黄河口凹陷L油田复杂断块油气成藏模式

HYDROCARBON ACCUMULATION MODEL OF COMPLEX FAULT BLOCK IN L OILFIELD OF HUANGHEKOU SAG

L油田位于渤海湾盆地黄河口凹陷中央构造脊,是油气运聚的有利区带,主力含油层位为新近系明化镇组,为受复杂断块控制的岩性-构造油气田,L油田周边油气成藏潜力巨大。通过油源对比、流体包裹体、埋藏史及流体动力学分析认为,渤海湾盆地黄河口凹陷L油田油气成藏具有以下特征:油源主要来自古近系沙三段,部分来自沙一段;切入古近系的深层断裂成为油源断裂;馆陶组厚层辫状河流相砂砾岩成为临时仓储层,油气从油源断裂运移至馆陶组砂岩,运移路径从纵向转化为横向;油气通过砂体-次生断裂疏导网络,在浅层明化镇组曲流河-浅水三角洲"泥包砂"环境下的薄层砂岩储层中,晚期运聚成藏,油气藏分布明显受到次生断裂和砂岩耦合关系所控制。通过该模式指导下,L油田通过老区扩边、发现新区块和新区块滚动勘探开发等3种方式精细勘探与评价,新增探明原油地质储量超过2 000×10~4t,该模式对渤海湾盆地黄河口凹陷的滚动勘探开发具有指导意义。

L oilfield is located in the central structural ridge of Huanghekou Sag,Bohai Bay Basin. It is a favorable area for oil and gas migration and accumulation. The main oil-bearing horizon is Minghuazhen Formation of Neogene. L oilfield is a lithologic-structural oil and gas field controlled by complex fault blocks,the oil and gas accumulation potential around L oilfield is huge. Through oil source correlation,fluid inclusion,burial history and fluid dynamics analysis,it is considered that L oilfield in Huanghekou Sag of Bohai Bay Basin has typical network-carpet reservoir-forming characteristics: the oil source mainly came from the third member of Shahejie Formation of Eogene,and partly from the first member of Shahejie Formation;oil-source faults cutting into Eogene become the oil source channel network layer;the thick braided fluvial sandy conglomerate of Guantao Formation becomes a temporary reservoir,oil and gas migrate from oil source faults to Guantao Formation sandstone,and the migration path changes from vertical to horizontal;thin sandstone in meandering river-shallow water delta environment of Minghuazhen Formation becomes the upper oil and gas accumulation network layer,then oil and gas migrate and accumulate through sand body-secondary fault dredging network. Under the guidance of this model,L oilfield has added more than 20 million tons of proven oil geological reserves through three ways: enlarging the boundaries of old areas,discovering new blocks and progressive exploration and development of new blocks. This model has guiding significance for progressive exploration and development of Huanghekou Depression in Bohai Bay Basin.