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Well blowout rates in California Oil and Gas District 4--Update and Trends

Description: Well blowouts are one type of event in hydrocarbon exploration and production that generates health, safety, environmental and financial risk. Well blowouts are variously defined as 'uncontrolled flow of well fluids and/or formation fluids from the wellbore' or 'uncontrolled flow of reservoir fluids into the wellbore'. Theoretically this is irrespective of flux rate and so would include low fluxes, often termed 'leakage'. In practice, such low-flux events are not considered well blowouts. Rather, the term well blowout applies to higher fluxes that rise to attention more acutely, typically in the order of seconds to days after the event commences. It is not unusual for insurance claims for well blowouts to exceed US$10 million. This does not imply that all blowouts are this costly, as it is likely claims are filed only for the most catastrophic events. Still, insuring against the risk of loss of well control is the costliest in the industry. The risk of well blowouts was recently quantified from an assembled database of 102 events occurring in California Oil and Gas District 4 during the period 1991 to 2005, inclusive. This article reviews those findings, updates them to a certain extent and compares them with other well blowout risk study results. It also provides an improved perspective on some of the findings. In short, this update finds that blowout rates have remained constant from 2005 to 2008 within the limits of resolution and that the decline in blowout rates from 1991 to 2005 was likely due to improved industry practice.
Date: October 1, 2009
Creator: Jordan, Preston D. & Benson, Sally M.
Partner: UNT Libraries Government Documents Department

Exact solutions in a model of vertical gas migration

Description: This work is motivated by the growing interest in injectingcarbon dioxide into deep geological formations as a means of avoidingatmospheric emissions of carbon dioxide and consequent global warming.One of the key questions regarding the feasibility of this technology isthe potential rate of leakage out of the primary storage formation. Weseek exact solutions in a model of gas flow driven by a combination ofbuoyancy, viscous and capillary forces. Different combinations of theseforces and characteristic length scales of the processes lead todifferent time scaling and different types of solutions. In the case of athin, tight seal, where the impact of gravity is negligible relative tocapillary and viscous forces, a Ryzhik-type solution implies square-rootof time scaling of plume propagation velocity. In the general case, a gasplume has two stable zones, which can be described by travelling-wavesolutions. The theoretical maximum of the velocity of plume migrationprovides a conservative estimate for the time of vertical migration.Although the top of the plume has low gas saturation, it propagates witha velocity close to the theoretical maximum. The bottom of the plumeflows significantly more slowly at a higher gas saturation. Due to localheterogeneities, the plume can break into parts. Individual plumes alsocan coalesce and from larger plumes. The analytical results are appliedto studying carbon dioxide flow caused by leaks from deep geologicalformations used for CO2 storage. The results are also applicable formodeling flow of natural gas leaking from seasonal gas storage, or formodeling of secondary hydrocarbon migration.
Date: June 27, 2006
Creator: Silin, Dmitriy B.; Patzek, Tad W. & Benson, Sally M.
Partner: UNT Libraries Government Documents Department

Modeling Leaking Gas Plume Migration

Description: In this study, we obtain simple estimates of 1-D plume propagation velocity taking into account the density and viscosity contrast between CO{sub 2} and brine. Application of the Buckley-Leverett model to describe buoyancy-driven countercurrent flow of two immiscible phases leads to a transparent theory predicting the evolution of the plume. We obtain that the plume does not migrate upward like a gas bubble in bulk water. Rather, it stretches upward until it reaches a seal or until the fluids become immobile. A simple formula requiring no complex numerical calculations describes the velocity of plume propagation. This solution is a simplification of a more comprehensive theory of countercurrent plume migration that does not lend itself to a simple analytical solution (Silin et al., 2006). The range of applicability of the simplified solution is assessed and provided. This work is motivated by the growing interest in injecting carbon dioxide into deep geological formations as a means of avoiding its atmospheric emissions and consequent global warming. One of the potential problems associated with the geologic method of sequestration is leakage of CO{sub 2} from the underground storage reservoir into sources of drinking water. Ideally, the injected green-house gases will stay in the injection zone for a geologically long time and eventually will dissolve in the formation brine and remain trapped by mineralization. However, naturally present or inadvertently created conduits in the cap rock may result in a gas leak from primary storage. Even in supercritical state, the carbon dioxide viscosity and density are lower than those of the indigenous formation brine. Therefore, buoyancy will tend to drive the CO{sub 2} upward unless it is trapped beneath a low permeability seal. Theoretical and experimental studies of buoyancy-driven supercritical CO{sub 2} flow, including estimation of time scales associated with plume evolution, are critical for developing ...
Date: August 20, 2007
Creator: Silin, Dmitriy; Patzek, Tad & Benson, Sally M.
Partner: UNT Libraries Government Documents Department

