鄂尔多斯盆地南缘三叠系延长组优质烃源岩中碳酸岩的发现及其成因研究

Tight oil has become a bright spot for global oil and gas exploration and development. Ordos Basin is rich in tight oil resources, has achieved initial success in the exploration. But in general the tight oil is still in the technical preparation and research stage. Its research is relatively weak. Chang 7 reservoir is the main target of the tight oil and development horizon of the high grade hydrocarbon source rocks. High grade hydrocarbon source rocks control the formation of tight oil. Therefore, it is very important to study the development and hydrocarbon generation mechanism of high grade hydrocarbon source rocks, for the exploration and development of tight oil. This project aims to study the genesis and distribution of carbonatite and its relationship with high grade hydrocarbon source rocks, which is found for the first time in the high grade hydrocarbon source rocks of the Triassic Yanchang Formation in the Tongchuan area, southern Ordos Basin. Through a large number of field geologic investigation and a variety of analytical methods, the purpose of this project is to reveal the occurrence and distribution of carbonatite in Chang 7 Section, to clarify its origin and material source, to analyze its relationship with development of Chang 7 high grade hydrocarbon source rocks, and to summarize the hydrocarbon generation mechanism of high grade hydrocarbon source rocks. This is of great significance for revealing the sedimentary background of depression-type lake basin, and it provides theoretical basis for the study of tight oil accumulation and hydrocarbon generation, which could effectively guides the exploration and development of tight oil in Ordos Basin.

致密油已成为全球油气勘探开发的亮点领域，鄂尔多斯盆地致密油资源丰富，已初见勘探成效。但总体致密油仍处于技术准备和攻关阶段，研究较为薄弱。长7油层组是致密油攻关的主要目标，也是优质烃源岩发育的层位。优质烃源岩控制着致密油的形成。因此，研究优质烃源岩发育及生烃机制，对于致密油的勘探开发而言尤为重要。本次项目拟针对鄂尔多斯盆地南缘铜川地区三叠系延长组优质烃源岩中首次发现的碳酸岩，开展碳酸岩成因、分布规律研究及其与优质烃源岩关系研究。通过大量野外地质剖面考察及多种分析实验手段。旨在揭示碳酸岩在长7地层中的产状及分布规律，明确其成因及物质来源，分析其与长7优质烃源岩发育的关系，总结优质烃源岩的生烃机制。这对于揭示坳陷型湖盆沉积背景而言具有重要的意义，为致密油成藏、生烃研究提供理论依据，进而有效地指导鄂尔多斯盆地致密油的勘探开发工作。

在鄂尔多斯盆地南缘铜川地区三叠系延长组长7油页岩中发现了钙质结核，前期有研究表明其为首次发现的碳酸岩。三叠系延长组长7油层组是致密油攻关的主要目标，也是优质烃源岩发育的层位。为探究长7油页岩中钙质结核的成因，研究其对优质烃源岩发育的影响作用，本项目通过大量野外地质剖面考察及多种分析实验手段，展开了钙质结核成因、分布规律及其与优质烃源岩形成关系的系列研究。结果表明：鄂尔多斯盆地南缘铜川地区三叠系延长组长7油页岩中所发现钙质结核，主要呈透镜状、椭球状顺层状发育于延长组长7段泥页岩中，与围岩呈包绕接触，与长7段油页岩为同生期产物；钙质结核主要成分为低镁方解石，岩性为灰岩，属于湖相碳酸盐岩，形成于较强的还原性环境，为热液成因，几乎不受陆源碎屑物质供给影响，其物质来源主要为水成化学沉淀碳酸盐矿物；这是首次在鄂尔多斯盆地延长组湖相地层中发现热液成因灰岩；认为盆地南缘基底断裂为深部热液作用提供构造条件；发育钙质结核的长7油页岩属于具有生烃能力的较好的烃源岩，热液成因钙质结核对优质烃源岩的发育具有积极的影响作用。上述研究为进一步揭示深部热液作用对优质烃源岩发育的影响作用以及坳陷性湖盆生烃机制及致密油富集规律的研究提供了理论依据。