EA010068B1 - Method for imaging subterranean formations - Google Patents

Abstract

Disclosed is a method for imaging a subterranean formation traversed by a wellbore using a tool comprising a transmitter for transmitting electromagnetic signals through the formation and a receiver for detecting response signals. In the method the tool is brought to a first position inside the wellbore, after which the transmitter is energized to propagate an electromagnetic signal into the formation. A response signal that has propagated through the formation is detected, and a derived quantity for the formation is calculated based on the detected response signal for the formation. The derived quantity for the formation is plotted against time. The tool is moved to at least one other position within the wellbore and the procedure above is repeated. Then an image of the formation within the subterranean formation is created based on the plots resulting from the repeated procedure above.

Description

FIELD OF THE INVENTION

The present invention relates to a method for imaging an underground formation intersected by a borehole. In a specific embodiment, the invention relates to a method for determining the location of an anomaly and, in particular, to locating a resistive or conductive anomaly in a formation surrounding a wellbore for drilling applications. In another aspect, the invention relates to a method for enabling rapid identification and imaging of formation anomalies.

State of the art

In applied tasks of controlling the parameters of drilling while logging (BAUE), it is advantageous to detect the presence of formation anomalies in front of or around the drill bit or the bottom of the drill string equipment. There are many examples in which prognostic capabilities are desirable in LUT logging environments. Prognostic logging is to detect an anomaly at some distance ahead of the drill bit. Some lead examples include predicting a pressure zone in advance, or detecting a failure of a drill bit front in horizontal wells, or determining the profile of a massive salt structure ahead of a 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 an anomaly at a sufficient distance ahead of the drill bit or the bottom of the drill string.

When evaluating a formation, the depth of exploration of most logging tools, wireline, or LUO logging is limited to a few feet from the wellbore. One such tool is disclosed in US Pat. No. 5,678,643 to PoBn et al. U.S. Patent No. 5,678,643 BioBi8 et al. discloses an anomaly location tool. The instrument transmits acoustic signals to the borehole and receives returning acoustic signals including reflections and refractions. Receivers detect returning acoustic signals and the time between transmission and reception can be measured. The distances and directions to the detected anomalies are determined by the microprocessor, which processes the time delay information from the receivers. As stated above, the depth of research with the tool is limited.

Another method that provides a limited depth of study is disclosed in US Patent No. 6181138 by Nadgetag. This method for determining the location of the anomaly uses tilt-coil induction tools and research methods with excitation at different frequencies. To achieve depth of study with such an instrument, a longer instrument would be required. However, longer instruments, generally speaking, result in poorer spatial resolution.

To increase the possibility of increasing the depth of research, methods for transient electromagnetic (EM) processes are proposed. One such method for increasing the depth of research is proposed in US Pat. No. 5,955,884 by RauJup et al. The tool disclosed in this patent uses electric and electromagnetic transmitters to supply electromagnetic energy to the formation at selected frequencies and waveforms that maximize the radial penetration depth into the design formation. In the aforementioned EM transient process method, the current mainly ends at the transmitter antenna, and the change in voltage induced in the receiver antenna is monitored over time. This method made it possible to detect anomalies at distances in depth from ten to hundreds of meters. However, although Rau! Op discloses a transient EM process that provides the ability to detect anomalies, it does not provide a method for detecting anomalies in front of the drill bit.

Other references, such as the published PCT application XU0 / 03/019237, also disclose the use of directional resistivity measurements in logging applications. This link uses measurements to generate an image of the earth formation after measuring the acoustic velocity of the formation and combining the results. The reference does not disclose a specific method for determining the distance and direction to the anomaly.

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

Triaxial induction logging tools, including wireline and BAUE devices, are capable of providing directional resistivity measurements. However, no methods have been proposed for using these directional resistivity measurements to identify the direction to the anomaly.

In addition, there is no express method for quickly presenting distance information in a visible form to allow the driller to precisely control the direction of the BAUE of the bottom hole equipment

- 1 010068 column to the desired location. These methods typically use inverse modeling to estimate the distance to formation features. This inversion process is a process in which data is used to construct a reservoir model that is consistent with the data. The time and computational resources required to complete the inversion can be significant, which can lead to a delay in identifying formation features, such as locations.

Accordingly, a new solution is needed to determine the distance from the instrument to the anomaly. In particular, such a solution is necessary for viewing ahead of the drill bit.

In addition, a real-time solution with an increased analysis depth is needed so that measurements can be immediately available to equipment operators. Finally, a means is needed for quick identification or imaging of features or formation boundaries for applied tasks of controlling drilling parameters.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a method for imaging an underground formation traversed by a borehole. The method can be implemented using a tool containing a transmitter for transmitting electromagnetic signals through the formation and a receiver for detecting response signals.

The method comprises the steps of introducing a tool into a first position inside a borehole;

the transmitter is excited to propagate the electromagnetic signal into the formation;

a response signal is detected that propagates through the formation;

calculating a derived value for the formation based on the detected response signal for the formation;

a graph of the derivative value for the formation versus time is constructed

Then the tool is moved to at least one more position inside the well, after which the steps described above are repeated.

Additionally, this procedure can be carried out again. An image of the formation within the subterranean formation is then created based on the plots of the derived quantity.

Additionally, then the tool again moves to at least one more position inside the well, and the whole procedure can be repeated again.

Brief Description of the Drawings

The invention is further explained in the description of specific embodiments with reference to the accompanying drawings, in which FIG. 1 is a block diagram showing a system according to an embodiment of the invention;

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

FIG. 3 is a graph illustrating guide angles between tool coordinates and anomaly coordinates;

FIG. 4A is a graph showing resistivity anomaly in a tool coordinate system;

FIG. 4B is a graph showing the resistivity anomaly in the coordinate system of the anomaly;

FIG. 5 is a graph illustrating tool rotation inside a wellbore;

FIG. 6 is a graph showing guide components;

FIG. 7 is a graph showing the voltage response for coaxial ν _ζζ (1), coplanar ν _χχ (1) and cross ν _ζχ (ΐ) measurements for b = 1 m, for θ = 30 ° and at a distance to the salt of Ό = 10 m;

FIG. 8 is a graph showing the voltage response for coaxial ν _ζζ (1), coplanar ν _χχ (1) and cross ν _ζχ (ΐ) measurements for b = 1 m, for θ = 30 ° and at a distance to the salt deposit Ό = 100 m ;

FIG. 9 is a graph showing an apparent drop (θ _αρρ (1)) for the arrangement as in FIG. 7;

FIG. 10 is a graph showing apparent conductivity (σ _αρρ (1)) calculated from both coaxial ν _ζζ (ΐ) and coplanar ν _χχ (1) responses for the same conditions as in FIG. nine;

FIG. 11 is a graph showing the ratio σ _3ρρ-οορ ι _3η3Γ (1) / st _arr-coax1a1 (1) for the same approach angle (θ) and distance (Ό) to the plane of the salt deposit, as in FIG. 3;

FIG. 12 is a graph showing the apparent drop (θ _αρρ (1)) for a tool in an assembly with b = 1 m, when the distance to the salt deposit is Ό = 10 m, for different angles between the tool axis and the object;

FIG. 13 is a graph similar to FIG. 12, according to which the distance to the salt deposit from the tool is Ό = 50 m;

FIG. 14 is a graph similar to FIG. 12, according to which the distance to the salt deposit from the tool is Ό = 100 m;

FIG. 15 is a schematic diagram showing apparent conductivity with a coaxial tool;

- 2 010068 FIG. 16 is a graph showing the voltage response of the coaxial tool of FIG. 15 in a uniform formation for various resistivities of the formation;

FIG. 17 is a graph showing the stress response in a homogeneous formation as a function of formation resistivity at different times (1) for the same coaxial tool;

FIG. 18 is a graph showing the stress response in a uniform formation as a function of formation resistivity for a greater transmitter-receiver diversity than in FIG. 17;

FIG. 19 is a schematic view showing apparent conductivity with a coplanar instrument;

FIG. 20 graphically depicts the voltage response of the coplanar instrument of FIG. 19 with spacing of the transmitter-receiver L = 1 m in a homogeneous formation as a function of the resistivity of the formation at different points in time (1);

FIG. 21 is a voltage response in a homogeneous formation as a function of formation resistivity for greater transmitter-receiver diversity than in FIG. twenty;

FIG. 22 is a graph showing the voltage response as a function of time 1 defined by the coaxial tool of FIG. 15, in a two-layer formation at different distances from the reservoir;

FIG. 23 is a graph showing the voltage response data of FIG. 22 in terms of apparent conductivity (σ _αρρ (1));

