塔里木盆地寒武系玉尔吐斯组优质烃源岩的发现及其基本特征

Discovery and basic characteristics of the high-quality source rocks of the Cambrian Yuertusi Formation in Tarim Basin

塔里木盆地古生界海相油气资源丰富,已发现了塔河、哈拉哈塘、塔中等多个亿吨级的大型油气田,探明海相油气储量超过25×10^8t当量,并已建成年产海相油气超过1 400×10^4t当量产能,但是对主力烃源岩的认识,不同学者和勘探家们各持己见,寒武系还是奥陶系哪套是主力烃源岩一直存在争议。虽然诸多地球化学家做了大量卓有成效的工作,并有效指导了塔里木盆地油气勘探工作;但是由于盆地的复杂性和样品的限制,制约了一些研究工作的开展和精细对比,油气来源的观点未能得到勘探家们的充分认可和共识。通过对塔里木盆地寒武系野外详细踏勘和实验分析,在阿克苏地区10余个露头点发现了玉尔吐斯组优质烃源岩,岩性为黑色页岩,有机碳（TOC）值主要分布在2%-16%之间,特别是在于提希、什艾日克沟等剖面,黑色页岩层有机碳值高达4%-16%,是中国目前发现的有机碳值最高的海相烃源岩。这套优质烃源岩在阿克苏一带分布稳定,厚度在10-15m之间,主要形成于中缓坡至下缓坡沉积环境,有机质的富集受上升洋流控制。玉尔吐斯组之上的肖尔布拉克组发育厚层白云岩,野外露头未发现烃源岩,台内滩和微生物礁滩发育,储层较好;中寒武统发育厚层膏岩和泥岩,是一套良好的盖层;下寒武统玉尔吐斯组优质烃源岩与肖尔布拉克组微生物礁滩相储层和中寒武统膏泥岩盖层构成一套良好的生储盖组合,成藏条件优越,具有较大勘探潜力。

The Upper Paleozoic strata of Tarim Basin have abundant resources of marine oil and gas.In the Tahe area,Halahatang area,Tazhong area of the basin,many large-scale oilfields have been found.These oilfields have been confirmed with oil and gas reserves more than 2.5 billion tons of oil equivalent and have completed the annual output of more than 14 million tons of marine oil and gas equivalent.The view that the main hydrocarbon source rocks are the Cambrian or Ordovician is still controversial.Geochemists have made much work and effectively guide the oil and gas exploration in Tarim Basin.Because of the complexity of the basin and the limitation of samples,the research work and fine contrast are restricted.In this article,we investigated the Cambrian strata outcrop of Tarim Basin in detail.Through analyzing large amount of outcrops,high-quality hydrocarbon source rocks of Yuertusi Formation have been found in more than 10 outcrop points in Aksu region.The source rocks lithology is black shale,of which total organic carbon （TOC） content are between 2%-16%.Total organic carbon （TOC） of the black shale layer can be up to 4%-16%,especially in outcrops of the Yutixi and Shiairike.This is the best marine hydrocarbon source rock which has found in China by now.The source rocks distribute stably in the Aksu region,the thickness of which is about 10-15m.It is formed in sedimentary environment of middle gentle slope to low gentle slope.Organic matter enrichment is controlled by upwelling currents.Thick strata of dolostone developed in Xiaoerblak Formation are considered as good reservoir of beach and microbial reef in the upper strata of Yuertusi Formation.No hydrocarbon source rocks have been found in outcrop of Xiaoerblak Formation.Thick strata of gyprock and mudstone development are a set of good cap layer in the Lower Cambrian.This hydrocarbon accumulation combination has great exploration potential.