Power Density Assessment of Geothermal Fields In Indonesia

This study evaluates geothermal resource estimation using power density approach. During exploration phase of geothermal development where subsurface data is limited, power density method is frequently utilized by geothermal industry practitioners as an initial resource estimation which is usually expressed in MW/km2. This technique estimates geothermal resource using the extent of indicative area by statistical means and associates them to other commercially productive fields based on similarities of temperature indication and geological condition.

Power density evaluation in this assessment is carried out on 29 medium and high temperature (>200 oC) geothermal fields in Indonesia, in which exploration drilling and/or development drilling are already completed. This enables comparison to be taken place equally between prospects in which geothermal subsurface conditions such as temperature, chemistry and resource dimension are identified and confirmed by exploratory/ development drilling.

This study suggests that medium to high temperature fields in Indonesia exhibit the range of power density from 0,3 to 28,3 MW/km2. The mean power density in this study is 9,7 MW/km2. The result is comparatively within the range of findings that has been formulated by Grant and Bixley (2011) whom suggest that typical power density is typically 10-15 MW/km2 and slightly near from results that have been proposed by Wilmarth and Stimac (2015) which suggested that mean power density distribution from 66 geothermal fields is 15.4 MW/km2.

This paper proposed that the mean area of proven reserves during exploration and field development phase is 6,9 km2 and tend to be less than the mean area in production phase which is approximately 16,1 km2. This is possibly due to increasing number of step-out production wells which may expand proven geothermal delineation area. Meanwhile the power density analysis results for geothermal fields located in different regions in Indonesia indicate that the geothermal fields in Java and Sumatra show a power density of 10.7 to 12.4 MW/km2. This value is far greater than the power density in the fields located in Sulawesi and Nusa Tenggara, which is 5.3 to 6 MW/km2.