FIG. 24 is similar to FIG. 23, except that the resistivities of layers 1 and 2 were mutually changed;

FIG. 25 is a graph comparing σ _αρρ (1) of FIG. 23 and 24, assigned to 6 = 1 m;

FIG. 26 is a graph of σ _αρρ (1) for various spacings b of the transmitter-receiver in the case 6 = 1 m;

FIG. 27 shows graphical curves σ _αρρ (1) for 6 = 1 m and b = 01 m for two resistivity ratios;

FIG. 28 is a graph of σ _αρρ (1) for the case 6 = 1 m and b = 01 m, for different ratios of resistivity, while the design resistivity is fixed at K ₂ = 1 Ohm-m;

FIG. 29 depicts a comparison of apparent electrical conductivity at large values of 1 for coaxial responses, where 6 = 01 m and b = 01 m, as a function of the electrical conductivity of the design layer, while the design local electrical conductivity is fixed at 1 cm-m;

FIG. 30 graphically depicts the same data as in FIG. 29, constructed in the form of the ratio of the design conductivity of the local layer, depending on the ratio of the apparent conductivity at large times of the conductivity of the local layer;

FIG. 31 is a graph containing apparent conductivity σ _αρρ (1) versus time for various combinations of 6 and b;

FIG. 32 graphically depicts the relationship between beam distance and transition time (1 _s );

FIG. 33 - graphs of apparent conductivity σ _αρρ (ζ; 1) in both coordinates ζ- and 1-;

FIG. 34 is a schematic diagram showing apparent conductivity with a coaxial tool;

FIG. 35 is a graph showing the voltage response as a function of time 1 specified by the coaxial tool of FIG. 34, at various distances from the reservoir;

FIG. 36 is a graph showing the voltage response data of FIG. 35 in terms of apparent conductivity σ _αρρ (1);

FIG. 37 is similar to FIG. 36, except that the resistivities of layers 1 and 2 were mutually changed;

FIG. 38 is a graph comparing σ _αρρ (1) of FIG. 36 and 37, assigned to 6 = 1 m;

FIG. 39 is a graph of the same data that is displayed in FIG. 36, but now on a linear scale of apparent conductivity;

FIG. 40 is a graph of σ _αρρ (1) on a linear scale for various spacings b of the transmitter-receiver, in the case 6 = 1 m;

FIG. 41 is a graph of electrical conductivity at large times as a function of various spacings b of the transmitter-receiver;

FIG. 42 - graphical curves σ _αρρ (1) for 6 = 5 m and b = 01 m for different ratios of resistivity;

FIG. 43 is a graph of σ _αρρ (1) for the case 6 = 5 m and b = 01 m, but for different ratios of resistivity, whereas the design resistivity is fixed at K ₂ = 1 Ohm-m;

FIG. 44 graphically depicts a comparison of the apparent conductivity at large times at 1 = 1 s with a model calculation, for the case of design resistivity K ₂ = 1 Ohm * m;

FIG. 45 is the same data as in FIG. 44, constructed in the form of a more apparent conductivity at large times at 1 = 1 s, depending on the ratio of the apparent specific conductivity

- 3 010068 electrical conductivity at large times at the moment 1 = 1 s in the specific conductivity of the local environment;

FIG. 46 graphically depicts the distance to the anomaly in front of the instrument versus the transition time (1 _s ) determined from the data of FIG. 36;

FIG. 47 depicts a graph of the apparent conductivity σ _αρρ (ζ; 1) in both coordinates ζ- and 1-;

FIG. 48 is a schematic diagram showing apparent conductivity with a coplanar instrument;

FIG. 49 is a graph showing voltage response data in terms of apparent conductivity (σ _αρρ (1)) as a function of 1 provided by the coplanar instrument of FIG. 48 at various distances from the reservoir;

FIG. 50 is a comparison of the more apparent specific conductivity p _arr (1 ^ -ye) at large times 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 cm / m;

FIG. 51 graphically depicts the same data as in FIG. 50, constructed in the form of the ratio of the design conductivity of the local layer, depending on the ratio of the apparent conductivity at large times of the conductivity of the local layer;

FIG. 52 graphically depicts the distance to the anomaly in front of the instrument as a function of the transition time (1c) determined from the data of FIG. 49;

FIG. 53 is an image of a two-layer model for profiling a salt dome using a coaxial tool;

FIG. 54 is a graph similar to FIG. 22, showing the voltage response as a function of time 1 defined by the coaxial tool of FIG. 53, in a two-layer formation at different distances from the salt deposit;

FIG. 55 is a model of a coaxial tool in a conductive local layer, a very resistive layer and an additional conductive layer;

FIG. 56 is a graph showing the response of the resistivity versus time for the geometry defined in FIG. 55 for various thicknesses of a very resistive layer;

FIG. 57 is a model of a coaxial tool in a resistive local layer, a conductive layer and an additional conductive layer;

FIG. 58 is a graph similar to FIG. 56, showing the response of the resistivity versus time for the geometry defined in FIG. 57 for various thicknesses of the conductive layer;

FIG. 59 schematically depicts a model of a coaxial tool in a conductive local layer (1 Ohm-m) in the vicinity of a highly resistive layer (100 Ohm-m) with a separation layer between them of varying thickness having an intermediate resistivity (10 Ohm-m);

FIG. 60 is a graph similar to FIG. 56, showing the response of the resistivity versus time for the geometry defined in FIG. 59 for various thicknesses of the separation layer;

FIG. 61 schematically depicts a model of a structure comprising a highly resistive layer (100 ohm-m) coated with a conductive local layer (1 ohm-m) that is coated with a resistive layer (10 ohm-m), whereby a coaxial tool is imaged in a resistive layer and a conductive layer;

FIG. 62 on the left side shows the apparent conductivity in both ζ and 1 coordinates, according to which the inflection points are connected using fitted line curves;

FIG. 62 on the right side depicts an imaginary logs derived from the left side;

FIG. 63 on the right side schematically depicts a coaxial tool visible as approaching a highly resistive formation at an incidence angle of approximately 30 °, and FIG. 63 on the left side depicts the response of the apparent dip angle in both coordinates ζ and 1 for locations ζ corresponding to those depicted on the right side.

Detailed Description of Preferred Embodiments

Embodiments of the invention relate to a system and method for determining distance and direction to anomalies in a formation in a borehole. To excite electromagnetic fields in order to use anomalies in detection, we used both activation of the frequency analysis and activation of the time analysis. When the frequency analysis is activated, the device transmits an undamped wave with a fixed or mixed frequency and measures the responses in the same frequency band. When the time analysis is activated, the device transmits a rectangular waveform, a triangular waveform, a pulse signal or a pseudo-random binary sequence as the initial signal and measures the broadband response of the earth. Sudden changes in the transmitter current cause signals to appear in the receiver caused by induction currents in the formation. The signals that appear in the receiver are called transient responses, since the signals of the receiver

- 4 010068 start from the initial value and then fade out or increase over time to a constant level. The method disclosed here implements a method for invoking a temporary analysis.

As previously mentioned, embodiments of the invention provide a general method for determining the direction of a resistive or conductive anomaly using transient EM responses. As will be explained in detail below, the direction to the anomaly is determined by the dip angle and the azimuth angle. Embodiments of the invention propose to set the apparent dip of the formation to 0 _arr (1) and the apparent azimuth φ, _{ι | Φ} (1) through combinations of triaxial transient measurements. The apparent direction ({θ _αρρ (ΐ), φ _αρρ (ΐ)}) reaches the true direction ({θ, φ}) as time increases (1). Both values of θ _αρρ (ΐ) and φ _αρρ (первоначально) initially show zero, when the apparent electrical conductivity in _coax1a1 (1) and σ _{οορ1αηαΓ} (ΐ) from coaxial and coplanar measurements both show the electrical conductivity around the instrument. The apparent conductivity will be further explained below and can be used to locate the anomaly in the borehole.

FIG. 1 illustrates a system that can be used to implement embodiments of the method of the present invention. The computing unit 10 located on the surface can be connected to an electromagnetic measurement tool 2 located in the borehole 4 and supported by the cable 12. The cable 12 can be constructed from any cable of a known type for transmitting electrical signals between the tool 2 and the computing unit 10 located on the surface. One or more transmitters 16, and one or more receivers 18 may be provided for transmitting and receiving signals. A data acquisition unit 14 may be provided for transmitting data from transmitters 16 and receivers 18 to a 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 3 orthogonal components. Each receiver may include at least one single or multi-axis electromagnetic receiving component and may be a receiver of 3 orthogonal components.

