Research on Mechanism and Effect of Enhancing Gas Recovery by CO2 Huff-n-Puff in Shale Gas Reservoir
CO₂提高天然气采收率（CO₂-EGR）技术在碳捕获、利用与封存（CCUS）产业中发挥着关键作用，有助于实现气田的经济效益和环境效益双赢。页岩气藏凭借其独特的地质和地表工程优势，是CCUS实施最有前景的选择之一。本研究聚焦于四川盆地中部深层区块的页岩地层，开展了多组分气体的竞争吸附实验。通过物理模拟和单井数值模拟，考察了注入量、注入时机、焖井时间和吞吐轮次等因素对采收率的影响。结果表明，注入介质中CO₂含量越高，气体在页岩表面的吸附优势越明显。当注入介质中CO₂含量为80%至100%、注入量为0.2−0.3 PV、焖井时间超过6小时且注入时机相对较晚时，效果最佳。在第一轮吞吐中，采收率提高了24.2%至47.8%，充分发挥了吞吐的作用，并取得了良好的效益。基于中部深层地质参数，建立了单井数值模拟，表明与未进行CO₂注入的气井相比，单井最终采收量（EUR）可提高14.2%至19.8%。本研究为通过CO₂吞吐提高页岩气藏采收率提供了重要的指导。
CMG软件应用情况
利用CMG数值模拟软件的GEM组分模型，对单页岩气井的压裂、生产以及CO₂吞吐进行了全面的模拟研究。采用网格细化技术，处理了页岩井的多阶段转变。双孔隙模型考虑了页岩气藏基质孔隙度高、渗透率低以及裂缝渗透率高的情况。利用朗格缪尔气体吸附参数和扩散因子，模拟了气体吸附、解吸、扩散和流动等各种传输机制。
结论
- 多组分气体的竞争吸附实验表明，注入介质中CO₂含量越高，竞争吸附效果越明显。CO₂在页岩上的吸附能力约为CH₄的2−3倍。
- 提高天然气采收率的物理模拟结果表明，气体注入介质中CO₂比例越高、焖井时间越长，越有利于提高页岩气采收率。
- 多轮次吞吐的效果表明，第一轮吞吐可使采收率提高24.2−47.8%。这一初始轮次充分发挥了吞吐技术的作用，带来了较高的效益。
- 基于中部深层地质参数建立的单井数值模拟显示，与未进行CO₂注入的气井相比，单井EUR可提高14.2−19.8%。
作者单位
中国石油西南油气田公司页岩气研究院
ABSTRACT:
The technology of CO2-enhanced gas recovery (CO2-EGR) plays apivotal role in the CCUS (Carbon Capture, Utilization, and Storage) industry,which helps to achieve a win−win situation of economic benefit and environmentalbenefit for gas fields. Shale gas reservoirs, with their unique geological and surfaceengineering advantages, are one of the most promising options for CCUSimplementation. Focusing on shale formations within the mid-deep blocks of theSichuan Basin, this study conducted competitive adsorption experiments usingmulticomponent gases. Through physical simulations and single-well numericalmodeling, factors such as injection volume, timing, shut-in time, and huff-n-puffrounds were examined for their impact on recovery. The results show that thehigher the CO2 content in the injected medium, the more pronounced advantage ingas adsorption on shale surfaces. Optimal performance was achieved with a CO2content in the injection medium of 80% to 100%, an injection volume of 0.2−0.3PV, a shut-in time exceeding 6 h, and a relatively delayed injection timing. The recovery in the first round of huff-n-puff wasincreased by 24.2% to 47.8%, which gave a full play to the role of huff-n-puff and achieved favorable benefits. Based on the middle-deep geological parameters, a single-well numerical simulation was established, which demonstrates that single-well EUR (estimatedultimate recovery) can be increased by 14.2% to 19.8% compared to gas wells without CO2 injection. This study provides essentialguidance for the enhanced recovery in shale gas reservoirs through CO2 huff-n-puff
