RU2691920C1 - Method and device for electric logging of cased wells - Google Patents

Abstract

FIELD: geophysics.SUBSTANCE: invention relates to the field of well geophysical investigations and is intended for determination of electric resistivity of mine rocks surrounding casing string cased with metal string. Invention is based on use of metal column 1.1 of well as grounding of one of poles of source 3.1 of bipolar current pulses, the second pole of which is connected through geophysical cable 5 with current electrodes 2.2 of multi-element submersible probe 2. At current depth of logging in current electrodes 2.2 of probe 2, bipolar pulses of electric current are alternately sent relative to upper part of casing pipe 1.1. After each current supply with measuring electrodes 2.3 of probe 2, potential of one of electrodes 2.3 of probe 2 is measured relative to upper part of casing pipe 1.1 and potential difference (voltage) between electrodes 2.3. Based on measured values of potentials and voltages between electrodes 2.3 and using data on running electrical resistance of casing pipe 1.1, resistivity is calculated. In the probe there are insulating inserts 2.1 between current electrodes 2.2 and group of measuring electrodes 2.3.EFFECT: expansion of capabilities due to possibility to measure resistivity of rocks in conditions when earth surface is a layer of insulator, for example dry sand in conditions of desert or layer of permafrost, higher accuracy of determination of resistivity and reduced time of logging.9 cl, 9 dwg

Description

The field of technology.

The invention relates to the field of geophysical research wells and is intended to determine the electrical resistivity (resistivity) of rocks surrounding a cased metal column well.

The level of technology.

The idea of conducting electrical logging through a metal casing suggested LM. Alpin in 1939 [Patent of the USSR №56026]. However, the practical implementation of this method became possible only with the appearance of technical means allowing to measure the electric field parameters at the casing with the required accuracy. In the development of this type of logging made a great contribution [Krivonosoe R.I., Kashik A.S., Ryhlinskiy N.I. Apparatura dlya elektricheskogo karotazha obsazhennoy skvazhiny EKOS-31: Doklad na II kitaysko-rossiyskom nauchnom simpoziume po geofizicheskim issledovaniyiy skvazhin. Shanhay, noyabr, 2002] N.I. Rykhlinsky, A.S. Kashik, R.I. Krivonosov, B.X. Stewart, V.B. Weil. The many devices developed by them and a number of electric-logging methods through a column combine the location of a surface current electrode at a distance from the wellhead. With this traditional method of measuring the electrical resistivity (CES) of rocks, the current from the feeding electrode on the probe goes through the casing string and, gradually penetrating into the surrounding rocks, passes through the earth layer to electrical grounding (B-electrode), located as far as possible from the mouth wells. The potential of the probe is determined relative to the remote electrode, which is also located on the earth's surface. FIG. 1a, these electrodes are labeled 1.2 and 1.3, respectively.

One of the prerequisites for the implementation of such a scheme is to ensure reliable grounding of the B-electrode. And it depends on the resistivity of the surface layer of the earth, which is determined by many factors, the main of which are: the structure and composition of the soil, climatic and weather conditions of the area (temperature, humidity), time of year, the presence of salts, the depth of groundwater. In this case, the top layer is subject to intense seasonal changes caused by temperature fluctuations, as well as the amount and intensity of moisture entering the soil. The range of variation of resistivity of various soils is huge, for example, clay has a resistance of 1-50 Ohm * m, sandstone 10-100 Ohm * m, and quartz 10 ¹² -10 ¹⁴ Ohm * m. In the middle lane, typical values for chernozem and wet sandy and loamy soils are several tens of Ohm * m. However, in desert conditions, the top layer of dry sand is an insulator (up to 4000 or more Ohm * m) and cannot provide good electrical contact between the surface B-electrode and the ground. This makes it almost impossible to implement the traditional EDC scheme. A similar situation in terms of the electrical properties of the soil can also occur in permafrost areas in winter conditions. The capabilities of the EDC are also limited by the imperfection of the probe design (the quality contact of the measuring electrodes with the casing string is not always ensured and there are disturbance currents on the probe design) and the non-optimality of the logging data processing algorithms. These shortcomings are inherent in all existing methods of EDC. In connection with the above, as a prototype of the invention, patent RU No. 2408039 dated December 7, 2009, Bull. No. 36, 2010. Authors: Rykhlinsky N.I., Kashik A.S. and others.

