The Bakken formation in the Williston Basin is a closed, low permeability petroleum system that generated approximately 200 to 400barells of oil (Janet K. Pitman, Leigh C. Price, and Julie A. LeFever, 2001). The middle member of the bakken is an oil reservoir with high thermal maturity and has been extensively cored, offers the opportunity to examine the major control of reservoir quality (Janet K. Pitman, Leigh C. Price, and Julie A. LeFever, 2001). The multiple fractures occurs on the macroscopic and microscopic level in the bakken formation and most are abundant in the lower and middle members, the majority of these factures are open and discontinuous features (Janet K. Pitman, Leigh C. Price, and Julie A. LeFever, 2001). The open and discontinuous factures are oriented sub parallel to the bedding with aperture width exceeding 30µm (Janet K. Pitman, Leigh C. Price, and Julie A. LeFever, 2001). These factures are the typical form of dense network that is highly visible on the wetted and slabbed rock surfaces. The few factures in the middle member are V Shaped (Janet K. Pitman, Leigh C. Price, and Julie A. LeFever, 2001). The V Shaped factures tend to be small, resemble fluid – escaped structure. The facture in the lower member are typically open bedding plane (Janet K. Pitman, Leigh C. Price, and Julie A. LeFever, 2001). The facture density in the middle member, whose source rock have high levels of thermal maturity and can vary significantly as a function of source rock thickness (Janet K. Pitman, Leigh C. Price, and Julie A. LeFever, 2001). The regional fractures study is to test regional trends within the Williston basin and outcrops sites against tectonic fracture models that apply to the Williston basin (Stephen Angster, 2011). The purpose of localized fracture study is to observe fracture pattern on potcrops and basi structures and compare fracture models (). The regional fractures are dominant at north east and north west (Stephen Angster, 2011). The NE and NW trends within the basin, while outcrops location shows more variation in fracture orientation. The mechanical stratigraphy was conducted to understand local and regional fracture distribution within bakken equivalent strata (Stephen Angster, 2011). There are different techniques used for determining principal stress orientation, especially the major assumption associated with each technique as well as difficulties and uncertainties (M L Zoback and M Zoback, 1980). The principal stress orientation can be divided in to two category, the observations of fault slip and alignment of young (< 5) The detailed information on fault slip can be used to determine the net horizontal component of motion on oblique slip normal and thrust faults, and net horizontasl extension direction on oblique slip normal faults (M L Zoback and M Zoback, 1980). The in Suit stress study was the direction determination of the both orientation and magnitude of techtonic stress at the depth (M L Zoback and M Zoback, 1980). The primary consideration made by the hydraulic fracturing technique, currently the only method of measuring stress at the large distance from the surfaces (M L Zoback and M Zoback, 1980). The technique hydraulic isolating a section of a well or bore hole and pressuring the isolated section until a tension fracture is induced at the well bore (M L Zoback and M Zoback, 1980). The principal stress a vertical fracture will form at the azimuth of greatest horizontal principal stress, which generally determined to better than 10º(M L Zoback and M Zoback, 1980). The orientation of the principal horizontal stress direction throughout this province averages about east-west; the consistent stress axis however appears to be alined with the greatest principal stress, a horizontal N-S compression (M L Zoback and M Zoback, 1980). The Williston basin and range province to the south is characterized by WNW-ESE extension tectonics (M L Zoback and M Zoback, 1980). The province on faults striking at the large angles to the NW-SE (M L Zoback and M Zoback, 1980). The least principal horizontal stress direction horizontal stress direction trend WNW-ESE to E-W not appear gradually to rotate until they are trending approximately NW-SE in southern sierra (M L Zoback and M Zoback, 1980). The principal stress are in three orthogonal direction one near – vertical, normal to surface of the earth and two orthogonal horizontal direction (SHMIN to SHMAX) (M L Zoback and M Zoback, 1980).
The bakken formation produced oil since 1953, the 2000 discovery of Elm Coulee Oil field in Richland land is expected to produce the oil of 270 million barrels, but in 2007 the oil exploration was averaged 53, 000 million barrels/ day (4). Later Elm Coulee oil field had become the key place for oil production, because it has the combined horizontal well and hydraulic fracturing (4). The R & D has deeply involved reducing the factors influencing the production in Elm coulee oil field.
References
- Janet K. Pitman, Leigh C. Price, and Julie A. LeFever, 2001. “Diagenesis and Fracture Development in the Bakken Formation,Williston Basin: Implications for Reservoir Quality in the Middle Member” .1653, 1-18.
- Stephen Angster. 2011. “FRACTURE ANALYSIS OF THE BAKKEN FORMATION, WILLISTON BASIN. FIELD STUDIES IN THE LITTLE ROCKY MOUNTAINS AND BIG SNOWY MOUNTAINS, MT, AND BEARTOOTH MOUNTAINS, WY, AND 3D SEISMIC DATA, WILLISTON BASIN” .27, 1-17.
- M L Zoback and M Zoback. 1980.“ State of Stress in conterminous United States”.85, 6113-6156.
- Wikipedia, “The Bakken Formation”, accessed on 19 Dec 2013, http://en.wikipedia.org/wiki/Bakken_formation
