Saskatchewan Geological Survey 1 Summary of Investigations 2005, Volume 1

Williston Basin Architecture and Hydrocarbon Potential: A Targeted Geoscience Initiative Project 1

S.G. Whittaker

Whittaker, S.G. (2005): Williston Basin architecture and hydrocarbon potential: A Targeted Geoscience Initiative Project; in Summary of Investigations 2005, Volume 1, Saskatchewan Geological Survey, Sask. Industry Resources, Misc. Rep. 2005-4.1, CD-ROM, Paper A-2, 6p.

Abstract The Williston Basin Architecture and Hydrocarbon Potential Project is a two-year collaborative geoscience program involving: Saskatchewan Industry and Resources; Manitoba Industry, Economic Development and Mines; the Geological Survey of Canada; the University of Saskatchewan; and the University of Alberta. The project involves identifying and mapping the major Phanerozoic stratigraphic units in a 380 000 km2 region covering much of eastern Saskatchewan and western Manitoba. A comprehensive and consistent stratigraphic database will be integrated with aeromagnetic and gravity geophysical data, hydrogeological investigations and remotely sensed imagery to produce three-dimensional geological models and an interactive geological atlas on a publicly accessible website (www.willistontgi.com). Also included in the project is an inventory of known hydrocarbon occurrences within the study region. A searchable bibliography of geoscience literature associated with the Williston Basin is also being constructed for the website. This regional geoscience synthesis is expected to assist further exploration and development of resources within the region.

Keywords: Williston Basin, Targeted Geoscience Initiative, stratigraphy, hydrogeology, geophysics, bibliography, hydrocarbon, remotely sensed imagery, geological atlas.

1. Introduction The Williston Basin Architecture and Hydrocarbon Potential Project is a two-year collaborative program involving Saskatchewan Industry and Resources (SIR); Manitoba Industry, Economic Development and Mines (IEDM); the Geological Survey of Canada (GSC); the University of Saskatchewan; and the University of Alberta. This program is one of several second-round Targeted Geoscience Initiative (TGI) projects sponsored by Natural Resources Canada and is currently in its second and final year. The project involves an area more than 380 000 km2 including much of eastern Saskatchewan and western Manitoba (Figure 1). Geological mapping includes all Phanerozoic strata from the outcrop belt along the margin of exposed Precambrian Shield into the subsurface nearly 3.5 km deep at the Canada–U.S. border. The primary objective of the Williston Basin TGI Project is to develop an integrated geoscience dataset incorporating new and revised stratigraphic information; seismic, gravity and aeromagnetic data; hydrogeological mapping; and remotely sensed imagery from the Phanerozoic succession of the northeastern portion of the Williston Basin. These data will be synthesized into an interactive geological atlas on a publicly accessible website: www.willistontgi.com. Known hydrocarbon occurrences will be documented and the resulting information will be made available on the website, along with a static three-dimensional geological model constructed for the entire project area. In addition, a searchable bibliography of geoscience documents relevant to the Williston Basin is also publicly available on the website.

Regional geological syntheses such as the Williston TGI provide a consistent framework to develop new exploration ideas in a mature basin, and are an essential component in deciphering large-scale basin processes that lead toward effective hydrocarbon- and mineral-exploration strategies. Enhanced knowledge of the distribution of subsurface minerals (e.g., brines and potash), hydrocarbon migration pathways, and entrapment mechanisms within and beyond traditional geographic areas of hydrocarbon production are being realized from this regional and integrated approach.

1 Funding for the Williston Basin TGI Project was largely provided by NRCan with in-kind support and some additional funding from Saskatchewan Industry and Resources and Manitoba Industry, Economic Development and Mines.

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Figure 1 - Digital elevation model of the Williston Basin TGI study area covering eastern Saskatchewan and western Manitoba. The northern limit of the distribution of Phanerozoic strata is shown by the red line outlining the exposed edge of the Precambrian Shield. The area included in the mapping project is more than 380 000 km2 and strata reach a thickness over 3.5 km near the U.S.–Canada border. Major Canadian oil fields are shown in green.