According to this patent, a known method consists in step-by-step lifting from a well with a cased metal pipe 1.1. multi-electrode probe 2. Probe 2 of a logging device that implements a known logging method consists of N measuring equidistant distances L from each other along the axis of the well of adjacent electrodes. 2.3. Outside and on either side of the measuring electrodes 2.3 there are two current electrodes 2.2. In the process of measuring the electrical resistivity at each logging step, bipolar electric current pulses are alternately applied to current electrodes 2.2 and the potential of one of the measuring electrodes 2.3 and the potential difference between each measuring electrode and distances from it are measured. L measuring electrodes 2.3 probe 2. On the basis of these measurements determine the electrical resistivity (resistivity) of the surrounding rock rocks. When this resistivity at each step logging is determined in N-2 points at depths corresponding to the location of the measuring electrodes with numbers 2 ÷ N-1. To find each of these resistive electrical sensors use data related to three adjacent measuring electrodes 2.3, hereinafter referred to as "middle, upper, lower" and forming a measuring triple, the middle of which corresponds to the depth of the current logging, which measure resistivity. The disadvantages of the prototype:

- it is almost impossible to work in conditions when the top layer of the earth's surface is an insulator (dry desert sand or permafrost);

- the imperfection of the formula for calculating the resistivity, since it contains an empirical coefficient and does not take into account the diameter of the casing;

- errors in the measurement of potentials and potential differences of the measuring electrodes, due to the presence of parasitic currents in the design of the probe;

- the time spent by the probe at each depth point is not regulated in accordance with the current accuracy characteristics of the measured electrical parameters of the measuring electrodes, which leads to an unjustified increase in the well logging time.

The objective of the invention is to develop a method and device for electrical logging of cased wells, allowing to carry out electrical divergent logs EDM with higher accuracy, in less time and in complex geological and technical conditions.

The technical result obtained as a result of solving the task set is the expansion of the capabilities of the electric logging tool of cased wells by ensuring operability in situations where the earth’s surface is an insulator layer. This may be dry sand in desert conditions or a permafrost layer that does not allow the traditional method of electric logging with the location of the ground and the remote electrode at a distance from the well. This provides increased accuracy of determination of resistivity and reducing the time of logging.

Disclosure of the invention.

The solution of the task and the achievement of the stated technical result is ensured by the fact that the method of electrical logging of cased wells consists in step-by-step lifting from a borehole with a cased metal pipe 1.1. multi-electrode probe 2, consisting of N measuring equidistant at a distance L from each other along the axis of the borehole measuring electrodes 2.3, outside and on opposite sides of which there are two current electrodes 2.2. In the process of measuring the electrical resistivity at each logging step, bipolar electric current pulses are alternately applied to current electrodes 2.2 and the potential of one of the measuring electrodes 2.3 and the potential difference between each measuring electrode and the probe electrodes separated from it are measured. Based on these measurements determine the electrical resistivity (resistivity) of the surrounding rock rocks. When this resistivity at each step logging is determined in N-2 points at depths corresponding to the location of the measuring electrodes with numbers 2 ÷ N-1. To find each of these resistive electrical sensors use data related to three adjacent measuring electrodes 2.3, hereinafter referred to as "middle, upper, lower" and forming a measuring triple, the middle of which corresponds to the depth of the current logging, which measure resistivity.

According to the invention, bipolar electric current pulses are applied between the electrodes 2.2 and the upper part of the casing 1.1 of the well, and the potential of the probe electrode is measured relative to the upper part of the casing 1.1. In this case, first, a current I _{1 is} supplied between the upper current electrode 2.2 of the probe and the upper part of the casing 1.1 of the well. At each supply of current I _1, the absolute value of the potential U _{01 of} one of the measuring electrodes 2.3 of probe 2 is measured relative to the upper part of the casing 1.1. Next, measure the absolute value of the potential difference ΔU ₁ (1) between the "middle" and "upper" measuring electrodes 2.3, as well as the absolute value of the potential difference ΔU ₁ (2) between the "lower" and "average" measuring electrodes 2.3. A current I _{2 is} then applied between the lower current electrode of the probe 2.2 and the upper part of the casing 1.1 of the well. At each supply of current I _2, the absolute value of the potential U _{02 of} one of the measuring electrodes 2.3 of probe _{2 is} measured relative to the upper part of the casing 1.1. Next, measure the absolute value of the potential difference ΔU ₂ (1) between the "middle" and "upper" measuring electrodes, as well as the absolute value of the potential difference ΔU ₂ (2) between the "lower" and "average" measuring electrodes 2.3. Further, based on the linear electrical resistance of the casing 1.1 and the measured values of the potentials U ₀₁ , U ₀₂ and their differences ΔU ₁ (1), ΔU ₁ (2), ΔU ₂ (1) and ΔU ₂ (2) at the current logging depth h Resistivity of rocks by the formula

