RU2466431C1 - Method and apparatus for induction well logging during drilling process - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: method involves passing current pulses through an exciter coil and recording emf of transient processes in a measuring coil. The effect of emf of the drill column on the measured signal is eliminated by a transient process signal measured at time t>30 mcs.

EFFECT: high accuracy of measurements by taking into account the effect of the drill column on the results.

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Description

The invention relates to the field of geophysical research of wells during drilling and can be used to determine the electrical resistance (resistivity) of the formations surrounding the well.

In the process of drilling a well, information about resistivity can be used for geosteering, which is especially important when drilling wells in thin formations, when additional information eliminates the approach of the wellbore to the oil-water contact (WOC) or clay coating.

The use of logging devices during drilling is associated with harsh operating conditions (high temperature and pressure, abrasive effects of the walls of the well, large mechanical loads).

When logging during drilling, it is necessary that the devices are as close to the bit as possible in order to reduce the “delay” of information on the physical properties of the formation transmitted to the surface, so the length of the devices should be taken into account when designing the equipment.

A known device for electromagnetic logging during drilling, embedded in the string of drill pipes and containing generator coils and electronic components. The design of the device is made of two coaxially arranged composite radiolucent pipes (RF patent No. 2231091, G01V 3/28, publ. 06/20/2004).

The disadvantage of this design is that the composite material is significantly inferior to steel and many other metals in terms of strength, abrasion resistance and many other metals, which reduces the service life and does not allow the implementation of small-diameter devices used in drilling sidetracks.

Based on patent No. 2231091, VIKPB-7 electromagnetic logging equipment was implemented (VIKPB-7 high-frequency electromagnetic logging sensing device during drilling. / New technologies, hardware and software for geophysical research and work in oil and gas wells // GIRS Consolidated Catalog. Volume 1 GIS equipment, 2007, p. A1.1.11.6).

The VIKPB-7 equipment includes a network of deep-seated electromagnetic logging probes with a research radius of 0.2-1.2 m. The total length of the device is 5.5 m.

The disadvantage of this equipment is: shallow research depth - 1.2 m with a significant length of the device, as well as the use of fiberglass pipes.

Geolink developed the TRIM induction logging tool while drilling at a frequency of 20 kHz ( www.geolink.co.uk ). Depth of research: with resistivity = 1 Ohm - 2.13 m, with resistivity = 10 Ohm - 2.845 m, and with resistivity = 100 Ohm - 3.09 m with a length of more than 3 m.

TRIM induction logging probes are mounted in a container with a longitudinal external groove on a beryllium bronze drill pipe. Such a placement of the probe does not allow large-diameter induction coils, which are limited by the dimensions of the external groove and the axial bore hole for the drilling fluid.

The small dimensions of the coil significantly reduce the sensitivity of the measurements, since the magnetic field emitted by the generator coil and the amplitude of the signal in the receiving coils are proportional to their area. The carrier metal pipe is a short-circuited coil and introduces distortion into the signal. The electrical conductivity of the metal depends on temperature and will change during the logging process, which leads to errors in determining the resistivity of the rocks.

A well-known electromagnetic well logging tool during drilling by Computalog Drilling Services, USA (Design, characteristics and field test results of a new multi-frequency resistivity resistivity logging tool) while drilling in a small-sized well. = The Design, Response, and Field Test Results of a New Slim Hole LWD Tool Multiple Frequency Resistivity Propagation Tool. / SGMack, M.Wisler, JQWu // Computalog Drilling Services. SPE 77483. Society of petroleum engineers. 2002. - p.1-11).

The generator and measuring coils are wound on a sleeve of non-magnetic metal alloy. The symmetrical design of the probe installation was chosen to reduce the influence of the borehole temperature pressure during drilling, which doubled the length of the probe part. Three independent transmitter-receiver pairs and two operating frequencies optimized the measurement value over a wide range of logging conditions.

The length of the probes is 508, 762, 1168, the minimum diameter of the device is 120.65 mm. The total length of the device is 5.250 m.

The resistivity is calculated by the phase difference and amplitude relationships. The maximum depth when measuring the phase difference at a frequency of 400 KG with resistivity = 2 Ohm is 1.6 m, at 20 Ohm - 2.430 m, at 200 Ohm - 3.20 m. At the same time, at a frequency of 400 KHz, the error in determining resistivity is higher due to great influence of the drill string. The maximum depth at a frequency of 2 MHz is 2.692 m.

The main disadvantage of this design is the large length of the device, which can lead to delays in information about the approach to the boundary of an adjacent formation in a horizontal well. In addition, the supporting metal pipe introduces additional measurement errors when the temperature in the well changes due to changes in the electrical conductivity of the metal.

