NATURALLY FRACTURED BASEMENT MODELLING IN BANDAR AGUNG-MERAKSA HIGH, SOUTH SUMATRA

• Main Author: Sapta Fitriana, Bayu
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/75779
• Institution: Institut Teknologi Bandung

The Bandar Agung-Meraksa high is located on the southernmost boundary of the South Sumatra basin. This area is managed by PT Pertamina Hulu Energi as an exploration area from the Ogan Komering block. From BDA-1 exploration well drilling in 2014, this high has been proven as hydrocarbon bearing reservoir in natural fractured basement reservoir, flowed gas with rate of 3.4 million cubic feet per day. Followed this success, several explorations well has been drilled in this area, they are JTB-1 (2015), NRM-1 (2015) and BDA-2 well (2022). Unfortunately, these wells have not indicated the presence of hydrocarbons in the basement, although natural fractures are identified developed. Characterization of criticallystressed fractures and modeling of natural fractures are needed to determine the characteristics and distribution of natural fractures that can flow hydrocarbons and their relationship with regional stress and geological structure that develops in the area. 3D seismic data covering an area of 336 Km2 and data from 5 exploration wells which include wireline log data, image logs, drilling logs, cuttings and SWC data were used in this study. The methods used in this study include subsurface mapping, palinspatic reconstruction, geomechanic analysis and fracture modeling using the Elastic Dislocation Model. Naturally fractured basement modeling is carried out by predicting the orientation, slope and intensity of fractures in basement. Furthermore, fractures that have the potential to open under current stress conditions (critically stress fractures) can be identified as permeable zones that have the potential to become productive zones in basement. From subsurface mapping and palinspatic reconstruction, study area is affected by several deformation phases, they are extensional phase, sagging phase and contractional phase, with orientation of the structure being northeast-southwest, northwest-southeast and east-west. Geomechanical analysis shows the strike slip regime prevailing in this area at present time. Based on the interpretation of image logs on basement interval, there are two groups of conductive fractures formed with a north-south orientation at Meraksa height and a northeast-southeast orientation at Bandar Agung height. Maximum horisontal stress orientations identified from borehole breakout and induced fractures with orientation northeast-southwest. The different orientation of the open fractures between the two heights shows the strong influence of local faults which cause variations in the direction of the main stresses which affect the different orientations of the open fractures in the current conditions. Naturally fractured modelling result shows basement interval in study area shows a tendency for fracture development with high intensity concentrated in fault zones and maximum curvature of structures. Zones with fracture conditions identified as critically stressed fracture have a direction parallel to the current direction of the main local stresses. Area with critically stressed fracture in 3D model are potential for permeable zone development in basement interval.