Where:

K ₀ (kr ₀ ) - the modified Bessel function of the second kind (the Macdonald function);

r ₀ is the outer radius of the casing (column);

- погонное сопротивление обсадной трубы;

- linear resistance of the casing;

h is the current depth of the probe;

L is the distance between the measuring electrodes;

H - depth casing shoe.

A device that implements the proposed method of electric logging of cased wells, contains a multielectrode probe 2 of bipolar sounding of rocks (AFC), current 2.2 and measuring electrodes 2.3 of which are connected through a geophysical cable 5 of the lifting winch 6 to the receiving-transmitting (PP) unit 3 connected by interface lines connection with the digital unit 4 measurement and registration (IR) of the electrical resistivity (resistivity) of rocks surrounding the casing 1.1 wells, and the unit DGPD is equipped with electrical contacts Ktami for connection to the current conductors of the geophysical cable 5, and the IR unit is equipped with a serial or parallel output port 4.8.

Proof of the connection of features of the invention with achievable technical result.

The proposed method and device compared to the prototype allow:

- conduct logging in complex geological and technical conditions, when the earth's surface is an insulator layer;

- on the basis of an improved formula that does not contain empirical coefficients, it is more accurate to relate the obtained values of the electrical resistivity of rocks with the measured downhole probe electrical parameters;

- improve the accuracy of determining the electrical parameters measured by the probe by eliminating parasitic currents in the design of the downhole probe;

- to speed up the logging process by optimizing the time spent at the depth point on the basis of a statistical assessment of the accuracy of the obtained resistivity values.

Such technical advantages and capabilities of the proposed method and device for electrical logging allow to expand the functionality of oil exploration in rock masses with high electrical resistivity and, as a result, to achieve the stated technical result.

The invention is illustrated by the drawings shown in FIG. 1 - FIG. eight.

FIG. 1 shows drawings illustrating the principle of electrical logging according to the known (FIG. 1a) and proposed (FIG. 1 c) methods; in fig. 2 is a functional diagram of the electric logging device; in fig. 3 and FIG. 4 - the design of a submersible multielectrode probe with dielectric inserts and the inclusion of a wire between the housings of current electrodes, respectively; in fig. 5 and FIG. 6 the design of the retractable probe electrodes without the use of and with welded or soldered joints, respectively; in fig. 7 - the design of the pointed electric leads of the retractable probe electrodes; in fig. 8 - dependence of the exponential potential drop rate along the well axis on the resistivity of the rocks surrounding the well; in fig. 9 is a drawing illustrating the principle of measuring the electrical resistance of rocks surrounding a well.

In figures 1-8 indicated:

1 - diagram of the current supply to the well;

1.1 - casing;

1.2 - grounding (V-electrode);

1.3 - remote electrode (Jude);

1.4 - current source;

2 is a schematic of a borehole multielectrode probe for bipolar sensing of rocks (HRSP);

2.1 - insulating inserts;

2.2 - current electrodes;

2.3 - measuring electrodes;

2.3.1 - insulators;

2.3.2 - pointed electric input;

2.3.3 - wires;

2.3.4 - soldering or welding;

2.3.5 - flexible conductor;

2.3.6 - bushings for soldering wires;

2.4 - connecting wire between the housings of current electrodes;

3 - interface unit with downhole tool;

3.1 - pulse shaping unit;

3.2 - power supply;

3.3 - cable mate;

3.4 - modem;

3.5 - measurement data;

4 - data logging and control unit;

4.1 - control unit;

4.2 - unit for analyzing the quality of current measurement results;

4.3 - block receiving and accumulation of measurement data;

4.4 - block operational calculation of electrical resistance (resistivity);

4.5 - signal transmission line “forming measurement conditions”;

4.6 - signal transmission line “end of measurement”;

4.7 - transmission line control commands modem 3.4 block 3;

4.8 - output port by resistivity values;

4.9 is the transmission line of the control signal for the parameters of bipolar pulses to block 3.1;

5 - geophysical cable.

