Using CT scanning technology to investigate microscopic pore structure characteristics of low-permeability reservoir rocks after water sensitivity experiments

Abstract

CT scanning and core flooding experiments were combined to investigate the change in microscopic pore structure of low-permeability reservoir rocks due to the water sensitivity effect. Water sensitivity experiments were conducted for low-permeability reservoirs using different permeability core plugs to study the pore throat radius distribution, coordination number, pore structure variation, physical property parameter variation, and effects on the seepage capacity. The comparison plates of the limit injection-production spacing were drawn. The results indicate that the pore throat damage increases while the mean coordination number decreases with the reduction of permeability, which leads to a higher flow resistance and a stronger damage to the microscopic pore structure. These combined effects lead to an increase in the starting pressure gradient. In addition, the damage extent of reservoir throats is much larger than that of pores in the reservoir. Moreover, the swelling of clay minerals and the particle migration mostly present in the pore space due to the water sensitivity effect, which would hardly influence the whole pore structure and distribution feature of the core plug. Furthermore, according to the limit injection-production spacing plates, the limit injection-production spacing of the Xingouzuizu Formation low-permeability reservoir decreases by 153 m, which is caused by the effect of water sensitivity. The injection-production well spacing must be adjusted by the infill well, which can be used to improve the injected water swept volume. This research could provide certain practical guidance for the development adjustment of low-permeability reservoirs featuring the water sensitivity effect under a long period of waterflooding