苏北盆地高邮凹陷北斜坡阜宁组成岩作用及储层特征

Clastic diagenesis and reservoir characteristics of Funing Formation in north slope of Gaoyou Depression in Subei Basin

高邮凹陷北斜坡阜宁组碎屑岩储层以细砂岩和粉砂岩为主 ,砂岩类型主要为长石砂岩、岩屑长石砂岩和少量长石岩屑砂岩。主要成岩矿物类型为粘土矿物、石英和碳酸盐等。储层以次生孔隙发育为主 ,粒间孔隙和骨架颗粒溶孔最为发育。阜宁组成岩演化阶段处于早成岩B期至晚成岩A期。机械压实作用比较明显 ,但次生溶蚀作用亦表现得十分强烈。阜宁组储层性质明显地受到沉积微相和成岩作用的影响。在阜一段三角洲主要砂体微相中 ,沉积物粒度较粗、厚度较大的河道和砂坝砂的储集物性明显优于各种粒度较细、厚度较薄的席状砂体。阜三段三角洲前缘砂体发育 ,水下分流河道和河口砂坝物性最好 ,前缘席状砂及其他侧翼砂体的物性较差。平面上储层性质主要表现为相控特点 。

The reservoirs of Funing Formation in the northern slope of Gaoyou Depression are of the fine_grained and moderately sorted sandstones that can be classified as arkoses, lithic arkoses and feldspathic litharenites. Funing reservoir sandstones contain a diagenetic mineral assemblage that recorded the major diagenetic events during burial history. The early calcite was formed at shallow burial, whereas later ferroan carbonates may record a deep diagenetic event. Kaolinite was generated mainly as randomly oriented or vermiform stacks of pseudohexagonal crystals that formed a loosely packed and erratially distributed pore infilling. Chlorite was generated in the deeply buried reservoirs and commonly formed the grain_sized masses. Illite was also generated in the sandstones and formed the grain rims that commonly bridged pores. Authigenic quartz overgrowth and micro crystals contained a variety of organic fluid inclusions that indicated the petroleum filling history. Secondary porosity was created mainly by feldspar, rock fragment and clay matrix dissolution. Based on the diagenetic events related to temperature,the diagenetic stage of reservoirs in Funing Formation was in the period from B_substage of early diagenesis to A_substage of later diagenesis. Reservoir quality was controlled mostly by the sedimentary microfacies and diagenesis. Distributary channel and mouthbar sandbodies commonly have high porosity and permeability, whereas interdistributary and distal sand sheets may have poor petrophisical properties. The reservoir property was controlled by facies in the plane.