Objective To address the problems of fluid loss, wellhead return loss, and productivity decline frequently encountered in conventional workover fluids during workover operations in shale gas production wells of China, a supramolecular associative polymer foam workover fluid was developed using the supramolecular associative polymer 4DH as a foam stabilizer and the polyether sulfonate composite FY-2055 as a foaming agent.

Method  The system formulation was screened and optimized. The properties and microscopic morphology of several conventional foam systems were compared, and the high-temperature and high-pressure foam properties were evaluated. Meanwhile, the foam plugging and permeability recovery performance of this foam system was compared with that of the conventional HPAM system.

Result The optimal formulation of the system is 0.15%-0.30% 4DH + 0.30% FY-2055. Compared with the surfactant system and the conventional HPAM system, it exhibits superior foam properties and foam structural strength, and the foam density is adjustable. Under the conditions of 9.5−10 MPa and 120−150 ℃, the foam stability time exceeds 90 min, the temperature- and shear-resistant viscosity exceeds 50 mPa·s. Simultaneously, the core permeability recovery rate reaches 100%, indicating no or minimal damage to the reservoir, which demonstrates significant advantages over the conventional HPAM foam system (permeability recovery rate of approximately 30%) under the same conditions.

Conclusion Based on its comprehensive performance, this supramolecular foam workover fluid can be recommended for field application pilot testing.