6 - lifting winch.

DISCLOSURE OF INVENTION

The invention was made possible thanks to the research of the authors in the field of electrical logging. As a result of the research, it was found that the upper part of the casing can be used as a ground current electrode (grounding) and a remote electrode (Fig. 1c). At first glance, this is a short circuit across the column, and current distribution in the rock massif is out of the question. However, one should not rely on the obvious. The authors evaluated the resistance of an isolated steel column 1000 m long and the same, but located in a rock massif with a resistivity of several OM * m.

It turned out that in the second case the resistance between the top and the bottom of the column decreases several times (3-4 times). This suggests that during the passage of current between the top and bottom of the column, most of the current is distributed in the rock mass. This makes it possible to use the wellhead as ground (B-electrode). In this case, the result of measuring the potential of the probe, obtained at the Jude electrode, must be corrected.

Earlier, on the basis of expert assessment, it was found that when the probe is located near the column shoe (casing pipe 1.1), the value of the measured potential should be halved. This was clearly confirmed when logging on one of the wells in Siberia, when logging was carried out using traditional and proposed methods. It was also successfully applied in Kuwait. Later on mathematical models it was found that with an arbitrary location of the probe in the well, the absolute value of the potential of the probe U can be represented by the dependence

where U ₀ - the absolute value of the potential of one of the measuring electrodes relative to the upper part of the casing;

h is the depth of the probe;

H is the depth of the column shoe.

We define the functional relationship between resistivity, casing parameters and potentials measured by the probe.

To measure the electrical resistivity of an array of rocks intersected by a well cased with a metal column, the phenomenon of current flowing away from the conductor into the surrounding low-conducting medium under the action of the radial component of the electric field is used.

The potential in the environment surrounding the casing, obeys the Laplace equation, which with axial symmetry has the form

and the condition U (r, z) → 0 as r → ∞.

The zero order solution satisfying (2) is U (r, z) = e ^{± kz} K ₀ (kr),

where K ₀ (kr) is the modified Bessel function of the second kind (the Macdonald function);

signs + and - correspond to currents propagating in negative and positive directions with respect to z, respectively;

k - parameter determined by the values of the electric field on the casing.

Let the metal casing has a cylindrical shape with an external radius of r ₀ and has specific specific resistance R, and the specific resistance of the environment is ρ.

Then, in accordance with (2), in the local area of space at a certain depth z _{0, the} potential can be represented by the function

Where

U ₀ is the potential value at r = r ₀ , z = z ₀ ;

A and B are numerical coefficients corresponding to the current components propagating in negative and positive directions, respectively (A + B = 1);

In accordance with Ohm’s law, the radial current density j _r , the potential U, and the electrical resistivity ρ in the environment surrounding the column are related by the formula

From (3) it follows

(функция Макдональда 1-го порядка). При z=z₀ и r=r₀ (5) приобретает видHere

(Macdonald function of the 1st order). At z = z ₀ and r = r ₀ (5) takes the form

Substituting (6) into (4), we obtain

Then the current outgoing from the casing element of unit height is

This radial current is equal to the decrease in current along the casing per unit length, which is determined by the change in potential on its surface along the z axis. It is equal to:

Therefore, from (8) and (9) it follows:

The potential and its second derivative with respect to z at z = z ₀ and r = r ₀ are equal to:

From here

Substitution (13) into (10) gives

For typical values of r ₀ = 0.1 m and R = 5⋅10 ^-5 Ohm / m, the dependence of k on ρ, defined by equation (14), is shown in FIG. 8. It follows from it that when the specific resistance of the rock mass ρ> 1 Ω * m, the value of k does not exceed 0.01. In this case, the value of kr near the well is not more than 0.001.

