Studying the Impact of Thermal Cycling on Wellbore Integrity during CO₂ Injection

Abstract:

Injection of supercritical CO₂ into storage reservoirs causes thermally induced expansion and contraction inside the wellbore, potentially leading to the creation of leakage pathways. Determining a safe operating range for temperature and assessment of thermal stresses during CO₂ injection is essential to ensure wellbore integrity. Although failure of well barrier materials, such as steel and cement, has been reported in the contemporary literature, most of these studies applied purely mechanical loads to replicate thermally induced stresses. Thus, a systematic investigation of thermally induced casing expansion and contraction affecting the cracking and debonding of the well barrier materials is yet to be performed.

In this work, we have applied a combination of experiments and simulations to analyze the thermo-mechanical behavior of the well barrier materials undergoing repeated thermal cycling. The objectives of these studies are to determine when fracturing or debonding occurs as a function of applied thermal cycles and time, where these defects appear, and how prevalent or extensive they are. The experiments were performed in the SINTEF Petroleum Research laboratory using downscaled wellbore samples, consisting of a steel pipe cemented inside a hollow sandstone cylinder. The effects of thermal cycling were visualized using X-ray computed tomography to determine the extent of fracture. The simulations were conducted at the Lawrence Livermore National Laboratory using a highly parallel, multiscale, multiphysics code named GEOS. The experimental results did not show any detectable change in the existing pore volume of the sample for a temperature range between –50°C to 80°C. However, the simulation results suggest that large thermal stresses can develop inside the materials, which may create radial fractures/debonding during the heating/cooling stage. The data gathered from these experiments and simulations can be used to assess the temperature range for minimal impact on well integrity.

Introduction

Carbon capture and storage (CCS) is a critical necessity to reduce the amount of atmospheric CO₂ (Haszeldine, 2009; Herzog and Golomb, 2004). An effective way for longterm storage of CO₂ is to inject it into underground reservoirs through petroleum wells. However, without proper care and risk assessment, the injected CO₂ may find leakage pathways out of the wells, affecting the surrounding environments and ultimately re-emerging into the atmosphere. Thus, preventing leakages from petroleum wells is crucial to establish safe storage of CO₂.