A novel apparatus and method for lab-scale study of wellbore integrity using CT imaging and analysis

Abstract

Well drilling, completions, stimulation, and enhanced oil recovery operations induce downhole conditions that may negatively impact the integrity of the annular seal and consequently hinder zonal isolation. Thus, the ability to accurately quantify the evolution of the annular seal in response to the prevailing downhole environment is critical for the optimal design of the annular barrier for the life of a well. Thanks to increased accessibility and recent advancements in computing power and techniques, X-ray computed tomography has gained popularity as a non-destructive analysis method in materials science and geomechanics due to its ability to reveal details about the interior volume of objects in real-time without physical disassembly.Therefore, in this study, a novel apparatus is presented for the construction of a lab-scale wellbore, with the purpose of simulating downhole processes while simultaneously monitoring wellbore elements of interest in real-time via x-ray computed tomography. The benefits of this novel setup for wellbore integrity are demonstrated via applications to two test cases: the mechanical evolution of annular cement under stresses induced by cyclic water injection as a function of the mechanical properties of the cased and cemented wellbore system; the evaluation of nano magnesium oxide performance as an additive for autogenous shrinkage mitigation in annular cement.The results of the studies presented illustrate the benefits of combining x-ray computed tomography with lab-scale wellbore process simulations. The results of the cyclic water injection study suggest that residual strain in the cement is the major factor in annular seal degradation under cyclic downhole pressure fluctuations. Nano magnesium oxide is also shown to be very effective in preventing autogenous shrinkage of Class H cement. However, more study is required to characterize its effectiveness in a wider range of cement formulations. Finally, suggestions are offered on how to improve the experimental procedure presented while future potential applications of the apparatus are discussed.