西昌盆地上三叠统白果湾组沉积相与油气勘探前景

西昌盆地是我国油气勘探的潜力区,但目前对于该盆地上三叠统白果湾组沉积的认识程度低,油气勘探尚未取得重大突破。为了加快对该盆地白果湾组油气勘探的进程,基于该盆地和四川盆地上三叠统的露头、钻井和分析化验等资料,系统研究了该盆地白果湾组沉积相类型及特征、沉积体系与砂体展布,探讨了其与四川盆地上三叠统须家河组的关系,并评价了油气勘探前景。研究结果表明:(1)西昌盆地白果湾组以砂岩和泥岩沉积为主,可划分为4个岩性段,与四川盆地须家河组三段—六段相对应,白果湾组二段砂岩发育;(2)白果湾组主要发育扇三角洲、河流三角洲和湖泊等3类沉积体系,在西昌盆地内以湖泊和河流三角洲为主,发育三角洲前缘砂体和砂坝砂体;(3)白果湾组沉积期,西昌盆地与四川盆地是一个整体,沉积体系相同,构造演化基本一致,水体主要从四川盆地流向西昌盆地;(4)白果湾组泥质烃源岩厚度大、生烃潜力较好,三角洲前缘砂体和湖泊中的砂坝砂体具有一定的油气储集能力。结论认为,西昌盆地白果湾组源储一体、大面积叠置,源储配置良好,具备较好的天然气勘探前景。

Sedimentary facies and oil and gas exploration prospect of the Upper Triassic Baiguowan Formation in the Xichang Basin

The Xichang Basin is a potential area for oil and gas exploration in China, but the sedimentation of the Upper Triassic Baiguowan Formation in this basin is less understood and no significant breakthrough has been made in its oil and gas exploration. In order to speed up the oil and gas exploration of the Baiguowan Formation in the Xichang Basin, this paper systematically studied the types and characteristics of sedimentary facies, the sedimentary systems and the distribution of sand bodies of the Baiguowan Formation in the Xichang Basin based on the outcrop, drilling and analysis assay data of Upper Triassic in the Xichang Basin and the Sichuan basin. Then, its relationship with the Xujiahe Formation of Upper Triassic in the Sichuan Basin was discussed, and its oil and gas exploration prospect was evaluated. And the following research results were obtained. First, the Baiguowan Formation in the Xichang Basin is mainly composed of sandstone and mudstone, which can be divided into four lithologic sections, corresponding to the third to sixth members of Xujiahe Formation in the Sichuan Basin, and sandstone is developed in the second Member of Baiguowan Formation. Second, there are mainly three types of sedimentary systems in the Baiguowan Formation, including fan delta, river delta and lake. In the basin, lakes and river deltas are dominant and delta front sand bodies and bar sand bodies are developed. Third, during the sedimentation of Baiguowan Formation, the Xichang Basin and the Sichuan Basin were a whole with the same sedimentary system and the basically accordant structural evolution, and the water body mainly flowed from the Sichuan Basin to the Xichang Basin. Fourth, the argillaceous source rocks of Baiguowan Formation are thick with good hydrocarbon generation potential. The sand bodies of delta front and the bar sand bodies in lakes have certain reservoir capacity. It is concluded that the Baiguowan Formation in the Xichang Basin has a good prospect of natural gas exploration because of its source–reservoir integration, large area superimposition and good source–reservoir allocation.