Analysis of electromagnetic response characteristics of hydraulic fracturing based on charging conductor model
LI Diquan1,2,3, LI Fu1,2,3, ZHANG Qiaoxun1,2,3, HUANG Ya4, BIE Yongjie4, HU Yanfang1,2,3
1. Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring, Ministry of Education, Central South University, Changsha, Hunan 410083, China; 2. Key Laboratory of Non-Ferrous and Geological Hazard Detection, Changsha, Hunan 410083, China; 3. School of Geosciences and Info-Physics, Central South University, Changsha, Hunan 410083, China; 4. Hunan Geosun Hi-technology Co., Ltd., Changsha, Hunan 410208, China
Abstract：With the vigorous development of unconventional and ultra-low permeability oil and gas resources in China， fracturing monitoring technology has ushered in a major development opportunity. The electromagnetic method has the advantages of low cost， high timeliness， and large exploration depth in geophysical exploration. However， in the face of large-depth fracturing environments， the feasibility of electromagnetic fracturing monitoring technology needs to be demonstrated urgently. Based on the theory of charged conductor and electric dipole source diffused electromagnetic field， this paper firstly constructs fracturing models with different fracture depths and lengths and calculates the electromagnetic response characteristics of the total ground field and anomalous field under different models. The calculation results show that when the borehole electromagnetic method is used for fracturing monitoring， the observed total field is not sensitive to the electromagnetic response caused by fracture length increase， and the abnormal field has a low value zone. When the depth is 4000 m， the electromagnetic anomaly is less than 1%. Larger depth indicates more serious attenuation of the abnormal field. Moreover， the absolute value of the abnormal field at adjacent measuring points is negatively correlated with the depth， and the electromagnetic fracturing monitoring technology is difficult to balance detection accuracy and detection depth. Then， through the physical model of fracturing monitoring， the characteristics of the electromagnetic anomaly curve of the measured data are analyzed， and the results verify the correctness of the theoretical calculation. Finally， a network-type electromagnetic fracturing monitoring and observing system with excitation in the well and reception on the ground is proposed by combining the theoretical achievements and practical experiences of the previous researchers， which imposes certain constraints on the range of the measurement area and the spacing of the measurement points. The system has the advantages of efficient field operation and large monitoring depth， which provides a new development direction for electromagnetic fracturing monitoring.
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