Transient Electromagnetic Cross-well Geometry Factor Exploration Method And Experimental Study On Perforation Of Cased Hole

Cross-well is the main distribution area of remaining oil.In order to carry out the detection of remaining oil between wells and improve the recovery factor,this paper proposes a transient electromagnetic cross-well exploration method with full-space geometric factors.Using Doll's formation current loop model,the useful signals excited by formation eddy currents at any point in space are studied and expressed as the weighted average of the electrical conductivity of each point in the space.The weight is the full-space geometry of the transient electromagnetic exploration between wells.Factors;and the full-space geometric factors corresponding to different directions are derived according to the different orientations of the receiving coil.The simulation results of the full-space geometric factors show that: the z-directional full-space geometric factor presents different polarities on both sides of the transmitting and receiving coils;the y-direction The spatial geometric factors exhibit different polarities on the left and right sides of the transmitter and the upper and lower sides of the receiving coil;almost all the spatial geometric factors in the x direction are concentrated near the transmitting coil,and the upper and lower sides exhibit different polarities.This is the manifestation of the magnetic field vector in the geometric factor,and also the main characteristic of the transient electromagnetic eddy current excitation response between wells.In the silo,the coil current is turned on and off to excite the transient electromagnetic field,which generates an induced electromotive force in the formation.The electromotive force slowly decreases after reaching a maximum value at the instant of turn-on or turn-off.Due to the conductivity of the formation,eddy currents are also generated in the formation,the amplitude of which is proportional to the conductivity of the formation,the induced electromotive force re-excited by the eddy current is a useful signal,and its amplitude is also proportional to the conductivity of the formation,superimposed on the induction caused by the current on and off Electromotive force.This paper studies the relationship between the amplitude of the useful signal received by the receiving coil in different directions and the source distance through theoretical simulation and experiment.The results show that when the receiving coil is placed in the z direction,the amplitude of the useful signal decreases with the increase of the well spacing.The peak amplitude of the eddy current excitation response is the largest when receiving at the same depth;when the receiving coil is placed in the y direction,the amplitude of the useful signal increases rapidly and then slowly decreases with the increase of the well spacing.The amplitude is the smallest;when the receiving coil is placed in the x direction,the amplitude of the useful signal decreases with the increase of the well spacing,and the peak amplitude of the eddy current excitation response is the smallest when the transmitting and receiving are at the same depth.These conclusions have certain guiding significance for the study of cross-well exploration methods and the design of cross-well exploration logging tools.There are perforations in actual casing wells,and the impact of perforation cannot be ignored.This paper describes the impact of perforation on the response through experiments.Corresponding perforation correction is required to ensure the conductivity of transient electromagnetic through casing logging Precision.