The role of optimality in characterizing CO2 seepage from geological carbon sequestration sites

Description: Storage of large amounts of carbon dioxide (CO{sub 2}) in deep geological formations for greenhouse gas mitigation is gaining momentum and moving from its conceptual and testing stages towards widespread application. In this work we explore various optimization strategies for characterizing surface leakage (seepage) using near-surface measurement approaches such as accumulation chambers and eddy covariance towers. Seepage characterization objectives and limitations need to be defined carefully from the outset especially in light of large natural background variations that can mask seepage. The cost and sensitivity of seepage detection are related to four critical length scales pertaining to the size of the: (1) region that needs to be monitored; (2) footprint of the measurement approach, and (3) main seepage zone; and (4) region in which concentrations or fluxes are influenced by seepage. Seepage characterization objectives may include one or all of the tasks of detecting, locating, and quantifying seepage. Each of these tasks has its own optimal strategy. Detecting and locating seepage in a region in which there is no expected or preferred location for seepage nor existing evidence for seepage requires monitoring on a fixed grid, e.g., using eddy covariance towers. The fixed-grid approaches needed to detect seepage are expected to require large numbers of eddy covariance towers for large-scale geologic CO{sub 2} storage. Once seepage has been detected and roughly located, seepage zones and features can be optimally pinpointed through a dynamic search strategy, e.g., employing accumulation chambers and/or soil-gas sampling. Quantification of seepage rates can be done through measurements on a localized fixed grid once the seepage is pinpointed. Background measurements are essential for seepage detection in natural ecosystems. Artificial neural networks are considered as regression models useful for distinguishing natural system behavior from anomalous behavior suggestive of CO{sub 2} seepage without need for detailed understanding of natural ...
Date: September 15, 2008
Creator: Cortis, Andrea; Oldenburg, Curtis M. & Benson, Sally M.
Partner: UNT Libraries Government Documents Department

Well blowout rates and consequences in California Oil and Gas District 4 from 1991 to 2005: Implications for geological storage of carbon dioxide

Description: Well blowout rates in oil fields undergoing thermally enhanced recovery (via steam injection) in California Oil and Gas District 4 from 1991 to 2005 were on the order of 1 per 1,000 well construction operations, 1 per 10,000 active wells per year, and 1 per 100,000 shut-in/idle and plugged/abandoned wells per year. This allows some initial inferences about leakage of CO2 via wells, which is considered perhaps the greatest leakage risk for geological storage of CO2. During the study period, 9% of the oil produced in the United States was from District 4, and 59% of this production was via thermally enhanced recovery. There was only one possible blowout from an unknown or poorly located well, despite over a century of well drilling and production activities in the district. The blowout rate declined dramatically during the study period, most likely as a result of increasing experience, improved technology, and/or changes in safety culture. If so, this decline indicates the blowout rate in CO2-storage fields can be significantly minimized both initially and with increasing experience over time. Comparable studies should be conducted in other areas. These studies would be particularly valuable in regions with CO2-enhanced oil recovery (EOR) and natural gas storage.
Date: May 15, 2008
Creator: Jordan, Preston; Jordan, Preston D. & Benson, Sally M.
Partner: UNT Libraries Government Documents Department

