Research On The Principle And Method Of Cross-well Electromagnetic Logging And The Rule Of The Influence Of Casing On Cross-well Electromagnetic Logging

Cross-well electromagnetic logging is an important front in the development of modern geophysics and is a most challenging research subject. It radically overcomes the weak point of logging in radial sounding ability and greatly improves the ability of describing the characteristics of oil deposits. Cross-well electromagnetic logging through metal casing is a hot point and a difficult point in current field of logging.Based on the theory of electromagnetic field, assuming the subsurface inhomogeneous medium is axially symmetrical in respect of the bole axis where the transmitter is located and the transmitter source is the n-loop winding with indirect current in it which is vertical or parallel to the bole axis, the principle and the method of cross-well electromagnetic logging, the method of obtaining the geometrical parameter and permeability of metal casing and the rule of the influence of metal casing, transmitting frequency and well-to-well distance on cross-well electromagnetic logging are systemically studied.First, based on the theory of electromagnetic field, according to the theories of geometric factor and skin effect geometric factor of inducing logging and considering all kinds of effects while electromagnetic wave spreads in the inhomogeneous medium which is axially symmetrical in respect of the bole axis, the theory of skin effect geometric factor about the cross-well electromagnetic logging is established. This theory combines propagation theory with the concept of geometric factor, and regards the subsurface inhomogeneous medium as infinite unit rings which have small section and co-axial to transmitting windings. When calculating the electromagnetic signal of the receiver in the receiving hole, not only the signal of unit ring isconsidered, but also the interactivity of eddy current between the unit ring(skin effect).With establishing geological models, this paper numerically simulates the electromagnetic field, in which the receiving winding is vertical and parallel to the bole axis respectively, analyzes the amplitude of induced electrical potential in receiving hole and its variation with geological body, well-to-well distance, and transmitting frequency, and testifies the results with the data sets from three cross-well electromagnetic loggings in Shengli Oil Field.As for cross-well electromagnetic logging through metal casing, based on the theory of electromagnetic field, starting from single-well electromagnetic logging through metal casing, this paper studies principle of this kind of electromagnetic logging and derives its theoretical formula, systemically analyzes the transmitter-receiver magnetic flux model of eight windings with the transmitting frequency of high, middle, low and super-lower frequency, respectively, establishes the method to obtain the geometrical parameter and permeability of metal casing, and presents the results of numerical simulating. And then, this paper also studies the principle of cross-well electromagnetic logging through metal casing, derives its theoretical formula when the transmitting hole is metal casing and the receiving hole is naked well. With this theory, this paper numerically simulates the relationship of the thickness, the inner radium, the permeability, and the conductivity of metal casing, transmitting frequency and the well-to-well distance with the receiving signal, systemically analyzed the influencing rules of the casing, transmitting frequency and well-to-well distance on cross-well electromagnetic logging.The analysis and study shows:The principle and method of cross-well electromagnetic logging established in this paper is feasible and valid. Meanwhile, as a kind of front logging technique, cross-well electromagnetic logging is prosperous and it can be used to study the connection of sand body, supervise the condition of drowning and study the6distribution of residue oil.The electromagnetic logging method, which measures formation resistivity through single metal casing with super-lower frequency electromagnetic wave, is...