logging the oil shale beingcharacterized by high natural gamma ray (GR) and resistivity ofinduction in lateral and deep (RILD) logs low ρ (density) andspontaneous potential (SP) logs (Fig 6) (Yang amp Zhang 2005Wang 2007)

Age

Biostratigraphic age

The biostratigraphy is based on phytoliths The DanaeopsisndashBernoullia assemblage with a CarnianndashNorian age (Si 1956BGMRSP 1989 1998) occurs in the upper part of the Yanchang

Formation suggesting the upper part of the Yanchang Formationis of late Triassic (CarnianndashNorian) age The AnnalepisndashTongchuanophyllum assemblage with a Ladinian age (Si 1956)occurring in the lower part of the Yanchang Formation below theChang 7Member indicates an middle Triassic age for the lower partof the Yanchang Formation The Chang 7 Member oil shale istherefore of Ladinian (ie middle Triassic) age

Zircon SHRIMP UndashPb ages

Zircon SHRIMP UndashPb ages have recently been published for thelowermost tuff units (K0) of the Chang 7 Member oil shale(stratigraphic horizon K0 see Fig 4) (Xie 2007 Wang et al 2014)These ages range from 2397 to 2413 Ma which are equivalent tothe Ladinian age as indicated by the phytoliths

In summary the Yanchang Formation is middlendashlate Triassic(LadinianndashNorian) age not just late Triassic age (Wang et al 2017)The Chang 7 Member oil shale is of middle Triassic (Ladinian) age

Thickness

Based on outcrops (Fig 1) and logging data (Fig 6) the thicknessof the oil shale ranges from 0 to 61 m with an average of c 28 m

Fig 5 Thickness distribution and burialdepth of the Chang 7 Member oil shale thelocation is shown in Figure 1a (modifiedand supplemented after Yang amp Zhang2005 Bai et al 2009 2010b)

Ordos oil shale


(Fig 5) The areas with a thickness greater than 20 m are elongatedapproximately NWndashSE and include Huanxian Huchi Qingyangand Zhengning counties and Tongchuan city (Fig 5) The oil shaleis thin at the edge of the basin and thickest in the central part where itis more than 40 m in thickness near Huanxian County andmore than20 m thick to the NW of Tongchuan city (Fig 5)

Petrological and geochemical characteristics

Petrological characteristics

The oil shales have a dark greasy lustre with a maroon-colouredsurface resulting from oxidation (Fig 7) The fresh oil shales have aflakey banded structure uneven conchoidal fractures low hardnessand light brown streak

The main components of the oil shale by average are 49 clays29 quartz 16 feldspars and iron oxides The composition fallswithin the muddy shale area in the shale classification scheme ofKuila amp Prasad 2012 (Fig 8) Carbonate minerals are rare Clayminerals comprise mainly mixed-layer illite and smectite followedby illite and chlorite and are partially affected by sericitization Theclastic minerals are mainly quartz followed by feldspars (Bai et al2009 2010b) Iron oxides and organic matter fill the pore spacesbetween the clay minerals (Fig 9a) The diameters of the detritalmineral grains vary from 003 to 006 mm (ie silt) occasionally upto 015 mm Sand-size mineral grains are angular subangular androunded and consist of quartz and feldspar (Fig 9b) indicating aproximal provenance trait

Chemical composition characteristics

The average chemical composition of the oil shale is shown inTable 1 Compared with lsquoNorth American shale compositersquo(NASC) (Gromet et al 1984) the oil shale has higher P2O5 andFe2O3 lower CaO SiO2 and MgO slightly lower Na2O and K2Oand similar Al2O3 and TiO2

The concentrations of CaO SiO2 and MgO in the oil shale arerelatively low which indicates limited terrigenous matter input intothe lake The concentrations of P2O5 and Fe2O3 in the oil shale is

relatively high if primary indicating that the nutrient content of thelake water was relatively high which may have been associated withvolcanism to the south of the lake numerous tuff layers are presentin the oil-shale seams

M (M = 100 timesMgOAl2O3) values of the shale could reflect thesalinity of the lake water and the provenance in general M lt 1 forfreshwater environments 1 ltM lt 10 for transitional environments10 ltM lt 500 for marine environments and M gt 500 for epicontin-ental seas or lagoons (Liu 1984) M = 61 for the oil shale indicatesa transitional brackish water environment However numerousspecimens of Leiosphaeridia and Micrhystridium are preservedwhich indicates that the lake was primarily freshwater (Ji et al2006) The SrBa ratios cited below also support this conclusion

The sum of SiO2 and Al2O3 reaches 6369 of the whole-rockchemical composition indicating a continental deposition Thiscorresponds to a siliceous ash on combustion (the criteria for siliceousash-type oil shale are SiO2 (40ndash70 wt) Al2O3 (8ndash50 wt) Fe2O3

(lt20 wt) and CaO (120 wt) (Zhao et al 1991) The oil shalesare slightly lower in SiO2 and Al2O3 than that of the Tertiary oilshales of the Fushun Basin which consist of 6159 wt SiO2 and2336 wt Al2O3 (Yuan et al 1979 The Office of the NationalCommittee ofMineral Reserves 1987) indicating that the latter havea more obvious continental deposition (Zhao et al 1991)

Oil-shale fusibility can be expressed by (SiO2 + Al2O3)(Fe2O3 +CaO +MgO) values which are lt5 for fusible ash 5ndash9 for mediumfusion ash and gt9 for refractory ash (Zhao et al 1991) Because the(SiO2 + Al2O3)(Fe2O3 + CaO +MgO) value for the oil shales is587 it belongs to a medium fusion ash

Trace element characteristics

The average trace element concentrations of the oil shale are givenin Table 1 BothMn and Ni have enrichment coefficients (relative toNASC according to Gromet et al 1984 see below) of less than 05Ba Zr Rb Cr Co and Th have coefficients ranging from 05 to 1Sr V and Zn have coefficients ranging from 1 to 15 Pb has acoefficient of 17 and Cu has a coefficient 302 Both Mo and U arevery strongly enriched The strong enrichment of U Mo Cu and Pb

Fig 6 Logging and organic geochemical profile of the Chang 7 Member oil shale in the Li 57 well which is located in the mid-west in Figure 1a in theSE of Huanxian County (after Yang amp Zhang 2005 Wang 2007) The legend is the same as in Figure 4

Y L Bai amp Y H Ma


if primary shows that the lake was rich in organic nutrientsThe eutrophic lake water would have enhanced the productivitypromoting algal booms and at the same time resulting in anoxiaof the water The enrichment of U Mo Pb and Cu is a positiverelationship with TOC (Zhang et al 2008b)

The SrBa ratio of a shale if primary is proportional to thesalinity of water SrBa gt1 indicates a marine or saline lakeenvironment 05 lt SrBa lt 1 indicates brackish water and SrBa lt05 indicates freshwater (Liu 1984) The SrBa ratio of 033 in the oilshale indicates that the lake was a freshwater environment

The Mn content of lake water is positively correlated with waterdepth The Mn abundance is about 10 ppm for lake shore about60 ppm for shallow lakes and about 400 ppm for semi-deep lakes todeep lakes (Liu 1984) The 313 ppmMn of the Chang 7Member oilshale indicates a semi-deep to deep lake environment

The geochemical behaviour of the variable valence elements Vand U is closely related to the sedimentary redox environment In areducing environment V and U have a low valency are less solubleand are readily enriched so that the ratios of VNi VCr and UThare often used as redox indicators (LewanampMaynard 1982) The oilshale has a VNi ratio of 78 and a UTh ratio of 48 indicating astrongly reducing environment

The SrCu ratio is climatically related A SrCu ratio of 13ndash50indicates a warm and humid climate a ratio value of gt5 indicates ahot dry climate and a ratio of lt13 indicates a cold humid climate(Liu 1984) The SrCu ratio of the oil shale is about 2 indicating awarm humid climate

Redox conditions in the original water settings controlled theconcentrations of some major and trace elements in sediments and

sedimentary rocks Thus their concentration could be used toreconstruct the redox of the original water (Liu 1984 Tribovillardet al 2006) Because of fine particles compacting construction andvery low porosity of the oil shale the concentration and ratios ofsome major and trace elements are very small change in thediagenetic alteration and could be used to indicating sedimentaryenvironment (Liu 1984)

