南川常压页岩气田注CO吞吐矿场实践

Field tests of CO huff-n-puff technology in Nanchuan normal-pressure shale gas field

高玉巧 郑永旺 张莉娜 任建华 张耀祖 房大志

GAO Yuqiao ZHENG Yongwang ZHANG Lina REN Jianhua ZHANG Yaozu FANG Dazhi

1. 中国石化 华东油气分公司 勘探开发研究院, 南京 210019; 2. 页岩油气富集机理与高效开发全国重点实验室, 北京 100083; 3. 中国石化 重庆页岩气有限公司, 重庆 408400

1. Research Institute of Exploration & Production, SINOPEC East China Oil & Gas Company, Nanjing, Jiangsu 210019, China; 2. State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Efficient Development, Beijing 100083, China; 3. SINOPEC Chongqing Shale Gas Company, Ltd., Chongqing 408400, China

受吸附态甲烷占比高、地层能量弱等影响，常压页岩气藏采收率普遍不足30%。中国石化率先在四川盆地南川常压页岩气田开展注CO2吞吐矿场试验，验证了海相页岩气注CO2提高采收率的可行性。为推广该技术，以南川常压页岩气田为研究对象，开展室内实验—数值模拟—吞吐动态分析全链条研究，分析CO2在不同页岩储层中竞争吸附差异性，探究矿场CO2注入、吞吐特征，明确页岩气注CO2吞吐提高采收率技术“增能+置换+解水锁”多机制协同机理，进而指导选井及方案优化。综合利用电镜扫描、测井解释、等温吸附实验等方法，揭示南川地区上奥陶统五峰组—下志留统龙马溪组常压页岩储层随埋深变浅、地层压力减小以及孔隙度、TOC和黏土矿物含量的增加，CO2竞争吸附能力增强，超临界态CO2吸附量最高可达CH4的6～7倍。现场页岩气井注CO2吞吐后，日产气可提高3.5～6.5倍，采收率提升1.9%～3.1%。根据2井3轮次注入—焖井阶段压力监测，CO2主要集中在近井地带微裂缝中，扩散距离与地层压力、压裂缝网导流能力有关，一般不超过70 m。CO2吞吐可划分为初期CO2快速返排、早期提产和中后期稳产3个阶段，增产机理分别为早期增能补能、中期膨胀助排+解水锁、后期吸附置换+分压促解吸。吞吐提产的主要影响因素为储层改造程度和采出程度。中深层压裂效果较差的井在吞吐中早期换气率高，浅层采出程度较高的井在吞吐中后期累增气量高。结合数值模拟，建议优选吸附能力强、采出程度20%～30%、携液能力较差且关井压力尽可能达到7 MPa的井开展矿场先导试验。在低压低产阶段，中深层井可开展小规模多轮次注CO2吞吐以增能助排，浅层井可开展大规模注CO2吞吐以补充地层能量、吸附置换实现采收率提升。

Due to the high proportion of adsorbed methane and weak formation energy, the recovery rate of normal-pressure shale gas reservoirs is generally less than 30%. SINOPEC took the lead in conducting CO2 huff-n-puff field tests in the Nanchuan normal-pressure shale gas field in the Sichuan Basin, verifying the feasibility of CO2 injection for enhanced recovery of marine shale gas. To promote this technology, a comprehensive study was carried out on the Nanchuan normal-pressure shale gas field, involving laboratory experiments, numerical simulations, and dynamic huff-n-puff analysis. The study analyzed the CO2 competitive adsorption differences in different shale reservoirs, explored the CO2 huff-n-puff characteristics in the field, and clarified the synergistic effects of CO2 huff-n-puff to enhance shale gas recovery (ESGR) technology through multi-mechanisms of energy enhancement, displacement, and water-unlocking, aiming to guide well selection and program optimization. Using techniques such as electron microscope scanning, well logging interpretation, and isothermal adsorption experiments, the study revealed that the CO2 competitive adsorption capacity of normal-pressure shale reservoirs in the Upper Ordovician Wufeng and the Lower Silurian Longmaxi formations of the Nanchuan area increased with decreased burial depth and formation pressure, and with increased porosity, TOC, and clay mineral content. The adsorption capacity of supercritical CO2 was found to be 6 to 7 times higher than that of CH4. After CO2 huff-n-puff operations in shale gas wells, the daily gas production increased by 3.5 to 6.5 times, and the recovery rate increased by 1.9% to 3.1%. Based on pressure monitoring during the injection and soaking stages of two wells over three rounds of CO2 injection, CO2 mainly concentrated in the near-well micro-fractures. The diffusion distance, generally not exceeding 70 m, was related to formation pressure and the conductivity of fracture network. The process of CO2 huff-n-puff can be divided into three stages: early rapid CO2 flowback, early production increase, and mid- to late-stage stable production. The production increase mechanisms include early energy enhancement and supplementation, mid-stage expansion and expulsion assistance + water lock removal, and late-stage adsorption displacement + desorption promotion by partial pressure. The main influencing factors for increased huff-n-puff production are the degree of reservoir modification and recovery. Wells with poor fracturing effects in medium and deep layers had a higher gas exchange rate during the early and middle stages of CO2 huff-n-puff, while wells with high recovery rates in shallow layers had a higher cumulative gas increase in the middle and late stages. Based on numerical simulations, it is recommended to prioritize wells with strong adsorption capacity, a recovery rate of 20% to 30%, poor liquid carrying capacity, and a shut-in pressure as close to 7 MPa as possible for field pilot tests. In the low-pressure and low-yield stage, small-scale multiple rounds of CO2 huff-n-puff can be carried out in medium-deep wells for energy enhancement and expulsion assistance, while large-scale CO2 huff-n-puff can be conducted in shallow wells to replenish formation energy and achieve enhanced recovery through adsorption displacement.

国家科技重大专项“彭水地区常压页岩气勘探开发示范工程”(2016ZX05061)，中国石化“十条龙”重大科技攻关项目“南川复杂构造带页岩气勘探开发关键技术研究”(P19017-3)和中国石化科技部项目“渝东南地区浅层页岩气勘探开发关键技术”(P24115)联合资助。

https://doi.org/10.11781/sysydz2025020395