On modeling the potential impacts of CO2 sequestration on shallow groundwater: Transport of organics and co-injected H2S by supercritical CO2 to shallow aquifers

Abstract

Proper site selection for CO 2 geologic storage requires assessing the impact of potential leakage of CO 2 from deep subsurface reservoirs to overlying drinking water aquifers.Although recent studies have largely focused on the mobilization of trace elements in response to the intrusion of CO 2 into such aquifers, in this paper we investigate two other leakage issues and potential effects on groundwater quality: the transport of organic compounds by supercritical CO 2 from deep storage reservoirs and the upward migration of CO 2 with co-injected H 2 S. Numerical simulations show that organic compounds that may be present at depth, such as benzene, could be mobilized by supercritical CO 2 and migrate with the leaking CO 2 . Modeling results also show that upon the transport of 2 CO 2 +H 2 S mixtures through a hypothetical leakage pathway, H 2 S arrival in the shallower aquifer is delayed in comparison with that of CO 2 due to the preferential dissolution of H 2 S into the aqueous phase. The potentially adverse impacts of leakage on shallow groundwater quality may be exacerbated for cases of leaking CO 2 +H 2 S, compared to intrusion of pure CO 2 , possibly leading to the mobilization of thiophilic elements such as arsenic. Geochemical reactions included in the simulations involve adsorption/desorption, reductive dissolution of goethite, precipitation of pyrite, siderite, and arsenic sulfide phases. The models presented are generic in nature, exploring important processes regarding organic compounds and co-injected H 2 S, and calling attention to the need for more site-specific studies taking into account the variability and uncertainty of key hydrogeologic and geochemical parameters.

Reactive transport codes for subsurface environmental simulation

“…Applications have included, for example, geothermal systems [143][144][145], nuclear waste repositories [146][147][148][149], geologic carbon sequestration [150][151][152][153][154], and environmental remediation [155][156][157]. The development of TOUGHREACT has been ongoing since the late 1990s.…”

Subsurface geochemical fate and effects of impurities contained in a CO2 stream injected into a deep saline aquifer: What is known

“…Experimental studies are essential in this effort; however, due to the large number of potential variables (pressure, temperature, water composition, mineralogy and gas composition), numerical studies are also required. These numerical simulations can be as simple as calculating the equilibrium mineral assemblage associated with the addition of gas components to water/mineral systems (e.g., Koenen et al, 2011), to highly complex large scale, multicomponent reactive flow models (e.g., Battistelli and Marcolini, 2009;Zheng et al, 2013). Effective integration of field, modelling and experimental works is essential for the timely development of this subject.…”

“…Further advances in TOUGHREACT have allowed for even more complex modelling of the effects of injecting H 2 S-contaminated CO 2 (i.e., Zheng et al, 2013). That study draws attention to, among other things, the suite of potential mineralogical reactions involving the reductive dissolution of iron hydroxides by co-injected H 2 S leaking into a shallow aquifer from a CO 2 storage site.…”

Geochemical sensitivity to CO2leakage: detection in potable aquifers at carbon sequestration sites

“…mineralogy, water quality, and groundwater dynamics) are collected from a representative aquifer, whereas a site‐specific model focuses on one location at which aquifers are well characterized, flow dynamics are understood, and detailed mineralogical analyses are available . Table summarizes selected numerical models that focus on not only the possibility of geochemical parameters for detecting CO 2 leakage signals in potable aquifers, but also assesses of potential degradation of groundwater quality by metals such as arsenic and lead …”