Specific objectives of the project include:

1) Identification and mapping of major geological units within the project area in Saskatchewan and Manitoba. 2) Development of a web-enabled compilation of existing literature and current geoscience knowledge for the

project area. 3) Production of regional isopach and structure maps for all major geological units in the study area and their

presentation in a GIS format with attached attribute data. 4) Acquisition and incorporation of seismic, aeromagnetic and gravity data, and of remotely sensed imagery into a

seamless three-dimensional regional geological model of the subsurface to improve our understanding of the Precambrian basement and its possible tectonic relationship with overlying Phanerozoic rocks.

5) Production of a regional hydrogeological model for strata of Paleozoic and Mesozoic age within the study area. 6) Provision of a comprehensive inventory of information associated with hydrocarbon occurrences in the

northeastern Williston Basin. Magoon and Dow (1994) discussed the levels of petroleum investigations required to better understand the genesis and habitat of hydrocarbons. These levels include: 1) sedimentary-basin analysis; 2) petroleum-systems analysis; 3) play; and 4) prospect.

Work within the Williston Basin TGI addresses aspects of all these levels, but is mainly focused toward providing data for the higher level investigations of sedimentary-basin and petroleum-systems analyses. It is anticipated these data will assist exploration within the Williston Basin by companies of all sizes, particularly those that do not have the resources to perform regional studies.

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2. Project Organization Work within the Williston Basin TGI Project is divided into eight tasks.

a) Task 1: Geoscience Inventory The primary role of Task 1 is to freely promote and communicate the results and products of the Williston Basin TGI for public use. This will mainly be performed through the development of an interactive website; www.WillistonTGI.com. The website will incorporate a geological atlas in GIS format that will include structural and isopach maps, cross sections, and attribute data. Geophysical data including gravity and aeromagnetic maps, hydrogeological characteristics, and remotely sensed imagery data will also be available. All final reports and datasets will be available for download from the website.

Also on the website is a searchable, comprehensive bibliography of technical geoscience publications that relate to the Williston Basin.

b) Task 2: Regional Geological Mapping The main function of Task 2 is to develop a consistent stratigraphic database for use by industry, academia, and government. During the project more than 4,000 wells in Saskatchewan and 3,000 wells in Manitoba have been studied. Most wells that penetrate the Devonian or deeper in the study area have been used. In addition, selected wells penetrating only down to the Mississippian or Mesozoic are included to provide a density of around four to six wells per township in densely drilled areas.

Task 2 will produce computer-generated structure and isopach maps for all major lithostratigraphic units. A regional grid of cross sections will also be constructed. Depositional and erosional edges for many units within the study area are being revised.

c) Task 3: Geophysical Investigations Work within Task 3 is being performed at the University of Saskatchewan and is focused on exploring methodologies for attribute extraction and integration of potential field and seismic data. Seismic investigations involve using existing data and will augment regional geological mapping. The seismic data will be reprocessed into stacked sections and integrated into three dimensional geological models. Basement characteristics are being investigated through attribute mapping of aeromagnetic anomalies and gravity data. The gravity and aeromagnetic data are being integrated to better resolve basement features. These data will also be incorporated into regional geological models.

d) Task 4: Regional Hydrogeology Regional hydrogeological work of Task 4 is being performed at the University of Alberta. This work intends to extend the hydrostratigraphic framework as developed previously during another regional study, the IEA GHG Weyburn CO2 Monitoring and Storage Project (Khan and Rostron, in press). This involves mapping the distribution of fluid potential, TDS, hydrochemical facies, and temperature in each hydrostratigraphic unit. Hydraulic properties such as porosity and permeability will also be assigned to units where possible. The fluid flow rates and directions in each hydrostratigraphic unit will be assessed and integrated into regional models.

e) Task 5: Remotely Sensed Imagery Task 5 involves the study of satellite and aerial-photographic imagery over the study area. Smaller regions are identified in this work for more detailed analyses. The analyses involve describing and interpreting the surface expression of subsurface lineaments and features previously identified through mapping and other studies. The surface features will be incorporated into regional geological models and will aid in interpretations of geological processes.

f) Task 6: Hydrocarbon Inventory Task 6 involves compiling a comprehensive database of hydrocarbon occurrences including oil compositions, oil field characteristics, source-rock data, and documented oil and gas shows in the study area. These data will be made available on the interactive map on the TGI website. The hydrocarbon inventory will be useful for evaluating undiscovered hydrocarbon potential and developing future basin and petroleum-systems modeling.

