EA013189B1

EA013189B1 - A method and an apparatus for determination of a distance to anomaly in a formation

Info

Publication number: EA013189B1
Application number: EA200700265A
Authority: EA
Inventors: Эрик Ян Баннинг; Терухико Хагивара; Ричард Мартин Остермейер
Original assignee: Шелл Интернэшнл Рисерч Маатсхаппий Б.В.
Priority date: 2003-11-05
Filing date: 2005-05-04
Publication date: 2010-02-26
Also published as: EA200700265A1

Abstract

A method and a system are provided for allowing determination of a distance from a tool to an anomaly ahead of the tool. The apparatus for performing the method includes at least one transmitter and at least one receiver. One embodiment of the method includes transmitting electromagnetic signals from the at least one transmitter through the formation surrounding the wellbore and detecting voltage responses at the at least one receiver induced by the electromagnetic signals. The method includes calculating apparent conductivity or apparent resistivity which are monitored over time, and the distance to the anomaly is determined from the apparent conductivity or apparent resistivity values.

Description

The present invention relates to a method and system for determining the distance to the anomaly in the formation ahead of the device. In a specific embodiment, the device may be located within the borehole.

The level of technology

In applied tasks, when adjusting the directionality of a logging geosignal while drilling (LV), it is advantageous to detect the presence of a formation anomaly in front of or around the drill bit or bottom-hole equipment. There are many examples in which the prognostic capabilities are desirable in BAUE logging environments. Predictive logging is to detect an anomaly at some distance ahead of the drill bit. Some examples of pre-emption include predicting in advance the pressure zone, or detecting the failure of the front of the drill bit in horizontal wells, or determining the profile of a massive salt structure ahead of the drill bit. Although currently available methods are able to detect the presence of an anomaly, they are not able to locate the anomaly with sufficient depth or speed, they are not able to detect the anomaly at a sufficient distance ahead of the drill bit or bottom-hole equipment.

When drilling measurements are used to locate a well, detection or identification of anomalies can be critical. Such anomalies can include, for example, a fracture, an inactive reservoir, a salt dome, or an adjacent layer of rock, or an oil-water contact. It would be advantageous to determine both the distance and the direction of the anomaly from the drilling site.

When evaluating a reservoir, the depth of exploration of most logging tools, wireline, or BAUE logging is limited to a few feet from the wellbore.

US Patent No. 6,181,138 to Nadtetat discloses a method for localizing an anomaly adjacent to a logging device using tilt-coil induction tools and methods of investigation with excitation at different frequencies. To reach the depth of the study with such a tool would require a longer tool. However, longer instruments, generally speaking, lead to worse spatial resolution.

To increase the possibility of increasing the depth of the study, methods for transient electromagnetic (EM) processes have been proposed. One such method for increasing the depth of research is proposed in US Pat. No. 5,955,884 by Rauloi C1 a1. The tool disclosed in this patent employs electrical and electromagnetic radiation sources to deliver electromagnetic energy to the formation at selected frequencies and signals that maximize the radial penetration depth into the target formation. In the above-mentioned EM transient process, the current mainly ends at the transmitter antenna, and the change in the voltage induced in the receiver antenna is monitored. This method provided the ability to detect anomalies at distances in depth from ten to hundreds of meters. However, although Rauloi discloses a method of transient EM processes that provides the ability to detect anomalies, he does not provide a method for detecting anomalies ahead of the drill bit.

Accordingly, a new solution is needed to determine the distance from the tool to the anomaly ahead of the specified tool. In particular, such a solution is necessary for review ahead of the drill bit. In addition, you need a real-time solution that has an increased depth of analysis so that measurements can be immediately available to equipment operators.

The term "coaxial response" in the framework of the present invention refers to the resulting response or characteristic on the receiver, in the case of orientation of the receiver and transmitter in the direction of the tool axis. The term "coplanar response" means the response or response obtained if the receiver and transmitter are oriented parallel to each other and their directions are perpendicular to the tool axis.

The term "transient response of the voltage of the electromagnetic field (EM)" refers to the surge voltage at the receiver to establish a steady state after switching the transmitter, which transmits an electromagnetic signal.

The term "tool voltage response" refers to the voltage response at the receiver after an induced change in the transmitted signal.

Summary of Invention

In one aspect, in accordance with an embodiment of the present invention, a method is provided for determining the distance to an anomaly in a formation ahead of a device in a borehole. The method can be implemented using a device comprising at least one transmitter and at least one receiver. The method includes calculating at least one of the parameters of the apparent conductivity and apparent resistivity based on the detected response, which may include a voltage response. At least one of the parameters of apparent conductivity and apparent resistivity is monitored over time, and the distance to the anomaly is determined based on the observed change in one

- 1 013189 of the parameters of apparent conductivity and apparent resistivity.

