The proposed study is part of a Structural Geology Initiative at EGI designed to advance our understanding of mechanical stratigraphy and its role in hydraulic stimulation. The goal is to improve existing techniques for predicting fracture geometry with a more realistic representation of geologic heterogeneity. In particular, we are studying how hydraulic fractures interact with bedding planes to create geometric complexity. Accurate prediction of fracture geometry helps to determine the spacing of fracture stages to optimize completion efficiency.
Fundamental to understanding how mechanical stratigraphy impacts hydraulic stimulation, this proposal is focused on the evolution of in-situ stress in mechanically-heterogeneous layered material. Sponsors are invited to contribute rock samples for mechanical testing of creep and relaxation parameters. In exchange for rock sample donations, EGI offers a complimentary suite of geomechanics testing including Young’s Modulus, Poisson Ratio, compressive strength, tensile strength, and compressibility.
In response to loading, rock masses become stressed and deform. Adjacent strata with contrasting mechanical properties develop different in-situ stresses. Bed-by-bed stress heterogeneity is not incorporated in most hydraulic fracture models on the assumption that stress has homogenized over geologic time through the process of creep and relaxation. We intend to test this hypothesis.
We propose that rock deforms as a standard linear solid and that creep and relaxation reduce loads but do not obliterate bed-by-bed stress variation. We are constructing a finite element numerical model, constrained by laboratory measurement of creep and relaxation parameters and using work minimization to determine the post-yield deformation path, to simulate the evolution of stress in two tectonic environments: a contracting coulomb wedge and an extending passive margin.