Bioremediation of metals and radionuclides: What it is and How itWorks

Description: This primer is intended for people interested in DOE environmental problems and in their potential solutions. It will specifically look at some of the more hazardous metal and radionuclide contaminants found on DOE lands and at the possibilities for using bioremediation technology to clean up these contaminants. Bioremediation is a technology that can be used to reduce, eliminate, or contain hazardous waste. Over the past two decades, it has become widely accepted that microorganisms, and to a lesser extent plants, can transform and degrade many types of contaminants. These transformation and degradation processes vary, depending on physical environment, microbial communities, and nature of contaminant. This technology includes intrinsic bioremediation, which relies on naturally occurring processes, and accelerated bioremediation, which enhances microbial degradation or transformation through inoculation with microorganisms (bioaugmentation) or the addition of nutrients (biostimulation).
Date: January 1, 1999
Creator: McCullough, J.; Hazen, Terry & Benson, Sally
Partner: UNT Libraries Government Documents Department

CO{sub 2} injection for enhanced gas production and carbon sequestration

Description: Analyses suggest that carbon dioxide (CO{sub 2}) can be injected into depleted gas reservoirs to enhance methane (CH{sub 4}) recovery for periods on the order of 10 years, while simultaneously sequestering large amounts of CO{sub 2}. Simulations applicable to the Rio Vista Gas Field in California show that mixing between CO{sub 2} and CH{sub 4} is slow relative to repressurization, and that vertical density stratification favors enhanced gas recovery.
Date: November 15, 2001
Creator: Oldenburg, Curtis M. & Benson, Sally M.
Partner: UNT Libraries Government Documents Department

Field-Measured Oxidation Rates of Biologically Reduced Selenium in Sludge

Description: Sludge generated during surface-water transport or biological treatment of selenium laden agricultural drainage water contains high concentrations (20-100 mg/kg) of selenium. Finding safe and economical sludge disposal methods requires understanding of the biogeochemical processes that change selenium speciation (after placed at a disposal site). Two experiments, each comparing 3 treatments for sludge disposal has resulted in data on changes in selenium speciation spanning an eight year period. Treatments included direct application to upland soils and application with tillage to depths of 15 cm and 30 cm. Soil cores, soil water samples and groundwater monitoring were used to track changes in selenium speciation and transport of re-oxidized forms of selenium. Measurements demonstrate the slow re-oxidation of reduced forms of selenium, largely elemental and organically associated forms, to selenate and selenite. Downward transport of these re-oxidized forms of selenium are driven by winter rains. Field measured re-oxidation rates for these field trials are presented and compared to selenium re-oxidation rates in formerly ponded areas at Kesterson Reservoir, California.
Date: May 1, 1999
Creator: Benson, Sally M.; Daggett, John & Zawislansi, Peter
Partner: UNT Libraries Government Documents Department

Relevance of underground natural gas storage to geologic sequestration of carbon dioxide

Description: The practice of underground natural gas storage (UNGS), which started in the USA in 1916, provides useful insight into the geologic sequestration of carbon dioxide--the dominant anthropogenic greenhouse gas released into the atmosphere. In many ways, UNGS is directly relevant to geologic CO{sub 2} storage because, like CO{sub 2}, natural gas (essentially methane) is less dense than water. Consequently, it will tend to rise to the top of any subsurface storage structure located below the groundwater table. By the end of 2001 in the USA, about 142 million metric tons of natural gas were stored underground in depleted oil and gas reservoirs and brine aquifers. Based on their performance, UNGS projects have shown that there is a safe and effective way of storing large volumes of gases in the subsurface. In the small number of cases where failures did occur (i.e., leakage of the stored gas into neighboring permeable layers), they were mainly related to improper well design, construction, maintenance, and/or incorrect project operation. In spite of differences in the chemical and physical properties of the gases, the risk-assessment, risk-management, and risk-mitigation issues relevant to UNGS projects are also pertinent to geologic CO{sub 2} sequestration.
Date: July 1, 2002
Creator: Lippmann, Marcelo J. & Benson, Sally M.
Partner: UNT Libraries Government Documents Department

Land disposal of San Luis drain sediments, Panoche Water District, South Dos Palos, California