In a particular embodiment of the invention, the voltage response is measured in time, and said response is used to calculate the apparent conductivity or apparent resistivity over a selected period of time. A point in time is determined at which the apparent conductivity deviates from a constant value, and this point in time can be used to determine the distance at which the anomaly lies ahead of the borehole.

In a specific embodiment of the invention, the distance to the anomaly is determined when at least one of the parameters of the apparent conductivity and apparent resistivity reaches an asymptotic value.

The device may contain a logging tool and / or it may be provided in the drilling section during the measurement or in the logging section during the drilling of the drill string carrying the drill bit.

Brief Description of the Drawings

The invention is further explained in the description of specific variants of its implementation with reference to the accompanying drawings, in which:

FIG. 1 is a block diagram illustrating a system according to an embodiment of the invention;

FIG. 2 is a flow chart illustrating a method according to an embodiment of the invention;

FIG. 3 is a schematic diagram showing apparent conductivity with a coaxial instrument;

FIG. 4 is a graph showing the voltage response of a coaxial tool according to FIG. 3 in a homogenous formation for different formation resistivity;

FIG. 5 is a graph showing the stress response in a uniform reservoir as a function of the formation resistivity at different times (1) for the same coaxial tool;

FIG. 6 is a graph showing the voltage response in a homogenous formation as a function of the formation resistivity for greater transmitter-receiver diversity than in FIG. five;

FIG. 7 is a graph showing the voltage response as a function of time I. defined by a coaxial tool according to FIG. 3, at different distances from the reservoir layer;

FIG. 8 is a graph showing the voltage response data of FIG. 7 in terms of apparent conductivity (σ _αρρ (1));

FIG. 9 is similar to FIG. 8, except that the resistivity of layers 1 and 2 were mutually modified;

FIG. 10 is a graph comparing σ _αρρ (1) of FIG. 8 and 9, referred to 6 = 11 m;

FIG. 11 is a graph of the same data as shown in FIG. 8 but now on a linear scale of apparent conductivity;

FIG. 12 is a graph of σ _αρρ (1) on a linear scale for different spacings L of a transmitter receiver in the case 6 = 1 m;

FIG. 13 is a plot of the later conductivity as a function of different transmitter-receiver spacings b;

FIG. 14 — graphical curves for 6 = 5 m and b = 01 m for various resistivity ratios;

FIG. 15 is a graph of σ _αρρ (1) for the case of 6 = 5 m and b = 01 m, but for different ratios of resistivity, while the design resistivity is fixed at a value of K ₂ = 1 Ω m;

FIG. 16 graphically depicts a comparison of the apparent conductivity later in time at time 1 = 1 s with a model calculation, for the case of design specific resistance K ₂ = 1 Ω-m;

FIG. 17 graphically depicts the same data as in FIG. 16, constructed as a later in time apparent conductivity at time 1 = 1 s, depending on the relation of a later time apparent conductivity at time 1 = 1 s in terms of the conductivity of the local environment;

FIG. 18 graphically depicts the distance to the anomaly ahead of the tool depending on the transition time (1 _s ), determined from the data of FIG. eight;

FIG. 19 - graphical curves of apparent conductivity σ, _{ι | φ} (ζ; 1) in both coordinates ζ- and 1-;

FIG. 20 is a schematic diagram showing apparent conductivity with a coplanar instrument;

FIG. 21 graphically depicts the voltage response of the coplanar tool according to FIG. 20 with transmitter-receiver spacing L = 1 m in a homogeneous reservoir as a function of the formation resistivity at different points in time (1);

- 013189 of FIG. 22 graphically depicts the voltage response in a uniform reservoir as a function of the formation resistivity for a greater separation of the transmitter-receiver than in FIG. 21;

FIG. 23 is a graph showing voltage response data in terms of apparent electrical conductivity (σ _3ρρ (ΐ)) as a function of 1 provided by the coplanar tool of FIG. 20 at various distances from the reservoir layer;

FIG. 24 is a comparison of the later apparent apparent conductivity σ _3ρρ (ΐ ^ “) for coplanar responses, where 6 = 05 m and b = 01 m, as a function of the specific conductivity of the local layer, while the design specific conductivity is fixed at 1 S / m;

FIG. 25 graphically depicts the same data as in FIG. 24 constructed as a ratio of the apparent conductivity later in time over the local layer depending on the ratio of the apparent conductivity later in time with respect to the conductivity of the local layer; and FIG. 26 graphically depicts the distance to the anomaly in front of the tool depending on the transition time (1 _s ), determined from the data according to FIG. 23.

In the drawings, the expression "x.E-y", "x.E + y" have the meanings of the corresponding values x.10- ^y and x.10 ^{+ y} , where x and y are numbers.

Detailed description of preferred embodiments of the invention.

