Origins and characteristics of the basin-centered continuous-reservoir unconventional oil-resource base of the Bakken Source System, Williston Basin Manuscript by Leigh C. Price (1999/2000) Table of Contents to Manuscript [not PDF] pages Cover Table of Contents.................................................................................................................. 1 Abstract/Executive Summary.................................................................................................................. 8 1.0 Introduction ................................................................................................................ 25 2.0 The Williston Basin................................................................................................................ 26 2.01 Synopsis................................................................................................................ 26 2.02 Background................................................................................................................ 27 2.03 Stratigraphy................................................................................................................ 28 2.04 The Bakken Source System.............................................................................................. 30 2.05 The Uniqueness of the Williston Basin Sample Base....................................................... 31 3.0 Classic Petroleum Geologic and Geochemical Williston Basin Studies ....................................... 33 3.01 Synopsis................................................................................................................ 33 3.02 Williams-Dow................................................................................................................ 34 3 03 Meissner................................................................................................................ 37 3.04 Accepted Model of Oil Expulsion and Accumulation...................................................... 38 3.05 ROCK-EVAL................................................................................................................ 39 3.06 ROCK-EVAL Data Supporting the Accepted Model of OilExpulsion and Accumulation............................................................................................ 41 4.0 Present-Day Williston Basin Petroleum-Geochemical Research .................................................. 43 4.01 Synopsis................................................................................................................ 43 4.02 Introduction................................................................................................................ 45 4.03 Bakken Oil to Mid Madison Oil Comparison................................................................... 45 4.04 Western Canadian Basin................................................................................................... 48 4.05 Alternate Oil Expulsion and Accumulation Model........................................................... 48 4.06 Basin Richness versus Structural Intensity....................................................................... 49 4.07 Implications of the Alternate Expulsion and Accumulation Model.................................. 50 5.0 Unconventional Energy Deposits .................................................................................................. 52 5.01 Synopsis................................................................................................................ 52 5.02 Introduction................................................................................................................ 53 5.03 Antrim Shale Gas.............................................................................................................. 54 5.04 San Juan Basin Coal Gas .................................................................................................. 57 5.05 Discontinuous (Conventional) versus Continuous (Unconventional) HC Deposits ......... 61 6.0 Characteristics, and Causes Thereof, of Bakken Source System Reservoir Rocks ....................... 63 6.01 Synopsis................................................................................................................ 63 6.02 Introduction................................................................................................................ 66 6.03 Stratigraphy................................................................................................................ 67 6.04 The Lowermost Lodgepole Shale ..................................................................................... 68 6.05 Traditional Core Analyses ................................................................................................ 70 6.051 Introduction.......................................................................................................... 70 6.052 NDGS #8177 Immature Shales (Pre-HC Generation) ......................................... 70 6.053 NDGS #8637 Less Mature Shales (Pre-HC Generation)..................................... 