Research On Reservoir Characteristics Of Triassic In The Lunnan Area In Tarim Basin

The paper studied the sandstone reservoir's petrography and diagenesis features of the third oil group of the Triassic in Lunnan area of Tarim Oilfield,by using geological logging,wirelogging,core,thin section,scanning electron microscopy clay,X-ray diffraction and other analysis data.In the end,we studied the characteristics of reservoir rocks types,summarized the diagenetic characteristics,diagenetic evolution sequence and analysed the heterogeneities of various diagenesis in different sedimentary facies zones.The diagenetic facies are quantitatively recognized by logging curves,so that the favorable reservoir zones can be predicted.The lithology of the third oil group is mainly composed of feldspthic lithic sandstone.There also developed lithic arkose sandstone and lithic sandstone.The overall characteristics of reservoir are high content of feldspar and rock debris,the maturity of composition and texture is relative low.The magmatic rock debris are dominated by neural and acid extrusive rocks and shallow intrusive rocks.The metamorphic rocks debris are mainly composed of metamorphic quartzites.The third oil group reservoir of Triassic in the Lunnan area is high-quality reservoir.There developed different types of diagenesis such as compaction,cementation,dissolution and metasomatism,which jointly influence the physical properties of the reservoir.Different types of lithologic facies are characterized by different types of diagenesis: gritstone with gravelly facies and gritstone facies developed at the bottom of the underwater distributary channel.The diagenesis is mainly medium-compacted,weak-cementation and medium-dissolution.The medium sandstone facies developed in the middle part of the underwater distributary channel and the degree of compaction,cementation and dissolution are all medium.The fine sandstone facies is fine in size and the content of plastic debris is high,and the diagenesis is mainly medium-strong compaction,strong cementation and weak dessolution.When the distributary channel mouth bar sand-body is cemented by early calcite cements,a dense calciferous interlayer is formed in the reservoir.The diagenetic evolution of the third oil group in Triassic reached middle diagenetic stage B.It experienced a long-term shallow burial in low-temperature and a rapid deep burial in high-temperature diagenesis process,mainly experienced two periods of alkaline fluids and one period of acidic fluid.The granular iron-free calcite is formed in the early alkaline fluid environment.When the lower source rock reached mature stage and released organic acids,caused dissolution in the early calcite cement,feldspar and magmatic rock debris,in this stage,authigenic kaolinite minerals are formed.Based on the critical diagenetic quantitative parameters,the study area can be divided into four different types of diagenetic facies: early calcite stronge-cemented facies,high content plasitc debris stronge-compacted facies,clay mineral mediumcemented facies and unstable components dissolution facies.Using the wirelogging of natural gamma,spontaneous potential,interval transit time,compensated neutron porosity,density,combined with "neutron-density porosity difference" which sensitive to lithology to establish the logging identification plate of the diagenetic facies.In the end,the paper achieved the single well logging diagenetic facies continuity identification.