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 a computing unit 10 located on the surface.

A computing unit 10 located on the surface may include computer components including a processor 30, an operator console 32, and a tool interface 34. The computing unit 10 located on the surface may also include a memory 40 including transformation data of the corresponding coordinate system and assumptions 42, an auxiliary direction calculating unit 44, an auxiliary apparent direction calculating unit 46, and a distance calculating unit 48. The computing unit 10 located on the surface may further include a bus 50 that couples various components of the system, including the system memory 40, to the processor 30. The environment of the computing system 10 is only one example of a suitable computing environment and does not imply any limitation on the scope use or functionality of the invention. In addition, although computing system 10 is described as a computing unit located on a surface, it may be located in other embodiments below the surface, embedded in a tool, located at a remote location, or located at any other convenient location.

The memory 40 preferably stores modules 44, 46 and 48, which can be described as program modules containing computer-executable instructions that are executed by a computing unit 10 located on the surface. The software module 44 contains computer-executable instructions necessary to calculate the direction of the anomaly inside the borehole. The software module 46 includes computer-executable instructions necessary to calculate the apparent direction, which will be explained later. The software module 48 contains computer-executable instructions necessary to calculate the distance to the anomaly. The stored data 42 includes data regarding the tool coordinate system and the anomaly coordinate system and other data required for use by the program modules 44, 46 and 48. These program modules 44, 46 and 48, as well as the stored data 42, will be explained below in combination with embodiments of the method of the present invention.

Generally speaking, program modules include routines, programs, components, data structures, etc. that perform specific tasks or perform specific abstract data types. Moreover, specialists can understand that the present invention can be practiced with other computer system configurations, including hand-held devices, multiprocessor systems, microprocessor-based or consumer-programmable electronics, minicomputers, host computers, etc. Invention also

- 5 010068 can be implemented in practice in distributed computing environments in which tasks are performed by remote processors that are linked through a communications network. In distributed computing environments, program modules can be located on both local and remote storage media, including storage devices.

Although computing system 10 is shown as having a generalized memory 40, computing system 10 typically includes a variety of computer-readable media. In a non-limiting example, computer-readable media may comprise computer storage media or communication media. The memory 40 of the computing system may include computer storage media in the form of volatile and / or non-volatile memory, such as read-only memory (KOM, ROM), and random access memory (KAM, RAM). A basic input / output system (B1O8), containing basic routines that help transfer information between elements within the computer 10, such as during startup, is usually stored in ROM. RAM typically contains data and / or program modules that are immediately available and / or currently in operation by processor 30. In a non-limiting example, computing system 10 includes an operating system, application programs, other program modules, and program data.

The components shown in memory 40 may also be included in other removable / non-removable, volatile / non-volatile computer storage media. For example, a hard disk drive can only read or write from a non-removable, non-volatile magnetic disk, a magnetic disk drive can read or write only from a removable, non-volatile magnetic disk, and an optical drive can read or write only from a removable, non-volatile optical disk such as SOKOM or other optical media. Other removable / non-removable, volatile / non-volatile computer storage media that can be used in an illustrative operating environment include magnetic tape cartridges, flash memory cards, universal digital disks, digital video tapes, solid state RAM, solid state ROMs, and the like. The drives and other corresponding computer storage media described above and illustrated in FIG. 1 provide storage of computer readable instructions, data structures, program modules and other data for computing system 10.

The user can enter commands and information into the computer system 10 through input devices, such as a keyboard and pointing device, usually called a mouse, trackball or touch button. Input devices may include a microphone, joystick, satellite dish antenna, and the like. These and other input devices are often connected to the processor 30 via an operator console 32, which is connected to the system bus 50, but can also be connected via other interface and bus structures, such as a parallel port or universal serial bus (I8V). A monitor or other type of display device may be connected to the system bus 50 via an interface, such as a video interface. In addition to the monitor, computers may also include another computing system, an operating system, application programs, other program modules, and program data.

Although many other internal components of computing system 10 are not shown, those skilled in the art will appreciate that such components and interconnects are well known. Accordingly, additional details regarding the internal structure of computer 10 need not be discussed in connection with the present invention.

FIG. 2 is a flowchart illustrating procedures included in a 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 and direction to the anomaly.

FIG. 3-6 illustrate a method for performing procedure C to determine the distance and direction to the anomaly.

Triaxial Transitional Responses

FIG. 3 illustrates guide angles between tool coordinates and anomaly coordinates. The transmitter coil T is located at the origin, which serves as the origin for each coordinate system. The receiver K is located at a distance b from the transmitter. The Earth coordinate system includes the Ζ axis in the vertical direction and the X and оси axes in the east and north directions, respectively.

Curved wellbore is specified in coordinates land angle deviation _s 0 and _s f azimuth angle. The resistivity anomaly A is located at a distance E from the transmitter in the direction given by the formation dip angle (0 _a ) and its azimuth (f _a ).

In order to put into practice embodiments of the method, FIG. 4A shows the definition of a tool / wellbore coordinate system having the x, y, and ζ axes. The ζ axis sets the direction from transmitter T to receiver K. The tool coordinates in FIG. 4A are determined by the rotation of the earth

- 6010068 whether (X, Υ, Ζ) in FIG. 3 by the azimuthal angle (φ _b ) around the оси axis and then rotation by the angle 0 b around the y axis in order to reach the tool coordinates (x, y, ζ). The direction of the anomaly is determined by the angle (θ) of incidence and the azimuthal angle (φ), where cos> 9 = · ά) = οο50 _α 008¾ + 8ίη <9 _β είη ^ cos (<p _a - (¾) ¢ 1)

СО8 # _а 8111¾ СО8 (р _а - (¾) 008¾ (2)

Similarly, FIG. 4B shows the definition of an anomaly coordinate system having axes a, b, and c. The axis c sets the direction from the transmitter T to the center of the anomaly A. The coordinates of the anomaly in FIG. 4B are determined by rotating the earth coordinates (X, Υ, Ζ) in FIG. 3 by an azimuthal angle (f _a ) around the Ζ axis and then rotating by an angle θ ₃ around the b axis to reach the coordinates of the anomaly (a, b, c). In the indicated coordinate system, the direction of the wellbore is determined in the reverse order by the azimuthal angle (φ) and dip angle (3).

Transitional responses in two coordinate systems

The method is further based on the relationship between transition responses in two coordinate systems. The transient responses of the magnetic field at the receivers [V _x , V _y , VD which are oriented in the direction of the tool coordinate axes [x, y, ζ], respectively, are denoted as

g ^r hk Part 1 At R I? l, k and, and,] (3) U ^t to at _a l!

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

When the resistivity anomaly is removed from the tool, the formation near the tool is visible as a uniform formation. For simplicity, in the method it can be assumed that the formation is isotropic. In a homogeneous isotropic reservoir, there are only three only nonzero transient responses. Mentioned responses include a coaxial response and two coplanar responses. The coaxial response ν _ζζ (ΐ) is the response when both the transmitter T and receiver B are oriented in the general axial direction of the instrument. The coplanar responses, ν _χχ (ΐ) and ν ^ ΐ), are responses in the case when both the transmitter T and receiver B are aligned parallel to each other, but their orientation is perpendicular to the axis of the instrument. All responses of the cross components are identical to zero in a homogeneous isotropic reservoir. Cross-component responses come either from a longitudinally oriented receiver with a transverse transmitter, or vice versa. Another cross-component response is also zero between mutually orthogonal transverse receiver and transverse transmitter.

The effect of the resistivity anomaly is visible in the transient responses as time increases. In addition to coaxial and coplanar responses, the responses of the cross components ν ^ ζΐ) (Щ: ί, _) x, y, ζ) become nonzero.

Transitional responses of the magnetic field can also be investigated in the coordinate system of the anomaly. Magnetic field transient responses at the receivers [B _a, B _b, B _c] which are oriented in the direction of axes [a, b, c] anomaly coordinates, respectively, may be designated as

from a magnetic dipole source in the direction of each axis [M _a , M _b , Ms].

When the anomaly is large and removed compared to the transmitter-receiver spacing, the diversity effect can be neglected, and the transient responses can be approximated by the responses of receivers located near the transmitter. Then, the method assumes that there is axial symmetry about the c axis, which is oriented in the direction from the transmitter to the center of the anomaly. In this axially symmetric configuration, the responses of the cross components in the anomaly coordinates are identical to zero in the time analysis measurements.

Uza UAB y ^ ' 'Y <w 0 0 ' Y * S Bc r = 0 Y <w 0 Gea Us 0 0 Uss.