Since kr ₀ << 1,

From (10) and (15) we get:

where, based on (13),

The algorithm below for determining the resistivity of an array of rocks is developed on the basis of formulas (16) and (17) and taking into account the measurement discreteness and the influence of interfering factors.

The voltage drop along the casing is due to its linear resistance and the magnitude of the current I passing through its cross section:

Then the second derivative

From here

This shows that the decrease in current per unit length of the casing cannot be determined when the casing is not uniform in terms of potential change only. But since when the current direction changes, the first term in (18) remains unchanged, and the second, caused by the heterogeneity of the pipe material, changes its sign, this allows us to eliminate the influence of the casing non-uniformity by using measurement circuits with a counter-current direction.

When performing measurements in the well, derivatives are replaced by differential analogues. The analogue of the second derivative requires measurements at three points spaced at a depth of L (this is the distance between the measuring electrodes):

по величине на несколько порядков меньше тех величин, разностью которых она является. Поэтому даже небольшие погрешности в определении первых разностей потенциалов приводят к значительным ошибкам. Одним из основных источником погрешностей является неравность сопротивлений участков колонны, обусловленная неоднородностью колонны и неравенством расстояний от среднего измерительного электрода до верхнего и нижнего электродов. Для исключения погрешностей применяется встречная система измерений, при которой определяются разности потенциалов между измерительными электродами при различном направлении тока в колонне.

magnitude several orders of magnitude less than those values of which it is the difference. Therefore, even small errors in determining the first potential differences lead to significant errors. One of the main sources of error is the unequal resistance of the sections of the column, due to the heterogeneity of the column and the inequality of the distances from the average measuring electrode to the upper and lower electrodes. To eliminate errors, a counter-measurement system is used, in which potential differences between the measuring electrodes are determined for different directions of current in the column.

The measurement circuit is illustrated in FIG. 9 where

L is the distance between the measuring electrodes;

R ₁ and R ₂ - the resistance of the upper and lower sections of the casing between the measuring electrodes;

the arrows indicate the direction of the current along the casing, when current is supplied through the supply electrodes А ₁ and А ₂ ;

i ₁ , i ₂ - reduction of current in the vertical section of length L when current is applied through the supply electrodes А ₁ and А ₂ ;

ΔU ₁ (1), ΔU ₁ (2), ΔU ₂ (1) and ΔU ₂ (2) are the first differences determined by the currents in the column, the resistances of the casing sections and the leakage currents i ₁ , i ₂ flowing into the rock mass.

In accordance with FIG. 9, the system of equations for the first differences can be written:

Perform some transformations and calculations.

(21) - (22) equals

Equality was used here:

From (23) it follows:

The decrease in current along the casing at length L is equal to the current flowing into the rock mass, therefore i ₁ and i ₂ are equal in magnitude to the corresponding radial currents from the same length L, so that, taking into account (8) and (15),

where U ₁ and U ₂ are the potentials of the probe when current is supplied from the electrode A ₁ and A _2, respectively.

Substituting expressions (25) for i ₁ and i ₂ into (24) we get

From here

The potentials of the probe U ₁ and U ₂ are equal, in accordance with (1),

where U ₀₁ and U ₀₂ are the potentials of the probe relative to the top of the casing (wellhead), to which the current and remote electrodes are attached. From (27) and (28) follows:

From (9), (13) and (24):

Formulas (29) and (30) take into account the nonuniformity of the linear resistance of the column and the inequality of the distances of the extreme measuring electrodes from the central one. They do not contain empirical coefficients.

Since kr ₀ << 1, for practical use, the Macdonald function included in formula (30) can be approximated with a high degree of accuracy by

, где постоянная Эйлера С≈0.5772.

where is the Euler constant C≈0.5772.

A device that implements the proposed method of electric logging of cased wells, contains a multielectrode probe 2 of bipolar sounding of rocks (ASG), current 2.2 and measuring 2.3 electrodes of which are connected through a geophysical cable 5 of the lifting winch 6 with a transmitter-transmitter (PP) unit 3 connected by interface lines connection with the digital unit 4 measurement and registration (IR) of the electrical resistivity (resistivity) of rocks surrounding the casing 1.1 wells, and the DGP unit is equipped with electric contacts Tami for connection to the current conductors of the geophysical cable 5, and the IR unit is equipped with a serial or parallel output port 4.8.

