Figure 2.1. Two-coil induction probe in a uniform conducting medium. |

If the area of the receiver coil of the induction probe is small with respect to its length (Fig. 2.1), one can assume that within this area the magnetic field is uniform, and it is directed perpendicular to the horizontal plane, i.e. [Pg.124]

Now we will find a signal at the receiver of a two-coil induction probe caused by an induced current from this ring. As was shown in Chapter 2 the current induced in the elementary unit ring is [Pg.171]

Now let us investigate the general case with the two-coil induction probe located in a uniform conducting medium. At the point of the receiver the magnetic field in accord with eq. 2.21 is described by an equation for its complex amplitude [Pg.125]

Falk, J. L., Zhang, J., Chen, R., and Lau, C. E., A schedule induction probe technique for evaluating abuse potential Comparison of ethanol, nicotine and caffeine, and caffeine-midazolam interaction. Special Issue Behavioural pharmacology of alcohol. Behavioural Pharmacology 5(4-5), 513-520, 1994. [Pg.301]

Figure 3.5. Position of an elementary ring with respect to the induction probe. |

Let us notice that in most cases, the field created by currents in the coil of an induction probe is equivalent to that of a magnetic dipole. [Pg.47]

This feature of the field is sometimes used in order to control the quality of an induction probe consisting of coils and wires. In the case when the magnetic field is created by one single coil, the points where the component Hz vanishes are easily calculated. [Pg.50]

The expression for the field in eq. 1.126 is used to evaluate the primary field magnitude of an induction probe. [Pg.50]

The minimal radius of the shell naturally coincides with the radius of nonconducting part of the induction probe. In those cases, when the argument mr is small mr 1), it is convenient to use approximate expressions for shell coefficients. For x > 0 functions h x) and Ki x) tend to x/2 and jx correspondingly and therefore instead of eq. 3.51 [Pg.158]

In the case in which the field or the electromotive force is investigated in the receiver of the two-coil induction probe the distance R is replaced by the length of the probe, L, that [Pg.129]

Furthermore, we will focus on the magnetic field and the electromotive force at the receiver of the two-coil induction probe. Substituting eq. 2.37 into 2.27 the magnetic field Hz can be represented as a sum of two components, namely the quadrature component which is shifted in phase by 90° with respect to the primary magnetic field, Hq, or the current in the source, and the inphase component which is shifted in phase by 0° or 180° with respect to the primary field, and we have [Pg.129]

Proceeding from these equations we will investigate the behavior of the electromotive force induced in the receiver of the two coil induction probe as well as the main features of the distribution of induced currents. [Pg.123]

The magnetic field of the vertical magnetic dipole, ho, in a horizontal layered medium is expressed in the explicit form. For example, if the induction probe is located symmetrically with respect to the formation boundary we have [Pg.182]

Finally, theoretical investigations were performed which demonstrate that induction probes with special orientations of coils allow us to evaluate an anisotropy of formations (Kaufman and Kagansky, 1971). This study is also useful for application of induction logging in horizontal wells. [Pg.3]

It is appropriate to notice that there will be cases when an electric field cannot be described by component only. In such cases, for example, when there is a displacement of an induction probe with respect to the well s axis, a more general approach to the solution of the boundary problem will be used. [Pg.144]

Now we will describe a method which under certain conditions takes correctly into account the skin effect, i.e. interaction of currents in a conducting medium. The idea of this method is very simple. Let us present all current space around the induction probe as a sum of two areas, namely [Pg.177]

An alternating electromagnetic field in which the current flow is tangential to interfaces between media of different conductivity so that the normal component of the electric field is zero and that charges do not arise. This happens for example when an induction probe is located on the axis of a borehole and the medium possesses cylindrical symmetry in this case, the electric field has a pure inductive character. [Pg.68]

Understanding this feature of field behavior is important for the further development of the interpretation of induction logging. Moreover, some of the induction probes, currently used in practice, are based on measuring both components of the magnetic field. [Pg.184]

Equations 2.47-2.48 describe the field and the electromotive force with an error not exceeding 10%, provided that the parameter p is smaller than 0.1. In this case the quadrature component of the electromotive force, containing the information about the conductivity, constitutes only 1% or less of the primary electromotive force. For this reason cancellation of the latter in the induction probe is usually performed with a high accuracy. [Pg.131]

By analogy the behavior of the inphase component of the magnetic field can also be explained with the use of the inphase component of currents. Here it is appropriate to notice the following. Unlike the previous case a zone of currents which gives the main contribution to the inphase component of the magnetic field is present in a confined zone, a position which essentially depends on conductivity and frequency. In particular, with a decrease of frequency is shifted far away from the induction probe and when it is located at [Pg.139]

When these functions are found along the contour I, we can determine the electric field inside the borehole by making use of the computational formula 3.95. This approach has been used for the investigation of radial and vertical responses of induction probes when the formation has a finite thickness. [Pg.169]

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