Monitoring the integrity of well casings is vital for oil and gas well management, which can help maintain production levels, reduce maintenance cost, and protect surrounding environment. An electromagnetic pipe inspection tool with multiple transmitter and receiver arrays operating at multiples frequencies was designed to accurately estimate the individual wall thicknesses of up to five nested pipes. Data acquired from this tool was originally processed based on an axis-symmetric forward model to invert for wall thicknesses of individual pipes. Such processing workflow is only applicable to a typical well completion with a single production tubing inside multiple nested casings. However, in a scenario with dual completions, two production tubings are generally installed to produce from more than one production zone. The presence of more than one tubing breaks the axial-symmetry of the completion structure. In this paper, we propose a new workflow to process data from electromagnetic tools for the application of integrity inspection of non-nested tubulars. A yard test with full-scale mockup demonstrates the performance of the tool.
The proposed workflow, including data calibration and model-based inversion, can estimate the magnetic permeability and electrical conductivity of the pipes, along with wall thicknesses, and eccentricity of the tubings with respect to the innermost casing. An in-situ calibration method is applied to mitigate interference from one tubing when the tool is logged inside the other tubing. Model-based inversion enables an accurate estimation of the thickness of outer casings along with the eccentricity of the tubings. In addition, a two-dimensional inversion algorithm is shown to provide more accurate assessment of small corrosion spots.
In the yard test, a 150 ft-long mockup includes two strings of 2⅞-in. tubings and two outer casings with four machined defects with different sizes. Logging inside each of the tubing strings was performed, and the two logs are processed to obtain the thicknesses of the tubings, outer casings as well as the eccentricity of the tubings.
The inversion results reveal that the tool can accurately detect various kinds of defects on outer casings from one single log, even in the presence of a second tubing. The measurements show that the interference from the adjacent tubing is minimal and its impact on the inversion result can be well mitigated by employing the in-situ calibration. The consistent results from two logs run in each tubing string suggests that it is sufficient to run the tool in only one of the tubing strings, if the goal is solely to inspect corrosion in the outer casings.
The techniques presented enable pipe integrity monitoring with a single run inside any one of the tubings and without pulling out any pipes. The data processing workflow based on two-dimensional inversion yields more accurate estimation, which provides critical information to significantly improve the efficiency of well intervention operations, therefore minimizing non-productive time and cost.