About This Item

Share This Item

The AAPG/Datapages Combined Publications Database

Montana Geological Society

Abstract

MTGS-AAPG

Montana Geological Society: 1991 Guidebook to Geology and Horizontal Drilling of the Bakken Formation
---, 1991

Pages 91 - 91

ABSTRACT: Reservoir Properties of the Bakken Shale

Lorraine Druyff, American Hunter Exploration, 410 17th Street, Suite 1220, Denver, Colorado 80202, (303) 825-5212

ABSTRACT

Three dominant fracture types occur within the Bakken Formation: structural-related tectonic fractures, stress-related regional fractures, and expulsion fractures associated with overpressuring due to hydrocarbon generation. The expulsion fractures are found throughout the basin on a macro and micro scale.

Lithology differences within the Bakken shale control the degree and type of fracturing. The shale contains quartz, feldspar, dolomite, pyrite, clay and minor calcite. The greatest degree of variation of composition is in the quartz and clay content An influx of the quartz and feldspar is associated with the higher clay content as opposed to the higher quartz and feldspar rocks, which have lower organic content. As expected, expulsion fractures are closely associated with higher clay content. These lithology changes can be tied into neutron density log responses.

Because the expulsion fractures are closely associated with the generation of hydrocarbon, they are immediately filled with oil when created. Cementation or the creation of druse surfaces is not possible. However, one theory suggests that the acids associated with thermal maturation of hydrocarbons are present and are capable of dissolving silicate and carbonate minerals. This process produces a micro porous surface identified only by Scanning Electron Microscope, and is useful in Previous HitdistinguishingTop true from induced fracturing.

Micro-porosity and the kerogen network could contribute to the reservoir. The micro-porosity is accessed by micro-fractures. Oil can easily (but slowly) flow through the kerogen network.