A Method to Determine Stress-Dependent Filtration Properties of Fractured Porous Rocks by Laboratory Test Data

Abstract

Within the dual porosity model the authors develop and theoretically, using synthetic data, substantiate the method for determining mass exchange coefficient and stress-dependent permeability of fractured porous reservoir rocks. The proposed filtration test circuit consists of three sequential measurements of flowrate in a specimen subjected to the varied external stress σ at the inlet fluid pressure P: by standard scheme (Q0) and with plugging of fissures at one (Q1) and at the other end (Q2) of the specimen. The model of the experiment is created, and the analytical solution is obtained for the direct problem on steady-state flow: dependences of Q0, Q1 and Q2 on σ and P. The input data are synthesized by superimposition of multiplicative noise on the exact solution of the direct problem. The synthesized data are used to derive the inversion relations for calculating the permeabilities k1 and k2 of fissures and matrix as well as the mass exchange coefficient by Q0, Q1 and Q2. Using LS method, the dependences k1(σ) and k2(σ) are reconstructed. The numerical experiments reveal low stability of inversion by input data. Thus, it is necessary to perform a cycle of measurements at the increasing input pressure with subsequent averaging of the results.