GEOLOGY AND CHARACTERIZATION OF NATURAL FRACTURES IN THE BASEMENT ROCK OUTCROP OF BUKIT LAWANG AND SURROUNDING REGION, BAHOROK, LANGKAT REGENCY, NORTH SUMATERA

• Main Author: Fikri Al-Ghifari, Muhammad
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/69696
• Institution: Institut Teknologi Bandung

Oil and gas are currently the main sources of energy in meeting domestic needs. Hydrocarbon exploration continues to be carried out using diversification and new reservoir concepts. Pre-Tertiary basement rock that is exposed and fractured intensively in the Bukit Lawang area, North Sumatra, is expected to be an analog model to understand the fracture characteristics of the surrounding basement rock which has the potential to become a new unconventional reservoir. This study presents the results of geological mapping and special studies on the characteristics of natural fractures using linear and window scanline methods. Study of fracture characteristics in basement rock using linear and window scanline methods was carried out on the lithology of metawacke and quartzite. A total of 1424 fractures were found and grouped into: 528 shear fractures oriented ENE – WSW and 896 extension fractures oriented WNW – ESE, NNW – SSE, and NNE – SSW with a dominant slope of 61° – 80° respectively. The linear intensity (1D) of fractures in the metawacke ranged from 6.2 m-1 – 32 m-1 and in the quartzite ranged from 11.4 m-1 – 16 m-1. The areal density value (2D) of fractures in metawacke ranged from 8.5 m-2 – 27 m-2 and in quartzite ranged from 23.5 m-2 – 34.5 m-2. There is the Batu Gajah Minor Fault and the Sei Musam Fault which triggers the high intensity and density of fractures in the basement rock with a fault damage zone width of 15 meters and 20 meters respectively. The fracture attributes in the form of space, length, and width of the fracture opening are fractal and power-law distributed with fractal dimensions 1.02 – 1.608 for the space attribute, 1.119 – 2.031 for the length attribute, and 1.138 – 1.671 for the fracture width attribute. The estimation results of the natural fracture porosity value with the minimum fracture opening width in the study area are in the range of 0.006% - 0.032% and the permeability value are in the range 1.65 - 8.43 darcy.