Effects of boundary layer and stress sensitivity on the performance of low-velocity and one-phase flow in a shale oil reservoir: Experimental and numerical modeling approaches

Abstract

Seepage flow is important because it is useful for production optimization and well spacing decisions. In this study, an enclosed high-precision seepage flow apparatus is used to determine the seepage flow characteristics of the Qianjiang shale reservoir in China under various pressures from 3 MPa to 24 MPa. The results revealed that the seepage flow curve has an inverse-spoon shape, which is completely different from the results for low-permeability and tight sandstone reservoirs, as reported in the literature. In addition, according to the full-scale pore size distribution technique, the modular automated processing system (MAPS), and the nuclear magnetic resonance (NMR) T2 spectrum before and after the seepage flow experiments, the seepage flow characteristics of the Qianjiang shale oil reservoir were not only caused by the boundary effect, but also dependent upon the stress sensitivity. It was also found that micro-fractures or macro-pore were compressed as the effective stress increased in the experiment. Moreover, a new non-Darcy model for a shale reservoir was derived, and the model was verified using experimental data. This model demonstrated it would be a good candidate for quantitative evaluation of affecting factors. It can also be applied to determine the main controlling factor. The calculated results showed that the shape of the nonlinear flow portion of the seepage flow curve for the Qianjiang shale oil reservoir was primarily dependent upon the effect of stress sensitivity. However, the linear flow portion of the seepage flow curve was dependent upon the combined effects of stress sensitivity and the boundary layer. Therefore, from the enhanced individual-well production point of view, the control of production pressure drops and selection of rational well spacing is important for the effective development of shale oil reservoirs.