ИСТИНА

The GALO system for basin modeling is utilized to restore numerically the burial and thermal histories of the Limau Graben in the South Sumatra Basin from the Oligocene to present time. Thermal and maturation history of the basin was considered on an example of numerical reconstructions for sedimentary sections of six wells (Pandan-81, Petanang-1, Tepus-2, Tepus-1, Gambir-1 and Lembak-8) located in the Basin along the profile crossing the graben Limau from the Pendopo High to Palembang Platform. The modeling suggests significant cooling of the basement during the first 15 – 20 My from the high initial heat flow of 105 mW/m2 typical of continental rifting and considerable heating of the basin lithosphere during last 2 – 5 My. An analysis of variations in tectonic subsidence suggests the lithosphere extension that lasted during Oligocene and Miocene with amplitude increased from β = 1.12 at the flanks of the Limau Graben (well Lembak-8) to 1.32 in its centre (wells Tepus-1 and 2). In addition, this analysis assumes considerable thermal activation of the Basin during the Pliocene, Pleistocene and Holocene. This activation is confirmed by high thermal gradient typical of present-day sedimentary sections of the South Suimatra Basin. The modeling assumes rather good perspective of the Lemat, Talangakar and Gumai formations of the South Sumatra Basin to generate liquid hydrocarbons in the Limau Graben. It shows that the Lemat source rocks are oil prone in the main part of the Limau Graben and only in deepest part of the Graben they become predominantly gas prone. According to the modeling, the rocks at the base and roof of the Talangakar formation must intensively generate oil excluding, may be, upper horizons of the formation in the must shallow areas of the Graben (w. Lembak-8). A peak of oil generation by the formation rocks occurred in the last 5 – 10 My. Oil generation by the rocks of the Gumai formation can be significant in the main part of the Graben. It is negligible only in fare flanks of the Graben (w. Lembak-8).