Yu Xu, Cheng Zhongwu, Hong Lei, Zhao Ning, Chen Aikun
Jiangsu Key Laboratory of Coal-Based Greenhouse Gas Control and Utilization, China University of Mining and Technology, 221008 Xuzhou, Jiangsu, China.
School of Safety Engineering, China University of Mining and Technology, 221116 Xuzhou, China.
ACS Omega. 2024 May 1;9(19):21440-21449. doi: 10.1021/acsomega.4c01799. eCollection 2024 May 14.
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.
脉冲水力压裂是一种环境友好型方法，可提高岩层渗透率以刺激天然气生产并降低灾害风险。它具有以较低破裂压力和较少水量压裂储层的优势，因为水力脉冲压力降低了岩石材料的机械强度。许多研究人员发现循环加载后硬岩有显著变化。然而，现有工作仍无法在短时间实验内清楚解释脉冲水力压裂对岩石损伤的机制。为解决该问题，已在实验室和现场应用中对脉冲水力压裂对煤层气生产的影响进行了研究。结果表明，长期水力脉冲压力会导致实验室直接测量的破裂压力呈线性下降。它通过为煤层气生产生成更多流动通道，在渗透率增强方面起着至关重要的作用。低场核磁共振定量评估了孔隙率的增加，这揭示了由疲劳损伤导致的煤的大孔、中孔和微孔孔隙率显著增加率超过20%。首次证明水力脉冲压力对大孔、中孔和微孔的孔隙率组分有显著影响。为验证该技术在现场规模的有效性，已在一座煤矿进行了脉冲水力压裂的现场应用。结果表明，施加脉冲载荷后，产气大幅增强，生产阶段长且稳定，气体通量更高。压裂钻孔的瓦斯浓度和瓦斯通量约为未压裂钻孔的2倍。这项工作对脉冲水力压裂对煤层气生产的影响进行了研究，有助于现场工程师更好地理解其机制。