Description: Lawrence Berkeley National Laboratory (LBNL), LFR Levine-Fricke (LFR), the U.S. Bureau of Reclamation (USBR) and the Panoche Water District, have completed a pilot-scale test of the viability of land application of selenium- (Se-) enriched San Luis Drain (SLD) sediments. The project was initiated in October 1998 by LBNL. LFR assumed the role of primary subcontractor on the project in July 2001. Substantial portions of this report, describing work performed prior to November 2000, were previously prepared by LBNL personnel. The data set, findings, and recommendations are herein updated with information collected since November 2000. Local land disposal is an attractive option due to its low cost and the proximity of large areas of available land. Two modes of disposal are being tested: (1) the application to a nearby SLD embankment, and (2) the application to and incorporation with nearby farm soils. The study of these options considers the key problems that may potentially arise from this approach. These include disturbance of SLD sediments during dredging, resulting in increased downstream Se concentrations; movement of the land-applied Se to groundwater; reduced productivity of farm crops; and Se uptake by wild and crop plants. This report describes field and laboratory activities carried out from 1998 through February 2002, and results of these investigations.
Date: July 1, 2002
Creator: Zawislanski, Peter; Benson, Sally; TerBerg, Robert & Borglin, Sharon
Partner: UNT Libraries Government Documents Department

Implications of surface seepage on the effectiveness of geologic storage of carbon dioxide as a climate change mitigation strategy

Description: The probability that long-term geologic storage or sequestration of carbon dioxide (CO{sub 2}) will become an important climate change mitigation strategy will depend on a number of factors, namely (1) availability, capacity and location of suitable sites, (2) the cost of geologic storage compared to other climate change mitigation options, and (3) public acceptance. Whether or not a site is suitable will be determined by establishing that it can meet a set of performance requirements for safe and effective geologic storage (PRGS). To date, no such PRGS have been developed. Establishing effective PRGS must start with an evaluation of how much CO{sub 2} might be stored and for how long the CO{sub 2} must remain underground to meet goals for controlling atmospheric CO{sub 2} concentrations. These requirements then provide a context for addressing the issue of what, if any, is an ''acceptable surface seepage rate''? This paper provides a preliminary evaluation of CO{sub 2} storage amounts, time-scales, and concordant performance requirements.
Date: July 30, 2002
Creator: Hepple, Robert P. & Benson, Sally M.
Partner: UNT Libraries Government Documents Department

The Rosetta Resources CO2 Storage Project - A WESTCARB GeologicPilot Test

Description: WESTCARB, one of seven U.S. Department of Energypartnerships, identified (during its Phase I study) over 600 gigatonnesof CO2 storage capacity in geologic formations located in the Westernregion. The Western region includes the WESTCARB partnership states ofAlaska, Arizona, California, Nevada, Oregon and Washington and theCanadian province of British Columbia. The WESTCARB Phase II study iscurrently under way, featuring three geologic and two terrestrial CO2pilot projects designed to test promising sequestration technologies atsites broadly representative of the region's largest potential carbonsinks. This paper focuses on two of the geologic pilot studies plannedfor Phase II -referred to-collectively as the Rosetta-Calpine CO2 StorageProject. The first pilot test will demonstrate injection of CO2 into asaline formation beneath a depleted gas reservoir. The second test willgather data for assessing CO2 enhanced gas recovery (EGR) as well asstorage in a depleted gas reservoir. The benefit of enhanced oil recovery(EOR) using injected CO2 to drive or sweep oil from the reservoir towarda production well is well known. EaR involves a similar CO2 injectionprocess, but has received far less attention. Depleted natural gasreservoirs still contain methane; therefore, CO2 injection may enhancemethane production by reservoir repressurization or pressure maintenance.CO2 injection into a saline formation, followed by injection into adepleted natural gas reservoir, is currently scheduled to start inOctober 2006.
Date: January 30, 2006
Creator: Trautz, Robert; Benson, Sally; Myer, Larry; Oldenburg, Curtis; Seeman, Ed; Hadsell, Eric et al.
Partner: UNT Libraries Government Documents Department

