A multi-frequency electromagnetic pipe inspection tool with multiple transmitter and receiver arrays was designed to accurately estimate the individual wall thicknesses of as many as five nested pipes. The new tool enables monitoring well casing integrity without having to pull out production tubings, therefore minimizing inspection time and cost. This paper demonstrates the performance of the tool using yard mockups with known defects. The principle of tool operation and the methodology for data processing are also detailed in the paper.
The tool relies on eddy current principle in its operation. It comprises two sections of transmitting and receiving coil antennas and operates in continuous-wave mode at multiple frequencies. The configuration of strategic transmitter-receiver spacing and multi-frequency operation delivers a suitable range of information to evaluate individual pipes for the majority of well configurations. An advanced inversion-based data processing workflow is executed to estimate pipe parameters, including electrical conductivity and magnetic permeability, wall thickness, and eccentricity.
The proficiencies of the technology are confirmed by performing yard tests with two long test mockups. Each mockup has multiple combinations of overlapping and non-overlapping man-made defects distributed along sections consisting of three, four, and five nested pipes, which mimic typical corrosion progression. The measurement data from the mockups are validated against synthetic data generated from a 2D electromagnetic forward solver. Then, a procedure including pipe material property estimation, calibration, and inversion algorithms is performed to retrieve pipe thickness.
Results from the yard tests reveal that this tool is fully capable of detecting various kinds of corrosions concurrently across five strings of pipes, even on the outer pipes with high severity. The impact of pipe eccentricity on the accuracy of thickness estimation is also shown by deliberately decentralizing the innermost pipe over a length of the testing setup.
The information provided by this tool can improve the efficiency of well intervention operations, especially in areas with high-corrosion rates, and could result in significant cost savings to the operator.
