RU2783988C1 - Method and device for electromagnetic flaw detection-thickness measurement of ferromagnetic metal pipes in multi-column wells - Google Patents

Abstract

FIELD: measuring technology.

SUBSTANCE: invention relates to flaw detection of metal pipes coaxially located in wells, including steel drill, casing and tubing pipes. The essence of the invention lies in the fact that the excitation of non-stationary electromagnetic fields in the metal columns of the well is carried out by generator coils in probes of different lengths when a current pulse T, selected from the condition T = ah, passes simultaneously through all generator coils, then, starting from the shortest probe, they are sequentially disconnected from the generator with an interval T_i and EMF measurement (E) as a function of time E(t_j,) induced in the receiving coils by eddy currents flowing in the metal pipes under study, at the same time, in probes of different lengths along the perimeter of each receiving coil, hereinafter referred to as the main receiving coil, additional receiving coils with an inductance equal to the inductance of the main receiving coil are placed on magnetic cores whose axes are parallel to the axis of the probe, and for each probe, starting with the shortest probe, the EMF (E) ratios are recorded as time functions E(t_j,) measured by each main and additional receiving coils:

in this case, the azimuthal inhomogeneity of the pipe is determined by the magnitude of the excess of the specified ratio over one, the greater the excess, the more pronounced the azimuthal inhomogeneity of the pipe, where E(t_j)main is the EMF measured on the main receiving coil, mV, E(t_j)add is the EMF measured on the additional coil, mV, T is the duration of the current pulse, s, T_i is the current cut-off interval, s, t_j is the step of the EMF measurement interval in the interval T_i, s, τ is the decay constant, 1/s, E is the measured EMF, mV, a is the proportionality coefficient, s/mm, h is the total thickness of the columns, mm.

EFFECT: increasing the accuracy of determining metal loss in local pipe defects in multi-column wells through the use of azimuthal and radial measurements.

2 cl, 8 dwg

Description

SUBSTANCE: group of inventions relates to geophysics and can be used for flaw detection of metal pipes located in wells, in particular, steel drill, casing and tubing pipes (tubing), with the possibility of radial and azimuthal sounding of each pipe in multi-string wells.

A method of electromagnetic flaw detection in multi-column wells and an electromagnetic downhole flaw detector are known (Pat. RF No. 2507393, prior 31.08.2012, publ. 20.02.2014).

A known method of electromagnetic flaw detection in multi-string wells includes measuring the electromotive force (EMF) of self-induction induced in the coil by eddy currents excited in the investigated metal barriers by the process of decay of the electromagnetic field caused by coil magnetization current pulses. A series of pulses of a fixed duration from the range of 0.1-1000 ms is separately applied to each of the receiving-and-exciting coils, sequentially magnetizing all metal barriers, starting from the nearest one, and the pulse duration increases for each subsequent metal barrier. The data obtained is stored and processed by comparison with model data, the processing results are used to judge the presence of a defect in the metal barriers.

The electromagnetic downhole flaw detector for implementing the method comprises a body, coils located along the device axis, the magnetic axis of which coincides with the device axis, an electronics unit, at least two receiving and generating coils, each of which consists of a generator and a receiving coil with a single core. Moreover, the receiving-generating coils are made of different sizes, spaced apart from each other on the axis of the device at a distance not less than the length of the larger receiving generator coil.

The disadvantage of the known technical solution lies in the fact that with the sequential magnetization of each magnetic metal tube, starting from the nearest one, with further measurement of the EMF, the influence of the electromagnetic and geometric parameters of the first tube will distort the measurement results in subsequent tubes, which makes it necessary to take into account this effect. The use of only axial probes makes it difficult to detect transverse cracks and identify local defects.

Known patent EA 034115 "Device for the implementation of multi-sensor magnetic flaw detection of well casing strings and monitoring the technical condition", G01N 27/90, E21B 47/00, LLC MIKS (RU), Appl. November 28, 2018, publ. 09/26/17

A well-known device for flaw detection of casing strings includes an electromagnetic field generation unit, a receiving sensor unit and a control unit, data recording and analysis, fixed in the housing, while the electromagnetic field generation unit for creating exciting pulses of a given amplitude and duration is a generator coil with a core made of material with high magnetic permeability, the block of receiving sensors includes an integral measuring coil and N radial measuring coils located around the winding of the generator coil, each measuring coil has a U-shaped core, the poles of which are directed perpendicular to the surface of the column under study, and the axis of symmetry of the winding is parallel axes of symmetry of the winding of the generator coil, the control unit, data recording and analysis includes N operational amplifiers with variable gain and analog-to-digital converters (ADC) that transmit signals from the measurement coils to a microcontroller connected to a computer with software for analyzing column defects, while the microcontroller is configured to control the electromagnetic field generation unit, as well as the gains and the ADC (taken as a prototype for the claimed device).

