With the rapid development of China’s economy,the demand for energy is increasing.Natural gas resources in China are very rich,but a large part of them are in low permeability to ultra-low permeability reservoir.The recoverable resources of tight sandstone reservoirs are 9.2×1012-13.4×1012 m3,and the proven reserves and annual reserves are gradually increasing.Therefore,the efficient development of tight sandstone gas reservoir is of great significance to improve the energy structure,protect the ecological environment and improve people’s living standard.In this paper,the pore structure and mineral composition of the core were studied by rate-controlled mercury penetration and X-ray diffraction experiments,and the distribution law of gas and water in the process of gas-water two-phase seepage was defined by nuclear magnetic resonance experiments.The damage characteristics of tight sandstone reservoir are comprehensively evaluated by means of experimental research.In order to clarify the mechanism of reservoir water locking damage,this paper studies the reservoir damage caused by water locking effect by experimental means,and analyzes the influence of different factors on gas well productivity by establishing the productivity equation of fractured horizontal well considering multiple factors.In the end,the most suitable method and formula of water lock release for the target reservoir are selected by experimental means.The results show that the core permeability is caused by porosity,pore structure and other factors,and is positively correlated with the porosity and quartz content,while negatively correlated with the clay mineral content.When the permeability is less than 0.2×10-3μm2,the core has a nonlinear seepage stage and the starting pressure is between 0.1028-0.1047 MPa.As the displacement process goes on,the gas and water prefer the large pore to flow.When the water in the large pore is driven out to a certain extent,the small pore will produce the phenomenon of self-imbibition,leading to its own blockage.Through sensitivity experiments,it can be seen that stress sensitivity and water sensitivity are the main factors leading to permeability decline,which cannot be ignored in actual production.The water lock damage experiment and productivity analysis show that the damage degree of permeability caused by water lock effect varies with the change of liquid accumulation conditions,and the water saturation and PV number of reverse effusion have the most significant effects on permeability.By comparing the variation law of productivity under different influencing factors,it can be seen that water locking effect is the most important factor causing the productivity decline of gas wells,which should be paid attention to in actual production.In the end,the experiment of water lock removal shows that the most effective method to solve the water lock damage is to inject various chemical agents into the formation.Among them,0.9%FS-3100+5%hydrofluoric acid+5%clay stabilizer can increase core permeability by about 10.47 times.In summary,the characteristics of gas-water two-phase seepage are further clarified in this paper,which is of great significance to the study of two-phase seepage mechanism in tight gas reservoirs.At the same time,the characteristics of water lock damage in tight gas reservoirs are revealed,and the effective method of water lock removal is put forward,which can provide certain theoretical guidance for the development and stimulation of tight gas reservoirs. |