RESERVOIR DISTRIBUTION AND QUALITY OF PLIOCENE DEPOSITS IN EASTERN OFFSHORE AREA, ITS IMPLICATION TO DEEPWATER EXPLORATION OF TARAKAN BASIN,EAST-KALIMANTAN

摘要

Petroleum geological research in Tarakan Basin is relatively less than Kutai Basin such as detailed and comprehensively sequence stratigraphy, variation of sediment layering from transition to outer-neritic zone and its relation to reservoir distribution and quality. Oil and gas exploration in Tarakan Basin, East Kalimantan, has been carried out since almost a hundred years ago and is one of the oledest basin in Indonesia. The problem of this research are how to determine parasequence set, system-tract type, sedimentation facies and modeling of Tarakan Formation in eastern part of onshore and offshore Tarakan Island and then relates to the reservoir rock distribution and quality. To solve the problem, we started from reference studies and steps of research are sequence analysis and wells correlation, interpretation and analysis of seismic stratigraphy, subsurface mapping, reservoir distribution and quality analysis and finally 3D properties modeling for Vsh and effective porosity of net-reservoirs.The finding of this research is Tarakan Formation can be divided into two sequences; Tl and T2 sequences. Both sequence has completely system-tract i.e. Lowstand System Tract (LST), Transgressive System Tract (TST) and Highstand System Tract (HST). The sequences include as type-1 sequence that lower sequence boundary is an erosion base due to forced regression. Each of sequence has variety of sedimentation, switching direction complex and intensively changing of geometry and position of sedimentation environmental unit.There is a relationsip between sequence stratigraphy analysis and reservoir distribution and quality,especially in western and centre part of research location. T2 sequence that has higher reservoir quality is due to regressive phase increasingly dominant. Based on result of 3D properties modeling, rate of reservoir distribution and quality is to be had influence over basinward changing of lower intertidal borders and sand bar deposits of intertidal area. This 3D modeling will also indicate the impact of deepwater exploration opportunity.