Research and application of the low-damage temperature-controlled phase change temporary plugging agent

Ultra-deep dense sandstone reservoirs are characterized by high stress, large stress difference, high temperature, etc. Compared with conventional fracturing techniques, temporary plugging fracturing techniques are more capable of increasing fracture complexity and improving the stimulation reservoir volume (SRV). Phase-change temporary plugging agent has received wide attention due to its easy injection and return characteristics, etc. However, the temporary plugging mechanism of phase-change temporary plugging agent on shot-holes and fractures is still unclear. Therefore, this study aimed to develop a temperature-controlled phase change temporary plugging agent (STPA). The main properties of STPA, such as gel formation time and plugging capacity, are studied. The results show that STPA completes the transition behavior of solution-gel-solution at different temperatures; the gel formation time and gel breaking time of STPA decrease with increasing temperature; the pressure-bearing capacity of the plugging increases with the width of the fracture; the pressure-bearing capacity of STPA is more than 20 MPa in the fracture, and more than 18 MPa in the "shot-hole + fracture"; the rate of injury to core permeability by STPA is about 1.2%. In addition, STPA was successfully applied in fracturing field practice, and the maximum injection pressure increment was about 12.08 MPa, with remarkable temporary plugging effect. These results help to reveal the plugging mechanism of phase change plugging agent, which is of guiding significance for the field application of STPA.