Three Malang Sag Santanghu Basin Sedimentary Jurassic Xishanyao Formation Of Middle Jurassic In The Research Phase

This paper takes the middle Jurassic stratum in Malang Sag,Santanghu Basin as the research object,systematically carries out stratigraphic division and comparison,provenance analysis,sedimentary facies and lithofacies palaeogeography.In order to evaluate the overall distribution and potential scale of the sandstone reservoirs in the Xishanyao formation in the Malang Sag,favorable geological theories and data support are provided for the development zones of favorable reservoirs.By systematically comparing well logging and drilling data in the Malang Sag in the study area and combining seismic data with the target horizon,the Xishanyao Formation in the Malang Sag is divided into two stages.The Xishanyao Formation section corresponds to the fourth-order sequence of MSC1.The study area is characterized by low-accommodating space,adequate material sources,and sedimentary thick sand bodies;the lower part of the Xishanyao Formation corresponds to the fourth-order sequence of MSC2.Pingbu Qi and developmental coal seams;the upper part of the second member of the Xishanyao Formation corresponds to the fourth-order sequence of MSC3.The sags of the depression basin can increase in space,but the supply of material is insufficient,mainly mudstone and argillaceous siltstone.Based on the latest test data and the identification results of the rock fragments,the authors systematically studied the sediment source direction of the Xishanya Formation in the Malang Sag of the Santanghu Basin by analyzing the detrital composition,heavy mineral composition and ZTR index characteristics of the sandstones in the Malang Sag..It reveals that there is a vertical source of skirts in the southern and northern orogenic belts of the Mashan Sag in early Xishanyao Formation.The sag develops north-south bidirectional sources,seven delta clusters,and mainly northern sources.Based on the detailed description of the drilling core,comprehensive logging data and other data,the sedimentary facies marks of the study area were accurately identified.According to the phase signs,the braided river delta facies in the first section of the Xishanyao Formation in the Malang Sag was identified,and the second section of the Xishanyao Formation mainly developed lacustrine facies.And from the bottom of the braided river delta upward transition to shallow lake swamps to shallow lakes.On this basis,the composition of the sedimentary subfacies and microfacies is further divided,and the characteristics of their respective typical signs are revealed.On the basis of provenance analysis,vertical analysis of single wells and wells,the process model and lithofacies paleogeographic characteristics of the Xishanya Formation in the Malang Sag were studied.It is revealed that the depression basin of the Xishanyao Formation shows a water inflow process.The center of the sedimentary basin depression migrates from south to north,and the shallow water near the source delta flows southwards.During the period of MSC1 rise of the first section of the Xishanyao Formation,three small layers of filling braided river deltas moved southwards and retreated northwards,with the south high and the north low.