Research On Sedimentary And Reservoir Characteristics Of The Upper Permian In Peripheral Region Of Bogda Mountain

Based on the data of cores,well logging and outcrops and taking the stratigraphy,petrology sedimentary and reservoir geology as theoretical guidance,by the methods of analysis of elements,heavy minerals and apatite fission tracks,the paper clears the source directions of the Upper Permian in peripheral regions of Mountain Bogda,clears the types of sedimentary facies and its distribution by the analysis of single well and cross-section sedimentary facies,clears the reservoir's petrological characteristics,reservoir spaces,diagenesis and controlling factors on reservoir by the observation of thin sections and the analysis of rock's physical property.The research results show the Wutonggou Formation of the Upper Permian in peripheral regions of Mountain Bogda is a third-order water transgressive cycle.And this formation can be divided into two members: Wutonggou Formation and the second section of Wutonggou Formation,and both of which include two transgressive cycles.The gravels' main composition of sedimentrary rocks,basalt,limestone and tuff in Dalongkou profile and Well Qi-1 indicates its source is the Shirenzigou Formation,Lucaogou Formation and Liushugou Formation in Mountain Bogda;the gravels' main composition of sedimentrary rocks and basic volcanic rocks in Guodikeng profile and Well Chaican-1,richment of light rare earth elements and europium anomaly in Well Chai-2 and Chai-3 and heavy mineral association of epidotite(20.2%),zircon(15.2%)and garnet(7.6%)in Well Chai-2 indicates its source is from Mountain Llynhabergen.While heavy mineral association of magnetite(17.1%),zircon(14.8%)and rutile(5.7%)in Well Bancan-1 indicates its source is from Mountains Llynhabergen and Bogda.Combination with the isopach of sandstone content,the paper reveals that the Mountain Llynhabergen,Mountain Bogda and Guqitai Uplift provide the main source for peripheral regions of Mountain Bogda.Among them,the Gusantai Uplift is weak to provide source in the sedimentary period of Wutonggou Formation and stopped in the sedimentary period of the second section of Wutonggou Formation.There are three types of sedimentary facies distributed in Wutonggou Formation: alluvial fan,braided river and meandering river.Large areas of alluvial fan-fluvial deposits are developed around the Mountain Llynhabergen,Mountain Bogda and Guqitai Uplift,among which the northern margin of Mountain Llynhabergen is the most widely distributed.During the sedimentary period of the second section of Wutonggou Formation,the basin was enlarged and the sedimentary range of alluvial fan-river was obviously smaller than that of Wutonggou Formation.The reservoir rock type of Wutonggou Formation is mainly litharenite,and compaction and dissolution are the most significant diagenesis.The pore types are mainly dissolution pores,followed by primary pores and micro-fractures.The average porosity and permeability of the reservoir are respectively 14.2% and 13.65 m D.The overall evaluation of reservoirs is medium-low porosity and low to ultra-low permeability.The "dessert reservoir" is mainly controlled by sedimentary and mechanical compression facies,and the reservoir development pattern of "gullys control the sandbody and sedimentary and mechanical compression facies control the reservoir" is established and finally the paper predicates the distribution of development zones of the favorable reservoirs.