71 6.054 NDGS #7851 Immature Shales Just Having CommencedHC Generation........................................................................... 73 6.055 NDGS #8709 Thick Moderately-Mature Shales.................................................. 75 6.056 NDGS #12494 Thin Mature Shales ..................................................................... 78 6.057 NDGS #11617 Thick Mature Shales ................................................................... 80 6.058 Discussion of Conventional Core Analyses......................................................... 82 6.06 ROCK-EVAL Analysis of Immature Core Samples ........................................................ 84 6.06 1 Introduction.......................................................................................................... 84 6.062 NDGS #8177 ....................................................................................................... 85 6.063 Early Movement of Oil ........................................................................................ 86 6.064 NDGS #2618 ....................................................................................................... 87 6.065 NDGS #9001 ....................................................................................................... 89 6.066 NDGS #8368 ....................................................................................................... 90 6.067 NDGS #2010 ....................................................................................................... 91 6.07 ROCK-EVAL Analysis of Mature Core Samples ............................................................ 94 6.071 NDGS #8474 ....................................................................................................... 94 6.072 Oil Loss to the Drilling Mud during Drilling....................................................... 95 6.073 NDGS #5088 ....................................................................................................... 96 6.074 Significance of Increased S2 Values .................................................................... 98 6.075 NDGS #1405 ..................................................................................................... 100 6.076 Evidence of Oil Loss to the Drilling Mud and Evaporation during Storage...... 101 6.08 Evidence and Causes of Super-Lithostatic Fracturing.................................................... 108 Leigh C. Price and Kathy Stolper 6.081 NDGS #4958 Immature Bakken Shales ............................................................ 108 6.082 NDGS #8824Slightly Increased Bakken Shale Maturity................................. 110 6.083 NDGS #13098 Mature Shales-Bakken HC Kitchen.......................................... 112 6.084 NDGS #12160 Thin Moderately-Mature Shale................................................. 116 6.085 NDGS #11689 ................................................................................................... 118 6.086 Causes of Super-Lithostatic Fracturing ............................................................. 121 6.087 Consequences of Super-Lithostatic Fracturing.................................................. 126 6.088 IFP 's Position on Hydraulic Fracturing............................................................. 128 6.089 Bakken Source System Oil to Water Ratios ...................................................... 129 6.09 Implication to Source Rock Expulsion ........................................................................... 130 6.10 Discussion and Conclusions: Bakken Reservoir Rocks.................................................. 133 7.0Williston Basin Maturity and Heat Flow..................................................................................... 136 7.01 Synopsis.............................................................................................................. 136 7.02 Introduction.............................................................................................................. 138 7.03 Vitrinite Reflectance (Ro) ............................................................................................... 139 7.04 Williston Basin Ro Profiles ............................................................................................. 140 7.041 NDGS #6464 ..................................................................................................... 140 7.042 NDGS #607 ....................................................................................................... 141 7.043 NDGS #527 ....................................................................................................... 143 7.044 All Analyzed Wells............................................................................................ 144 7.05 Corroborating Evidence.................................................................................................. 145 7.06 Discussion.............................................................................................................. 