Rare earth element characteristics

The amount of REE in the oil shales is slightly higher than theaverage amount of REE (1464 ppm) in the upper crust and slightlylower than that (197 ppm) in NASC (Gromet et al 1984)(cfTable 1 Figure 10) Fu amp Qi (1995) showed that the amountof both REE and TOC in the deposits of the warm damp climateenvironments is generally higher than that in arid and cold climateenvironments The amount of REE is relatively high in the oil shalewhich shows that the warm and damp climate prevailed during themiddle Triassic favouring biological productivity

The REE distribution patterns of the oil shales are characteris-tically rich in LREEs (light REE) and have a weakly negative Euanomaly similar to that of the upper crust (Fu amp Qi 1995) whichsuggests the degree of differentiation of REE is relatively high andthe deposition rate is relatively low in the lake which favouredenrichment in organic matter (Fu amp Qi 1995)

In sedimentary systems the Ce anomaly may reflect changes inthe redox conditions in water Ceanom = lg [3Cen(2Lan + Ndn)] (thesubscript n is standardized values for NASC) Ceanom gtminus01reflects a reducing water body and Ceanom ltminus01 reflects an

Fig 7 Examples of outcrops and specimens of the Chang 7 Member oil shale in the Ordos Basin (a) Hejafang village oil shale (mining face of oil shale in1960) (b) Bawangzhuang village oil shale (note the layer structure) (c) Jinsuoguan town oil shale (note the oil-shale layers interbedded with a thin layer ofgreyish-buff tuff ) and (d) Bawangzhuang oil-shale specimen (note the maroon colour of the surface of oil shale after weathering) The locations of theseoutcrops are shown in Figure 1a

Ordos oil shale


oxidized water body (Fu amp Qi 1995) The oil shale has Ce anomalygreater than minus01 (Ma et al 2016)

The oil shales have very similar REE characteristics to chondritedistribution patterns among the different samples (Fig 10) Thecoherence of the REE distribution patterns indicates a consistentprovenance

Organic geochemistry characteristics

The oil shale has a high residual organic matter content with anaverage TOC content of 18 wt (Table 2) The main component(kerogen) of the organic matter has reached maturity with a Ro

value of 0 9minus115 (Tmax = 445ndash455degC) a residual chloroformbitumen lsquoArsquo content of 01ndash04 wt (chloroform bitumen is asoluble organic matter in rocks that can be dissolved in chloroform

composed of saturated hydrocarbon aromatic hydrocarbon gumand asphaltene generally chloroform bitumen lsquoArsquo is the ratio of theextracted bitumen mass to the mass of rock sample) a hydrocarbonscontent of 03ndash06 wt and a pyrolytic hydrocarbon-generationpotertial (S1 + S2) content of about 70 mg HCg rock (Table 2) Theyield of the oil shale is up to 400 mg HCg rock IH has two intervalvalues (bimodal) of 200ndash300 and 600ndash650 mg HCg TOC and IOalso has two interval values lt5 and 50ndash100 mg CO2g TOC (Yangamp Zhang 2005 Ma et al 2016) which suggest that the kerogenscome from a variety of sourcesThe residual lsquochloroform bitumenArsquo conversion rates (ATOC) are 314ndash984 and the hydrocarbonconversion rates (HCTOC) are 211ndash577 (Yang amp Zhang 2005)The hydrocarbon-expulsion efficiency reaches an average of 72(Mu et al 2001 Yang amp Zhang 2005 Zhang et al 2006 2008b)

Fig 8 Shale mineral composition triangular diagram showing the Chang 7 Member oil shale characteristic composition (modified and supplemented afterKuila amp Prasad 2012) The square symbol shows the location of the average mineral composition of global shale regardless of the content of organic matterwhich indicates that the global shale generally has a higher clay mineral content but less quartz and feldspar content and almost no calcite and dolomitecontent The two ellipses indicate the range of the Green River oil shale the right ellipse is the distribution area of the Parachute Greek oil shale which isshown as black squares and the left ellipse is the distribution area of the Garden Gulch oil shale which is shown as circles The black rhombus is thelocation of the shales coming from all around the world and the triangle is the location of the Ordos Triassic oil shale

Fig 9 The characteristics of the oil shale under a light microscope (after Bai et al 2009 2010b) (a) Remaining argillaceous texture slab structure weaksericitization (perpendicular polarized light) (b) Angular subangular and rounded silt-sized mineral grains (feldspars) (perpendicular polarized light)

Y L Bai amp Y H Ma


The kerogens mainly consist of amorphous lipids with a fewHystrichosphaera and spores and are characterized by a uniformmonotonous biological component (Mu et al 2001 Yang amp Zhang2005 Ji et al 2007) They lack aryl isoprenoid alkane complexeswhich shows that the kerogens are mainly derived from algalmaterial of lacustrine origin of the IndashII1 type (Mu et al 2001 Yang

amp Zhang 2005 Ji et al 2007 Ma et al 2016) The high residualorganic matter content good-quality kerogens with 09ndash105 Ro

but low (S1 + S2) values (Table 2) indicate that the oil shales (sourcerocks) underwent strong hydrocarbon expulsion and a low ratio ofsaturated hydrocarbonaromatic hydrocarbon (SHAH of 086ndash30)also suggests this (Yang amp Zhang 2005)

Table 1 Major trace and rare-earth element analyses from the Chang 7 Member oil shale

Oxide(wt)

Chang 7 Memberoil shale (average

N = 54)1 NASC2

Traceelements(ppm)


N = 43)3 NASC4Rare-earth

elements (ppm)Chang 7 Member oilshale (average N = 8)5 Chondrite6 NASC7

SiO2 4869 5810 Mn 3130 9220 La 310 03 320Al2O3 1440 1540 Sr 1970 1420 Ce 560 10 730TiO2 051 065 Ba 5930 6360 Pr 65 01 79Fe2O3 854 402 V 1760 1300 Nd 240 07 330MgO 097 344 Zr 1320 2000 Sm 44 02 57CaO 114 311 Rb 1210 1250 Eu 09 01 12Na2O 096 130 Cu 980 324 Gd 39 03 52K2O 272 324 Pb 345 200 Tb 06 01 085FeO 400 324 Zn 745 700 Dy 36 09 58P2O5 030 017 Cr 652 1250 Ho 08 01 10

Ni 225 580 Er 23 03 34Co 171 260 Tm 04 01 05Mo 591 31 Yb 25 02 31U 319 30 Lu 04 01 048Th 66 123 Y 230 19 240

sumREE 1605 1605 1970

N number of samples1Chang 7 Member oil shale (N = 54) data were compiled from Miao et al (2005) Changqing Oilfield Company PetroChina (2008) Bai et al (2009) Zhang et al (2013) Sun et al(2015) and Wang et al (2016)2NASC according to Gromet et al (1984)3Chang 7 Member oil shale (N = 43) data were compiled fromMiao et al (2005) Zhang et al (2008a b) Bai et al (2009) Zhang et al (2013) Sun et al (2015) and Ma et al (2016)4NASC according to Gromet et al (1984)5Chang 7 Member oil shale (N = 8) data were compiled from Bai et al (2009) and Ma et al (2016)6Chondrite according to Taylor amp Melennan (1985)7NASC according to Gromet et al (1984)Analytical methods the analytical method for major elements uses X-ray fluorescence (XRF) in different laboratories following Chinesestandards GBT 1450614-2010 (AQSIQ amp SAC 2010c) and GBT 1450628-2010 (AQSIQ amp SAC 2010b) the analytical method for microelements uses XRF and inductivelycoupled plasma mass spectrometry (ICP-MS) following Chinese standard GBT 1450630-2010 (AQSIQ amp SAC 2010a) and the analytical method for rare earth elements uses XRFand ICP-MS in different laboratories following Chinese standard GBT 1450630-2010 (AQSIQ amp SAC 2010a)

Fig 10 Chondrite-normalized REE distribution patterns of the Chang 7 Member oil shale

Ordos oil shale


The Chang 7 Member oil shale kerogen and lsquochloroformbitumenrsquo are enriched in the light carbon isotope 12C Thekerogen and lsquochloroform bitumenrsquo have a limited range of δ13Cvalues which are minus3000 to minus285 and minus3300 to 322permil (Yang ampZhang 2005) respectively which shows that the kerogen formed ina terrestrial freshwater to low-salinity water body