Continuous active-source seismic monitoring of CO2 injection in abrine aquifer

Description: Continuous crosswell seismic monitoring of a small-scale CO2injection was accomplished with the development of a noveltubing-deployed piezoelectric borehole source. This piezotube source wasdeployed on the CO2 injection tubing, near the top of the saline aquiferreservoir at 1657-m depth, and allowed acquisition of crosswellrecordings at 15-minute intervals during the multiday injection. Thechange in traveltime recorded at various depths in a nearby observationwell allowed hour-by-hour monitoring of the growing CO2 plume via theinduced seismic velocity change. Traveltime changes of 0.2 to 1.0 ms ( upto 8 percent ) were observed, with no change seen at control sensorsplaced above the reservoir. The traveltime measurements indicate that theCO2 plume reached the top of the reservoir sand before reaching theobservation well, where regular fluid sampling was occuring during theinjection, thus providing information about the in situ buoyancy ofCO2.
Date: December 10, 2006
Creator: Daley, Thomas M.; Solbau, Ray D.; Ajo-Franklin, Jonathan B. & Benson, Sally M.
Partner: UNT Libraries Government Documents Department

Core Scale and Pore Scale Studies of Carbon Dioxide Migration Insaline Formations

Description: Understanding core scale and pore scale migration of CO2 will improve our ability to predict storage capacity and determine the effectiveness of solubility and capillary (residual CO2) trapping. While the theoretical underpinnings of multi-phase flow are well developed for oil and gas production, there are few, if any measurements relevant to CO2 storage in saline formations. To fill this gap, core scale and porescale measurements of CO2 migration in sandstone are being conducted.
Date: October 3, 2005
Creator: Benson, Sally M.; Tomutsa, Liviu; Silin, Dmitriy; Kneafsey,Timothy & Miljkovic, Ljubinko
Partner: UNT Libraries Government Documents Department

Carbon dioxide reuse and sequestration: The state of the art today

Description: Atmospheric concentrations of CO{sub 2} and other greenhouse gases (GHGs) are growing steadily. GHG levels seem likely to grow more quickly in the future as developed countries continue to use large amounts of energy, while developing countries become wealthy enough to afford energy-intensive automobiles, refrigerators, and other appliances (as well as live and work in larger, more comfortable structures). To keep GHGs at manageable levels, large decreases in CO{sub 2} emissions will be required. Yet analysts understand the difficulty of developing enough zero- and low-carbon-emission technologies to meet the goal of safe GHG stabilization. Carbon sequestration technologies can help bridge this gap. These technologies are only beginning to be developed, but their promise is already evident. In Europe, CO{sub 2} has been continuously and safely pumped into a below-sea limestone structure for over three years, where it remains. In New Mexico, CO{sub 2} is being used to drive out natural gas from within unminable coal seams 1,000 meters below the surface, and again, continuously injected CO{sub 2} has stayed sequestered for over three years, even though the project was designed for natural gas production, not CO{sub 2} sequestration. These and other beginnings suggest that much CO{sub 2} could be reused or sequestered over time. However, substantial R and D will be required so that CO{sub 2} can be captured inexpensively, and then reused or safely sequestered economically. Advanced concepts likely hold great promise as well.
Date: August 1, 2000
Creator: Benson, Sally M.; Dorchak, Thomas; Jacobs, Gary; Ekmann, James; Bishop, Jim & Grahame, Thomas
Partner: UNT Libraries Government Documents Department

In situ microbial volatilization of selenium in soils: A case history

Description: A pilot-scale field experiment has been conducted since 1990 to test the effectiveness of microbial volatilization in removing selenium (Se) from soils contaminated with agricultural drainage water. The experiment, in which only irrigation and aeration were employed to enhance microbial processes, was designed to measure all major Se fluxes, including not only selenium loss via volatilization, but also advection with infiltrating rainwater, evapotranspirative transport, and plant uptake. The goal was to account for the total Se mass balance and address questions as to the significance of microbial volatilization relative to other fluxes. Although data collected from 1990 to 1994 showed decreases of Se concentrations in the top soil, subsequent data demonstrated that advective Se fluxes due to rainwater infiltration and evapotranspiration are largely responsible for the observed changes. Se volatilization was measured to account for an annual loss of only about 1%, with volatilization rates decreasing significantly with time, presumably due to the depletion of soil organic carbon. The integrated results of this project demonstrate the advantages and even necessity of an inter-disciplinary and multi-phase approach to evaluating the effectiveness of bioremediation strategies. Extreme caution needs to be taken in interpreting early results; long-term data collection and follow-up are indispensable.
Date: January 2, 1999
Creator: Zawislanski, Peter T.; Benson, Sally M.; Jayaweera, Gamani R.; Wu, L. & Frankenberger, William T.
Partner: UNT Libraries Government Documents Department

