Depositional System Of Chang 4+5 Oil Formation Of Triassic Yanchang Formation Of The Western Nanliang Area

In this article we select Chang 4+5 oil formation of Triassic Yanchang Formation of the western Nanliang area in Ordos basin as the object of study, and analyzes the current situation in the study area combining previous research achievements. Under the direction of advanced theories of sedimentology, geophysics and geochemistry, based on outcrops and core observations, combining with drilling and logging data, we carry on the research of Chang 4+5 oil formation's stratigraphic division and correlation,and analyze the source directions, microfacies types, sedimentary system characters and their planar distribution rules.We divide the Chang 4+5 oil formation into 5 small beds,and establish 6 comparison of connecting-well sections to take more accurately strata contrast.Using the method of light and heavy minerals, palaeocurrent and rock trace element characteristics,we conclude that the source of the study area is northeast and north provenances in Ordos basin. The source rocks of northeast proveniences are deep metamorphic schist and gneiss of Archean Wulashan Group.Under the influence of the source,the study area mainly develop two sedimentary systems in the age of Chang 4+5, which are the delta river sedimentary system and the lacustrine depositional system. The main subfacies are the delta front subfacies and the shallow lacustrine subfacies. The distribution of sedimentary facies is closely related to the distribution of sand body,and the distribution of sedimentary facies control the trend of sand body. The study area develop three sand bodies which are nearly north-south to west distribution throughout the study area during the Chang 4+522 and Chang 4+512 period.In the Chang 4+511 period there are two sand bodies in the study area which distribution are consistent with the previous.