Paleocurrents and Reservoir Orientation of Middle Miocene Channel Deposits in Mutiara Field, Kutei Basin, East Kalimantan
Tobias H.D. Payenberg, F. Hasan Sidi, Simon C. Lang, 2003. "Paleocurrents and Reservoir Orientation of Middle Miocene Channel Deposits in Mutiara Field, Kutei Basin, East Kalimantan", Tropical Deltas of Southeast Asia—Sedimentology, Stratigraphy, and Petroleum Geology, F. Hasan Sidi, Dag Nummedal, Patrice Imbert, Herman Darman, Henry W. Posamentier
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Mutiara field produces hydrocarbons from middle Miocene fluvio-deltaic successions within the Kutei Basin, East Kalimantan, Indonesia. In strata exposed over the doubly plunging Sanga-Sanga and Samboja anticlines, a large number of cores and downhole logs provide an excellent opportunity to integrate surface and subsurface data to improve reservoir characterization for exploration and development. Sedimentary facies and paleocurrent analysis were used to gain insight into the distribution of the dominant channel deposits within the succession.
Channelized sandstone bodies identified in outcrops and cores constitute the main hydrocarbon reservoirs. They commonly comprise single-story distributary-channel sandstones and occasionally multistory alluvial-channel sandstones. Paleocurrent analysis revealed the distributary channels flowing in an overall southward direction, roughly parallel to the strike of the anticlines, while two of three multistory channels trend northeast. The third multistory channel has a strong westward flow direction, which might indicate a valley incision of a previously more sinuous channel. The orientation of the single-story distributary channels can be explained as a result of active tectonism during the middle Miocene. Incision of the Mahakam River into the uplifting hinterland means that a point source of sediment supply has existed to the north of Mutiara Field since middle Miocene times. Growth of anticlines through regional inversion of older, extensional basement faults has restricted the eastward progradation of the paleo–Mahakam Delta. As a result, the delta distributary channels and delta progradation was merely towards the south and north, parallel to depositional strike, and not perpendicular, as commonly thought. In addition, low directional variance among the single-story and multistory channels suggests that the paleo–Mahakam Delta comprised low-sinuosity channels, which has strong implications for the exploration of stratigraphic traps.
Periods of dominant alluvial sedimentation produced roughly west–east striking multistory channels, which can sometimes be linked to incised-valley fills. These sandbodies might have had sediment sources to the southwest of the Mutiara field, and thus belong to a totally different fluvial system.