Numerical simulation of transient electromagnetic over casing wells with compensating coils

Area of Science:

• Geophysics
• Petroleum Engineering

Background:

• Accurate resistivity measurement is crucial for residual oil saturation assessment in oil and gas fields.
• Traditional over-casing resistivity logging faces limitations like low efficiency, casing resistance interference, and poor environmental adaptability.

Purpose of the Study:

• To develop an improved transient electromagnetic (EM) method for accurate formation resistivity measurement in cased wells.
• To overcome the interference caused by casing's electrical and magnetic conductivity on EM signals.

Main Methods:

• A novel method using multiple coil systems for casing signal pre-compression was proposed.
• Finite element simulation was employed to analyze transient EM response curves, radial probing depths, and longitudinal resolutions.
• The study investigated the impact of varying formation resistivities and casing parameters.

Main Results:

• The proposed technique effectively suppresses casing response in the pre-transient EM signal.
• Formation responses become clearer, enabling more accurate resistivity measurements.
• The method demonstrates potential for enhanced residual oil evaluation in oil exploration and development.

Conclusions:

• The new transient EM method provides an accurate and reliable approach for formation resistivity measurement in cased wells.
• This advancement significantly enhances the accuracy of residual oil saturation evaluation.
• The technique offers a valuable tool for optimizing oil exploration and development strategies.