Impact of dissolution and precipitation on pore structure in CO2 sequestration within tight sandstone reservoirs

Abstract

Complex physical and chemical reactions during CO₂ sequestration alter the microscopic pore structure of geological formations, impacting sequestration stability. To investigate CO₂ sequestration dynamics, comprehensive physical simulation experiments were conducted under varied pressures, coupled with assessments of changes in mineral composition, ion concentrations, pore morphology, permeability, and sequestration capacity before and after experimentation. Simultaneously, a method using NMR T₂ spectra changes to measure pore volume shift and estimate CO₂ sequestration is introduced. It quantifies CO₂ needed for mineralization of soluble minerals. However, when CO₂ dissolves in crude oil, the precipitation of asphaltene compounds impairs both seepage and storage capacities. Notably, the impact of dissolution and precipitation is closely associated with storage pressure, with a particularly pronounced influence on smaller pores. As pressure levels rise, the magnitude of pore alterations progressively increases. At a pressure threshold of 25 MPa, the rate of change in small pores due to dissolution reaches a maximum of 39.14%, while precipitation results in a change rate of −58.05% for small pores. The observed formation of dissolution pores and micro-cracks during dissolution, coupled with asphaltene precipitation, provides crucial insights for establishing CO₂ sequestration parameters and optimizing strategies in low permeability reservoirs.