The Experimental Study On Gas Injection In Fractured Vuggy Carbonate Reservoir

The fractured vuggy carbonate reservoir in Tahe has the characteristics of high temperature,high pressure,complex fracture-cave construction and connectivity and high viscosity of crude oil.The energy of the bottom water is sufficient.And the development mainly depends on the formation energy at early stage.With the deepening of exploitation,there are many problems including energy shortage,water content increase,decreased of production in some production wells.In the oilfield,the technologies of single well water injection and multi well water injection can effectively solve the problems such as the increase of water cut and the decline of production.However,with the development of water flooding,the channel of water flooding is gradually formed,and the water injection scheme becomes invalid.This paper mainly discusses the feasibility of gas injection after water flooding invalid and the mechanism of enhancing oil recovery in the fractured vuggy carbonate reservoir.Through the high pressure physical properties’experiment by injecting gas compound formation oil,displacement experiment of visualization and three-dimensional physical simulation experiment,EOR of fractured vuggy carbonate by gas flooding,optimization method of gas injection and gas injection to improve the analysis of factors influencing the recovery rate are researched.The influencing factors of enhancing recovery efficiency by gas flooding are researched and optimal media is selected from the aspects of the relationship between the tunnel and the tunnel,the type of the gas medium,the relationship between injection and production by regarding Tahe 6-block as the research object.Through the experiment of gas mixture formation oil PVT understanding affects the solubility of different gases in the crude oil and crude oil viscosity,expansion of nature;in the visualization experiments of gas injection wells location,injection volume and way to improve recovery;physical experiment to optimize the gas injection and the analysis of the gas medium influence factors of flooding to enhance oil recovery in 3-D.The results show that under the same injection volume and formation conditions,property in the high pressure of different gas mixture of crude oil has a large gap.The effect of increase formation energy by N₂ is the best,the effect of viscosity reduction and crude oil expansion ability by CO₂ is best,and the effect by mixed gas（N₂+CO₂）between them,characteristic of air is close to N₂,viscosity reducing effect by dry gas is close to CO₂ but lower than mixed gas.The visualization experiments demonstrate that the formation of gas cap by gravitational differentiation of N₂ is the dominant role,the injection method by high injection and low production can reduce gas channeling;gas flooding effect increases with the increase of injection volume of gas,but the conversion rate gradually decreases.The method of using gas-water injection can slow down the gas channeling and the displacement effect of this is best.Three-dimensional physical simulation gas flooding experiment shows that the displacement effect of N₂ is the best,and the oil production of the well in the upper part of reservoir is higher.The displacement of N₂ is affected greatly by viscosity,and the displacement effect of CO₂is less affected by viscosity.The above studies provide experimental basis for the gas injection enhanced residual oil after water flooding,and has certain reference for the development of gas injection technology on the results of fracture cave type carbonate reservoir.