Experimental Study on the Influence of Supercritical Carbon Dioxide Soaking Pressure on the Mechanical Properties of Shale

Mechanical properties of shale rock is the basic issue of the drilling and development of shale oil and gas reservoir, and it is also one important issue of developing shale oil and gas reservoir fundamental theoretical research using supercritical carbon dioxide (SC-CO2). Experimental researching on basic aspects of shale mechanical properties after soaking in SC-CO2 can reveal the impact on the high efficiency of rock breaking, well-bore stability and fracturing. For this reason, soaking tests of shale under different carbon dioxide pressures have been done. Results showed in this paper that shale expands lightly at the beginning of soaking in SC-CO2 but shrinks afterwards and tends to be smooth at last. With the increasing of soaking pressure, the uniaxial compressive strength of shale decreases while the Elastic Modulus (Young's modulus) and Poisson's ratio increases; the mechanical properties of shale changes rapidly when the pressure of CO2 reaches the supercritical state. As the pressure keeps increasing, the change of mechanical properties of shale core is relatively slow and within a narrow range. In addition, the effect of CO2 on the mechanical properties is not related to the soaking pressure. In fact, CO2 affection on shale properties has not obviously changed when increasing the pressure after reaching supercritical state.