Mesoscale migration of oil in tight sandstone reservoirs by multi-field coupled two-phase flow

Abstract

The oil migration process plays a pivotal role in determining the distribution and scale of oil reservoirs in tight sandstone formations, while also simultaneously influencing their development outcomes. However, the mechanisms governing oil migration in these tight formations remain poorly understood. This study conducted numerical simulations to investigate the oil migration characteristics in tight sandstone at the mesoscale. Multivariate regression analysis was used to characterize the micromechanical parameters of a 3D digital core. In addition, the main equations describing the two-phase flow that couples the stress and seepage fields were proposed, thereby elucidating the oil migration process. Finally, the effects of the reservoir space type, pressure gradient, and stress on the oil migration efficiency were assessed. The results showed that: (1) Compared with the porous-type model, the fractured-type model had a higher level and more concentrated distribution of damage, better connectivity, and higher oil migration efficiency due to the seepage-stress coupling effect; (2) High fluid pressure gradients improved the efficiency of oil migration and enhanced the control of the three-dimensional distribution of the pore domain over oil distribution in the matrix domain. (3) When σ1 >σ3, the oil phase migration efficiency improves with the increasing axial stress. When σ1 <σ3, the oil phase migration efficiency decreases with the increasing confining stress. When σ1 = σ3, high stress leads to low oil phase migration efficiency. This study reveals the mesoscopic-scale mechanism of oil migration in tight sandstone reservoirs and may prove useful in the exploration and development in such reservoirs.