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Thermal single-well injection-withdrawal tracer tests for determining fracture-matrix heat transfer area

Description: Single-well injection-withdrawal (SWIW) tracer tests involve injection of traced fluid and subsequent tracer recovery from the same well, usually with some quiescent time between the injection and withdrawal periods. SWIW are insensitive to variations in advective processes that arise from formation heterogeneities, because upon withdrawal, fluid parcels tend to retrace the paths taken during injection. However, SWIW are sensitive to diffusive processes, such as diffusive exchange of conservative or reactive solutes between fractures and rock matrix. This paper focuses on SWIW tests in which temperature itself is used as a tracer. Numerical simulations demonstrate the sensitivity of temperature returns to fracture-matrix interaction. We consider thermal SWIW response to the two primary reservoir improvements targeted with stimulation, (1) making additional fractures accessible to injected fluids, and (2) increasing the aperture and permeability of pre-existing fractures. It is found that temperature returns in SWIW tests are insensitive to (2), while providing a strong signal of more rapid temperature recovery during the withdrawal phase for (1).
Date: January 15, 2010
Creator: Pruess, K. & Doughty, C.
Partner: UNT Libraries Government Documents Department

Oil Recovery Increases by Low-Salinity Flooding: Minnelusa and Green River Formations

Description: Waterflooding is by far the most widely used method in the world to increase oil recovery. Historically, little consideration has been given in reservoir engineering practice to the effect of injection brine composition on waterflood displacement efficiency or to the possibility of increased oil recovery through manipulation of the composition of the injected water. However, recent work has shown that oil recovery can be significantly increased by modifying the injection brine chemistry or by injecting diluted or low salinity brine. This paper reports on laboratory work done to increase the understanding of improved oil recovery by waterflooding with low salinity injection water. Porous media used in the studies included outcrop Berea sandstone (Ohio, U.S.A.) and reservoir cores from the Green River formation of the Uinta basin (Utah, U.S.A.). Crude oils used in the experimental protocols were taken from the Minnelusa formation of the Powder River basin (Wyoming, U.S.A.) and from the Green River formation, Monument Butte field in the Uinta basin. Laboratory corefloods using Berea sandstone, Minnelusa crude oil, and simulated Minnelusa formation water found a significant relationship between the temperature at which the oil- and water-saturated cores were aged and the oil recovery resulting from low salinity waterflooding. Lower aging temperatures resulted in very little to no additional oil recovery, while cores aged at higher temperatures resulted in significantly higher recoveries from dilute-water floods. Waterflood studies using reservoir cores and fluids from the Green River formation of the Monument Butte field also showed significantly higher oil recoveries from low salinity waterfloods with cores flooded with fresher water recovering 12.4% more oil on average than those flooded with undiluted formation brine.
Date: September 1, 2010
Creator: Robertson, Eric P.
Partner: UNT Libraries Government Documents Department

Two-Stage, Integrated, Geothermal-CO2 Storage Reservoirs: An Approach for Sustainable Energy Production, CO2-Sequestration Security, and Reduced Environmental Risk

Description: We introduce a hybrid two-stage energy-recovery approach to sequester CO{sub 2} and produce geothermal energy at low environmental risk and low cost by integrating geothermal production with CO{sub 2} capture and sequestration (CCS) in saline, sedimentary formations. Our approach combines the benefits of the approach proposed by Buscheck et al. (2011b), which uses brine as the working fluid, with those of the approach first suggested by Brown (2000) and analyzed by Pruess (2006), using CO{sub 2} as the working fluid, and then extended to saline-formation CCS by Randolph and Saar (2011a). During stage one of our hybrid approach, formation brine, which is extracted to provide pressure relief for CO{sub 2} injection, is the working fluid for energy recovery. Produced brine is applied to a consumptive beneficial use: feedstock for fresh water production through desalination, saline cooling water, or make-up water to be injected into a neighboring reservoir operation, such as in Enhanced Geothermal Systems (EGS), where there is often a shortage of a working fluid. For stage one, it is important to find economically feasible disposition options to reduce the volume of brine requiring reinjection in the integrated geothermal-CCS reservoir (Buscheck et al. 2012a). During stage two, which begins as CO{sub 2} reaches the production wells; coproduced brine and CO{sub 2} are the working fluids. We present preliminary reservoir engineering analyses of this approach, using a simple conceptual model of a homogeneous, permeable CO{sub 2} storage formation/geothermal reservoir, bounded by relatively impermeable sealing units. We assess both the CO{sub 2} sequestration capacity and geothermal energy production potential as a function of well spacing between CO{sub 2} injectors and brine/CO{sub 2} producers for various well patterns and for a range of subsurface conditions.
Date: February 2, 2012
Creator: Buscheck, T A; Chen, M; Sun, Y; Hao, Y & Elliot, T R
Partner: UNT Libraries Government Documents Department

