Response Mechanism of Multi-scale Electrical Logging in Fractured Formations

Fracture parameters play a crucial role in productivity prediction, reservoir evaluation and fracturing production of buried-hill reservoirs and carbonate reservoirs. The main method for calculating fracture parameters is electrical logging based on rock-electric experiments. However, due to significant differences in observation systems between rock-electrical experiments and various electrical logging methods, directly calibrating electrical logging data with cores in different fractured formations will lead to large errors. Based on the finite element method calibrated with core samples, we established micro-fractured formation models and conducted fracture parameter simulation experiments for plunger core samples, full-diameter core samples, electrical imaging logging, micro-spherical focusing logging, shallow lateral logging, and deep lateral logging, respectively, aiming at the influence of multiple fracture parameters. A comparison of the measurement results of the six models for the same fractured formation showed that the fracture-induced resistivity reduction rates were ranked in descending order as follows: electrical imaging logging, plunger core testing, micro-spherical focusing logging, full-diameter core testing, shallow lateral logging, and deep lateral logging, with the maximum discrepancy in resistivity reduction rates across these models reaching a factor of 45. Specifically, the resistivity reduction rate of plunger cores was 2.7 times higher than that of full-diameter cores, and the rate of electrical imaging logging was 11.8 times higher than that of micro-spherical focusing logging, whereas the values for shallow lateral logging and deep lateral logging were identical. Finally, this study proposed a correction rate required for fracture core calibration, which could comprehensively optimize the interpretation range of various resistivity logging methods and effectively improve the interpretation accuracy of reservoirs.