The transient responses of the magnetic field in the coordinates of the tool are correlated with those in the coordinates of the anomaly by a simple coordinate transformation P (3, φ), a given angle of incidence (3), and an azimuthal angle (φ).

- 7 010068

Y ** Pooh Yb ^ "1 y * U At „ Yoo wow garden (b> y * Phew v Mustache Y *> 'se. ow £ CO 8 ^ οοδ> 9εϊη ^ -t & -8W ^ СО5 ^ 0 (Ί) nn <9soz ^ 005.9

Definition of the project direction

The assumptions formulated above contribute to the determination of the project direction, which is defined as the direction of the anomaly from the origin. When axial symmetry is assumed in anomaly coordinates, the transient response measurements in the tool coordinates are constrained, and two guide angles can be determined using combinations of triaxial responses.

ν »UV Tso 0 ' Woo 0 Um 0 y y y ^{g g} x ^{g h} . 0 0 Y *.

(IN)

In terms of each triaxial response

K "= (E * ^CO5 '£ + ^ 60 ^ 5) 006 ^ + ^ 8111 ^

Ϊ "= (Bi 0OV ^a £ + 8W ¹ £) I"' ⁺ "OZ ¹

K, NP * £ + ^ 008 ^

V # = = < ^Κ σα -K ") for ² £ cO8 ^ 8m ^

At _a = g -r _{l se)} cos £! £ SH1 CD8 ^

Y ^ = = - (^ - ^) 0 (^ 8 ^ 8111 ^

The following ratios may be noted:

Do _{yy gg} -I = -E ^ Hsoz -yats ² £ ² £ ² £ nn) -You have _to ^ (Uss -TsDsoa ^{May 2-δίπ 2} ¢ £ οοδ ²⁾ (9) (10) / and;

Several special cases can be noted. In the first of these cases, when none of the cross components is equal to zero, Y _xy (1) ± 0, Y _y2 (1) ± 0, UTSC0, then the azimuthal angle (φ) is neither zero nor π / 2 ( 90 °), and can be defined by the expression

Noting the relation y, y - ^ - = 1ap £ nn ^ nn4 - - = 1ap £ co8 <>

the angle of incidence (deviation) is determined by the expression (13)

In the second case, when Y _xy (1) = 0 and Y _y2 (1) = 0, then 3 = 0 or φ = 0 or π (180 °), or φ = ± π / 2 (90 °) and 3 = ± π / 2 (90 °), since the coaxial and coplanar responses must differ from each other (At _aa + Uss).

If φ = 0, then the angle of incidence 3 is determined by the expression

- 8 010068

If φ = π (180 °), then the angle of incidence 3 is determined by the expression

Also, with regard to the second case, if 3 = 0, then V ^ V ^, and V _u = 0. If φ = ± π / 2 (90 °) and 3 = ± π / 2 (90 °), then Uy = Uxx and Y _u = 0. These examples are discussed below with reference to the fifth case.

In the third case, when Y _xy = 0 and Y _X2 = 0, then φ = ± π / 2 (90 °) or 3 = 0, or φ = 0 and 3 = ± π / 2 (90 °).

If φ = π / 2, then the angle of incidence 3 is determined by the expression, 9 = –1hap ~

-g _in (17)

If φ = -π / 2, then the angle of incidence 3 is determined by the expression

Also, with regard to the third case, if 3 = 0, Y = Y _{xx yy} and Y _yx = 0. If φ = 0 and 3 = ± π / 2 (90 °), then _Yy = Y _{/ x} and Yy _/ = 0. The listed examples are discussed below with reference to the fourth case.

In the fourth case, when V _xx = 0 and V _y = 0, then 3 = 0, or π (180 °), or ± π / 2 (90 °).

If 3 = ± π / 2, then the azimuthal angle φ is determined by the expression

U ^ + Uy * Uhk-Uuu (19)

Also, with regard to the fourth case, if 3 = 0 or π (180 °), then Y _xx = Y _yy and Y _y2 = 0. If φ = 0 and 3 = ± π // 2 (90 °), then _Yyy = _Yyy and _Yyy = 0. This situation is also shown below with reference to the fifth case.

In the fifth case, when all the cross components tend to zero, _Yyy = _Yyy = _Yyy = 0. then 3 = 0 or ± π / 2 (90 °) and φ = 0 or ± π / 2 (90 °).

If Uxx = Uyu, then 3 = 0 or π (180 °).

If _{у уу} = У ₂₂ , then 3 = ± π / 2 (90 °) and φ = 0.

If Y ₂₂ = Y _xx , then 3 = ± π / 2 (90 °) and φ = ± π / 2 (90 °).

Tool rotation around tool axis / wellbore

In the above analysis, all the transient responses UD!) (Ί, _) = x, y, ζ) are determined by the directions of the axes of the x-, y- and ζ-coordinates of the tool. However, the tool rotates inside the wellbore, and the azimuthal orientation of the transmitter and receiver no longer matches the direction of the x- or y- axis, as shown in FIG. 5. If the measured responses are equal to where axis

represent the direction of the antennas attached to the rotating tool, and ψ represents the angle of rotation of the tool, then

^g xx ^g xg Wooh 'clear Y *

(20) (21)

Then

- 9 010068

The following ratios apply:

Consequently,

The azimuthal angle φ is measured from triaxial responses if the rotation angle ψ of the tool is known. On the contrary, the angle of 3 incidence (deviation) is determined by the expression

(26) not knowing the orientation ψ of the tool.

Apparent angle of incidence and azimuth angle and distance to anomaly

The angle of incidence and the azimuthal angle described above show the direction of the resistivity anomaly determined by combinations of triaxial transient responses at time (1), when the angles deviate from zero. When the time is small or close to zero, the effect of such an anomaly is not visible in the transient responses, since all the responses of the cross components take a zero value. To identify the anomaly and evaluate not only its direction, but also the distance, it is useful to set the apparent azimuthal angle f _arr (1) by the expression

and effective angle of incidence Z _arr (1) by the expression

for the time interval when neither f _arr (1) ^ 0 nor π / 2 (90 °). For simplicity, the case considered below is a case in which none of the cross-component measurements is identical to zero: Y .. (1) -Ό. and U .... (1C0.

For the time interval when f _arr (1) = 0, 3 _arr (1) is given by

For the time interval when f _arr (1) = n / 2 (90 °), 3 _arr (1) is given by the expression

- 10 010068

SZO?

When ΐ few and transient responses do not feel the effect of the resistivity anomaly at a distance effective zero angles are identical, _app p (1) = E _app (1) = 0. As ΐ increases, when the transient responses feel the anomaly effect, the angles f _arr (1) and Z _arr (1) begin to show the true azimuthal angle and angle of incidence. The distance to the anomaly can be shown at the point in time when f _arr (1) and 3 _arr (1) begin to deviate from the initial zero values. As can be seen in the modeling example below, the presence of an anomaly is detected much earlier in time at effective angles than in the apparent conductivity (n _arr (1)). Even if the resistivity of the anomaly may not be known until the anomaly begins to influence st _arr (1), its presence and direction can be measured at apparent angles. With limitations in time measurements, the distance of the anomaly cannot be noticeable in the change of n _arr (1), but noticeable in f _arr (1) and 3 _arr (1).

Simulation example

FIG. 6 shows a simplified simulation example in which the resistivity anomaly A is a massive salt dome, and the salt interface 55 can be considered a flat interface. For further simplification, we can assume that the azimuth of the salt surface is known. Accordingly, the remaining unknowns represent the distance to the surface of the salt from the tool, the resistivity of the isotropic or anisotropic formation and the approach angle (or angle of incidence) θ, as shown in FIG. 6. FIG. 6 also shows coaxial (60), coplanar (62) and cross-component (64) measurement arrangements.

FIG. 7 and 8 show the voltage from coaxial ν _ζζ (ΐ), coplanar ν _χχ (ΐ) and cross ν _ζχ (ΐ) measurements for b = 1 m, for θ = 30 ° and at a distance from the salt Ό = 10 m and Ό = 100 m, respectively. The apparent angle of incidence θ ^ ΐ) is given by

К _ж (,) - Г „(0 (311

FIG. 9 shows the apparent drop of f _arr (1)) for an instrument in an assembly with b = 1 m, when the distance to the salt surface is Ό = 10 m, and at an approach angle θ = 30 °.

In addition, in FIG. _Figure 10 shows the apparent conductivity (n _arr (1)) calculated from both coaxial ν _ζζ (ΐ) and coplanar ν _χχ (ΐ) responses, with the approach angle (θ) and distance (Ό) from the salt surface being the same as on FIG. nine.

