Evaluation of Casing - Cement Debonding: Correlation Between Acoustic Logging, X-Ray Imaging and Leakage Rate

Abstract

Abstract Annulus barrier materials are an essential component of Oil & Gas wells to prevent fluid migration across geological layers. When a well is prepared to be plugged, evaluation of the integrity of the barrier is essential to decide whether the annulus materials can be left as such, or must be repaired or replaced. To support quantitative evaluation of the cement annulus, we have designed a laboratory-scale experimental setup, where we evaluate casing-cement debonding by acoustic logging, X-ray imaging and flow experiments. The main novelty of this experimental setup is that it allows for cement-casing evaluation with three different techniques. (1) We use Pulse-Echo ultrasonic logging tool. (2) We use an X-ray Computed tomography scanner to obtain images of the cement with a resolution of 30 or 12 μm. (3) We measure the gas permeability of the samples. Gas-permeability measurements evaluate the risk of leakage across the cement sample, it provides an estimation of the average thickness of debonding (microannulus). However, the debonding may not be uniform at the surface of the casing. Acoustic logging measurement and X-ray images are used to obtain insights on the morphology of the microannulus. In addition to these three evaluation techniques, the setup allows for the application of thermal loads in the casing by circulation cold or hot fluid. In this paper, we present the setup and give examples of results for all three measurements techniques. First, we show the observations in the reference state, i.e., before temperature loading. Then, we perform temperature cycling from room temperature to −20°C, and we measure how the casing-cement interface is affected by thermal loading. The goal of this setup is to provide experimental data about the geometry of microannulus formed by thermal cycling. The results can be used as input for models to predict leakage in full-scale wells. In addition, this work will support an improved interpretation of acoustic logging tools for quantitative evaluation of casing-cement debonding.