Distribution of Carboniferous source rocks and petroleum systems in the Junggar Basin

Abstract

With pre-Cambrian continental nuclei and Early Paleozoic accretionary folded belts as the collaged basement, the Junggar Basin underwent an evolution of intra-cratonic basin after the transitional period of Carboniferous to Permian. The Carboniferous Period was a critical phase for the cratonization of Junggar Terrane, with two continental passive margins developed on both the southern and northern margins, and with rifts and upswells in the basin interior. The rifts were full-filled with volcanic clastic rocks up to 2 000 to 5 000 m in thickness. Influenced by the marine transgression, the regional extended source-rocks of the Lower Carboniferous Dishuiquan Formation(C1d) and the Upper Carboniferous Batamayneishan Formation(C2b) occurred within or around the basin, with the former one as oil and gas source rocks, while the latter one as effective gas source rocks. Volcanic rocks in the Batamayneishan Formation are the main reservoirs. Two petroleum systems were formed: C1d-C (.) and C2b-C2b (!). The tectonic events in the Late Jurassic and Neogene gave rise to the formation, modification, and finalizing of the Carboniferous prospects. The difference between the evolutionary process of each structural unit resulted in the differentiation of the petroleum systems horizontally. A series of oil and gas fields have been discovered in Carboniferous, such as the Wucaiwan, Shixi, Kelameili, and Chepaizi oil and gas fields as well as the oil-bearing Block-2, 4, and 6 in the Karamay Oilfield. The exploration has proven that the Carboniferous has great potential for oil and gas discovery. 摘 要: 准噶尔盆地是在前寒武纪陆核和早古生代增生褶皱带的拼合基底之上经历石炭纪—二叠纪过渡阶段后形成的克拉通内坳陷盆地，石炭纪是准噶尔及邻区克拉通化过渡发展的关键时期，在准噶尔地块南、北缘发育了被动大陆边缘，地块内部断陷与凸起相间，断陷内沉积了厚度达2 000～5 000 m的火山碎屑岩系。受海侵范围控制，盆地内部及周缘发育区域展布的石炭系下统滴水泉组和上统巴塔玛依内山组两套有效烃源岩，前者可能是油、气烃源岩，后者是有效的气源岩，上石炭统巴塔玛依内山组火山岩是主要的储集体，由此形成了C1d—C(.)和C2b—C2b(!)两个含油气系统。中侏罗世晚期—晚侏罗世和新近纪以来的构造活动导致了石炭系圈闭的形成、改造与最终定型。不同构造单元后期演化历史的差异导致石炭系含油气系统在平面上产生分异。迄今在石炭系已发现了五彩湾、石西、克拉美丽、克拉玛依二/四/六井区、车排子等多个油气田，油气勘探实践表明准噶尔盆地石炭系具有较好的勘探前景。图8表3参41 Key words: Carboniferous, hydrocarbon source rock, volcanic rocks, petroleum system, Junggar Basin