广西十万大山盆地演化过程及油气资源响应

The evolution of the Shiwandashan Basin in Guangxi and its response to oil and gas resources

关键词:  十万大山盆地  演化  油气  广西

Key words:  Shiwandashan Basin  evolution  oil and gas  Guangxi

摘要:

广西西南部十万大山盆地,大地构造位置属于华南板块的西北缘,是在华南板块与扬子板块拼接之后,晚古生代华南洋再一次打开,又接受沉积的。泥盆纪-早二叠世,该地区形成被动大陆边缘;晚二叠世末,随着太平洋板块向西俯冲,该地区转变成弧后盆地;早三叠世-侏罗纪,进一步转化成前陆盆地。在被动大陆边缘的碎屑岩陆架沉积阶段,生成碎屑岩烃源岩;在碳酸盐台地沉降阶段,发育砂屑灰岩、藻灰岩、礁灰岩和暴露作用生成的白云岩储集岩。因而其早期被动大陆边缘阶段构成了古生新储组合;前陆盆地早期,在前渊盆地内沉积了一套碎屑岩烃源岩,它与早期的储集层构成了新生古储组合,同时也对下伏地层起到了封闭作用。随着逆冲体向西推进,沉积地层也逐层向克拉通斜坡上超覆,发育地层圈闭。前陆中期阶段快速沉积的巨厚的复理石和晚期的磨拉石促进了早期烃源岩的迅速埋藏、成熟和保存。十万大山盆地具备了典型前陆盆地的生烃成藏地质条件,因而该盆地有较好的油气远景。

Abstract:

The Shiwandashan Basin in southern Guangxi is tectonically located on the northwestern edge of the South China plate. The basin began to accept the sediments during the Late Palaeozoic when the South China Ocean opened once again posterior to the collage of the South China and Yangtze plates. During the Devonian to the Early Permian, this area appeared as a passive continental margin, and during the latest Late Permian, it was developed into a back-arc basin due to the westward subduction of the Pacific plate and further into a foreland basin during the Early Triassic to the Jurassic. The clastic rocks as the source rocks were formed during the deposition of the siliciclastic shelf on the passive continental margins, followed by calcarenite, algal limestones, reefal limestones and dolostones as reservoir rocks during the subsidence of the carbonate platforms, thus constituting an old source rock-new reservoir rock association. A sequence of clastic rocks as the source rocks was laid down in the foredeep basin during the early stage of the foreland basin, and constituted a new source rock-old reservoir rock association together with the early reservoir rocks. This kind of associations may serve as the sealing strata of the underlying strata. The westward progradation of the overthrusting faults permitted the sedimentary strata to overlap upslope upon the cratonic slopes and then the stratigraphic traps were formed. The flysch rapidly deposited-during the middle stages of the foreland basin and mollase during the late stages facilitated the rapid burial, maturation and preservation of the early source rocks. It can be seen that the Shiwandashan Basin provides a superb example of a representative foreland basin that is highly prospective for oil and gas resources.