Embodiments of the invention relate to a system and method for determining the distance to an anomaly in a formation ahead of a device in a borehole. For the excitation of electromagnetic fields for use in detecting anomalies, both activation of the frequency analysis and activation of the time analysis were used. When activating frequency analysis, the device transmits a continuous wave with a fixed or mixed frequency and measures the responses in the same frequency band. When activating time analysis, the device transmits a rectangular signal, a triangular signal, a pulse signal, or a pseudo-random binary sequence as an initial signal and measures the broadband response of the earth. Sudden changes in transmitter current cause signals to appear in the receiver due to induction currents in the reservoir. The signals that appear in the receiver are called transient responses, because the receiver signals start at an initial value and then fade out or increase with time to a constant level. The method disclosed here implements a method for activating a temporal analysis.

As mentioned earlier, embodiments of the invention propose a general method for determining the distance to a resistive or conducting anomaly using transient EM responses. As will be explained in detail, the distance to the anomaly is found by tracking the apparent electrical conductivity over time, based on the transient voltage response. The distance to the anomaly is determined based on the variation of the apparent conductivity over time. Time-dependent values for apparent conductivity can be obtained from coaxial and coplanar measurements and can be respectively denoted as n _coax- 1 (1) and n _with p 1 _apag (1). Both show electrical conductivity around the instrument.

FIG. 1 illustrates a system that can be used to implement embodiments of the method of the present invention. Computing unit 10 located on the surface can be connected to electromagnetic measurement tool 2 located in borehole 4 and supported cable 12. Cable 12 can be constructed from any cable of a known type for transmitting electrical signals between tool 2 and computing unit 10 located on a surface. One or more transmitters 16 and one or more receivers 18 may be provided for transmitting and receiving signals. Data acquisition unit 14 may be provided for transmitting data from transmitters 16 and receivers 18 to measurement unit 10 located on the surface.

Each transmitter 16 and each receiver 18 may be three-coordinate and therefore may contain components for sending and receiving signals along each of the three axes. Accordingly, each transmitter module may comprise at least one single or multi-axis antenna and may be a transmitter of three orthogonal components. Each receiver may include at least one single or multi-axis electromagnetic receiving component and may be a receiver of three orthogonal components.

The tool / borehole coordinate system is defined as having x, y and ζ axes. The axis ζ specifies the direction from transmitter T to receiver B. Hereafter, it will be assumed that the axial direction of borehole 4 coincides with the axis ζ, whereby the x and y axes coincide with two orthogonal directions in a plane perpendicular to the direction from the transmitter to the receiver and to borehole 4.

The data acquisition unit 14 may include a controller for controlling the operation of the tool 2. The data acquisition unit 14 preferably collects data from each transmitter 16 and receiver 18 and provides data to the computing unit 10 located on the surface.

- 3 013189

The computing unit 10 located on the surface may include computer components comprising a processor 30, an operator console 32 and an instrument interface 34. The computing unit 10 located on the surface may also include a memory unit 40 containing conversion data 42 of the corresponding coordinate system and assumptions, an auxiliary direction calculation unit 44, an auxiliary block for calculating the apparent direction 46 and a distance calculation block 48. Auxiliary units for calculating direction and apparent direction are disclosed in more detail in US patent application Ser. No. 10 / 897,585, the priority of which is currently claimed and which is hereby incorporated by reference.

The computing unit 10 located on the surface may further include a bus 50 that connects various system components, including the system memory unit 40, to the processor 30. The computing unit 10 environment is only one example of the computing environment and does not imply any limit on the frame use or functionality of the invention. In addition, although the computing unit 10 is described as a unit located on a surface, it may be located in other embodiments below the surface, embedded in an instrument, located at a remote location, or located at any other convenient location.

The memory unit 40 preferably stores the module 48 and the auxiliary modules 44 and 46, which can be described as program modules containing computer-executable instructions that are executed by the computing unit 10 located on the surface. Software module 44 contains computer-executable instructions needed to calculate the direction to the anomaly inside the borehole. Software module 48 contains computer-executable instructions needed to calculate the distance to the anomaly. The stored data 42 includes data on the tool coordinate system and anomaly coordinate system and other data required for use by software modules 44, 46 and 48.

For additional details on the computing unit 10, including data carriers and I / O devices, reference is made to US patent application Ser. No. 10 / 897,585, the priority of which is currently claimed and which is hereby incorporated by reference. Accordingly, additional details regarding the internal structure of the computer 10 (computing unit) need not be disclosed in connection with the present invention.

FIG. 2 is a flow chart illustrating the procedure associated with the method of the invention. In general, in procedure A, the transmitters 16 transmit electromagnetic signals. In procedure B, receivers 18 receive transient responses. In procedure C, the system processes the transient responses to determine the distance to the anomaly and also the direction.

In the case when the receiver of three orthogonal components is used, the transient responses of the magnetic field on the receivers [K _x , K _y , KD, which are oriented in the direction [x, y, ζ] of the tool coordinate axis, respectively, are denoted as

from a magnetic dipole source in each axial direction [M _x , M _y , Μ _ζ ].

