Factors Affecting Oil Productivity in a Shallow Shoreface Sandstone Reservoir – A Case Study from The Rebonjaro Field, South Sumatra Basin



Problems affecting oil production from the shallow (300 in) Laman Lului A Sand in Rebonjaro Field led to detailed study of this reservoir. The A Sand occurs near the top of the Lower Palembang Formation (Middle Miocene) in an interlaminated sand and shale sequence. Although the A Sand is widely distributed across the field, only two wells have established commercial production. The purpose of this study is to determine petrophysical properties and variability in the A Sand, to identify potential mechanisms for formation damage, and to identify drilling and completion practices that could eliminate or at least minimize the damage.
Detailed sedimentological studies of core and wireline log data reveal subtle variations in bioturbation, sedimentary structures, mineralogy, and clay content in the A Sand. The highest values of porosity, permeability, and oil saturation occur in association with crossbedded sandstones (lithofacies Sc and restricted zones within lithofacies Sb). In comparison, more moderate values characterize bioturbated sandstones. The development of diagenetic dolomite has affected fluid saturations and visible oil fluorescence is only associated with dolomite free zones.
The presence of kaolinite and illite in the pore systems indicates a potential for fines migration, whereas smectite demonstrates the potential for clay swelling if the reservoir is contacted by aqueous fluids without careful pH control. Mineralogic analysis thus indicates that the reservoir is potentially sensitive to formation damage during drilling, completion, stimulation, and production.
The results of this study have helped design a procedure using diesel fuel to drill, core, and complete the A Sand without exposing the formation to damaging fluids. The Rebonjaro-16A well was completed in this manner and flowed 300 bbls/day of 55.40 API oil and no water on 16/64 inch choke with 50 MCFG/day and 104 psi FTP. Rebonjaro 14 Twin, a later, well was drilled with the same non-damaging fluid and also produces oil at enhanced rates. This well produces less oil than Rebonjaro-16 because it is in a poorer quality bioturbated sandstone.

Gulf Indonesia Resources, Ltd.

Wisma-46 Kota BNI, Jalan Jendral Sudirman, Jakarta 12220

Phone: 5742120, Fax. 5752112, 5742113

E-mail : Agus Sudarsana/Gulf/ca@Gulf


Authors : Agus Sudarsana & Ermawan Maulana