Maria Richards

Impact of enhanced geothermal systems on US energy supply in the twenty-first century

Recent national focus on the value of increasing US supplies of indigenous renewable energy underscores the need for re-evaluating all alternatives, particularly those that are large and well distributed nationally. A panel was assembled in September 2005 to evaluate the technical and economic feasibility of geothermal becoming a major supplier of primary energy for US base-load generation capacity by 2050. Primary energy produced from both conventional hydrothermal and enhanced (or engineered) geothermal systems (EGS) was considered on a national scale. This paper summarizes the work of the panel which appears in complete form in a 2006 MIT report, ‘The future of geothermal energy’ parts 1 and 2. In the analysis, a comprehensive national assessment of US geothermal resources, evaluation of drilling and reservoir technologies and economic modelling was carried out. The methodologies employed to estimate geologic heat flow for a range of geothermal resources were utilized to provide detailed quantitative projections of the EGS resource base for the USA. Thirty years of field testing worldwide was evaluated to identify the remaining technology needs with respect to drilling and completing wells, stimulating EGS reservoirs and converting geothermal heat to electricity in surface power and energy recovery systems. Economic modelling was used to develop long-term projections of EGS in the USA for supplying electricity and thermal energy. Sensitivities to capital costs for drilling, stimulation and power plant construction, and financial factors, learning curve estimates, and uncertainties and risks were considered.

Geothermal Resource Analysis and Structure of Basin and Range Systems, Especially Dixie Valley Geothermal Field, Nevada

Publish new thermal and drill data from the Dizie Valley Geothermal Field that affect evaluation of Basin and Range Geothermal Resources in a very major and positive way. Completed new geophysical surveys of Dizie Valley including gravity and aeromagnetics and integrated the geophysical, seismic, geological and drilling data at Dizie Valley into local and regional geologic models. Developed natural state mass and energy transport fluid flow models of generic Basin and Range systems based on Dizie Valley data that help to understand the nature of large scale constraints on the location and characteristics of the geothermal systems. Documented a relation between natural heat loss for geothermal and electrical power production potential and determined heat flow for 27 different geothermal systems. Prepared data set for generation of a new geothermal map of North American including industry data totaling over 25,000 points in the US alone.

Heat flow and thermal modeling of the Appalachian Basin, West Virginia

Recent heat flow studies indicate that the Appalachian Basin in West Virginia may represent an important location for high heat flow and future geothermal energy development. Currently, however, only limited one-dimensional (1-D) heat flow studies exist in this region, making it difficult to assess the potential for geothermal development. Here, we develop the first high resolution 2-D basin model for a portion of West Virginia. The model uses 2-D finite difference heat conduction, basin cross sections, equilibrium temperature, and oil and gas bottom-hole temperature data to quantify heat flow at the surface and at the base of the sedimentary basin. The temperature data show elevated temperature gradients in the eastern portion of the basin. A 2-D advection-diffusion model, created using available lithologic and structural data, was designed to test whether variations in crustal properties, structure, erosion, or fluid advection can account for the observed temperatures in the basin. Thermal properties were populated using measured values as well as published averages. A linear heat flow vs. heat production relationship was used to determine heat flow at the base of the model. The model constrains the heat flow at the base of the sedimentary basin to 49–55 mW/m 2 . Analysis of modeling results suggests that heat flow at the base of the sedimentary basin is nearly uniform. Variations in basin temperatures are most likely due to variations in sediment thermal properties, complex structures, and/or localized fluid advection.

Geothermal energy characterization in the Appalachian Basin of New York and Pennsylvania

Analysis of geothermal energy resources in the Appalachian Basin of the eastern United States is of interest, given the region’s population- and climate-driven demand for thermal energy. This study provides a fuller picture of geothermal resources across New York and Pennsylvania than previous studies by providing a rigorous statistical analysis of temperature-depth data using records from nearly 8000 locations. The compilation of thousands of temperature-depth data enables a significant increase in the spatial resolution of geothermal resource assessment maps for this region. In addition, this project has contributed to the compilation of geothermal data at a national level through the National Geothermal Data System. These temperature-depth measurements are byproducts of historical and recent drilling for petroleum and natural gas in the sedimentary basin. Bottom hole temperatures (BHTs) were recorded before the wells reached thermal equilibrium and at a wide range of depths. To extract a comprehensive description of the thermal state of the Appalachian Basin strata required application of both a BHT correction scheme and a simple thermal model. The model results for individual wells were combined with geostatistical interpolation employing kriging to produce maps that reveal significant variations in subsurface thermal gradient and surface heat flow with markedly improved spatial resolution. An area in south-central New York State displays favorable geothermal resource potential, with heat flow estimates of 50–60 mW/m 2 . There are 2 elongate, 200–300 km long, northeast-trending bands of favorable geothermal resource potential in central and western Pennsylvania, with heat flow of 55–90 mW/m 2 .