Also in FIG. 11 a graph is plotted showing the ratio (st _arr-sor 1 _apag (1) / n _arr-coax1a 1 (1), which is accessible without cross ν _ζχ (ΐ) measurements, with the approach angle (θ) and the distance (Ό) to the surface salts are the same as in Fig. 3,

Note that the direction to the surface of the salt is directly identified in the graph of the apparent angle of incidence (0 _arr (1)) of FIG. 9 as 10 ⁻⁴ s, when the presence of the resistivity anomaly is simply detected in the apparent conductivity graph (n _arr (1)) of FIG. 10. In order for the apparent conductivity to reach an asymptotic value (at large и) and for the ratio of the apparent conductivity to show θ = 30 °, a time of almost 10 ⁻³ s is required.

FIG. 12 shows the apparent drop (st _arr (1)) for the tool in the assembly with b = 1 m, when the distance to the salt surface is Ό = 10 m, but at different angles between the axis of the tool and the object. The approach angle (θ) can be identified at any angle.

FIG. 12, 13 and 14 compare the apparent angle of 0 _arr (1) of incidence for various distances (Ό) to the surface of the salt and for different angles between the axis of the tool and the object.

The distance to the salt surface can also be determined by the transition time at which θ ^ ΐ) assumes an asymptotic value. Even if the distance (Ό) to the surface of the salt deposit is 100 m, it can be identified and its direction can be measured by the apparent angle of incidence

So, the method considers the coordinate transformation of transient EM responses between the coordinates tied to the tool and the coordinates tied to the anomaly. When the anomaly is large and far compared with the diversity of the transmitter-receiver, we can neglect the diversity effect and approximate the transient EM responses with the responses of the receivers near the transmitter. Further, it can be assumed that there is axial symmetry about the c axis, which sets the direction from the transmitter to the anomaly. In this axially symmetric configuration, the responses of the cross components in the coordinates of the anomaly are identical to zero. With this assumption, a general method is provided for determining the direction of resistivity anomaly using triaxial transient EM responses.

The method sets the apparent dip (θ ^ ΐ) and the apparent azimuth f _arr (1) of the formation through combinations of triaxial transient measurements. The apparent direction ({θ ^ ΐ), f _spr (1)}) reaches the true

- 11 010068 directions ({θ, φ}) at long times. Both values 0 _arr (1) and φ _αρρ (ΐ) show zero when I is small and the anomaly effect is not perceived in the transient responses or in the apparent conductivity. Specific conductivity (n _soah1a 1 (1) and n 1 _{litter APAGA} (1)) from the coaxial and coplanar measurements both indicate the conductivity around the tool.

The deviation of the apparent direction ({θ _3ρρ ( _ί ), φ _3ρρ ( _ί )}) from zero identifies the anomaly. The distance to the anomaly is measured by the time when the apparent direction ({θ _3ρρ ( _ί ), <p _arr (1)}) reaches the true direction ({θ, φ}). Distance can also be measured from changes in apparent conductivity. However, the anomaly is identified and measured much earlier in time in the apparent direction than in the apparent conductivity.

Apparent conductivity

As stated above, apparent conductivity can be used as an alternative method for apparent angles to locate an anomaly in a borehole. The time-dependent apparent conductivity can be set at each point in the time sequence at each depth of study. The apparent conductivity at a certain depth of study ζ is defined as the conductivity of a homogeneous formation, which can generate the same tool response measured in the selected position.

In logging using EM transient processes, transient data is collected at a certain depth of investigation or at the location ζ of the instrument in the form of a time sequence of induced voltages in the receiver circuit. Accordingly, the time-dependent apparent conductivity σ _3ρρ (ζ; I) can be set at each point in the time sequence at each depth of study, for the corresponding range of time intervals depending on the conductivity of the formation and the technical characteristics of the tool.

Apparent conductivity for coaxial tool

The induced voltage of the coaxial instrument with the transmitter-receiver L spaced in a homogeneous formation with electrical conductivity (σ) is given by the expression ,, / Л - (/ 'Х ’.- And in which ί

and C is a constant.

FIG. 15 illustrates a coaxial tool in which both the transmitter coil (T) and the receiver coil (B) are wound around a common axis ζ of the tool. Symbols σ ₁ and σ ₂ represent the electrical conductivity of two layers of the reservoir. This tool is used to illustrate the voltage response for various values 1 and b in FIG. 17-18 below, where σ ₁ = σ ₂ .

FIG. 16 depicts the voltage response of a coaxial tool with b = 01 m in a homogeneous formation for various resistivities (V) of the formation from 1000 Ohm-m to 0.1 Ohm-m. The voltage is positive at all times 1 for 1> 0. The slope of the voltage curve is approximately constant <E1tS 2 in the time interval from 10 ^-8 s to 1 s (or later) for any formation resistivity of more than 10 Ohm * m. The slope changes sign at earlier times about 10 ^-6 s, when the resistivity is as low as 0.1 ohm-m.

FIG. 17 depicts a stress response as a function of formation resistivity at different times (1) for the same spacing of a coaxial tool (b = 1 m). For a range of resistivities from 0.1 to 100 Ohm-m, the voltage response is unambiguous as a function of formation resistivity for a measurement time (1) later than 10 ^-6 s. At earlier times (1), for example, at the moment of 10 ^-7 s, the voltage is no longer unique. The same stress response is realized at two different values of the formation resistivity.

FIG. 18 depicts a voltage response as a function of resistivity for greater diversity of the transmitter-receiver L = 10 m on a coaxial instrument. The time interval when the voltage response is unambiguous shifts toward large times (1). The voltage response is unique for resistivities from 0.1 to 100 Ohm-m for a measurement time (1) later than 10 ⁴ s. At lower values of 1, for example at the moment of 10 ^-5 s, the voltage is no longer unique. The apparent conductivity is not well defined from just one measurement (coaxial instrument, single spacing).

For a relatively compact spacing of the transmitter-receiver (b = 1 to 10 m), and for the interval

- 12 010068 time measurements, where 1 is greater than 10 ^-6 s, the transient EM voltage response is mainly unambiguous as a function of the formation resistivity between 0.1 and 100 Ohm-m (and above). This makes it possible to determine the apparent time-varying electrical conductivity from the voltage response (ν _ζΖ (1)) at each measurement time moment as

C _ί33)

3ί% in which

and ν _ζΖ (1) on the right side is the measured voltage response of the coaxial tool. Of one type of measurement (coaxial instrument, one spacing), the larger the spacing b, the longer the measurement time (1) could be applied to the concept of apparent conductivity. The value of σ ,,,,,, (1) can be constant or equal to the electrical conductivity of the formation in a homogeneous formation: st _arr (1) = p. Deviation from a constant value (σ) at time (I) implies an anomaly in electrical conductivity in the region specified by time (1).

Apparent conductivity for coplanar instrument

The induced voltage of the coplanar instrument with the transmitter transmitter-receiver L spaced in a homogeneous formation with electrical conductivity (σ) is given by expression (34) in which

AND"

4d and C is a constant. At low values of 1, the coplanar voltage changes polarity depending on the spacing b and the electrical conductivity of the formation.

FIG. 19 illustrates a coplanar instrument in which the transmitter (T) and receiver (B) are parallel to each other and oriented perpendicular to the axis of the instrument. The symbols σι and σ ₂ represent the electrical conductivities of the two layers of the formation. This tool is used to illustrate the voltage response for various values of ΐ and b in FIG. 21-22 below, where σ ₁ = σ ₂ .

FIG. 20 depicts the stress response of a coplanar tool with a length of b = 1 m as a function of the formation resistivity at various times (1). For a range of resistivity (V) of the formation from 0.1 to 100 Ohm-m, the voltage response is unambiguous as a function of the resistivity of the formation for values greater than 10 ^-6 s. For lower values of 1, for example, at 10 ^-7 , the voltage changes polarity and is no longer unique.

FIG. Figure 21 depicts the stress response as a function of the formation resistivity at various times (1) for a longer coplanar instrument with a length of b = 5 m. The time interval when the stress response is unambiguous shifts toward higher values of ΐ.

Similar to the response of a coaxial instrument, the time-varying apparent conductivity is specified from the response of the coplanar instrument ν _χΧ (1) at each measurement time as

and ν _χΧ (ΐ) on the right side is the measured voltage response of the coplanar instrument. The larger the diversity, the greater the value (1) could be applied to the concept of apparent conductivity from one type of measurement (coplanar, single diversity). The value of σ ,,,,,, (1) can be constant or equal to the electrical conductivity of the formation in a homogeneous formation: ^{σ arr (ΐ)} = ^σ .

