Calibrated Natural State Model in Sorik Marapi Geothermal Field, Indonesia

Understanding the reservoir conditions through 3D subsurface modeling is the key to optimize the exploration stage in geothermal field. A calibrated reservoir model based on updated data can be very important for this process. The main challenge of reservoir characterization in a geothermal field is the lack of subsurface data, therefore surface data are useful for reservoir modeling. This study utilized Sorik Marapi geothermal field data as a reference for reservoir modeling. This field is one of the geothermal fields in Indonesia that has been recently drilled, with results indicating the existence of a high temperature-neutral acidity resource. Initial reservoir model has been built from the previous study to create conceptual 3D subsurface model which includes structural, lithology, resistivity, and temperature distribution from surface exploration data, including surface mapping, remote sensing image interpretation, the magnetotelluric method, and subsurface data from six wells data. The objective of this paper is to calibrate the initial reservoir model with information from an additional ten new wells data to improve delineation for updated reservoir area in the field. Software that allowed multidisciplinary data integration from surface to subsurface information was used for the calibration of the initial 3D model. The workflow to calibrate the model started with data loading and quality control, preparing the old 3D model and comparing it to new well data, analyzing the comparison, and updating the 3D model. Finally, the new delineation of reservoir zone can be determined. The result of this study is an updated 3D subsurface static model defining the vertical and lateral reservoir boundaries, as well as the prime resource areas, which would be the basis for designing future well targets, and parameters for a dynamic reservoir model. The same model can be expanded to construct the numerical model to match the natural state condition of the field and make forecasts of the future reservoir behavior at different operating conditions. The main properties of the updated 3D model are lithology and temperature, which are important in geothermal reservoir delineation.