|The Bakken-An Unconventional Petroleum and Reservoir System
||Last Reviewed 5/11/2012
The goals of this project are to accurately assess the hydrocarbon potential for the Bakken stratigraphic interval on a sub-regional basis; to construct an integrated exploration model for the Bakken; and to build a fully integrated three-dimensional reservoir geo-model for the Middle Bakken reservoirs in the Elm Coulee area.
Colorado Energy Research Institute, Colorado School of Mines, Golden, CO
Fidelity Exploration Company, Denver, CO
Samson Resources Company, Denver, CO
The Discovery Group, Denver, CO
Idaho National Laboratory, Idaho Falls, ID
The Bakken resource is a significant emerging play located throughout the Williston Basin in the Rocky Mountain region. The United States Geological Survey (USGS) has recently estimated that the Bakken contains 3–4.3 billion bbl of undiscovered, recoverable oil. The Bakken Petroleum System contains all the aspects of a large resource play (e.g., widespread source and reservoir rocks). It contains reservoir rocks, organic-rich source beds, and abundant seals. The various productive lithologies are all low porosity and permeability. Sedimentation occurred throughout the Phanerozoic, and the thickness of the stratigraphic section is approximately 16,000 feet. The Devonian-Mississippian Bakken Formation of the Williston Basin has been the focus of several cycles of exploration activity since the 1950s. The discovery and development of the Elm Coulee area of Montana is the latest and most significant of these cycles to date. Expansion of the play into North Dakota is currently underway and has resulted in new discoveries, including the Parshall Field. The new discoveries in North Dakota suggest the existence of an extremely large resource play; however, no predictive hydrocarbon system or reservoir geo-model currently exists for this play.
Elm Coulee, a new field, has produced in excess of 41 million barrels of oil and 24 BCF of gas from over 400 horizontal wells. The field is being developed using horizontal drilling in the middle member of the Bakken. The Bakken is generally fracture stimulated with gelled water and sand (~5,000 bbl gelled water and 400,000 pounds of sand per horizontal lateral). The area was targeted for vertical drilling in the late 1990s and horizontal drilling began in 2001. The middle Bakken in this area is interpreted to be a dolomitized carbonate bar complex. The reservoir is developed over a large area (450 square miles) and has relatively low porosity (8%–10%) and permeability (average of 0.05 md). Natural fracturing is thought to contribute to production. Initial production from wells range from 200 to 1900 BOPD. The field is being developed on 640 and 1280 acre drilling and spacing units. The Elm Coulee area has many of the characteristics of a resource play (i.e., continuous accumulation, large areal extent, predictable, repeatable, technology driven, etc.). Estimated recovery per well is 350 to 600 thousand bbls. Estimated ultimate recovery for the field is greater than 200 MMBO (Walker et al., 2006).
Location of Williston Basin, which is semi-circular in shape and a site of subsidence through much of Paleozoic time
Index map of Williston Basin showing fields and the various petroleum systems, note the position of the Elm Coulee Field
The successful results of this study will aid in the development of an initial alpha version of a predictive exploration model that could be used for future identification of high potential fairways and traps for the Bakken hydrocarbon system. The initial model will be based on the integration of a sub-regional stratigraphic and reservoir characterization, rock physics calibrated seismic attribute analyses, and acoustic impedance developed for different levels of organic richness and maturity. The model will also include a secondary permeability potential that will be derived from a fracture analysis. Finally, validation of, and revisions to the model will be conducted to compare predictive attributes to known seismic, log, and core data throughout the Williston Basin.
- The integrated geological-geophysical study has accomplished five major objectives over the three-year project life: (1) characterization of the lithofacies and mineralogy of the Bakken to identify high performing reservoirs; (2) established that the organic-rich Bakken shales have similar elastic properties and effective stress as the Middle Bakken siltstones and sandstones, suggesting that the shales will not contain induced fractures, and will contribute hydrocarbons from interconnected micro-fractures; (3) established criteria for identifying and mapping natural fractures that are both regional and related to local structures to guide horizontal well drilling to optimize fracture intersection; (4) constructed a dual-porosity Petrel geo-model for a portion of the Elm Coulee Field to provide a starting model for reservoir simulation; and (5) developed criteria to assess the Bakken exploration potential in undrilled areas of the basin.
- The construction of a fully integrated exploration model for the Bakken hydrocarbon system was completed.
- An integrated 3-dimensional reservoir geo-model for the Elm Coulee field was developed.
- Results of the project to date were presented at the 2011 AAPG Annual meeting in Houston and the Williston Basin meeting in Regina, Canada.
- With the construction of the fully integrated exploration model and an integrated 3-D stratigraphic/structural geomodel for the Elm Coulee field, the main objectives of the project have been met. The models were the result of a three-year effort which included the integration of the sub-regional stratigraphic and reservoir characterization, rock physics calibrated seismic attribute analyses, acoustic impedance developed for different levels of organic richness and maturity, and detailed fracture analysis. The models have the potential to provide an assessment of the hydrocarbon potential of Bakken frontier oil resources and help predict high potential fairways and traps in the Bakken hydrocarbon system.