145 7.07 Basin Cooling.............................................................................................................. 148 7.08 Maturity versus Rank...................................................................................................... 150 7.09 Suppression of Organic Metamorphism in Hydrogen-Rich OM.................................... 152 7.091 Introduction........................................................................................................ 152 7.092 Examples/Consequences of Suppression of Organic Metamorphism............... 152 7.10 Causes of Suppressed Organic Metamorphism in Hydrogen-Rich OM......................... 157 7.101 Controlling Parameters of Organic Metamorphism........................................... 157 7.102 Hydrolytic Disproportionation of OM............................................................... 159 7.103 Water Availability versus OM Type.................................................................. 161 7.11 Conclusions and Implications......................................................................................... 166 8.0 Recent Publications.............................................................................................................. 167 8.01 Synopsis.............................................................................................................. 167 8.02 Burrus et al. (1996) ......................................................................................................... 171 8.03 Reasons for the Burrus et al. (1996) Model .................................................................... 176 8.04 Schmoker (1996)............................................................................................................. 177 8.05 Carlisle et al. (1992)........................................................................................................ 183 8.06 LeFever et al. (1991)....................................................................................................... 187 9.0 The Lower Lodgepole Waulsortian Mound Play......................................................................... 196 9.01 Synopsis.............................................................................................................. 196 9.02 Introduction.............................................................................................................. 197 9.03 The Source Rock............................................................................................................. 198 9.04 Oil Source-Rock Maturity............................................................................................... 200 9.05 Reservoir Porosity and Permeability .............................................................................. 201 9.06 Fracturing.............................................................................................................. 204 9.07 Salt Collapse.............................................................................................................. 205 10.0 Mass Balance Estimates of Bakken-Generated Oil ..................................................................... 208 10.01 Synopsis.............................................................................................................. 208 10.02 Introduction.............................................................................................................. 210 10.03 Inputs and Assumptions.................................................................................................. 211 10.04 Schmoker and Hester (1993), Webster (1984)................................................................ 214 10.05 Starting TOC Contents.................................................................................................... 216 10.06 Estimated Amounts of Generated Oil ............................................................................. 217 10.061ROCK-EVAL .................................................................................................... 217 10.062Closed System Measurements ........................................................................... 219 10.063HC Generation Models ...................................................................................... 224 10.064Hydrolytic Disproportionation of OM............................................................... 225 10.065The Present Estimate of Bakken-Generated Oil ................................................ 233 10.066Small-Scale Estimates........................................................................................ 235 10.067Comparisons to Other Source Systems.............................................................. 237 11.0 Other Considerations.............................................................................................................. 239 11 .01 Synopsis.............................................................................................................. 239 11.02 Introduction.............................................................................................................. 