Research On Reservoir Characteristics Of The Silurian Kepingtage Formation In Tazhong Area,tarim Basin

Based on the data of well-logging,geology logging,core,thin section and analysis test,the sequence stratigraphic are classified and the reservoir characteristics about petrology,diagenesis,pores and physical properties are studied for the Kepingtage formation of Tazhong area and outcrop in Keping area,with the comparison of the reservoir characteristics between outcrop and underground,summarizing the reservoir characteristics in different sequence stratigraphic framework. The main conclusions and understandings are as follows:Four sequences can be recognized in the Kepingtage formation of outcrop in Keping area. The SQ1 is composed of lowstand system tract,transgressive system tract and highstand systems tract. Both SQ2 and SQ3 consist of transgressive system tract and highstand system tract. The SQ4 is made up of transgressive system tract. The contents of mineral element are abnormal in the boundary of sequence and system tract as the evidence of sequence stratigraphic classification.The SQ4-TST of outcrop mainly consist of lithic quartz sandstone,with the rest primarily composed of litharenite. K-feldspar is the major typy of feldspar. The rock debris is dominated by metamorphic rock. The SQ4-TST and SQ1-LST are rich in chert. There are vermicular chlorite in the form of inclusion in the SQ4-TST,with the sheet and granular chlorite existing in the SQ1 and SQ2.The carbonate cement in outcrop,which can be divided into six types including homogeneous distribution type,conglomeration type,coagulum type,dotted type and bioclastic coexistence type,is mainly made up of calcite. The carbonate cement is relatively developed in the boundary of sequence and system tract and the place where there are rich in bioclasts, developed bioturbation and coarse grain.The secondary enlargement cementation is the most developed in the SQ4-TST.The residual intregranular primary pore,intragranular dissolved pore and micropore are the main pore types of the reservoir of outcrop. The reservoir is belong to especially low porosity and low permeability,which is influenced by the composition,size of the clastic grain and diagenesis.The underground study section, which corresponds to the upper member of Kepingtage formation of outcrop,can be divided into two sequences. The SQ1 is composed of transgressive system tract and highstand system tract. The SQ2 is only made up of transgressive system tract. The SQ2-TST is gradually thicker along the northwestsoutheast direction. The SQ1-HST and SQ1-TST pinch out along the northwest- southeast and northeast-southwest direction.The lithology of underground study section is characterized by litharenite and feldspathic-lithic quartz arenite in the second place. K-feldspar and metamorphic debris is in the majority. The carbonate cement is mainly composed of calcite. The carbonate cement content in the SQ2-TST is higher than that in the SQ1-TST.The underground pore types are mainly include the residual intregranular primary pore,intragranular dissolved pore and micropore. The reservoir,influenced by the composition,size of the clastic grain and diagenesis,is belong to low porosity and low permeability. The physical property of the SQ1-TST is better than that of the SQ2-TST in a whole.There are some similarities to a certain degree in the reservoir characteristics between the outcrop and underground. By the fine study on the reservoir of outcrop, the heterogeneity of underground reservoir can be better realized to provide theory basis for the further oil and gas exploration.