Unstable Pressure Analysis of Gas Drive in Low Permeability Carbonate Reservoirs

Unstable pressure analysis is an important technology to monitor and evaluate the development performance of gas drive. The study divides the fluid distribution into three zones, namely, pure gas zone, miscible zone, and pure oil zone. Considering the complexity of carbonate reservoirs, a three-zone unsteady channeling well test model is established, and through perturbation transformation, pulling the Laplace transform realizes the solution of the model, obtains the solution of the unstable bottom hole pressure of gas drive in low-permeability carbonate reservoir, and analyzes the influence of reservoir physical properties and fluid physical properties on the pressure derivative. Studies have shown that the bottom hole pressure derivative curve has obvious transition characteristics in the fluid transition zone, and the distribution range of the oil and gas transition zone can be judged from this, and the inversion of reservoir parameters and fluid physical properties can be achieved by fitting a double logarithmic curve. It is found that the interface radius between the first zone and the second zone mainly affects the second stage to the fifth stage. As the interface radius decreases, the radial flow stage in the first zone gradually disappears. The interface radius of the second zone and the third zone mainly affects the sixth stage to the seventh stage. As the interface radius decreases, the radial flow stage in the second zone gradually disappears. At the same time, the radial flow in the third zone gradually expands. The findings of this study can help for better understanding of pressure transient behaviors of gas drive in low permeability carbonate reservoirs.