AN APPLICATION OF GRAVITY METHOD TO IDENTIFY SUBSURFACE FAULT GEOMETRY AND ITS IMPLICATION TO DRILLING RESULT IN MONTELAGO GEOTHERMAL FIELD, PHILIPPINES

• Main Author: Hasbi Assiddiqy, Muhamad
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/53743
• Institution: Institut Teknologi Bandung

Montelago geothermal field has been through long exploration stages. Even so, the drilling campaign in this geothermal field met no satisfactory. Only 1 out of 4 wells found the high temperature fluid inflow. These failures might be related to the insufficiency of the subsurface fault geometry understanding. The fault geometry information that has been considered as guidance to assist the well targeting is only based on fault geometry on the surface. By applying a method which provide better understanding of the subsurface fault geometry, the implication between fault geometry to the drilling results could be understood. This research applies gravity methode to identify the subsurface fault geometry. It involves residual gravity anomaly map, total horizontal derivative anomalu map, second vertical derivative map, horizontal gradient magnitude anomaly map, Euler deconvolution analysis, and the two-dimension forward modeling. Furthermore, geological mapping result, surface manifestation distribution, surface alteration distribution, and mercury gas anomaly map were used in this research as secondary data to provide the spatial permeability value within the study area. The result of fault geometry identification will be combined with the secondary data and visualized into a three-dimensional model. By comparing the drilling results to the three-dimensional model, the implication between fault geometry and drilling result could be understood. 34 impermeable faults and 8 permeable faults are shown within the three-dimensional model, including the horizontal and vertical extent of each fault. The comparison between the fault geometry model and those four drilling results shows that those dry wells are intercepted the impermeable faults. In contrast, the productive well is not intercepted by a permeable fault in the model.