特低渗透油藏注气驱长岩心物理模拟

西部某油藏的储层物性为低孔特低渗,平均孔隙度12.32%,平均渗透率2.1×10-3μm2,在开发过程中存在注水困难的问题.为了研究油藏注气可行性,在室内进行长岩心驱替实验,得到了不同气体(CO2、N2及烃类干气)改善原油物性的效果,以及注入不同流体(纯水驱、纯N2驱、纯CO2驱、烃类干气驱、N2泡沫驱)提高原油采收率的效果.研究结果表明:在CO2、N2及烃类干气中,CO2能明显改善原油的物性,对原油的降黏效果和膨胀效果较明显,而N2和烃类干气对原油的膨胀不是很明显.与注水相比,注入4种气体都可以大幅度提高特低渗油藏的采收率.在4种气驱中,N2泡沫驱的驱油效率最高,达到57.12%,但驱替压差随着驱替进行而一直升高,而且在实验过程中注入压力超过了地层破裂压力,且注入量也达到7.10 PV的体积,现场实施时应引起高度重视.其次是纯CO2驱,N2驱最差.

Physical simulation of gas driving with long ultralow permeability core

The research object is a reservoir in west China,which is low porosity and ultralow permeability.The average porosity of the reservoir is 12.32%,and the average permeability of it is 2.1×10-3 μm2.The water flooding result of the reservoir is poor.In order to study the feasibility of gas driving in the ultra-low permeability reservoir,the oil displacement experiments of long cores are carried out by injecting different types of fluid(water,N2,CO2,dry hydrocarbons gas and N2 foam).The improving effect of CO2,N2 and dry hydrocarbons gas driving on the physical properties of crude oil and the enhanced oil recovery results by water,N2,CO2,dry hydrocarbons gas and N2 foam displacement are studied.It is shown that,the physical property improvement,viscosity reduction and volume expansion effects of CO2 gas on the crude oil is best among CO2,N2 and dry hydrocarbons gas,and that compared with water driving,all the 4 gas driving forms can greatly enhance the recovery factor of ultralow permeability reservoirs,of 4 gas drivings,nitrogen-foam flooding has highest oil displacement efficiency,which reaches to 57.12%,but the driving pressure exceeds the formation fracturing pressure,the injection volume also reaches to 7.10 PV,and therefore the high attention should be paid on the application of N2 foam flooding.The oil displacement efficiency of CO2 flooding is secondary,and the oil displacement efficiency of N2 flooding is lowest.