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Impacts of Methane on Carbon Dioxide Storage in Brine Formations
Author(s) -
Soltanian Mohamad R.,
Amooie Mohammad A.,
Cole David R.,
Darrah Thomas H.,
Graham David E.,
Pfiffner Susan M.,
Phelps Tommy J.,
Moortgat Joachim
Publication year - 2018
Publication title -
groundwater
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.84
H-Index - 94
eISSN - 1745-6584
pISSN - 0017-467X
DOI - 10.1111/gwat.12633
Subject(s) - carbon dioxide , methane , brine , environmental science , enhanced coal bed methane recovery , waste management , negative carbon dioxide emission , carbon sequestration , environmental protection , environmental chemistry , chemistry , engineering , coal , coal mining , organic chemistry
Abstract In the context of geological carbon sequestration (GCS), carbon dioxide (CO 2 ) is often injected into deep formations saturated with a brine that may contain dissolved light hydrocarbons, such as methane (CH 4 ). In this multicomponent multiphase displacement process, CO 2 competes with CH 4 in terms of dissolution, and CH 4 tends to exsolve from the aqueous into a gaseous phase. Because CH 4 has a lower viscosity than injected CO 2 , CH 4 is swept up into a ‘bank’ of CH 4 ‐rich gas ahead of the CO 2 displacement front. On the one hand, this may provide a useful tracer signal of an approaching CO 2 front. On the other hand, the emergence of gaseous CH 4 is undesirable because it poses a leakage risk of a far more potent greenhouse gas than CO 2 if the cap rock is compromised. Open fractures or faults and wells could result in CH 4 contamination of overlying groundwater aquifers as well as surface emissions. We investigate this process through detailed numerical simulations for a large‐scale GCS pilot project (near Cranfield, Mississippi) for which a rich set of field data is available. An accurate cubic‐plus‐association equation‐of‐state is used to describe the non‐linear phase behavior of multiphase brine‐CH 4 ‐CO 2 mixtures, and breakthrough curves in two observation wells are used to constrain transport processes. Both field data and simulations indeed show the development of an extensive plume of CH 4 ‐rich (up to 90 mol%) gas as a consequence of CO 2 injection, with important implications for the risk assessment of future GCS projects.