A Novel Method for Stress Calculation Considering the Creep Behaviour of Shale Gas Reservoir

Abstract

To study the creep effect on the stress field under gas-solid thermal coupling, a novel method for stress calculation considering the creep behaviour of shale gas reservoir was proposed based on the principle of least energy consumption. Then, laboratory tests and mathematical fitting methods were adopted to analyze the creep constitutive model for shale, existence states of shale gas, stress, and temperature. In addition, the nonlinear relationship among permeability coefficient, porosity, and volumetric strain was theoretically derived. Results indicated that the established creep damage model can describe not only the decay and steady creep stages, but also the accelerating creep stage. The temperature effect on the mechanical properties of the rock mass conformed to polynomial characteristics. The elastic modulus slowly decreased and the viscosity coefficient rapidly decreased with increasing temperature. The temperature effect on shale gas adsorption conformed to linear characteristics. The Langmuir volume and Langmuir pressure were inversely proportional to temperature; the deceleration of the former was faster than that of the latter. The proposed method can be used to evaluate the stress field of shale gas wells. This research provides a novel approach for refracturing and analysis of gas flow in shale gas wells.