Closest to the claimed invention is a technical solution according to the patent of the Russian Federation No. 2377607 "Method for eliminating the parasitic effect of conductive drill pipes on the measurement results of transient electromagnetic components during drilling" (Prior. 04.02.2005, publ. 27.12.3009, G01V 3 / 28).

The known method is implemented using a device containing: a transmitter installed in the layout of the bottom of the drill clone (BHA), which is used to generate a signal of formation of an electromagnetic field directed into the rock mass. The receiver installed in the BHA receives signals reflecting the resistivity of the rock mass and the distance to the boundaries of the formations. The axis of the transmitter and receiver can be parallel or at an angle to the axis of the BHA. The transmitter and receiver are mounted on a tubular BHA element. The tubular element has a damping part, including a transverse slot to weaken the flow of eddy currents in the tubular element. The damping part further has at least one longitudinal slot made in the tubular element. Non-conductive material may be placed in the slot. The damping part includes a pipe section with non-conductive material placed on the outer surface of this section such as ferrite. Effect: attenuation of spurious signals caused by eddy currents, without increasing the distance between the transmitter and receiver.

A disadvantage of the known technical solution is as follows: in order to weaken the parasitic effect of the drill string on the measurement results, longitudinal and transverse slots are made on the BHA tubular element, which weaken the drill string, which experiences significant loads during drilling. In addition, the length of these slots is 10-20 m to effectively reduce parasitic influences, which significantly increases the length of the probe. In this case, the influence of the column is taken into account by the reference signal in a homogeneous medium.

In fact, when drilling a well, the ambient temperature increases with depth, which leads to a decrease in the electrical conductivity of the metal, and as a result, to an additional error in determining the resistivity of the formation, which is not taken into account in the well-known patent.

The objective of the proposed method is to increase the measurement accuracy of the induction logging probe during drilling by taking into account the influence of the drill string on the measurement results.

The problem is solved in that in the method of induction logging of wells during drilling, including passing current pulses through the generator coil, registering the EMF by the transient (PP) method in the measuring coil, the influence of the EMF of the drill string on the measured signal is eliminated by subtracting the EMF from the recorded signal signal emf PP measured at times t> 30 μs.

Figure 1 shows a diagram of a BHA with an induction logging probe.

Figure 2 shows the design of the induction logging probe.

Figure 3 presents a section of the probe along aa.

Figure 4 shows the geometric factors G (R) at times t:

1 μs, 5 μs, 10 μs, and 30 μs.

Figure 5 shows the results of the simulation of measurements of induction logging by the transient method (MPP) on the drill string with resistivity of the formation of 1 Ohm and 10 Ohm.

Figure 6 shows the measurement results depending on the ambient temperature: 1 - 10 ° C, 2 - 50 ° C, 3 - 100 ° C, 4 - 150 ° C.

Figure 7 shows an example of taking into account the influence of the drill string on the resistivity measurements.

Figure 8 shows the dependence of the signal on the thickness of the dielectric layer H: 1 - H = 15 m, 2 - H = 10 m, 3 - H = 5 m, 4 - H = 0 m.

The method of induction logging of wells during drilling includes passing current pulses through a generator coil, registering an emf method in a measuring coil by a transient process, while a current pulse of 50-200 μs is passed through a generator coil, the transient emf is measured in the range 0.1- 50 μs, and the influence of the EMF of the drill string on the measured signal is eliminated by subtracting the signal EMF PP measured at times t> 30 μs from the recorded signal EMF PP in the measuring coil and get the true signal al from the formation.

The implementation of the method is carried out in the process of the device.

The induction well logging device during drilling (Fig. 1) comprises a bottom hole assembly (BHA) 1 with a drill bit 2, an induction logging probe 3 located in close proximity to the bit 2, containing generator 4 and measuring coils 5 mounted on a non-magnetic a metal pipe 6 integrated in the BHA, the electronic unit 7 (figure 2). Non-magnetic metal pipe 6 in diameter 8 is made with radially directed stiffeners 9. Stiffeners 9 are located between the coils 4 and 5 and at the ends of the probe. The ribs 9 are covered with a layer of dielectric material 10, forming the basis for winding the turns of the generator 4 and the measuring coils 5 (figure 3). The height h of the ribs 9 is less than the thickness H of the layer of dielectric material 10 (Fig.2). Drill bit 2 with a downhole motor 11, an over-bit module 13, an induction logging probe 3 and a downhole telesystem (ZTS) 14 during drilling are lowered into the well on a drill pipe string 14.

Start up the electronic unit 7, which can be equipped with an autonomous power supply or receive power from the operation of the turbogenerator, which is part of the ZTS (not shown in figure 1). The electronic unit 7 provides a pulsed current supply to the generator coil 4 with a duration of 50-200 μs, which leads to the appearance of eddy current in the rock. It was found that a stepwise change in current in the generator coil 4 in the range of 50-200 μs increases the depth of induction logging during drilling.

