Influence of stress sensitivity on pore structure of tight reservoirs: A Digital core based analysis

Abstract

During the development of tight reservoirs, as the formation pressure decreases, the effective stress on the rock matrix increases. This leads to rock deformation and, consequently, changes in the physical parameters of the reservoirs, affecting reservoir productivity. Therefore, it is crucial to identify the influence of stress variation on the pore structure of tight reservoirs at the pore scale. Based on 3D grayscale images of representative samples under different confining pressures using micrometer computed tomography, this study obtained corresponding 3D digital cores through binary segmentation using the maximum class spacing algorithm. Based on digital cores with the same physical size under different confining pressures, the binary data volume was subtracted using a Boolean algorithm to obtain the pore variation space under different confining pressures. The pore variation and permeability damage rate under different confining pressures were then determined. Pore network models of digital cores under different confining pressures were extracted using the maximal ball algorithm, and the corresponding pore-throat radius distribution, coordination number distribution, length/diameter ratio, and shape factor distribution were calculated. The results show that as the confining pressure increases, the pore-throat distribution curve shifts to the direction of smaller pore-throats, the average coordination number decreases, and the throat length/diameter ratio distribution curve and shape factor distribution curve shift to the direction of larger pore-throats. This is because compaction reduces pores and throats, decreases the overall pore-throat connectivity, narrows the throats, and makes the cross-sections of the pore-throats more circular. This research serves as a basic platform for efficient development under stress sensitivity in tight reservoirs, and its findings have important academic significance and practical application value.