Research On The Characteristics And Main Controlling Factors Of Dolomite Reservoirs In The Lower Qiulitage Group In The Central Part Of The Shaya Uplift

The oil and gas resources in the Cambrian dolomite reservoir of Shaya uplift in Tarim Basin is very rich,Up to now,there has been able to find several oil and gas fields such as Tahe oil field,Yaha,Yingmai 32,Yingmai 7 oil and gas fields,etc.With the progress of ex-ploration and research,in this area there are many wells drilling dolomite formation in Lower Qiulitage group of Cambrian,and different levels of oil and gas shows in the process of drill-ing,cores are also observed to have good reservoir development,show that the group has bet-ter exploration potential.Guided by the mineralogy,sedimentary petrology and reservoir ge-ology theory and based on the data of the regional geological background,logging,well log-ging,core and test analysis data and the previous research results of the middle of Shaya Up-lift,the detailed analysis and summary of characteristics of dolomite reservoir were carried out with comprehensive research of multidisciplinary and various methods.Finally,the main controlling factors of dolomite reservoir development were analyzed from 4 aspects of lithol-ogy,sedimentary facies,diagenesis and tectonic action.According to the core data and thin section,scanning electron microscope and cathodo-luminescence analysis method,the dolomite of Lower Qiulitaga group in the middle of Shaya Uplift are divided into crystal dolomite,grain dolomite,micrite dolomite,cameule dolomite and transitional dolomite,the crystal dolomite can be classified into silty crystal dolomite,fine crystal dolomite,medium-coarse crystal dolomite and unequal crystal dolomite.The res-ervoir space types of dolomite in the study area include intergranular pore,intergranular dis-solved pore,intragranular dissolved pore,moldic pore,vuggy and fracture,and there are var-ious types of reservoir space combinations,which constitute the dissolution cavity reservoirs,fractured reservoirs and the two types of composite reservoirs.Through related data about core,well logging and laboratory test,the relationship among the lithological characteristics,the physical property,hydrocarbon bearing property and elec-tric property were analyzed.The results show that the physical property of fine crystal dolo-mite in study area is relatively good;and evidences of oil and gas from borehole log mainly shows oil trace;the values of deep lateral resistivity and shallow lateral resistivity in fine crystal dolomite are lower than other lithology,and there is a certain positive difference be-tween them;the reservoir in fine crystal dolomite shows physical property with low density,higher neutron porosity and higher acoustic travel time,all of which display as the character-istic of high porosity.Finally,according to the research results of reservoir characteristics and evaluation standard of carbonate reservoir in the study area,the synergisti evaluation of do-lomite reservoir has been carried out.The development of dolomite reservoir of Lower Qiulitage group in the middle of Shaya Uplift is mainly controlled by lithology,sedimentary facies,diagenesis and tectonism.There is a close relationship between the development of reservoir and lithology,and the porosity and permeability of reservoir are obviously different.The sedimentary facies control the res-ervoir rock types and rock structure,which are the basic condition for the preservation of primary pores and the development of secondary pores.And the diagenesis and tectonism are the keys to the formation of high quality reservoirs.The diagenesis types of dolomite reser-voir of Lower Qiulitage group in the middle of Shaya uplift are various and complex,and they play decisive role in the development and preservation of pores,which mainly include compaction,pressure solution,cementation,dolomitization and packing action.The dolomites of study area are reconstructed by multi-stage diagenesis.The shallow-middle burial dolo-mitization,freshwater dissolution,hydrothermal dissolution and supergene karstification play the most important role in pore development.The structural fracture formed by tectonism is not only the important reservoir space type,but also provides a favorable channel for the late diagenetic fluid and hydrocarbon migration.Moreover,it plays an important role in improving the reservoir permeability and reservoir performance.