Study On Calculation Method Of Magnetic Ranging Based On Low Frequency Injection Current

Accurate measurement and control of adjacent well distance is one of the core technologies in guided drilling projects such as relief well and infilling well.The active magnetic ranging technology based on low frequency injection current can not only avoid the cumulative error of conventional borehole trajectory measurement,but also accurately measure the distance of adjacent wells.It also does not need to run instruments in the target borehole,and has been widely used in the relief well steering drilling project.At present,foreign countries only provide this technical service,the cost is quite high.The research on this technology started late in China,and the core algorithms and hardware devices of ranging are far behind those of foreign countries.Therefore,there is an urgent need for domestic breakthroughs in this field of technology to alleviate the passive situation in dealing with operational problems in this field.In this paper,the calculation method of magnetic ranging based on low-frequency injection current is studied,and the calculation model of magnetic induction intensity at the current boundary of the target well casing and current intensity on the target well casing is established considering the influence of multi-layer media around the electrode(drilling fluid,intrusion zone and original formation).The distribution law of current intensity is revealed and relevant influencing factors are analyzed.A method of optimizing the distance between the electrode and the probe is proposed based on the principle of maximizing the magnetic induction at the measuring point.Based on the COMSOL numerical simulation software,the geometric models of double-layer and multilayer media were established to simulate the propagation process of low-frequency injection current in the media and the target well casing.The calculation results of the numerical simulation and the theoretical model were compared and analyzed,and the reliability of the calculation results of the theoretical model was verified from the two aspects of the electric field intensity in the media and the current intensity in the target well casing.The results of theoretical model and numerical simulation are further verified by physical simulation experiments.Combined with the multi-layer medium model,the relative position calculation method of adjacent well based on magnetic field intensity measurement and magnetic field gradient measurement is proposed.Based on Java language,a magnetic ranging calculation software based on low frequency injection current is developed,which includes two computing modules: magnetic field intensity ranging and magnetic field gradient ranging.Through the simulation experiment of magnetic ranging based on low frequency injection current,the correctness of the magnetic ranging algorithm is verified,and the results show that considering the influence of electrode multi-layer media is beneficial to improve the calculation accuracy of magnetic ranging.Combined with the actual rescue capability,the calculation method of rescue success rate under the condition of magnetic ranging is proposed,and the key steps of relief well design are given.Based on the statistical analysis,the "time-cumulative success rate of plugging" model was established,and the influencing factors of success rate of rescue were analyzed.The results show that the number of relief wells and the start-up time can be calculated based on this calculation method,combined with the site infrastructure,human resources and key technologies.