Research on High-Pressure Energy Injection and Response Mechanism in Tight Sandstone Reservoirs

To reveal the energy transfer mechanism of water injection and the dynamic response characteristics of pore pressure in tight sandstone reservoirs, and to clarify the influence of lithology, injection pressure, and injection method on the energy enhancement effect of water injection, a high-pressure energy injection and response testing system and nuclear magnetic resonance (NMR) testing technology were used to conduct systematic water injection energy enhancement experiments on three rock types: mudstone, sandstone, and naturally fractured sandstone. Combined with pressure dynamic monitoring and pore structure evolution analysis, the pressure response characteristics and energy enhancement mechanism of rock samples under different experimental conditions were explored. The experimental results showed that the NMR T2 distribution of the three rock samples exhibited bimodal characteristics, corresponding to small pores (pore size < 1000 nm) and large pores/microcracks (pore size > 1000 nm), respectively. There were significant lithological differences in the evolution of pore structure during water injection, with a cumulative decrease of 7.2% in the proportion of large pores in mudstone and an increase of 9.3% in the proportion of large pores in sandstone with natural fracture development. There is a positive correlation between injection pressure and the energy enhancement effect. Under an injection pressure of 40 MPa, the pressure increment at the outlet end of sandstone with natural fracture development reaches 8.06 MPa, and the energy enhancement effect is 24% higher than that under the 30 MPa working condition, while the mudstone only increases by 15%. The energy enhancement effect of intermittent water injection is significantly better than that of depleted water injection, and the energy enhancement effects of the three rock samples are increased by 18.6%, 12.0%, and 6.9%, respectively. Overall, sandstone with natural fractures has the best energy enhancement effect, followed by sandstone, and mudstone has the worst. The connectivity of pores and the degree of fracture development are the core factors that dominate the water injection energy enhancement effect and pressure transmission efficiency. The research results can provide reliable experimental basis and theoretical support for optimizing water injection development plans, improving energy efficiency, and dynamically regulating stress fields in tight sandstone reservoirs.