Analytical model and numerical simulation of relief well adjacent distance considering multi-layer media

Accurate measurement of adjacent well distance (AWD) is the key factor restricting the successful plugging of relief well (RW). Traditional ranging technology can't meet the accuracy requirements of AWD. Fortunately, magnetic ranging technology has shown great superiority in this respect. However, the magnetic ranging algorithm based on low-frequency injected current has always been a difficult problem. Therefore, based on the magnetic ranging principle of low frequency injection current, the propagation law of current in medium is revealed. Considering the effect of mud on current propagation, a multilayer medium model is established to improve the calculation accuracy of current intensity in adjacent casing. Through numerical simulation and experimental comparison, the validity of the analytical model is verified. Analysis results show that the intensity of injected current, the conductivity of medium and the distance between electrode and casing axis have a significant effect on the current of the casing. The radial electric field intensity fluctuates obviously on the interface of the medium. When the distance from the electrode to the casing axis is constant, the magnetic field strength of the measuring point is also affected by the distance from the electrode to the probe pipe and the relative inclination angle. According to the distance between the electrode and the axis of the casing, the optimal distance between the electrode and the probe tube can be obtained, so that the magnetic induction intensity of the measuring point is maximized. The results show that the multi-layer medium model is more suitable for the actual working conditions and the calculation error is minimal.