| Abstract |
One of the first steps in geothermal project development is to perform a geothermal resource assessment. This resource assessment is necessary to decide if the geothermal resource can be successful and sustainably developed. Generally, geothermal resources are classified in two main categories: conduction and convection dominated type plays. In the Netherlands only conductive dominant plays are present and utilized for geothermal heat production. In the Netherlands, Dinantian carbonate reservoirs are considered to have a high potential for geothermal development. However, during the early exploration phase no validated resource assessment method is currently available for naturally fractured geothermal systems, such as these carbonate reservoirs. This study presents a newly developed resource assessment method for carbonate reservoirs. In order to develop a new resource assessment method, three existing methods are reviewed. The methods are evaluated based on their applicability for naturally fractured geothermal systems in the Netherlands. The three methodologies evaluated are: the volumetric method (Muffler & Cataldi, 1978), power density method (Cumming, 2016) and DoubletCalc (Mijnlieff et al., 2014). Since the power density method only includes high enthalpy settings, the database is extended and the power density plot updated with data from low enthalpy geothermal projects. A workflow was created to obtain insight in the parameters which influence the fracture-dominated reservoir potential. With the insights of the workflow and inspired by the currently existing resource assessment methods, two new methods for fracture dominated geothermal reservoirs are developed and tested: the recovery factor method and the probability of success (POS) method. Since in the early exploration insufficient data is available to develop a numerical model, a qualitative approach was chosen. Especially the POS method appears to be a promising tool for resource evaluation during the early exploration phase of a geothermal project. This qualitative POS is based on scoring tables, which makes risk quantification standardized and less biased by individual expert opinion. Also, geothermal projects under development can be compared based on their geological risk in a consistent way. Because the POS can be determined relatively fast and is understandable for most parties involved in the development of a geothermal project, the POS is still of value in later stages of the project. The new method is tested based on conceptual geological models and a real project, however it should be tested empirically in the future for validation. |