Effect of Stress Sensitivity on Gas Reserves Evaluation of Ultra-Deep Fractured Tight Sand Gas Reservoirs

Different from conventional gas reservoirs, ultra-deep fractured tight sandstone gas reservoirs have the characteristics of abnormal high pressure, tight matrix, and natural fractures developed in heterogeneity, and strong stress sensitivity. Taking Keshen2 gas reservoir in Tarim basin as example, based on routine core analysis, overburden core analysis, well logging and production data, the stress sensitivity of reservoir rocks and its influence on gas reserves estimation are evaluated. The results show that for this kind of gas reservoir, not only the permeability is strong stress sensitive, but also the porosity is strong sensitive. If the stress sensitivity of porosity is neglected, on the one hand, the geological reserves evaluated by volume method will be overestimated by 30%–40%, on the other hand, the dynamic reserves evaluated by pressure drop method will be overestimated by 1.5–1.8 times, which will affect the rational design of gas field development plan. The research results are of great significance to the rational development of ultra-deep fractured tight sandstone gas reservoirs.