A Combined Saline Formation and Gas Reservoir CO2 Injection Pilotin Northern California

Description: A geologic sequestration pilot in the Thornton gas field in Northern California, USA involves injection of up to 4000 tons of CO{sub 2} into a stacked gas and saline formation reservoir. Lawrence Berkeley National Laboratory (LBNL) is leading the pilot test in collaboration with Rosetta Resources, Inc. and Calpine Corporation under the auspices of the U.S. Department of Energy and California Energy Commission's WESTCARB, Regional Carbon Sequestration Partnership. The goals of the pilot include: (1) Demonstrate the feasibility of CO{sub 2} storage in saline formations representative of major geologic sinks in California; (2) Test the feasibility of Enhanced Gas Recovery associated with the early stages of a CO{sub 2} storage project in a depleting gas field; (3) Obtain site-specific information to improve capacity estimation, risk assessment, and performance prediction; (4) Demonstrate and test methods for monitoring CO{sub 2} storage in saline formations and storage/enhanced recovery projects in gas fields; and (5) Gain experience with regulatory permitting and public outreach associated with CO{sub 2} storage in California. Test design is currently underway and field work begins in August 2006.
Date: April 28, 2006
Creator: Trautz, Robert; Myer, Larry; Benson, Sally; Oldenburg, Curt; Daley, Thomas & Seeman, Ed
Partner: UNT Libraries Government Documents Department

Capacity investigation of brine-bearing sands of the Fwwm formation for geologic sequestration of CO{sub 2}

Description: The capacity of fluvial brine-bearing formations to sequester CO{sub 2} is investigated using numerical simulations of CO{sub 2} injection and storage. Capacity is defined as the volume fraction of the subsurface available for CO{sub 2} storage and is conceptualized as a product of factors that account for two-phase flow and transport processes, formation geometry, formation heterogeneity, and formation porosity. The space and time domains used to define capacity must be chosen with care to obtain meaningful results, especially when comparing different authors' work. Physical factors that impact capacity include permeability anisotropy and relative permeability to CO{sub 2}, brine/CO{sub 2} density and viscosity ratios, the shape of the trapping structure, formation porosity and the presence of low-permeability layering.
Date: May 1, 2001
Creator: Doughty, Christine; Pruess, Karsten; Benson, Sally M.; Hovorka, Susan D.; Knox, Paul R. & Green, Christopher T.
Partner: UNT Libraries Government Documents Department

Preliminary Geologic Characterization of West Coast States for Geologic Sequestration

Description: Characterization of geological sinks for sequestration of CO{sub 2} in California, Nevada, Oregon, and Washington was carried out as part of Phase I of the West Coast Regional Carbon Sequestration Partnership (WESTCARB) project. Results show that there are geologic storage opportunities in the region within each of the following major technology areas: saline formations, oil and gas reservoirs, and coal beds. The work focused on sedimentary basins as the initial most-promising targets for geologic sequestration. Geographical Information System (GIS) layers showing sedimentary basins and oil, gas, and coal fields in those basins were developed. The GIS layers were attributed with information on the subsurface, including sediment thickness, presence and depth of porous and permeable sandstones, and, where available, reservoir properties. California offers outstanding sequestration opportunities because of its large capacity and the potential of value-added benefits from enhanced oil recovery (EOR) and enhanced gas recovery (EGR). The estimate for storage capacity of saline formations in the ten largest basins in California ranges from about 150 to about 500 Gt of CO{sub 2}, depending on assumptions about the fraction of the formations used and the fraction of the pore volume filled with separate-phase CO{sub 2}. Potential CO{sub 2}-EOR storage was estimated to be 3.4 Gt, based on a screening of reservoirs using depth, an API gravity cutoff, and cumulative oil produced. The cumulative production from gas reservoirs (screened by depth) suggests a CO{sub 2} storage capacity of 1.7 Gt. In Oregon and Washington, sedimentary basins along the coast also offer sequestration opportunities. Of particular interest is the Puget Trough Basin, which contains up to 1,130 m (3,700 ft) of unconsolidated sediments overlying up to 3,050 m (10,000 ft) of Tertiary sedimentary rocks. The Puget Trough Basin also contains deep coal formations, which are sequestration targets and may have potential for enhanced ...
Date: September 29, 2005
Creator: Myer, Larry; Downey, Cameron; Clinkenbeard, John; Thomas, Steven; Stevens, Scott; Benson, Sally et al.
Partner: UNT Libraries Government Documents Department

