鄂尔多斯盆地上古生界天然气藏类型辨析

针对鄂尔多斯盆地上古生界天然气藏是否为深盆气藏的问题,从成藏条件、成藏期次和气水分布特征等方面与典型的加拿大阿尔伯达深盆气藏进行综合对比。研究结果表明鄂尔多斯盆地上古生界气藏烃源岩分布广泛、生气中心不明显、生气速率较低、持续供气条件较差且供气分散,难以形成满足深盆气藏气驱水的动力;储层物性差、非均质性强、展布方向与构造走向一致且上倾方向为物性较差的致密层,不具备深盆气藏储层向上倾方向物性变好的条件;源储配置样式为"自生自储"式和"垂向叠置"式,由于砂体规模小、分布不连续,源储接触局限,不具备深盆气藏源储大面积接触的特征;天然气发生3期成藏,在盆地埋藏期与抬升期均可成藏,成藏时间较早,后期气藏调整改造强烈,不具备深盆气藏的保存条件。气水分布主要受储层物性和区域构造控制,分布复杂、分异不明显,没有气驱水形成的"气水倒置"界面。成藏特征综合对比分析表明鄂尔多斯盆地上古生界气藏并非深盆气藏,应为主要由储层物性控制的岩性气藏,该区油气勘探应以优质储层研究为重点。

Discussion on Types of Upper Paleozoic Gas Reservoirs in Ordos Basin

In order to estimate whether the Upper Paleozoic gas reservoirs in Ordos Basin are deep basin gas reservoirs or not,the accumulation conditions,accumulation periods and gas-water distribution regularity were studied and compared with those of the deep basin gas reservoirs in Alberta Basin.The results show that the Upper Paleozoic gas reservoirs in Ordos Basin have the characteristics of extensive distribution of source rocks,unobvious gas generation center,low gas generation rate,bad persistent and decentralized gas-providing condition,so that the force of gas driving water is not enough to form deep basin gas reservoirs for the Upper Paleozoic natural gas.For the low porosity and permeability,strong heterogeneity,similar distribution direction between sand bodies and regional structure,surrounded by mudstones in the updip direction,the Upper Paleozoic reservoirs in Ordos Basin were different from those of deep basin gas reservoirs characterized by porosity and permeability being better and better along the updip direction.The source-reservoir assemblage styles,with limited contact areas between source rocks and reservoirs due to small scale and discontinuous sand bodies,are "self-generation & self-accumulation" and "sand bodies superposed on source rocks" and are different from those of deep basin gas reservoirs which have great scale contact areas.The Upper Paleozoic gas reservoirs have three accumulation periods including the burial and uplift periods of basin,experienced strong late reformation,and don't have the conservation condition of deep basin gas reservoirs.Gas and water,controlled by the physical properties of reservoirs and the regional structure,have complicated distribution,unobvious partition and no "gas-water inversion" interface resulted from gas driving water in the reservoirs.The characteristics of the Upper Paleozoic gas reservoirs in Ordos Basin show that the Upper Paleozoic gas reservoirs are the stratigraphic gas reservoirs mainly controlled by the physical properties of reservoirs and not deep basin gas reservoirs.This indicates that the study of favorable reservoirs should be paid more attention in the future petroleum exploration.