Corrosion Evaluation in Dual Completions Using a Multifrequency Electromagnetic Tool

Abstract

Early detection of corrosion in well casings is of great importance to oil and gas well management. A typical well completion includes a production tubing inside a number of nested casings, which provide necessary well integrity and environmental protections. A multifrequency electromagnetic pipe inspection tool with multiple transmitter and receiver arrays was designed to accurately estimate the individual wall thicknesses of up to five nested pipes. The tool uses an axis-symmetric forward model to invert for wall thicknesses, among other pipe parameters. However, in cases where production occurs from two or more segregated zones, the well is generally equipped with more than one production tubing, which breaks the axial symmetry. In this paper, we show how the tool can further be employed to inspect the integrity of non-nested tubulars, such as dual completions. The performance of the tool is demonstrated using a full-scale yard mockup with known defects. A data-processing workflow, including multizone calibration and model-based inversion, is proposed to estimate the tubulars electrical conductivity, magnetic permeability, wall thickness, and eccentricity. An in-situ, multizone calibration method is applied to remove adjacent tubings influence, thus enabling accurate estimation of the thickness of outer casings without having to pull out the production tubing. In order to demonstrate the capabilities of the tool in wells with dual completions, a log was run in a 150 ft-long yard mockup with two strings of 2⅞ inch. tubing, two outer casing strings, and four different man-made defects on the casings. The tool is logged inside each of the tubing strings, and the two logs are inverted for the thickness and eccentricity of the tubing as well as the thickness of outer casings. Results from the yard test reveal that when the tool is logged in one tubing, it can accurately detect various kinds of defects on outer casings, even in the presence of a second tubing. The interference from the second tubing is shown to be minimal due to the employed calibration algorithm. A high degree of consistency is seen between the logs run in each tubing string. This suggests that if the goal is solely to monitor corrosion in the outer casings, it suffices to run the tool in only one of the tubing strings, further cutting nonproductive time. The techniques presented here enable pipe integrity monitoring without pulling the production tubings; tubings, therefore, minimizing inspection time and cost. The information provided by this tool can significantly improve the efficiency of well intervention operations, especially in areas with high corrosion rates.