John A. Apps

Experimental and numerical simulation of dissolution and precipitation: implications for fracture sealing at Yucca Mountain, Nevada

Plugging of flow paths caused by mineral precipitation in fractures above the potential repository at Yucca Mountain, Nevada could reduce the probability of water seeping into the repository. As part of an ongoing effort to evaluate thermal-hydrological-chemical (THC) effects on flow in fractured media, we performed a laboratory experiment and numerical simulations to investigate mineral dissolution and precipitation under anticipated temperature and pressure conditions in the repository. To replicate mineral dissolution by vapor condensate in fractured tuff, water was flowed through crushed Yucca Mountain tuff at 94 degrees C. The resulting steady-state fluid composition had a total dissolved solids content of about 140 mg/l; silica was the dominant dissolved constituent. A portion of the steady-state mineralized water was flowed into a vertically oriented planar fracture in a block of welded Topopah Spring Tuff that was maintained at 80 degrees C at the top and 130 degrees C at the bottom. The fracture began to seal with amorphous silica within 5 days.A 1-D plug-flow numerical model was used to simulate mineral dissolution, and a similar model was developed to simulate the flow of mineralized water through a planar fracture, where boiling conditions led to mineral precipitation. Predicted concentrations of the major dissolved constituents for the tuff dissolution were within a factor of 2 of the measured average steady-state compositions. The mineral precipitation simulations predicted the precipitation of amorphous silica at the base of the boiling front, leading to a greater than 50-fold decrease in fracture permeability in 5 days, consistent with the laboratory experiment.These results help validate the use of a numerical model to simulate THC processes at Yucca Mountain. The experiment and simulations indicated that boiling and concomitant precipitation of amorphous silica could cause significant reductions in fracture porosity and permeability on a local scale. However, differences in fluid flow rates and thermal gradients between the experimental setup and anticipated conditions at Yucca Mountain need to be factored into scaling the results of the dissolution/precipitation experiments and associated simulations to THC models for the potential Yucca Mountain repository.

Analysis of mineral trapping for CO2 disposal in deep aquifers

Analysis of Mineral Trapping for CO 2 Disposal in Deep Aquifers Tianfu Xu, John A. Apps, and Karsten Pruess Earth Sciences Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, CA 94720. Abstract. CO 2 disposal into deep aquifers has been suggested as a potential means whereby atmospheric emissions of greenhouse gases may be reduced. However, our knowledge of the geohydrology, geochemistry, geophysics, and geomechanics of CO 2 disposal must be refined if this technology is to be implemented safely, efficiently, and predictably. As a prelude to a fully coupled treatment of physical and chemical effects of CO 2 injection, we have analyzed the impact of CO 2 immobilization through carbonate precipitation. A survey of all major classes of rock-forming minerals, whose alteration would lead to carbonate precipitation, indicated that very few minerals are present in sufficient quantities in aquifer host rocks to permit significant sequestration of CO 2 . We performed batch reaction modeling of the geochemical evolution of three different aquifer mineralogies in the presence of CO 2 at high pressure. Our modeling considered (1) redox processes that could be important in deep subsurface environments, (2) the presence of organic matter, (3) the kinetics of chemical interactions between the host rock minerals and the aqueous phase, and (4) CO 2 solubility dependence on pressure, temperature and salinity of the system. The geochemical evolution under both natural background and CO 2 injection conditions was evaluated. In addition, changes in porosity were monitored during the simulations. Results indicate that CO 2 sequestration by matrix minerals varies considerably with rock type. Under favorable conditions the amount of CO 2 that may be sequestered by precipitation of secondary carbonates is comparable with and can be larger than the effect of CO 2 dissolution in pore waters. The precipitation of ankerite and siderite is sensitive to the rate of reduction of ferric mineral precursors such as glauconite, which in turn is dependent on the reactivity of associated organic material. The accumulation of carbonates in the rock matrix and induced rock mineral alteration due to the presence of dissolved CO 2 lead to a considerable decrease in porosity. The numerical experiments described here provide useful insight into sequestration mechanisms, and their controlling geochemical conditions and parameters.

Thermochemical properties of gibbsite, bayerite, boehmite, diaspore, and the aluminate ion between 0 and 350/degree/C

A requirement for modelling the chemical behavior of groundwater in a nuclear waste repository is accurate thermodynamic data pertaining to the participating minerals and aqueous species. In particular, it is important that the thermodynamic properties of the aluminate ion be accurately determined, because most rock forming minerals in the earths crust are aluminosilicates, and most groundwaters are neutral to slightly alkaline, where the aluminate ion is the predominant aluminum species in solution. Without a precise knowledge of the thermodynamic properties of the aluminate ion aluminosilicate mineral solubilities cannot be determined. The thermochemical properties of the aluminate ion have been determined from the solubilities of the aluminum hydroxides and oxyhydroxides in alkaline solutions between 20 and 350/degree/C. An internally consistent set of thermodynamic properties have been determined for gibbsite, boehmite, diaspore and corundum. The thermodynamic properties of bayerite have been provisionally estimated and a preliminary value for ..delta..G/sub f, 298//sup 0/ of nordstrandite has been determined. 205 refs., 17 figs., 25 tabs.