Gas chromatography shows that the saturated hydrocarbonchromatogram is of unimodal type and the main carbon peak isnC16ndashnC19 showing an oddndasheven equilibrium with an OEP (oddndasheven performance) of 095ndash121 PrPh is 056ndash117 PrnC17 is011ndash033 and PrnC18 is 016ndash040 which also indicates a reducingenvironment The low PrPh lower PrnC17 and PrnC18 ratiosindicate that the sedimentary environment was a deep reducingwater body and the source of the organic material was primarilylower aquatic organisms in addition it has reached the peak of theoil source mature phase (Yang amp Zhang 2005 Zhang et al 2006Ji amp Xu 2007 Ji et al 2007)

Hopane is composed primarily of C30αβ The content ofgammacerane and tricyclic terpane is low and the content of Tsis high Sterane is given priority to with regular Sterane withpreponderant C29 slightly low C28 low C22 and a high content ofdiasteranes Both a low content of gammacerane and a high contentof diasteranes indicate that the oil shale formed in a low salinitysedimentary environment (Yang amp Zhang 2005)

Quality

Oil yield and calorific value are the most common parameters forevaluating oil shales (Yuan et al 1979 Smith 1980 The Office ofthe National Committee of Mineral Reserves 1987 Zhao et al1991 Zhao amp Liu 1992 Guan et al 1995 Dyni 2006a b Liu et al2006 2009) The oil yield of the oil shale was measured by theGrayndashKing low-temperature dry distillation assay method followingChinese standard methods (GBT 1341-2007) (AQSIQ amp SAC2007) and the calorific value of the oil shale was measured byisothermal oxidation bomb calorimetry following Chinese standardmethods GBT 213-2008 (AQSIQ amp SAC 2008a b)

Based on our own and previously published data the oil shale hasan average oil yield of 8 wt a calorific value of 835 MJ kgminus1 (net

calorific value at constant volume) and an apparent specific gravityof 179 (Table 2)

The grade of oil shale can be divided into three types by oil yieldof oil shale (dry basis) which is respectively low (35 wt lt oilyieldle 5 wt) medium (5 wt lt oil yield≧ 10) and highgrades (oil yield gt10 wt) (Liu et al 2009) The oil shale ismedium quality

The calorific value is useful for determining the quality of oilshale that is burned directly in a power plant to produce electricityThe calorific value of a given oil shale is a useful and fundamentalproperty of the rock although it does not provide informationon the amounts of shale oil or combustible gas that would beyielded by retorting (destructive distillation) The oil shale ishigh grade compared with other Chinese oil-shale depositswhich have average calorific values of 57 MJ kgminus1 (Fushun)73 MJ kgminus1 (Maoming) 70 MJ kgminus1 (Yaojie) 36 MJ kgminus1

(Nongan) 42 MJ kgminus1 (Dongsheng) 66 MJ kgminus1 (Huadian) and42ndash50 MJ kgminus1 (Guyang) respectively (Zhao et al 1991 Liuet al 2009) but it is low grade compared with the high-gradekukersite oil shale of Estonia which fuels several electric powerplants and has a calorific value of about 1003ndash1262 MJ kgminus1 on adry-weight basis (Dyni 2006a b) The higher calorific value arelinked to the higher oil yields TOC and lower Ad (ash content drybasis) in the oil shale (Fig 11andashc)

The oil shale averages 69 wt ash yield (dry basis) a high ashtype (Zhao et al 1991 Liu et al 2009) The higher ash yield islinked to the lower calorific value and oil yield (Fig 11b and d)Considering the above data of the oil shale fusibility it is a mediumfusion high ash type

The data analysis indicates that there is an obvious positivecorrelation between the oil yields and Cad (carbon air dry basis)(Fig 10e) The higher the total sulphur content the greater thepotential environmental pollution in oil-shale utilization Oil shalecan be divided into five levels ultra-low sulphur (le10 wt) lowsulphur oil shale (10minus15 wt) medium sulphur (15ndash25 wt)rich sulphur (25ndash40 wt) and high sulphur (gt40 wt)(The Office of the National Committee of Mineral Reserves1987) The total sulphur is 469 wt indicating a high sulphuroil shale

Table 2 Proximate and organic matter analysis from the Chang 7 Member oil shale

Proximate analysis1 items Chang 7 Member oil shale2 (average N = 35) Organic matter abundance analysis items3 Chang 7 Member oil shale4 (average)

Oil yield (wt) 800 TOC (wt) 1776 (N = 72)Qnetvar (MJ kgminus1) 835 Chloroform bitumen A (wt) 04ndash1Ad (wt) 6924 S1 (mg HCg rock) 306 (N = 41)Std (wt) 469 S2 (mg HCg rock) 6051 (N = 40)Mt (wt) 337 S3 (mg CO2g rock) 778 (N = 41)Vdaf (wt) 6816 S1 + S2 (HCg rock) 7000 (N = 76)Cad (wt) 1908 IH (mgg) 40780 (N = 434)Had (wt) 213 IO (mgg) 6339 (N = 19)

ARD (g cmminus3) 177

N number of samples1Proximate analysis Qnetvar net calorific value at constant volume Ad ash content (dry basis) Std sulphur content(dry basis) Mt total moisture Vdaf volatile (dry ash-free basis)Cad carbon (air dry basis) Had hydrogen (air dry basis) ARD apparent density2Chang 7 Member oil shale data were compiled from Lu et al (2006) Zhang et al (2006) Ren (2007) Changqing Oilfield Company PetroChina (2008) Bai et al (2009) and Zhanget al (2013)Analytical methods the analytical method for the oil yield uses GrayndashKing low-temperature distillation in different laboratories following Chinese standard GB-T 1341-2007 (AQSIQ amp SAC 2007) the analytical method for ash yield uses the fast ashing method in different laboratories following Chinese standard GBT 212-2008 (AQSIQ amp SAC2008a) and the analytical method for calorific value uses the environmental isothermal automatic oxygen bomb calorimeter in different laboratories following Chinese standard GBT213-2008 (AQSIQ amp SAC 2008b)3Organic matter abundance analysis TOC (total organic carbon) is the content of residual organic matter in oil shale () chloroform bitumen lsquoArsquo() is the ratio of the extracted bitumen mass to the mass of rock sample S1 is the content of soluble hydrocarbon in oil shale (mg HCg rock) S2 is the content of pyrolytic hydrocarbonin oil shale (mg HCg rock) S3 is the content of pyrolytic carbon dioxide in oil shale (mg CO2g rock) S1 + S2 is the potential amount of hydrocarbon generation (mg HCg rock)IH = QHCCOT times 100 and IO frac14 QCO2

=COT 100 (where QHC is hydrocarbon from kerogen pyrolysis and extractable hydrocarbon components COT is total organic carbon andQCO2

is the amount of CO2)Analytical methods the analytical method for total organic carbon (TOC) uses the CarbonSulfur Determinator in different laboratories following Chinesestandards GBT 19145-2003 (AQSIQamp SAC 2003) the analytical method for chloroform bitumen A analysis uses Soxhlet extraction equipment in different laboratories following theenterprise standard of CN-PC SYT5118-2005 (NDRC 2005) and the analytical method for rock pyrolysis analysis uses Rock-Eval pyrolysis apparatus in different laboratoriesfollowing Chinese standard GBT 18602-2012 (Tmax = 425ndash450degC) (AQSIQ amp SAC 2012)4Chang 7 Member oil shale data were compiled from Yang amp Zhang (2005) Ren (2007)Changqing Oilfield Company PetroChina (2008) Bai et al (2009) Zhang et al (2013) Ma et al (2016) and Yang et al (2016b)

Y L Bai amp Y H Ma


Oil shale can be divided on moisture content into highmoisture content (Mt of 20ndash30 wt) medium moisture content(Mt of 10ndash20 wt) low moisture content (Mt of less than 10 wt)(The Office of the National Committee of Mineral Reserves1987)The oil shale has Mt of 337 wt a low moisture contentoil shale

The oil shale has an average density of 177 kg mminus3 which isquite high related to the higher silicon and aluminum componentsthis means a lower oil yield per tonne

The oil shale has an average Vdaf (volatile dry ash-free basis) of68 wt which is also quite high reflecting the relatively highmetamorphic grade and relatively high organic matter content ofthe shale (Liu et al 2009)

The average TOC of the oil shale is high (Table 2) Thecorrelation between the TOC and oil yield in the outcrop oil shale

samples is very obvious (Fig 11f ) but there is no obviouscorrelation between TOC and (S1 + S2)