The disadvantage of the known device is that the inductance of each of the N measuring coils is not determined, which does not allow taking into account the influence of the main measuring coil on the readings of N radial measuring coils, which reduces the accuracy of azimuthal (sector) measurements to detect azimuthal inhomogeneity of the pipe in coaxially cylindrical media.

Known application WO 2020257761 A1, prior. 06/21/2019, publ. December 24, 2020 "Method and device for multi-barrier electromagnetic (TEM) through-hole measurements".

The known system is intended for electromagnetic flaw detection in multi-column wells, carried out in the process of measuring the EMF induced in the receiving coils by eddy currents flowing in the investigated metal magnetic pipes after excitation of the electromagnetic field by current pulses in the generator coils and measuring the EMF induced in the receiving coils by eddy currents flowing in the investigated metal magnetic tubes, while

a plurality of sensor signals (receiving coils) are received, where each signal from a plurality of sensor signals is marked with the corresponding time and depth, in addition, a base signal is selected and the selected sensor signal is compared from a plurality of sensor signals with the base signal, then a threshold value for exceeding the difference between the base signal is determined. (reference) signal and a selected sensor signal corresponding to depth and time, and based on the established difference, a feature of interest associated with the selected sensor signal is identified. Under the feature of interest associated with the selected signal, we mean the feature of the state of the studied metal magnetic tubes, thus, each tube is tested according to the readings of the corresponding sensor (receiving coil).

The disadvantage of the known method is that the EMF measurements of each measuring coil are influenced by the base signal, which reduces the resolution of the measurements.

A known method of electromagnetic flaw detection-thickness measurement in multi-column wells (Pat. RF No. 2636064, Appl. 07/14/2016, publ. 11/20/2017) (Accepted as a prototype for the claimed method).

The well-known method of electromagnetic flaw detection-thickness measurement in multi-string wells includes the excitation of a non-stationary electromagnetic field by current pulses in generator coils of different lengths and the measurement of the EMF induced in the receiving coils by eddy currents flowing in the metal magnetic pipes under study, while simultaneously exciting all generator coils with a current pulse of duration T , and then they are sequentially disconnected from the generator with an interval Ti, starting with a short generator coil, and sequentially with each measuring coil corresponding to the disconnected generator coil, the EMF (E) is measured as a function of time E(t _j ,), and the signal from the most recent, long measuring coil is recorded as a decay constant - τ=[E(t _j+1 )-E(t _j )]:[(t _j+1 -t _j ,)E(t _j ,)]. In this case, the duration T is chosen according to the dependence T=a h,

where T is the duration of the current pulse, s,

Ti - current cutoff interval, s,

t _j - step of the EMF measurement interval in the interval Ti, s,

τ - decay constant, 1/s,

E - measured EMF, mV,

a - coefficient of proportionality, s / mm,

h is the total thickness of the columns, mm.

The use of only axial probes makes it difficult to detect transverse cracks and identify local defects.

The objective of the claimed invention in terms of an electromagnetic flaw detector is to improve the design of an electromagnetic downhole flaw detector-thickness gauge, which makes it possible to improve the accuracy of azimuthal (sector) measurements in coaxially cylindrical media by exciting an electromagnetic field with an axisymmetric source, and measuring the eddy current-induced EMF - with non-axisymmetric receivers located along the perimeter device.

The objective of the claimed invention in terms of the method of electromagnetic flaw detection-thickness measurement of ferromagnetic metal pipes in multi-column wells is to increase the resolution of the measurement method.

The technical result of applying the group of inventions is to increase the accuracy of determining the loss of metal in local pipe defects in multi-column wells through the use of azimuthal and radial measurements.

The task in terms of the device is solved by the fact that an electromagnetic downhole flaw detector, containing a housing, an electronics unit, probes located along the axis of the device with electromagnetic coils of different lengths, the magnetic axes of which coincide with the axis of the device, including the main receiving and generating coils, each of which consists from the generator and receiving coils with a single core, the magnetic axes of which coincide, while along the perimeter of each main receiving coil there are N additional receiving coils on magnetic cores, the axes of which are parallel to the probe axis and shifted from the probe axis by a distance R, and the inductance of each of the additional pickup coils is chosen equal to the inductance of the corresponding main pickup coil.

