关键词: 致密储层, 孔隙度演化, 长81储层, 姬塬西部地区, 鄂尔多斯盆地

Abstract:

Several sets of calcareous interlayers are well developed in Zhujiang Formation in Nanhai A oilfield, and they are the main factors controlling bottom water rising and remaining oil distribution. Based on rock thin section identification, carbon and oxygen isotope analysis, the rock components in calcareous interlayers were studied, and its origin and forming stages were defined. Combined with sedimentary characteristics, the controlling factors of calcareous interlayers were discussed. The results show that calcareous interlayers have consistency at microscopic origin, and they are formed by the chemical precipitation of rock pore fluid during the diagenetic process. The calcareous material came from the crystallization of contemporaneous carbonates, the dissolution of bioclasts and the transformation of clay minerals. The distribution of calcareous interlayers are controlled by structural depth, their thickness ratio to mudstone and sedimentary cycle, with the characteristics of continuity and discontinuity in lateral. The enrichment degree of remaining oil is high in the large distribution area of bottom calcareous interlayers.

Key words: tight reservoir, porosity evolution, Chang 8₁ reservoir, western Jiyuan area, Ordos Basin