延长油田致密砂岩油藏CO2驱油机理研究

CO2 EOR mechanism of tight sandstone reservoir in Yanchang oilfield

关键词:  低渗透  CO₂驱  驱油机理  储层伤害  采收率

Key words:  low permeability  CO₂ flooding  flooding mechanism  reservoir damage  recovery efficiency

摘要:

CO₂驱是提高低渗透油田产量、缓解温室效应的有效途径。针对鄂尔多斯盆地油藏压力系数低、原油轻质组分含量高的特点,通过 PVT和最小混相压力等测试分析方法,揭示了低压、低孔、低渗油藏CO₂ 驱提高采收率主要机理。开展了CO₂注入储层与无机、有机物作用后的沉淀研究,表明CO₂在无机盐溶液中不会形成沉淀堵塞孔隙,CO₂与有机质作用后沉积点高于油藏压力,且注入压力越高,CO₂在地层原油中的溶解能力越强,目标区块CO₂注入后不易形成沥青质沉淀。物模驱替实验结果表明,均质岩心的采出程度明显高于非均质岩心,且随着岩心非均质性的增加,水驱采出程度、气驱采出程度及最终采出程度均明显下降。

Abstract:

CO₂ flooding is an effective way to increase production in low permeability oil field,and alleviate the greenhouse effect. Aiming at the features of low pressure coefficient and high content of light crude for Ordos Basin reservoir,and by using the analysis methods of PVT and minimum miscibility pressure, the main mechanism of improving recovery efficiency by CO₂ flood in reservoirs with low-pressure, low porosity and low permeability was revealed. The precipitate research was carried out after CO₂ injection organic and inorganic reservoirs. The result shows that CO₂ in inorganic salt solution will not form precipitate to plug pores, sedimentary points are higher than the reservoir pressure after CO₂ flooding into the organic matter,and the higher injecting pressure,the stronger solubility of CO₂ in the formation crude oil, and the target block is difficult to form asphaltene precipitation after injecting CO₂. The physical model displacement experiment shows that homogeneous cores recovery degree was significantly higher than that of heterogeneous cores, and the degree of water flooding,CO₂ flooding and finally recovery all significantly declines with the heterogeneity increasing of core.