Research On Genetic Mechanism And Key Controlling Factors Of Xiaqiulitage Formation Reservoir In Bachu Region Of Tarim Basin

Carbonate reservoir and gas indication have been found in Upper CambrianXiaqiulitage formation of Tarim basin through date of wells. The aim of this thesis isto study the genetic mechanism and key controlling factors of reservoir inXiaqiulitage formation of Bachu area. This paper studies the lithologicalcharacteristic,sedimentary facies,diagenesis and formation of dolomite through theComprehensive utilization of well drilling and logging,seismic interpretation andgeochemistry analysis(including isotope,trace elements,rare earth elements,fluidinclusion and SEM).Under the theoretical guidance of sedimentary petrology andreservoir geology,this dissertation studies the reservoir characteristic,reservoirevolution, as well as analyses the mechanism and key controlling factors. Accordingto the analysis of all the influencing factors,this paper finally predicts the betterreservoir distribution.By utilization of well logging and seismic interpretation, this paper studies thesedimentary facies distribution and microfacies evolution in Bachu area. Thefeatures of drill core and slice indicate different dolomite and diagenesis types.Eachdiagenesis type has its own effect on reservoir body. Dolomitization, cataclasis andcorrosion are the most advantageous diagenesis types. Based on the study andanalyses of different genetic models of dolomitization in Xiaqiulitage formation,although the hydrothermal dolomitization does not develop widely in Bachuarea,Hydrothermal fluid may takes an important adjustive role in dolostone,such assolution and recrystallization.On the basis of well logging,bore core and thin section observation, solutioncave and solution cave-crack form the main reservoir space. Considering the structure and genesis of dolomite, this paper come up with structural geneticclascification criteria of Xiaqiulitage formation in Bachu area. Reservoir spacemostly results from burial dissolution,while the weathering crust karstification andsyndepositional karstification are not development in Xiaqiulitage formation.According to the comprehensive analysis of the datum on wells and seismic,the Xiaqiulitage Formation could be divided into four sequence stratigraphic units inBachu area. Each sequence consists of transgression system tract (TST) and highsystem tract (HST).The HST does not develop completely,while the low systemtract (LST) is hardly found.The reservoir body on wells,as well as indication of oiland gas, demonstrate that the sequence have essential effect on dolomite reservoirdistribution.The dolomite reservoir primarily developes in the HST of sequence,especially near the sequence boundary.Through synthetical analysis of diagenesis, burial dissolution is the mostadvantageous diagenesis type to the present reservoir. There are several factorscontrolling the dolomite reservoir in Bachu area, such as sedimentary facies,ectonicaction and dolomitization.By comprehensive analysis of all the relativefactors,the better reservoir body results from burial karstification,which relate withstructurally controlled hydrothermal fluids and the key controlling factor is burialhydrothermal karstification affected by the fault system.Finally this thesis predicts the better reservoir body develop along the activestructure fractures in period of hercynian,according to the key controlling factor.