辽河盆地大民屯凹陷沈95区块砂岩储层中钙质夹层研究

钙质夹层是控制剩余油形成与分布的主要因素之一.辽河盆地大民屯凹陷沈95区块钙质夹层十分发育,利用丰富的岩心、测井资料,识别并探讨了钙质夹层的分布规律及成因.研究表明:本区钙质夹层是早期无铁碳酸盐与晚期含铁碳酸盐胶结形成的两期夹层;早期钙质夹层主要分布于泛滥平原亚相、三角洲平原亚相;晚期钙质夹层主要发育于三角洲前缘亚相,且一般位于砂泥岩接触带,厚层砂岩顶底部碳酸盐胶结物较中部高.早期钙质夹层是沉积期、成岩早期,蒸发作用使富钙孔隙水中的钙质沉淀形成的;晚期钙质夹层是在有机酸作用下,Ca2+、Mg2+在烃源岩(泥岩)中溶解,再于储集岩(砂岩)中沉淀形成的.根据夹层的分布规律可以更有效地挖掘剩余油.

Calcareous interbeds in the sandstone reservoir of Shen 95 Block within Damintun Sag, Liaohe Basin

Calcareous interbeds are one of the main factors controlling the formation and distribution of remaining oil. Calcareous interbeds are extraordinarily developed in Shen-95 Block, Damintun Sag. Using rich core and logging data available, the authors have dealt in detail with the genesis and distribution of calcareous interbeds. Studies show that calcareous interbeds in this area were formed by early nonferrous carbonate and telogenetic ferroan carbonate cementation. Early calcareous interbeds are mainly distributed in the flood plain and delta plain, whereas telogenetic calcareous interbeds are mainly spread in the delta front, lying in the interface between sandstone and mudstone, with their contents higher at the bottom or top of the thick sand body than in the middle part. Early calcareous interbeds were produced in the process of evaporation resulting in the precipitation of calcium-rich pore water in the deposition phase, whereas telogenetic calcareous interbeds were formed during the dissolution of Ca2+ and Mg2+ in the hydrocarbon source rock (mudstone) and the precipitation of Ca2+ and Mg2+ in the reservoir rock (sandstone) under the condition of organic acid. The distribution regularity of the calcareous interbeds is obviously helpful to the exploration of remaining oil.