Effect of temperature on permeability of geopolymer: A primary well sealant for carbon capture and storage wells

Abstract

Geological sequestration of carbon dioxide has been found to be the most promising solution to reduce anthropogenic greenhouse gas emissions without affecting the usage of fossil fuel. Wellbore integrity needs to be maintained for leak-free storage and well cement plays a major role in wellbore integrity as it provides the required zonal isolation. Ordinary Portland cement (OPC)-based sealant has been used in injection wells and it has been found that it experiences cement degradation and is unstable under CO2-rich down-hole conditions. Therefore, an experimental program was conducted to study the suitability of geopolymer as well cement and the apparent CO2 permeability of geopolymer was tested under the following test conditions using a high pressure triaxial experiment: (a) temperatures of 23–70°C; (b) CO2 injection pressures of 6–17MPa; and (c) confining pressures of 12–20MPa. From the preliminary experimental results, it was noted that the apparent CO2 permeability of geopolymer increases with the curing temperature and increment rates are as high as 200–1000%. However, the maximum permeability (0.04μD) value obtained for any temperature studied is approximately 5000 times lower than the permeability value (200μD) recommended by the American petroleum industry (API) for a typical well sealant. The increase in permeability is related to increased pore diameter and highly heterogeneous pore structure at elevated temperatures for longer curing periods. Even though the permeability of geopolymer increases with the temperature, the values are well below those of traditional OPC cement and API recommended limits. Therefore, geopolymers have potential as primary sealant material in a typical wellbore. An attempt is made to develop an empirical formulation to predict the permeability of geopolymer at different temperatures under various confining pressures.