The average content of Cad (carbon air dry basis) and Had

(hydrogen air dry basis) in the oil shale are respectively 1908 and213 wt (Table 2) so an average HC ratio of 14 is obtained Maet al (2016) pointed out that the oil shale has average HC and OCratios of 134 and 01 respectively Therefore the organic matter ofthe oil shale belongs to Type I and II1 Tissot ampWelte (1978) statedthat the Type I kerogen has a HC ratio of gt15 a OC ratio of lt01and the precursors of the kerogen are mainly from marine orcontinental deep-water lake algae and bacteria the Type II kerogenhas a HC ratio of 10ndash15 a OC ratio of 01ndash02 and the precursorsof the kerogen are mainly from continental deep-bathyal lake sporesand pollen plankton micro-organisms and other mixed organicmatter and the Type III kerogen has has a HC ratio of lt10 a OC

Fig 11 The relationships between key parameters of the Chang 7 Member oil shale Qnet v ar net calorific value at constant volume Ad ash content drybasis Cad carbon air dry basis

Ordos oil shale


ratio of gt02 and the precursors of the kerogen are mainly fromterrestrial higher plants Based on content of Cad and Had and theHC and OC ratios in the oil shale the organic matter is mainlyderived from lacustrine algae spores and pollen Thus lsquocarbonrsquo inthe organic matter of the oil shale is unlikely to have been derivedfrom seawater or carbonate minerals with a probable lake waterorigin

Origin

Classification of the Ordos Basin oil shale

Oil shales can be classified by their depositional environment (eglarge lake shallow marine deltaic and lagoonalsmall lake settings)(Carman amp Bayes 1961 Surdam amp Wolfbauer 1975 Yuan et al1979 Macauley 1981 Boyer 1982 Francis ampMiknis 1983 Hutton1987 Brendow 2003 Altun et al 2006 Dyni 2006a b Ots 2007Lu et al 2006 Durham 2010) Oil shales of great lakes have largethicknesses and areas and are of good quality A typical example isthe Green River oil shale in the NW USA which is black in colourwith a thickness of several hundred metres and with an oil yield ofgenerally lt15 wt (SurdamampWolfbauer 1975 Smith 1980 Boyer1982 Dyni 2006a b)

Shallow sea and continental shelf oil shales are generally muchthinner than the large lake deposits and are associated withcarbonates siliceous and phosphatic facies They do not exceed2ndash3 m in thickness and are distributed over very large areas up tothousands of square kilometres (Hutton 1987) They are black tolight brown in colour with a high oil yield (c 20 wt) A typicalexample is the Kukersite oil shale of Ordovician age in Estoniawhich is in a single calcareous layer 25ndash3 m in thickness with anaverage oil yield of 20 wt Most of the organic matter is derivedfrom green algae (Hutton 1987)

Oil shales deposited in lagoonal or small lake environments arerarely extensive and are often associated Despite having a high oilyield they are thin and are unlikely candidates for commercialexploitation A typical example is the Yaojie oil shale of Jurassicage in NW China which is black in colour 4ndash11 m thick with anoil yield of 46ndash89 wt and most of the organic matter is derivedfrom macrophytes (Bai et al 2010b)

The Chang 7 Member oil shale formed in a larger-scale lakesetting The lsquoOrdos Lakersquo itself covers an area of 400 000 km2 witha maximum water depth of about 60 m (Yang et al 2016a) duringthe middle Triassic resembling the Green River oil shale (Surdamamp Wolfbauer 1975 Smith 1980 Boyer 1982 Dyni 2006a b) Theoil shale covers an area of around 30 000 km2 has an averagethickness of 28 m and an average oil yield of 8 wt

The Chang 7 Member oil-shale clay mineral content of 49 issimilar to the composition of the Darden Gulch oil-shale seam of theGreen River which has a clay mineral content of 40ndash70However it differs from the Kukersite oil shale in Estonia whichhas a clay mineral content of only 139 and a carbonate mineralcontent of 561 (Hutton 1987)

The relatively low concentration of CaO SiO2 and MgO andthe relatively high concentration of P2O5 and Fe2O3 and MgOAl2O3 ratio show that the lake was a coastal lake lackedsignificant terrigenous matter inputs and that the lake water hada high nutrient content The coherence of the REE distributionpatterns among the different samples indicates a consistentprovenance The PrPh PrnC17 and PrnC18 ratios alsoindicate that the biological source material is dominated bylower aquatic organisms (Yang amp Zhang 2005 Ji amp Xu 2007Ji et al 2007)

The oil shale formed in a reducing environment Its surface ismaroon after oxidation indicating enrichment in Fe2+ and thus adeep-water reducing environment Pb Cu Mo and U are stronlyenriched the the ratios of VNi UTh FeOFe2O3 PrPh PrnC17

and PrnC18 also indicate that the lake was a strongly reducingenvironment

The lake where the oil shale formed may have been a freshwaterto brackish water environment The SrBa ratio indicates that thelake was a freshwater lake but the M value of the oil shale indicatesa transitional brackish water environment Both the low content ofgammacerane and high content of diasteranes also indicates that theoil shale formed in a low-salinity sedimentary environment (Yangamp Zhang 2005)

The SrCu ratio indicates a warm humid climateRecent research shows that the sapropel group in the kerogens in

the Chang 7 Member oil shale contains abundant Leiosphaeridiawhich is multicellular macro red algae andor chlorophytes rootedin the lacustrine macroscopic algae fomed in a freshwaterenvironment different to the Proterozoic and PaleozoicLeiosphaeridia which is commonly thought as a marine unicellularphytoplankton (Ji amp Xu 2007 Ji et al 2007) AlthoughLeiosphaeridia is abundant in the area it is not only monotone inspecies but also conspicuous in echinulate process suggesting thatsome marine acanthomorphic acritarches survived in freshwater andhad experienced long-term evolution Therefore the sedimentaryenvironment of the Chang 7 Member oil shale is a lacustrineenvironment which turned into the climax of lake transgression inthe Chang 7 sedimentary interval indicating the supply of a large-scale lake water body that came from rivers rather than from a rise insea level (Ji amp Xu 2007 Ji et al 2007)

The limited range of δ13C values of lsquochloroform bitumenrsquo showsthat the kerogen formed in a deep reducing low-salinity water bodyConsidering that the composition of the kerogen is monotonous it isconjectured that the water body of the Ordos Basin was indistinctlystratified (Yang amp Zhang 2005) A low gammacerane content andthe absence of aryl isoprenoid compounds in the kerogen structure ofthe oil shale also indicate that the lake basin was not significantlydelaminated (Zhang et al 2008b) Both the low content ofgammacerane and the high content of diasteranes indicate that theoil shale formed in a low-salinity sedimentary environment (YangampZhang 2005) The PrPh PrnC17 and PrnC18 ratios also indicate areducing deep-water environment within which the biologicalsource material was dominated by lower aquatic organisms (Yangamp Zhang 2005 Ji amp Xu 2007 Ji et al 2007)

To sum up the Ordos Basin oil shale formed in a deep-waterreducing environment with awarm humid climate context The lakemay have been freshwater or brackish water and was indistinctlystratified The biological source material was dominated by loweraquatic organisms

Volcanism in the Ordos area

The andesiticndashdacitic tuff interbeds in the Chang 7 Member oil-shale seams and the Yanchang Formation (Fig 7c) indicate itsformation close to a volcanic arc and that the lake was a relativelyhigh-energy environment In addition the sandstone types in theupper and lower host layers of the oil-shale seams are mostlyfeldspar quartz sandstone and arkose also indicating a relativelyhigh-energy environment The Ordos Basin was not a stableintracratonic basin (Yang 2002) and was subject to relativelyenergetic sedimentary processes Moreover the angular sandydebris grains suggest a proximal provenance (Fig 9b)

As stated above the Ordos Lake was a reducing sedimentaryenvironment however the atmospheric oxygen level was not low atthe time of the oil-shale formation and questions arise regarding theorigin of the reducing lake environment Multiple layers of andesiticacid tuff (Figs 4 and 7c) are present in the Yanchang Formation andthe oil-shale seams therefore it is possible that their deposition wasto some extent responsible for the reducing conditions in the lakebasin There may have been a catastrophic death of organisms due to

Y L Bai amp Y H Ma


ash falls which may be the main reason why organic matter wasenriched in the lake At the same time the tuff layers also providednutrients for the next cycle of oil-shale formation (Yang amp Zhang2005)

