State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing, 400044, China.
College of Resources and Environmental Science, Chongqing University, Chongqing, 400044, China.
Environ Sci Pollut Res Int. 2019 Apr;26(11):11458-11469. doi: 10.1007/s11356-019-04539-x. Epub 2019 Feb 26.
The effective area of hydraulic fracturing is the core index to evaluate its effects. Through conducting transient electromagnetic tests, this paper deals with the influential range of the underground hydraulic fracturing as well as water-cut detection and gas extraction in the fracturing area. The resistivity response law of the coal seam in hydraulic fracturing process is explored, and the water-bearing area is determined. The obtained results from the tests show that the water-cut areas of the coal seam, measured by anti-interference transient electromagnetic instrument after fracturing, are commonly placed in the low-resistance area of the transient test. Further, the variations of amplitude of the low-resistance area in various directions of the test line are different. According to the variation law of the apparent resistivity of the coal seam before and after fracturing, the effective influential area of the hydraulic fracturing is defined, and the influence range is evaluated to be 35 m. The water cut and the gas extraction tests of the coal seam before and after fracturing are performed. The results reveal that the growth of water content in the coal seam is inversely proportional to the distance from the hydraulic fracturing borehole. The effective fracturing zone with the increment of the water content reaching 0.2% is the effective fracturing zone, and the effective fracturing zone of #9 and #10 is 38 m. After hydraulic fracturing, the gas extraction concentration would be in the range of 25.4-75.4%, with the average of 70.22%, which is 21.22% higher than that of the original coal body. The net amount of the gas extraction after fracturing is about eight times of that before fracturing. The effective fracturing range, which is determined by transient electromagnetic, is verified successfully. Exploring the effective fracturing regions of the hydraulic fracturing process would be very helpful in improving the evaluation system of the hydraulic fracturing effect.
水力压裂的有效区域是评估其效果的核心指标。通过进行瞬变电磁测试，本文研究了地下水力压裂的影响范围以及压裂区域的水含量检测和瓦斯抽采。探讨了水力压裂过程中煤层的电阻率响应规律，确定了含水区。测试结果表明，压裂后采用抗干扰瞬变电磁仪测量的煤层水含量区域通常位于瞬变测试的低阻区。此外，测试线上各个方向低阻区的幅度变化不同。根据压裂前后煤层视电阻率的变化规律，定义了水力压裂的有效影响区域，并对影响范围进行了评价，结果为 35m。对压裂前后的煤层进行了水含量和瓦斯抽采测试。结果表明，煤层中水分含量的增加与距水力压裂孔的距离成反比。水分含量增加 0.2%的有效压裂带是有效压裂带，#9 和 #10 的有效压裂带为 38m。水力压裂后，瓦斯抽采浓度范围在 25.4%-75.4%之间，平均为 70.22%，比原始煤体高 21.22%。压裂后的瓦斯抽采量约为压裂前的 8 倍。瞬变电磁确定的有效压裂范围得到了验证。探索水力压裂过程中的有效压裂区域将有助于完善水力压裂效果的评价体系。
