Extending the Capability of Electromagnetic Corrosion Inspection Beyond Five Tubulars

Abstract

Well completions typically consist of multiple nested tubulars that provide the necessary well structure to ensure integrity for production and to protect the aquifers from contaminants. Monitoring the condition of multiple strings of tubulars is crucial in oil and gas wells and environmental management. For wells that had to drill through multiple pressure regimes, or with geomechanical and geology challenges, or those in highly corrosive environments, the number of well casings may exceed five pipes to provide better protection. Surveillance of pipe integrity in such wells is extremely challenging. A multifrequency electromagnetic pipe inspection tool with multiple transmitter and receiver arrays was designed to accurately estimate the individual wall thicknesses of multiple tubulars. In this paper, we present a workflow to process the measurements and demonstrate the performance of this tool to inspect the integrity of more than five nested pipes. The tool is based on electromagnetic eddy current principle and comprises multiple transmitting and receiving coil antennas with different spacings and operates in continuous-wave mode at multiple frequencies. To increase sensitivity to outer pipes, receiver coils are placed at larger spacings from the transmitter, and low frequency excitation is used. Feasibility studies show that the measurements are sensitive to the outer pipes beyond the fifth pipe, suggesting the possibility to inspect all nested pipes in one single logging run. An advanced data processing workflow including multi-zone calibration and model-based inversion is executed to estimate the tubulars electrical conductivity and magnetic permeability, wall thickness, and eccentricity. In the process of inversion, a regularization term is added to the cost function to obtain a more accurate solution based on the corrosion profile on the pipes as inferred from the data. The capabilities of the tool in wells with more than five pipes are demonstrated using synthetic data. The tests demonstrated accurate estimation of the location and severity of corrosion in each one of a multiple pipe configuration. This also reveals that the tool can detect various kinds of corrosion in wells with up to seven concurrent strings of pipes. This is the first time a corrosion inspection tool is shown to have the capability of estimating the individual thicknesses of well completions with more than five pipes. Such capability eliminates the necessity to pull the tubing and provides a complete picture on the integrity of the well casings. The information provided by this tool can significantly minimize inspection time and cost and improve the overall efficiency of well intervention operations.