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Mechanical Stratigraphy of the Eagle Ford Formation, West Texas

Guangjian Xu
Texas A&M University, Department of Geology and Geophysics, College Station, Texas, USA
[email protected]

Results of hydraulic fracturing treatment in shale gas reservoirs are often poorly predicted because they depend on natural fracture geometries and in-situ stress. Defining the density and orientation distribution of natural fractures as a function of mineralogy, texture, and mechanical behavior is critical to determining the parameters that control hydraulically induced fracture. The Eagle Ford Formation outcrops in West Texas provide an excellent opportunity to study the relation between intrinsic and extrinsic parameters that control fracture formation and extent in carbonate-rich shales. This formation has been divided into five stratigraphic facies that are cut by natural fracture systems displaying variations in geometry, orientation, and spacing. We hypothesize that the orientation and spacing of natural fracture sets are controlled by mechanical stratigraphy (i.e., layer thickness, mineralogy, grain size, and clay content) and extrinsic parameters (e.g., stress state and load paths) during the fracture process. By carefully characterizing the orientation distribution of natural fractures as a function of facies characteristics, and defining key mechanical properties of each facies, we hope to improve the ability to predict the induced hydraulic-fracture response of carbonate-rich shale reservoirs in the subsurface. To date, I have characterized the mesoscale and microscale density and orientation distribution of natural fractures in surface outcrops and collected representative samples for rock mechanics testing. Combining these data with detailed stratigraphic, mineralogic, and geochemical data of others, I will define representative mechanical-stratigraphic units of the exposed formation to better understand the fracture characteristics under a series of well-defined load paths and stress states.

AAPG Search and Discovery Article #90183©2013 AAPG Foundation 2013 Grants-in-Aid Projects