Temporary plugging, diverting and acid fracturing technology used in carbonate reservoirs of Puguang Gasfield

The principal gas reservoir of Puguang Gasfield is an ultra deep structural-lithological gas reservoir of high sulfur content, moderate porosity and low permeability, and its main gas bearing layers are the Triassic Feixianguan Formation and the Permian Changxing Formation. Production profiles show that some intervals are not produced or less produced. Temporary plugging, diverting and acid fracturing technology can improve the gas production profile and increase the reservoir producing degree. And Puguang Gasfield tends to adopt this technology. At present, microseismic monitoring technology can be used to analyze quantitatively the diverting and propagation laws of fractures created by temporary plugging fracturing, but its error is larger due to the signal interference. Experiments on temporary plugging, diverting and acid fracturing were conducted by using the independently developed degradable temporary plugging agent for acid fracturing and high-temperature clean diverting acid system. In the experiments, the true triaxial simulation experiment device was used to apply the triaxial stress corresponding to the actual reservoir, and the outcrop cores whose physical property is similar to that of the reservoir were adopted. The temporary plugging and acid fracturing experiment on the outcrops shows that the diverting acid, acting as the fracturing fluid, is obviously favorable for the formation of complex fractures. And after the temporary plugging agent is added, the fracture initiation pressure is increased by 5−10 MPa and new fractures emerge obviously, indicting remarkable effect of temporary plugging. The on-site temporary plugging and acid fracturing experiment reveals that when the temporary plugging agent moves into the reservoir, its maximum temporary plugging pressure is 66.13 MPa, which is nearly 20 MPa higher than the maximum construction pressure without temporary plugging agent, indicating that the temporary plugging agent is compacting and sealing the high-permeability layers continuously. And when the diverting acid moves into the reservoir, the construction pressure fluctuates greatly, indicating that the diverting acid is transferring to the low-permeability layers and initiating new fractures continuously. The on-site experimental results are similar to the experimental results of outcrop cores, verifying the reliability of the temporary plugging, diverting and acid fracturing technology.