渤海湾盆地渤中凹陷太古界潜山气藏BZ19-6的气源条件与成藏模式

Gas resources and accumulation model of BZ19-6 Archean buried-hill large-scale gas reservoir in Bozhong Sag,Bohai Bay Basin

传统上认为渤海湾盆地是受湖相泥岩生油母质烃源岩控制的富油型盆地,新构造断裂发育等因素不利于天然气聚集和保存。在认识渤海海域渤中凹陷发育的构造成因、演化与沉积充填特征基础上,开展了烃源岩热演化及生气产率热模拟研究,重新认识了富油型盆地在快速生烃的背景下,初次裂解气发育阶段的油气藏在深埋过程中也具备形成大型天然气藏的生烃强度。区域性分布的巨厚古近系超压泥岩,不仅防止了天然气的散失,也为天然气运移充注提供了超压动力。流体包裹体研究显示渤中凹陷普遍经历了早期油藏、晚期气藏的成藏过程。BZ19-6潜山构造由于多源高强度生气、靠近烃源的快速强充注、厚层泥岩超压封盖,形成大型高丰度凝析气藏。BZ19-6凝析气田的成藏认识和成功发现,突破了富油型盆地难以寻找大气田的认识,拓展了天然气勘探领域,对深埋古老变质岩潜山和活动断裂带天然气勘探具有重要的理论价值。

Traditionally the Bohai Bay Basin is prone to oil rather than gas pooling because it is dominated by lacustrine mudstones.Factors such as the development of young structural faults are not conducive to natural gas accumulation and preservation.Based on the understanding of the dynamics,evolution,and sedimentary filling characteristics of the Bozhong Sag in the Bohai Sea area,a thermal simulation of source rock evolution and gas generation rate was carried out.Under the background of rapid hydrocarbon generation in oil-rich basins,the reservoirs in the secondary gas generation stage have the hydrocarbon generation intensity to form large natural gas reservoirs during deep burial.The regionally distributed thick Paleogene overpressure mudstones not only prevent the loss of natural gas,but also provide the drive for natural gas migration and charging.Research on fluid inclusions shows that the Bozhong Sag has generally experienced the accumulation of early oil and late gas.The BZ19-6 buried hill structure has formed a large-scale high-abundance condensate gas reservoir due to multiple sources of high-intensity gas generation,rapid and strong charging close to the hydrocarbon source,and thick mudstone overpressure sealing.The understanding and successful discovery of the BZ19-6 condensate gas field has broken through the understanding that it is difficult to find large gas fields in oil-rich basins,expanded the field of natural gas exploration,and is important for natural gas exploration in deep buried ancient metamorphic buried hills and active fault zones.