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鸡西盆地深部煤系气CO2前置增能压裂实践与认识

Practice and insights on CO2 pre-enhanced fracturing in deep coal measure gas reservoirs of Jixi Basin

  • 摘要: 针对鸡西盆地深部煤系气储层渗透率低(0.006×10−15~0.066×10−15 m2)、破裂压力高(最高达52.8 MPa)、裂缝扩展难等问题,基于黑鸡地2井工程实践,创新提出CO2前置增能压裂技术体系。该技术通过液态CO2的低温效应与化学增溶作用,显著降低煤基质破裂压力,激活天然裂缝网络,形成多尺度复杂缝网结构;结合CO2超临界态吸附置换机理,增强煤层气解吸效率,并通过相态转变产生的体积膨胀效应提升储层能量,实现压裂液高效返排。技术实施采用“液态CO2增能造缝+活性水携砂导流”组合工艺,分层注入液态CO2 101.4~113.3 t/层,配合投球分压(50~52个暂堵球)与多粒径石英砂组合支撑,构建“近井高导流+远场全支撑”裂缝系统。微地震监测表明,压裂形成了东西和北东向复杂缝网,单层缝长400~431 m,缝高75~110 m,缝网宽度为168~173 m,C14+C13煤组与C16煤组累计产气量为156 131 m3,最高日产气量为1 145 m3。实践成果证实,CO2前置增能压裂通过“物理破岩−化学增渗−能量驱动”多机制协同,突破了深部煤系储层(埋深>2 000 m)低渗改造瓶颈,为鸡西盆地煤系气资源高效开发提供了理论与技术支撑。

     

    Abstract: In response to challenges such as low permeability (0.006×10−15−0.066×10−15 m2), high breakdown pressures (up to 52.8 MPa), and difficult in fracture propagation in deep coalbed methane reservoirs of Jixi Basin, a novel CO2 pre-enhanced fracturing technology is innovatively proposed based on engineering practices from Well Heijidi-2. This technology utilizes the cryogenic effect and chemical dissolution enhancement of liquefied CO2 to significantly reduce the breakdown pressures of coal matrices, reactivate natural fracture networks, and create multi-scale complex fracture networks. Furthermore, utilizing the adsorption-displacement mechanism of supercritical CO2, it enhances coalbed methane desorption efficiency. The volumetric expansion during phase transition also boosts reservoir energy, achieving highly efficient fracturing fluid flowback. The implementation employs a combined process of “liquefied CO2-enhanced fracturing + active water proppant transport for fracture conductivity”. This involves staged injection of 101.4−113.3 tons of liquefied CO2 per target layer, integrated with ball-sealing staged fracturing (using 50−52 temporary diverting balls) and multi-size quartz sand proppant placement. This methodology constructs a fracture system characterized by “high-conductivity near-wellbore fractures and fully-supported far-field fractures”. Microseismic monitoring revealed that the generated complex fracture networks were oriented east-west and northeast. Individual layers exhibited fracture lengths of 400−431 m, heights of 75−110 m, and network widths of 168−173 m. The cumulative gas production from coal groups C14+C13 and C16 reached 156 131 m3, with a peak daily gas output of 1 145 m3. Field results demonstrate that CO2 pre-enhanced fracturing overcomes the bottleneck in low-permeability and deep coalbed methane reservoirs (>2 000 m depth) through synergistic mechanisms of “physical breaking-chemical permeability enhancement-energy driven”. This provides both theoretical and technical foundations for efficient coalbed methane development in the Jixi Basin.

     

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