Abstract

Secure retention of CO₂ in geological reservoirs is essential for effective storage. Solubility trapping, the dissolution of CO₂ into formation water, is a major sink on geological timescales in natural CO₂ reservoirs. Observations during CO₂ injection, combined with models of CO₂ reservoirs, indicate the immediate onset of solubility trapping. There is uncertainty regarding the evolution of dissolution rates between the observable engineered timescale of years and decades, and the >10 kyr state represented by natural CO₂ reservoirs. A small number of studies have constrained dissolution rates within natural analogues. The studies show that solubility trapping is the principal storage mechanism after structural trapping, removing 10–50% of CO₂ across whole reservoirs. Natural analogues, engineered reservoirs and model studies produce a wide range of estimates on the fraction of CO₂ dissolved and the dissolution rate. Analogue and engineered reservoirs do not show the high fractions of dissolved CO₂ seen in several models. Evidence from natural analogues supports a model of most dissolution occurring during emplacement and migration, before the establishment of a stable gas–water contact. A rapid decline in CO₂ dissolution rate over time suggests that analogue reservoirs are in dissolution equilibrium for most of the CO₂ residence time.

Supplementary material: Dissolution rate for all plots and exponential function curves for scenarios A and B are available at https://doi.org/10.6084/m9.figshare.c.5476199

Thematic collection: This article is part of the Geoscience for CO₂ storage collection available at: https://www.lyellcollection.org/cc/geoscience-for-co2-storage