When the resistivity anomaly is removed from the tool, the formation near the tool looks like a uniform formation. For simplicity, in the indicated method it can be assumed that the formation is isotropic. In a homogeneous isotropic formation, there are only three non-zero transient responses. The responses mentioned include a coaxial response and two coplanar responses. The coaxial response is the response ν _ζζ ( _ί ), in the case when both the transmitter T and receiver K are oriented in the general axial direction of the tool. The coplanar responses, _νχχ ( _ί ) and ν ^ ί), are responses in the case when both transmitter T and receiver K are aligned parallel to each other, but their orientation is perpendicular to the tool axis. All cross-component responses are identical to zero in a uniform isotropic formation. Cross-component responses are either from a longitudinal receiver with a transverse transmitter, or vice versa. The other cross-component response is also zero between the mutually orthogonal transverse receiver and transverse transmitter.

The effect of resistivity anomaly is seen in transient responses as time increases. In addition to the coaxial and coplanar responses, the responses of the cross components ν ,, (Ι) (ί # ί; ί, ΐ = χ, y, ζ) become non-zero.

When the anomaly is large and the distance is comparable to the diversity of transmitter-receiver B, the effect of diversity can be neglected and transient responses can be approximated by responses from receivers near the transmitter.

- 4 013189

Apparent electrical conductivity.

Apparent electrical conductivity or its own inverse value, equivalent to apparent resistivity, can be used to determine the location or distance to the anomaly in a borehole. The time-dependent apparent conductivity can be set at each point in the time sequence at each depth of the well survey. The apparent conductivity at a certain depth of the borehole survey ζ is defined as the conductivity of a homogeneous reservoir that can generate the same tool response measured in the selected position.

In logging using the transient EM process, the transient data is collected at a certain logging depth or tool location as a time sequence of induced voltages in the receiver circuit. Accordingly, the time-dependent apparent conductivity σ _αρρ (ζ; ΐ) can be set at each point in the time sequence at each logging depth for the corresponding range of time intervals depending on the formation conductivity and technical characteristics of the tool.

Coaxial tools.

FIG. 3 illustrates a coaxial tool in which both the transmitter coil (T) and the receiver coil (K) are wound around a common tool axis ζ. The receiver K is placed at a distance E from the transmitter T. The symbols σι and σ ₂ represent the specific electrical conductivities of two layers of the formation.

Apparent electrical conductivity for coaxial tools.

The induced voltage of a coaxial instrument with a transmitter-receiver spacing E in a homogeneous reservoir with a specific conductivity (σ) is given by the expression (2)

8ί ^{/ 2} „2 ο ^σ in which 4 (and С is a constant.

The coaxial tool shown in FIG. 3, is used below to illustrate the voltage response for the various values of ΐ and E in FIG. 4-6, where σ ₁ = σ ₂ .

FIG. 4 depicts the voltage response of a coaxial instrument with b = 01 m in a homogeneous reservoir for various resistivities (K) of the reservoir from 1000 to 0.1 ohm-m. The voltage is positive at all times for ΐ> 0. The slope of the stress curve is approximately constant ₃₁ Κ _Κ Χ ( _ян 5 ÅЫ ЗЗ 2 in the time interval from 10 ^-8 to 1 s (or later) for any formation resistivity, more than 10 Ohm-m. The slope changes sign at earlier times around 10 ^{- 6} s when the resistivity is as low as 0.1 ohm-m.

FIG. 5 depicts the voltage response as a function of formation resistivity at different times (ΐ) for the same coaxial instrument separation (L = 1 m). For the resistivity range from 0.1 to 100 Ohm-m, the voltage response is unambiguous as a function of formation resistivity for time (ΐ) of measurement later than 10 ^-6 s. In smaller time intervals (ΐ), for example, at a time of 10 ^-7 s, the voltage is no longer unique. The same voltage response is realized at two different formation resistivity values.

FIG. 6 depicts the voltage response as a function of resistivity for a greater separation of the transmitter-receiver L = 10 m on a coaxial instrument. The time interval when the voltage response is unambiguous shifts toward longer time intervals (ΐ). The voltage response is unambiguous for resistivity from 0.1 to 100 Ω-m, for measurement time (ΐ) later than 10 ^-4 s. At smaller values of ΐ, for example, at a time of 10 ^-5 s, the voltage is no longer unique. The apparent conductivity is not well determined from only one measurement (coaxial instrument, single separation).

For a relatively compact separation of the transmitter-receiver (L = 1-10 m) and for the time measurement interval, where ΐ is greater than 10 ^-6 s, the transient EM-voltage response is basically unique as a function of formation resistivity between 0.1 and 100 Ohm m (and above). This provides the ability to determine the time-varying apparent conductivity from the voltage response (ν _ζΖ (ΐ)) at each time point of measurement as (3) C = k, (H)

And _and ¢) ² _ Ρο ^σ αρρ ^> L ² in which ^app 4 ί and ν _ζΖ (ΐ) on the right side in the measured voltage response of a coaxial instrument.

