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in creator/contributor: "Pruess, Karsten"

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Proximity functions for modeling fluids and heat flow in reservoirs with stochastic fracture distributions

Conventional approaches to geothermal reservoir modeling have employed a porous medium approximation, but recently methods have been developed which can take into account the different thermodynamic conditions in rock matrix and fractures. The multiple interacting continua method (MINC) treats the thermal and hydraulic interaction between rock matrix and fractures in terms of a set of geometrical parameters. However, this approach was restricted to idealized fracture distributions with regularl… more

Date: October 1982

Creator: Pruess, Karsten & Karasaki, Kenzi

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Role of Fluid Pressure in the Production Behavior of EnhancedGeothermal Systems with CO2 as Working Fluid

Numerical simulation is used to evaluate mass flow and heatextraction rates from enhanced geothermal injection-production systemsthat are operated using either CO2 or water as heat transmission fluid.For a model system patterned after the European hot dry rock experimentat Soultz, we find significantly greater heat extraction rates for CO2 ascompared to water. The strong dependence of CO2 mobility (=density/viscosity) upon temperature and pressure may lead to unusualproduction behavior, where h… more

Date: April 13, 2007

Creator: Pruess, Karsten

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Enhanced Geothermal Systems (EGS) comparing water with CO2 as heattransmission fluids

This paper summarizes our research to date into operatingEGS with CO2. Our modeling studies indicate that CO2 would achieve morefavorable heat extraction than aqueous fluids. The peculiarthermophysicalproperties of CO2 give rise to unusual features in the dependence ofenergy recovery on thermodynamic conditions and time. Preliminarygeochemical studies suggest that CO2 may avoid unfavorable rock-fluidinteractions that have been encountered in water-basedsystems. To morefully evaluate the potenti… more

Date: November 1, 2007

Creator: Pruess, Karsten

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Exploratory Simulation Studies of Caprock Alteration Induced byStorage of CO2 in Depleted Gas Reservoirs

This report presents numerical simulations of isothermalreactive flows which might be induced in the caprock of an Italiandepleted gas reservoir by the geological sequestration of carbon dioxide.Our objective is to verify that CO2 geological disposal activitiesalready planned for the study area are safe and do not induce anyundesired environmental impact.Gas-water-rock interactions have beenmodelled under two different intial conditions, i.e., assuming that i)caprock is perfectly sealed, or ii)… more

Date: November 23, 2005

Creator: Gherardi, Fabrizio; Xu, Tianfu & Pruess, Karsten

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Liquid-phase dispersion during injection into vapor-dominated reservoirs

The behavior of water injection plumes in vapor-dominated reservoirs is examined. Stressing the similarity to water infiltration in heterogeneous soils, we suggest that everpresent heterogeneities in individual fractures and fracture networks will cause a lateral broadening of descending injection plumes. The process of lateral spreading of liquid phase is viewed in analogy to transverse dispersion in miscible displacement. To account for the postulated “phase dispersion” the conventional two-p… more

Date: January 20, 1994

Creator: Pruess, Karsten

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Injection plume behavior in fractured, vapor-dominated reservoirs

We discuss fluid flow and heat transfer processes during water injection into hot, fluid-depleted vapor zones. Numerical simulations of injection plumes in fractures, modeled as two-dimensional heterogeneous porous media, indicate complex behavior. Under certain conditions it is possible to make detailed quantitative predictions of vaporization behavior. However, when effects of reservoir heterogeneity are dominant it will only be possible to predict the behavior of injection plumes in general … more

Date: January 24, 1996

Creator: Pruess, Karsten

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Grid orientation effects in the simulation of cold water injection into depleted vapor zones

Vapor-dominated geothermal reservoirs such as Larderello, Italy, and The Geysers, California, are fundamentally water-short systems. This is apparent from the relatively low pressures in the natural state, typically about 35 bars at 1000 m depth, which is much below hydrostatic pressures. It is also apparent from the high heat content of the produced fluids, typically superheated steam. Large-scale production from these systems has caused reservoir pressures and well flow rates to decline, lead… more

Date: January 1991

Creator: Pruess, Karsten

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Numerical studies of fluid-rock interactions in EnhancedGeothermal Systems (EGS) with CO2 as working fluid

There is growing interest in the novel concept of operating Enhanced Geothermal Systems (EGS) with CO{sub 2} instead of water as heat transmission fluid. Initial studies have suggested that CO{sub 2} will achieve larger rates of heat extraction, and can offer geologic storage of carbon as an ancillary benefit. Fluid-rock interactions in EGS operated with CO{sub 2} are expected to be vastly different in zones with an aqueous phase present, as compared to the central reservoir zone with anhydrous… more

Date: January 17, 2008

Creator: Xu, Tianfu; Pruess, Karsten & Apps, John

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Coupled modeling of non-isothermal multiphase flow, solutetransport and reactive chemistry in porous and fractured media: 1. ModelDevelopment and Validation