, при этом азимутальную неоднородность трубы устанавливают по величине превышения указанного отношения над единицей, чем больше превышение, тем больше выражена азимутальная неоднородность трубы,The problem posed in terms of the method is solved by the fact that in the method of electromagnetic flaw detection-thickness measurement of ferromagnetic metal pipes in multi-column wells, including the excitation of non-stationary electromagnetic fields in the metal columns of the well by generator coils in probes of different lengths while passing simultaneously through all the generator coils of a current pulse T selected from conditions T = a h, then, starting from the shortest probe, their sequential disconnection from the generator with an interval T _i , and the measurement of EMF (E) as a function of time E(t _j ,), induced in the receiving coils by eddy currents flowing in the studied metal magnetic tubes, while in probes of different lengths along the perimeter of each receiving coil, hereinafter referred to as the main receiving coil, additional receiving coils are placed on the magnetic cores with an inductance equal to the inductance of the main receiving coil, and for each probe, starting from the shortest probe, register EMF ratio (E), as a function of time E(t _j ,), measured by each main and additional receiving coils

, while the azimuthal inhomogeneity of the pipe is set by the value of the excess of the specified ratio over unity, the greater the excess, the more pronounced the azimuthal inhomogeneity of the pipe,

where:

E(t _j )ocn. - measured EMF on the main coil, mV,

E(t _j )add.- measured EMF on the additional coil, mV,

T is the duration of the current pulse, s,

T _i - current cutoff interval, s,

t _j - step of the EMF measurement interval in the interval T _i , s,

τ - decay constant, 1/s,

E - measured EMF, mV,

a - coefficient of proportionality, s / mm,

h is the total thickness of the columns, mm.

In FIG. 1 shows a schematic diagram of the placement of the probes of the claimed electromagnetic flaw detector in a well with a multi-column design.

In FIG. 2 shows the device of the probe with a set of main and additional receiving coils relative to the axis of the downhole tool - flaw detector.

In FIG. 3 shows a set of registered impulses of decay curves. E1, E2, E as a function of the off time of the generator coils - T1, T2, T.

In FIG. Figure 4 shows an example of registering decay curves E for a single-string well model with a wall thickness of 8 mm and 10 mm.

In FIG. 5 shows a model of a two-string well.

In FIG. 6 shows an example of registering the ratio of signals - A _5.10 , - A _5.9 in a two-column model.

In FIG. 7 shows the results of measurements using a physical model of a two-string well.

In FIG. 8 shows the time J(t) and frequency J(w) characteristics of the current pulse source.

The implementation of the proposed method is ensured by the use of an electromagnetic downhole flaw detector, selected with three probes of different lengths, and shown in Fig. 1 and FIG. 2.

The downhole flaw detector tool contains three probes of different lengths: short 1, medium 2 and long 3, each of which consists of a generator 4, and a main receiving coil 5 with a single core 6. N additional receiving (measuring) coils are placed along the perimeter of each main receiving coil. on magnetic cores 7, the axes of which are parallel to the axis of the probe 8 and shifted from the axis 8 of the probe by a distance R, which is selected experimentally, and the inductance of each of the additional receiving coils is chosen equal to the inductance of the corresponding main receiving (measuring) coil (in Fig. 2, Fig. Fig. 5 and Fig. 6 two additional coils 9 and 10 from the number N) are indicated.

The flaw detector is lowered into the well with five magnetic pipes 11, 12, 13, 14, 15.

The method of magnetic-pulse electromagnetic flaw detection-thickness measurement is based on the study of the spatial distribution in the pipe string of eddy currents damped in time, inducing an electromotive force (EMF) in the measuring inductance coil after the passage of a magnetization current pulse in the generator coil.

It allows sounding of multi-column structures with time division of the signal from different columns. This is done by choosing the duration of the eddy current excitation current pulse - T in the generator coil, the time t for measuring the EMF of the transient decay curves (TP) in the measuring coil and the design of the probe.

The choice of the duration of the excitation current, the time interval on the decay curves and the duration of the pulse makes it possible to assess the technical condition of a particular column.

According to the theory of electromagnetic flaw detection-thickness measurement, the EMF of the decay curves of the transient process (TP) of eddy currents in the column is a function of E(t)=f(μ,σ,h,D,M _g ,M _p ),

where

t - registration time of PP,

μ, σ are, respectively, the magnetic permeability and specific conductivity of the metal,

h - column wall thickness,

M _g , M _p - the magnetic moment of the generator and receiver coils.

