Publications

Most hydrocarbon exploration activities in the Tarakan Basin have been focused on the shallow targets of Upper Miocene-Pliocene deltaic sediments of Tarakan and Santul Formations. In the Bangkudulis and Sembakung Fields, however, hydrocarbon was found from Middle Miocene Meliat Formation. Therefore to study Meliat Formation reservoirs in the basin, deeper exploration targets have become more important. Meliat Formation in the Tarakan Island appears to be previously unidentified. This unit has been encountered as an incomplete section in Barat-1 well only. An integrated study of the well logs, biostratigraphy, with 2D and 3D seismic data have been carried out to understand the stratigraphic correlation, distribution and geometry of the formation both on and off the Island. In the Barat-1 the formation is more than 630 m thick siliciclastics, with thin limestone at its top. The lower (250 m thick sandstone-rich) unit is interpreted to have been deposited in an estuarine underlying fluvial channel fills in the unintersected section. The upper (380 m thick) unit represents deltaic cycles of shelf shale with carbonate, and lower delta front sand. Sequence Stratigraphic interpretation of the formation suggests that the unit is divisible into two sequences, sequences M1 and M2. The interpreted fluvial channel fills of the lowest part of Sequence M1 developed above a regional unconformity (SB 16.5 Ma) as late lowstand systems tract (LST) deposits. These deposits are likely to be associated stratigraphically with equivalent sand-bearing slope fan facies overlying early lowstand basin floor fan turbidites eastward from the island. The overlying aggradational tidal influenced estuarine (distal deltaic distributary channels) LST sand of the Lower Unit could be shale out distally eastward. The highstand systems tract of Sequence M1 and the overlying sequence 2 reveal slightly progradational deltaic cycles developed in association with sea-level fluctuations and higher accommodation space, with periods of lacking coarse siliciclastic influx lead to carbonate sedimentation on top of the formation. Locally identified sand-bearing nearshore facies of the sequence M2 located both in the northern part and south of the island are interpreted to have been related to relative sea level drop due to force regression event. The reservoir-bearing facies of the basin floor with the overlying slope fans, channel-fill facies, and forced regressive sands are thought to have been regionally developed in the Tarakan basin. In addition, thin carbonate bed on top of Meliat Formation in the Tarakan Island is lateral to the west and southwest changing facies into thick and better developed carbonate-build-ups.