致密油储层微观非均质性及成因探讨

Discussion of microscopic heterogeneity and its cause of formation tight oil reservoirs

应用CT技术对鄂尔多斯盆地延长组长7油层组块状致密砂岩样品进行扫描，发现外观均质的块状砂岩内部表现出明显的CT响应差异，并且由样品顶端至底端CT吸收值呈现出逐渐变低的递变趋势。据此对该砂岩样品不同部位取样，并进行铸体薄片分析。结果显示，该致密砂岩样品具有微观非均质性，在整体致密、可见孔隙少，压实和胶结作用明显的背景下，不同部位孔隙特征有差异。最显著的差异是样品底端广泛发育微裂缝．以务状延伸和顺层展布为主，并多见有机质充填。分析认为长7块状砂岩重力流滑塌成因机制造成微裂缝广泛分布，差异溶蚀造成孔隙分布不均匀。这种块状致密砂岩内部的微观非均质性，尤其是广泛发育的微裂缝对致密油勘探及开发具有重要意义．说明了储层微“甜点”的存在．也指出了储层改造潜在的有利部位。

A sample of blocky tight sandstone, from Chang7 oil reservoirs group of Yanchang Formation in Ordos Basin, was scanned with CT technology. It is tound that there are signifieant differences in CT response inside the massive sandstone with a homogeneous appearance, and the CT absorption value be the sample from the top to the bottom shows a gradual decreasing tendency. In view of the above, the different parts of the sandstone were sampled, and analysis of casting lamella was conducted. The results show that the tight sandstone sample is with microscopic heterogeneily. Under the background of overall tightness, less visible pores, and obvious compaction and cementation. characteristics of pores in diffcrent paris are diffefent. The most signitiemll difl~：,renee is the exlensi＇~e nfiero-fraetures developed on Ihe bottom of the sanlple. These micro-fractures mainly extend in strips and are distributed along the bedding. with organic matter filling frequently found. It is eonsidered by analysis that the mechanism of genesis of gravity flow slump of Chang7 massive sandstone caused the v, idespread distfibution of micro-cracks. while differential corrosion caused the uneven distribution of pores. This microseopie heterogeneity inside the tight sandsLone in blocks, especially the extensively developed mierofractures are of great significance for exploration and development of light oil. indicating that the micro ＂sweet＂points exist in the reservoirs,and pointed out the favorable positions of potential rescrvoir stimulation.