Apparent conductivity for a pair of coaxial instruments

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

- 13 010068 ι ^ (^ ι ₌ (36) in which b ₁ and b ₂ are the diversity of the transmitter-receiver of two coaxial instruments.

Conversely, a time-varying apparent conductivity is defined for a pair of coaxial instruments by the expression

(37) at each instant of measurement time. The value of σ _αρρ (ΐ) can be constant or equal to the electrical conductivity of the formation in a homogeneous formation: st _arr (1) = p.

The apparent conductivity is similarly set for a pair of coplanar instruments or for a pair of coplanar and coaxial instruments. The value of σ _αρρ (ΐ) can be constant or equal to the electrical conductivity of the formation in a homogeneous formation: st _arr (1) = p. Deviation from a constant value (σ) at time (1) implies an anomaly in electrical conductivity in the region specified by time (1).

Coaxial Transient Response Analysis in Two-Layer Models

To illustrate the concept of apparent conductivity, the transient response of the instrument in a two-layer earth model was investigated, for example as in FIG. 15. A coaxial tool with diversity transmitter-receiver b can be placed in a horizontal well. The apparent conductivity σ ^ ΐ)) detects three parameters, including the following:

(1) electrical conductivity (in the present example, σ ₁ = 0.1 S / m is assumed) of the first layer in which the tool is placed;

(2) electrical conductivity (in the present example, σ ₂ = 1 S / m is assumed) of an adjacent deposit and (3) the distance of the tool (horizontal wellbore) to the boundaries of the layer, for which 6 = 1, 5, 10 are shown in this example, 25 and 50 m.

Under general circumstances, the relative direction of the wellbore and tool to the interface between the deposits is not known. In the case of horizontal well logging, it is easy to conclude that the tool is parallel to the interface, since the response does not change when the tool moves.

The voltage response of the coaxial tool with the transmitter-receiver spacing b = 01 m at different distances is shown in FIG. 22. Information can be inferred from the responses using apparent conductivity, as will be explained below with reference to FIG. 23. FIG. 23 shows the voltage data of FIG. 22, constructed in terms of apparent conductivity. A graph of apparent electrical conductivity shows electrical conductivity at short times 1; electrical conductivity at large times 1; and transition time, which shifts as the distance changes (6).

As will be explained below, in the two-layer resistivity profile, the apparent conductivity as ΐ approaches zero can identify the conductivity of the layer around the tool, while the apparent conductivity as ΐ approaches infinity, can be used to determine the conductivity of an adjacent layer at a distance . Also, from the transition time observed on the apparent conductivity graph, the distance to the boundaries of the deposit from the instrument can be measured. The graph of apparent conductivity, both for time and for the location of the instrument can be used as a figurative representation of the transition data. Similarly, FIG. 24 illustrates the apparent conductivity in a two-layer model, where σ ₁ = 1 S / m (B ₁ = 1 Ohm-m) and σ ₂ = 0.1 S / m (K. ₂ = 10 Ohm-m).

Electrical conductivity at short times

At short times ΐ the instrument perceives the apparent conductivity of the first layer around the instrument. For large values of ΐ, the instrument perceives 0.4 S / m for a two-layer model in which σ ₁ = 0.1 S / m (B ₁ = 10 Ohm-m) and σ ₂ = 1 S / m (K. ₂ = 1 Ohm-m), which is the average value between the conductivities of two layers. The change in distance (6) is reflected in the transition time.

The electrical conductivity at low values of 1, represents the electrical conductivity of the local layer in which the tool is located. At short times ΐ the signal reaches the receiver directly from the transmitter, without interfering with the boundaries of the deposit. Therefore, it is affected only by the electrical conductivity around the instrument. Conversely, the conductivity of a layer can be easily measured by apparent conductivity at small values of ΐ.

- 14 010068

Electrical conductivity at large times 1

The electrical conductivity at large values of 1 represents a certain average value of the electrical conductivity of two layers. For large values of 1, almost half of the signals exit the reservoir under the instrument and the remaining signals exit the reservoir above the instrument if the time to travel the distance (b) of the instrument to the boundaries of the deposit is short.

FIG. 25 compares the graph p _arr (1) of FIG. 23 and 24 for b = 1 m and b = 1 m, where the ratio of resistivities K4 / K.2 is 10: 1 in FIG. 23 and equal to 1:10 in FIG. 24. Although not shown, the electrical conductivity at large values of 1 has a slight dependence on b. When the dependence is neglected, the conductivity at large values of 1 is determined simply by the individual conductivities of the two layers, and it is not affected by the location of the tool in layer 1 or layer 2.

FIG. 26 compares the plots p _arr (1) for b = 1 m, but with different spacings b. The value of σ _αρρ (1) reaches an almost constant electrical conductivity at large values of 1 with increasing b. However, the electrical conductivity at large values of 1 is almost independent of the spacing b for the considered range b and specific conductivities.

FIG. 27 compares the plots n _arr (1) for b = 1 m and for b = 1 m, but for different ratios of resistivities. The apparent conductivity at large times 1 is proportional to the value for the same ratio (σ ₁ / σ ₂ ). for example

Sad, (4: -4 00 ^ 1 / K ₂ = 10, “2.0 bt-t) (38)

20 * σ ₄ Ρ ρ (»-»>>; Βι / La ^{β sh} Ю

FIG. _Figure 28 shows examples of graphs n _arr (1) for b = 1 m and for b = 1 m, but for different ratios of resistivities of the design layer 2, while the local electrical conductivity (σι) is fixed at 1 S / m (Κ.ι = 1 Ohm * m). The apparent conductivity at large values of 1 is determined by the conductivity of the design layer 2, as shown in FIG. 29, when σ _{1 is} fixed at a value of 1 S / m.

Numerically, the electrical conductivity at large times can be approximated by the rms value of the electrical conductivity of the two layers as

(39)

To summarize, the electrical conductivity at large values of 1 (when 1 approaches infinity) can be used to estimate the electrical conductivity (σ ₂ ) of an adjacent layer, when the local electrical conductivity (σι) near the instrument is known, for example, from the electrical conductivity at times, when approaching 0, as illustrated in FIG. thirty.

Estimation of the distance b to the adjacent deposits

The transition time, at which the apparent electrical conductivity Щ _arr (1)) begins to deviate from the local electrical conductivity (σι) to the electrical conductivity at large values of time 1, depends on b and on b, as shown in FIG. 31. For convenience, the transition time (1 _s ) is given by the time at which σ ^ ρ) takes the value of the boundary conductivity U _c ). In this example, the boundary conductivity is the arithmetic mean between the conductivity when 1 approaches zero and the conductivity when 1 approaches infinity. Transition time (1 _s ) is dictated by the distance along the beam

(40) that is, the shortest distance that the EM signal must travel from the transmitter to the boundaries of the reservoir, to the receiver, regardless of the resistivity of the two layers. Conversely, distance (b) can be estimated from the transition time (1 _s ). as shown in FIG. 32.

Other uses of apparent conductivity

Like well-known induction tools, apparent conductivity (σ ^ ζ)) is useful for analyzing transient signal processing errors. The noise effect in the transient response data can be investigated as the error in determining the conductivity.

The plot of apparent conductivity (σ _α ^ (ζ; 1)) for different distances (b) in both coordinates ζ- and 1- can serve as a figurative representation of the transition data, as shown in FIG. 33 for a tool with a spacing of b = 1 m. The coordinate ζ represents the depth of the tool along the wellbore. The graph σ _α ^ (ζ; 1) shows the approximation of the boundaries of the reservoir as the tool moves along the wellbore.

The apparent electrical conductivity should be constant or equal to the electrical conductivity of the formation in a homogeneous formation. Deviation from a constant value of electrical conductivity at time (ΐ) implies the presence of anomalies in electrical conductivity in a time-domain (ΐ).

Predictive capabilities of the method of transient EM processes

By analyzing the apparent conductivity or its own inverse equivalent (apparent resistivity), the present invention can identify the location of the resistivity anomaly (for example, a conductive anomaly or resistive anomaly). Further, the resistivity or conductivity can be determined from coaxial and / or coplanar transient responses. As explained above, the direction of the anomaly can be determined if cross-component data is also available. To further illustrate the applicability of these concepts, the previous analysis can be used to detect anomalies at a distance ahead of the drill bit.