To calculate the decline curves, the algorithm given in the following works is used: Potapov A.P. Numerical solution of direct and inverse problems of pulsed electromagnetic thickness measurement of casing strings in wells. /A.P. Potapov, L.E. Kneller //Geology and geophysics. - Novosibirsk: Nauka, 2001. - Volume 42. - No. 8. -FROM. 1279-1284, and Potapov A.P. On the theory of the method of downhole magnetic-pulse flaw detection-thickness measurement. /A.P. Potapov, L.E. Kneller, V.V. Danilenko // "Geophysics". - M.: EAGO, 2012. - Issue. 2. -S. 20-26.)

To determine an unsteady process in a coaxial-cylindrical medium, a spectral approach based on the application of the Fourier integral is used. (Kaufman A.A. Non-stationary field of a vertical magnetic dipole on the axis of the well. / A.A. Kaufman, V.P. Sokolov // In the collection "Electromagnetic field on the axis of the well", preprint. Academy of Sciences of the USSR SO IG and G, 1971 .-S.31-50).

When the field is excited by the step function of the current:

determined that

where:

h(ω) - magnetic field on the borehole axis, expressed in units of the magnetic dipole field in air. (Dmitriev V.I. Axisymmetric electromagnetic field in a cylindrically layered medium. / V.I. Dmitriev //Physics of the Earth. - M.: Izv. AN SSSR, 1972. - No. 12. - P. 56-61).

We apply the formulas for calculating the z and r components of the magnetic field:

where:

z и r - компоненты электромагнитного поля в однородной среде с удельной проводимостью σ_о.

z and r - components of the electromagnetic field in a homogeneous medium with specific conductivity σ _o .

и С₀ - определяются из рекуррентных формул:

and С ₀ - are determined from recurrent formulas:

(Daev D.S. High-frequency electromagnetic methods of well research. M.: Nedra, 1974).

To take into account the real dimensions of the field source, taking into account the cores, the following approach is proposed.

In expression (2), we replace l/iω with the source function J (ω) - the frequency response of the source (the inductor is protected by a non-magnetic conductive casing).

The function J(ω) for a specific probe is determined experimentally. To do this, measure the decay curve for this device in air. The received signal as a function of time (J(t)) is translated by the discrete Fourier transform program into the frequency domain - J(ω).

In FIG. 8 shows the function J(t) and its frequency spectrum of the probe with the main receiving coil - J(ω).

In the process of implementing the method, magnetization current pulses with a duration T are simultaneously applied to all windings 4, generator coils (Fig. 1, Fig. 2), while the duration of the pulses is calculated depending on the total thickness of the columns 11, 12, 13, 14, 15 according to the formula T=a h, where the coefficient "a" is set experimentally, h is the total thickness of the columns, while non-stationary electromagnetic fields are excited in the metal columns of the well by generator coils in probes of different lengths when the current pulse T passes through all the generator coils simultaneously. Then, starting from the shortest probe 1, all probes are sequentially disconnected from the generator with an interval T _i , and the EMF (E) is measured as a function of time E(t _j ,) (Fig. 3) induced in the main receiving coils 5 and additional receiving coils 9 and 10, which can be set N number, eddy currents flowing in the investigated metal magnetic tubes 11, 12, 13, 14, 15, while registering the EMF ratio (E), as a function of time E(t _j ,), measured by each main and additional receiving coils 9 and 10, installed along the perimeter of the main coil 5 at a distance R from the axis of the device 8:

where:

E(t _j )ocn. - measured EMF on the main coil, mV,

E(t _j )add. - measured EMF on the additional coil, mV,

T is the duration of the current pulse, s,

T _i - current cutoff interval, s,

t _j - step of the EMF measurement interval in the interval T _i , s,

τ - decay constant, l/s,

E - measured EMF, mV,

a - coefficient of proportionality, s / mm,

h is the total thickness of the columns, mm.

In the process of measurements, the azimuthal inhomogeneity of each pipe is set by the value of the excess of the ratio over unity, the greater the excess, the more pronounced the azimuthal inhomogeneity of the pipe.

In FIG. 6 shows an example of registering the ratio of signals - A _5.10 , - A _5.9 in a two-column model. According to the position of the points of the curves A _5,10 and A _5,9 determine the magnitude of the excess of signal ratios over unity.

In FIG. 3 shows a set of registered pulses of decay curves: E1, E2, E as functions of the off time of the generator coils T1, T2, T - E(t _j ).

In FIG. Figure 4 shows an example of registering E decay curves for a single-string well model and shows the results of calculations for a pipe with a wall thickness h of 8 mm and 10 mm, a diameter of 245 mm for different magnetic permeability μ=30.40.60. The greater the magnetic permeability of the medium, the longer the transient process.

