Effects of Trapped Gas in Fracture-Pore Carbonate Reservoirs

Abstract Fracture-pore carbonate reservoirs exhibit strong microscopic heterogeneity and complex seepage characteristics, resulting in suboptimal oil drive efficiency and development outcomes. Moreover, water channeling is often a serious problem in the development of fractured porous carbonate rocks, and the blockage of degassed bubbles in the throat is one of the reasons that cannot be ignored. In order to reveal the degree of influence of bubbles on waterflood sweep, this paper employs microfluidic technology to design three distinct chips, namely fracture-type, composite-type, and cave-type, to visually illustrate the influence of the gas phase on three-phase flow. A quantification method is established to analyze the variation characteristics of pore diameter utilization ratio in different types of carbonate reservoirs. Compared with water flooding experiments without the gas phase, the recovery factor of water flooding with the presence of the gas phase decreases by 0.6,3.4, and 15.3 percentage points for three distinct chips, respectively. In fracture-type reservoirs, the main focus is on sealing the primary fracture seepage channel and mitigating the shielding effect of the gas phase on matrix utilization. For composite-type reservoirs, the primary objective is to seal fractures and eliminate the shielding effect of the gas phase. In cave-type reservoirs, the primary goal is to eliminate the sealing effect caused by the discontinuous gas phase within small pore throats.