Analysis of coaxial transient responses in two-layer models

FIG. 34 shows a coaxial tool with transmitter-receiver spaced at a distance b located, for example, in a vertical well approaching an adjacent deposit, which is an resistivity anomaly. The tool includes both the transmitter coil T and the receiver coil I, which are wound around the common axis ζ of the tool and oriented in the direction of the tool axis. Symbols σ ₁ and σ ₂ represent the electrical conductivity of two layers of the reservoir.

To show that the method of transient EM processes can be used as a predictive method of logging based on resistivity, you can check the transient response of the tool in a two-layer model of the earth. There are three parameters that can be defined in a two-layer model.

The specified parameters are as follows:

(1) electrical conductivity or resistivity (in the present example, σ ₁ = 0.1 S / m or I ₁ = 10 Ohm-m) of the local layer in which the tool is placed;

(2) electrical conductivity or resistivity (in the present example, σ ₂ = 1 S / m or Z ₂ = 1 Ohm-m) of an adjacent deposit; and (3) the distance of the tool to the boundaries of the layer, for which 6 = 1, 5, 10, 25, and 50 m are assumed in the present example. Under general circumstances, the relative direction of the wellbore and the tool to the interface between the deposits is not known.

The voltage response at b = 1 m (transmitter-receiver offset) of the coaxial instrument at various distances (6) as a function of ΐ is shown in FIG. 35. Although there is a difference among the responses at different distances, the resistivity anomaly cannot be identified directly from these responses.

The same voltage data of FIG. 35 are constructed in terms of apparent conductivity σ ^ ΐ) in FIG. 36. From this figure, it is clear that the coaxial response can identify an adjacent reservoir of higher conductivity at some distance. Even an instrument with a spacing of L = 1 m can detect a deposit at a distance of 10, 25, and 50 m if the low-voltage response can be measured over a period of 0.1 to 1 s.

The graph σ ^ ΐ) exhibits very distinctly at least three parameters in the figure: electrical conductivity at short times; electrical conductivity at large times; and transition time, which shifts as the distance changes (6). It should be noted that, as shown in FIG. 36, at short times, the tool perceives an apparent conductivity of 0.1 S / m corresponding to that of the layer immediately around the tool. At a later time, the instrument perceives a value close to 0.55 S / m, the arithmetic mean between the electrical conductivities of the two layers. The change in distance (6) is reflected in the transition time.

FIG. 37 illustrates a graph of the coaxial transient response σ ^ ΐ) in the two-layer model of FIG. 34 for a tool with a spacing b = 1 m at different distances (6), except that the specific conductivity (σι) of the local layer is 1 S / m (Κι = 1 Ohm-m) of the local layer, and the specific conductivity (σ ₂ ) of the design layer is 0.1 S / m (I ₂ = 10 Ohm-m). Again, at short times, the tool perceives an apparent conductivity of 0.1 S / m, which is such a layer directly around the tool. At a later time, the instrument perceives a value of approximately 0.55 S / m, the same average conductivity as in FIG. 36. The change in distance (6) is reflected in the transition time.

Electrical conductivity at short times (σ _ΑΡΡ (1 ^ 0))

It is obvious that the electrical conductivity at short times, corresponding to small values of ΐ, represents the electrical conductivity of the local layer in which the tool is located. At such small times, the signal reaches the receiver directly from the transmitter, without interfering with the boundaries of the reservoir. Therefore, it is affected only by the electrical conductivity around the instrument. Conversely, the conductivity of a layer can be easily measured by apparent

- 16 010068 conductivity in the early time.

Electrical conductivity at large times (σ _ΑΡΡ (1 ^ о>))

On the other hand, the electrical conductivity at large times should represent some average value of the electrical conductivity of the two layers. At large times, almost half of the signals out of the reservoir under the tool and the other half out of the reservoir above the tool if the time to travel the distance (b) of the tool to the boundaries of the deposit is short.

FIG. 38 compares the graph σ _αρρ (1) of FIG. 36 and 37 for b = 01 m and b = 01 m. The electrical conductivity at large times is determined simply by the individual electrical conductivity of the two layers No. and σ ₂ ). It is not affected by where the tool is located in two layers. However, due to the large depth of investigation, the electrical conductivity at large times is not easily achieved even at 1 = 1 s, as shown in FIG. 31 for the same tool. In practice, the electrical conductivity at large times should probably be approximated by the value of σ _αρρ (1 = 1 s), which slightly depends on b, as illustrated in FIG. 39.

FIG. 40 compares the graphs σ _αρρ (1) for b = 1 m, but with different spacings b. The value of σ _αρρ (1) reaches an almost constant electrical conductivity at large times at later times with increasing b. The electrical conductivity at large times σ, is almost independent of b. However, the electrical conductivity at large times given at 1 = 1 s depends on the distance (b), as shown in FIG. 41.

FIG. 42 compares the graphs σ _αρρ (1) for b = 5 m and for b-01 m, but for different ratios of resistivities. The indicated figure shows that the apparent conductivity at large times is proportional to the value of σι for the same ratio (σ ₁ / σ ₂ ). For example, σ, βρ№1 / «2 ¹⁰ ί Κι - 10 bn-w (41)

2 * adrr (± -> oo) (¾ / d, = 10? Κι - 20 oL-w)

FIG. 43 shows examples of graphs σ _αρρ (1) for b = 5 m and for b = 01 m, but for different ratios of resistivities, whereas the design resistivity is fixed at K ₂ = 1 Ohm-m, the apparent conductivity at large times at 1 = 1 s, it is determined by the electrical conductivity of the local layer, as shown in FIG. 44. Numerically, the electrical conductivity at large times can be approximated by the arithmetic mean of two layers as

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

To summarize, the electrical conductivity (σ _3ρρ (1 ^ ο)) at large times, 1 = 1 s, can be used to estimate the electrical conductivity (σ ₂ ) of the adjacent layer, when the local electrical conductivity (σι) near the instrument is known, for example, electrical conductivity (σ _3ρρ (1 ^ 0) = σι) at small times. This is illustrated in FIG. 45.

Estimation of the distance (b) to an adjacent deposit

The transition time (1 _s ) at which the apparent electrical conductivity begins to deviate from the local electrical conductivity (σι) to the electrical conductivity at large times clearly depends on b, the distance from the instrument to the boundaries of the deposit, as shown in FIG. 36 for a tool with b = 01 m.

For convenience, the transition time (1 _s ) is _determined by the time at which σ _αρρ ( _ί <.) Takes the value of the boundary conductivity (a _s ), that is, in this example, the arithmetic mean between the early and specific conductivities at large times is

The transition time (1 _s ) is dictated by the distance along the beam (b) minus b / 2, that is, half the distance that the EM signal must travel from the transmitter to the boundaries of the deposit, to the receiver, regardless of the resistivity of the two layers. Conversely, the distance (b) can be estimated from the transition time (1 _s ), as shown in FIG. 46 when b = 01 m.

Shaped representation with apparent conductivity

The graph of the apparent conductivity σ _αρρ (ζ; 1) in both coordinates ζ- and 1- can serve as a figurative representation of the transition data, which are graphs of the apparent conductivity for the same instrument at different depths, as shown

- 17 010068 in FIG. 47. The ζ coordinate represents the depth of the tool along the wellbore. The graph σ _αρρ (ζ; ΐ) helps to clearly visualize the approximation of the boundaries of the reservoir as the tool moves along the wellbore.

Analysis of coplanar transient responses in two-layer models

Although coaxial transient data has been discussed above, coplanar transient data from a coplanar tool is also useful as a predictive resistivity based logging method. FIG. 48 shows such a co-planar instrument with a transmitter transmitter-receiver L located in a borehole approaching an adjacent reservoir, which is an resistivity anomaly. On a coplanar instrument, both transmitter T and receiver K are oriented perpendicular to the axis of the instrument and are parallel to each other. The symbols σι and σ ₂ represent the electrical conductivities of the two layers of the formation.

In accordance with FIG. 36 for a coaxial instrument, where b = 01 m, the apparent conductivity (σ _αρρ (ΐ)) for coplanar responses is plotted graphically in FIG. 49 for various tool distances from the boundaries of the reservoir. It is clear that the coplanar response can also identify an adjacent reservoir of higher conductivity at a certain distance. Even an instrument with a spacing of L = 1 m can detect a deposit at distances of 10-, 25- and 50- m, if low-voltage responses can be measured over a period of 0.1-1 s. The graph σ _αρρ (ΐ) for coplanar responses exhibits three parameters, the same as for coaxial responses.