In FIG. 5, a model with an asymmetric defect is considered, where pos. 11 - the whole first column, 12 - the second column with an asymmetric defect, 6 - the core with the main receiving coil 5, pos. 9 and 10 - additional receiving coils with core 7, installed at a distance R along the perimeter of the main coil (Fig. 5 shows one probe out of three).

In FIG. 6 shows an example of registering the ratio of signals - A _5.10 , - A _5.9 in a two-column model.

The calculation of the ratios as a result of recording the signals E(t _j ,) of the main 5 and additional coils 9 and 10 is embedded in the algorithm of the electronic computer program for measuring the flaw detector, which shows the final result according to the characteristic of the azimuthal inhomogeneity of the pipe in terms of the excess of the ratio over unity, the greater the excess, the more pronounced is the azimuthal inhomogeneity of the pipe. As a result of calculations, we cut off the signal from the main coil to the results of measurements of additional coils, which increases the resolution of the method.

It has been experimentally established that for a two-column model, the sensitivity to a local defect starts from 100 ms (the ratio is greater than one). The sensitivity increases with the increase in the registration time of the transient process -t, so, for the three-column model, the sensitivity starts from 270 ms.

In FIG. 7 shows the results of physical modeling in real casing strings. The diameter of the first column is 146 mm, the wall thickness is 8 mm, the diameter of the second column is 324 mm, the wall thickness is 11 mm, in which three probes with main receiving coils and 6 additional receiving coils are placed along the perimeter of each main coil, where Depth is the depth in m , completion deagram - model, D1, D2 - pipe diameter, LR01, LR02, - LR03 EMF readings as a function of time E(t _j ,) on the main measuring coil on three probes, I, II, III - time registration channels, R= - the ratio of the EMF of the main and additional coils, 1-6 numbers of coils, t _j - the time of registration of the EMF of the decay curves of the transient process (TP) in the measuring coils, An detected anomaly from a defect with a size of 550 × 140 × 6 mm on a pipe of 324 mm.

The use in coaxially cylindrical media of the method of excitation of an electromagnetic field by an axisymmetric source (the main generator coil located along the axis of the probe), and the reception of EMF - by non-axisymmetric receivers located along the perimeter of the device, allows, along with radial depth scanning, to achieve deep azimuthal scanning of the surrounding space in multicolumn well designs, at the same time, due to the exclusion from the measurement results of the influence of the main receiving coil on the readings of additional receiving coils, the resolution of the method increases.

Claims (11)

1. Electromagnetic downhole flaw detector, containing a housing, an electronics unit, probes located along the axis of the device with electromagnetic coils of different lengths, the magnetic axes of which coincide with the axis of the device, including the main receiving and generating coils, each of which consists of a generator and a receiving coil with a single core , the magnetic axes of which coincide, while along the perimeter of each main receiving coil there are N additional receiving coils on magnetic cores, the axes of which are parallel to the probe axis and shifted from the probe axis by a distance R, and the inductance of each of the additional receiving coils is chosen equal to the inductance of the corresponding main receiving coil coils. 2. The method of electromagnetic flaw detection-thickness measurement of ferromagnetic metal pipes in multi-column wells, including the excitation of non-stationary electromagnetic fields in the metal columns of the well by generator coils in probes of different lengths while passing simultaneously through all generator coils of a current pulse T selected from the condition T=ah, then, starting from the shortest probe, their sequential disconnection from the generator with an interval T _i and measurement of the EMF (E) as a function of time E(t _j ,) induced in the receiving coils by eddy currents flowing in the metal pipes under study, while in probes of different lengths along the perimeter of each receiving coil, hereinafter referred to as the main receiving coil, on magnetic cores, the axes of which are parallel to the probe axis, additional receiving coils are placed with an inductance equal to the inductance of the main receiving coil, and for each probe, starting from the shortest probe, the EMF ratios ( E) as functions in time E(t _j ,), measured by each main and additional receiving coils:

at the same time, the azimuthal inhomogeneity of the pipe is set by the value of the excess of the specified ratio over unity, the greater the excess, the more pronounced the azimuthal inhomogeneity of the pipe, where E(t _j )ocn. - measured EMF on the main receiving coil, mV, E(t _j )add. - measured EMF on the additional coil, mV, T is the duration of the current pulse, s, T _i - current cutoff interval, s, t _j - step of the EMF measurement interval in the interval T _i , s, τ - decay constant, 1/s, E - measured EMF, mV, a - coefficient of proportionality, s / mm, h is the total thickness of the columns, mm.

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