CHARACTERISTICS OF SEDIMENTARY MICROFACIES OF CHANG 4+5 OIL-BEARING FORMATION OF YANCHANG F0RKATION IN HUJIANSHAN-GENGWAN AREA,ORDOS BASIN

Base on well's core data,integrated with reservoir lithology,depositional structure and grain size analyses,the sedimentarymicrofacies of chang 4+5 oil-bearing formation of yanchang formation in hujianshan-gengwan area is studied. The result shows thatfront-delta is the main sedimentary system of Chang6 in the studied area,the subaqueous distributary channel,channel-mouth bar,interdistributary,distal bar and front sheet sandstone are the main sedimentary microfacies. The underwater distributary channel sandstone are crossed and connected of Chang 4+52 of Yanding delta,anbian delta and wuqi delta and the compartmentation of underwater distributary channels is strong. While with the decrease of the lake basin,the underwater distributary channels are reduce,and the interdistributary extend of chang 4+51. The compartmentation of underwater distributary channels of chang 4+52 is more obviously,and subaqueous distributary channel sandstone is thickenss,is the major reservoirs in the study area.