Zhidan Exploration In The Ordos Basin Triassic Depositional System

Apllied with field profile observation,core description,logging data interpretation, thin section identification, reservoir lithology and physical analysis, and some effcective theories of other subjects such as sedimentology, lithofacies- paleogeography, reservoirgeology, and sequence stratigraphy, the sedimentology systerm of Triassic Yanchang Formation of Zhidan region was studied deeply.By the primary marks of contrast in region, data of reconnaissance in field and interface of sequence stratigraphy, stratum of the oil-containing interval Yanchang formation were devised.Based on the tectonic movement surface, super long-term base level cycles are marked off.All the sequences are identified from logging profiles, including sequence boundaries, maximum flooding surface, first flooding surface, ubsequences and subsequence sets; meanwhile, identified and classified system tracts and datum level cycles, From all the work above, Yanchang Formation are divided into a tectonic supersequence and five pieces of third class sedimentary sequences, which are use to analysis the control of the reserviors.This paper investigated source of Yanchang formation in Zhidan region, by the study of the regional geology, palaeocurrent direction, light and heavy mineral debris analysis, trace element and REE analysisi as well as ancient land distribution feature. These make sure that NE is the main direction of sediment provenance, and that metamorphic rock of Archeozoic and lower Proterozoic.According to outcop observation, core description, single well log facies analysis and connecting-well section comparison, combining with rock type, depositional tecxture, structure characteristics, paleontology, litho-electric features, profile structures and sedimentary cycles, ect. It shows that Yanchang formation is composed of the lacustrine system and the delta system in Zhidan region, which are subdibide carefully into 5 subfacies and 16 microfacies, the modal is the deltaic front microfacies.The sedimentary microfacies and sandstone distribution character of Yanchang formation in Zhidan region is displayed for the first time by this thesis.Considering that subaqueous distributary channels in deltaic front microfacies and distributary channels are the main frame sandbodies for oil and gas reservoir.The distribution rule of sandbodies is determined by sedimentary facies. Sedimentary environments of Yanchang formation have good inheritance, which make all the sandbodies of different time spreading in the NE direction in the region. The favorable source-reservoir-caprock group can be formed for the frequency of lacustrine transgression and regression. Through analysisi of sedimentary facies, the distribution of sandbodies, the character of structure and the property of reservior, etc, the favorable exploration area can be found out in the main oil-bearing beds of Yanchang formation in the region.