贵阳乌当二叠系茅口组白云岩型古油藏的初步观察与研究

在滇黔桂地区的晚古生界中发育各种类型的古油藏,尤其以泥盆系和二叠系的生物礁型古油藏最为引人注目。这些古油藏大多以沥青显示为主,特别是发育在连陆台地边缘以及孤立台地上的二叠系海绵生物礁型古油藏。发育在连陆台地内部的贵阳乌当二叠系茅口组白云岩型古油藏以油显示为特征,而与二叠系海绵生物礁型古油藏存在明显的区别。由于远离二叠系深水台盆相泥页岩系构成了潜在性烃源岩系,该古油藏的主要烃源可能来自浅水台地相的栖霞组暗色灰岩。该古油藏的产出特征和地层位置表明:在由大套灰岩组成的二叠系茅口组所构成的两个三级层序之中,与强迫型海退过程相关的环境变浅过程中常常有利于白云石化而形成白云岩型储集层,在相关的油气聚集与运移过程中形成较为特殊的地层和岩性油气藏,这为今后的油气勘探提供了具有一定价值的线索,因而具有较为重要的油气勘探意义。

PRELIMINARY OBSERVATION AND STUDY ON THE OLD OIL POOL OF DOLOMITIC- TYPE FOR THE PERMIAN MAOKOU FORMATION IN WUDANG OF GUIYANG

Various types of the old oil pools are developed in the Late Paleozoic strata of the Dianqiangui area, those developed in reef rocks of Devonian and Permian are especially widespread. These old oil pools, especially for those belonging to sponge reef types that are developed in the margin of attached carbonate platform and on the isolated platforms, are almost characteristic of asphalt indications. The old dolomitic type oil pool developed in the intraplatform limestone strata of the Permian Maokou Formation is formed in the interior part of the attached platform, and is marked by oil indication and is obviously different to those old oil pools of sponge reef type. Apart from the potential source rocks that are constituted by deep water argilutites of interplatform basin, the hydrocarbon source for the old dolomitic type oil pool in Wudang of Guyang maybe come from the potential source rocks that are composed of the shallow platform dark limestone of the Permian Qixia Formation underlying the Maokou Formation.The stratigraphic position and the outputting features for this old dolomitic type oil pool indicate several regularities as follow: Firstly, two third-order sequences can be divided in the limestone strata of the Maokou Formation ; Secondly, the dolomitic type reservoir is frequently formed in the top part of the third-order sequence, which is genetically related to the shoaling process of sedimentary environment caused by the forced regression; Thirdly, in the process of both accumulation and migration of oil and gas the special oil pool of the stratigraphic-lithologic type could be formed in the top part of the carbonate third-order sequence. All of these features show that the finding of this old dolomitic type oil pool could provide an important clue for the future exploration of oil and natural gas.