Experimental Study on Gas-Water Two-Phase Seepage Law of Fracture-Developed Carbonate Sour Gas Reservoirs

Most deep carbonate gas reservoirs contain original formation water in different degrees. Fractures developed in such reservoirs facilitate water channeling, which limits the fluidity of gas phase and leads to locally sealed gas, resulting in yield reduction of gas well, and the decrease in reservoir producing degree and recovery ratio. Especially for sour gas reservoirs, the sulfur deposition caused by fluid temperature and pressure changes during seepage can complicate the impact of gas-water two-phase flow on development. Thus, it is urgent to understand the characteristics of the two-phase flow under formation conditions in actual production process, so as to provide a reliable reference for well production system. Taking the deep carbonate sour gas reservoir DF2 as an example, considering the influence of temperature, this study improved the experiment of gas-water two-phase seepage under formation conditions, and then carried out the experiment for cores with fracture developed. By comparing and analyzing the seepage laws of different reservoir types under various experimental conditions, it is found that under formation conditions, the seepage capacity is enhanced and the efficiency of gas displacing water improved, meanwhile, the water saturation affecting water phase flow is reduced. However, the existence of fractures can weaken the influence of high temperature and high pressure on fluids, lower the gas displacing water efficiency, and are unfavorable for the production of gas well after water breakthrough. Therefore, for wells of fracture-developed carbonate sour gas reservoirs, it is suggested to maintain the proper production pressure difference after water breakthrough, so as to mitigate the impact of water phase on production.