In this study, we examine the variation of viscoplastic creep properties of Wolfcamp shale samples from an area in the Permian Basin of West Texas. In this area, multiple horizontal wells are drilled and hydraulically fractured at different depths to exploit the hydrocarbons in different reservoirs. Following Sone and Zoback, ., 2014) we are studying the degree to which viscoplastic creep leads to creation of high stress frac barriers. We report here a series of creep experiments on samples with various mineral contents and from different depths to test this concept. The experiments were conducted in a multistage pattern at three different stress levels. A comparison between inelastic time-dependent deformation of shale samples with different mineralogies at high pressures demonstrates that carbonate-rich shales show creep-hardening behavior at higher levels of stress whereas clay rich shales appear to creep more at high pressures and show creep-softening behavior.

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