Publications

Tanjung field is PERTAMINA EP own operation located in the Barito Basin, South Kalimantan which is known as the largest basin in South East Kalimantan. The main reservoir is the Eocene age Lower Tanjung formation (LTF), which was deposited on rifted series of NW-SE horst and graben structures as a transgressive sequence of alluvial fans in the lower part, to shallow marine deposits at the top. The Lower Tanjung formations consist of sandstone and conglomerates. It was discovered in 1937 by Shell with the successful discovery well T-001. The focus of this study is to derive a better understanding of the LTF’s subsurface evaluation in Tanjung field especially in the low permeability oil reservoirs of zones A and B which are the main productive zones. This study also provides a summary of recent work which has been conducted in the diagnosis and remediation of problems associated with tight conglomeratic reservoirs. Low permeability zones occur in the main reservoir sands A and B from the lower part of Tanjung Formation. Some of the research studies showed that the low permeability was caused by a significant concentration of clay. Smectite and kaolinite are present due to the reduced rock-fluid interaction, and high concentration of radioactive content that came from plagioclase (feldspar) also make it harder to evaluate the volume of clay. Low salinity with indication of possible two water systems in the reservoir makes the evaluation even more complicated. In summary, when a conventional petrophysical analysis has limitation for predicting log properties in identifying lithology or facies changes, the multi mineral evaluation formation combined with a seismic inversion may help to solve the problem. In term of dynamic model, stochastic geological modeling guided with seismic can give more opportunities for identifying reservoir connectivity, better spatial distribution and reduce the uncertainty in conglomeratic reservoirs.