Coupled modeling of subsurface multiphase fluid and heat flow, solute transport and chemical reactions can be used for the assessment of acid mine drainage remediation, mineral deposition, waste disposal sites, hydrothermal convection, contaminant transport, and groundwater quality. Here they present a numerical simulation model, TOUGHREACT, which considers non-isothermal multi-component chemical transport in both liquid and gas phases. A wide range of subsurface thermo-physical-chemical proces… more

Date: September 1, 1998

Creator: Xu, Tianfu & Pruess, Karsten

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Multiphase fluid flow and subsequent geochemical transport invariably saturated fractured rocks: 1. Approaches

Reactive fluid flow and geochemical transport in unsaturated fractured rocks has received increasing attention for studies of contaminant transport, groundwater quality, waste disposal, acid mine drainage remediation, mineral deposits, sedimentary diagenesis, and fluid-rock interactions in hydrothermal systems. This paper presents methods for modeling geochemical systems that emphasize: (1) involvement of the gas phase in addition to liquid and solid phases in fluid flow, mass transport and che… more

Date: August 8, 2000

Creator: Xu, Tianfu & Pruess, Karsten

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Some effects of non-condensible gas in geothermal reservoirs with steam-water counterflow

A mathematical model is developed for fluid and heat flow in two-phase geothermal reservoirs containing non-condensible gas (CO{sub 2}). Vertical profiles of temperature, pressures and phase saturations in steady-state conditions are obtained by numerically integrating the coupled ordinary differential equations describing conservation of water, CO{sub 2}, and energy. Solutions including binary diffusion effects in the gas phase are generated for cases with net mass throughflow as well as for b… more

Date: January 1, 1988

Creator: McKibbin, Robert & Pruess, Karsten

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Numerical modeling of injection experiments at The Geysers

Data from injection experiments in the southeast Geysers are presented that show strong interference (both negative and positive) with a neighboring production well. Conceptual and numerical models are developed that explain the negative interference (decline of production rate) in terms of heat transfer limitations and water-vapor relative permeability effects. Recovery and overrecovery following injection shut-in are attributed to boiling of injected fluid, with heat of vaporization provided … more

Date: January 28, 1993

Creator: Pruess, Karsten & Enedy, Steve

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Numerical modeling of water injection into vapor-dominatedgeothermal reservoirs

Water injection has been recognized as a powerful techniquefor enhancing energy recovery from vapor-dominated geothermal systemssuch as The Geysers. In addition to increasing reservoir pressures,production well flow rates, and long-term sustainability of steamproduction, injection has also been shown to reduce concentrations ofnon-condensible gases (NCGs) in produced steam. The latter effectimproves energy conversion efficiency and reduces corrosion problems inwellbores and surface lines.This r… more

Date: November 6, 2006

Creator: Pruess, Karsten

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Numerical simulation experiments on the long-term evolution of a CO2 plume under a sloping caprock

We have used the TOUGH2-MP/ECO2N code to perform numerical simulation studies of the long-term behavior of CO{sub 2} stored in an aquifer with a sloping caprock. This problem is of great practical interest, and is very challenging due to the importance of multi-scale processes. We find that the mechanism of plume advance is different from what is seen in a forced immiscible displacement, such as gas injection into a water-saturated medium. Instead of pushing the water forward, the plume advance… more

Date: August 15, 2009

Creator: Pruess, Karsten

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Formation dry-out from CO2 injection into saline acquifers: Part 2, Analytical model for salt precipitation

From a mass balance for water dissolved into the flowing CO{sub 2} stream, and a consideration of saturation profiles from the Buckley-Leverett (1942) fractional flow theory, we derive an equation that directly relates gas saturation S{sub g,d} at the dry-out front to temperature, pressure and salinity dependence of fluid properties. The equation is easily solved by iteration or interpolation. From gas saturation at the front we derive the average gas saturation in the dry-out region, from whic… more

Date: February 1, 2009

Creator: Pruess, Karsten

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Effects of capillarity and vapor adsorption in the depletion of vapor-dominated geothermal reservoirs

Vapor-dominated geothermal reservoirs in natural (undisturbed) conditions contain water as both vapor and liquid phases. The most compelling evidence for the presence of distributed liquid water is the observation that vapor pressures in these systems are close to saturated vapor pressure for measured reservoir temperatures (White et al., 1971; Truesdell and White, 1973). Analysis of natural heat flow conditions provides additional, indirect evidence for the ubiquitous presence of liquid. From … more

Date: January 1, 1992

Creator: Pruess, Karsten & O'Sullivan, Michael

Item Type: Article

Partner: UNT Libraries Government Documents Department

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On Leakage from Geologic Storage Reservoirs of CO2

