Mitigating Water-Blocking Damage in Shale Gas Reservoirs Using a Mixed Surfactant System (COLA-P): A Macro-to-Micro Integrated Evaluation and Mechanistic Study

During the development of shale gas, the intrusion of exogenous working fluids frequently triggers water-blocking damage, leading to a significant decline in well productivity. To address this issue, this study developed a composite surfactant-based water-blocking removal system (COLA-P) and evaluated its performance and functional mechanisms using an integrated “macro–micro” linkage approach. Macroscopic evaluations demonstrate that the COLA-P system significantly reduces both surface and interfacial tensions while successfully reversing the wettability of the shale surface. In core flow experiments, the system achieved a high permeability recovery efficiency of 84.72%. Regarding the microscopic mechanism, the integration of XRD, SEM-EDS, and molecular dynamics (MD) simulations reveals a triple synergistic mechanism of “Attraction-Anchoring-Shielding” (1): quaternary ammonium groups and protonated amine oxides suppress clay swelling through charge neutralization; (2) phosphate groups enhance adsorption stability via coordination complexation with Ca2+; and (3) the four surfactant components align orderly to form a dense hydrophobic film. This research not only confirms the superior efficiency of the COLA-P system in mitigating water-blocking but also provides a scientific foundation and a novel pathway for the performance evaluation and mechanistic analysis of shale water-blocking removal agents.