In situ horizontal stress distribution in Colville basin and North Slope

Principal Investigator: Catherine L. Hanks

Participating students: Melissa Parker, Emily Jemison

In situ stresses play a significant role in hydrocarbon exploration and production. Low differential stresses in the foreland basin of a fold-and-thrust belt can be an important factor in developing and maintaining an open fracture network in rocks forward of the growing thrust belt (e.g., Lorenz and others, 1991). These fractures in turn can be influential in controlling fluid movement through the foreland basin from source to reservoir and can enhance reservoir characteristics in potential reservoir rocks. In situ stresses also influence fluid flow in producing reservoirs by controlling the direction of fracture permeability. Determining the direction of the in situ stress can therefore be a powerful predictive tool for evaluating both fluid movement within a basin and the development of fracture porosity and permeability in potential and producing reservoir rocks.

A pilot study of the distribution of in situ horizontal stresses in the subsurface of northeastern Alaska was conducted during 1996-1998 using borehole breakouts. The results of this study suggest that significant variations exist in the orientation of horizontal in situ stresses in the North Slope of northeastern Alaska. Borehole breakouts in 30 wells north and west of the Arctic National Wildlife Refuge (ANWR) can be interpreted to reflect two different in situ horizontal stress regimes. Maximum horizontal stress orientations generally are perpendicular to the exposed deformation front immediately north of the exposed northeastern Brooks Range fold-and-thrust belt. Maximum horizontal stress orientations range from north-northeast in Tenneco Aurora #1 offshore of northern ANWR to northwest in ARCO Nora Federal #1 near the Dalton Highway. In situ stresses in this region are probably due to active compression related to the fold-and-thrust belt. In contrast, borehole breakout orientations in wells on or near the Barrow arch are more variable and commonly have bimodal orientations. These can be interpreted to represent maximum in situ horizontal stress orientations that are northwest and northeast trending. These orientations could reflect in situ stresses resulting from extension along the northern Alaska continental margin, or from interaction between the Barrow arch and stresses generated by thrusting from the south.

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