| Title | Overview of Darajat Reservoir Characterization; a Volcanic Hosted Reservoir |
|---|---|
| Authors | Julfi Hadi, Chris Harrison, Joao Keller, Sri Rejeki |
| Year | 2005 |
| Conference | World Geothermal Congress |
| Keywords | |
| Abstract | Reservoir Characterization using a combination of geothermal techniques and geostatistical modeling tools has been used to produce a realistic fine scale volcanic reservoir model that consists of discontinuous layers of rock with a distributed fracture system. This geological model used as a framework to estimate reserves and productivity for the field is especially critical since in a vapor dominated geothermal system the reserves are believed to be stored primarily within the rock matrix, while productivity is dominated by the fractures. An existing undisturbed andesite stratovolcanic model was compared to cores and cuttings from 24 wells that have been drilled and surface samples to produce a subsurface volcanic facies model. The model indicates that the reservoir consists of thick lava and intrusive rock of a stratovolcano central facies that dominates the center of the reservoir and thick pyroclastic sequences of proximal to medial facies that were deposited on the margin. X-ray fluorescence analysis (XRF) on key samples and gravity data were used to confirm the model. Fractures in the wells were analyzed using FMS data and were related to well productivities via PLT and interference tests gOcadÆ modeling incorporated the correlations between petrophysical groupings and matrix and alteration porosities with fracture density and connectivity and permeabilities in the wells. To capture pore volume uncertainties within the model, factors controlling pore volume were identified and different geology cases were created modeling reservoir geometry, lithology type proportion, alteration zone and porosity distribution. The fine scale models have been scaled up and are currently being history matched using 3D simulation. Predictions based on the models will be used to validate the technical feasibility of a major expansion of the Darajat facilities planned for 2004. |