Numerical Simulation Of Stress - Sensitive Fractured Bottom Water Reservoir

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 et al. With complex fracture system in gas reservoir, during the development process, 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 numerical simulation of fracture gas reservoirs with bottom water under consideration of stress sensitivity" 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, and studying the changes of reservoir permeability, porosity and rock compressibility with effective stress, simplified geometric model of dual media was established considering fracture characteristics, and then a 3D mathematical model of gas-water biphase 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, bottom water size, water invasion index, reservoir stress sensitivity and matrix and fracture 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)Permeability and effective stress meet the exponential, power function and polynomial, and stress sensitivity in different permeability intervals is not the same; Also reservoir porosity and effective stress meet the exponential, power function and polynomial; Reservoir rock compressibility and effective stress satisfies the exponential logarithmic or power function, and the fitted formulas would be not the same in different permeability intervals;(2)Simplified geometric model of dual media was established considering fracture characteristics, and then a 3D mathematical model of gas-water biphase 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 In water features, water body size and water intrusion index mainly affect the water breakthrough time in gas well and cumulative water production. With the water body size and water intrusion index increasing, the cumulative water production increases and the water breakthrough time is in advance.② Stress sensitivity has little influence on water breakthrough time. Considering stress sensitivity, as the stress sensitive coefficient increases, cumulative gas and water production decrease, and recovery percent reduces also.③ In the fracture features, when fracture azimuth or dip is greater than 20°, with fracture azimuth or dip increasing, the stable yield time increases, water breakthrough time puts off and cumulative water production decreases; As fracture dip increases, cumulative gas production and recovery percent both increase; As fracture azimuth increases, cumulative gas production decreases, and meanwhile, recovery percent reduces.④ Matrix and fracture permeability ratio has little influence on cumulative gas production and recovery percent. With matrix and fracture permeability ratio increasing, the stable yield time increases, water breakthrough time puts off and cumulative water production decreases.