CRITICALLY-STRESSED FRACTURE CHARACTERIZATION AND NATURALLY FRACTURED BASEMENT STATIC MODELING IN BERUK HIGH CENTRAL SUMATRA BASIN

• Main Author: Hydra Sahara, Virga
• Format: Theses
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/57912
• Institution: Institut Teknologi Bandung

Basement fracture reservoir is the main target for exploration and development activities in the oil and gas sector in Indonesia. One of the basins that has produced hydrocarbons from basement fracture reservoirs is the Central Sumatra Basin, which is a Tertiary back-arc basin. The fracture network model is needed to determine the characteristics of fractures that can flow hydrocarbons including critically-stressed fractured and their distribution to determine areas with good permeability zones. Beruk high was chosen as the research area because this area has been proven to produce hydrocarbons sourced from pre-Tertiary basement reservoirs. This study aims to determine the characteristics of critically-stressed fractured and make fracture network modeling, so that it can be determined areas that have the potential to have basement fracture reservoirs. This study uses three well data, BK 1, BK 2 and BK 3 which shows hydrocarbons in the basement interval in the BK 2 well and 3D seismic data covering an area of 225 km2. The methods used in this research are geomechanical analysis, paleostress inversion, scanline, and fracture modeling using the Discrete Fracture Network (DFN) method. These methods are used to determine the critically-stressed fractured characteristics and their distribution, the history of fracture formation and working stress, the reservoir property values in the form of fracture porosity and permeability zone. The results of subsurface mapping show that the study area is dominated by structural trends trending North – South and North West – South East at basement intervals. The trend of the structure which is trending North - South is dominated by a normal fault while the structure which is trending Northwest - Southeast consists of a thrust fault. Based on fracture data from wells BK 1 and BK 2 and the fault structure in the study area, paleostress inversion simulations were carried out which resulted in two tectonic events controlling fracture formation in the study area. Geomechanical analysis is obtained from the calculation of the wireline log by applying the empirical equation by Zoback et al. (1989), showed that the stress regime at the Beruk Height is normal fault to shear fault because it has an insitu stress value of Sv > SHmax > Shmin. The maximum horizontal stress at Beruk High oriented Northeast – Southwest ranges from N 40 o E to N 60 o E. The critically-stressed fractured characterization was analyzed using the Mhor diagram obtained from the insitu stress value, and using the slip limit value, namely the coefficient of friction strength of 0.6 and the biot coefficient, which is one, is then integrated with open fracture data, namely conductive and partial fractures. The critically-stressed fractured characteristics at the Beruk High have a dip ranging from 40o to 80o and the majority of the critically-stressed fractured orientations are northeast-southwest (parallel to the maximum horizontal stress direction). The fracture network modeling applies the Discrete Fracture Network (DFN) method by integrating fracture intensity data, fracture orientation obtained from the paleostress inversion modeling, fracture length and aperture resulting in areas with high fracture density located in the fault zone and in areas with high fracture density. closer to the basement surface. The results of the porosity of basement fractures in the Beruk High area are 0.01% to 2.1% with an average porosity value of 0.6% and good fracture permeability is in the fault zone and close to the basement surface. The recommended location for drilling the next well is in a zone with high permeability and the type of well is a directional well following the NW - SE trend in the direction of the minimum horizontal stress orientation and perpendicular to the critically-stressed fractured orientation.