Numerical modeling of carbon dioxide sequestration on the rate of pressure solution creep in limestone: Preliminary results

TL;DR

This study uses a 2D numerical model to quantify how high partial pressures of CO2 accelerate pressure solution creep in limestone, affecting compaction rates and rock viscosity, with implications for CO2 storage.

Contribution

It introduces a numerical simulation approach to analyze the impact of CO2-rich fluids on pressure solution creep in limestone, highlighting significant effects on compaction and viscosity.

Findings

High CO2 pressures increase compaction rates by 50-75 times.

Elevated CO2 levels decrease rock matrix viscosity.

Pressure solution creep significantly influences long-term CO2 storage capacity.

Abstract

When carbon dioxide (CO2) is injected into an aquifer or a depleted geological reservoir, its dissolution into solution results in acidification of the pore waters. As a consequence, the pore waters become more reactive, which leads to enhanced dissolution-precipitation processes and a modification of the mechanical and hydrological properties of the rock. This effect is especially important for limestones given that the solubility and reactivity of carbonates is strongly dependent on pH and the partial pressure of CO2. The main mechanism that couples dissolution, precipitation and rock matrix deformation is commonly referred to as intergranular pressure solution creep (IPS) or pervasive pressure solution creep (PSC). This process involves dissolution at intergranular grain contacts subject to elevated stress, diffusion of dissolved material in an intergranular fluid, and precipitation in pore spaces subject to lower stress. This leads to an overall and pervasive reduction in porosity due to both grain indentation and precipitation in pore spaces. The percolation of CO2-rich fluids may influence on-going compaction due to pressure solution and can therefore potentially affect the reservoir and its long-term CO2 storage capacity. We aim at quantifying this effect by using a 2D numerical model to study the coupling between dissolution-precipitation processes, local mass transfer, and deformation of the rock over long time scales. We show that high partial pressures of dissolved CO2 (up to 30 MPa) significantly increase the rates of compaction by a factor of ~ 50 to ~ 75, and also result in a concomitant decrease in the viscosity of the rock matrix.