东营凹陷古近系砂岩透镜体钙质界壳形成机理及其对油气成藏的影响

砂岩透镜体 / 泥岩接触带钙质界壳是含油气盆地泥岩（烃源岩）－流体（油、气、水）－砂岩（储集岩）相互作用过程中的产物。烃源岩－地层水相互作用生成的有机酸促使烃源岩中矿物、特别是碳酸盐矿物的溶解。烃源岩中生成的烃类流体和地层水，在驱动力的作用下，向临近的砂岩透镜体内运移，同时携带含碳酸盐的有机酸一起运移。烃源岩－水溶液作用后的流体重新进入到一个新的储集岩，在新的物理化学环境中要与储集岩再次发生作用。流体与储集岩作用的直接结果是方解石和白云石沉淀到储集岩中，它们将占有原岩的部分孔隙空间，形成胶结物，进而形成钙质界壳。这样形成的碳酸盐胶结物为晚期胶结物，主要为含铁方解石和铁白云石。砂岩透镜体碳酸盐胶结物含量与孔隙度、渗透率和含油饱和度存在很好的负相关性。钙质界壳的存在使得孔隙结构也发生变化：原生孔隙被碳酸盐胶结物充填，发育的次生孔隙是碳酸盐胶结物的晶间和晶内微孔隙；压汞曲线较陡，排驱压力和中值压力高；喉道偏细，分选较差。东营凹陷牛35井沙三中段2 939 ～3 003 m井段6个主要砂层组的精细解剖表明，砂岩透镜体 / 泥岩接触带钙质界壳是控制砂岩透镜体成藏的重要因素。

Formation mechanism of calcareous incrustation in lenticular sandbody of the Shahejie Formation of Paleogene and its influence on hydrocarbon accumulation in Dongying Sag

 Calcareous incrustation in the sand-mud interface of lenticular sandbody is the production of interacting process of mudstone (hydrocarbon source rock), liquid (oil, gas and water) and sandstone (reservoir rock) in petroliferous basins. The interaction of hydrocarbon source rocks and formation water produces organic acid that can dissolve minerals, especially carbonate minerals. Hydrocarbon liquid which is produced in hydrocarbon source rock and formation water, transfer to the lenticular sandbody in the vicinity under the effect of impetus. The organic acid bearing carbonates also migrates with them. The liquid which is produced after the interaction of hydrocarbon source rocks and aqueous solution will enter a new reservoir rock. In the new physicochemical environment, it will react with the reservoir rock again. The direct result of interaction of liquid and reservoir rock is the precipitation of calcite and dolomite, which will occupy some pore space of the source rocks and create cements, then the calcareous incrustation will be formed. The carbonate cements, mainly consisting of ferroan calcite and ankerite, are telogenetic cements. The content of carbonate cements in lenticular sandbody has a negative correlation with porosity, permeability and hydrocarbon saturation of lenticular sandbody. The existence of calcareous incrustation causes the change of pore structure: the primary pores are infilled by carbonate cements, the secondary pores being developed are intercrystal and intracrystal micropore; mercury-injection curves are steep, displacement pressure and median pressure are high; pore interconnections are too small and sediments are poorly sorted. Refined analysis on the anatomization of six sand-bed groups in 2 939～3 003 m of Well Niu 35 of the middle part of Member 3 of Shahejie Formation of Paleogene in the Dongying Sag indicates that calcareous incrustation in sand-mud interface is an important factor to control the hydrocarbon accumulation of lenticular sandbody.