Preparation and performance of pH-temperature responsive low-damage gel temporary plugging agent

Temporary plugging to fracturing has become the main production enhancement and transformation method for low-permeability, unconventional oil and gas reservoirs. In this paper, copolymers (PANA) were firstly prepared by free-radical aqueous solution polymerization with monomers acrylamide, N-vinylpyrrolidone, and 2-acrylamido-2-methylpropanesulfonic acid, and then gel temporary plugging agents (PJPs) were prepared using polyethyleneimine as cross-linker. The successful preparation of the target products was also demonstrated by using infrared and nuclear magnetic characterization. The results of rheological performance tests on PJPs show that they have good temperature and shear resistance. Validation experiments on the pH and temperature response performance of PJPs based on the visual code method and viscoelastic strength showed that PJPs could not be gelled at low temperature (<30 °C) and low pH (<7), thus proving that PJPs is controlled by both temperature and pH. Then the gelling mechanism of PJPs was investigated by characterizing the state of PJPs before and after gelling by SEM. The experiments to evaluate the temporary plugging performance of PJPs show that when the pH is 10 and the temperature is 120 ℃, the temporary plugging agent can completely seal the fracture with a repellent pressure of 2 MPa, and the final flow rate tends to 0 mL/min. The maximum breakthrough pressure reaches 12.6 MPa with a fixed repellent flow rate of 5 mL/min, which has good plugging pressure-bearing performance. Finally, the damage performance evaluation experiment of PJPs concluded that the permeability damage of fractured cores was below 13 %, thus indicating that PJPs have good protection performance for the reservoir.