Physical simulation test of true triaxial rock mechanics for waterflood dilation in offshore oilfields

Abstract The reservoirs in the western South China Sea oilfield are characterized by low permeability, poor pore connectivity, high laminated content, severe pollution, and prominent interlayer contradictions. For this reason, the water injection dilation technology exploits it. This paper examines the impact of water-injection technical parameters on the dilation of low-permeability reservoirs in the western South China Sea. In this paper, tests on uniaxial compressive strength, Kaiser acoustic emission effect, and true triaxial rock mechanics waterflood dilation physical simulation are conducted. Through uniaxial compressive tests, it is found that the uniaxial compressive strength of the rock in the target reservoir is 35.36 MPa, the elastic modulus is 10.39GPa, and the Poisson ratio is 0.15. The Kaiser acoustic emission test indicates that the vertical stress gradient of the target reservoir is 2.22 MPa/100 m, the maximum horizontal principal stress gradient is 2.04 MPa/100 m, and the minimum horizontal principal stress gradient is 1.67 MPa/100 m. Through a true triaxial rock mechanics simulation of water injection dilatation, it is found that the effect of water injection dilatation can be improved by pre-treating samples with stepped pore pressure, low injection rates, a cyclic oscillatory injection mode, and increased liquid viscosity. Using CT (Computed Tomography) scanning results and CT reconstruction of the sample, the maximum volume porosity can be increased to 7.13%. The test’s results can guide field construction of water-injection dilation.