At the same time, the multi-electrode probe 2 of the OGPU of the electrical logging tool of cased wells is made with the possibility of reducing leakage currents between current 2.2 and measuring electrodes 2.3. To do this, it contains an elongated body, from the upper and lower sides of which current electrodes 2.2 are installed. Between the current electrodes 2.2 a group of measuring electrodes 2.3 is installed, electrically isolated from the current electrodes 2.2 by dielectric inserts 2.1. Current 2.2 and measuring 2.3 electrodes of probe 2 are made pointed 2.3.2 and mounted on retractable dielectric levers 2.3.1. They are also equipped with electrical terminals 2.3.6 with flexible conductors 2.3.3 for connecting current 2.2 and measuring 2.3 electrodes via a geophysical cable 5 with a current output and a signal input of the block 3 PP, respectively.

Block 3 PP, made with the possibility of generating bipolar current pulses and contains a series-connected power source 3.2 power supply and block 3.1 of the formation of bipolar pulses (FDI). The FDI unit is equipped with electrical contacts to connect the FDI unit to the current conductors of the logging cable 5 and to the top of the casing 1.1. The FDI unit also contains serially connected receiver 3.3 of the signals of measuring electrodes 2.3 and modem 3.4. The signal output and the control input of the modem 3.4 are measured according to the measurement of electric potentials and their differences 3.5 and the control commands 4.7 are connected respectively to the signal input and the first control output of the digital 4 IR module.

Digital block 4 IR, made with the possibility of calculating the resistivity of rocks with a short effect of the casing 1.1 on the measurement process of resistivity of rocks. To do this, it contains a series-connected unit 4.3 for receiving and accumulating data for measuring potentials and the difference in electric potentials between measuring electrodes 2.3. Block 4.4 of operational calculation of resistivity with output port 4.8, block 4.2 of quality analysis of current resistivity measurement results and block 4.1 of logging management is equipped with a set of interface lines 4.5, 4.6, 4.7, 4.9 communications for transmitting commands for controlling sounding of rocks and receiving measurement data of potentials and their differences on block 3 PP.

The complex of interface communication lines includes line 4.5 for transmitting the signal “forming metering conditions”, signal transfer line 4.6 “metering completion” to the power supply source 3.2, bipolar pulse parameter control signal transfer line 4.9 to FDI unit 3.1 and modem control command transfer line 4.7 block 3 PP.

Block 4.4 of Block 4 of the IR is equipped with a program for calculating the resistivity of rocks by the formula

Where:

K ₀ (kr ₀ ) - the modified Bessel function of the second kind (the Macdonald function);

r ₀ is the outer radius of the casing;

- погонное сопротивление обсадной трубы;

- linear resistance of the casing;

h is the current depth of the probe;

H is the depth of the column shoe.

Digital block 4 IR made modular design on reprogrammable logic integrated circuits (FPGA) or in the form of an electronic computer (computer), equipped with a program for measuring and recording resistivity.

The operation of the electrical logging device according to the proposed method consists in the following.

Before starting logging, the contact wire of the FDI block 3.1 is grounded at the “mouth” of the casing 1.1, and another contact wire is connected to the current cores of the geophysical cable 5 to supply a bipolar current pulse to the current electrodes 2.2 of the probe 2. The contact wire of the block 3.3 is connected to the measuring cores of the geophysical cable 5, and another contact wire is connected to the mouth of the casing 1.1. The probe 2.2 is immersed in the well to the depth of the beginning of logging. Then, with a given measurement step, the resistivity is lifted using a winch 6, probe 2 inside the casing 1.1. At each step of the deep logging, current 2.2 and measuring 2.3 electrodes are connected with the inner walls of the casing 1.1 with the help of sliding levers 2.3.1.

After electrical contact with the walls of the casing 1.1, the control unit 4.1 specified in the IR block program issues a command on line 4.5 to function according to the measurement conditions of a power source 3.2, which, by means of a pulse shaping unit 3.1 (FDI), produces a series of bipolar pulses whose parameters are transmitted to This block from the control block 4.1 on line 4.9.