240 11.03 The Uniqueness of the Baken Source System................................................................ 241 11.031Williston Basin Paleo-Heat Flow ...................................................................... 241 11.032The Unparalleled Williston Basin Sample Base................................................ 242 11.033The Source-Reservoir Relationship................................................................... 242 11.04 Additional Positive Aspects of the Bakken Source System............................................ 244 11.05 Oil Recovery.............................................................................................................. 244 12.0 Conclusions.............................................................................................................. 247 13.0 Bibliography.............................................................................................................. 263 List of Figures.............................................................................................................. 282 Tables Figures Origins and characteristics of the basin-centered continuous-reservoirunconventional oil-resource base of the Bakken Source Syslem, Williston BasinLeigh C. Pricel'Denver Federal Center, Box 25046, Denver, CO 80225AbstractlExecutive Summary1.0 Introduction2.0 The Williston Basin2.01 Synopsis2.02 Background2.03 Stratigraphy2.04 The Bakken Source System2.05 The Uniqueness of the Williston Basin Sample Base3.0 Classic Petroleum Geologic and Geochemical Williston Basin Studies3.01 Synopsis3.02 Williams-Dow3.03 Meissner3.04 Accepted Model orOil Expulsion and Accumulation3.05 ROCK-EVAL3.06 ROCK-EVAL Data Supporting the Accepted Model orOil Expulsion andAccumulation4.0 Present-Day Williston Basin Petroleum-Geochemical Research4.01 Synopsis4.02 Introduction4.03 Bakken Oil to Mid Madison Oil Comparison4.04 Western Canadian Basin"4.05 Alternate Oil Expulsion and Accumulation Model4.06 Basin Richness versus Strucrurallntensity4.07 Implications of the Alternate Expulsion and Accumulation Model5.0 Unconventional Energy Deposits5.01 Synopsis5.02 Introduction5.03 Antrim Shale Gas5.04 San Juan Basin Coal Gas5.05 Discontinuous (Conventional) versus Continuous (Unconventional) HC Deposits6.0 Characteristics, and Causes Thereof, of Bakken Source System Reservoir Rocks6.0I Synopsis6.02 Introduction6.03 Stratigraphy6.04 The Lowennost Lodgepole Shale6.05 Traditional Core Analyses6.051 Introduction6.052 NDGS #8177 Immatute Shales (pte-HC Generation)6.053 NDGS #8637 Less Immature Shales (pre-HC Generalion)6.054 NDGS #7851Immature Shales Just Having Commenced HC Generation6.055 NDGS #8709 Thick Moderately-Mature Shales6.056 NDGS #12494 Thin Mature Shales6.057 NDGS #11617 Thick Mature Shales26.058 Discussion of Conventional Core Analyses6.06 ROCK-EVAL Analysis oflrnmature Core Samples6.061 Introduction6.062 NDGS #81776.063 Early Movement of Oil6.064 NDGS #26186.065 NDGS #90016.066 NDGS #83686.067 NDGS #20106.07 ROCK-EVAL Analysis of Mature Core Samples6.071 NDGS #84746.072 Oil Loss to the Drilling Mud during Drilling6.073 NDGS #50886.074 Significance of{ncreased Sz Values6.075 NDGS #14056.076 Evidence of Oil Loss to the Drilling Mud and Evaporation during Storage6.08 Evidence and Causes of Super-Lithostatic FracturingLeigh C. Price and Kathy Stolper6.081 NDGS #4958 Immature Bakken Shales6.082 NDGS #8824 Slightly Increased Bakken Shale Maturity6.083 NDGS #13098 Mature Shales-Bakken HC Kitchen6.084 NDGS #12160 Thin Moderately- Mature Shale36.085 NDGS #116896.086 Causes of Super-Lithostatic Fracturing6.087 Consequences of Super-Lithostatic Fracturing6.088 IFP's Position on Hydraulic Fracturing6.089 Bakken Source System Oil to Water Ratios6.09 Implication to Source Rock Expulsion6.10 Discussion and Conclusions: Bakken Reservoir Rocks7.0 Williston Basin Maturity and Heat Flow7.01 Synopsis7.02 Introduction7.03 Vitrinite Reflectance (R,,)7.04 Williston Basin~ Profiles7.041 NDGS #64647.042 NDGS #6077.043 NDGS #5277.044 All Analyzed Wells7.05 Corroborating Evidence7.06 Discussion7.07 Basin Cooting7.08 Maturity versus Rank7.09 Suppression of Organic Metamorphism in Hydrogen-Rich OM7.091 Introduction47.092 Examples/Consequences of Suppression of Organic Metamorphism7.10 Causes of Suppressed Organic Metamorphism in Hydrogen-Rich OM7.101 Controlling Parameters of Organic Metamorphism7.102 Hydrolytic Disproportionation of OM7.103 Water Availability versus OM Type7.11 Conclusions and Implications8.0 Recent Publications8.01 Synopsis8.02 Burrus et at. (1996)8.03 Reasons for the Burrus et at. (1996) Model8.04 Schmoker (1996)8.05 Carlisle et at. (1996)8.06 LeFever et at. (1991)9.0 The Lower Lodgepole Waulsortian Mound Play9.01 Synopsis9.02 Introduction9.03 The Source Rock9.04 Oil/Source-Rock Maturity9.05 Reservoir Porosity and Permeability9.06 Fracturing9.07 Salt Collapse510.0 Mass Balance Estimates of Bakken-Generated Oil10.0I Synopsis10.02 Introduction10.03 Inputs and Assumptions10.04 Schmoker and Hester (1983), Webster (1984)10.05 Starting TOC Contents10.06 Estimated Amounts of Generated Oil10.061ROCK-EVAL10.062 