AN OUTCROPS ANALOGUE TO BASEMENT FRACTURED RESERVOIRS OF THE SUBAN GAS FIELD, SOUTH SUMATRA BASIN, INDONESIA

Exploration activity in the western Indonesian region is mostly concentrated in targeting new prospects in the basement fractured reservoirs. Suban field is one the biggest gas field in Indonesia, which mostly delivered from basement fractured reservoirs. However, limited information on fractures orientation an fracture density is available from core and borehole image log data, particularly in relation to information concerning fractures parameters such as fracture length, relationship lithology to fracture density, cross-cutting relationships. All of this information is very important for understanding not only fluid flow and reservoir performance but also trapping mechanism, which is very important to the exploration program. Many study have been proved the role of outcrops in helping to solve this issues. This paper is presented results of outcrop scale fractures characterization study along E-W traverse across central Sumatra region as an analogue for basement fractured reservoir in the Suban Field, South Sumatra. Fractures characterization study is concentrated in the basement outcrop from more than 10 locations using both scan-line and window mapping. The main goal of the study is using outcrop scale fractured characterization for understanding reservoir behavior in the Suban Field, which in turn can be used for exploring other area with similar geology. Sumatra basement consist of amalgamated terrain with various lithology such limestone, metasediments, marble, slate, phylite, quarzite, granite and andesite with ages ranging from Permo-Carbon to Cretaceous.

The results of study show that two main fractures orientation was observed in the basement, which is dominantly NW-SE and N-S. Almost in every outcrop, this trend was observed as dominant structural pattern where similar pattern was indicated by regional basement orientation. Fractures density is varies significantly in various different lithologies where granitic rocks and limestone show as the highest compared to other basement lithology. However, local structures such major faults and folds are highly influenced in term fractures density. Results of this study will be used as an important input to discrete fracture network (DFN) as well as for distributing fracture properties in reservoir models in the Suban Field.