Study on the Creep Characteristics of Acidized Sandstone

Acidizing is a critical technique for enhancing production in sandstone reservoirs by dissolving rock cement and plugging materials within pores and fractures through acid-rock reactions, thereby restoring and improving reservoir permeability. However, the chemical-mechanical coupled creep behavior induced by acidizing results in a progressive reduction in fracture conductivity and wellbore instability, which represents a significant engineering challenge that limits the effectiveness of acidizing treatments. The study addresses the insufficient understanding of the creep mechanisms in acidized sandstone by conducting triaxial creep tests. It reveals the chemical damage-stress aging coupled evolution mechanism of the time-dependent mechanical behavior of sandstone under acid treatment. The results show that when axial stress ranges from 30 to 40 MPa, the sandstone exhibits a typical steady-state creep phase. When stress exceeds the critical threshold of 50 MPa, the sample enters an accelerated creep phase, with a sharp increase in strain rate, leading to structural instability. The acid dissolution of siliceous cement creates micro-cracks within the rock, significantly affecting the stability of the sandstone structure. After acid treatment, the rock’s long-term compressive strength decreases by 20% compared to untreated samples, while the steady-state creep rate increases threefold, confirming the reinforcing effect of chemical dissolution on the rock’s time-dependent deformation. The study provides a chemical-mechanical coupled perspective on the changes in mechanical properties and creep characteristics of sandstone after acidizing, offering a theoretical foundation for optimizing acidizing process parameters in sandstone reservoir stimulation.