Development of Models to Simulate Tracer Tests for Characterization of Enhanced Geothermal Systems

Abstract

A comprehensive 2006 Massachusetts Institute of Technology (MIT) report found that electrical power derived from engineered (or enhanced) geothermal systems (EGSs) "represents a large, indigenous resource that could provide base-load electric power and heat that can have a major impact on the United States, while incurring minimal environmental impacts." EGS resources differ from high-grade hydrothermal resources in that they lack sufficient temperature distribution, permeability/porosity, fluid saturation, or recharge of reservoir fluids. Therefore, quantitative characterization of temperature distributions and the surface area available for heat transfer in EGS is necessary for the design and commercial development of the geothermal energy of a potential EGS site. The goal of this project is to provide integrated tracer and tracer interpretation tools to facilitate this characterization. This project was initially focused on tracer development with the application of perfluorinated tracer (PFT) compounds, non-reactive tracers used in numerous applications from atmospheric transport to underground leak detection, to geothermal systems, and evaluation of encapsulated PFTs that would release tracers at targeted reservoir temperatures. After the 2011 midyear project review and subsequent discussions with the U.S. Department of Energy Geothermal Technology Program, emphasis was shifted to interpretive tool development, testing, and validation. Subsurface modeling capabilities are an important component of this project for both the design of suitable tracers and the interpretation of data from in situ tracer tests, be they single-or multi-well tests.This project was a collaborative effort between Brookhaven National Laboratory (BNL), Los Alamos National Laboratory (LANL), Pacific Northwest National Laboratory (PNNL), and the Energy and Geoscience Institute (EGI) at the University of Utah. The project covered a wide array of activities including bench-scale testing of tracers, numerical modeling, interpretation of existing tracer tests, and design and conducting field tracer tests at a demonstration EGS site. The initial PFT development was led by BNL along with high temperature column studies by LANL. Various numerical models described in this study were applied by PNNL and LANL to bench-scale batch and column testing results of conservative and reactive tracers with different mineralogy, temperature regimes, and flow rates. These models were also used to 1) analyze an existing field reactive and conservative tracer test data set at a naturally fractured geothermal site at Soda Lake, Nevada, and 2) design the reactive and conservative tracer tests for an EGS demonstration site near Newberry Crater, Oregon, that was led by Alta Rock Energy, Inc. PNNL and EGI led tracer testing operations during this EGS demonstration that was conducted from October to December 2012. The numerical models developed under this project for the Newberry Crater EGS test will provide a useful tool for interpreting tracer test respon...

Inert and Adsorptive Tracer Tests for Field Measurement of Flow‐Wetted Surface Area

“…Vetter and Crichlow (1979) proposed the use of an adsorbing tracer to overcome limitations of inert tracer tests in the context of geothermal reservoirs. Since then, numerous investigations into practical application of the method have been met with disappointing results (e.g., Breitenbach, 1982;Dean et al, 2015;Horne et al, 1982;Vetter & Zinnow, 1981;Williams et al, 2010Williams et al, , 2013. Broadly, three reasons accounted for the method's failure: (1) poorly constrained reaction parameters; (2) incomplete models for adsorption; and (3) complex fracture fluid/matrix interactions (e.g., Fox & Horne, 1988;Pot & Genty, 2005;Reimus & Callahan, 2007;Reimus et al, 2003;Sullivan et al, 2003;Toride et al, 1993Toride et al, , 1995Vetter & Zinnow, 1981).…”

“…In the study by Dean et al (), for instance, lithium and cesium appeared to exhibit dual‐porosity behavior at high temperature in a column specifically designed to have single‐porosity. In the study by Williams et al (), the adsorptive tracer method failed to adequately constrain reservoir properties at the Soda Lake Geothermal Field near Fallon, Nevada. Field measurements did indicate the adsorbing tracer experienced reduced mass recovery relative to an inert tracer.…”

Flume Experiments for Optimizing the Hydraulic Performance of a Deep-Water Wetland Utilizing Emergent Vegetation and Obstructions

“…Each test case was repeated three times to ensure the repeatability of the results. The concentration based on the measurements from the automatic recording detector was calculated using Equation (7) to derive the measured total amount of the fluorescence agent, thus enabling the recovery rate of the tracers to be calculated [15]:…”

Enhanced geothermal systems

“…The traditional means for studying transport processes in porous media are breakthrough studies where a tracer is injected at one well and extracted at another well; such studies are well described in the literature (e.g. [55,56,57]). These experiments are typically several days to a week in length and give at best an average characterization of a heterogenous medium, so it is important to consider faster methods as well as methods with more spatial resolution for characterizing the reservoir.…”