Report on the U.S. DOE Geothermal Technologies Program's 2009 Risk Analysis

Description: NREL conducted an annual program risk analysis on behalf of the U.S. Department of Energy Geothermal Technologies Program (GTP). NREL implemented a probabilistic risk analysis of GTP-sponsored research, development, and demonstration (RD&D) work, primarily for enhanced geothermal systems (EGS). The analysis examined estimates of improvement potential derived from program RD&D work for two types of technology performance metric (TPM): EGS-enabling technologies potential and EGS cost improvement potential. Four risk teams (exploration, wells/pumps/tools, reservoir engineering, and power conversion) comprised of industry experts, DOE laboratory researchers, academic researchers, and laboratory subcontractors estimated the RD&D impacts and TPM-improvement probability distributions. The assessment employed a risk analysis spreadsheet add-in that uses Monte Carlo simulation to drive the Geothermal Electric Technology Evaluation Model (GETEM). The GETEM-based risk analysis used baseline data from the experts' discussion of multiple reports and data sources. Risk results are expressed in terms of each metric's units and/or the program's top-level metric: levelized costs of electricity (LCOE). Results--both qualitative comments and quantitative improvement potential--are thorough and cohesive in three of the four expert groups. This conference paper summarizes the industry's current thinking on various metrics and potential for research improvement in geothermal technologies.
Date: February 1, 2010
Creator: Young, K. R.; Augustine, C. & Anderson, A.
Partner: UNT Libraries Government Documents Department

Development of Direct-Use Projects: Preprint

Description: A geothermal direct-use project utilizes a natural resource, a flow of geothermal fluid at elevated temperatures, which is capable of providing heat and/or cooling to buildings, greenhouses, aquaculture ponds, and industrial processes. Geothermal utilization requires matching the varied needs of the user and characteristics of the resource in order to development a successful project. Each application is unique; guidelines are provided for the logical steps required to implement a project. Recommended temperature and flows are suggested for spas and pools, space and district heating, greenhouse and aquaculture pond heating, and industrial applications. Guidelines are provided for selecting the necessary equipment for successfully implementing a direct-use project, including downhole pumps, piping, heat exchangers, and heat convectors. Additionally, the relationship between temperature, flow rate, and the use of heat exchangers to provide heat to a space with hot water or hot air is provided for a number of applications, with suggested 'rules of thumb'.
Date: January 1, 2011
Creator: Lund, J.
Partner: UNT Libraries Government Documents Department

The Role of Low-Angle Extensional Tectonics, Flat Fracture Domains, and Gravity Slides in Hydrothermal and EGS Resources of the Western United States

Description: The Steamboat Springs geothermal system provides the most dramatic example of subhorizontal thermal-fluid aquifers in crystalline rock in the Basin and Range, but this is by no means an isolated case. Similar but more diffuse subhorizontal permeability has been reported at Roosevelt Hot Springs and Cove-Fort Sulphurdale, Utah; and a km-scale gravity-slide block channels injectate at Dixie Valley, Nevada. During the course of this phase of the project 2543 reports including text, figures and large format enclosures, 1428 maps, and 698 well logs were scanned. The information is stored in a Microsoft Access Database on the Geothermal Server. Detailed geologic cross sections of the Desert Peak geothermal field were developed to identify the structural controls on the geothermal system and locate possible fluid flow paths. The results of this work were published by Lutz and others (2009, Appendix 1) in the Stanford Reservoir Engineering Conference Proceedings.
Date: August 24, 2011
Creator: Moore, Joseph
Partner: UNT Libraries Government Documents Department

Mapping Diffuse Seismicity Using Empirical Matched Field Processing Techniques

Description: The objective of this project is to detect and locate more microearthquakes using the empirical matched field processing (MFP) method than can be detected using only conventional earthquake detection techniques. We propose that empirical MFP can complement existing catalogs and techniques. We test our method on continuous seismic data collected at the Salton Sea Geothermal Field during November 2009 and January 2010. In the Southern California Earthquake Data Center (SCEDC) earthquake catalog, 619 events were identified in our study area during this time frame and our MFP technique identified 1094 events. Therefore, we believe that the empirical MFP method combined with conventional methods significantly improves the network detection ability in an efficient matter.
Date: January 21, 2011
Creator: Wang, J; Templeton, D C & Harris, D B
Partner: UNT Libraries Government Documents Department

DOE 2009 Geothermal Risk Analysis: Methodology and Results

Description: This presentation summarizes the methodology and results for a probabilistic risk analysis of research, development, and demonstration work-primarily for enhanced geothermal systems (EGS)-sponsored by the U.S. Department of Energy Geothermal Technologies Program.
Date: February 1, 2010
Creator: Young, K. R.; Augustine, C. & Anderson, A.
Partner: UNT Libraries Government Documents Department