A new 'geothermal play type' catalog: Streamlining exploration decision making

摘要

Up to now there is no standardized global approach in the assessment of geothermal resources. In the standard assessment process for hydrocarbon resources, the lowest unit in a bottom up approach is the geologically based play type. This approach leads to prospects, recoverable or non-recoverable resources and ultimately to reserves and producing fields. A play type in petroleum geology represents a particular stratigraphic or structural geological setting, defined by source rock, reservoir rock and trap. Translated to geothermal systems, a play type might be defined by the heat source and the geological controls on heat transport and thermal energy storage capacity. Plays can best help if they comprise meaningful natural groups that can be used both for reliable field analog comparison and for exploration decision making in a specific geologic context. A logical and consistent framework for a geothermal play type catalog needs to be simple enough to communicate important aspects of geothermal energy potential to both non-experts and the general public. A play type catalog must also be comprehensive enough to provide a globally applicable geological framework to cover the whole range of possible geothermal systems. We therefore propose a catalog of geothermal play types based on geologic controls. Key defining elements of this catalog are whether heat transfer is dominated by conduction or convection, and the characteristics on a regional scale of the heat source, reservoir and host rock, porosity-permeability structure and fluid types. This new catalog is explicitly not based on temperature, depth or enthalpy, because these criteria cannot be reliably known prior to exploration. Although there might be future modifications and additions required the advantage of this new play type catalog is the facility to compare similar geothermal plays worldwide and their development to producing fields. Eventually this catalog may help to accelerate the learning curve in geothermal exploration and to a reliable assessment process towards commerciality of geothermal resources.