Bipolar and current pulses, alternately fed to the upper and lower current electrodes 2.2. In this case, the current passes through the current cores of the geophysical cable, enters the casing at the point of contact of the current electrode, then spreads along it up and down, gradually decreasing in size due to leakage of a part of the current into the surrounding rock mass. Near the mouth of the siege pipe, the reverse process of collecting the current from the array and adding to the current through the pipe occurs. Through the contact wire coming from the mouth of the casing, the current returns to the block forming pulses.

The primary measurements of the potential of the probe 2 and the potential differences between the measuring electrodes 2.3 are received through the interface 3.3 with the cable and the modem 3.4 to the measurement acquisition unit 4.3, which are used to quickly calculate the electrical resistivity in block 4.4. The obtained value of resistivity and the primary measurement data on the probe electrodes are transmitted to the unit 4.2 of the analysis of the quality of the result. In this block, the statistical error of the result is estimated and a decision is made to complete logging at a given depth with the output of the resistive electrical output at output port 4.8, or further continuation of the bipolar current supply series in order to improve the accuracy of determining the resistive electrical potential by increasing statistics. In the first case, from block 4.2 of the analysis of the results, the control unit 4.1 sends a signal on line 4.6 that the measurement has been completed at this depth, and in the second case, the measurement has continued. Block 4.1 is also connected by line 4.7 with modem 3.4 to control the data collection process. The results of measurements of resistivity at the current logging depth is transmitted to the output port 4.8 of the logging device. Next, the winch 6 produces the rise of the probe 2 at the next logging point and the process of measuring the electrical resistivity of rocks surrounding the casing (metal pipe 1.1) well, is repeated.

Industrial Applicability

Prototypes manufactured in accordance with the claimed invention, successfully tested in the fields of Western Siberia and Kuwait. At the same time, an increase in the accuracy of determining the resistivity of rocks surrounding the casing and a decrease in the time of logging was observed.

Claims (25)

1. Method of electrical logging of cased wells, consisting in step-by-step raising of a multielectrode probe 2 cased by a metal pipe 1.1, consisting of N measuring equidistant at a distance L from each other along the axis of the well of adjacent electrodes 2.3, outside and on opposite sides of which there are two current electrodes 2.2, in which, at each logging step, bipolar pulses of electric current are alternately applied and measure the potential of one of the measuring electrodes 2.3, the currents and differences supplied the potential between each measuring electrode and measuring electrodes spaced L from it, on the basis of these measurements of electrical signals determine the electrical resistivity (CES) of the rocks surrounding the well, and the CES at each logging step is determined at N-2 points at depths corresponding to the location measuring electrodes with numbers 2 ÷ N-1, and for finding each of the mentioned resistivity using data related to three adjacent measuring electrodes, referred to below as “average, in Top, bottom "and forming a measuring triple, the middle of which corresponds to the depth of the current logging, which measure resistivity, characterized in that the bipolar pulses of electric current is supplied between the electrodes 2.2 and the upper part of the casing 1.1 of the well, casing 1.1, while in the logging process, firstly, a current I _{1 is} supplied between the upper current electrode 2.2 of the probe and the upper part of the well casing, with each current I _{1 being} measured, the absolute value potential U _0l one of the measuring electrodes 2.3 probe 2 relative to the upper part of the casing 1.1, then measure the absolute value of the potential difference ΔU ₁ (1) between the "middle" and "upper" measuring electrodes 2.3, as well as the absolute value of the potential difference ΔU ₁ (2 ) between "lower" and "average" measurement electrodes 2.3, then the current I ₂ is supplied between the lower current electrode 2.2 probe and the top of the well casing 1.1, at each application of a current I ₂ measured absolute value of the potential of one of the U ₀₂ measuring elec genera 2.3 probe 2 with respect to the upper part of the casing 1.1, more measured absolute value between "medium" and "upper" ΔU ₂ (1) of the potential difference measuring electrodes 2.3, and an absolute potential difference value ΔU ₂ (2) between "lower" and “Average” measuring electrodes 2.3, further on the basis of linear electrical resistance of the casing 1.1 and measured values of the potentials U ₀₁ , U ₀₂ and their differences ΔU ₁ (1), ΔU ₁ (2), ΔU ₂ (1) and ΔU ₂ (2 ) at the current depth h logging calculate the resistivity of rocks. 2. The method according to p. 1, characterized in that the calculation of the electrical resistivity of rocks produced by the formula