Research Project on CO2 Geological Storage and Groundwater Resources: Water Quality Effects Caused by CO2 Intrusion into Shallow Groundwater

Research Project on CO 2 Geological Storage and Groundwater Resources Water Quality Effects Caused by CO 2 Intrusion into Shallow Groundwater Z Y X SG X Y Technical Report, October 2008 Contact: Jens Birkholzer Earth Sciences Division, Lawrence Berkeley National Laboratory 1 Cyclotron Rd., MS 90-1116; 510-486-7134; jtbirkholzer@lbl.gov Contributors: Jens Birkholzer, John Apps, Liange Zheng, Yingqi Zhang, Tianfu Xu, Chin-Fu Tsang EPA Program Managers: Bruce Kobelski, Anhar Karimjee Z

Reactive geochemical transport simulation to study mineral trapping for CO2 disposal in deep saline arenaceous aquifers

Reactive Geochemical Transport Simulation to Study Mineral Trapping for CO 2 Disposal in Deep Saline Arenaceous Aquifers Tianfu Xu, John A. Apps, and Karsten Pruess Earth Sciences Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, CA 94720, USA Abstract. A reactive fluid flow and geochemical transport numerical model for evaluating long-term CO 2 disposal in deep aquifers has been developed. Using this model, we performed a number of sensitivity simulations under CO 2 injection conditions for a commonly encountered Gulf Coast sediment to analyze the impact of CO 2 immobilization through carbonate precipitation. Geochemical models are needed because alteration of the predominant host rock aluminosilicate minerals is very slow and is not amenable to laboratory experiment under ambient deep-aquifer conditions. Under conditions considered in our simulations, CO 2 trapping by secondary carbonate minerals such as calcite (CaCO 3 ), dolomite (CaMg(CO 3 ) 2 ), siderite (FeCO 3 ), and dawsonite (NaAlCO 3 (OH) 2 ) could occur in the presence of high pressure CO 2 . Variations in precipitation of secondary carbonate minerals strongly depend on rock mineral composition and their kinetic reaction rates. Using the data presented in this paper, CO 2 mineral-trapping capability after 10,000 years is comparable to CO 2 dissolution in pore waters (2-5 kg CO 2 per cubic meter of formation). Under favorable conditions such as increase of the Mg-bearing mineral clinochlore (Mg 5 Al 2 Si 3 O 10 (OH) 8 ) abundance, the capacity can be larger (10 kg CO 2 per cubic meter of formation) due to increase of dolomite precipitation. Carbon dioxide-induced rock mineral alteration and the addition of CO 2 mass as secondary carbonates to the solid matrix results in decreases in porosity. A maximum 3% porosity decrease is obtained in our simulations. A small decrease in porosity may result in a significant decrease in permeability. The numerical simulations described here provide useful insight into sequestration mechanisms, and their controlling conditions and parameters. Key words. CO 2 sequestration, CO 2 disposal, numerical simulation, mineral trapping, deep saline aquifer, reactive geochemical transport, Gulf Coast sediments, natural diagenesis.

Geochemistry of natural and contaminated subsurface waters in fissured bed rocks of the Lake Karachai area, Southern Urals, Russia

Abstract Hydrogeochemical investigations of natural and contaminated subsurface waters were conducted between 1992–94 in an area where liquid radioactive waste (RAW) was impounded in a small lake, and subsequently leaked into an underlying water bearing horizon. The waste was discharged from the radiochemical plant of the Mayak Amalgamated Industry near Chelyabinsk, Russia. The underlying water-bearing horizon in fissured metavolcanic rocks was penetrated by uncased observation wells in order to log the hydrogeochemistry. Logging was carried out using a specially designed hydrogeochemical probe, which contained 8 channels to measure continuously the temperature, pressure, electric conductivity, pH, Eh, the dissolved O2 concentration, and the activities of Na, and NO3 in the wells. The logging technique enabled the natural hydrogeochemical setting to be characterized and permitted delineation of bodies of contaminated waters of different origins using measurements of pH, pNa and pNO3. The technique also permitted an evaluation of variations in the chemical composition of the RAW solutions due to radiolytic processes and to chemical interactions with the geologic medium. A conceptual model is proposed for the chemical evolution of the migrating contaminated subsurface waters in the area investigated.

