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ABSTRACT: Reservoir facies of the Miocene Mahakam successions in the Kutei basin, east Kalimantan and their comparision with the modern Mahakam delta

Wiweko, Agung1, Stefano Mora1, and Irfan Cibaj2
(1) Total Indonesie, Balikpapan, Indonesia
(2) Consultant for TotalFina, St.Remy les Chevreuse, France

Several types of reservoir bodies have been defined from facies-architectural analyses of Miocene outcrops and cores in the Kutei Basin, East Kalimantan, by G.P. Allen et al. These reservoirs consist of distributary channel-fills and distributary mouth bars. In the proximal delta plain, the distributary channel is a typical high-energy channel dominated by suspension and traction currents. Whilst in the distal delta plain to delta front, the channel facies is typically of low-energy channels dominated by either combined suspension and traction currents, or traction currents. Some of these channel-fills are interpreted as having been formed in the delta front, as they generally lack the overlying rooted carbonaceous mudstones or coals which are so common in the channels of the delta plain. The distributary mouth-bar successions record three major depositional processes: a) a high-energy mouth bar dominated by traction currents and combined suspension-traction, b) a high-energy density flow dominated mouth bar, and c) a low energy mouth bar dominated by suspension and traction.

In marked contrast to the Miocene sediments, the distributary channels on the modern delta front do not contain any significant volume of sand. These distributary channels extend across the delta-front, approximately 5km with no obvious sidebars and relatively straight thalwegs. The sedimentary structures and bedding of the distributary mouth-bars, indicate an overall low energy regime, current ripples are rarely preserved.

The Miocene and the modern Mahakam deposits have similarities in terms of geometry and facies patterns, but the Miocene delta exhibits higher energy environment compared to the modern delta.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia