DE-08NT0005643

Goal
The goal of this project is to determine the geomechanical properties of the Bakken Formation in North Dakota, and use these results to increase the success rate of horizontal drilling and hydraulic fracturing in order to improve the ultimate recovery of this vast oil resource.

Performer
University of North Dakota, Grand Forks, ND 58202-7134

Background
Compared to the success of producing crude oil from the Bakken Formation in eastern Montana, the horizontal drilling and hydraulic fracture stimulation technology applied in western North Dakota has been less successful, thus requiring the development of new completion and fracturing technologies. The biggest challenges were that (1) the horizontal well could not hit the natural fracture, and (2) the hydraulically generated fractures did not develop in the designed, linear orientation and symmetric shape, but in many cases skewed into complicated shapes.

The geological heterogeneity and inadequate knowledge of the in situ stresses and other geomechanical parameters of the Bakken Formation resulted in many failures of horizontal well completions in North Dakota, with each costing several millions of dollars. Based on past research efforts, the following can be concluded:

• Horizontal well drilling with hydraulic fracturing is a required completion technology for recovering crude oil from the Bakken Formation.
• Well orientation is the essential factor for the success of hydraulic fracturing and wellbore stability during drilling and production.
• Hydraulic fracture geometry and orientation (longitudinal, transverse, or oblique) is fully controlled by the local in situ stress field and geomechanical properties of the Bakken Formation. More often than not, a longitudinal or transverse fracture in design became a skewed fracture in reality, which eventually limited well productivity, left in-place reserves around the well, and exhausted the investment.
• In situ stress field and geomechanical properties may change from location to location, even along the axis of horizontal wells being drilled in the Bakken Formation, which are often several thousand feet long.
• Knowing the in situ stresses and the fundamental geomechanical properties of the rock are key to designing successful horizontal well and hydraulic fracture stimulation.

Impact
The results of this study will be used to produce an application guide that can be used for horizontal drilling and/or hydraulic fracturing operations in the Bakken Formation. New technology for in situ stress determination using the Kaiser effect will be developed and tested to help the petroleum industry improve horizontal drilling and hydraulic fracturing in the Bakken Formation. With a better knowledge of in situ stresses and other related geomechanical parameters, the success rate for drilling and hydraulic fracturing will be greatly improved.

U.S. domestic oil production increased rapidly in the past several years. While crude oil production in many conventional fields is declining, North Dakota?s oil production from the unconventional Bakken Formation is increasing rapidly. The results from this project may directly benefit oil production in Williston Basin, and the related technologies developed under this project will contribute to the exploration and production of oil and gas from other unconventional resources.

Accomplishments

• Developed a detailed Bakken Geomechanical Laboratory Testing Plan to maximize the usage of the Bakken specimens, which includes both non-destructive and destructive tests.
• Developed a Recommendation of Research Activities for the remaining project funding.
• Prepared 80 Bakken samples.
• Completed a set of the recommended non-destructive and destructive tests in samples from one of the selected wells (Well 96), including:
  • Permeability
  • P- and S-wave velocities
  • Static moduli and Poisson?s ratio
  • Uniaxial compressive strength
  • Triaxial compressive strength
• Constructed 3-D Bakken geological models using data from 2800+ wells. Figure 1 shows the surface of the upper Bakken Formation (a) and current ground topography (b) in the Williston Basin, North Dakota.

  
  Fig.1 (a)Three-dimensional Bakken geological model in Williston Basin, North Dakota (vertical coordinate exaggerated for display purposes) and (b)corresponding topography on surface

• Developed the Bakken Formation maximum horizontal in situ stress orientation map based on data in 16 wells (Figure 2).

  
  Fig. 2. Orientation of maximum horizontal in-situ stress in the Bakken Formation , Williston Basin, North Dakota.

• Developed an innovative plugging system and techniques for cutting Bakken cores, reaching 90% rate of success.
• Described fractures in the 95 cored Bakken wells, measured rock quality designation (RQD) data of all the available Bakken cores, and developed a 3-D RQD model of the Bakken Formation in the Williston Basin, North Dakota (Figure 3).

  
  Fig. 3. Three-dimensional rock quality designation (RQD) model of Bakken Formation, Williston Basin, North Dakota.

• Created a web-based Bakken geomechanical database. The URL of the web-based database is http://www.petrodata.und.edu/.
• Prepared equipment and developed experimental techniques for testing Bakken geomechanical properties, including:
  • Equipment development and preparation
    • In-house developed sample preparation system for Bakken Formation cores and other water-sensitive rocks
    • Autolab 1500 Testing System
    • MTS 816 Rock test System
    • Computer Numerically Controlled (CNC) machine for fracture toughnees sample preparation
    • In house developed uniaxial tensile strength testing system
  • Experimental and analytical techniques:
    • New method for measuring Biot?s coefficient on ultra-low permeable rocks
    • Fracture toughness measurement using small specimens
    • Measurement of permeability and its change while the rock specimen is compressed to failure
    • Advanced logging analysis method for anisotropy of Bakken Formation and other rocks
    • New dual porosity analytical model with geomechanical parameter for interpreting the Bakken Formation and other naturally fractured reservoirs.
    • A new device for cutting high TOC shale (Upper and Lower Bakken units) samples was purchased and installed and is currently being tested.
• Obtained approval from North Dakota Geological Survey for cutting up to 360 plugs of Bakken specimens for conducting geomechanical tests. The specimens will be cut from cores of upper, middle and lower Bakken units in six wells, each located in one of the six Assement Units (AUs) defined by US Geological Survey, as shown in Fig. 4.

