Although organic-rich shale formations are being extensively produced in many places in the United States, the unexpected early production decline is still not fully understood. This phenomenon could have many physical or operational reasons. One of the physical attributes is the time-dependent characteristics of the shale mineral assemblage when interacting with the fracturing fluid. Creep deformation is one of those time-dependent characteristics through which rocks exhibit continuous deformation under constant load that affects reservoir completion and hydraulic fracture stimulation. In this study, shale creep deformation was characterized and rheological models were developed. Triaxial creep experiments were conducted on rock samples from the Eagle Ford shale from southern Texas. Samples were tested with water, decane, or without any circulating fluid to assess fluid-shale interaction. Eagle Ford shale mineral compositions were also investigated using X-Ray Diffraction analyses in an attempt to correlate minerals fluid sensitivity. Problems such as loss of fracture width and length due to shale viscoelastic behavior while embedding the proppant can be better understood if the magnitude of shale creep is well characterized. The experimentally calibrated viscoelastic model not only addressed the instantaneous, transient, and long term sample deformations, but also enabled the estimation of proppant embedment depth during production. The creep deformation was most pronounced when the shale was impregnated with water. Decane-impregnated samples produced less creep deformation and the least creep was measured on the dry ones. The theory of linear viscoelasticity was used to model the samples time-dependent deformation when subjected to their respective constant loads.

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