Abstract
High-pressure deep shale gas reservoirs are usually highly stress-sensitive. When the reasonable production mode of shale gas well is built, the impact of strong stress sensitivity should be fully considered. First, this study calculated the relationship between permeability and formation pressure under different elastic modulus based on the shale lithology of Long Ma Xi formation in Sichuan Basin by testing and analysing the mechanical parameters of the rock. According to numerical simulation result, when the elastic modulus exceeds 14.0GPa, the stress sensitivity of the matrix will slight affect the cumulative gas production of shale gas. Second, the changing relation between fracture conductivity and permeability with fracture pressure and the time of pressure acts were experimentally studied. The numerical simulation result suggested that the 30-year cumulative gas production considering the stress sensitivity was reduced by 13.5% compared with the 30-year cumulative gas production without considering the stress sensitivity. Finally, the production of different production modes under different stress sensitive characteristics was predicted using numerical simulation method. When the matrix and fractures are fixed with a same stress-sensitive curve, the initial production allocation will not significantly impact the cumulative gas production. When the fractured fractures are subjected to a varying stress sensitive curve, the lower production allocation will result in higher post-production and cumulative gas production.
Highlights
The stress-sensitive phenomenon refers to the variations of rock and oil reservoirs’ permeability and other physical properties with the effective stress
In 2014, Zhang et al [Zhang, Kamenov, Hill et al (2014)] performed an experiment to study the relationship between supported fracture permeability and pressure, as the results suggested that the fracture conductivity could be reduced several or even hundreds of times
Using drilling core technology, the required experimental samples from the different exploratory wells of the Long Ma Xi Formation shale are to be obtained; the core samples are cut and processed, a circular core column with a diameter of 25×100 mm and a rectangular rock slab of 38×200×5 mm are to be prepared, respectively, the former core column will be used for the experiment of shale matrix stress sensitivity, and the latter rectangular rock slab will be used for the experiment of shale fractures stress sensitivity
Summary
The stress-sensitive phenomenon refers to the variations of rock and oil reservoirs’ permeability and other physical properties with the effective stress. In 2009, Cipolla et al [Cipolla, Lolon and Mayerhofer (2009)] used the numerical simulation method to simulate the well dynamic with propped fractures that were stresssensitive in shale gas reservoir effectively, whereas the reliable stress-sensitive experimental data for propped fractures was lacked. The fracture conductivity was tested by varying the effective stress, stress action time, temperature, proppant size, etc. (2014); Zhang, Kamenov, Hill et al (2014)] all performed longterm fracture conductivity tests of the fracture stress-sensitive on major shale in North America. Most of the noted studies focused on the test of shale fracture conductivity and permeability caused by stress-sensitive, and the stress-sensitive features of shale matrix rock were ignored. The stress-sensitive matrix and stress-sensitive fracture are considered, and the reasonable production mode of shale gas well is discussed based on the study of their stress sensitive characteristics
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