| Due to the characteristics of complex reservoir space,poor continuity of reservoir space distribution and strong reservoir heterogeneity in fractured vuggy carbonate reservoirs,it's a big challenge for developing the ones.The Tahe oil field is one of the main fields for the development of carbonate fractured vuggy reservoirs in China.In recent years,after water flooding of Tahe fractured vuggy reservoirs,the gas injection of single well is carried out,and EOR is significant.However,In the middle and late stage of reservoir development,water injection and the effect of gas injection in single well are becoming worse,and a large amount of "attic oil" between wells has not been used developed.Thus,to improve the gas injection development effect of this kind of reservoir,tt is necessary to carry out research on gas injection EOR mechanism for multi well development unit in fractured vuggy reservoir,so as to deeply understand the oil displacement mechanism of well group gas injection in fractured vuggy reservoir and to form a set of gas injection parameters optimization method.In this paper,the recovery efficiency of gas injection flooding in well group unit of fractured vuggy reservoir in Tahe oilfield is studied after water flooding.Based on the conventional phase experiment,gas injection expansion test and long tube displacement test of T401 crude oil in Tahe oilfield,the design and development of large scale visual gas injection displacement device for well group unit of indoor fractured vuggy reservoir are carried out.The experimental study on gas flooding after visualization of water flooding in well group unit is conducted.Combined with reservoir numerical simulation method,the influence factors of gas injection after water flooding of well group are simulated and analyzed,and the main production parameters are optimized.Finally,the field application effect of well group gas injection in fractured vuggy reservoir in Tahe oilfield is evaluated.The main research work and research results are as follows:1)Crude oil expansion experiments of fractured vuggy reservoir in Tahe Oilfield by injecting N2,CO2 and air and natural gas are studied.The study shows that under the formation pressure,the formation of four kinds of gas into the crude oil is difficult to achieve miscible phase,and the solubilization capacity of crude oil by injection gas is CO2>natural gas>N2and air.2)The oil displacement efficiency of N2,CO2 and air and natural gas by long tube experiment are studied.When the injection pressure is 60MPa and 1.2PV is injected,the displacement efficiency is CO2>natural gas>air>N2.Taking into account the recovery degree,economic profit,anti-corrosion operation and other conditions,it is determined that the N2 gas flooding enhanced oil recovery test is suitable for the Tahe oilfield unit.3)Considering the different geological factors(water,well storagerelationship),the gas injection is started after fw>90%of water flooding,the gas injection simulation mechanism model and the dynamic parameters of the development effect by single well numerical simulation orthogonal are studied.The simulation results show that the gas injection rate should match the appropriate well soaking time,and the different gas injection matching time should be combined with the well production dynamics and reservoir geological conditions.Based on the comprehensive numerical simulation results,the optimum gas injection well selection conditions and the principle of nitrogen injection well selection are determined under different influencing factors.4)The remaining oil distribution and the strategy of gas injection optimization of three kinds of karst reservoirs in Tahe oilfied are studied.The results show that the cyclic gas injection is used in weathered crust reservoir and ancient channel reservoir,and alternate gas-water injection is used in broken channel reservoir;gas injection is 0.2PV in weathered crust reservoir and ancient channel reservoir,and 0.15PV in broken channel reservoir.The gas injection rate of weathered crust reservoir is 5×104 m3/d,that of paleochannel reservoir and fault solution reservoir is 3×104 m3/d.And the gas injection cycle of weathered crust reservoir is 3 months,that of paleochannel reservoir is 2 months,and that of fault solution reservoir is 3 months and 1 month.5)On the basis of physical simulation experiment and numerical simulation results of unit gas injection chamber in well group,S48 unit well group unit gas injection is designed and the application effect of field gas injection is evaluated.As well as other gas injection wells,the application effect of well group gas injection is good.The results of this study can determine the feasibility of fractured vuggy reservoir in Tahe wells gas injection to improve the development effect,provide theoretical support for Tahe oilfield improve recovery rate of technology policy,also provide valuable experience for the development of similar reservoirs. |
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