四川盆地元坝地区茅口组台缘浅滩天然气勘探的突破与启示

2018年，元坝地区元坝7井在中二叠统茅口组钻遇台缘浅滩储层并获得高产工业气流，取得了四川盆地茅口组台缘高能相带新领域油气勘探的重大突破。为了进一步深化对于茅口组的地质认识，在分析区域构造运动的基础上，利用岩石矿物学等手段，结合地震剖面精细解剖成果，研究了茅口组的岩性、厚度、古地貌、地震反射结构，明确其沉积相展布；利用岩心观察、薄片鉴定、扫描电镜及物性分析等资料研究了茅口组储层的特征及控制因素，并初步确定其天然气成因与来源、盖层特征及天然气成藏的主要控制因素。研究结果表明：①元坝地区受茅口晚期峨眉地裂运动的影响，发育碳酸盐岩台缘-斜坡-陆棚沉积相带，台缘发育高能浅滩碳酸盐岩和沉凝灰岩两类储层；②茅口组储层的发育主要受台缘相带、暴露溶蚀、东吴运动抬升和火山灰沉积蚀变作用等的联合控制；③四川盆地海相碳酸盐岩天然气勘探潜力大，台缘相带是大中型气田发育的有利区域。结论认为，加强地质研究、创新地质认识是油气勘探取得突破的基础，发展面向储层识别的地震勘探关键技术是高效勘探获得成功的保障。

Breakthrough in natural gas exploration in the platform margin shoal at the Maokou Fm in the Yuanba area,Sichuan Basin,and its implications

In 2018, Well Yuanba 7 drilled into the platform margin shoal reservoir of the Middle Permian Maokou Fm in the Yuanba area of the Sichuan Basin and a high-yield industrial gas flow was obtained, indicating a great breakthrough of oil and gas exploration in the new field of high-energy platform marginal facies belt of the Maokou Fm in the Sichuan Basin. In order to deepen the geological understanding on the Maokou Fm, this paper analyzed the regional tectonic movement. Then, the lithology, thickness, paleogeomorphology and seismic reflection structure of the Maokou Fm were studied by means of petrology and mineralogy based on fine seismic interpretation results, and the distribution of sedimentary facies was defined. Finally, the reservoir characteristics and control factors of the Maokou Fm were researched by means of core observation, thin section analysis, SEM analysis and physical property analysis. What's more, the origins and sources of natural gas, the characteristics of caprocks and the main control factors of hydrocarbon accumulation in the Maokou Fm were preliminarily determined. And the following research results were obtained. First, due to the effect of the Emei taphrogenic movement in the late Maokou period, the sedimentary facies belt of carbonate platform margin–slope–continental shelf is developed in the Yuanba area, and two types of reservoirs are developed at the platform margin, i.e., high-energy shoal carbonate and sedimentary tuff. Second, the development of Maokou Fm reservoir is mainly under the joint control of platform marginal facies belt, exposed dissolution, the Dongwu movement uplift and volcanic ash sedimentary alteration. Third, in the Sichuan basin, marine carbonate rocks have great exploration potential of natural gas, and the platform marginal facies belt is a favorable area for the development of large- and medium-sized gas fields. In conclusion, strengthening geological research and innovating geological cognition are the foundation of exploration breakthrough, and developing key seismic exploration technology for reservoir identification is the guarantee of efficient exploration.