Pulsating hydraulic fracturing has been an environmentally friendly method to improve the permeability of rock formations to stimulate gas production and reduce hazard risks. It has the advantage of fracturing the reservoir with lower cracking pressure and less water volume, as the mechanical strength of rock materials has been reduced by the hydraulic pulse pressure. Many researchers have found significant changes in hard rocks after cyclic loading. However, the existing work still cannot clearly explain the mechanism of the rock damage by pulsating hydraulic fracturing within a short-time experiment. To solve the issue, an investigation of the effects of pulsating hydraulic fracturing on CBM production has been carried out in lab and field applications. Results indicate that the long-term hydraulic pulse pressure can cause a linear decline in cracking pressure directly measured in the lab. It plays an essential role in the permeability enhancement by generating more flow channels for CBM production. The low-field NMR quantitatively evaluates the increase in porosity, which reveals significant incremental ratios of over 20% in the porosity of macropores, mesopores, and micropores of coal caused by fatigue damage. It is first proven that hydraulic pulse pressure has a significant influence on the porosity components of macropores, mesopores, and micropores. To validate the effectiveness of the technique on the field scale, a field application of pulsating hydraulic fracturing has been carried out in a coal mine. It shows that gas production has been largely enhanced with a long and stable production stage and higher gas flux after the applied pulsating load. The gas concentration and gas flux of the fractured boreholes are about 2 times that of the nonfractured boreholes. This work provides an investigation of the effects of pulsating hydraulic fracturing on CBM production, which gives a better understanding of the mechanism for the engineers in the field.

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基于NMR和AE谱预测脉动水力压裂对煤孔隙结构和渗透率的影响

脉动水力压裂是一种环境友好的方法，可提高岩层的渗透性，从而刺激天然气生产并降低灾害风险。由于水力脉冲压力降低了岩石材料的机械强度，因此具有以较低的破裂压力和较少的水量对储层进行压裂的优点。许多研究人员发现硬岩在循环加载后发生了显着变化。然而，现有的工作仍然无法在短时间内清楚地解释脉动水力压裂对岩石的损伤机制。为了解决这个问题，我们在实验室和现场应用中研究了脉动水力压裂对煤层气生产的影响。结果表明，长期的液压脉冲压力会导致实验室直接测量的开启压力线性下降。它通过为煤层气生产提供更多的流动通道，在提高渗透率方面发挥着重要作用。低场核磁共振定量评价了孔隙率的增加情况，发现疲劳损伤引起的煤大孔、中孔、微孔孔隙率显着增加，增幅均超过20%。首次证明水力脉冲压力对大孔、中孔和微孔的孔隙率成分具有显着影响。为了验证该技术在现场规模的有效性，在煤矿进行了脉动水力压裂的现场应用。结果表明，施加脉动负荷后，产气量大幅提高，产气阶段较长且稳定，产气通量较高。压裂钻孔瓦斯浓度和瓦斯通量约为非压裂钻孔的2倍。这项工作研究了脉动水力压裂对煤层气生产的影响，使现场工程师更好地了解其机理。