- 5 013189

From one type of measurement (coaxial instrument, one separation), the greater the separation b, the longer the measurement time (ΐ) could be applied to the concept of apparent conductivity. The value of σ _αρρ (ΐ) can be constant or equal to the conductivity of the formation in a homogeneous formation: σ _αρρ (ΐ) = σ. The deviation from the constant value (a) at time () implies an anomaly of conductivity in the region defined by time (ΐ).

Apparent electrical conductivity for a pair of coaxial tools.

When there are two coaxial receivers, the relationship between a pair of voltage measurements is given by

where b ₁ and b ₂ are the transmitter / receiver spacings of two coaxial instruments.

On the contrary, the time-varying apparent conductivity is given for a pair of coaxial tools by the expression (5)

(0 =

four;

^_ (d ^! -a) a.

at each time point of measurement.

The value of σ _αρρ (ΐ) can be constant or equal to the conductivity of the formation in a homogeneous formation: σ _αρρ (ΐ) = σ.

The apparent conductivity is similarly defined for a pair of coplanar tools or for a pair of coplanar and coaxial tools. The value of σ _αρρ (ΐ) can be constant or equal to the conductivity of the formation in a homogeneous formation: σ _αρρ (ΐ) = σ. The deviation from the constant value (σ) at the moment of time (ΐ) implies an anomaly of conductivity in the region defined by time (ΐ).

The predictive capabilities of the EM transient process.

To illustrate the applicability of these concepts, a prior analysis can be used to detect the anomaly at a distance ahead of the drill bit, as will be explained in the rest of the detailed description mentioned. Thus, σι and σ ₂ will have different values, one of which is an anomaly.

Analysis of coaxial transient responses in two-layer models.

FIG. 3 shows a coaxial tool with a transmitter and receiver spacing a distance b located, for example, in a vertical well approaching the adjacent layer of the formation (reservoir), which is a resistivity anomaly. The tool includes both the transmitter coil T and the receiver coil K, which are wound around a common tool axis ζ and oriented in the direction of the tool axis. The symbols σι and σ ₂ represent the specific electric conductivities of two layers of the reservoir.

To show that the EM transient method can be used as a predictive resistivity logging method, you can check the transient response of the tool in a two-layer model of the earth. A coaxial tool with transmitter transmitter-receiver separation b can be placed in a borehole, whereby the reservoir layer (reservoir) is in front of the borehole. There are three parameters that can be determined in a two-layer model using apparent conductivity (σ _αρρ (ΐ)).

The specified parameters are as follows:

(1) electrical conductivity (in this example, σι = 0.1 S / m is assumed) or specific resistance (the corresponding specific resistance of this example is K ₁ = 10 Ohm-m) of the local layer in which the tool is placed;

(2) electrical conductivity (in the present example, σ ₂ = 1 S / m is assumed) or specific resistance (the corresponding specific resistance of this example is K ₂ = 1 Ω-m) of the adjacent layer of the formation and (3) the distance of the tool to the layer boundaries. An example will be illustrated using several values 6 = 1, 5, 10, 25, and 50 m.

The voltage response at b = 1 m (transmitter-receiver offset) of a coaxial instrument at different distances (b) as a function of ΐ is shown in fig. 7. Although there is a difference among responses at different distances, it is not possible to identify the resistivity anomaly directly from these responses.

How information from said responses can be derived using apparent conductivity will be explained next with reference to FIG. 7

- 6 013189

The same voltage data of FIG. 7 are constructed in terms of the apparent electrical conductivity n _arr (1) in FIG. 8. From this table it is clear that the coaxial response can identify the adjacent layer of the reservoir (reservoir) of higher conductivity at a distance in front of the tool. Even a tool with a separation of L = 1 m can detect a layer of the reservoir at a distance of 10, 25 and 50 m, if the low voltage response can be measured in a time from 0.1 to 1 s.

The graph of Art _Appr (1) shows very clearly at least three parameters in the figure: the electrical conductivity of an earlier time; electrical conductivity at large times and the transition time, which shifts as the distance (L) changes.

As will be explained further, in a two-layer resistivity profile, the apparent conductivity as 1 approaches zero can identify the electrical conductivity of the layer around the tool, while the apparent conductivity as it approaches 1 infinity can be used to determine the conductivity of the adjacent layer from a distance. Also, from the transition time observed on the graph of apparent conductivity, the distance to the deposit boundaries from the tool can be measured. The graph of apparent conductivity for both time and instrument location can be used as a figurative representation of transient data.

It should be noted that, as shown in FIG. 8, for short periods of time, the instrument perceives an apparent electrical conductivity of 0.1 S / m, corresponding to such a layer directly around the instrument. At a later time, the tool perceives a value close to 0.55 S / m, an arithmetic average between the specific conductivities of the two layers. The change in distance (L) is reflected in the transition time.