Modeling Studies on the Transport of Benzene and H2S in CO2-Water Systems

LBNL-4339E Ernest Orlando Lawrence Berkeley National Laboratory Technical Report November 2010 Modeling Studies on the Transport of Benzene and H 2 S in CO 2 -Water Systems Lawrence Berkeley National Laboratory (LBNL) Contact: Jens T. Birkholzer Ph: (510) 486-7134 Email: jtbirkholzer@lbl.gov Authors: Liange Zheng, Nicolas Spycher, Jens Birkholzer, Tianfu Xu, John Apps (LBNL) Yousif Kharaka (USGS) Submitted to: U.S. Environmental Protection Agency EPA Project Manager: Sean Porse

The Hydrothermal Chemistry of Gold, Arsenic, Antimony, Mercury and Silver

A comprehensive thermodynamic database based on the Helgeson-Kirkham-Flowers (HKF) equation of state was developed for metal complexes in hydrothermal systems. Because this equation of state has been shown to accurately predict standard partial molal thermodynamic properties of aqueous species at elevated temperatures and pressures, this study provides the necessary foundation for future exploration into transport and depositional processes in polymetallic ore deposits. The HKF equation of state parameters for gold, arsenic, antimony, mercury, and silver sulfide and hydroxide complexes were derived from experimental equilibrium constants using nonlinear regression calculations. In order to ensure that the resulting parameters were internally consistent, those experiments utilizing incompatible thermodynamic data were re-speciated prior to regression. Because new experimental studies were used to revise the HKF parameters for H2S0 and HS-1, those metal complexes for which HKF parameters had been previously derived were also updated. It was found that predicted thermodynamic properties of metal complexes are consistent with linear correlations between standard partial molal thermodynamic properties. This result allowed assessment of several complexes for which experimental data necessary to perform regression calculations was limited. Oxygen fugacity-temperature diagrams were calculated to illustrate how thermodynamic data improves our understanding of depositional processes. Predicted thermodynamic properties were used to investigate metal transport in Carlin-type gold deposits. Assuming a linear relationship between temperature and pressure, metals are predicted to predominantly be transported as sulfide complexes at a total aqueous sulfur concentration of 0.05 m. Also, the presence of arsenic and antimony mineral phases in the deposits are shown to restrict mineralization within a limited range of chemical conditions. Finally, at a lesser aqueous sulfur concentration of 0.01 m, host rock sulfidation can explain the origin of arsenic and antimony minerals within the paragenetic sequence.

The Regulatory Climate Governing the Disposal of Liquid Wastes in Deep Geologic Formations: A Paradigm for Regulations for the Subsurface Storage of CO2?

Federal and state regulations covering the deep injection disposal of liquid waste have evolved over the past several years in response to legislation designed to protect underground sources of drinking water (USDW). These regulations apply to so-called Class I wells (wells injecting below the lowest aquifer containing a potential source of drinking water) and address issues relating to the confinement of hazardous and nonhazardous wastes below the lowermost USDW. They have been made progressively more stringent with time, and are now quite effective in protecting USDWs. The deep injection disposal of compressed carbon dioxide (CO 2 ) into similar environments will undoubtedly require similar regulation. This chapter reviews the history and resulting regulations relating to the development of legislation to protect groundwater supplies. The conclusions are drawn regarding the extent to which these regulations might eventually be applied to CO 2 injection.

Injection of CO2 with H2S and SO2 and Subsequent Mineral Trapping in Sandstone-Shale Formation

Carbon dioxide (CO{sub 2}) injection into deep geologic formations can potentially reduce atmospheric emissions of greenhouse gases. Sequestering less-pure CO{sub 2} waste streams (containing H{sub 2}S and/or SO{sub 2}) would be less expensive or would require less energy than separating CO{sub 2} from flue gas or a coal gasification process. The long-term interaction of these injected acid gases with shale-confining layers of a sandstone injection zone has not been well investigated. We therefore have developed a conceptual model of injection of CO{sub 2} with H{sub 2}S and/or SO{sub 2} into a sandstone-shale sequence, using hydrogeologic properties and mineral compositions commonly encountered in Gulf Coast sediments of the United States. We have performed numerical simulations of a 1-D radial well region considering sandstone alone and a 2-D model using a sandstone-shale sequence under acid-gas injection conditions. Results indicate that shale plays a limited role in mineral alteration and sequestration of gases within a sandstone horizon for short time periods (10,000 years in present simulations). The co-injection of SO{sub 2} results in different pH distribution, mineral alteration patterns, and CO{sub 2} mineral sequestration than the co-injection of H{sub 2}S or injection of CO{sub 2} alone. Simulations generate a zonal distribution of mineral alteration and formation of carbon and sulfur trapping minerals that depends on the pH distribution. The co-injection of SO{sub 2} results in a larger and stronger acidified zone close to the well. Precipitation of carbon trapping minerals occurs within the higher pH regions beyond the acidified zones. In contrast, sulfur trapping minerals are stable at low pH ranges (below 5) within the front of the acidified zone. Corrosion and well abandonment due to the co-injection of SO{sub 2} could be important issues. Significant CO{sub 2} is sequestered in ankerite and dawsonite, and some in siderite. The CO{sub 2} mineral-trapping capability can reach 80 kg per cubic meter of medium. Most sulfur is trapped through alunite precipitation, although some is trapped by anhydrite precipitation and minor amount of pyrite. The addition of the acid gases and induced mineral alteration result in changes in porosity. The limited information currently available on the mineralogy of natural high-pressure acid-gas reservoirs is generally consistent with our simulations.