Chapter Four - In situ stress and mechanical properties of unconventional gas reservoirs

Abstract

In situ stress distribution and mechanical properties both control the engineering performance of shale, coal, and tight sandstone gas/oil reservoirs. A clear understanding of the above parameters is of significance for engineering design and gas/oil recoveries. The detailed utilization of well logging data combined with basic laboratory tests can provide insight to both mechanical property and in situ stress distributions. The comprehensive combination of in situ stress and mechanical properties is presented here to clarify the understanding of unconventional reservoirs. The acquisition of static and dynamical parameters, brittleness of shale and present in situ stress magnitude is presented with a case study from southern China. The Lower Silurian Longmaxi formation is one of the most promising shale gas reservoirs in China. In this chapter, Longmaxi formation shale samples from the Jiaoshiba area, Sichuan Basin, China, were selected for laboratory experiments, and a series of testing methods such as scanning electron microscope, uniaxial compression, and triaxial compression were carried out. The analysis presented combines logging data with the geomechanics and petrophysical properties of the Longmaxi formation shale. The results reveal the mechanical properties and in-situ stress characteristics of this shale reservoir, and provide the necessary information for field hydraulic fracturing and wellbore stability applications in the Longmaxi shale gas development process.