The Research Of Sedimentary Microfacies And Reservoir Geologic Feature Of Shan Xi Formation, Yan Qi 2 Well Field Of Yan Chang Oil Region

Shanxi formation was one of the most important zones in mid-eastern Ordos Basin. Thus, on basis of a myriad of previous studies, the outcrop research and some existing well datum of log, well logging and core description, this paper researched the fine division and correlation of strata in yanqi2 well field, and then conducted research on reservoir geologic feature of the study area, in which combining modern testing means with many course theoretics.In combination with the analysis of regional geological setting, generally, Shanxi formation of yanqi 2 well field was divided into six submembers in this paper by studying on marker beds, sedimentary cycle, and logging curves'features. Each submember was stable in their regional distribution, with the thickness of 10.5-28.7m. Shan23 submember, obviously, developed sand body sediment with continuous distribution, however, up to shan11 submember the thickness varying from thick to thin and the distribution area from large to small. At the same time, through analyzing data of core description, log and thin section identification, it concluded that delta front which included underwater distributary channel, interdistributary bay, interdistributary bay swamp and channel-mouth bar, etc, obviously, was the main sedimentary facies in the study area. Furthermore, the main sandstone belt sedimentary and the interdistributary bay distribution in the study area extended nearly NS and NE-SW direction. Underwater distributary channel distribution was different in each submember due to the lateral migration, diversion and catchments of the underwater distributary channel, as well, from shan23 submember to shan11 submember become gradually smaller.According to the studies of casting thin section, scanning electron microscopy and X diffraction, it showed that:â‘ Dthe reservoir sandstone of shanxi formation was mainly made of quartzy sandstone, in which the quartz maximum content reach about 85%, more than lithic, then feldspar. The interstitial matrix of reservoir consisted amount of clay minerals, silicoide and siderite, etc. Meanwhile, the reservoir sandstone experienced complex diagenesis, likely compaction, pressolution, cementation, metasomatism and dissolution. Therefore, the grains mainly contacted with point-line, concave-convex and stylolite pattern, among which the reservoir developed pore cementation, besides, detritus or fragment and its internal are dissolved.â‘¡When it comes to the pore spaces of reservoirs, it was mainly composed of intergranular dissolution pores, fragment dissolution pores, a little feldspar dissolution pores, iniercrystalline microspores of kaolinite and residual intergranular pores.â‘¢Ultimately, all these factors have created the reservoir with extraordinary low porosity and low permeability. Reservoir physical differ widely in each submember, with Shan23 submember best and shan12 submember better than other submembers. Moreover, the reservoir of shanxi formation showed stronger unhomogeneity, and the pore structure types were fine pore-small throat through the research of capillary pressure curves.To sum up, the reservoir of shanxi formation in yanqi 2 well field could be classified into four types, with theâ…¡,â…¢types as the dominant effective reservoirs, while, I type developed in shan23 submember.