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.
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It is the objective of this volume to bring to the fore a category of deltas with which many sedimentologists and stratigraphers are, at best, vaguely familiar. It is expected that this volume also will stimulate new research on tropical deltas by highlighting how their facies and stratigraphic architectures differ from mid- and high-latitude ones, by emphasizing their significance to the global sediment budget, and by stressing their uniqueness within a petroleum systems framework. This special publication emphasizes the need for models intrinsic to tropical deltas of Southeast Asia to supplement the more conventional general models currently in vogue, based on past studies of large and small mid-latitude deltas. The papers in this book explore how the combination of these complex factors has shaped deltas in this region. Sedimentological surprises such as distributary channels floored by thick accumulations of fluid mud lend a bit of “mystery” to tropical deltas. We hope that, rather than being merely a summary of tropical deltas, this book may open the door to a new and active phase of sedimentological and stratigraphic research in tropical environments across the globe.