氧煤吐气:煤层气藏氧化溶蚀减量增渗方法及前景

Oxidative stimulation on CBM reservoir recovery enhancement:methods for oxidative dissolution, permeability enhancement, and prospects

  • 摘要: 单井产量低是制约我国煤层气经济开发的重大难题。为此,考虑煤中有机质与黄铁矿易被氧化溶蚀的特征,基于“物质净移除−减量增渗”的技术思想,利用强氧化剂的氧化作用使固相溶蚀转变为多尺度传质空间,提出了煤层气藏氧化溶蚀减量增渗技术设想,构建了煤层气藏氧化溶蚀减量增渗方法框架,并分析了该方法在提高煤层气井采收率方面的前景。结果表明:基于氧化液对煤岩的差异性溶蚀作用,在水力压裂形成的支撑诱导裂缝基础上形成溶蚀孔缝,并促使裂缝扩展延伸,形成具有高导流能力的氧化溶蚀协同水力压裂裂缝体,以此协调煤层气开发工程作业技术目前存在的三大矛盾,可以实现煤层气井的经济生产。该方法目前最佳应用条件是镜质组体积分数大于60%、超低含水饱和度、临储比小于0.57的低效井。氧化溶蚀协同水力压裂施工方案整体思路为“先造缝、再溶蚀、后提产”,压裂施工原则:水力压裂先行造缝;氧化溶蚀溶孔扩缝;适当焖井沟通缝网;合理排采保稳产。煤层气井氧化溶蚀协同水力压裂提产评价结果表明,氧化溶蚀可以缩短气井见气时间,使煤层气井更早进入产气高峰,增加煤层气井产量。该方法为煤层气藏增渗提产及储层保护提供了另一种选择,对未来煤层气的经济开发具有重要的借鉴意义。

     

    Abstract: The low single-well production is a major challenge restricting the economic development of Coalbed Methane (CBM) reservoirs in China. To address this, considering the characteristics of organic matter in coal and pyrite are easy to be oxidative dissolved, a concept based on “net material removal-matter reduction and permeability enhancement” is proposed. This concept utilizes the oxidation effect of strong oxidants to transform solid-phase dissolution into a multi-scale mass transfer space. The technical idea of oxidative dissolution of coal on permeability and production enhancement technology for CBM reservoirs is presented, along with a workflow for the technical idea. The paper also analyzes the potential of this technical idea to enhance recovery of CBM reservoirs. The results indicate that considering the selective dissolution effect of oxidation solution on coal, the dissolution pore fracture was formed based on the induced fracture formed by hydraulic fracturing, and the fractures are extended to form the oxidative dissolution coordinated hydraulic fracturing fracture system with high conductivity. This helps resolve the three major issues currently facing CBM development engineering, achieving the goal of economically development of CBM wells. The best application conditions for this technical idea are CBM reservoirs with more than 60% vitrinite volume fraction, ultra-low water saturation, and a storage ratio of less than 0.57 for low-efficiency wells. The overall strategy for the combined oxidative dissolution and hydraulic fracturing construction scheme is “first create fractures, then dissolve, and finally increase production.” The principle of hydraulic fracturing synergistic with oxidative dissolution has been formulated: Hydraulic fracturing should be done first to create fractures; Oxidative dissolution and pore/fracture propagation; Properly controlling the shut-in time to promote fracture network communication; Reasonable drainage gas to stable production. The evaluation results of the potential for enhanced production of CBM wells through oxidation treatment indicated that treated CBM well entered the peak gas production earlier, enhancing the production of CBM well, which further verified the possibility of realizing the technical idea of oxidation treatment on permeability enhancement of CBM reservoir. A methodological framework for oxidation treatment aimed at permeability enhancement in CBM reservoirs is established, providing an important reference for the efficient development and utilization of CBM reservoirs.

     

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