北部湾盆地涠西南凹陷油气成藏特征研究

摘 要] 涠西南凹陷是南海北部湾盆地重要的富烃凹陷之一。本文通过开展涠西南凹陷油气成藏条件及成藏模式等方面的研究,得出该区具有优异的成藏条件:流沙港组二段是最主要的烃源岩层,达到好烃源岩的标准;发育石炭系灰岩、古近系长流组、流沙港组三段和一段、涠洲组等多套储集层,其中涠洲组三段和流沙港组一段储层物性最好,具有高孔隙度、高渗透率的特征,属玉类储层;存在始新统流二段及中中新统角尾组上部的大套泥岩两套区域盖层,生储盖组合以下生上储型为主;圈闭类型主要为构造型和地层型或两者的复合,圈闭形成时间与油气充注时间配置较好。最后指出研究区2 号断层和3 号断层之间的洼槽带是下一步油气勘探的有利区带。

Hydrocarbon Accumulation Characteristics in the Weixinan Sag, Beibu Gulf Basin

Abstract:The Wenxinan sag is one of the major sags rich in oil and gas in the Beibu Gulf basin, South China Sea. This paper studies the hydrocarbon accumulation conditions and accumulation model for the Wenxinan sag. The results show that this area has excellent accumulation conditions. The Member 2 of the Liushagang Formation is the most important source rock. It is ranked as good source rocks. The area plays host to several sets of reservoir rocks, i. e. , the Carboniferous limestone, Paleogene Changliu Formation, the Member 1 and Member 3 of the Paleogene Liushagang Formation and Weizhou Formation. The Member 3 of the Weizhou Formation and the Member 1 of the Liushagang Formation exhibit the best reservoir properties, with high porosity and high permeability. They are evaluated as grade-I reservoirs. In addition, the study area has two sets of regional cap rocks. Those are the large sets of mudstones in the Member 2 of the Eocene Liushagang Formation and the upper of the mid-Miocene Jiaowei Formation, with the lower-generation and upper-storage type as the main source rock-reservoir-cap rock combinations. And the traps are dominated by structural, stratigraphic, and/ or their combination in the area. Moreover, the trap forming periods have a well configuration with the oil charging time. The comprehensive research reveals that the subsag zone between No. 2 fault and No. 2 fault may be the next favorable zone for oil and gas exploration.