考虑纳米限域效应的页岩油二氧化碳吞吐适应性

Adaptability of CO₂ Huff and Puff in Shale Oil Considering Nano Confinement Effect

王 雨 赵凤兰 黄世军 孙浩月 杨晨曦 毕善群

WANG Yu ZHAO Fenglan HUANG Shijun SUN Haoyue YANG Chenxi BI Shanqun

页岩储层通常物性差，孔喉细小，采用常规的注水、注化学剂等措施往往无法取得较好的开发效果。CO2吞吐不仅能有效降低油气界面张力、降低原油黏度等，达到提高页岩油采收率的目的，而且注入地层中的部分CO2还能实现永久封藏，有助于实现碳达峰、碳中和。采用数值模拟方法研究页岩油CO2吞吐的适应性。页岩储层以微纳米级孔喉系统为主，在流体流动过程中会产生较大的毛管压力，影响原油组分的热力学相行为，进而影响组分的计算和多孔介质中的流体流动，因此在流体模型中引入纳米限域效应，通过临界压力和临界温度变化来模拟纳米限域效应对流体组分相行为的影响。同时为探究页岩油CO2吞吐在压裂改造增产区不同缝网渗透率与基质渗透率比值（Kf /Km）和含油饱和度（So）下的适应性，以采出程度增量和换油率为参考指标，得到不同Kf/Km和So下的适应性图版。结果表明，与不考虑纳米限域效应相比，考虑纳米限域效应的组分p-T相图整体向上偏移，泡点压力升高。当Kf /Km为1000、CO2吞吐采出程度增量达到1.5%时，So适应性界限为0.54；而Kf /Km为1000、 CO2吞吐采出程度增量达到2.0%时，So适应性界限为0.57。当So为0.500、CO2吞吐换油率达到0.3时，Kf /Km适应性界限为 700；当So为0.548、CO2吞吐换油率达到0.6时，Kf /Km适应性界限为 10。Kf /Km-So图版可用于确定页岩油CO2吞吐适应性的物性界限。研究结果对于CO2吞吐现场试验方案设计和应用具有一定的指导意义。

Shale reservoirs usually have poor physical properties，small pore throats，while conventional measures such as water injection and chemical injection often fail to achieve good development results. CO2 huff and puff can not only effectively reduce the oil-gas interfacial tension and the viscosity of crude oil，etc，and then achieve the purpose of improving shale oil recovery，but also inject some CO2 in the formation to achieve permanent storage，which helps to realize the carbon peaks，carbon neutrality. This article used numerical simulation methods to study the adaptability of CO2 huff and puff in shale oil. Shale reservoirs were mainly composed of micro and nano scale pore throat systems，which generated significant capillary pressure during fluid flow，affecting the thermodynamic phase behavior of crude oil components and subsequently affecting component calculations and fluid flow in porous media. Therefore，nano confinement effect was introduced into the fluid model to simulate the impact of that on fluid component phase behavior through the changes in critical pressure and critical temperature. At the same time，in order to explore the adaptability of CO2 huff and puff in shale oil under different ratio of fracture network permeability to matrix permeability（Kf /Km） and oil saturation（So）in the increased production area of fracturing transformation，with the increase of recovery degree and oil change rate as reference indicators，the adaptability charts under different Kf /Km and So were obtained. The results showed that compared to not considering the nano confinement effect，the p-T phase diagram of the components considering the nano confinement effect shifted upwards as a whole，meanwhile the bubble point pressure increased. When Kf/Km was 1000 and the increase in CO2 recovery rate reached 1.5%，the adaptive limit of So was 0.54. When Kf /Km was 1000 and the increase in CO2 recovery rate reached 2.0%，the adaptive limit of So was 0.57. When So was 0.500 and the oil change rate of CO2 huff and puff reached 0.3，the adaptability limit of Kf /Km was 700. When So was 0.548 and the oil change rate of CO2 huff and puff reached 0.6， the adaptability limit of Kf /Km was 10. The Kf /Km-So charts could be used to determine the physical property limits of shale oil’s adaptability to carbon dioxide huff and puff. The research results had certain guiding significance for the design and application of CO2 throughput field testing schemes.

10.19346/j.cnki.1000-4092.2024.03.017