Closed System Measurements10.063HC Generation Models10.064 Hydrolytic Disproportionation of OM10.065 The Present Estimate of Bakken-Generated Oil10.066 Small-Scale Estimates10.067 Comparisons to Other Source Systems11.0 Other Considerations11.01 Synopsis11.02 Introduction11.03 The Uniqueness of the Bakken Source System11.031Williston Basin Paleo-Heat Flow11.032 The Unparalleled Williston Basin Sample Base1t.033 The Source-Reservoir Relationship611.04 Additional Positive Aspects of the Bakken Source System11.05 Oil Recovery12.0 Conclusions13.0 Bibliography71.0 ABSTRACTfEXECUTlVE SUMMARYAs discussed in section 2.0, the Williston Basin. the most structurally-simple basin in theworld, is characterized by unvarying flat-lying sediments. Most (75%) of the conventional oilproduction of this basin is found in the Mississippian mid-Madison limestones, the principal oilreservoir of the basin. Sediment age in the basin ranges from Cambrian to early Tertiary withnumerous unconfonnities present. The lower Mississippian-upper Devonian Bakken Formationcontains nvo black shales, the richest source rocks in the basin, indeed, among the richest sourcerocks worldwide. The rocks adjacent to the two Bakken shales are organic-poor. carbonate-rich,brittle, low-porosity, impermeable rocks, which, with the two shales, form a tight, closed-fluidsystem which cannot transmit fluids. These rocks have been tenned the "Bakken Source System"(price and LeFever, 1992).Due to several unrelated circumstances, theNorth Dakota portion of the Williston Basinhas the best rock, oil, and well-history sample base worldwide. Because of this sample base, andbecause of the relatively simple geologic history of the basin (compared to many other basins), theWilliston Basin is also one of the best-studied petroleum basins worldwide. This unique sampleand data base, and the structural simplicity of the Williston Basin, has led to the recognition anddelineation of anbasin-centered oil-resource base there, possibly 200-400 billionbarrelss in place, the point of this discussion.In section 3.0, we discuss how early classic research by Amoco Oil Company personnel(Dow, 1974; Williams, 1974) in the Williston Basin established important petroleum-geochemicalconcepts, now universally applied in oil exploration. Indeed, this early research by Amoco helped8lay thefoundationfor thenfledgling new science of petroleum geochemistry. Dow (1974) andWilliams (1974) concluded that the richest source rocksin the Williston Basin, the Bakken shales,had sourced the most important conventional oil resource base in the basin, the oils in theMississippian mid Madison reservoirs about 800 to1,000 ft (244 to 305 m) above the Bakkenshales. Subsequent research by other investigators supported the early Amoco work,andled tothe synthesis of themodel of oil expulsion fromsource rocks, and accumulation into conventionaloil deposits, now universally acceptedin the petroleum geosciences, to wit:1) Petroleum basins, including petroleum-basin depocenters, are open-fluidsystems wherefluid movement is very easy.2) Source rocks expel almost all of the oil thatthey generate.3) Only a small fraction oftbis expelled oil is actually caught in commercial traps.Thus,most oil expelled from source rocks is believed to be irrevocably lost over geologictime. Countless ROCK-EVAL analyses,the most widely-used analytical instrument inpetroleml1geochemistry, appear to support the above model of oil expulsion and accumulation.Many of the concepts developed by Dow (1974) and Williams (1974) have stood the test of timeand remain unmodified tothis day. However, newer research conclusively demonstrates that amajor conclusion of these studies, that the Bakken shales are the source rocks for the mid-Madison oils, is wrong.Section 4.0 discusses how the analytical instruments and methods available when Amococarried out their early (1968 to1972) Williston Basin work are (understandably) archaic comparedto today's tools. Petroleum geochemistry's most reliable analysisis oil-to-oil correlation, whereinit can be irrefutably determined if two or more oils haveb e ~ n sourced from the same rock,and are9thus of one oil family, or not. State of the art analyses, and comparison of mid-Madison oils withoils produced directly from the Bakken Source System, demonstrate that these two oil suites aredifferent. Thus, the Bakken shales could not have sourced the mid Madison oils. Moreover, nooil sourcedfrom the Bakken shales has beenfound in a conventional oil reservoir on the U.S. sideof the Williston Basin. Because of the structural simplicity of, and lack of faulting in, theWilliston Basin,it is inconceivable, by any model of basin evolution, that the oil generated by theBakken shales leaked out of the basin without charging at least one conventional oil reservoir inthe basin. Thus, the inescapable conclusion follows, that all the oil generated by the Bakkenshales remains in the Bakken Source System. Hard data (section 6.0) support this conclusion.That the richest source rock in the Williston Basin has contributed nothing to theconventional oil