Physical Simulation And Numerical Simulation Of Water Intrusion In Fractured Bottom Water Gas Reservoirs

Fracture gas reservoirs with bottom water are widely distributed in our country, such as Weiyuan Sinian gas reservoir in Sichuan, Zhongba Xu-2 gas reservoir, Dabei-2 gas reservoir and so forth. During the development process, due to the complex fracture system in gas reservoir, formation pressure would drop, porosity and permeability parameter would decreases, and bottom water would invade gas reservoir, which leads to complex seepage law in gas reservoir. Therefore, conventional gas reservoir seepage theory can not be able to accurately predict the production performance of gas reservoirs. "A physical and numerical simulation of fracture gas reservoirs with bottom water" is important for correctly understanding gas reservoir seepage law and formulating rational development plan.Based on analyzing geological and development features of fracture gas reservoirs with bottom water, bottom water invasion experiments with three different sizes of aquifer, two kinds of different depletion rate were carried out by simulating the actual gas reservoir exploitation process. A simplified geometric model of dual media was established considering fracture characteristics, and then a 3D mathematical model of gas-water bi-phase was established under the consideration of reservoir stress sensitivity and bottom water intrusion. Matlab software was used to complete the corresponding solving program, and influences of different factors, such as fracture azimuth and dip, aquifer size, water invasion index, production rate, reservoir stress sensitivity and fracture and matrix permeability ratio, on the development of fracture gas reservoirs with bottom water was analyzed. The impacts of these factors on development were summed up as follows.The main research results of this paper are as follows:1. Based on the physical simulation experiment:The larger the bottom water size is, the higher the depletion rate is, the earlier the water breakthrough time is, the lower the gas production is, the faster the water content increase, the lower gas reservoir recovery degree is.2. Simplified geometric model of dual media was established considering fracture characteristics, and then a 3D mathematical model of gas-water bi-phase was established under the consideration of reservoir stress sensitivity and bottom water intrusion. Matlab software was used to complete the corresponding solving program, with the comparative analysis by numerical simulation software Eclipse, the reliability of the model was verified.3. According to the seepage mathematical model and its analog solution water intrusion mechanism model, simulation study results obtained as follows:(1) Bottom-water has a great effect upon fractured gas reservoirs, but gas well changes little it bottom-water size exceeded a certain extent.(2) when fracture azimuth or dip is lower than 20, they have little influence on the with recovery and water/gas ratio; when fracture dip is bigger than 20°, the greater the fracture dip is, the smaller the water/gas ratio is and the greater the recovery is; when fracture azimuth bigger than 20, with fracture azimuth increasing, both recovery and the water/gas ratio decreases.(3) A critical gas production rate existed. If the production rate was smaller than the critical value, the greater the production is, the higher the recovery is; If the production rate was bigger than the critical value bottom water, production has little effect on recovery.(4) the Greater the ratio of fracture permeability to matrix permeability, the sooner the water break through, the quicker the ratio of water/gas ratio, the lower the recovery is.(5) The effect on water/gas ratio was little while the reservoir stress sensitivity was weak. And the water/gas ratio would rise very quickly with the increasing of the stress sensitivity.