Quantification of solubility trapping in natural and engineered CO 2 reservoirs

Abstract

Secure retention of CO 2 in geological reservoirs is essential for effective storage. Solubility trapping, the dissolution of CO 2 into formation water, is a major sink on geological timescales in natural CO 2 reservoirs. Observations during CO 2 injection, combined with models of CO 2 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 CO 2 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 CO 2 across whole reservoirs. Natural analogues, engineered reservoirs and model studies produce a wide range of estimates on the fraction of CO 2 dissolved and the dissolution rate. Analogue and engineered reservoirs do not show the high fractions of dissolved CO 2 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 CO 2 dissolution rate over time suggests that analogue reservoirs are in dissolution equilibrium for most of the CO 2 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 CO 2 storage collection available at: https://www.lyellcollection.org/cc/geoscience-for-co2-storage