Characteristics And Genetic Analysis Of Uranium-rich Strata In Ordovician Of Tahe Oilfield

Energy minerals such as oil,gas,coal,and uranium often exist in the same basin,which environment,distribution location,and mechanism of accumulation(mineralization)are closely related.The Tarim Basin is a large-scale cratonic basin with rich minerals.It has been explored large amount of oil and gas and has rich geological and geophysical data.During the exploration and development of oil and gas fields,the phenomenon of abnormally high uranium content was found in the Ordovician strata.However,the current research on its distribution and genetic mechanism is relatively low.Therefore,this paper takes the uranium-rich section in the Ordovician strata of Tahe Oilfield as the object,and uses the multi-disciplinary theories and methods such as petrology,tectonic geology,sedimentology,geochemistry and geophysics,etc.Comprehensively utilize the basic geological data include,drilling data,well logging data,geophysical data combined with XRF elemental analysis and C,O,Sr isotope test,etc.Focus on the characteristics,distribution law and genetic mechanism of uranium-rich section,and discussed its petroleum geological significance such as indicating the paleo-ocean environment,identifying sequence interfaces,and identifying reservoirs,etc.The main understandings of this thesis are as follows:(1)Three high-radioactive section are identified by natural gamma logging data.Combined with background values and correlation analysis,two types of uranium-rich section,fault-controlled and layer-controlled,are classified.(2)It is found that the layered high uranium section is mainly developed in the dark marl interlayer of the condensate segment.Its distribution is located in the vertical direction at the bottom of the Chalbak group.It is controlled by many factors such as paleogeographic evolution conditions,stratigraphic distribution and paleogeomorphology on the plane,and it is characterized by regional wide distribution.The fault-controlled high-containing uranium section is located in the middle of the Ordovician unified compartment group,mainly in the vicinity of the deep fault zone,and the distribution is relatively scattered.(3)The formation of uranium-rich section is mainly controlled by the sedimentary environment of carbonate rock under-compensation,reduction and peace water in the background of global sea level rising.The slope facies belt of the platform is affected by rising ocean currents and has good organic matter conditions.The degradation of organic matter under the action of bacteria and microorganisms in the early diagenetic stage leads to the pore fluid in a strong reducing sulfurization environment,which is the main factor controlling the precipitation of uranium elements in sediments.(4)The large-deep fault system is a good water-rock-hydrocarbon-uranium transport reaction site.During the process of migration of uranium-bearing fluid along the fault,it is affected by deep reducing gases,hydrocarbons and other precipitation and favorable structures.The location is an important factor affecting the formation of the off-control uranium-rich section.(5)The stratigraphic-controlled high-yield uranium section is easily identified and widely distributed in the well logging,and can be used as a marker layer for the comparison of the Ordovician strata in the Tahe Oilfield.The off-control high-uranium segment is often developed near the fracture system with large porosity and is closely related to the reduction of oil and gas,which often indicates the favorable reservoir development position.