The Study On Depositional System And Distribution Of The Chang6 And Chang4+5 Sets, Yanchang Formation, The Upper Triassic, In Middle-east Ordos Basin

Based on the observation and study of several field sections and three drill cores, the analysis of all drilling and logging data, the observation and identification of thin-sections and the measurement of light and heavy minerals of sandstones of chang6 and chang4+5 sets , the upper Triassic Yanchang formation, in Hejiaji oilfield of Zizhou, Ordos Basin, the detail distinguish and correlation of the sets, the palaeocurrent and source direction, the depositional system and facies are detail dicussed, with many new theories and technological methods in sedimentology and petroleum geology. Then we detail analysis the spreading rules and genetic type of the sandstone.According to the rock types, sedimentary architecture and structure, grain distribution as well as logging facie, the sedimentary system of chang6 and chang4+5 sets in the study area is distinguished, belonging to distributary channel and inter-distributary area microfacies in delta plain. The distributary channel deposits is the main reservoir bodies in the Zizhou area of Hejiaji oilfield.According to the analyzing of the vertical evolution and spreading of sandstone bodies, the oil-bearing sandstone bodies of chang6 and chang4+5 sets are distinguished by its regular spreading along northeast-southwest direction. The sandstone bodies are gradually developed fully form chang6~4 to chang6~1, and the depositional pattern of the chang4+5 has no difference from chang6 except not well development. The detail analysis of the main reservoir sand-bodies indicates its genetic type of distributary channel in delta plain, witch give a good reference for further oil and gas exploration...