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type     January, 2009

Reactive Transport of CO2 in Saline Aquifers with implicit geomechanical analysis

Bjørn Kvamme, Shunping Liu

Geological storage of CO2 in saline aquifers is a promising way to reduce the concentration of the greenhouse gas in the atmosphere. Injection of CO2 will, however, lead to dissolution of minerals in regions of lowered pH and precipitation of minerals from transported ions in regions of higher pH. The geomechanical implications of these changes on the stability of the reservoir are of crucial importance in the evaluation of potential injection reservoirs. The possible injection rate for given over-pressures of the injected CO2 depends on the porosity and permeability of the rock matrix in the vicinity of the injection well. Local fracturing in this region can be a tool for increasing the injection flow rate but a geomechanical analysis will be needed in order to make sure that this fracturing will not affect the geomechanical stability outside this limited region to a significant degree. This paper presents a new rewritten version of RetrasoCodeBright (RCB) for simulations of CO2 storage in saline aquifers. An advantage of this code compared to other codes is the implicit geo-mechanical module. The code has been rewritten to account for non-ideal gas through corrections of gas density and gas solubility in all transport terms. Newton-Raphson method used to solve the flow and mechanics in RCB has been improved so as to improve convergence even under high gas injecting pressures. A 2D hydro-chemical-mechanical problem is used to illustrate the modified RCB code. This particular test case is chosen as a block of pure calcite embedded in top or bottom sections with mineralogy similar to that of the Utsira formation. The test case is designed so as to investigate horizontal migration and injection is controlled by a pressure difference between injection on the right hand side (140 bar) and a constant pressure (100 bar) on the left hand side of the system. For this particular test case the Soave Redlich Kwong (SRK) equation of state has been applied for compressibility factors and fugacity coefficients but can easily be replaced with more accurate equations of state for CO2. The simulated results show as expected a significant buffering effect which slows down the mineral erosion close to the injection zone and for the specific example the only region which appear to have potential geomechanical implications of the injected CO2 is close to the left side of the block where the difference between stress and overpressure indicate region of instability after 100 years of injection.

© 2008 Elsevier Ltd. All rights reserved.

Keywords: Carbon dioxide; storage; geochemistry; geomechanics.

Source: Greenhouse Gas Control Technologies (GHGT) conference, 16-20 November 2008

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