reservoirs there is a staggering conclusion as related to petroleum geochemistry.Moreover, independent research demonstrates that the same situation exists in the WesternCanadian Alberta Basin. The Williston and Alberta Basins are at the opposite ends of thespectrum regarding structural style and degree of structural intensity. Two such disparate basinstyles having the same source rock-reservoir problem strongly suggests that the accepted model ofoil expulsion and accumulation may be widely inoperable. [n this light, an alternate model of oilexpulsion and accumulation was proposed (price, 1994a), to wit:t) The deep parts of petroleum basins, where the sediments are thickest (the.depocenters), are closed-fluid systems, where fluidmovement is difficult orimpossible.2) Oil expulsion from source rock systems is uncommon.3) Unless source rocks are physically disrupted by intense structural activity, such10as faulting or salt diapirism, or are directly adjacent to good fluid conduits, suchas sandstones, oil expulsion does not occur at all.4) Therefore, in many cases, most generated oil remains in or adjacent to its sourcerock.This hypothesized alternate model of oil expulsion and accumulation is easily tested. Ifthe model is valid, a strong correlation should exist between increasing structural intensity in thedepocenters of petroleum basins with increasing amounts of recoverable conventionalhydrocarbons (HCS) for well-explored, petroleum-bearing basins worldwide. A pronouncedcorrelation berween increasing basin richness and increasing deep-basin structural intensity doesexist (Price, 1994a). This observation in tum suggests that the alternate model ofoil expulsionand accumulation may be correct and that the accepted expulsion-accumulation model could beinvalid, or at least widely inapplicable. This last conclusion has profound implications forpetroleum geology, one of which concerns us here: huge unconventional oil-resource bases shouldthen theoretically exist over large basinal areas,as continuous oil reservoirs, in and around sourcerocksin the deep unstructured parts of some sedimentary basins.In section 5.0 we discuss the general characteristics of unconventional-resource bases, allof which have a number of attributes in common, two of which immediately concern us here.First, economic exploitation of unconventional resources is almost completely governed by'.technology. Second, unconventional resources, which can be economically produced due totechnological advances, can be very large. Many examples exist of different unconventionalresources where these characteristics apply, just one being the bulk-tonnage, low-grade golddeposits of northern evada, which were once "unconventional", but are now considered11eminently conventional. However, we are concerned here principally with unconventional-energydeposits.Examples of unconventional, or once unconventional, energy deposits are: basin-centeredgas deposits, tight-sand gas deposits, deposits, shale-gas deposits, and coal-gas deposits.One unconventional shale-gas resource at one time involved the most intense gas-drilling play inthe U.S., the Antrim shale-gas play of northem Michigan, where, as of 1996, over 4,300 wellswere producing 425million cubic feet of gas per day. Antrim shale-gas production began becauseof the Section 29 Federal Tax Credit, but quickly became a technological play, based on researchcarried out, and applied by, the preeminent research group, the Gas Research Institute. TheAntrim shale-gas resource base, and the play itself, have numerous parallels to the Bakken oil-resource base, which we discuss.Coal gas has become a major source of natural gas, especially in the San Juan Basin (NewMexico and Colorado). Coal-gas production, like Antrim shale-gas production and production ofoil fromthe Bakken Source System, requires specific drilling, completion, and stimulationprocedures, to economically produce the resource base. In all three of the aforementioned cases,geologyis constant, or nearly so, in the respective basins, and economic HC retrievals are almostentirely-dependent on appropriate recovery procedures specifically designed for the resource basein question. If recovery procedures are applied, the wells are economic failures andthe resource base is incorrectly viewed as non-recoverable. San Juan Basin coal-gas productionhas other pointed parallels with production of Bakken oil, which we also discuss.Section 6.0 discusses the origin and characteristics of the huge continuous oil deposit intbe Bakken Source System. Because of the oil shows encountered whenever the drill penetrated12even marginally-mature Bakken Source System rocks, these rocks have been cored in at least 107wells in the North Dakota portion of the Williston Basin Moreover, at least 41of thesecored wells have had traditional core analyses performed on them: porosity, permeability,residual-oil and water saturations, and visual examinations, analyses which exist in the publicdomain. Detailed ROCK-EVAL analyses on Bakken Source System reservoir rocks, withspacings of 6" to 24"m) between samples, for 26 