Qi Yufei, Tian Lin, Cao Yunxing, Wu Jinghao, Zhang Junsheng, Cao Yongxing, Cui Baoku
Institute of Resources & Environment, Henan Polytechnic University, Jiaozuo 454000, People's Republic of China.
Gas Geology and Engineering Research Center, Henan Polytechnic University, Jiaozuo 454000, People's Republic of China.
ACS Omega. 2023 Feb 9;8(7):6584-6596. doi: 10.1021/acsomega.2c07001. eCollection 2023 Feb 21.
The geological conditions of coal reservoirs in China are complex, and the reservoir permeability is generally lower. Multifracturing is an effective method of improving reservoir permeability and coalbed methane (CBM) production. In this study, two types of dynamic loads, CO blasting and a pulse fracturing gun (PF-GUN), were used to conduct multifracturing engineering tests in nine surface CBM wells in the Lu'an mining area in the central and eastern parts of the Qinshui Basin. The curves of pressure versus time of the two dynamic loads were obtained in the laboratory. The prepeak pressurization time of the PF-GUN was 200 ms, and that of the CO blasting was 2.05 ms, which just falls in the optimum pressurization time of multifracturing. The microseismic monitoring results revealed that, in terms of the fracture morphology, both the CO blasting and PF-GUN loads produced multiple sets of fractures in the near-well zone. In the six wells used for the CO blasting tests, an average of three branch fractures were produced outside of the main fracture, and the average angle between the main fracture and the branch fractures exceeded 60°. In the three wells stimulated by PF-GUN, an average of two branch fractures were produced outside of the main fracture, and the average angle between the main fracture and the branch fractures was 25-35°. The multifracture characteristics of the fractures formed via CO blasting were more obvious. However, a coal seam is a multifracture reservoir with a large filtration coefficient; the fracture will not extend after reaching the maximum scale under a certain gas displacement condition. Compared with the traditional hydraulic fracturing technique, the nine wells used in the multifracturing tests exhibited an obvious stimulation effect with an average increase of 51.4% in daily production. The results of this study provide an important technical reference for the efficient development of CBM in low- and ultralow-permeability reservoirs.
中国煤层气储层地质条件复杂，储层渗透率普遍较低。多缝压裂是提高储层渗透率和煤层气产量的有效方法。本研究采用CO爆破和脉冲压裂枪（PF-GUN）两种动载，在沁水盆地中东部潞安矿区的9口地面煤层气井中进行多缝压裂工程试验。在实验室获得了两种动载的压力-时间曲线。PF-GUN的峰值前增压时间为200ms，CO爆破的峰值前增压时间为2.05ms，均落在多缝压裂的最佳增压时间范围内。微地震监测结果表明，从裂缝形态来看，CO爆破和PF-GUN载荷均在近井地带产生了多组裂缝。在用于CO爆破试验的6口井中，主裂缝外平均产生3条分支裂缝，主裂缝与分支裂缝的平均夹角超过60°。在PF-GUN增产的3口井中，主裂缝外平均产生2条分支裂缝，主裂缝与分支裂缝的平均夹角为25°-35°。CO爆破形成的裂缝多缝特征更明显。然而，煤层是一个滤失系数大的多裂缝储层，在一定的气体驱替条件下，裂缝达到最大规模后将不再延伸。与传统水力压裂技术相比，多缝压裂试验的9口井增产效果明显，日产量平均提高51.4%。本研究结果为低渗透和特低渗透储层煤层气的高效开发提供了重要的技术参考。
