Construction and validation of the upscaling model of organic-rich shale by considering water-sensitivity effects

Abstract

Due to the complexity of its microscopic composition, the mechanical changes produced by the hydration process of organic-rich shale are more complicated than those of pure clay minerals. Although predecessors have researched the upscaling model of shale, the construction and evaluation of the water-saturated model remain a long-standing challenge. In this work, the combination of the differential effective medium (DEM) model and the self-consistent (SC) model (DEM-SC) was used to obtain a universal stiffness tensor of the clay matrix based on reverse modeling of ultrasonic pulse velocity (UPV) test results. Subsequently, a new water-sensitivity -based upscaling model was constructed that simultaneously considers: (1) the interlayer swelling, confining, and substitution effects of clay matrix under water-saturated conditions; and (2) the influence of depositional environment on the pore morphology of organic matter and the influence of maturity on its elastic properties. The upscaling model showed that the interlayer swelling effect is the most critical water-sensitivity effect, and the confining and the substitution effect can only compensate for part of the modulus reduction caused by interlayer swelling. In addition, the model behaved better when dealing with problems with a large volume ratio of inclusions (such as marine shale) and achieved good prediction results by controlling the relative errors compared with the microindentation experiments at less than 15%. Finally, the model was further applied to the well scale with better prediction results by considering the water-sensitivity effect, proving that the model has a wide range of application potential in formation evaluation and construction operations in shale gas production.