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g) Task 7: Three-dimensional Geological Model Task 7 will involve the integration of much of the geoscience data produced in the other tasks including stratigraphic, hydrogeological, geophysical, remotely sensed, and hydrocarbon-occurrence data. A static three-dimensional model will be produced using these data sets that will cover the entire study region. This model may serve as the basis for more detailed petroleum-systems and basin-modeling exercises.

h) Task 8: Summary Report Task 8 involves synthesizing outputs from all other tasks. An overall report will be produced and presented as a geological atlas on the project website.

3. Sedimentary-basin Analysis A major intent of the Williston Basin Architecture and Hydrocarbon Potential TGI Project is to enhance the exploration and development of hydrocarbon and mineral resources within the Phanerozoic succession of the northern Williston Basin. Much of this work revolves around developing a consistent stratigraphic database that addresses jurisdictional differences and other nomenclature and picking discrepancies that have arisen and become increasingly apparent over decades of drilling. A well constrained regional stratigraphic dataset is a necessary underpinning for petroleum-systems analyses and basin-modeling techniques that are often used to refine or develop new regional exploration strategies in under-explored portions of the basin.

Information from almost 7,000 oil and gas wells, and from outcrop studies in Saskatchewan and Manitoba, was used to develop the stratigraphic database for this study. All wells penetrating to the Bakken Formation (Lower Mississippian) or deeper in the TGI Project area were used. These were augmented by additional shallower wells to achieve a data distribution of about four wells per township wherever possible. Approximately 200 stratigraphic divisions ranging from Precambrian basement to the uppermost mappable Cretaceous units were identified as surfaces to be picked, where present, in each well. A network of regional cross sections is being constructed to assist in correlation, and structural and isopach maps are being generated for all major lithostratigraphic units

(Figure 2). This work has also resulted in refinement of the stratigraphic equivalencies within the northeastern basin and of depositional or erosional limits to many of the units within the Phanerozoic sedimentary succession. Within the project, the stratigraphic data are required to develop a detailed hydrostratigraphy by researchers at the University of Alberta. The influence of basement characteristics, as determined by workers at the University of Saskatchewan, on the distribution of overlying strata (including ground level), and processes affecting these rocks, will also be studied as part of the overall summary. These stratigraphic data will also be required for future work involving petroleum-systems analyses and basin modeling.

Researchers involved in the Regional Geological Mapping task include: Ruth Bezys, Carol Martiniuk, and Michelle Nicolas of Manitoba Industry, Economic Development and Mines; Kim Kreis, Melinda Yurkowski, and Andre Costa of Saskatchewan

Figure 2 - Three-dimensional representation of structural surfaces generated for several Lower Paleozoic formations spanning the study area. Depositional edges including outcrop distribution are being refined by this mapping project. This diagram is presented as a perspective view and the southern map edge is coincident with the Canada–U.S. border.

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Industry and Resources; and consultants Dan Barchyn, Jim Christopher, Don Kent, and Patty Thomas.

4. Petroleum-systems Investigations Petroleum-systems investigations begin with documenting discovered hydrocarbon accumulations from large oil fields to trace residues in core. As such, an inventory of the distribution of hydrocarbons in strata from Cambrian to Cretaceous age across much of the northern Williston Basin is being performed as part of the Williston Basin Architecture and Hydrocarbon Potential TGI Project. The known hydrocarbon occurrences in this portion of the basin are being mapped according to their stratigraphic and spatial distribution, and where genetic relationships are known this information is used to link associated oils to possibly delineate hydrocarbon migration pathways and identify apparently isolated occurrences (Figure 3). The hydrocarbon distribution is being related to processes associated with basin evolution such as subsidence, salt dissolution, and erosion, the timing and extent of which are also determined through the integrated geoscience investigations performed in this project. Source-rock potential is also being assessed for selected stratigraphic intervals. This information is being provided as the basis for future more in-depth petroleum-systems analyses and basin modeling. Although additional resources and new plays continue to drive exploration in the Williston Basin, traditional targets are becoming more elusive. It is anticipated that better understanding of the controls over hydrocarbon distributions provided by regional, integrated studies linking structural, stratigraphic, hydrogeological, and geochemical data will lead to more effective exploration strategies. Part of this program includes generating comprehensive databases of publicly available data including: documented oil and gas shows, geochemical analyses of oil, and source-rock characterization. As part of summary report to the Williston Basin TGI Project, an evaluation of undiscovered hydrocarbon potential will be presented.

