The paper described novel methods, including calibration, casing correction and inversion.

What is it about?

Several novel signal processing methods for crosswell EM imaging systems are proposed 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, anew calibration method is proposed. 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 was determined that only the casing required a correction. The influence of the metal casing was corrected by establishing a database. The difference between the corrected data and data obtained without a metal casing was less than 1%. There was 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 proposed, which significantly reduced the error and improved the inversion accuracy.

Featured Image

Photo by WORKSITE Ltd. on Unsplash

Photo by WORKSITE Ltd. on Unsplash

Why is it important?

Crosswell EM imaging can be utilized in two wells with a separation distance of up to 1000m. As an important method of contemporary geophysical exploration, crosswell EM imaging has excellent application prospects in improving the exploration process of oil and gas reservoirs. We proposed three methods to address the associated data processing to quickly achieve an accurate description of oil distribution between cased wells separated by distances in the range of 500m to 1000m within a relatively acceptable time.