Where: K ₀ (kr ₀ ) - the modified Bessel function of the second kind (the Macdonald function); r ₀ is the outer radius of the casing;

- linear resistance of the casing; h is the current depth of the probe; H is the depth of the casing shoe. 3. An electrical logging tool for cased wells, characterized in that it contains a multielectrode probe 2 of bipolar sounding of rocks (GDF), consisting of N measuring equidistant at a distance L from each other along the well axis of adjacent electrodes 2.3, outside and on opposite sides of which are two current electrodes 2.2, current 2.2 and measuring 2.3 electrodes are connected via a geophysical cable 5 of the lifting winch 6 to the receiving-transmitting (PP) unit 3 connected by interface lines with digit a new measurement unit 4 and registration (MI) of electrical resistivity (CES) of rocks surrounding the well casing 1.1, the DGPP unit is equipped with electrical contacts for connecting the geophysical cable 5 to the current cores, and the MI unit is equipped with a serial or parallel output port 4.8, and the potential of one of the measuring electrodes 2.3 is measured relative to the upper part of the casing 1.1 of the well. 4. The device according to p. 3, characterized in that the multielectrode probe 2 OGPP is designed to reduce leakage currents between the current 2.2 and measuring 2.3 electrodes and contains an elongated body, from the upper and lower sides of which current 2.2 electrodes are installed, between which a group of measuring electrodes 2.3, electrically isolated from current electrodes 2.2 by dielectric inserts 2.1, current 2.2 and measuring 2.3 electrodes of probe 2 are made pointed 2.3.2, mounted on retractable dielectric levers 2.3.1 and c Electrical terminals 2.3.6 are fitted with flexible conductors 2.3.3 for connecting current 2.2 and measuring 2.3 electrodes via a geophysical cable 5 with a current output and a signal input of the PP unit 3, respectively. 5. The device according to p. 3, characterized in that block 3 PP is designed to generate bipolar current pulses and contains a series-connected power source 3.2 power supply and block 3.1 forming bipolar pulses (FDI), equipped with electrical contacts, to connect the FDI block to current the cores of the geophysical cable 5 and to the upper part of the casing 1.1, as well as the FDI unit, contain a series 3.3 receiver of measuring electrodes 2.3 and modem 3.4, a signal output and a control input of which According to the measurement of electrical potentials and their differences commands 3.5 and 4.7 are respectively connected to control signal input and the first output of the digital control unit 4 TS. 6. The device according to p. 3, characterized in that the digital block 4 IR made with the possibility of calculating the electrical resistivity of rocks with a short effect of the casing 1.1 on the measurement process of electrical resistivity of rocks and contains series-connected unit 4.3 receiving and accumulating data measuring potentials and electrical differences potentials between measuring electrodes 2.3, block 4.4 of operational calculation of resistivity with output port 4.8, block 4.2 of analysis of the quality of results of resistivity measurements and block 4.1 of logging management, equipped with a complex of interface lines d 4.5, 4.6, 4.7, 4.9 for the communication of control commands sensing rocks potentials and reception of measured data and their differences on the block 3 PP. 7. The device according to claim 6, characterized in that block 4.4 of block 4 of the IR is equipped with a program for calculating the resistivity of rocks by the formula

Where: K ₀ (kr ₀ ) - the modified Bessel function of the second kind (the Macdonald function); r ₀ is the outer radius of the casing;

- linear resistance of the casing; h is the current depth of the probe; H is the depth of the casing shoe. 8. The device according to p. 6, characterized in that the complex of interface communication lines includes line 4.5 for transmitting the signal “forming measurement conditions”, line 4.6 for transmitting the signal “end of measurement” to the power source 3.2 of power supply, line 4.9 for transmitting the control signal for bipolar pulse parameters on unit 3.1 FDI and line 4.7 transfer of control commands by modem 3.4 unit 3 PP. 9. The device according to claim 6, characterized in that the digital block 4 IR made modular design on reprogrammable logic integrated circuits (FPGA) or in the form of an electronic computer (computer), equipped with a program for measuring and recording resistivity.

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