Marine facies or lacustrine facies

It is problematic that recently one paper proposed that the Chang 7Member oil shale in the Ordos Basin was deposited in a marineintrusion (Wang et al 2017) Their evidence is a typical marinecoelacanth fossil with a rounded tail that was found in the lateTriassic stratum in the Huachi County area a broken marinecoelacanth fossil was discovered in Tongchuan city area about20 years ago by Liu et al (1999) The research shows that thesemarine organisms actually belong to a lsquoterrestrial organism with seaoriginrsquo rather than a marine organism (Liu et al 1999 Wang 1995)and the terrestrial organism with a sea origin represents the survivalof early marine creatures in the lake and does not represent aseawater intrusion In combination with the geochemical evidencedescribed above (SrBa ratio of 033) it is proposed that the Chang 7Member oil shale in the Ordos Basin was principally deposited in afreshwater or brackish water body neither marine environment norsalinized lake

In fact the North China Plate including the Ordos Basin sufferedthe subduction of the Qinling oceanic plate in the middlendashlateTriassic resulting in a decline in sea level in such a tectonic settinghow did seawater rise over the island arc belt and invade the area

Conclusion

Oil-shale resources are abundant in the Ordos Basin in central northChina There are multiple oil-shale seams in the basin but theChang 7Member oil-shale seam is the main oil shale seam (MOSS)with a thickness of 28 m and an area of around 30 000 km2 The oilshale is usually found in layers developed at the top of the lower partof the Yanchang Formation of middle Triassic (Ladinian) age TheYanchang Formation was deposited in a great lake in the middlendashlate Triassic (LadinianndashNorian) The oil shale is mainly brown-black to black in colour of a medium ash type with a TOC of 18 wt an oil yield of 8 wt a calorific value of 835 MJ kgminus1 and arelatively high P2O5 and Fe2O3 content It is strongly enriched inMo U and LREE and is kerogen type IndashII1 Volcanism may havefavoured the formation of the oil shale The oil shale formed in alarge deep to moderately deep lake the Ordos Lake with alow input of terrigenous material but abundant algal growth Thewater is freshwater or brackish and strongly reducing The tectoniccontext of the lake is a back-arc basin which was formed by thenorthwards subduction of the Qinling oceanic lithosphere beneaththe southern margin of the Ordos Kratogen during the middlendashlateTriassic (T2ndash3)

Acknowledgements We thank Mr Yang Jie (Dean of NWGI) ProfYang Hua Prof Wang Daxing and senior engineers Sun Liuyi Mao MingluBao Hongping and Ren Junfeng for their help in this work We thank Dr PAFChristie for his valuable modification advice and Professor Jan Bloemendal forhis polishing of this paper We also thank Bruce Levell Co-Editor of PetroleumGeoscience and two experts in the field for many good revision suggestions

Funding This work was funded by the PetroChina Company Limited (serialgrant number 20160821)

Correction notice The spelling of Ma Yuhus name has been corrected

ReferencesAltun NE Hiccedilyilmaz C Hwang JY Suat BA amp Koumlk MV 2006 Oil

shales in the world and Turkey reserves current situation and futureprospects a review Oil Shale 23 211ndash227 httpsdoiorg102516ogst2006011x

AQSIQ amp SAC 2003 Determination of Total Organic Carbon in SedimentaryRock GBT 19145-2003 General Administration of Quality SupervisionInspection and Quarantine of the Peoplersquos Republic of China (AQSIQ) ampChina Standardization Administration Commission StandardizationAdministration of the Peoplersquos Republic of China (SAC) Standards Press ofChina Beijing

AQSIQ amp SAC 2007 GrayndashKing Assay of Coal GBT1341-2007 GeneralAdministration of Quality Supervision Inspection and Quarantine ofthe Peoplersquos Republic of China (AQSIQ) amp China StandardizationAdministration Commission Standardization Administration of the PeoplersquosRepublic of China (SAC) Standards Press of China Beijing

AQSIQ amp SAC 2008a Proximate Analysis of Coal GBT212-2008 GeneralAdministration of Quality Supervision Inspection and Quarantine of thePeoplersquos Republic of China (AQSIQ) amp China StandardizationAdministration Commission Standardization Administration of the PeoplersquosRepublic of China (SAC) Standards Press of China Beijing

AQSIQamp SAC 2008b Analytical Method for Calorific Value of Coal GBT213-2008 General Administration of Quality Supervision Inspection andQuarantine of the Peoplersquos Republic of China (AQSIQ) amp ChinaStandardization Administration Commission Standardization Administrationof the Peoplersquos Republic of China (SAC) Standards Press of China Beijing

AQSIQ amp SAC 2010a Methods for Chemical Analysis of Rocks ndash Part 30Determination of 44 Elements GBT1450630-2010 General Administrationof Quality Supervision Inspection and Quarantine of the Peoplersquos Republic ofChina (AQSIQ) amp China Standardization Administration CommissionStandardization Administration of the Peoplersquos Republic of China (SAC)Standards Press of China Beijing

AQSIQ amp SAC 2010b Methods for Chemical Analysis of Rocks ndash Part 28Determination of 16 Major and Minor Elements Content GBT1450628-2010 General Administration of Quality Supervision Inspection andQuarantine of the Peoplersquos Republic of China (AQSIQ) amp ChinaStandardization Administration Commission Standardization Administrationof the Peoplersquos Republic of China (SAC) Standards Press of China Beijing

AQSIQ amp SAC 2010c Methods for Chemical Analysis of Silicate Rocks ndash Part14 Determination of Ferrous Oxide Content GBT 1450614-2010 GeneralAdministration of Quality Supervision Inspection and Quarantine of thePeoplersquos Republic of China (AQSIQ) amp China StandardizationAdministration Commission Standardization Administration of the PeoplersquosRepublic of China (SAC) Standards Press of China Beijing

AQSIQ amp SAC 2012 Rock Pyrolysis Analysis GBT 18602-2012 GeneralAdministration of Quality Supervision Inspection and Quarantine of thePeoplersquos Republic of China (AQSIQ) amp China Standardization AdministrationCommission Standardization Administration of the Peoplersquos Republic ofChina (SAC)Standards Press of China Beijing

Bai YL Wang XM Liu HQ amp Li TS 2006 Determination of theborderline of the western Ordos Basin and its geodynamics background ActaGeolodica Sinica 80 702ndash813 [in Chinese with English abstract] httpwwwgeojournalscndzxbchindexaspx

Bai YL Ma L amp Wu WJ 2009 Geological characteristics and resourcepotential of oil shale in the Ordos BasinGeology in China 36 1123ndash1137 [inChinese with English abstract] httpgeochinacgsgovcngeochinachreadercreate_pdfaspxfile_no=20090516ampflag=1ampyear_id=2009ampquarter_id=5

Bai YL Zhao YC Ma L Wu WJ amp Ma YH 2010a GeologicalCharacteristics and Resource potentials of Oil Shale in Ordos Basin CenterChina In In World Energy Congress 2010 Montreal Quebec Canada 12ndash16 September 2010 World Energy Council (WEC) London

Bai YL Zhao YC amp Xu D 2010b Geological characteristics and developingprospecting of oil shale in TongchuanndashHuangling district Shaanxi ProvinceChina Geoscience 24 158ndash165 [in Chinese with English abstract]

Bai YL Tang H amp Yan K 2011 Geological characteristics and someproblems in development for oil shale in northwest China Oil Shale 28380ndash397 httpsdoiorg103176oil2011303

Bai YL Ma YH Huang Y Liao JB amp Liu XG 2013 Properties ofcontinental margin and its hydrocarbon exploration significance in Cambrianin the southern Ordos kratogen of north China Acta Geologica Sinica (EnglishEdition) 87 777ndash803 httpsdoiorg1011111755-672412089

Bai YL Ma YH Huang Y amp Liu XG 2014 On the Cambian aulacogen ofthe southern Ordos continental margin and its hydrocarbon explorationimplications Natural Gas Geosciences 25 1706ndash1717 [in Chinese withEnglish abstract] httpsdoiorg1011764jissn1672-19262014111706

Boyer BW 1982 Green River laminites Does the playa -lake model reallyinvalidate the stratified-lake modelGeology 10 321ndash324 httpsdoiorg1011300091-7613(1982)10lt321GRLDTPgt20CO2

Brendow K 2003 Global oil shale issues and perspective-Synthesis ofthe Symposium on Oil Shale held in Tallinn (Estonia) on 18 and 19November 2002 Oil Shale 20 81ndash92 httpwwwdoc88comp-9052394455179html

Bureau of Geology and Mineral Resources of Shaanxi Province (BGMRSP)1989 Regional Geology in Shaanxi Province Geological Publishing HouseBeijing [in Chinese with English abstract]

