During the exploitation of low permeability gas-condensate reservoirs, the mud filtrate, acidizing liquid, and fracturing fluid invade the reservoir and condensate gas, severely reducing the permeability of the reservoirs due to increased capillary pressure and water wettability. For the current paper, an oligomeric silicone surfactant (OSSF) containing sulfonic acid groups was synthesized to improve the flowback of such fluids. The critical micelle mass concentration and critical surface tension were determined by equilibrium surface tension. The surface tension increased with the hot rolling temperature and decreased with the addition of NaCl, KCl, or CaCl₂. When the concentration exceeded critical micelle mass concentration, a micelle was formed and its size increased with mass concentration. OSSF adsorption through solid–liquid surface changed the surface chemical composition of the cores and transferred the wettability of cores from water-wet to preferential gas-wet by decreasing the surface energy. At the same time, the increasing temperature led to a change in the adsorption isotherm of quartz sand from Langmuir type (L-type) to “double plateau” type (LS-type) in the OSSF solution. In addition, NaCl decreased the relative foam volume of OSSF while extending the half-life. OSSF decreased the initial foaming volume and stability of the induction period and accelerated sodium dodecyl benzene sulfonate (SDBS) formation.

The stability of deep marine shale wellbores is influenced by both bedding anisotropy and drilling fluid intrusion. Existing models fail to adequately account for the coupled effects of intrusion depth and strength degradation. This study, targeting Longmaxi Formation shale, established a collapse pressure prediction model incorporating drilling fluid intrusion depth through direct shear tests and nuclear magnetic resonance (NMR) techniques. Experimental results indicate that shear strength reaches its minimum at β = 45°, decreasing by approximately 60% compared to β = 0° or 90°. Intrusion causes exponential decay in bedding plane strength, with the cohesion degradation coefficient λ_c = 0.158 mm⁻¹ significantly exceeding the internal friction angle degradation coefficient λ_φ = 0.089 mm⁻¹. Sensitivity analysis indicates that bedding angle and invasion depth rank third (±3%) and fourth (±1.5%), respectively, in influencing collapse pressure. Field validation confirmed excellent model prediction accuracy (R² = 0.956; RMSE = 0.55 MPa; MAPE = 1.05%), with all errors below 4%. This model accurately predicts the time-varying characteristics of collapse pressure, providing a theoretical basis for optimizing the design of drilling fluid density.