Modeling of changes in caprock during CO2 underground geological storage

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Authors:

S.R. Bobliakh, Cand. Sci. (Tech.), National University of Water Management and Nature Resources Use, Senior Instructor of the Department of Mineral Mining, Rivne, Ukraine

O.S. Stadnyk, National University of Water Management and Nature Resources Use, Rivne, Ukraine

R.M. Ignatiuk, National University of Water Management and Nature Resources Use, Postgraduate Student, Rivne, Ukraine

P.K. Vorobyov, National University of Water Management and Nature Resources Use, Rivne, Ukraine

Abstract:

Purpose. Geologic fixation represents an immediately available option for reducing the global environmental impact of CO2 by removing large amounts of the gas from the atmosphere. The overall objective of this article is to assess the factors that impact injection and storage of CO2 in deep saline aquifers and to understand how destabilization of chemical equilibrium can potentially damage the caprock.

Methodology. Because of the large spatial extent and long time scale, it is difficult to study the effect of CO2 sequestration in saline aquifers via laboratory or field studies conducted over short periods of time. To address issues related to viability and risk of CO2 injection into the subsurface we used geochemical software, which takes into account the thermodynamics and kinetics of chemical reactions and mass transport. A series of calculations were performed with a reactive transport program Crunch Flow, which gave us a chance to compare simulation results of pH and porosity profiles in the caprock in the acidified reservoir water and in non-acidified reservoir water.

Findings. The results of the modeling show that the injection of CO2 can potentially have a significant effect on the caprock by changing the porosity due to the dissolution and precipitation of minerals, but that impact is limited to a zone from several decimeters to several meters of the caprock. After modeling, we observed that pH variations along the profile are much smaller in amplitude in the non-acidified water reservoir than in the acidified water reservoir. On the other hand, the impact on porosity by the non-acidified water reservoir is greater than by the acidified water reservoir.

Originality. The impact of the diffusion of dissolved CO2 in the caprock is limited in vertical extension. The amplitude depends essentially on the pH of the water in the reservoir at the interface with the caprock. In this scenario, the consequences of the long term CO2 influence on the caprock integrity appear to be small, especially in the context of carbonate-dominant storage systems.

Practical value. The obtained results will help us to predict what will happen with the carbonate caprock minerals, when CO2 will be injected underground.

References:

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9. Steefel, C.I. (2009), “CrunchFlow software for modeling multicomponent reactive flow and transport. User’s manual”, Earth Sciences Division. Lawrence Berkeley, National Laboratory, Berkeley, CA. October 12 – 91 p.

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ISSN (print) 2071-2227,
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