Sedimentary Microfacies Characteristics And Distribution Of The Middle Ordovician Yijianfang Formation In Tahe Oilfield

In this thesis,high-precision sequence stratigraphy and fine sedimentary facies were studied in the main area of Tahe oilfield?mainly the 7th and 8th zones?by comprehensively using drilling cores,thin sections,imaging logging,conventional logging,field outcrop and seismic profile data.The aim is to clarify the sequence structure and control the formation and distribution of relatively high-energy sedimentary particles,and to provide a basis for predicting the distribution of favorable beach facies reservoirs.The main achievements and understandings obtained in this thesis are as follows:1.According to field data,cores,thin sections and well logging data,and after the comprehensive identification,the first-order sequence interface?T₇⁴?,the top interface of Yijianfang Formation,and the third-order sequence interface?T₇⁵?,the bottom interface of Yijianfang Formation are identified.Based on lithology and logging characteristics,two four-level sequence interfaces are identified in Yijianfang Formation(T₇^4-1,T₇^4-2),and according to this,the Yijianfang Formation is divided into three four-level sequences,Yjq1?the first section of Yijianfang Formation?,Yjq2?the second section of Yijianfang Formation?,Yjq3?the third section of Yijianfang Formation?.The four-level of sequence contrast framework is established.2.Based on the observation of cores and thin sections,9 types of sedimentary microfacies are identified in the four-level sequence stratigraphic framework:Oolitic limestone?Mf1?,sparry intracrystalline clastic limestone?Mf2?,sparry bioclastic limestone?Mf3?,micrite bioclastic limestone?Mf4?,granular micrite?Mf5?,sparry granular limestone?Mf6?,bioclastic micrite?Mf7?,micrite?Mf8?and micrite granular limestone?Mf9?,It is further combined into four sedimentary environments:intershoal sea,low energy beach,medium energy beach and high energy beach.3.The response characteristics and identification charts of different sedimentary microfacies on imaging logging and conventional logging curves are established by means of the step by step calibration method from core to imaging logging and then to conventional logging curves.Based on the analysis of sedimentary microfacies of single well and connected wells,the plane distribution and longitudinal evolution of sedimentary microfacies are determined.The Yijianfang Formation mainly developed medium beach and high energy beach deposits.In the third section of the Yijianfang Formation,the individual beach body and the overall beach body were relatively thick and with good connectivity.In the first section,the beach body was relatively thin and still with certain connectivity.4.According to the distribution of sedimentary microfacies,core thin sections and the development thickness of beach body,the development range of favorable beach facies reservoir was determined,mainly corresponding to the sedimentary environment of medium and high energy beach facies.Micritic granular limestone,micritic bioclastic limestone and arenaceous micritic limestone are mainly developed with a thickness of about 90m.