黄骅坳陷歧口凹陷斜坡区中深层碎屑岩储集层特征

Medium-deep clastic reservoirs in the slope area of Qikou sag,Huanghua depression,Bohai Bay Basin

为了查明渤海湾盆地黄骅坳陷歧口凹陷斜坡区中深层碎屑岩有利储集相带分布规律,寻找相对优质的储集层段,对歧口凹陷中深层开展储集层特征及控制因素分析。构造背景、物源、沉积体系、储集性能综合研究表明,歧口凹陷古近系具有多凹多坡的地质特点,各类斜坡区占全凹陷面积70%以上;来自盆内外物源的多个大型辫状河(扇)三角洲前缘-重力流砂带与多类斜坡区匹配,为歧口凹陷斜坡区中深层油气有效储集层的形成奠定了良好的物质基础;中深层碎屑岩埋深一般大于2 500 m,主要为岩屑长石类砂岩,以次生孔-缝储集空间为主。歧口凹陷中深层碎屑岩整体处于中成岩演化阶段,该阶段跨越深度范围较大,储集物性的主控因素可以通过数学地质的方法识别出9项,虽其总体物性较差、孔隙结构复杂,但较高的沉降速率、中等地温场、高流体压力、高长石含量、较高溶蚀率、早期烃类充注等有利因素促使中深层碎屑岩发育纵向延伸上千米的3～4个异常高孔隙带,均是有利的油气储集层段。

To get a better understanding of the distribution pattern of favorable reservoir belts in the medium-deep clastic rocks in the Qikou sag of the Huanghua depression,and find out premium reservoir zone,the characteristics and controlling factors of the medium-deep reservoirs in the Qikou sag were analyzed.Comprehensive study into the structural setting,provenance,depositional system,and reservoir properties shows that the Paleogene in the Qikou sag has multi-sags and multi-slopes,with slopes accounting for over 70% of the total sag area.A number of large braided river（fan） delta front-gravity flow sand bodies matching with multi-slope zones lay a good material foundation for the formation of medium-deep effective reservoirs there.Generally buried at over 2500 m,the medium-deep clastic rocks are mainly lithic feldspathic sandstone,with secondary pores and cracks as major reservoir space.Being in the medium diagenesis evolution stage,the medium-deep clastic rocks in the Qikou sag span over a large depth.Nine major factors affecting reservoir properties have been identified by mathematical geology.Although the medium-deep clastic rock interval is poor in physical properties and complex in pore structure,high sedimentation rate,medium geothermal field,high fluid pressure,high feldspar content,relatively high dissolution rate and early oil and gas charge have given rise to three to four belts with abnormally high porosity in it,which are all favorable hydrocarbon reservoir zones.