KARAKTERISTIK DAN DISTRIBUSI REKAHAN ALAMI, STUDI ANALOG PADA SINGKAPAN BATUAN DASAR CEKUNGAN OMBILIN, SUMATRA BARAT

• Main Author: YOAN TORENO , EKO
• Format: Theses
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/20061
• Institution: Institut Teknologi Bandung

Naturally fractured basement is an important element of hydrocarbon reservoirs that have been produced, but it is still difficult to describe the characteristics bellow the surface, although it can be studied using image log data, core, and geophysics, but not many wells penetrated it and equipped with the log image. One of the best method to predict and provide an understanding of the characteristics of naturally fractured basement at subsurface is a measurement with scanline method and windows scan with observations on basement outcrops. Ombilin basin basement age ± 3.5 to 112 ± 287 2.4 million years ago that is at Mergui microplate. Characteristics of naturally fractures in the basement comprised of shear fractures, extention fracture, and fault. A total of 4693 naturally fractured obtained from basement in Ombilin basin, 2466 shear fractures, 1668 joint, 405 veins, and 151 faults. Three general orientation, northwest-southeast, north-south, and northeast-southwest. The intensity and significant naturally fracture density derived from granitic rocks, decreasing to limestones and andesitic. Distance to fault is a factor of intensity and density of naturally fractured basement. Naturally fracture geometry (spacing, length, aperture) follows the power-law distribution pattern, shows a regular pattern in the line of slope of the curve (c) varies. Naturally fracture spacing shows the slope (c) the average on the granite c = 1.28, c = 1.39 granodiorite, limestones c = 1.50, c = 1.57 and andesite. Naturally fracture openings at each location shows well distributed data form a regularity along the line with a slope of the curve (c) in the granite c = 1.73, c = 1.67 granodiorite, limestones c = 0.94, and andesite c = 1 , 57. Value of the slope of this curve shows that the smaller the value of c the more gentle slope of the curve that shows the data range of naturally fracture width without limitation scale, the brittle rocks. While the slope of the line that is increasingly steep curve shows the data range of naturally fractures are narrow. This can be seen on the granite slope of the curve ramps have data that is tightly spaced fractures and high intensity. The average value of the naturally fracture porosity estimation obtained from the calculation in the limestones 3.17 to 17.11%, granite 2.92 to 16.35%, granodiorite 4.2 to 13.37%, and andesite 5,61- 11.35%. Average permeability of naturally fractures in limestone 45.31 to 787.27 md, granite 27.30 to 857.39 md, granodiorite 34.55 to 747.05 md, and andesite 86.03 to 641.94 md.