The ultra-deep tight sandstone gas reservoir is prone to severe reservoir damage during well construction and production due to its special geological conditions and complex engineering operations.Fracture stress sensitivity damage is an important form of damage in ultra-deep tight gas reservoirs.Taking the ultra-deep and ultra-tight sandstone gas reservoir in the Tarim Basin as the research object,we carry out the experimental evaluation of stress-sensitive damage on the fractured rock samples in their original state,repeated loading/unloading stress change paths,and treated with drilling fluid and acid solutions.The experimental results show that the stress sensitivity coefficient of the undisturbed sandstone fracture during stress loading ranges from 0.36 to 0.72,with an average of 0.56,and the sensitivity degree is moderately strong.The stress unloading process ranges from 0.18 to 0.62,with an average of 0.44,and the sensitivity is moderately weak.During cyclic loading,fracture permeability tends to decrease continuously,and the recovery rate of permeability is extremely low after effective stress reduction.The fracture stress sensitivity coefficient of tight sandstone after oil-based drilling fluid treatment ranges from 0.57 to 0.58,and the fracture stress sensitivity coefficient increases from 0.64 to 0.69 after acid fluid treatment.It is concluded that the decrease of Young's elastic modulus and compressive strength and the increase of Poisson's ratio caused by solid-phase intrusion of drilling fluids and working fluid treatment are the main mechanisms of working fluid aggravating fracture stress sensitivity damage.Sensitivity analysis shows that the change in Young's modulus significantly affects the degree of fracture stress sensitivity compared to Poisson's ratio.The research results have a certain reference significance for selecting working fluid and the formulation of reasonable production pressure differences in ultra-tight gas reservoirs.
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