Wally Waluyo*, Sardjito*, Wawan G. A. Kadir**
Bunyu is a small island located in the northeast edge of Kalimantan. It is well known island as oil and gas producing area with the reservoirs depth vary from few hundreds to more than 3000 thousands meters. The formations containing hydrocarbon are Bunyu, Tarakan, Tabul and Santul Formations of supra lithoral through shallow marine sediments deposited during Tertiary. A series of seismic surveys conducted from 1972 up to now using various field seismic parameters and advanced processing technology did not result in good enough seismic sections. As a consequence the development of reservoir layers cannot be done optimally, neither shallow nor deep targets. Seismic surveys face some technical obstacles such as an extreme hilly surface of the islands with elevation difference up to 50 meters for 30 meter lateral distance. The other field’s problem is that most the Bunyu surface area covered by thick layer of coal and loose sand. This surface condition results in poor quality of seismic data. Other approach is needed. Gravity and its gradient measurements conducted in 2005 using very sensitive gravimeter seem to be an appropriate technology compensation to unravel the problem. Modeling of the Bouguer anomaly and its derivation combined with the pattern of gravity gradient successfully defined the pattern faults in the South Bunyu. Based on the secondary vertical derivation (SVD) the geometry of fault planes can be identified, so that the strike and dips of fault planes can be determined. This can also be used to elaborate the ambiguity of poor quality seismic section in the coinciding area. Further more the fault pattern resulted in from gravity measurements can be used as the most level of confidence in proposing the wells location for both exploration and well injection in this area. Compartmentalizing of South Bunyu based on gravity data interpretation helps the plan of development of this oil field through water injection program.
* Pertamina EP Jakarta, Indonesia ** Institute Technology of Bandung (ITB), Bandung, Indonesia
Emails: wallywaluyo@pertamina.com sdjito@pertamina.com wawan@gf.itb.ac.id