Large amounts of CO2 would need to be injected underground to achieve a significant reduction of atmospheric emissions. The large areal extent expected for CO2 plumes makes it likely that caprock imperfections will be encountered, such as fault zones or fractures, which may allow some CO2 to escape from the primary storage reservoir. Leakage of CO2 could also occur along wellbores. Concerns with escape of CO2 from a primary geologic storage reservoir include (1) acidification of groundwater res… more

Date: February 14, 2006

Creator: Pruess, Karsten

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Numerical simulation of CO2 leakage from a geologic disposal reservoir including transitions from super- to sub-critical conditions, and boiling of liquid of CO2

The critical point of CO{sub 2} is at temperature and pressure conditions of T{sub crit} = 31.04 C, P{sub crit} = 73.82 bar. At lower (subcritical) temperatures and/or pressures, CO{sub 2} can exist in two different phase states, a liquid and a gaseous state, as well as in two-phase mixtures of these states. Disposal of CO{sub 2} into brine formations would be made at supercritical pressures. However, CO{sub 2} escaping from the storage reservoir may migrate upwards towards regions with lower t… more

Date: March 31, 2003

Creator: Pruess, Karsten

Item Type: Report

Partner: UNT Libraries Government Documents Department

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TMVOC-MP: a parallel numerical simulator for Three-PhaseNon-isothermal Flows of Multicomponent Hydrocarbon Mixtures inporous/fractured media

TMVOC-MP is a massively parallel version of the TMVOC code (Pruess and Battistelli, 2002), a numerical simulator for three-phase non-isothermal flow of water, gas, and a multicomponent mixture of volatile organic chemicals (VOCs) in multidimensional heterogeneous porous/fractured media. TMVOC-MP was developed by introducing massively parallel computing techniques into TMVOC. It retains the physical process model of TMVOC, designed for applications to contamination problems that involve hydrocar… more

Date: February 15, 2008

Creator: Zhang, Keni; Yamamoto, Hajime & Pruess, Karsten

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Numerical Modeling of CO2 Sequestration in Geologic Formations - Recent Results and Open Challenges

Rising atmospheric concentrations of CO2, and their role inglobal warming, have prompted efforts to reduce emissions of CO2 fromburning of fossil fuels. An attractive mitigation option underconsideration in many countries is the injection of CO2 from stationarysources, such as fossil-fueled power plants, into deep, stable geologicformations, where it would be stored and kept out of the atmosphere fortime periods of hundreds to thousands of years or more. Potentialgeologic storage reservoirs inc… more

Date: March 8, 2006

Creator: Pruess, Karsten

Item Type: Article

Partner: UNT Libraries Government Documents Department

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On CO2 Behavior in the Subsurface, Following Leakage from a Geologic Storage Reservoir

The amounts of CO2 that would need to be injected intogeologic storage reservoirs to achieve a significant reduction ofatmospheric emissions are very large. A 1000 MWe coal-fired power plantemits approximately 30,000 tonnes of CO2 per day, 10 Mt per year(Hitchon, 1996). When injected underground over a typical lifetime of 30years of such a plant, the CO2 plume may occupy a large area of order 100km2 or more, and fluid pressure increase in excess of 1 bar(corresponding to 10 m water head) may ex… more

Date: February 9, 2006

Creator: Pruess, Karsten

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Numerical simulation of leakage from a geologic disposal reservoirfor CO2, with transitions between super- and sub-criticalconditions

The critical point of CO2 is at temperature and pressureconditions of Tcrit = 31.04oC, Pcrit = 73.82 bar. At lower (subcritical)temperatures and/or pressures, CO2 can exist in two different phases, aliquid and a gaseous state, as well as in two-phase mixtures of thesestates. Disposal of CO2 into brine formations would be made atsupercritical pressures. However, CO2 escaping from the storage reservoirmay migrate upwards towards regions with lower temperatures andpressures, where CO2 would be in … more

Date: April 13, 2003

Creator: Pruess, Karsten

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Modeling Supercritical Carbon Dioxide Injection in Heterogeneous Porous Media

We investigate the physical processes that occur during the sequestration of carbon dioxide (CO2) in liquid-saturated, brine-bearing geologic formations using the numerical simulator TOUGH2. CO2 is injected in a supercritical state that has a much lower density and viscosity than the liquid brine it displaces. In situ, the supercritical CO2 forms a gas-like phase, and also partially dissolves in the aqueous phase, creating a multi-phase, multi-component environment that shares many important fe… more

Date: April 10, 2003

Creator: Doughty, Christine & Pruess, Karsten

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Thermal Effects During CO2 Leakage from a Geologic Storage Reservoir

Leakage of CO2 from a geologic storage reservoir along an idealized fault zone has been simulated, including transitions between supercritical, liquid, and gaseous CO2. We find strong non-isothermal effects and nonmonotonic leakage behavior, due to an interplay between multiphase flow and heat transfer effects.

Date: June 30, 2004

Creator: Pruess, Karsten

Item Type: Article

Partner: UNT Libraries Government Documents Department