Reactivity of Mount Simon sandstone and the Eau Claire shale under CO2 storage conditions.

The Mount Simon sandstone and Eau Claire shale formations are target storage and cap rock formations for the Illinois Basin-Decatur Geologic Carbon Sequestration Project. We reacted rock samples with brine and supercritical CO(2) at 51 °C and 19.5 MPa to access the reactivity of these formations at storage conditions and to address the applicability of using published kinetic and thermodynamic constants to predict geochemical alteration that may occur during storage by quantifying parameter uncertainty against experimental data. Incongruent dissolution of iron-rich clays and formation of secondary clays and amorphous silica will dominate geochemical alterations at this CO(2) storage site in CO(2)-rich brines. The surrogate iron-rich clay in the model required significant adjustments to its thermodynamic constants and inclusion of incongruent reaction terms to capture the change in solution composition under acid CO(2) conditions. This result emphasizes the need for experiments that constrain the conceptual geochemical model, calibrate mean parameter values, and quantify parameter uncertainty in reactive-transport simulations that will be used to estimate long-term CO(2) trapping mechanisms and changes in porosity and permeability.

Experimental Study of Cement - Sandstone/Shale - Brine - CO2 Interactions.

BACKGROUND: Reactive-transport simulation is a tool that is being used to estimate long-term trapping of CO2, and wellbore and cap rock integrity for geologic CO2 storage. We reacted end member components of a heterolithic sandstone and shale unit that forms the upper section of the In Salah Gas Project carbon storage reservoir in Krechba, Algeria with supercritical CO2, brine, and with/without cement at reservoir conditions to develop experimentally constrained geochemical models for use in reactive transport simulations. RESULTS: We observe marked changes in solution composition when CO2 reacted with cement, sandstone, and shale components at reservoir conditions. The geochemical model for the reaction of sandstone and shale with CO2 and brine is a simple one in which albite, chlorite, illite and carbonate minerals partially dissolve and boehmite, smectite, and amorphous silica precipitate. The geochemical model for the wellbore environment is also fairly simple, in which alkaline cements and rock react with CO2-rich brines to form an Fe containing calcite, amorphous silica, smectite and boehmite or amorphous Al(OH)3. CONCLUSIONS: Our research shows that relatively simple geochemical models can describe the dominant reactions that are likely to occur when CO2 is stored in deep saline aquifers sealed with overlying shale cap rocks, as well as the dominant reactions for cement carbonation at the wellbore interface.

Assessing the impact of animal waste lagoon seepage on the geochemistry of an underlying shallow aquifer.

Evidence of seepage from animal waste holding lagoons at a dairy facility in the San Joaquin Valley of California is assessed in the context of a process geochemical model that addresses reactions associated with the formation of the lagoon water as well as reactions occurring upon the mixture of lagoon water with underlying aquifer material. Comparison of model results with observed concentrations of NH4+, K+, PO4(3-), dissolved inorganic carbon, pH, Ca2+, Mg2+, SO4(2-), Cl-, and dissolved Ar in lagoon water samples and groundwater samples suggests three key geochemical processes: (i) off-gassing of significant quantities of CO2 and CH4 during mineralization of manure in the lagoon water, (ii) ion exchange reactions that remove K+ and NH4+ from seepage water as it migrates into the underlying anaerobic aquifer material, and (iii) mineral precipitation reactions involving phosphate and carbonate minerals in the lagoon water in response to an increase in pH as well as in the underlying aquifer from elevated Ca2+ and Mg2+ levels generated by ion exchange. Substantial off-gassing from the lagoons is further indicated by dissolved argon concentrations in lagoon water samples that are below atmospheric equilibrium. As such, Ar may serve as a unique tracer for lagoon water seepage since under-saturated Ar concentrations in groundwater are unlikely to be influenced by any processes other than mechanical mixing.