- The 2011 spring meeting of the Colorado School of Mines Bakken Consortium was held in Golden, Colorado on April 20, 2011. Consortium members, including many top Bakken oil producers in the Williston Basin, received updates on the status of ongoing research being funded to investigate the geological, geophysical and geomechanical controls on oil production from the Bakken Petroleum system.
- Nine Bakken samples have been returned from Idaho National Lab (INL), where wet and dry pyrolysis experiments were performed on each sample. Determination of impedance values using the Scanning Acoustic Microscope at CSM is complete. These data have been added to the initial nano-indentation analysis to aid in mapping maturity. Based on the initial nano-indentation work, the impedance of Organic-Rich Shales (ORS) is directly related to maturity. Seismic and well data will be used to attempt to map Bakken impedance values in a test area of the basin that will be, by inference, a map of maturity levels. These efforts will lead to the development of an impedance-related maturity model for the organic-rich shale of the Bakken.
- Technology transfer activities included presentations of research results at the AAPG-SEPM International Meeting in Calgary in September 2010, at the COGA-RMAG meeting in July 2010, and at a PTTC sponsored Bakken Core Workshop.
- CSM completed the stratigraphic framework for the Bakken and the underlying Three Forks and overlying Lodgepole formations across the Williston Basin. QEMSCAN quantitative analysis of Bakken mineralogy, including the upper and lower shale as well as the middle Bakken, was also completed. Additionally, CSM researchers completed the initial region and local fracture analysis and 3-D seismic attribute interpretation.
- CSM has completed construction of a regional stratigraphic framework for the Bakken, and the over- and underlying Lodgepole and Three Forks formations, both of which are part of the Bakken Petroleum System. This has involved detailed description of cores stored at the USGS in Denver, at the North Dakota Geologic Survey, and at the core repository at CSM. The framework includes compilation of subsurface data, and stratigraphic interpretation using wells and 3-D seismic contributed by industry participants. A major conclusion gained from this activity has been the recognition that the Parshall and Elm Coulee fields have a significant lateral trap for hydrocarbons. Industry can make use of this knowledge to identify new exploration opportunities in the Bakken oil play trend. High resolution scanning electron microscopy (SEM) using the QEMSCAN® tool has shown that the Bakken units have a diverse mineralogy including illite, quartz, pyrite, calcite, and dolomite, all of which may affect fracability and reservoir performance.
- Rock physics analysis has been performed on outcrop and core samples to calibrate seismic response of the reservoirs. The analysis used compressional and shear velocities at in situ conditions on core samples and compared these measurements to log data. These measurements are being used to construct predictive models to assess the effects of organic content, fluids, mineralogy, stress, etc. A2D Technologies is contributing a digital log database that will provide critical sonic and density logs to tie geology to seismic response, which will help determine thin-bed petrophysical characteristics of the Bakken shale, Middle Bakken sandstone, and limestone reservoirs. Forty-seven wells across the basin have been used to define relationships between maturity-dependent rock properties. The goal is to develop a quantitative relationship between impedance and kerogen content that can be used to build predictive rock physics models. Total organic carbon linked to porosity, Tmax, and normalized S2 have the best potential for predicting impedance in organic rich shale (ORS). This information will also assist in determining the natural fracture characteristics in the Bakken interval. Industry will be able to use this information to optimize hydraulic fracturing for production of oil.
- Fracture data have been collected from the Little Rocky Mountains and Big Snowy Mountains in Montana and from the Beartooth Mountains in Wyoming and will be used to construct a 3-D digital model of the sub-regional fracture system. Initial results show that there are differences in mechanical stratigraphy between the Middle Bakken sandstones, siltstones, and dolomites, and the Bakken shales. This data will be compared to fracture and small fault trends derived from seismic data. The results may be helpful to industry to determine the best intervals for hydraulic fracturing in the Bakken oil fields.
- Complementary to this project and as part of technology transfer, the research team has organized the CSM Bakken Consortium. Consortium members include MJ Systems, IHS, Shell, ConocoPhillips, Hess, Marathon, Total, Inerplus, Red Willow, Whiting Petroleum, EOG Resources, Hendricks and Associates, Fidelity Exploration and Production Co., Samson, The Discovery Group, XTO, Questar, Savant, Mike Johnson & Associates, and most recently, StatoilHydro, Husky Oil Canada, and Chesapeake Energy. Samson, Fidelity, and The Discovery Group are the original industry partners in this NETL project. Consortium membership will provide funding and data to the overall project.
Current Status (May 2012)
The project has been completed after a three-month no-cost time extension through December 31, 2011. The final report is available below under"Additional Information".
Project Start: October 1, 2008
Project End: December 31, 2011
DOE Contribution: $1,480,815
Performer Contribution: $852,878
NETL - Skip Pratt (firstname.lastname@example.org or 304-285-4396)
Colorado Energy Research Institute, Colorado School of Mines – J. Frederick Sarg (email@example.com or 303-273-3729)
If you are unable to reach the above personnel, please contact the content manager.
Final Project Report [PDF-6.50MB]
New Models Help Optimize Development of Bakken Shale Resources - News Release February, 2012
Technology Status Assessment [PDF-207KB]