Experimental study of microstructure and rock properties of shale samples

Abstract

The study of shale mechanical properties is very important for well completion and stimulation in shale gas reservoirs. Thus,the geomechanical properties of Paleozoic marine shale in Lower Yangtze Basin were studied.With the application of argon ion polisher,high-solution CT and scanning electron microscope,the shale samples were processed and their microstructures were observed. Besides, mineral compositions of this shale were analyzed by XRD technique. In order to get the compression characteristic of shale, the scratch and uniaxial experiments were performed. In addition, the loading and unloading situations were simulated under different effective stress conditions in order to reduce negative effects of natural fissures and rock relaxation. Finally,the multi-stage triaxial compression deformation experiment was performed on the triaxial rock testing system for calculating cohesive strength and inherent friction angle. The study of shale mechanical properties is veryimportant for well completion and stimulation in shale gas reservoirs. Thus, a systematic experiments was performed on Paleozoic marine shale samples collected from Lower Yangtze Basin, and the microscopic structure,mineral compositions and the geomechanical properties of marine shale samples were studied. Testing result shows that except for shale sample with natural fractures,both the values of Youngs modulus and Poissons ratio increase with the increase of confining pressure. But in the unloading condition, the Young s modulus increases with the decrease of confining pressure,whereas the Poisson s ratio is greater than that in its loading condition. The inherent friction angle is within approximately 40°and the shale sample with high brittleness index tends to crack as fracture network according to the multi-stage triaxial compression test. This research is greatly helpful for the study of shale mechanical properties,and provides technical parameters for well completion design and stimulation.