碳酸盐岩烃源岩气藏的发现及其油气地质意义——以四川盆地涪陵地区中二叠统茅口组一段气藏为例

四川盆地中二叠统茅口组一段(以下简称茅一段)以往一直都被视为一套碳酸盐岩烃源岩,未有针对性地对其开展储层评价与测试工作。近年来,借鉴非常规天然气的勘探思路,借助于兼探井对川东南涪陵地区茅一段进行测试并获得了工业气流。为了进一步弄清该区茅一段的天然气勘探潜力,基于野外剖面实测、钻井系统取心以及实验室分析化验等资料,对其沉积特征、天然气成藏条件及主控因素等进行了研究。研究结果表明:①涪陵地区茅一段气藏源储一体,天然气主要富集在黑灰色灰泥灰岩和瘤状灰泥灰岩中;②储集空间主要为粒缘孔(缝)、成岩收缩孔(缝)、有机质孔和裂缝;③孔隙以纳米级孔为主,主体孔径为5～50 nm,介于页岩储层与常规储层之间,并且非均质性强;④气藏具有源储共生、岩性控藏、大面积层状分布的特点,表现为两段式油气差异富集——"早期层内近源富集"与"晚期层间泄压调整";⑤外缓坡相带中伴随阵发性上升流沉积的黑灰色富有机质细粒灰泥灰岩的发育是天然气成藏的基础,黏土矿物转化控制了相对优质储层的发育,良好的保存条件是天然气成藏的关键,裂缝发育有利于天然气的富集高产。结论认为,该区茅一段是一种特殊类型的气藏——碳酸盐岩烃源岩气藏,并且具有较大的天然气勘探潜力,已有多口井获气;该类气藏的发现,不仅拓展了四川盆地天然气勘探的领域,而且还可以为中国南方其他地区的天然气勘探提供借鉴。

Discovery of carbonate source rock gas reservoir and its petroleum geological implications: A case study of the gas reservoir in the first Member of #br# Middle Permian Maokou Formation in the Fuling area,Sichuan Basin

Carbonate rocks in the first Member of Maokou Formation, Middle Permian in the Sichuan Basin (hereinafter "Mao 1 Member" for short) have been taken as a set of source rocks, and they have not been specifically studied from the aspects of reservoir evaluation and testing. By referring the exploration ideas of unconventional natural gas, the Fuling area of southeastern Sichuan Basin have obtained industrial gas flow in development well from Mao 1 Member in recent years. In order to clarify the natural gas exploration potential of Mao 1 Member in this area, it is necessary to study its sedimentary characteristics, natural gas reservoir forming conditions and main control factors based on the data of field section measurement, drilling system coring and laboratory testing. And the following research results were obtained. First, the gas reservoir in Mao 1 Member in the Fuling area is of source-reservoir integration, and its natural gas is mainly enriched in blackish gray marlite and nodular marlite. Second, its reservoir spaces are dominated by grain boundary pores (fractures), diagenetic shrinkage pores (fractures), organic pores and fractures. Third, the pores are mostly in a nanometerscale, and the main pore diameter is in the range of 5–50 nm, which is between shale reservoir and conventional reservoir and with a strong heterogeneity. Fourth, the gas reservoir is characterized by source-reservoir coexistence, lithology controlling reservoir and extensive layered distribution, presenting two-stage differential hydrocarbon enrichment, namely intraformational near-source enrichment in the early stage and interformational blowdown adjustment in the late stage. Fifth, the development of blackish gray organic-rich fine marlite which is deposited with the episodic upwelling in the outer ramp facies belt is the foundation for the formation of natural gas reservoir, the transformation of clay minerals controls the development of quality reservoirs, good preservation condition is the key to the formation of natural gas reservoir, and fracture development is favorable for the enrichment and high yield of natural gas. In conclusion, Mao 1 Member in this area is a special type of gas reservoir, i.e., carbonate source rock gas reservoir, which has greater potential of natural gas exploration and industrial gas flow have been obtained in many wells. What's more, the discovery of such type of gas reservoirs not only expands the field of natural gas exploration in the Sichuan Basin, but provides the reference for the natural gas exploration in South China and other areas.