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Collaborating Authors
Zang, Defu
Signal processing methods for crosswell electromagnetic imaging system
Zang, Defu (GEO-MWD/LWD & Logging Research Institute of SINOPEC MATRIX Corporation) | Ji, Yongli (China Research Institute of Radio Wave Propagation) | Chao, Yongsheng (GEO-MWD/LWD & Logging Research Institute of SINOPEC MATRIX Corporation) | Li, Zhiqiang (China Research Institute of Radio Wave Propagation)
Abstract The principle of crosswell electromagnetic (EM) imaging is similar to that of induction logging. The difference between them is that conventional induction logging can only measure the formation conductivity within a few meters around the well. However, crosswell EM imaging can be used in two wells with a separation distance of up to 1000 m. Several novel signal processing methods for crosswell EM imaging systems are developed for calibration, casing correction, and hybrid Jacobian matrix calculation. To conveniently perform calibration on the ground, the EM field formula in a vertical layered media is derived based on Maxwell equations, and the relationships between the received signal and frequency, formation conductivity, and transceiver spacing are subsequently derived. Furthermore, a new calibration method is developed. The EM field formula for a radial layered media is derived, and the analytical expressions describing the relationship between the receiving signal and borehole parameters, metal casing parameters, formation parameters, and receiver location are obtained. The effects of mud resistivity, metal casing position, metal casing resistivity, permeability, cement ring resistivity, transmitting frequency, and receiver location on the crosswell EM receiving signal are simulated. It is determined that only the casing required a correction. The influence of the metal casing is corrected by establishing a database. The difference between the corrected data and data obtained without a metal casing is less than 1%. There is a large error in the calculation of the Jacobian matrix in some regions when Green’s function was used. A hybrid Jacobian matrix calculation method combining local perturbation and a global Green’s function is developed, which significantly reduced the error and improved the inversion accuracy.
- Asia > China (0.70)
- Africa > South Africa > Western Cape Province > Indian Ocean (0.44)
- Asia > China > Shandong > North China Basin > Shengli Field (0.99)
- Africa > South Africa > Western Cape Province > Indian Ocean > Bredasdorp Basin > Block 9 > EM Field (0.99)
Through-Casing Formation Conductivity Measurement Based on Transient Electromagnetic Logging Data
Sheng, Xiaofei (Tianjin University) | Shen, Jianguo (Tianjin University) | Shen, Yongjin (Beijing Huahui Shengshi Energy Technology) | Zhu, Liufang (Logging Company of Shengli Petroleum Engineering Co.) | Zang, Defu (Logging Company of Shengli Petroleum Engineering Co.)
Transient electromagnetic (TEM) logging is a promising noncontact method for through-casing formation conductivity measurements. We studied the through-casing TEM logging method based on the processing of TEM logging data measured in a production well. Similar to Doll's work in borehole induction logging, we presented the expressions of the ‘useful signal’ and the ‘useless signal’ in casedhole logging based on which, the methods of removing the ‘useless signal’ and obtaining the formation conductivity curve are introduced. We analyzed the influence of the casing on the TEM signals, described the characteristics of TEM response signals, and obtained the ‘useful signal’ carrying formation conductivity data. Casedhole formation conductivity curves, which are subsequently compared with the known openhole conductivity log, are obtained by dealing with the ‘useful signal’. We identified the characteristics of casedhole formation conductivity curves, and some problems that need to be considered in their practical application. Due to the influence of the casing, the radial detection depth of the TEM logging tool in a cased hole is small, so the detection result is mainly the equivalent conductivity of the cement ring and formation near the outer casing wall. Although the casedhole conductivity curves are in good agreement with openhole logging results in regular formations, due to the influence of the casing and the changes in the physical environment in the well, complete consistency is unrealistic for these two kinds of curves in all well intervals. Therefore, a thorough analysis is required before practical application. Moreover, the effects of well temperature and casing deformation must be corrected for accordingly.