Dynamic stress sensitive analysis of fractured tight reservoirs under compound damage from drilling and fracturing fluids

Abstract

With the growing global demand for energy, the exploration and development of unconventional oil and gas resources have become increasingly urgent. Fracturing technology, widely used to enhance production in tight reservoirs, faces challenges when dealing with fractured tight reservoirs that are prone to leakage. The combined effects of drilling and fracturing fluids on these reservoirs often causes significant deep reservoir damage, which greatly reduces the overall effectiveness of fracturing operations. This paper examines the sequential impact of drilling and fracturing fluids on fractured tight reservoirs experiencing well leakage, aiming to thoroughly assess the compound effects of these fluids on the reservoir. The research involved conducting stress sensitivity experiments on propped fractures in tight reservoirs subjected to compound damage. Using three-dimensional scanning technology to portray the morphological changes of the crack surface, combined with nuclear magnetic resonance (NMR) experiments to reveal the underlying stress sensitivity mechanisms. Additionally, the study quantified the effect of changes in reservoir elastic modulus on the stress sensitivity of single-layer supported fracture. The findings indicate that compared with the undamaged, drilling fluid-damaged and fracturing fluid-damaged states, the stress sensitivity coefficients of the propped fracture rock samples increased by 56.57%, 35.35%, and 37.99%, respectively, after compound damage. This compound damage leads to a significant increase in the stress sensitivity of the propped fractures, affecting the fracturing performance and reducing oil and gas production. Under an effective stress of 50 MPa, the maximum permeability loss of the propped fracture is 71.62% and 90.27% when the reservoir's elastic modulus is 5 GPa and 20 GPa, respectively. This demonstrates that a decrease in the reservoir's elastic modulus will increase its stress sensitivity. This research outcome will provide novel theoretical and practical foundations for the efficient enhancement of recovery rates in fractured tight reservoirs.