有水气藏注气提高天然气采收率理论技术与矿场实践OA

Water-bearing gas reservoir and edge and bottom water-driven gas reservoir are two types of major contributors to the reserves and production of gas reservoirs with water in China.As the gas reservoirs advance to the middle and late stages of development,the gas-water distribution relationships get increasingly complicated,and the water invasion becomes more severe.In this context,gas injection is growing to a key technology to enhance the gas recovery of the gas reservoirs with water throughout the entire life cycle.Limited to the influence factors like physical and chemical properties of injected medium,reservoir heterogeneity and gas reservoir characteristics,however,the enhanced gas recovery by gas injection still needs researching and breaking through in mechanism understanding,key technologies and other aspects.Through laboratory displacement experiments and numerical simulation of gas reservoirs,this paper clarifies multiple physical and chemical mechanisms of enhanced gas recovery by gas injection,and systematically discusses the main development technologies for enhanced gas recovery by gas injection in three typical types of gas reservoirs with water(i.e.,tight sandstone,carbonate,and unconsolidated sandstone)based on field practice system.The following results are obtained.First,gas injection has multiple effects such as reservoir energy replenishment,gravity segregation,slug water plugging,water lock release,competitive adsorption,water invasion delay,and miscible displacement.Compared with N2,CO2 is significantly better in the miscibility with CH4,and smaller in volume required to achieve the same increase in recovery efficiency of natural gas.Second,the injection-production mode of injection at low positions and production at high positions is beneficial to maintain the stability of gas injection front,early gas injection is favorable for extending the water-free gas injection period of gas reservoirs,and in combination of the countermeasures like optimizing injection and production parameters,the recovery efficiency of gas reservoirs can be enhanced further.Third,enhanced gas recovery by gas injection exerts different functions in different types of gas reservoirs,such as CO2 miscible flooding in tight sandstone/carbonate gas reservoirs,N2 injection for water lock release in porous gas reservoirs with edge and bottom water,and N2 injection for unsealing and coning control in fractured-porous gas reservoirs with edge and bottom water.Fourth,the practical gas injection in a certain unconsolidated sandstone gas reservoir with edge and bottom water in the Sebei Gas Field shows that N2 injection significantly recovers the gas and water production rates of the neighboring producers,achieving positive results of enhanced gas recovery,such as pressurization for water plugging,and displacement&replacement.In conclusion,the research results provide systematical understanding on the mechanisms of enhanced gas recovery by gas injection in the gas reservoirs with water,develop a technical chain from mechanical study to field application,and are of important reference value for the efficient development of complex gas reservoirs and the promotion of CCUS-EGR technologies in China.