Research On Gathering And Transportation Critical Conditions Of Carbon Dioxide Flooding

At present,the development of most low permeability oilfields in China has entered the stage of water flooding with low recovery rate.In order to improve the recovery rate,some oilfields have successively carried out CO₂ oil flooding tests.However,the physical properties of the produced fluid changes a lot after CO₂ flooding,which affects the pressure drop of the gathering and transportation pipeline and thus affects the critical conditions of gathering and transportation.Therefore,it is necessary to study gathering and transportation critical conditions of CO₂flooding.Through the experiment of basic physical properties and rheological properties of degassed crude oil and dissolved crude oil,based on the Beggs-Brill pressure drop equation,the calculation models of solubility,crude oil volume coefficient and dissolved gas crude oil density which is suitable for CO₂ flooding gathering and transportation pipeline is optimized,and then the calculation formula of liquid holdup in downslope section of relief pipeline is modified,after which the coupling model of MB-BB-E*XB modified by parameters is put forward.Finally,the coupling mode is verified by using lots of datas.Based on the coupling model of MB-BB-E*XB modified by parameters,the thermo-hydraulic calculation of CO₂ flooding ground gathering and transportation system is studied.It is found that the friction pressure drop,elevation pressure drop and acceleration pressure drop of gathering and transportation pipeline show different law of change with the variation of parameters such as the produced liquid's gas-oil ratio and CO₂ concentration.And the law of change is interpreted by the point that CO₂ reduces the viscosity and liquid holdup of relief pipeline varies with topography.According to the gathering and transportation model in actual working conditions,the critical conditions of gathering and transportation about produced liquid temperature,water content,gas-oil ratio,produced fluid volume and CO₂concentration of produced liquid are given,after which the law of change of gathering and transportation radius under different gathering and transportation conditions is determined.