Field observations and analytical modeling of fracture network permeability in hydrocarbon reservoirs

Abstract

Determining the magnitude and orientation of in situ stresses is one of the most critical factors in designing underground excavations and choosing ground support systems. Generally as mining progresses deeper, in situ stress plays a significant role in design considerations. In an effort to further characterize the rock mass in the deep levels of the Homestake Mine, researchers from the Spokane Research Center have completed overcore, i.e. stress relief, measurements using the Bureau of Mines-developed borehole deformation gage. The Homestake Mine geology is comprised of three main geologic formations (Homestake, Ellison, and Poorman) each with distinct material properties. The drill site was chosen in an attempt to collect all the stress relief data in the ore-bearing Homestake formation alone. However, as drilling progressed, overcore measurements were taken in two different rock types and across a geologic contact. This paper examines the effects of variable geology on stress determinations and compares these recent stress measurements and field observations with other in situ measurements collected in previous research investigations at the mine.