FIG. 9 illustrates a plot of n _arr (1) coaxial transient response in the two layer model of FIG. 3 for b = 1 m in the instrument at different distances (L), except that the specific electrical conductivity (σι) of the local layer is 1 S / m (B ₁ = 1 Ω-m) of the local layer and the specific electrical conductivity (σ ₂ ) the design layer is 0.1 S / m (K. ₂ = 10 ohm-m). Again, for short periods of time, the instrument perceives an apparent electrical conductivity of 0.1 S / m, which makes up such a layer directly around the instrument. At a later time, the instrument perceives a value of approximately 0.55 S / m, the same mean value of electrical conductivity as in FIG. 8. The change in distance (L) is reflected in the transition time.

Electrical conductivity at short times (σ ,,,,,, (1 ^ -0)).

The conductivity at small intervals of time, corresponding to small values of 1, reflects the (apparent) conductivity of the local layer in which the tool is located. At such short time intervals, the signal reaches the receiver directly from the transmitter, without interfering with the boundaries of the deposit.

Therefore, it is only affected by the conductivity around the instrument. Conversely, the conductivity of a layer can be easily measured by the apparent conductivity at an earlier time.

Conductivity at late times 0 _pp (1 ^ «>)).

On the other hand, the conductivity at late times, at relatively large values of 1, reflects a certain average value of the specific conductivities of the two layers. Almost half of the signals out of the reservoir under the tool and the other half of the reservoir above the tool, if the time to travel distance (L) tool to the boundaries of the deposits is small.

FIG. 10 compares the plot of σ _α ^ (1) of FIG. 8 and 9 for L = 01 m and L = 01 m. The specific electrical conductivity at late times is determined simply by the individual specific electrical conductivities of the two layers σ1 and σ2. It is not affected or, at least, little affected by where the tool is located in two layers in terms of the distance L. However, due to the large depth of research, the specific electrical conductivity in late times is not easily achieved even at 1 = 1 s, as shown in FIG. 11 for the same tool. In practice, the conductivity at late times may need to be approximated by the value σ _α ^ (1 = 1 s), which slightly depends on L, as illustrated in FIG. eleven.

FIG. 12 compares the graphs σ _α ^ (1) for L = 1 m, but with different spacings b. The value of σ _α ^ (1) reaches an almost constant specific electrical conductivity during late periods of time at later moments of time with increasing b. The conductivity at late periods of time σ ,,,,,, ΐΜχ) is almost independent of b. However, the conductivity at late periods of time, given at 1 = 1 s, depends on the distance (L), as shown in FIG. 13.

- 7 013189

FIG. 14 compares the graphs σ _αρρ (1) for 6 = 5 m and for b = 01 m, but for different ratios of resistivity. This table shows that the apparent conductivity during late periods of time is proportional to the value for the same ratio (σ ₁ / σ ₂ ). For example (b) a _ap p (b-> ° o) (¾ / # 2 = Yu; Κι = 20 oB-t)

2 * Г _арр ('б-Эоо) (Кт / -К ₂ = Ю; Κι = 20 oct-гп)

FIG. 15 shows examples of graphs σ _αρρ (1) for 6 = 5 m and for b = 01 m, but for different ratios of resistivity, whereas the design resistivity is fixed at a value of K ₂ = 1 ohm-m. The apparent conductivity at large times at 1 = 1 s is determined by the conductivity of the local layer, as shown in FIG. 16. Numerically, electrical conductivity at late periods of time can be approximated by the arithmetic average of two layers, σι + σ ₂ ^σ α _ΡΡ °° ί σι, σ ₂ ) =.

Under the circumstances, it is rational that, with a coaxial tool, an axial transmitter induces a eddy current parallel to the reservoir boundaries. At a later time, the axial receiver receives a horizontal current approximately equal from both layers. As a result, the conductivity for later periods of time should take into account the conductivity of both layers with approximately equal weight.

To summarize, the conductivity (σ _αρρ (Χ ^)) for later periods of time, 1 = 1 s, can be used to estimate the conductivity (σ ₂ ) of the adjacent layer when the local conductivity (σ1) near the instrument is known, for example, from early conductivity (σ _αρρ (Χ0) == σ ₁ ). This is illustrated in FIG. 17

Estimation of the distance (6) to the adjacent reservoir.

The transition time (1 _s ), in which the apparent conductivity begins to deviate from the local conductivity (σ ₁ ) to the conductivity at long times, clearly depends on 6, the distance from the tool to the deposit boundaries, as shown in FIG. 8 for a tool with b = 01 m.

For convenience, the transition time (1 _s ) is given by the time at which σ _8ρρ (ΐ «) takes the value of the boundary conductivity (σ,), i.e. in this example, the arithmetic average between the early and late specific conductivities at large times is {σ _ΆΡΡ (£ - + 0) + _арр (£ - + ° о)} / 2.

