沾化凹陷沙河街组浊积砂岩透镜体成岩作用特征及其意义

沾化凹陷古近系沙河街组沙三段深湖-半深湖暗色泥岩中发育大量的砂岩透镜体。通过密集采样，利用铸体薄片、X衍射、扫描电镜、荧光和阴极发光等分析方法研究了埋深3 199～3 201 m的典型砂岩透镜体表面和内部的各类成岩作用特征及其变化，发现透镜体砂岩内部强烈溶蚀，自砂体表面向砂体内部，碳酸盐胶结和石英、长石次生加大逐渐减弱。砂体表面的晚期碳酸盐胶结物形成致密胶结带，降低了砂岩物性，但这并不影响砂岩透镜体成藏。通过成藏时间与成岩次序研究，认为透镜体表面的晚期胶结发生在成藏之后，内部溶蚀发生在成藏之前。透镜体内部发育的次生孔隙表明早期溶蚀强烈，这为排烃高峰期的油气成藏提供了足够的储集空间，并减小了油气充注的毛细管阻力;后期砂体表面的晚期碳酸盐胶结物降低储层表面物性，导致毛细管阻力变大，抑制了油气充注，但成为透镜体油气藏的有利保存条件。因此，并非所有的透镜体表面致密胶结带都对透镜体成藏起到阻碍作用。

Characteristics and Significance of the Turbidite Lenticular Sandbody Diagenesis in Shahejie Formation, Zhanhua Depression

Many lenticular sandbodies developed in dark shales of Shahejie Formation in Zhanhua depression. With analysis of cast thin section, X-ray diffraction, scanning electron microscopy， fluorescent light and cathodoluminescence micrography, diagenetic differences from the exterior to the interior of the typical lenticular sandbody were analyzed by dense sampling from 3 199 m to 3 201 m. There was intense dissolution in the sandstones, but carbonate cementation, quartz overgrowth and feldspar overgrowth decreased from the exterior to the interior of sandbody. The later carbonate cement formed a tight cemented layer, which decreased the sandstones porosity. However, the oil and gas accumulation was not impacted by the tight cemented layer. By analysing the sequence of diagenesis and the oil accumulation, we find the cementation was later than the oil accumulation. The secondary porosity of the sandbody showed the early intense dissolution, which supplied enough space for the hydrocarbon charging peak and decreased the capillary resistant force. After the oil and gas accumulation, the later carbonate cement decreased the exterior sandstones porosity and increased the capillary resistant force, which depressed the oil charge and protected the reservoir. In a word, not all tight cemented layers near the exterior sandbody could disturb the oil and gas accumulation.