  
  Fig. 4. Distribution of the six wells (red) for geomechanical test and their backups (blue).

Current Status (December 2012)
The non-destructive and destructive tests have been completed for Middle Bakken samples and are progressing for the Upper and Lower Bakken samples. Innovative technologies are being used to cut high TOC shale (Upper and Lower Bakken units) samples. One shale specimen was prepared successfully. Intensity maps of vertical, maximum horizontal, and minimum horizontal stresses in the Middle Bakken study area have been developed.

Project Start: October 1, 2008
Project End: September 30, 2013

DOE Contribution: $1,016,626
Performer Contribution: $353,639

Contact Information:
NETL ? John Terneus (John.Terneus@netl.doe.gov or 304-285-4254)
University of North Dakota ? Dr. Kegang Ling (kegang.ling@engr.und.edu or 701-777-3194)
If you are unable to reach the above personnel, pleaase contact the content manager.

Additional Information

Technology Status Assessment [PDF-59KB]

Technology transfer

• Website-based database:
  • A website database, http://www.petrodata.und.edu/, was launched, and is searchable in major search engines under the unique name of ?petroleum data research project.?
• Papers and Presentations
  • Zeng, Z. 2008.?Geomechanical Study of Bakken Formation for Improved Oil Recovery,? the DOE Bakken Kick-off meeting held in Morgantown, WV on December 3, 2008.
  • Zeng, Z. and Jiang, A. 2009. ?Geomechanical Study of Bakken Formation for Improved Oil Recovery,? SINOROCK2009 paper No. 341, Proc. ISRM Int. Symp. Rock Mech., Hong Kong, China. May 19?22. p.p. 1?5.
  • Jiang, A., Zeng, Z., Zhou, X. and Han, Y. 2009. ?A strain-softening model for drilling-induced damage on boreholes in Williston Basin,? paper ARMA09-026, Proc. 43rd U.S. and 4th U.S.-Canada Rock Mech. Symp., Ashville, NC, USA. June 28 ? July 1. p.p.1?8.
  • Zhou, X., Zeng, Z., Liu, H. and Boock, A. 2009. ?Laboratory testing on geomechanical properties of carbonate rocks for CO2 sequestration,? paper ARMA09-011, Proc. 43rd U.S. and 4th U.S.-Canada Rock Mech. Symp., Ashville, NC, USA. June 28?July 1. p.p. 1?9.
  • Zhou, X., Zeng, Z., and Liu, H. 2010. ?Laboratory testing on Pierre shale for CO2 sequestration under clayey caprock,? paper ARMA10-107, Proc. 44th U.S. and 5th U.S. ? Canada Rock Mech. Symp., Salt Lake City, UT, USA. June 27?30. 12 pages.
  • Fa, L., Zeng, Z., and Liu, H. 2010. ?A new device for measuring in-situ stresses by using acoustic emissions in rocks,? paper ARMA10-160, Proc. 44th U.S. and 5th U.S.-Canada Rock Mech. Symp., Salt Lake City, UT, USA. June 27?30. 7 pages.
  • Pei, P., Zeng, Z., and He, J. 2010. ?Feasibility study of underground coal gasification combined with CO2 capture and sequestration in Williston Basin, North Dakota,? paper ARMA10-240, Proc. 44th U.S. and 5th U.S.-Canada Rock Mech. Symp., Salt Lake City, UT, USA. June 27?30. 8 pages.
  • Wang, C. and Zeng, Z. 2010. ?Methodology of in situ stress analysis and its application to a pumped-storage hydro-power station in China,? paper ARMA10-238, Proc. 44th U.S. and 5th U.S.-Canada Rock Mech. Symp., Salt Lake City, UT, USA. June 27?30. 9 pages.
  • Jabbari, H., Kharrat, R., Zeng, Z., Mostafavi, V.R., and Emamzadeh, A. 2010. ?Modeling the Toe-to-Heel Air Injection Process by Introducing a New Method of Type-Curve Match,? paper SPE 132515, Proc. the Western North America Regional Meeting held in Anaheim, California, USA, 26?30 May. 14 pages.
  • Zeng, Z. and Jiang, A. 2010. ?Geomechanical Study of Bakken Formation,? American Oil and Gas Reporter. April Issue, p.123?127.
  • Zeng, Z., He, J., Pei, P. and Wang, Y. 2009. ?Development of a Three-dimensional Bakken Formation Model for Improved Oil Recovery,? paper abstract No. 101-5, presented at The Geological Society of America Annual Meeting, Portland, OR, USA. October 18?21. Program Book, p.187.
  • Zeng, Z., Zhou, X., Boock, A. and Liu, H. 2009. Experimental Simulation of CO2-Water-Rock Interaction for Carbon Sequestration and Enhanced Oil Recovery in North Dakota Williston Basin, paper abstract No. 117-16, presented at The Geological Society of America Annual Meeting, Portland, OR, USA. October 18?21. Program Book, p.196.
  • Zeng, Z., and Pei, P. 2009. Underground Coal Gasification Process Coupled with On-site Carbon Storage and Enhanced Hydrocarbon Recovery in North Dakota Williston Basin, paper abstract No. 166-3, presented at The Geological Society of America Annual Meeting, Portland, OR, USA. October 18?21. Program Book, p.218