The transition time (1 _s ) is dictated by the distance along the beam (6) minus b / 2, i.e. half of the distance that the EM signal must travel from the transmitter to the boundary of the reservoir, to the receiver, regardless of the resistivity of the two layers. Conversely, the distance (6) can be estimated from the transition time (1 _s ), as shown in FIG. 18, when b = 01 m.

Figurative representation with apparent conductivity.

The graph of apparent conductivity σ _αρρ (ζ; 1) in both ζ- and 1- coordinates can serve as a figurative representation of transient data, which are graphs of apparent conductivity for the same tool at different depths, as shown in FIG. 19. The coordinate represents the depth of the tool along the borehole. The σ _αρρ (ζ; 1) plot helps to clearly visualize the approach of the reservoir boundaries as the tool moves along the wellbore. The deviation from the constant value of conductivity at time (1) implies the presence of anomaly of conductivity in the area determined by time (1).

Coplanar tools.

Although coaxial transient data was considered above, coplanar transient data from a coplanar tool is also useful as a prognostic tool based on resistivity logging. FIG. 20 shows such a coplanar tool with transmitter transmitter-receiver diversity, located in a well approaching an adjacent reservoir, which is a resistivity anomaly. On a coplanar instrument, both the transmitter T and the receiver K are oriented perpendicular to the tool axis and parallel to each other. The symbols σ ₁ and σ ₂ represent the electrical conductivities of two layers of the reservoir, the boundary between which is located ahead on the tool axis.

- 8 013189

Apparent electrical conductivity for coplanar tools.

The induced voltage of a coplanar tool with the transmitter-receiver spacing b in a homogeneous reservoir with a specific electrical conductivity (σ) is given by

in which 4ί and С is a constant.

At small values of ΐ, the coplanar stress changes polarity depending on the separation b and the specific conductivity of the formation.

FIG. 20 illustrates a coplanar tool in which the transmitter (T) and receiver (K) are parallel to each other and oriented perpendicular to the tool axis. Symbols σι and σ ₂ represent the electrical conductivity of two layers of the reservoir. This tool is used to illustrate the voltage response for different values of ΐ and b in FIG. 21, 22, where σ ₁ = σ ₂ .

FIG. 21 depicts the voltage response of a coplanar instrument of length b = 1 m as a function of the formation resistivity at various times (ΐ). For the range of resistivity (K) of the formation from 0.1 to 100 Ω-m, the voltage response is unambiguous as a function of the formation resistivity for values greater than 10 ^-6 s. For smaller values of ΐ, for example, when 10 ^-7 , the voltage changes polarity and is no longer unique.

FIG. 22 depicts the stress response as a function of the formation resistivity at different times (ΐ) for a longer coplanar tool of length b = 5 m. The time interval when the stress response is unambiguous shifts to higher values of ΐ.

Like the response of a coaxial instrument, the time-dependent apparent conductivity is set from the response of the coplanar instrument Uxx (1) at each time point of measurement as

_and (A ² - &

Ж ~ d _{ and _νχχ (ΐ) on the right side is the measured voltage response of the coplanar instrument.

The greater the separation, the greater the value (ΐ) could be applied to the concept of apparent conductivity from one type of measurement (coplanar, one separation). The value of σ _αρρ (ΐ) may be constant or equal to the conductivity of the reservoir in a homogeneous reservoir

Analysis of coplanar transient responses in two-layer models.

Like FIG. 8 for a coaxial tool, where b = 01 m, the apparent conductivity (σ ^ (ΐ)) determined from the voltage responses of the coplanar tool, as shown in FIG. 20 is graphically plotted in FIG. 23 for different distances from the boundaries of the deposit. It is clear that a coplanar response can also identify an adjacent reservoir of higher conductivity at some distance. Even a tool with a separation of L = 1 m can detect a deposit at distances of 10, 25, and 50 m, if the low-voltage responses can be measured in a period of 0.1–1 s. The σ _αρρ (ΐ) plot for coplanar responses exhibits three parameters, as well as coaxial responses.

ν (<7 _a pp (G—> 0))

Electrical conductivity for early periods of time - * - ---------.

For coplanar responses, it is also true that the conductivity during early periods of time (σ _{; 1 | 1 |} , (ΐ> 0)) is the conductivity σ _{1 of the} local layer in which the tool is located. Conversely, the conductivity of a layer can be easily measured by the apparent conductivity in early periods of time.

Conductivity at later periods of time

The conductivity at late periods of time (σ. _{1 | η} , (ΐ ->&)) is a certain average value of specific conductivities of two layers. Conclusions made for coaxial responses can also be applied to coplanar responses. However, the value of electrical conductivity for late periods of time for coplanar responses is not the same as for coaxial responses. For coaxial responses, the electrical conductivity for late periods of time is close to the arithmetic average of the specific electric conductivities of two layers in two-layer models.

- 9 013189

FIG. 24 shows the electrical conductivity for late periods of time (σ. _{1 | Ψ} (1> /)) for coplanar responses, where b = 05 m and for b = 01 m, but for different specific conductivities of the local layer, while the design specific conductivity is fixed on the value of 1 Cm / m. The apparent conductivity at late periods of time is determined by the conductivity of the local layer and is numerically close to the rms value.