geographically-separated wells in theWilliston Basin, have also measured the amount of oil in Bakken Source System rocks (much likeresidual-oil saturation analyses) and the general organic richness of these rocks.We present examples of conventional core analyses from six different wells whereinBakken Source System rocks were cored. The conclusions drawn from these six examples arerepresentative of the analyses from all 41cored wells. The three reservoir rocks adjacent to thel\vo Bakken shales always have low matrix penneabilities (0.01to 0.03 millidarcies, or less) andzero residual-ail-saturation percentages in basin areas where the Bakken shales are at shallowdepths of burial and are thus very immature and have not begun HC generation. Moreover, thesethree adjacent rocks also have no, or only few, fractures in basin areas where the Bakken shalesare immature. As maturity increases in the Bakken shales, so do the residual-oil concentrationsand the incidence of fracturesin the rocks adjacent to the shales. Where the Bakken shales areboth thick and maturethe shales have extensively generated HCS), the three rocks adjacentto the two Bakken shales always have both high residual-oil saturations and also a high incidenceof fractures. These fractures dramatically increase the permeability of the rocks in which theyoccur. Both the fracturing and the high residual-oil saturations are a result of oil and gasgeneration in the extremely organic-rich Bakken shales.13Our close-spaced ROCK-EVAL analyses of Bakken Source System reservoir rockscorroborate the observations from the traditional core analyses: For example, the three rocksadjacent to the rwo Bakken shales, where the Bakken shales are immature, are extremely organic-poor and, throughout the area of investigation have no capability to generate indigenous HCS.Second, progressive movement of Bakken-shalegenerated oil into these three rocks occurs withincreasing maturity of the Bakken shales. Third, samples of these three rocks adjacent to the twoBakken shales from basinal areas where the Bakken shales are both thick and mature, alwavs haveverY large increases in organic richness compared to background levels, due to massive injectionof Bakken-shate-generated oilinto them.We present calculations demonstrating that the conversion of solid organic matter (OM;kerogen)in source rocks to oil and gas during HC generation with sediment burial is a volume-expansive reaction. That is, the products of the reaction (oil and gas) occupy a greater volumethan the reactants (kerogen). Because all the rocks of the Bakken Source System are "tight", withessentially no permeability, they cannot transmit fluids. Thus, during HC generation, the newly-generated oil and gas from the Bakken shales could not be transported from the shales, resultingin a volume expansion of material within a fixed volume. This expansion in tum created veryhigh fluid pressures which compressed the solid OM (the kerogen) in the Bakken shales, resultingin stored potential energy of compression. The abnormally high pressure from He generationeventually became so high that the rocks were fractured, thereby relieving the accumulated stressin the system. However, the energy of compression stored within the Bakken shales actuallycreated superlithostatic pressures, pressures greater than the weight of the overlying column ofrocks. The resulting expulsion of oil from the Bakken shales under these super-lithostatic14pressure events in tum created super-lithostatic fracturing events, resultingin extremely well-interconnected reservoirs in the three rocks adjacent to the two Bakken shales with a dominantly-horizontalfracture system.Section 7.0 concerns Williston Basin heat flow and sediment-burial temperatures.Increasing burial temperatures principally cause HC generationIn source rocks. High heat flowscause abnonnally high geothermal gradients, which either in the geologic past, paleo geothennalgradients, or occurring today, result in relatively high sediment-burial temperatures at relativelyshallow depths. High geothennal gradients thus result in HC generation occurring in source rocksat shallower than normal burial depths.Paleo-geothermal gradients may be estimated by measuring different petroleum-geochemical parameters versus depth ("maturity indices"). Vitrinite reflectance (RJ, and to alesser extent, ROCK-EVAL Tmax'are the two very best maturity indices in petroleumgeochemistry, especially when these two analyses can be executed on coal samples. PreviouslypublishedR." profiles versus depth suggested extreme paleo temperatures existed in the WillistonBasin in the geologic past. We have augmented the previously published database with furthervitrinite reflectance analyses, versus depth including coal samples in the shallowest samples. OUfdata corroborate the previousfindings: Extreme paleo-geothermal gradients existed in theWilliston Basin in the geologic past. Moreover, the heat flow causing these gradients occurredrecently in the geologic past, in Eocene or younger time. In point of fact, the Williston Basin hashad the highest heat flow we have observed in