CO2驱微观可视化技术在超低渗储层中的应用可行性研究:以鄂尔多斯盆地为例

CO₂驱油是提高特低渗、超低渗油藏驱油效率的重要途径,但目前由于匮乏CO₂驱油微观可视化实验技术,制约了CO₂驱油微观机理研究及驱油效果评价。本研究提出特低、超低渗油藏高温高压下CO₂驱油微观可视化实验技术,为该类油藏CO₂驱油机理研究提供良好的研究手段。以鄂尔多斯盆地超低渗储层为例,利用首次研制成功的高温、高压、防暴真实砂岩模型,成功进行了CO₂驱油微观可视化实验研究,首次镜下观察不同相态CO₂在超低渗储层复杂孔喉中驱替原油的动态现象,重新认识超低渗油藏注CO₂驱油时不同孔喉结构中CO₂赋存状态和渗流规律。结果表明,储层微观孔喉结构,尤其是孔喉大小分布的均匀程度,对CO₂驱油效率的重要影响超出预期,直接决定着CO₂能否进入储层以及其后的渗流路径。CO₂驱油微观可视化实验技术可有效进行CO₂驱油微观机理研究及驱油效果评价研究,并为后期进行油藏矿场试验提供指导意见。

Feasibility Study on Applying CO_2-flooding Micro-visualization Technology in Ultra-low Permeability Reservoirs:A Case Study in Ordos Basin

CO₂-flooding is an important way to improve oil displacement efficiency in extra-/ultra-low permeability reservoirs. However, the microscopic mechanism of CO₂-flooding and oil displacement effect evaluation are hampered by the lack of micro-visualization technology. In this study, we suggested that micro-visualization experiments of CO₂-flooding in extra-/ultra-low permeability reservoirs under high temperature and pressure can satisfactorily reveal the CO₂-flooding mechanism.Ultra-low permeability reservoirs in the Ordos Basin are taken as examples, and micro-visualization experiments of CO₂-flooding were newly and successfully carried out by using the high temperature, high pressure and anti-riot real sandstone model. Dynamic phenomena of the different CO₂ phases (in crude oil displacement) in the complex pore throat of the ultra-low permeability reservoirs were simultaneously observed under the microscope, and the occurrence and seepage of CO₂ in the different pore throat structures were obtained. The pore throat structure, especially the uniformity of pore throat size distribution (critical for the CO₂-flooding efficiency), directly determines whether the CO₂ can enter the reservoir and the subsequent seepage path. The micro-visualization experiment of CO₂-flooding can not only effectively reveal the microscopic mechanism of CO₂-flooding and evaluate the oil displacement effect, but can also provide guidance for later-stage reservoir analyses.