Bureau of Geology and Mineral Resources of Shaanxi Province (BGMRSP)1998 Multiple Classification and Correlation of the Stratigraphy of China(61) ndash Stratigraphy (lithostratic) of Shaanxi Province China University ofGeosciences Press Wuhan [in Chinese]

Ordos oil shale


Carman EP amp Bayes FS 1961Occurrence properties and uses of some naturalbitumens information circular 7997 US Dept of the Interior Bureau ofMinesWashington pp 18ndash20 httpwwwdoc88 comp-7304586824313html

Changqing Oilfield Company PetroChina 2008 Oil Shale in the Ordos BasinChangqing Institute Xian China [in Chinese]

Chen FZ 2002 Metallogenic geologic prerequisites of sandstone-typeuranium deposits and target area election Taking Erlian and Ordos basinsas example Uranium Geology 18 138ndash143 [in Chinese with Englishabstract] httpswenkubaiducomviewf125afa433687e21ae45a948html

Chen YJ 2010 Indosinian tectionic setting magmatism and metallogenesis inQinling orogen central China Geology in China 37 854ndash865 [in Chinesewith English abstract] httpwwwdoc88comp-2963493801439html

Chen RL Luo XR Chen ZK Yu J amp Yang Y 2006 Restoration of burialhistory of four periods in Ordos Basin Acta Petrolei Sinica 27 43ndash47 [inChinese with English abstract] httpwwwsyxb-cpscomcnCNabstractabstract183shtml

Deng XQ Fu JH Yao JL Peng JL amp Sun B 2011 Sedimentary facies ofthe middlendashupper Triassic Yanchang Formation in Ordos Basinand breakthrough in petroleum exploration Journal of Palaeogeography13 443ndash456 [in Chinese with English abstract] httpmanu22magtechcomcngdlxbCNabstractabstract9145shtml

Deng SH Lu YZ et al 2017 Subdivision and age of the Yanchang Formationand theMiddleUpper Triassic boundary in Ordos Basin North China ScienceChina Earth Sciences 61 1ndash21 httpsdoiorg101007s11430-017-9215-3

Duan Y Zhang H Wu BX Zheng CY ampWang CY 2004 Distribution ofnitrogen compounds and migration of the oils in the Xifeng Oilfield OrdosBasin NW China Petroleum Exploration and Development 31 17ndash20 [inChinese with English abstract] httpwwwcpedmcomCNarticleopenArticlePDFjspid=905

Durham LS 2010 Bakken fractures yield the goods oil shale takes turn inspotlight AAPG Explorer 31 34ndash36 httpwwwaapgOrgexplorer201010octbakken1010cfm

Dyni JR 2006a Geology and Resources of Some World Oil-Shale DepositsScientific Investigations Report 2005-5294 United States Department of theInterior United States Geological Survey Reston VA httppubsusgsgovsir20055294pdfsir5294_508pdf [accessed 9 July 2007]

Dyni JR 2006b Oil shale developments in the United States Oil Shale 2397ndash98 httpsdoiorg102516ogst2006011x

Francis P amp Miknis JF 1983 Geochemistry and Chemistry of Oil ShalesAmerican Chemical Society Washington DC

Fu JM amp Qi KZ 1995 Geochemistry of Kerogen Guangdong Science andTechnology Publishing House Guangzhou DC 28ndash74 [in Chinese]

Fu JM Li S Liu X amp Deng XQ 2012 Sedimentary facies and its evolutionof the Chang 9 interval of Upper Triassic Yanchang Formation in Ordos BasinJournal of Palaeogeography 14 269ndash284 httpsdoiorg107605gdlxb201203001

Fuller ML amp Clapp FG 1926 Formation of the North Shensi Basin ChinaThe Journal of Geology 34 434ndash440 httpsdoiorg101086623330

Gromet LP Dymek RF amp Haskin LA 1984 The lsquoNorth American shalecompositersquo Its composition major and trace element characteristicsGeochimica et Cosmochimica Acta 48 2469ndash2482 httpsdoiorg1010160016-7037(84)90298-9

Guan DS Niu JY ampGuo L 1995Unconventionality Oil and Gas Geology inChina Petroleum Industry Press Beijing 228ndash287 [in Chinese]

Hutton AC 1987 Petrographic classification of oil shales International Journalof Coal Geology 8 203ndash231 httpsdoiorg1010160166-5162(87)90032-2

James GO 2012 Triassic In F M Gradstein et al (eds) The Geologic TimeScale Elsevier Amsterdam Holland httpsdoiorg101016B978-0-444-59425-900025-1

Ji LM amp Xu JL 2007 Triassic acritarchs and its relation to hydrocarbonsource rock in Ordos Basin Acta Petrolei Sinica 28 40ndash43 [in Chinese withEnglish abstract] httpsdoiorg107623syxb200206007

Ji LM Wang SF amp Xu JL 2006 Acritarch assemblage in YanchangFormation in eastern Gansu province and its environmental implications EarthScience ndash Journal of China University of Geosciences 31 789ndash807 [in Chinesewith English abstract] httpwwwdoc88comp-6971874998149html

Ji LM Wu T amp Li L 2007 Geochemical characteristics of kerogen inYanchang Formation source rocks Xifeng area Ordos Basin PetroleumExploration and Development 34 424ndash429 [in Chinesewith English abstract]

Jia CZ He DF Shi X amp Yang G 2006 Characters of late-stage formationreservoirs of China Science in China Series D Earth Sciences 36 412ndash420[in Chinese] httpknscnkinetkcmsdetaildetailaspxdbcode=CJFDampfilename=JDXK200605001ampdbname=CJFD2006

Kuila U amp Prasad M 2012 Compositional controls on mud rock pore-sizedistribution an example from Niobrara Formation Paper presented at theSociety of Petroleum Engineers Annual Technical Conference and Exhibition8ndash10 October 2012 San Antonio Texas USA

Lewan MD amp Maynard JB 1982 Factor controlling the enrichment ofvanadium and nickel in the bitumen of organic sedimentary rock Geohimicaet Cosmochimica Acta 46 2547ndash2560 httpsdoiorg1010160016-7037(82)90377-5

Li ST 2000 The dynamics of sedimentary basins and energy resources ndashretrospective and prospects at the turn of the century Earth Science Frontiers7 1ndash8 [in Chinese with English abstract] httpwwwearthsciencefrontiersnetcnCN

Liu GB Zhou ZX amp Zhang XL 1999 A coelacanthid fossil from Huacharea Gansu ProvinceGeological Journal of China University 5 474ndash480 [inChinese with English abstract] httpgeologynjueducnCNabstractabstract9063shtml

Liu SL 1986 The existence of a large-scale Trassic sedimentary basin in northChina Acta Geologic Sinica 60 128ndash138 [in Chinese with English abstract]httpwwwgeojournalscndzxbchreadercreate_pdfaspxfile_no=19860212ampflag=1ampjournal_id=dzxbampyear_id=1986

Liu YJ 1984 Element Geochemistry Science and Technology Press Bejing [inChinese]

Liu ZJ amp Liu R 2005 Oil shale character and exploitation and utilizationprospect Earth Science Frontiers 12 315ndash323 [in Chinese with Englishabstract] httpwwwearthsciencefrontiersnetcnCN

Liu ZJ Dong QS et al 2006 The situation of oil shale resources in ChinaJournal of Jilin University (Earth Science Edition) 36 869ndash876 [in Chinesewith English abstract] httpxuebaojlueducndxbCN

Liu ZJ Yang HL amp Dong QS 2009Oil Shale in China Petroleum IndustryPress Beijing [in Chinese]

Lu JC Li YH amp Wei XX 2006 Research on the depositional environmentand resources potential of the oil shale in the Chang 7 Member TriassicYanchang Formation in the Ordos Basin Journal of Jilin University (EarthScience Edition) 36 928ndash932 [in Chinese with English abstract] httpxuebaojlueducndxbCN

Ma ZH Chen QS Zhong W Wang C Du WG amp Zhao CY 2016Geochemistry of oil shale from Chang-7 reservoir of Yanchang Formation inSouth Ordos Basin and its geogical significance Geological Bulletin ofChina 35 1550ndash1558 [in Chinese with English abstract] httpdzhtbcgscngbcchreaderview_abstractaspxfile_no=20160921ampflag=1

Macauley G 1981 Geology of the Oil Shale Deposits Canada GeologicalSurvey of Canada Ontario Canada 26ndash36

