National Engineering Research Center of China United Coalbed Methane Corp., Ltd.
PetroChina Coalbed Methane Company Limited
CNPC Exploration Software Co., Ltd.
PetroChina Qinghai Oilfield Company
Chinese Petroleum Society

鄂尔多斯盆地东缘大宁−吉县区块深部煤层气资源丰度高，煤储层天然裂缝与煤自身割理裂隙发育、煤体结构好、机械强度高、顶底板封盖能力强，为大规模体积压裂缝网的形成提供了有利条件。超大规模压裂改造工艺使深部煤层气单井产量获得重大突破，但示踪剂监测结果显示，水平井各压裂段产气效果贡献不均一、资源动用存在盲区、综合效益未达预期。指出深部煤储层形成超大规模有效缝网面临两类主要挑战：(1) 深部煤层裂缝扩展规律认识不清；(2) 现有压裂技术存在过度改造及改造不充分区域。基于此问题，提出适合深部煤储层改造的多轮次转向缝网弥合压裂技术。首先，分析深部煤层超大规模缝网形成的可行性；其次结合现场压裂数据与微地震监测结果，分析地层曲率、倾角等对压裂裂缝扩展的影响；最后建立应力场计算方法，以此为依据，进行多轮次转向工艺优化及现场试验。在大宁−吉县区块现场进行试验验证，井周微应力场非均匀区域水力裂缝实现了较为均匀的扩展，增大了裂缝整体改造体积，单井产气效果较周边井有明显提升，其中DJ55井5轮次压裂，储层改造体积达到243.6×104 m3，生产340 d累产气量970.5×104 m3，平均日产气量2.85×104 m3，日产量和压力均保持稳定，改造效果较好，预计采收储量(EUR)大于3 000×104 m3，产气潜力较大；JS8-6P05井第1—7段采用2 ~ 3轮次压裂，压后日产气量8.59×104 m3，相比各段均采用单轮次压裂的JS8-6P04井加砂规模降低41.9%、压裂费用降低21%，但2口井水平段千米日产气量相当。试验效果表明，多轮次压裂工艺在一定程度上解决了水平井两侧应力差异而导致的裂缝单侧扩展问题，促进井筒两侧压裂裂缝趋于均匀扩展，极大程度上保障了深部煤储层资源动用程度和压后产量，是深部煤层气压裂工艺降本增效的主要技术途径。

The Daning-Jixian block on the eastern margin of the Ordos Basin exhibits high-abundance deep coalbed methane (CBM) resources, well-developed natural fractures of coal reservoirs, well-developed cleats and fractures in coals themselves, coals with excellent structures and high mechanical strength, and strong sealing ability of coal roofs and floors. All these create favorable conditions for the formation of a large-scale fracture network through volume fracturing. The ultra-large-scale fracturing process has contributed to a major breakthrough in the single-well output of deep CBM. However, the tracer monitoring results show that various fracturing stages of horizontal wells exhibited different contribution rates to gas production, there exhibited blind zones of resource production, and expected comprehensive benefits were not achieved. This study proposed two major challenges posed to the formation of ultra-large-scale effective fracture networks in deep coal reservoirs: (1) unclear understanding of fracture propagation patterns in deep coal seams and (2) the presence of areas subjected to over and insufficient stimulation using current fracturing technologies. Given these challenges, this study developed a multi-round diverting fracturing technology to form a merged fracture network for the stimulation of deep coal reservoirs. This technology involved: (1) analyzing the feasibility of the formation of a super-large fracture network of deep coal seams. (2) determining the effects of microstructures, such as the curvatures and dip angles of strata, on fracture propagation based on the field fracturing data and microseismic monitoring results. (3) Establishing a stress field calculation method, which laid the foundation for the process optimization and field experiments of multi-round fracturing diverting. This technology was verified through field experiments in the Daning-Jixian block. The results revealed the uniform propagation of hydraulic fractures in areas with nonuniform micro-stress fields around wells. This uniform propagation increased the overall fractured volume, with single-well gas production in the experiment area significantly improving compared to surrounding wells. Well DJ55, experiencing five rounds of fracturing, exhibited a stimulated reservoir volume of up to 243.6×104 m3, 340-day cumulative gas production of 970.5×104 m3, and an average daily gas production of 2.85×104 m3, with daily gas production and pressure remaining stable. These results indicate excellent stimulation results. With an estimated ultimate recovery greater than 3000×104 m3, this well had great potential for gas production. Well JS8-6P05 in the block yielded a daily gas production of 8.59×104 m3 after 2‒3 rounds of fracturing at fracturing stages 1‒7. Compared to well JS8-6P04, which employed single-round fracturing at each fracturing stage, well JS8-6P05 witnessed reductions in the proppant volume and fracturing cost by 21% and 41.9%, respectively. However, the horizontal sections of both wells produced comparable daily gas production. The experimental results indicate that the multi-round diverting fracturing technology, partially solving the problem that fractures propagate on one side of a horizontal well due to the stress differences on both sides, promotes the uniform propagation of induced fractures on both sides of a wellbore and thus ensures a high production degree and post-fracturing production of deep coal reservoirs. This technology serves as a main technical method for reducing the costs and increasing the efficiency of fracturing technology for deep CBM.

国家科技重大专项项目(2016ZX05042)；中国石油天然气股份有限公司攻关性应用性技术攻关项目(2023ZZ18)；中国石油天然气股份有限公司科技专项“非常规储层改造关键技术研究”项目

熊先钺，甄怀宾，李曙光，等. 大宁–吉县区块深部煤层气多轮次转向压裂技术及应用[J]. 煤田地质与勘探，2024，52(2)：147−160.

XIONG Xianyue，ZHEN Huaibin，LI Shuguang，et al. Multi-round diverting fracturing technology and its application in deep coalbed methane in the Daning-Jixian block[J]. Coal Geology & Exploration，2024，52(2)：147−160.