Impact of Heterogeneity on CO2 Storage in Carbonate Saline Aquifers

Abstract

Abstract This paper provides an investigation into the feasibility of carbon storage in saline aquifers, with a specific focus on the potential of injecting CO2 into heterogeneous carbonate rock aquifers that feature both conventional pore type system (referred to as the matrix) and secondary dissolution pore systems (non-matrix). Key areas of interest include the storage potential of the saline aquifer, injectivity of the wells, and the shape and size of CO2 plumes at the end of injection as well as several decades after injection. To explore the potential of carbonate aquifers for CO2 storage and investigate the complex nature of carbonate rocks on CO2 migration and storage efficiency, the investigation builds twelve distinct geological scenarios that entail varying the quality of matrix systems into three distinct matrix sets: low-quality, moderate-quality, and high-quality matrix porosity and permeability properties. In addition, different non-matrix abundance is superimposed on the three matrix sets, producing significantly different levels of permeability contrast between matrix and non-matrix pore systems. Sensitivity of the results to fluid properties and rock-fluid interactions, such as different scenarios of displacement functions, salinity, and vertical transmissibility, are also tested and benchmarked. The study demonstrates that non-matrix properties and distribution plays a crucial role in both injectivity and CO2 plume size, particularly in low-quality matrix conditions. The research also highlights that geological heterogeneity significantly affects plume growth and vertical distribution, particularly when there is a substantial contrast between matrix and non-matrix reservoir properties. Additionally, the most effective storage efficiency and minimal plume overprint occur when the matrix is of moderate quality (8%-24% porosity) and non-matrix features are present in low abundance.