Geomechanics and Fractures Characteristic of Pre-Tertiary Basement Fractured Reservoir in Sumatra Basins

Abstract

Basement fractured reservoir becomes one of the main focus of exploration target in Sumatra basins, Indonesia following several new exploration drilling which have been successfully discovered hydrocarbon. However, there are numerous challenges in understanding behavior and fractures distributions due to limited data coverage as well as resolution both from exploration well and seismic data. These issues are very important particularly in relation to building 3D fractures modeling for determining best production well. One of the solutions is using outcrop analog as main source of information. Evaluating fractures characteristic and attributes (length, apertures and filling) are the most important parameters. This paper is demonstrated results of integrated study of detail outcrop scale fractures characterization with subsurface data (FMI and Core) of basement fractured reservoir fields in the South Sumatra Basin. Pre-Tertiary basement outcrops scattered in the central and west Sumatra provinces. More than 20,000 structures data and several shallow drilling cores have been collected from the outcrops. These outcrops are representative of basement lithology found in subsurface at South Sumatra Basin. Basement lithology consists of low-grade metamorphism, quartzite, marble, andesite and granite with age ranging from Permian to Cretaceous. Fractures in the outcrops are recognized as veins, extension (open fractures) and shear fractures with size ranging from centimeters to meters scale. Hairline fractures are found associated with granite basement. Highest fractures density mostly occurred in granite following by quartzite and marble. Faults are characterized by single planar and fault zone with several meters of damage zone. The results of field measurements indicates three main fractures orientation NW-SE, NE-SW and N-S. Field evidence indicates that fractures density significantly increasing along major NW-SE trending fault zone, which are mostly associated with present-day Sumatra Fault Zone. Overall, the results of surface fractures characterization are matched with FMI and core data from several fields at South Sumatra Basin particularly Suban and Sumpal fields. Integrated outcrop results with subsurface data not only gives better understanding as well as control of fractures distributions, geometry, geomechanics and scale but also helping in generating best fractures modeling.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015