TOWARDS DEVELOPING A CALIBRATED EGS EXPLORATION METHODOLOGY USING THE DIXIE VALLEY GEOTHERMAL SYSTEM, NEVADA

摘要

A calibrated Engineered Geothermal System (EGS) exploration methodology is being developed using the Dixie Valley Geothermal Wellfield (DVGW) and its surroundings in central Nevada as a laboratory test site. The DVGW was chosen because in the public domain, it is a highly characterized Basin and Range site with considerable geoscience and well data. This paper presents the qualitative and quantitative geoscience assessment used to develop a baseline geothermal system conceptual model based on existing available data. This assessment includes the integration of geophysical, geological, and geochemical data sets coupled with subject matter expertise (SME), and geostatistical exploratory data analysis (EDA). The baseline model is then used to generate paired EGS favorability and trust maps from the integrated evaluation of the following three principal EGS parameters of interest: temperature, rock type, and stress, at depths from +1km to -4km above sea level. Trust maps provide a data reliability indicator. When coupled, the two maps provide an EGS favorability determination, a SME evaluation of the reliability of the underlying data used in this determination, and an indication where additional data may be required. For example, an area could be mapped as being highly favorable but the underlying supporting data used in the favorability determination is of low reliability. Statistical relationships among select geoscience parameters are also described. In part, these relationships have provided insight into which geoscience parameters may be used as a predictor of subsurface temperature and rock type. Calibration of the exploration assessment methodology is based on the cross-correlation of the aforementioned findings with known well results. This paper builds upon the progress report provided in Iovenitti et al. (2011a, 2011b) and presents additional details of the geoscience assessment, EDA, and baseline EGS favorability/trust maps. Finally, much of the data and the approach presented herein are also applicable to the exploration/development of the hydrothermal component of the geothermal system.