南苏丹Melut盆地下组合近源白垩系成藏模式与勘探潜力

Hydrocarbon accumulation models and exploration potential of near-source Cretaceous in the lower assemblage of Melut Basin,South Sudan

为了研究Melut盆地下组合近源白垩系成藏模式与勘探潜力,开展有利储盖组合识别、重点油藏解剖、典型成藏模式建立及勘探潜力分析等石油地质条件分析工作。结果表明:①近源白垩系发育3套有利储盖组合,包括源上Galhak组内部砂泥互层储盖组合、Al Renk组生油岩内“自生自储”储盖组合、及Al Renk组生油岩与Al Gayger组砂岩形成的“上生下储”储盖组合;②湖泛泥岩是Galhak组内部储盖组合成藏的主要控制因素,辫状河三角洲内前缘发育厚层分流河道砂岩与厚层湖泛泥岩,是Galhak组高产断块油藏发育的有利相带区;③Al Gayger组反向断块圈闭具有良好的油源和侧向遮挡条件,斜坡区大断距反向断块圈闭是Al Gayger组勘探的首选目标;④沉积相带控制扇体内部油藏的类型与分布,扇根与扇中砂体厚、物性好,是发育高产断块及断层-岩性油藏的有利相带;⑤北部富油凹陷远源古近系主力产层的勘探难度越来越大,近源白垩系是北部凹陷成熟探区深化勘探的重要领域;⑥盆地南部凹陷规模小,沉积充填粗,Adar组区域盖层质量差,远源古近系Samma+Yabus-Adar组储盖组合已不是中南部有利的储盖组合,近源白垩系在中南部具有良好的成藏条件,是中南部有利的勘探层系。该研究成果对Melut盆地北部成熟探区深化勘探及中南部低探区白垩系的区域勘探具有指导意义。

In order to study the hydrocarbon accumulation models and exploration potential of the near-source Cretaceous in the lower assemblage of Melut Basin,the petroleum geological analyses of Cretaceous,such as identification of favorable reservoir-caprock assemblage,anatomy of key oil reservoirs,establishment of typical oil reservoir models and analysis of exploration potential,were carried out.The results show that:(1)Three sets of reservoircaprock assemblage were developed in the near-source Cretaceous,including interbedded reservoir-caprock assemblage of sandstones and mudstones in above-source Galhak Formation,inner-generation and inner-accumulation reservoir-caprock assemblage of Al Renk Formation,and upper-generation and lower-accumulation reservoircaprock assemblage of Al Renk and Al Gayger formations.(2)The flooding mudstones are the main controlling factor for the hydrocarbon accumulation of the inner reservoir-caprock assemblage of Galhak Formation,and the inner front of braided river delta is the favorable sedimentary facies for the development of high-production faulted blocks,with thick distributary channel sandstones and thick flooding mudstones.(3)The antithetic faulted blocks of Al Gayger Formation have good oil-source and lateral sealing conditions,and the antithetic faulted blocks with big fault throw in the slope are the preferred drilling targets.(4)The sedimentary facies determine the types and distribution of oil reservoirs in the fans,and the root and middle parts of the fans develop thick sandstones with good physical properties,which are the favorable zones for the development of high-production faultblock and fault-lithological reservoirs.(5)The exploration of the main producing layers in far-source Paleogene gets more and more difficult,and the near-source Cretaceous formations are the important targets for deepening exploration in the mature Northern Sub-basin.(6)The sub-basins in the south Melut Basin have small areas and coarse sediment infillings,which makes the regional caprocks of Adar Formation get worse,and the far-source Paleogene Samma,Yabus and Adar Formations not be favorable reservoir-caprock assemblage.The near-source Cretaceous formations have good accumulation conditions,and are the major exploration formations in the south Melut Basin.The research results have certain guiding significance for the fine exploration in the mature north Melut Basin and regional exploration of Cretaceous in the low-level south Melut Basin.