Multi-Scale Investigation of Caprock-Cement Integrity for CO2 Storage

Abstract

CO2 storage in saline aquifers and depleted oil and gas reservoirs is a promising solution to help mitigating CO2 emissions and tackling global warming. However, storage security and CO2 leakage over a long period remain as a major concern. Cement degradation after CO2 injection, especially in poorly cemented wells, can provide pathways for CO2 leakage to groundwater and the atmosphere. Therefore, to assess the potential risks of CO2 leakage, it is critical to understand the interactions between the major components of a storage system including CO2, brine, wellbore cement, and caprock/reservoir rocks. In this work, we performed a series of experiments simulating deep wellbore environments to investigate the chemical, physical, and mechanical alterations in cement and rock as a result of being exposed to CO2-rich brine. X-ray micro-computer tomography (µCT), petrophysical evaluation and geomechanical testing were conducted before and after experiments. It was observed that dissolution and precipitation of some minerals started from early stage of exposure and continued as time passed, and, as a result, cement and cement-caprock interface were affected. The high-permeable hairline cracks in the cement were filled due to mineral precipitation and reduced the composite permeability significantly. This phenomenon may help mitigate against CO2 leakage at conditions similar to those used in this work.