Miao JY Zhao JS Li WH Han ZY amp Ma J 2005 Research on thedeposit environments about source rocks in South Ordos Basin Journal ofNorthwest University (Natural Science Edition) 35 771ndash777 [in Chinese withEnglish abstract] httpmallcnkinetonlineviewMagaViewaspxfn=xbdz2005061

Mu ZH Zhu HH amp Zhang KY 2001 The Oil-Forming System of Mesozoicin South Ordos Basin Petroleum Industry Press Beijing 1ndash10 [in Chinese]

National Development and Reform Commission (NDRC) 2005 Oil and gasindustry standard of the Peoplersquos Republic of China (SY5118-2005)Determination of bitumen from rocks by chloroform extraction

Ots A 2007 Estonian oil shale properties and utilization in power plantsEnergetika 53 8ndash18 httpsdoiorg101007978-1-4757-9223-2_24

Pan Z X 1934 Oil shale in northern Shaanxi In The Geological Survey FrontMinistry of Industry Memoirs of the Geological Survey of China 24 10ndash56[in Chinese]

Qian XL 2009 Chinese oil shale business is still going on Oil Shale26 97ndash98 httpsdoiorg103176oil2009201

Ren L 2007 Characteristics and resource evaluation of Mesozoic oil shales inBinxianndashTongchuan Ordos Basin PhD thesis Jilin University ChangchunChina

Ren ZL 1991 Research on the relations between geothermal history and oil-gasaccumulation Acta Petrolei Sinica 17 17ndash24 [in Chinese with Englishabstract] httpsdoiorg107623syxb199601003

Shu Y 2012 The developments of Chinese oil shale activitie Oil Shale 29101ndash102 httpsdoiorg103176oil2012201

Si XJ 1956 Floral in the Northern Shaanxi Science and Technology PressBeijing [in Chinese with English abstract]

Smith JW 1980 Oil shale resources of the United States Mineral and EnergyResources 23 15ndash23 httpxueshubaiducomusercenterpapershowpaperid=79785876241a952512ee83e9a082e563ampsite=xueshu_se

Smith RMH 1990 A review of stratigraphy and sedimentary environments ofthe Karoo Basin of South Africa Journal of African Earth Sciences 10117ndash137 httpsdoiorg1010160899-5362(90)90050-O

Sun SS Yao YB amp Lin W 2015 Elemental geochemical characteristics ofthe oil shale and the paleo-lake environment of the Tongchuan area southernOrdos Basin Bulletin of Mineralogy Petrology and Geochemistry 34642ndash645 [in Chinese with English abstract] httpsdoiorg103969jissn1007-2802201503021

Surdam RC amp Wolfbauer CA 1975 Green River oil shale play ndash a patternBulletin of Geological Society of America 86 335ndash345 httpsdoiorg1011300016-7606(1975)86lt335GRFWAPgt20CO2

Taylor SR amp Melennan SM 1985 The Continental Crust Its Compositionand Evolution Blackwell Oxford UK

The Office of the National Committee of Mineral Reserves 1987 ReferenceManual of Mineral Industrial Geological Publishing House Beijing [inChinese]

Tissot BP ampWelte DH 1978 Petroleum Formation and Occurrence ndash A NewApproach to Oil and Gas Exploration Springer Berlin 67ndash94

Tribovillard N Algeo TJ amp Riboulleau A 2006 Trace metals as paleo redoxand paleoproductivity proxies An update Chemical Geology 232 12ndash32httpsdoiorg101016jchemgeo200602012

Wan TF 2004 China Tectonics Outline Geological Publishing House Beijing[in Chinese]

Wang C Wang Q X Chen G J He L Xu Y Chen L amp Chen D F 2017Petrographic and geochemical characteristics of the lacustrine balck shale from

Y L Bai amp Y H Ma


the Upper Triassic Yanchang Formation of Ordos Basin China Implicationfor the organic matter accumulation Marine and Petroleum Geology 8652ndash65 httpsdoiorg101016jmarpetgeo201705016

Wang DY Xin BS amp Yang H 2014 Zircon SHRIMP UndashPb age andgeological implications of tuff at the bottom of Chang-7 Member of YanchangFormation in the Ordos Basin Science China Earth Sciences 44 2160ndash2171httpsdoiorg101007s11430-014-4979-0 [in Chinese with Englishabstract]

Wang PX 1995 Talassogenous fauna and lsquoCenosoic transgressionsrsquo in ChinaJournal of Tongji University (Natural Science) 23 129ndash135 [in Chinese withEnglish abstract]

Wang SY Xu JM amp Wang ZH 1992 Present state of China oil shaledevelopment and utilization Geological Economy of China 5 16ndash19 [inChinesewith English abstract] httpswwwdoc88comp-7843590321056html

Wang YM 2007 Geophysical logging of oil shale in exploration of the Triassiccoal-fields in northern Shaanxi Geology of Shaanxi 26 59ndash72 [in Chinesewith English abstract] httpwwwdoc88comp-113710777424html

Wang Z Chen QM Yang WB amp Yao XB 2016 Characteristics andresources evaluation for oil shale in Tongchuan area of Ordos BasinUnconventional Oil ampGas 3 32ndash39 [in Chinese with English abstract] httpwwwdocincomp-1750919340html

Xie XY 2007 Sedimentary record of Mesozoic intracontinental deformation inthe South Ordos Basin China PhD thesis University of Wyoming LaramieWY USA

Yang H amp Zhang WZ 2005 Leading effect of the Seventh Memberhigh-quality source rock of Yanchang Formation in Ordos Basin during theenrichment of low-penetrating oil-gas accumulation geology and geochem-istryGeochimica 34 147ndash154 [in Chinese with English abstract] httpsdoiorg103321jissn0379-1726200502007

Yang H Xi SL Wei XS amp Li ZH 2006 Evolution and natural gasenrichment of multi cycle superimposed basin in the Ordos Basin ChinaPetroleum Exploration 1 17ndash25 [in Chinese with English abstract] httpsdoiorg103969jissn1672-7703200601004

Yang H Fu Q Qi YL Zhou XP Gong N amp Huang SX 2016a Thegeological significance on the late Triassic Yanchang stage palaeo-lacustrineOrdos Basin Acta Sedimentologica Sinica 34 688ndash694 [in Chinese withEnglish abstract] httpsdoiorg1014027jcnkicjxb201604009

Yang H Niu XB et al 2016b Exploration potential of shale oil in Chang 7Member Upper Triassic Yanchang Formation Ordos Basin NW ChinaPetroleum Exploration and Development 43 560ndash569 httpsdoiorg101016S1876-3804(16)30066-0 [in Chinese with English abstract]

Yang JJ 1991 Discover for gas of Lower Palaeozoic in Shanganning BasinGas Industry 11 1ndash6 [in Chinese with English abstract] httpwwwdoc88comp-95727915621html

Yang JJ 2002 Geotectonic Evolution and Hydrocarbon DistributionRegularities Petroleum Industry Press Beijing [in Chinese] httpwwwdoc88comp-95727915621html

Yang JJ amp Pei X 1996 Natural Gas Geology of China Volume 4 PetroleumIndustry Press Beijing [in Chinese]

Yang M amp Liu CY 2006 Sequence stratigraphic framework and its control onaccumulation of various energy resources in the Mesozoic continental basinsin OrdosOil amp Gas Geology 27 563ndash570 [in Chinese with English abstract]httpsdoiorg1011743ogg20060419

Yuan JQ Zhu SQ amp Zhai YS 1979 Mineral Deposits GeologicalPublishing House Beijing 327ndash329 [in Chinese]

Zhang H Bai QZ amp Zhang XW 1995 Formation and Evolution of theOrdos Coal-Forming Basin Shaanxi Science and Technology Press XianChina [in Chinese]

Zhang H He Z L amp Jin X L 2005 Tectonic evolution and coal accumulationof the Ordos Basin In A Brief Explanation of the Geological Tectonic Map ofthe Ordos Coal Basin (with a Scale of 1500 000) Geological PublishingHouse Beijing [in Chinese with English abstract] pp 3ndash31

Zhang QC Wang KM Luo SS amp Wu XZ 2013 Study on thecharacteristics and origin of the oil shale in the Chang 7 Member YanchangFormation in Ordos Basin Advances in Geosciences 2013 197ndash209 httpsdoiorg1012677AG201334028 [in Chinese with English abstract]

