Study on combination of surfactant and acid for depressure and increasing injection oil displacement in heterogeneous sandstone reservoirs

This study addresses the challenges faced by unconventional tight sandstone reservoirs, including low porosity, permeability, high clay content, and complex wettability, which lead to increased flow resistance and injection pressures. The research aims to optimize depressure and increasing injection methods by investigating the effects of various two-phase and three-phase displacement systems, employing experimental treatments including acids, alkalis, and surfactants. Nuclear magnetic resonance, computed tomography, scanning electron microscopy, inductively coupled plasma, and wettability tests are utilized to investigate the mechanisms of these treatments. Key findings indicate that weak alkaline ethylenediaminetetraacetate tetrasodium and weak acids like hydroxyethylidene diphosphonic acid and acetic acid can cause significant pore blockage, while hydrochloric acid can dissolve pore minerals, achieves a high depressure rate of 89.42%. Although surfactants exhibit a negative effect in two-phase displacement systems, they demonstrate considerable potential in three-phase displacement. Surfactants can modify the wettability of rock surfaces, reduce oil saturation, and improve water phase permeability, resulting in a depressure rate of 11.68%. Notably, the combination of surfactants and HCl enhances the depressure rate to 60.82% and improves oil displacement efficiency from 26.12% to 57.96%. The optimal formulation identified is “0.5% unconventional agent (CNI-A) +3% HCl,” which improves oil displacement capacity and alleviates injection pressure, providing valuable insights for the management of heterogeneous sandstone reservoirs.