苏北盆地3种退积型三角洲沉积体系及砂体储集性能对比

苏北盆地由一系列小型断陷组成，不同部位发育了不同类型的三角洲沉积体系。在湖盆扩张期发育的退积型三角洲沉积体系中，扇三角洲坡降大、近物源，碎屑流沉积发育，颗粒粗、磨圆度低、分选差，前缘相中一般缺少河口坝和远砂坝微相，平原水道物性差，一般不是有效储集层，水下分流河道和前缘席状砂是重要的储集体；辫状三角洲坡降中等，平原亚相以辫状河道发育为特征，前三角洲亚相发育水下滑塌重力流和浊流，分流河口砂坝、远砂坝、前缘席状砂和水下分流河道砂体是滚动勘探的重点层位，但浊积岩和水下滑塌重力流水道砂体也是重要储集体；正常河流三角洲坡降较缓，岩性细，分选好，与滨浅湖相伴生，生物碎屑灰岩、滩坝和分流河口砂坝厚度大，位于沉积序列的上部，是最有利的储集层。图7表1参6

Three delta deposition systems and reservoir property correlation in Subei Basin

Subei Basin is composed of a series of small rift basins. Different delta systems such as fan delta with coarser, low rounded and badly sorted gains are developed on precipitous slop, closing to source rock. Channel sand bodies in fan delta plain with low physical properties are not effective oil and gas reservoirs. Its submerged branch channel and sand sheet are the important reservoirs. Braided delta usually developed on middle part of the slop. Braided rivers are well developed on fan delta plain. Gravity flow channel and turbidity currents are often found on fan delta-front zones. The distributary mouth bar, distal bar, sand sheet and submerged branch channel could be the important play targets. Normal delta with thin and well sorted grains developed on low slop and accompanies shallow lake facies. Biotic clastic limestone, beach bar and distributary mouth bar with thick sand could be the beneficial reservoirs.