| Ultra-deep microbial dolomite plays an important role in the exploration of global oil and gas resources.The microbial dolomite reservoir developed in the Sinian in the northwestern margin of the Tarim Basin in my country has the potential to become a high-quality reservoir,but the lack of deep understanding of the reservoir characteristics limits the oil and gas exploration in this area.In order to solve the problem of reservoir characteristics,this paper selects the Kungaikuotan section,Shierike section and Xigou section Qigeblak Formation in the Keping outcrop area in the northwestern margin of the Tarim Basin to carry out in-depth research,and obtains the following five aspects:（1）Through field section observation and casting thin section observation,the lithostratigraphic sequence and microbial dolomite classification of the Upper Sinian Qigeblak Formation were studied,and the developmental characteristics of microbial dolomite were analyzed by means of geochemistry,and the results were summarized.sedimentary environment and establish a sedimentary model.The study area mainly develops three kinds of microbial dolomite,stromatolite,thrombus and foamed granite,and two kinds of granular rocks,oolites and cohesive particles,which are related to microbial action.According to the combination of facies sequence,it can be divided into4 sections.The sedimentary sequence of inner gentle slope tidal flat and microbial mound beach under the background of carbonate gentle slope is formed from bottom to top;the Qigeblak period was generally in a warm and arid climate background,with a near-shore shallow water environment,and seawater with high salinity and high Water temperature and oxidation-weak oxidation characteristics,sea level rises gradually and then falls rapidly.Through the study of the sedimentary environment,the microbial dolomite sedimentary model based on the gentle slope background of the Qigeblak Formation in the study area was established.（2）Low dolomite order,δ13C,δ18O and 87Sr/86Sr values,higher Sr/Ba value,lower V/Cr value andΣREE value,Ce weak negative anomaly,and late The Sinian-equivalent U-Pb age of microbial dolomite and petrological characteristics comprehensively indicate that the dolomite of the Qigeblak Formation was formed in a diagenetic environment with relatively low temperature during the quasi-contemporaneous-shallow burial period,and the dolomitization fluid is a relatively high-salt diagenetic environment.degrees of sea water.（3）On the basis of microscopic petrological research,combined with the analysis of industrial CT imaging technology and argon ion polishing scanning electron microscopy technology,it can be concluded that the common types of pores in the study area include intergranular（dissolution）pores and intragranular（dissolution）pores,microbial framework pores,intergranular（dissolved）pores,dissolution pores and various types of fractures,etc.,among which foam sponge,stromatolite dolomite and bonded granular dolomite are favorable reservoir rock types.（4）Through the geochemical analysis of different types of dolomite and the elemental laser surface scanning imaging test of dolomite cements of different stages,the Qigeblak formation rock-pore evolution history was constructed,and the formation process was obtained.It has experienced seawater diagenetic environment,atmospheric precipitation diagenetic environment,extremely shallow buried plutonic environment,buried diagenetic environment and hydrothermal diagenetic environment.At the same time,combined with the sedimentary environment and pore characteristics,the main controlling factors of the reservoir are analyzed.The Qigeblak Formation reservoir is mainly affected by sedimentary facies,epigenetic dissolution,burial dissolution and tectonic effect.（5）The reservoirs in the study area are pore-vug reservoirs with medium-high porosity and medium-low permeability,with an average porosity of 3.3%and a maximum porosity of 19.6%,of which Type I reservoirs account for about 20%,and Type II reservoirs account for about 20%.Class III reservoirs account for about 10%,and Class III reservoirs account for 15%.The average thickness of the high-quality reservoirs in the three profiles is about 53.7 m（porosity≥2.5%）,and the storage-to-land ratio is about 0.31,showing a large scale. |