Figure 3 - Map of the distribution of known hydrocarbons in Devonian strata including the Bakken Formation. The Bakken oil fields are shown in light orange and the remaining Devonian oil fields are highlighted in yellow. Drill stem tests having oil shows from Bakken strata are shown as orange circles whereas other Devonian shows are represented by green circles. The geographic extent of the Devonian strata is represented by the Ashern Formation shown as dark blue, and the distribution of the Torquay Formation is shown as light blue. Attribute data associated with features on maps, in this case drill stem tests, can be accessed through the website as depicted in the upper right inset.

DST location

Devonian Oil show

Bakken Oil show

Devonian Oil Pool

Bakken Oil Pool

Legend

Extent of Ashern strata

Extent of Torquay

Saskatchewan Manitoba

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The concept of petroleum-systems analyses originated with investigations into oil systems of the Williston Basin by Dow (1974). Since this landmark study, many other investigations have been performed attempting to classify oil families and develop models for Williston Basin hydrocarbon systems: Pasadakis et al. (2004) present a recent discussion of work characterizing oil families in the Williston Basin. Although the Williston Basin has been subjected to considerable study, many questions remain regarding the mechanisms influencing hydrocarbon distribution. Gaps in knowledge and procedures include:

• general simplification of stratigraphy for modeling purposes; • understanding the efficiency of Bakken and Lodgepole petroleum systems; • identifying the amount of mixing of oils in genetic classification; and • existence or not of a source-rock interval within Upper Cambrian Lower Ordovician strata. The TGI project is providing data to assist in addressing some of these questions, and will help refine future models investigating Williston Basin petroleum systems.

5. Summary The Williston Basin TGI Project is providing a consistent geoscience dataset for the northern portion of the basin that will incorporate stratigraphic, geophysical, hydrogeological, hydrocarbon and remotely sensed data. All data are being synthesized to develop an interactive geological model that will be available on the Williston Basin TGI website at www.WillistonTGI.com. A static, three-dimensional geological model will be developed from the resulting work of this project. The distribution of known hydrocarbon occurrences and available source-rock information along with the updated stratigraphic architecture of the northern part of the basin will serve as the basis for future basin modeling and petroleum-systems studies. It is expected that this project will lead to further academic studies, and enhance the availability of consistent data for continued exploration and development of resources within the Williston Basin.

6. References Dow, W.G. (1974): Application of oil-correlation and source-rock data to exploration in Williston Basin; Amer.

Assoc. Petrol. Geol., Bull. 58, p1253-1262.

Khan, D. and Rostron, B. (in press): Regional hydrogeological investigation around the IEA Weyburn CO2 Monitoring and Storage Project site; in Rubin, E.S., Keith, D.W., and Gilboy, C.F. (eds.), Proceedings of the 7th International Conference on Greenhouse Gas Control Technologies, Volume 1, Peer-Reviewed Papers and Plenary Presentations, Elsevier, U.K.

Magoon, L.B. and Dow, W.G. (1994): The petroleum system; in Magoon, L.B. and Dow, W.G. (eds.), The Petroleum System – From Source to Trap, Amer. Assoc. Petrol. Geol, Mem. 60, p3-24.

Pasadakis, N., Obermajer, M., and Osadetz, K.G. (2004): Definition and characterization of petroleum compositional families in Williston Basin, North America, using principal component analysis; Organ. Geochem., v35, p453-468.