Study On Propagation Law Of Low Frequency Alternating Magnetic Field In Drilling Guidance Process

With the consumption of oil resources,the oil and gas reservoirs which are easy to exploit have been unable to meet the needs of society,and the exploitation of the complex well resources represented by difficult-to-produce heavy oil resources,coalbed methane and underground soluble minerals have drawn more and more attentions.Guidance drilling techniques are created to deal with the exploitation of the complex well resources,among which,the magnetic guiding technology has gradually become the most important guidance drilling technology in complex well mining by adopting the low-frequency alternating electromagnetic signal which has high precision,strong anti-interference ability.Therefore,the research on the influence factors of magnetic field signal propagation of the magnetic steering drilling technology is more and more important.In this paper,the propagation law of low-frequency alternating magnetic field and its influence factors are researched.Magnetic guidance drilling technology can be divided into MGT system and RMRS system.A solenoid is used by MGT technology as the transmitting source to send low-frequency alternating magnetic field,and the low-frequency alternating magnetic field produced by strong magnetic sub is used by RMRS technology as the transmitting source.Based on the basic theory of the electromagnetic,magnetic dipole is analyzed as the simplest model of propagation characteristics of alternating magnetic field,in addition,the propagation characteristics of static magnetic dipoles and the propagation law of the dynamic rotating magnetic dipoles are analyzed in theory,which are the simplest theoretical models of magnetic field signal propagation in MGT and RMRS of magnetic drilling technology,respectively.Use ANSYS finite element software as the model to analyze the propagation law of low-frequency alternating magnetic field in the formations during the process of guidance drilling,and the modeling is based on the application of MGT technology in the drilling process of double horizontal wells,so as to study the effect of the change of conductivity and permeability on the signal of low-frequency alternating magnetic field and the precision of trajectory guidance in homogeneous and layered formations.Analyze the effect of casing and cement sheath on low-frequency alternating magnetic field in the process of guidance drilling by using ANSYS finite element software,to establish a model of casing and cement sheath in the formations,researching the effect of the casing thickness,permeability changes and cement sheath thickness,as well as permeability changes on the signal of low-frequency alternating magnetic field and the precision of trajectory guidance.The response of different formation factors,casing factors and cement sheath factors to the signal of magnetic field are analyzed in this paper by researching the propagation of low-frequency alternating magnetic field in the guidance drilling,which provides a theoretical basis for improving the electromagnetic detection signal and the detection precision in the magnetic guidance drilling process,and then provides a theoretical reference for meeting the technical requirements of the practical engineering of complex wells in complex geologies.