In the measuring coil 5, the EMF is recorded by the transient method in the range of 0.1-50 μs, derived by calculation.

MPP can provide a greater depth of research with relatively short double-coil probes (A.A. Kaufman, V.P. Sokolov “Theory of induction logging by transient processes”, - Novosibirsk: publishing house “Science”, Siberian Branch, 1972).

Let us evaluate the depth of the method, under which the radius R of the conducting cylinder, which creates a signal equal to 50% of the signal in a homogeneous medium, is taken. To estimate the depth, we use the expression for the integral characteristic

,

,

Where

G (R) is the integral radial geometric factor, the quantity is dimensionless,

r is the radius (coordinate), m,

R is the radius of the study, m,

g (r) is the differential geometric factor, the dimensionless

p, u - integration variables, dimensionless quantities.

,

,

Where

L is the length of the probe, m

r is the radius (coordinate), m,

z - coordinate along the axis of the well, m,

σ - electrical conductivity, S / m,

µ is the magnetic permeability of the vacuum, 4π 10 ^-7 GN / m,

t - time, sec.

Figure 4 shows the radial characteristics of the value of G (R), equal to 0.5, corresponding to 50% of the signal for the probe length L = 1 m

G (R) = 0.5 for a time of 1 μs with a research radius (depth) of R = 1.4 m, (1);

G (R) = 0.5 for a time of 5 μs with a research radius (depth) of R = 3.2 m, (2);

G (R) = 0.5 for a time of 10 μs with a research radius (depth) of R = 4.5 m, (3);

G (R) = 0.5 for a time of 30 μs with a research radius (depth) of R = 6.4 m, (4).

(1), (2), (3), (4) are the dependences of G (R) on the radius R for various times t.

Thus, the MPP allows reaching a depth of 6.4 m at a time of 30 μs, with a probe length of 1 m.

Consider the effect of a metal column on the induction logging signal depending on the resistivity of the formation.

Figure 5 shows the results of measurements of resistivity of the reservoir 1 Ohm (1) and 10 Ohm (2). From the results it follows that the effect of reservoir resistivity on the signal is significant only in the range of 25 μs. At t> 30 μs, the signal is determined by the parameters of the metal pipe. Curves (1) and (2) - EMF PP as a function of time.

Figure 6 shows the measurement results for a reservoir model with a resistivity of 1 Ohm depending on the ambient temperature in the range of the device in the well from 1 to 150 ° C, where 1 - T = 1 ° C, 2 - T = 50 ° C, 3 - T = 100 ° C, 4 - T = 150 ° C. An increase in temperature leads to a change in the signal in the range of 1-10 μs to 100%. Curves (1), (2), (3), (4) - EMF PP as a function of time at different ambient temperatures.

Changes in the time range greater than 30 μs depend on the parameters of the column.

Consider an example of the implementation of the method of accounting for the influence of the drill string on the example of changes at a temperature of 1 ° C (1) and 150 ° C (2), shown in Fig.7.

EMF can be approximated by two exponents

,

,

,

,

Where

E ₁ (t) - EMF at a temperature of 150 ° C, mV,

E ₂ (t) - EMF at a temperature of 1 ° C, mV,

A ₁ , B ₁ - the initial amplitudes of the measured signals from the reservoir at t = 0 (curve 7),

A ₂ , B ₁ - the initial amplitudes of the signal from the column at t = 0 (curves 3 and 4),

t is the time, sec

λ ₁ , λ ₂ , λ ₃ , λ ₄ are the decay constants, the quantities are dimensionless, while λ ₃ = λ ₁ .

Consider the algorithm for accounting for the influence of the drill string on the example of E ₁ (t).

At times t ₁ and t ₂ > 30 ms, the signal is determined by the drill string parameters.

Having measured at these times, we obtain

,

,

.

.

We divide the values of (6) by (7) and prologarithm the result, we obtain

.

.

Substituting expression (8) into equation (6), we obtain

.

.

Subtract respectively from the values of the signals of the curve (1) the values of the signals of the curve (3) and get the signal from the reservoir (curve 7), similarly - from the values of the signals of the curve 2 we subtract the values of the signals of the curve 4 and get the signal from the reservoir (curve 7). Thus, the effect of temperature is taken into account (the values of the signals coincide).

Values (5) and (6) are tangent to signals (1) and (2).

Claims (1)

A method of induction logging of wells during drilling, including passing current pulses through a generator coil, recording transient EMF in a measuring coil, characterized in that the influence of the drill string EMF on the measured signal is eliminated by subtracting the PP EMF from the recorded signal in the measuring coil The emf of the PP measured at times t> 30 μs.

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