Design And Performance Optimization Of Small-size At-bit Azimuthal Gamma While Drilling Geosteering Tool

As an important component of horizontal well sidetracking,geosteering while drilling is an effective technical means to revitalize old wells,reduce costs,and excavate remaining reservoirs.With the support of the school-enterprise cooperation project of CNPC Chuanqing Drilling Company,this dissertation focuses on the practical engineering problem of the limited size of downhole instruments for sidetracking of old wells with the slim hole in Changqing Oilfield.The dissertation takes geosteering tools as the research object and conducts the design and performance optimization of the small-size at-bit azimuthal gamma while drilling geosteering tool.This geosteering tool has the advantages of real-time measurement and steering,precise control of wellbore trajectory,improved recovery ratio,and so on.The research results can provide theoretical guidance for the structural design and field application of geosteering tools.The main research contents of the dissertation are as follows:(1)Research on the mechanism and measurement principle of azimuthal gamma geosteering while drilling.Based on geological radioactivity theory and the nuclear physics theory of gamma logging,the dissertation studies the principle of azimuthal gamma measurement while drilling through sector division and sector counting calculation methods,which provides a theoretical basis for the structural design and geological response analysis of geosteering tools.(2)The dissertation completes the structural design of the small-size at-bit azimuthal gamma geosteering tool based on the axiomatic design theory and methods.The dissertation not only determines the composition of the small-size at-bit measurement system and the tool hook mode but also completes the functional structure decomposition mapping and various functional module designs of the small-size azimuthal gamma tool.Then,the dissertation completes the structural design of the at-bit azimuthal gamma sub under the axiomatic design framework.(3)The dissertation completes azimuthal gamma geological response analysis of the geosteering tool based on the Monte Carlo method.Taking normalized statistical errors and radial detection depth as targets,the dissertation constructs a Monte Carlo calculation model and calculation method to study the influence law of detector diameter,detector length,and shield thickness on the geological response of the tool,providing a reference for the optimization design of geosteering tools.(4)According to the structural and working characteristics of the small-size at-bit azimuthal gamma while drilling geosteering tool,the dissertation carries out statics,dynamics,and fluid mechanics simulations of the geosteering tool by using the finite element analysis software,and analyzes the static and dynamic characteristics and erosion resistance of the tool.The analysis results indicate that the structural design of the azimuthal gamma while drilling geosteering tool meets the actual working conditions requirements of the slim hole.(5)The dissertation completes multi-objective optimization of the azimuthal gamma geosteering tool while drilling based on the response surface method.The dissertation takes the mechanical strength,erosion resistance,and detection performance of the geosteering tool as evaluation indexes,and quantitatively analyzes the overall performance of the optimized tool by constructing a multi-objective optimization numerical model.The analysis shows that the optimized geosteering tool has better overall performance and can provide a reference for the actual design of the tool.