Zhang WZ Yang H Li JF amp Ma J 2006 Leading effect of high-classsource rock of Chang 7 in Ordos Basin on enrichment of low permeability oil-gas accumulation ndash hydrocarbon generation and expulsion mechanismPetroleum Exploration and Development 33 289ndash294 httpwwwdoc88comp-7813707435776html

ZhangWZ Yang H amp Li SP 2008a Hydrocarbon accumulation significanceof Chang 91 high-quality lacustrine source eocks of Yanchang FormationOrdos Basin Petroleum Exploration and Development 35 557ndash561 httpsdoiorg101016S1876-3804(09)60088-4

Zhang WZ Yang H Yang YH amp Kong QF 2008b Petrology and elementgeochemistry and development of Yanchang Formation Chang-7 high qualitysource rock in Ordos basin Geochimica 37 59ndash64 [in Chinese with Englishabstract] httpwwwdocincomp-1185993616html

Zhao LY Chen JN amp Wang TS 1991 Grade dividing and composition ofshale in China Geoscience 5 423ndash429 [in Chinese with English abstract]

Zhao YT amp Liu WB 1992 Advance in synthesized usage of oil shale inforeign Countries Advance in Earth Science 7 49ndash50 [in Chinese withEnglish abstract] httpsdoiorg1011867jissn1001-81661992020048

Zhou JG Yao GS Deng HY Xin YG Hu H Zheng XP amp Gong QS2008 Exploration potential of Chang 9 member Yanchang Formation OrdosBasin Petroleum Exploration and Development 35 289ndash293 httpsdoiorg101016S1876-3804(08)60074-9

Ordos oil shale


Fig 1 (a) Location map showing two cross-sections through the Ordos Basin XndashX and YndashY together with outcrops of the middlendashlate Triassic and the oilshale (i) Location map of the Ordos Basin in China and (ii) the location map for Figure 5 (b) Cross-sections XndashX and (c) YndashY through the Ordos Basinshowing the spatial distribution of the Chang 7 Member oil shale and its host strata (modified and supplemented after Bai et al 2009 2010a b) Key QQuaternary System N Neogene System E Paleogene System Mz Mesozoic K Cretaceous System J Jurassic System T Triassic System C-PCarboniferousndashPermian systems isin-O CambrianndashOrdovician systems Pt Proterozoic Ar Archean

Y L Bai amp Y H Ma





Ordos oil shale





Geological context

Tectonic setting



Sedimentary fill



Y L Bai amp Y H Ma




















Ordos oil shale














Y L Bai amp Y H Ma





Age







Thickness



Ordos oil shale


















Y L Bai amp Y H Ma














Ordos oil shale










Y L Bai amp Y H Ma






Oxide(wt)


N = 54)1 NASC2

Traceelements(ppm)






sumREE 1605 1605 1970



Ordos oil shale





Quality
















Y L Bai amp Y H Ma










Ordos oil shale



Origin


















Y L Bai amp Y H Ma






Conclusion


























Ordos oil shale

























































Y L Bai amp Y H Ma



























Ordos oil shale





Ordos oil shale





Geological context

Tectonic setting



Sedimentary fill



Y L Bai amp Y H Ma




















Ordos oil shale














Y L Bai amp Y H Ma





Age







Thickness



Ordos oil shale


















Y L Bai amp Y H Ma














Ordos oil shale










Y L Bai amp Y H Ma






Oxide(wt)


N = 54)1 NASC2

Traceelements(ppm)






sumREE 1605 1605 1970



Ordos oil shale





Quality
















Y L Bai amp Y H Ma










Ordos oil shale



Origin


















Y L Bai amp Y H Ma






Conclusion


























Ordos oil shale

























































Y L Bai amp Y H Ma



























Ordos oil shale





Geological context

Tectonic setting



Sedimentary fill



Y L Bai amp Y H Ma




















Ordos oil shale














Y L Bai amp Y H Ma





Age







Thickness



Ordos oil shale


















Y L Bai amp Y H Ma














Ordos oil shale










Y L Bai amp Y H Ma






Oxide(wt)


N = 54)1 NASC2

Traceelements(ppm)






sumREE 1605 1605 1970



Ordos oil shale





Quality
















Y L Bai amp Y H Ma










Ordos oil shale



Origin


















Y L Bai amp Y H Ma






Conclusion


























Ordos oil shale

























































Y L Bai amp Y H Ma



























Ordos oil shale




















Ordos oil shale














Y L Bai amp Y H Ma





Age







Thickness



Ordos oil shale


















Y L Bai amp Y H Ma














Ordos oil shale










Y L Bai amp Y H Ma






Oxide(wt)


N = 54)1 NASC2

Traceelements(ppm)






sumREE 1605 1605 1970



Ordos oil shale





Quality
















Y L Bai amp Y H Ma










Ordos oil shale



Origin


















Y L Bai amp Y H Ma






Conclusion


























Ordos oil shale

























































Y L Bai amp Y H Ma



























Ordos oil shale














Y L Bai amp Y H Ma





Age







Thickness



Ordos oil shale


















Y L Bai amp Y H Ma














Ordos oil shale










Y L Bai amp Y H Ma






Oxide(wt)


N = 54)1 NASC2

Traceelements(ppm)






sumREE 1605 1605 1970



Ordos oil shale





Quality
















Y L Bai amp Y H Ma










Ordos oil shale



Origin


















Y L Bai amp Y H Ma






Conclusion


























Ordos oil shale

























































Y L Bai amp Y H Ma



























Ordos oil shale





Age







Thickness



Ordos oil shale


















Y L Bai amp Y H Ma














Ordos oil shale










Y L Bai amp Y H Ma






Oxide(wt)


N = 54)1 NASC2

Traceelements(ppm)






sumREE 1605 1605 1970



Ordos oil shale





Quality
















Y L Bai amp Y H Ma










Ordos oil shale



Origin


















Y L Bai amp Y H Ma






Conclusion


























Ordos oil shale

























































Y L Bai amp Y H Ma



























Ordos oil shale


















Y L Bai amp Y H Ma














Ordos oil shale










Y L Bai amp Y H Ma






Oxide(wt)


N = 54)1 NASC2

Traceelements(ppm)






sumREE 1605 1605 1970



Ordos oil shale





Quality
















Y L Bai amp Y H Ma










Ordos oil shale



Origin


















Y L Bai amp Y H Ma






Conclusion


























Ordos oil shale

























































Y L Bai amp Y H Ma



























Ordos oil shale














Ordos oil shale










Y L Bai amp Y H Ma






Oxide(wt)


N = 54)1 NASC2

Traceelements(ppm)






sumREE 1605 1605 1970



Ordos oil shale





Quality
















Y L Bai amp Y H Ma










Ordos oil shale



Origin


















Y L Bai amp Y H Ma






Conclusion


























Ordos oil shale

























































Y L Bai amp Y H Ma



























Ordos oil shale










Y L Bai amp Y H Ma






Oxide(wt)


N = 54)1 NASC2

Traceelements(ppm)






sumREE 1605 1605 1970



Ordos oil shale





Quality
















Y L Bai amp Y H Ma










Ordos oil shale



Origin


















Y L Bai amp Y H Ma






Conclusion


























Ordos oil shale

























































Y L Bai amp Y H Ma



























Ordos oil shale






Oxide(wt)


N = 54)1 NASC2

Traceelements(ppm)






sumREE 1605 1605 1970



Ordos oil shale





Quality
















Y L Bai amp Y H Ma










Ordos oil shale



Origin


















Y L Bai amp Y H Ma






Conclusion


























Ordos oil shale

























































Y L Bai amp Y H Ma



























Ordos oil shale





Quality
















Y L Bai amp Y H Ma










Ordos oil shale



Origin


















Y L Bai amp Y H Ma






Conclusion


























Ordos oil shale

























































Y L Bai amp Y H Ma



























Ordos oil shale










Ordos oil shale



Origin


















Y L Bai amp Y H Ma






Conclusion


























Ordos oil shale

























































Y L Bai amp Y H Ma



























Ordos oil shale



Origin


















Y L Bai amp Y H Ma






Conclusion


























Ordos oil shale

























































Y L Bai amp Y H Ma



























Ordos oil shale






Conclusion


























Ordos oil shale

























































Y L Bai amp Y H Ma



























Ordos oil shale

























































Y L Bai amp Y H Ma



























Ordos oil shale



























Ordos oil shale


Geology of the Chang 7 Member oil ... - Petroleum Geoscience · Northwest Branch of Research...

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Transcript of Geology of the Chang 7 Member oil ... - Petroleum Geoscience · Northwest Branch of Research...