Thus, the conductivity during late periods of time (σ. _Ιρρ (1> /)) can be used to estimate the conductivity (σ ₂ ) of the adjacent layer when the local conductivity (σ ₁ ) near the instrument is known, for example, from the early electrical conductivity ^^ (ΐ ^ - Ο ^ σ ^. This is illustrated in Fig. 25.

Estimation of the distance (b) to the adjacent reservoir.

The transient time (1 _s ) can deviate from the local conductivity (σ ₁ ) to the conductivity at late periods of time, obviously depends on b, the distance from the tool to the borders of the deposit, as shown in FIG. 20.

time (1 _s ) is given by the time in which σ. _ιρρ (1 _ρ ) takes the value of the boundary specific conductivity (σ ^, ie, in this example, the arithmetic average between the early and specific conductivities at late periods of time is а _с = (σ _Άρρ (b - + O) + a _apr (£ -> oo)} / 2.

Transition time (1 _s ) is determined by the distance along the beam (b) minus B / 2, i.e. half of the distance that the EM signal must travel from the transmitter to the boundary of the reservoir, to the receiver, regardless of the resistivity of the two layers. On the contrary, the distance (b) can be estimated from the transition time (1 _C ), as shown in FIG. 26, when b = 1 m.

The present invention has been described with respect to specific embodiments, which in all aspects are illustrative and not restrictive. Alternative embodiments that do not fall outside the scope of the present invention will become apparent to those skilled in the art for which it is intended.

From the above it should be seen that the present invention is well adapted to achieve all the goals and objectives set forth above, along with other advantages that are obvious and inherent in the system and method. It should be understood that some features and subcombinations are practical and can be used without reference to other features and subcombinations. They are considered and are within the scope of the claims.

Claims

CLAIM

1. The method of determining the distance to the anomaly in the reservoir, which consists in introducing into the borehole a device containing a transmitter of electromagnetic signals through the reservoir and the receiver for detecting responses;

transmit an electromagnetic signal;

changing the transmitter current to cause a change in the transmitted electromagnetic signal;

detecting a transient response at the receiver after a change in the transmitted electromagnetic signal;

calculate the time-dependent apparent conductivity or time-dependent apparent resistivity based on the time dependence of the transient response detected by the receiver due to a change in the transmitted electromagnetic signal;

determine the distance from the device to the anomaly on the basis of changes in the value of the apparent conductivity or the value of the apparent resistivity with time.

2. The method according to claim 1, in which the change in the electromagnetic signal represents the termination of the transmission of the electromagnetic signal and in which the transient response detected by the receiver contains attenuation.

3. The method according to claim 1 or 2, in which the time range is determined by the distance between the transmitter and receiver.

4. The method according to claims 1, 2 or 3, in which the attenuation time range lasts at least from ^10-8 to at least 0.1 s, preferably at least up to 1 s.

5. The method according to one of claims 1 to 4, in which the time range is chosen sufficient to achieve a steady state value of apparent conductivity or value of apparent resistivity, and the distance to the anomaly is determined when the value of apparent conductivity or value of apparent resistivity reaches steady with

- 10 013189 standing.

6. The method according to any one of the preceding claims, wherein the response detected by the receiver represents the voltage response.

7. A method according to any one of the preceding claims, in which the calculation of the value of the apparent conductivity or the value of the apparent resistivity involves converting the induced voltage signal into the average conductivity of the formation.

8. The method according to any of the preceding paragraphs, in which the value of the apparent conductivity and the value of the apparent resistivity of the formation in which the device is located are calculated.

9. The method according to any of the preceding paragraphs, in which the value of the apparent conductivity or the value of the apparent resistivity of the formation ahead of the device is calculated.

10. A method according to any one of the preceding claims, in which a point in time is determined at which the value of apparent conductivity or the value of apparent resistivity begins to deviate from the corresponding value of apparent conductivity or apparent resistivity of the formation in which the device is located.

11. The method according to any of the preceding paragraphs, in which the electromagnetic signal is transmitted in the direction of the anomaly.

12. The system for determining the distance to the anomaly in the reservoir, which contains a device that includes a transmitter of electromagnetic signals through the reservoir and a receiver for detecting responses, includes a memory unit computing unit that calculates the value of the time-dependent apparent conductivity or the value of the time-dependent apparent resistivity, based on the time dependence of the transient response detected by the receiver to a change in the transmitted electromagnetic signal; determining the distance from the device to the anomaly based on the change in the value of the apparent conductivity or the value of the apparent resistivity with time.

13. The system indicated in paragraph 12, in which the device contains a logging tool.

14. The system according to claim 12 or 13, in which the device is installed in the drilling section during energy measurement or in the logging section during drilling of the drill string up the borehole relative to the drill bit.