SU1072620A1 - Method of electric logging of cased boreholes - Google Patents

Abstract

METHOD OF ELECTRIC WELDING OF DIFFERENT WELLS, including excitation of an electromagnetic field on the section of a casing string and measurement of the longitudinal current by electromagnetic converters, characterized in that, in order to increase the accuracy of measurements, a single electric dipole and different distances from it at the same time, two values of the longitudinal current are measured, with respect to which the conductivity of the medium surrounding the casing string is determined.

Description

The invention relates to a geophysical study of wells and serves to measure the specific electrical conductivity of rocks discovered by a well in the presence of a casing string.

The known method of electrical logging of cased wells, in which a radial diver is recorded. current generation due to voltage drop across the column section, which is very low due to the high electrical conductivity of the column.

When registering the potential difference in various modifications of this logging, electrical ncwehi arises, which are a consequence of the movement of the scraping electrodes along the column, which significantly impair the signal-to-noise ratio and practically do not provide the necessary information.

The closest is the method of electric logging of cased wells, including the excitation of an electromagnetic field in a section of a casing string and the measurement of a longitudinal current by electromagnetic

converters.

At the same time, in the section of columns, two opposing

O) electric dipole, whose current,

To dissolve in the column, it leaves the installation center to the environment. The main disadvantage of this method is the complexity of the method, which ensures the divergence of current in the radial direction, which requires the presence of two pathogens of the field, and this conditions the downhole part of the device.

Changing the gap due to scale, rust, shells, etc. in a casing string leads to destabilization of a constant magnetic flux and a change in the magnetic resistance in the gap, and this in turn leads to a change in the EMF of the electric dipole induced on the column, which introduces errors in measuring the leakage current in the studied medium. The purpose of the invention is to increase the measurement accuracy. The goal is achieved by the method of electric casing of cased wells, including excitation of an electromagnetic field on the casing string and measurement of the longitudinal current by electromagnetic transducers, excites one electric dipole and at different distances from it on the casing string. at the same time, two values of the longitudinal current are measured, flowed along the column past the measuring sensors, and the ratio of the values of these currents determines the production dyes surrounding the casing pipe. The drawing shows the developed method. The method includes a section of the wall of the casing 1 with the plot studied. my environment is ttast 2 and having it by birth 3 and 4). On column 1, an electromagnetic white current converter - inductor 5 excites an electric dipole 6, conventionally shown by a box with the + and - signs, and two electromagnetic eddy current transducers located at different distances below it. 7 and 8. Arrow 9 conditionally shows the current flowing from the section of the column enclosed between the electromagnetic measuring current transducers 7 and 8. Current thrashing from the lower end of the pipe. That is, from the section of the column below the lower measuring sensor Figure 10. Current flowing from the section of the column located between the inductor 5 and. , the upper measuring sensor 7. is designated by the number 11.. In the casing string (see drawing), well borehole, on the outer side of the casing using an electromagnetic inductor, an electric dipole is excited by an electromagnetic inductor, the current of the column spreads into its surrounding the wire is j tual medium and exponentially decays. Current strength (i (z)) through trans. The column cross section and distance from the inductor is:. g h 1 dvz g ° - “G dzfz) g where W is the resistance of a single segment of the axial current to the current associated with the column specific resistance (p ifoft) and its thickness (D – d) as follows; Ap col r Y (), where V is the potential at the point of observation, with coordinate z; dvz, 1-7 first derivative of the potential .z (, z) of the dial at the point of observation with the coordinate; - the strength of the current branching from the column into its environment on the unit depth interval is Cg resistance of the medium of the radial component of the current, i.e. i (j (2).. By selecting a column segment with height Dg and centered at the observation point z, applying to the closed surface SA of this distance the continuousTi current vector divi O, taken in the integral formula, we have: J (idS) (idS) "- i, (z - Af-) & z I (idS) i (z - | -) I6d R (since the surface S consists of the end surfaces of the section of the column Sg and 8 c and its side surface, therefore, the left part of the expression (4) represents the sum of three streams. In this way, we get (.. -H) -i. (H (r) yr or -4i & z) Entering the notation i- (z4 -2) f-z - JL5z - Ы Нсг) Л Ц: expression 8 can be written i, - Hz 0. By rewriting expression 10 in the form of i, ie, and dividing it, by i, we get: .a. From this it follows: if the medium adjacent to the controlled section of the column is an insulator and there is no current leakage into it, i.e. IR O, In the case of servants, i, i, and 1. In the case of, when the environment surrounding the casing string is conducting, for a while, and i is equal to 1, expressed in fractions of i. If the power is changed by destabilizing factors the supply dipole, or the amount of current that flows from the section of the column enclosed between the supply dipole by the upper measuring electrode Teli then synchronously in the same proportions, will be varied. both i and i and their in / i ratio will be held with high accuracy and only change if the resistance of the layer of rock adjacent to the casing on the outside and between the electromagnetic converters is changed mi 7 and 8.; The conductivity of rocks is proportional to the radial current ig. Uft determination of this value is prov. measurement of the current axial direction; neither 1 and i | in two different parts of the column at different distances from; supply electric dipole. in order to eliminate the effect of destabilizing factors on the BenH rank measured and thus increase the measurement accuracy by one of the measuring electromagnetic converters, for example 8, control the value of the current i flowing through the cross section of the column past it and control the electromagnetic capacitance of the inductor the electric dipole column so that regardless of the grounding resistance of the part of the column located below the control electromagnetic converter 8, the current remains at a given level out, i.e. i const. Then the current value is 1., fixed by measuring electron-magnetic converter 7. will be greater than the control current 1, by vedyn i, i.e. by the amount of current 9 branching into the conducting medium surrounding the section of the column enclosed between electromagnetic converters 8 and 7. Since the emf of the supply dipole and V, therefore, its current is destabilized by various factors: a change in the magnetic gap between the column and the magnetic circuit of the electromagnetic converter due to scale, rust, cavities, due to the instability of the supply current of the windings of the alternating current - the exciter floor, the influence of the host rocks. These factors are practically impossible to take into account; therefore, it is not the difference of the currents that is measured, but their ratio, measured as a percentage of the control current, as a result of which errors introduced into the measurements are automatically excluded. Thus, a measure of the imperfection of the isolation of a column by its environment is the ratio of the currents of the axial direction simultaneously measured in two sections of the column at different distances from the supplying electric dipole. Otherwise, the conductivity of the medium surrounding the section of the column, enclosed between the remote control with two electromagnetic converters (control and out of test), is expressed in units of the amount of current flowing from the section of the column located below the lower controlled electrically-transformable. tel. Measuring the ratio of currents from one source significantly improves the accuracy of the estimation of the conductivity of the medium by automatically eliminating errors introduced by the instability of the supply current of the coil of the inductor, which distorts the measurement of the influence of the host rocks and the formation of the rocks with their large contact;

Claims (1)

METHOD OF ELECTRIC LOGGING OF UPLINED WELLS, including excitation of an electromagnetic field in a section of a casing string and measurement of a longitudinal current by electromagnetic transducers, characterized in that, in order to increase the accuracy of measurements, one electric dipole is excited in a section of a column and two are simultaneously measured at different distances from it values of the longitudinal current, in relation to which the conductivity of the medium surrounding the casing is determined.