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Assessing fracture network connectivity of prefeasibility-level high temperature geothermal projects using discrete fracture network modelling Mak, Stephen W.

Abstract

The Meager Creek geothermal anomaly has been identified as one of Canada’s most promising high temperature geothermal sites. Results from exploratory drilling and the presence of natural hot springs indicate that a convective hydrothermal system exists within the crystalline basement rocks at the site. These positive results prompted several companies to engage in production drilling campaigns as early as 1981. To date, all attempts to establish sustainable levels of geothermal fluid production have been unsuccessful. Low permeability and poor hydraulic connectivity of the basement granodiorites are often cited as the key geological factors limiting the development of the Meager Creek site. These conclusions are inferred from qualitative assessments of core samples and the low production yields of completed test wells, and are not based on a detailed analysis of the geometric properties of the underlying fracture network. Through the interpretation and analysis of geomechanical and hydrogeological data collected during historical field investigations at the site, stochastic discrete fracture network (DFN) models were constructed. An iterative process of simulation and analysis of individual DFN models led to a rigorous assessment of the existing connectivity of the natural fracture network. The connectivity of the existing fracture network at the Meager Creek site appears to be favourable in the area surrounding the Meager Creek Fault, which was not intersected by any of the test wells drilled. It was found that the use of DFN models was useful in estimating fracture network connectivity and can serve as a tool for optimizing the location and orientation of production wells. A high degree of uncertainty is associated with fracture network connectivity estimates due to the absence of downhole linear fracture intensity measurements and a rigorous surface mapping methodology. Fracture network connectivity estimates can be greatly improved by adjusting the design of prefeasibility-level field investigations. The additional cost and time required to incorporate these adjustments into standard prefeasibility-level geothermal field investigations is minimal.

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Attribution-NonCommercial-NoDerivs 2.5 Canada

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