any sedimentary basin worldwide.Other evidence also exists that extreme heat flows occurred in the Williston Basin.Moreover, other investigators have also hypothesized high paleo-heat flowsfrom completely15separate lines of research. However, still other investigators, dealing with petroleum-geochemicalcomputer modeling have simply assumed, with no supporting data, that heat flows in theWilliston Basin have been constant through geologic time at the moderate present-day levels. Wecontend that these assumptions were made simply to facilitate construction of the aforementionedmodels, and thus have no basis in reality.In recent geologic time, the Williston Basin has been significantly cooled by strong cross-basinal meteoric-water recharge, via five Tertiary to Cambrian aquifers very transmissible tofluids. This rapid (in a geologic sense) basin cooling explains loday's moderate burialtemperatures in the Williston Basin.Marine-derived, hydrogen-rich kerogen, the OM type which has sourced most of theworld's oil, requires far higher burial temperatures than generally recognized to initiate andsustain He generation. This situation has largely gone undetected because all aspects of organicmetamorphism, and hence all organic maturation indices, are strongly suppressed in hydrogen-rich OM compared to hydrogen-poor type III OM buried at the same rank.. Examples, and causes,of this suppression are presented, and discussed. Because of this strong suppression of organicmetamorphism in hydrogen-rich kerogen, the extreme paleo-heat flows in the Williston Basin,and the resulting extreme paleo-burial temperatures thereof, have created a highly unusualsituation. Specifically, world-class source rocks, the Bakken shales, have generated hundreds ofbillions of barrels of oil and created superlative oil reservoirs in the rocks adjacent to the twoshales, all at shallow burial depths (9,000-11,500 ft; 2,743-3,505 rn). Similar oil-resource bases inother basins worldwide will occur only at depths of 20,000 to 30,000 ft (6,095-9,144 m) becauseof the significantly lower present-day or paleo-geothennal gradients in these basins. Thus,16extraction of oil from these as yet unrecognizedresource bases will be much more difficult thanfromthe Bakken Source System, because of the much greater depths,and therefore highertemperatures and pressures, involved.Four different investigations (BUmlS et aI., 1996; Schmoker, 1996; Carlisle et al., 1992;andLeFever et aI., 1991) have reached conclusions divergentfrom those herein regarding theorigin, fate, and recoverability of the oil generated by the Bakken shales. Each of these studiesare discussedin some detail in section 8.0.BUmls et al. (1996), in a computerized model of the Williston Basin, assumed that theheatflow, and therefore the geothermal gradients, of the Williston Basin had been constantthroughgeologic time at loday's moderate values. They further assumed that abnonnal fluidpressuresnever occurred from He generation in the Bakken shales, and therefore, that nohydraulicfracturing of any Bakken Source System rocks had occurred. On the basis of theseassumptions, Burrus et al.(1996)thus concluded that allthe oil generated by the Bakken shaleshad been dispersed throughout the Williston Basin at irreducible oil saturations in porous andpermeable Lodgepole limestones. In fact,because of this hypothesized dispersion, Bakken oilsaturations in the Lodgepole were predicted to be too low to be analytically detectable.BUffils et al.(1996) made very unrealistic inputs for their model, those inputs thus yieldingunrealistic results in their calculations. In one such example, Burrus et at.(1996) assumedanaveragelateralpermeability of 40 millidarcies in the Lodgepole limestone. This assumed value is4,000 times greater than measured average lateral matrix permeabilities fromhundreds of coreanalyses fromnumerous wells throughout the Williston Basin. Moreover, predictions from themodel of Burrus et al.(1996) strongly contradict actual observations from Bakken Source System17rocks. These contradictions reveal that key computer predictions of Burrus et al. (1996) arewrong. We examine how this came to be.Schmoker (1996) observed marked heterogeneities in the oil productivities of WillistonBasin Bakken wells at both local and regional levels. Local production heterogeneities (e.g.,where two spatially.c1ose wells produced vastly different amounts of oil) were assumed to be dueto heterogeneities in reservoir geology between the two wells over short lateral distances.However, no proof was offered to support this assumption. In contrast, we demonstrate thatreservoir geology is constant over the entire area of discussion in the Williston Basin.Schmoker's (1996) assumption on this point is incorrect. Schmoker (1996) also attributed thecause of the highest Bakken well productivities to date in the RIVER REO000"I.....,I>-'t'IDEAD wOODx2i""- "- w"- w Q~""tJ1(A)""QN""-~UJJ:>r--~ ' "wQU> r-.N & l ~'"~ Q(n0> &-t':!-,J ~ \gWr- r"-Na",-N '" '"O ~ ~('>(r) ....FIG.33ANDGS 11397 LODGEPOLE LIMESTONE3306.....

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