Development, Analysis, And Application Of A Well By Well Method For Estimating Surface Heat Flow For Regional Geothermal Resource Assessment

The potential to utilize widespread low-grade geothermal resources of the Northeastern U.S. for thermal direct use and combined heat and power applications can be realized using technologies embodied in Enhanced Geothermal Systems (EGS). In lower grade regions, accurate knowledge of small variations in temperature gradient will be crucial to the economic viability of EGS development. To accurately map local temperature variations, resource assessments have relied largely on bottom hole temperature (BHT) measurements, primarily from oil and gas wells. As the volume of BHT data grows due to increased drilling activity, the ability to quickly analyze and incorporate additional data is critical. To accomplish this task, a thermal model was developed that is a refined and streamlined version of work previously started at Southern Methodist University (SMU) to map out the heat flow of the entire nation. The model developed for this work expands on their contributions and makes it much easier to incorporate the large amounts of data collected. Also, by being developed in Visual Basic for Applications, an Excel add-on, it is hoped that the model will help researchers at all levels of academia, government, and private industry look to EGS as a possible energy source. In order to facilitate EGS project placement and design, the model was used to draw a more complete picture of geothermal resources in the Northeastern United States, with a particular focus on New York and Pennsylvania, by incorporating thousands of new temperature-depth data collected as a result of continuing drilling for unconventional natural gas in the region. This project follows the entire evolution of an organic geothermal resource study from data collection to map production. Well data in the form of archived oil and gas well logs were collected from SMU, the Pennsylvania Geological Survey, the New York State Museum, and the New York State Department of Environ- mental Conservation. Using these new data, a series of maps covering the Appalachian Basin of New York and Pennsylvania were produced that show variations in subsurface thermal gradient and surface heat flow. The increased spatial accuracy and resolution compared to earlier geothermal maps of the Northeast U.S. illuminate better spatial variations in the resource quality and have a much smaller degree of uncertainty in both extent and magnitude. The maps indicate that the temperatures required for direct-use applications are available at technically viable drilling depths over a majority of the region. Smaller hot spot areas of higher than average heat flow are found in the Pennsylvania counties of Indiana, McKean, Lawrence, and Warren, as well as Cayuga County in New York. These anomalies represent the most ideal candidates for further exploration and characterization of their EGS potential. The model was then subjected to rigorous uncertainty analysis using Oracle Crystal Ball, a commercially available Monte Carlo simulator. This work integrated increasing complexity in the sedimentary cover of the Appalachian basin to test the precision of the predicted temperature at 6 km under Steuben County, NY. The results indicate that while the model does have inherent limitations that the user must be mindful of, it predicts temperature to a degree of precision and accuracy that is reasonable given its original purpose of incorporating very large datasets in an efficient manner