DE-NT0005672

Goal
The goals of this project are to accurately assess the hydrocarbon potential for the Bakken stratigraphic interval on a sub-regional basis and 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.

Performers
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

Background
The Bakken resource play is a significant emerging play throughout the Williston Basin, Rocky Mountain region. The 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, currently, no predictive hydrocarbon system or reservoir geo-model exists for this play.

Location of Williston Basin, which is semi-circular in shape and a site of subsidence through much of Paleozoic time

Elm Coulee, a new field, has produced in excess of 41 million barrels of oil and 24 BCF 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 ranges 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 MMBO. Estimated ultimate recovery for the field is greater than 200 MMBO (Walker et al., 2006).

Index map of Williston Basin showing fields and the various petroleum systems, note the position of the Elm Coulee Field

Impact
The successful results of this study will develop 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 is to be based upon 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 is to also include a secondary permeability potential that will be derived from a fracture analysis. Finally, validation of and revisions to the model shall be conducted to compare predictive attributes to known seismic, log and core data throughout the Williston Basin.

Accomplishments
Several of the key successes include:

• CSM has completed construction of a regional stratigraphic framework for the Bakken, and the over- and underlying Lodgpole 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 SEM analysis 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 compare these measurements to log data. These measurements are being used to construct predictive models to assess the affects 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 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 has been collected from the Little Rocky Mountains and Big Snowy Mountains in Montana and from the Beartooth Mountains in Wyoming. The data will be used to construct a 3D 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 displayed on 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, Marathon, Total, Inerplus, Red Willow, Whiting Petroleum, EOG Resources, Hendricks and Associates, Fidelity Exploration and Production Co., Samson, The Discovery Group, XTO, Questar, Savant, and Mike Johnson & Assocs, and most recently, Statoil. Samson, Fidelity, and The Discovery Group are our original industry partners in this NETL project. Consortium membership will provide funding and data to the overall project.

Current Status (January 2010)
The first quarter of project activities focused on start-up of technical work including stratigraphy,sedimentology of the Bakken interval and source characterization using the Scanning Acoustic Microscope (SAM). A consortium contract was signed by 13 companies, and partner collaborations were initiated with the North Dakota projects. The CSM Bakken Consortium has expanded to 17 members.

The second quarter of the project focused on initial description of cores from Montana and North Dakota, stored at the USGS in Denver and at CSM. Researchers are currently working on the initial calibration of the Scanning Acoustic Microscope (SAM) for impedance vs. maturity measurements on Bakken organic-rich shales. On March 9-10, 2009, CSM hosted a joint core workshop with the University of North Dakota.

The national laboratory (INL) will be supporting the main project during the second budget period. They willl participate in activities describing the maturity as expected to be seen in nature and relate this data to acoustical and high frequency measurements. INL will be conducting three types of retorting experiments in an effort to vary the maturity levels of Bakken shale. Procedures shall include fully saturated hydrous retorting experiments, anhydrous retorting experiments under similar temperature regimes as hydrous retorting experlments, and partial hydrous experiments where a known quantity of water will be added to the retort vessel to generate a desired partial vapor pressure. Prior to and after the thermal treatment, geophysical and petrophysical characterization of the shale core samples will be performed by CSM and relate this set of characterization to the maturity level of the Bakken shale.

Researchers are using a Scanning Acoustic Microscope (SAM) and high resolution lenses to measure impedance changes at different source rock maturity levels in Bakken organic rich shale (ORS). The research will examine lateral and vertical variation in organic richness and maturity levels of the Bakken ORS across the Williston basin. When completed, this analysis of impedance related to maturity will be used to calibrate seismic data for mapping maturity levels of ORS across the basin. This will allow industry to identify oil sweet spots and target high grade exploration areas.

The project team at Colorado School of Mines achieved several accomplishments during Budget Period I toward meeting their objectives to accurately assess the hydrocarbon potential for the Bakken stratigraphic interval on a sub-regional basis, construct an integrated exploration model for the Bakken, and to build a fully integrated three-dimensional reservoir geo-model for reservoirs in the Elm Coulee area. During Budget Period II CSM will integrate seismic, well, rock, and engineering data to identify and map the reservoir compartments, connectors, and the pore system geometries. This initial study of the Bakken will include detailed, integrated subsurface mapping of depositional and fracture systems using seismic attributes, core and well logs, and sequence stratigraphic analysis; and reservoir characterization using a new high-resolution scanning electron microscope (SEM) to quantify pore systems.

The first quarter of Budget Period II is complete, and project objectives are on schedule. A regional stratigraphic framework has been completed and the field study at Parshall is complete. Preliminary rock physics parameters have been identified to help interpret SAM results. Calibration of the SAM is nearly complete. Samples are being collected for retorting experiments at INL. Regional fracture analysis has progressed to interpretation of a 3D seismic data set, and outcrop data will be used as analogs to develop a regional fracture framework.

Project Start: October 1, 2008
Project End: September 30, 2011

DOE Contribution: $1,480,815
Performer Contribution: $851,878

Contact Information:
NETL - Skip Pratt (skip.pratt@netl.doe.gov or 304-285-4396)
Colorado Energy Research Institute, Colorado School of Mines – J. Frederick Sarg (jsarg@mines.edu or 303-273-3729)

Additional Information

Technology Status Assessment [PDF-205KB]