Vadose Zone Remediation of CO2 Leakage from Geologic CO2 Storage Sites

Description: In the unlikely event that CO2 leakage from deep geologic CO2 sequestration sites reaches the vadose zone, remediation measures for removing the CO2 gas plume may have to be undertaken. Carbon dioxide leakage plumes are similar in many ways to volatile organic compound (VOC) vapor plumes, and the same remediation approaches are applicable. We present here numerical simulation results of passive and active remediation strategies for CO2 leakage plumes in the vadose zone. The starting time for the remediation scenarios is assumed to be after a steady-state CO2 leakage plume is established in the vadose zone, and the source of this plume has been cut off. We consider first passive remediation, both with and without barometric pumping. Next, we consider active methods involving extraction wells in both vertical and horizontal configurations. To compare the effectiveness of the various remediation strategies, we define a half-life of the CO2 plume as a convenient measure of the CO2 removal rate. For CO2 removal by passive remediation approaches such as barometric pumping, thicker vadose zones generally require longer remediation times. However, for the case of a thin vadose zone where a significant fraction of the CO2 plume mass resides within the high liquid saturation region near the water table, the half-life of the CO2 plume without barometric pumping is longer than for somewhat thicker vadose zones. As for active strategies, results show that a combination of horizontal and vertical wells is the most effective among the strategies investigated, as the performance of commonly used multiple vertical wells was not investigated.
Date: March 3, 2004
Creator: Zhang, Yingqi; Oldenburg, Curtis M. & Benson, Sally M.
Partner: UNT Libraries Government Documents Department

Hydrological and geochemical monitoring for a CO2 sequestration pilot in a brine formation

Description: Hydrological and geochemical monitoring are key components of site characterization and CO2 plume monitoring for a pilot test to inject CO2 into a brine-bearing sand of the fluvial-deltaic Frio formation in the upper Texas Gulf Coast. In situ, injected CO2 forms a supercritical phase that has gas-like properties (low density and viscosity) compared to the surrounding brine, while some CO2 dissolves in the brine. The pilot test employs one injection well and one monitor well, with continuous pressure and flow-rate monitoring in both wells, and continuous surface fluid sampling and periodic down-hole fluid sampling from the monitor well. Pre-injection site-characterization includes pump tests with pressure-transient analysis to estimate single-phase flow properties, establish hydraulic connectivity between the wells, determine appropriate boundary conditions, and analyze ambient phase conditions within the formation. Additionally, a pre-injection tracer test furnishes estimates of kinematic porosity and the geometry of flow paths between injection and monitor wells under single-phase conditions. Pre-injection geochemical sampling provides a baseline for subsequent geochemical monitoring and helps determine the optimal tracers to accompany CO2 injection. During CO2 injection, hydrological monitoring enables estimation of two-phase flow properties and helps track the movement of the injected CO2 plume, while geochemical sampling provides direct evidence of the arrival of CO2 and tracers at the monitor well. Furthermore, CO2-charged water acts as a weak acid, and reacts to some extent with the minerals in the aquifer, producing a distinct chemical signature in the water collected at the monitor well. Comparison of breakthrough curves for the single-phase tracer test and the CO2 (and its accompanying tracers) illuminates two-phase flow processes between the supercritical CO2 and native brine, an area of current uncertainty that must be better understood to effectively sequester CO2 in saline aquifers.
Date: May 17, 2004
Creator: Doughty, Christine; Pruess, Karsten; Benson, Sally M.; Freifeld, Barry M. & Gunter, William D.
Partner: UNT Libraries Government Documents Department