砂岩油藏CO2驱提高采收率油藏筛选与潜力评价

由于能够满足环境保护和提高采收率的双重需求,CO2驱越来越受重视。CO2驱油藏筛选与潜力评价方法是进行中长期发展规划和规模化矿场应用的基础,但以混相-非混相驱理论为指导的筛选标准难以适应中国陆相砂岩油藏的需求。为此,首先利用数值模拟方法研究CO2驱混相特征,揭示初期注入端出现暂时混相,之后混相区向采出端移动并呈现相分离、前缘界面张力降低、采出井界面张力升高的规律;分析混相程度的变化特征,并提出近混相驱划分界限;在现有标准的基础上,提出新的CO2驱油藏筛选标准。将该标准与模糊评判和层次分析法相结合,建立了砂岩油藏CO2驱筛选方法,并应用于中国石化CO2驱油藏筛选。结果表明,剔出化学驱油藏和稠油油藏后,中国石化适合CO2驱的石油地质探明储量达22.62×108t,其中混相驱、近混相驱和非混相驱的石油地质探明储量分别为4.89×108,6.59×108和11.14×108t,预计增加可采储量2.03×108t。

Screening method and potential evaluation for EOR by CO2 flooding in sandstone reservoirs

Because CO2 flooding can meet the demand of both environmental protection and enhanced oil recovery,it has attracted increasing attention. The reservoir screening and potential evaluation methods of CO2 flooding are the basis of medium and long-term development planning and large-scale field application,but the screening criteria guided by miscibleimmiscible flooding theory are difficult to adapt to China’s continental sandstone reservoirs. Therefore,the miscibility characteristics of CO2 flooding are firstly studied by numerical simulation. The transient miscibility at the initial injection end appears. Afterwards,the miscibility zone moves to the production end,and phenomena including phase separation,interfacial tension reduction at leading edge and interfacial tension rise in the production well appears. The variation characteristics of miscibility degree are analyzed and the boundaries of near-miscibility flooding are proposed. On the basis of existing standards,a new standard for screening CO2 flooding reservoirs is proposed. It is combined with fuzzy evaluation and analytic hierarchy process,and a screening method for CO2 flooding in sandstone reservoirs is proposed and applied to the screening of CO2 flooding reservoirs of SINOPEC. The results show that SINOPEC has 2.262 billion tons of proven reserves suitable for CO2 flooding except for chemical flooding reservoirs and heavy oil reservoirs,of which,489 million tons are miscible flooding,659 million tons are near miscible flooding and 1 114 million tones are immiscible flooding,and the recoverable reserves are expected to increase by 203 million tons.