Marcelo J. Lippmann

State of the art of geothermal reservoir simulation

Computer modeling of geothermal systems has become a mature technology with application to more than 100 fields world-wide. Large complex three-dimensional models having computational meshes with more than 4000 blocks are now used routinely. Researchers continue to carry out fundamental research on modeling techniques and physical processes in geothermal systems. The new advances are adopted quickly by the geothermal industry and have also found application in related areas such as nuclear waste storage, environmental remediation and studies of the vadose (unsaturated) zone. The current state-of-practice, recent advances and emerging trends in geothermal reservoir simulation are reviewed.

MODELING OF GEOTHERMAL SYSTEMS

During the last decade the use of numerical modeling for geothermal resource evaluation has grown significantly, and new modeling approaches have been developed. In this paper we present a summary of the present status in numerical modeling of geothermal systems, emphasizing recent developments. Different modeling approaches are described and their applicability discussed. The various modeling tasks, including natural-state, exploitation, injection, multi-component and subsidence modeling, are illustrated with geothermal field examples. 99 refs., 14 figs.

A review of the hydrogeologic-geochemical model for Cerro Prieto

Abstract With continued exploitation of the Cerro Prieto, Mexico, geothermal field, there is increasing evidence that the hydrogeologic model developed by Halfman and co-workers presents the basic features controlling the movement of geothermal fluids in the system. In mid–1987 the total installed capacity at Cerro Prieto reached 620 MW c , requiring a large rate of fluid production (more than 10,500 tonnes/hr of a brine-steam mixture; August 1988). This significant mass extraction has led to changes in reservoir thermodynamic conditions and in the chemistry of the produced fluids. Pressure drawdown has caused an increase in cold water recharge in the southern and western edges of the field, and local and general reservoir boiling in parts of the geothermal system. After reviewing the hydrogeologic and geochemical models of Cerro Prieto, the exploitation-induced cold water recharge and reservoir boiling (and plugging) observed in different areas of the field, are discussed and interpreted on the basis of these models and schematic flow models that describe the hydrogeology.

Pre-exploitation state of the ahuachapán geothermal field, el salvador

Abstract The lithology and structural features of the Ahuachapan geothermal area and their impact on the movement of cold and hot fluids within the system are described, as well as the development and evaluation of the natural state model of the field. Four major lithologic units are present in Ahuachapan and three major aquifers have been identified; flow patterns and zones of fluid mixing were located on the basis of temperature and geochemical data from wells and surface manifestations. Geologic structures control the heat and fluid recharge and the flow within the reservoir. Modeling studies suggest, in agreement with field data, an overall average transmissivity of 25–35 darcy-meters, and indicate that the system is recharged by waters with temperatures greater than 250°C. The total thermal throughflow for the Ahuachapan reservoir in the unexploited state is estimated to be about 250 MW t .

Exploration and Development of the Cerro Prieto Geothermal Field

A multidisciplinary effort to locate, delineate, and characterize the geothermal system at Cerro Prieto field, Baja California, Mexico, began in the late 1950s. It led to the identification of an important high-temperature, liquid-dominated geothermal system which went into production in 1973. This paper summarizes and discusses the exploration and monitoring studies related to this field.

An exploitation model and performance predictions for the Ahuachapan Geothermal field, El Salvador

The Ahuachapan geothermal field in El Salvador has been producing electrical power since 1975. The field currently produces at only about 50 percent of the installed capacity of 95MWe. The reasons for this low power production include a 1WF reservoir Presdrawdown and limited drilling of make-up wells. J: * The focus of &ssrudy is to develop means for inmasing the power production over the next 30 years. One possible option is to devise an injection scheme to &crease the pressure decline and the energy

Improved Energy Recovery From Geothermal Reservoirs

Numerical simulation methods are used to study how the exploitation of different horizons affects the behavior of a liquid-dominated geothermal reservoir. The reservoir model is a schematic representation of the Olkaria field in Kenya. The model consists of a two-phase vapor-dominated zone overlying the main liquid dominated reservoir. Four different cases were studied, with fluid produced from: 1) the vapor zone only, 2) the liquid zone only, 3) both zones and 4) both zones, but assuming lower values for vertical permeability and porosity. The results indicate that production from the shallow two-phase zone, although resulting in higher enthalpy fluids, may not be advantageous in the long run. Shallow production gives rise to a rather localized depletion of the reservoir, whereas production from deeper horizons may yield a more uniform depletion proces, if vertical permeability is sufficiently large.

GEO-SEQ Best Practices Manual. Geologic Carbon Dioxide Sequestration: Site Evaluation to Implementation

LBNL-56623 GEO-SEQ Best Practices Manual Geologic Carbon Dioxide Sequestration: Site Evaluation to Implementation GEO-SEQ Project Team Lawrence Berkeley National Laboratory, Lawrence Livermore National Laboratory, Oak Ridge National Laboratory, Stanford University, University of Texas Bureau of Economic Geology, Alberta Research Council September 30, 2004 Earth Sciences Division Ernest Orlando Lawrence Berkeley National Laboratory Berkeley, CA 94720 This work was supported by the Assistant Secretary for Fossil Energy, Office of Coal and Power Systems, of the U.S. Department of Energy (DOE) under Contract No. DE-AC03-76SF00098.

Health, Safety and Environmental Risk Assessment for Geologic Storage of Carbon Dixide: Lessons Learned from Industrial and Natural Analogues

Publisher Summary A study has been conducted to gather and interpret information regarding potential approaches for assessing, managing and mitigating risks associated with the deep geologic storage of CO2. Information was gathered from two principle sources: industrial analogues such as natural gas storage, deep injection of hazardous wastes, and nuclear waste storage, and natural analogues (especially those with CO2 leaks at the surface). For the industrial analogues, the following were evaluated: history, status and scope of the activity; risk assessment framework and methods; including key issues, performance specifications and performance assessment methods; risk management approaches, including regulatory oversight and permitting; site characterization methods; risk mitigation and remediation methods employed or planned in the event that performance specifications are not met or other unintended consequences arise; and case studies documenting responses to historical situations. Information about natural analogues for surface leakage of CO2 were reviewed and evaluated in light of what is known about human and ecological impacts of exposure to elevated concentrations of CO2. A set of lessons learned from these analogues was compiled, which forms the basis for recommendations in the areas of risk assessment framework and methodology, risk management approaches, and risk mitigation and remediation methods. This chapter reviews the lessons learned and also provides recommendations for additional research.

A History of Geothermal Energy Research and Development in the United States. Reservoir Engineering 1976-2006

This report, the third in a four-part series, summarizes significant research projects performed by the U.S. Department of Energy (DOE) over 30 years to overcome challenges in reservoir engineering and to make generation of electricity from geothermal resources more cost-competitive.