Electrical conductivity at short times (and _APP (1 ^ 0))

It is also true for coplanar responses that the electrical conductivity at short times (σ _3ρρ (ΐ ^ 0)) is the electrical conductivity σι of the local layer in which the instrument is located. Conversely, the conductivity of a layer can be easily measured by apparent conductivity in the early days.

Electrical conductivity at large times (and _APP (ΐ ^ α>))

The electrical conductivity at large times (σ _3ρρ (ΐ ^^)) is a certain average value of the electrical conductivity of two layers. Conclusions made for coaxial responses can also be applied to coplanar responses. However, the conductivity at large times for coplanar responses is not the same as for coaxial responses. For coaxial responses, the electrical conductivity at large times is close to the arithmetic average of the electrical conductivities of two layers in two-layer models. FIG. 49 shows the conductivity at large times _app u (1 ≤ da)) for coplanar responses where D = 05 m and L = 01 m, but for different conductivities of the local layer while the target conductivity is fixed at a value of 1 See / m The apparent conductivity at large times is determined by the conductivity of the local layer and is numerically close to the rms value

To summarize, the electrical conductivity at large times (σ _Ημι , (1 ^^)) can be used to estimate the electrical conductivity (σ ₂ ) of the adjacent layer, when the local electrical conductivity (σ1) near the instrument is known, for example, from the early electrical conductivity ( σ ^ ΐ ^ -θ ^ σΟ. This is illustrated in Fig. 51.

Estimation of the distance (s) to an adjacent deposit

The transition time at which the electrical conductivity begins to deviate from the local electrical conductivity (σ ₁ ) to the electrical conductivity at large times clearly depends on the distance (s) from the tool to the boundaries of the deposit, as shown in FIG. 48.

The transition time (1 _s ) is _determined by the time for which σ _αρρ ( _ί <.) Takes the value of the boundary conductivity (σ ₀ ), that is, in this example, the arithmetic mean between the early and late conductivities is σ ₀ * + σ ^ ( ΐ: - * ")) / 2,

The transition time (1 _s ) is dictated by the distance along the beam (s) minus b / 2, that is, half the distance that the EM signal must travel from the transmitter to the boundaries of the deposit, to the receiver, regardless of the resistivity of the two layers.

Conversely, the distance (s) can be estimated from the transition time (1 _s ), as shown in FIG. 52 when b = 1 m.

Fast imaging using apparent conductivity

The use of apparent conductivity and apparent angle of incidence can be used to create images or represent features of the formation. This is accomplished by collecting transient apparent conductivity data at various positions.

- 18 010068 nines inside the borehole. Using the distance and directional information, as obtained above, the collected data can be used to create an image of the formation relative to the tool.

The first example can confirm the change in the stress response based on the distance to the design formation using a coaxial tool exploring a two-layer model in which the formation was parallel to the axis of the tool. FIG. 53 depicts a coaxial tool in a two-layer formation in which the axis of the tool is parallel to the layer interface. This may be the case of placing a horizontal well above the oil-water contact when the layers are horizontal and the tool is in a horizontal position. The middle layer is modeled as a layer saturated with brine, resulting in a low resistivity (1 Ohm-m). Alternatively, a model can be used to represent the tool in a vertical wellbore, where the tool is used for profiling the salt dome, and the salt dome is represented by a high resistivity layer located radially or to the side of the well. In this model, borehole effects are ignored due to large-scale measurements. The tool of FIG. 53 is modeled as having two spacings, 1 m and 10 m, spacing between the coils of the transmitter and receiver. To characterize the model, three basic parameters are used: the electrical conductivity of the near formation where the tool is located (σι), the electrical conductivity of the project or remote formation, σ ₂ , and the distance Ό to the interface with the high resistivity formation. FIG. 54 depicts the voltage response in a two-layer model with an antenna spacing of 1 m, with an approaching instrument, where σ ₁ = ₁ S / m (V ₁ = ₁ Ohm-m), σ ₂ = 0.01 S / m (V ₂ = 100 Ohm -m). In FIG. 54, you can clearly see the change in voltage response as a function of distance.

Based on the voltage response, it is clear that the transient response can vary with the distance of the more resistive layer.

The following model uses a conductive middle layer, a very resistive layer and another conductive layer. The applicable configuration is depicted in FIG. 55. The apparent resistivity (the reciprocal of the apparent conductivity) of a coaxial tool 10 m from the resistive deposit (salt) is shown in FIG. 55 for various thicknesses of salt deposits. The tool is modeled parallel to the interface with the resistive layer at a distance of 10 m. The thickness of the resistive layer varies from a fraction 1 m thick to a fraction 100 m thick. A simulated response of apparent resistivity is depicted in FIG. 56.

The first rise of B _arr (!) Is the response to salt, measured with a tool with a spacing of b = 1 m, and occurs at the moment of 10 ^-4 s, when the salt is at a distance of 10 m. If the salt is fully resolved (an infinitely thick layer of salt at a distance above Ό = 10 m), the apparent resistivity may show asymptotically 3 Ohm-m. The subsequent decline of Warr (!) Represents the response to the conductive layer below the salt (resistive deposit). Warr (at large I) is a function of the resistivity of the conductive reservoir and the thickness of the salt. If the measurement time is limited to a time of 10 ^-2 seconds, then the Varr drop (!) May not be detected for salt thicker than 500 m.

Regarding the resolution of the resistive deposit, the coaxial instrument responds to a thin (1-2 m thick) deposit. The time at which B _arr (!) Reaches a maximum or begins to deviate depends on the distance to the conducting reservoir below the salt. As noted earlier, when plotting in terms of apparent conductivity σ ^!), The transition time can be used to determine the distance to the boundaries of the reservoir.

A three-layer formation was also modeled. In this case, the intermediate layer was a more conductive layer. An image of the model is shown in FIG. 57. On it, a coaxial tool having a spacing of 1 m is located in the wellbore in the formation having a resistivity of 10 Ohm-m and is located at a distance of 10 m from a less resistive (more conductive) layer having a resistivity of 1 Ohm-m. The third layer is below the conductive deposit and also has a resistivity of 10 ohm-m. The conductive reservoir was modeled for fractions of varying thickness from 1 m to infinity. A conductive reservoir could be considered as representing a shale layer. The resistivity is shown in FIG. 58.

The decrease in B _arp (!) Is due to the introduction of a shale (conducting) layer and appears at times! ^ 10 ^-5 s. The shale response is fully resolved by an infinitely thick conductive layer that reaches a resistivity of 3 ohm-m. The subsequent growth of Warr (!) Represents the response to the resistive formation below the shale layer. Transition time is used to determine the distance to the interface between the second and third layers. Warr (at large!) Is a function of the resistivity of the conductive reservoir. As the thickness of the conductive layer increases, the measurement time should also increase (> 10 ^-2 s) in order to measure the growth of Varr (!) For conductive layers thicker than 100 m.

Another three layer model is shown in FIG. 59, on which, the coaxial tool is in the conductive layer (1 Ohm-m), and there is a high-resistivity layer (100 Ohm-m), which can take place in the salt dome. The two layers are separated by a layer of variable thickness having an intermediate specific

- 19 010068 resistance (10 Ohm-m). The apparent resistivity response is shown in FIG. 60.

The response to the intermediate resistive layer is visible at the moment of 10 ^-4 s, where Β _αρρ (1) increases. If the intermediate layer is fully resolved by an infinitely thick reservoir, then the apparent resistivity reaches an asymptote of 2.6 Ohm-m. As noted in FIG. 60, Β _αρρ (1) undergoes an increase in the second stage in response to a highly resistive layer (100 Ohm-m). Based on the transition time, the distance to the interface is determined to be 110 m.

Due to complexity, the apparent resistivity or apparent conductivity in the examples described above indicates the presence of many layers. When the graphs (1, Κ _αρρ (1)) of the apparent resistivity at different positions of the tool are located together, the entire graph can be used as a figurative log diagram to examine the geometry of the formation, even if the resistivity of the layer may not be immediately accurately determined. An example is shown in FIG. 61, in which a three-layer model is used in combination with a coaxial tool having design diversity in two different positions in the formation. The results are graphically depicted in FIG. 62.

The apparent conductivity Β _αρρ (1) is plotted at various points as the coaxial tool approaches the resistive layer. In the beginning, in the layer of 10 Ohm-m, the drop Κ_ _αρρ (1) can be attributed to the layer 1 Ohm-m, and the subsequent increase Β _αρρ (1) can be attributed to a layer of 100 ohm-m. The curves can easily be adjusted to inflection points to identify responses for different reservoirs, effectively forming an image of the formation. Moreover, the 1 Ohm-m curve can be easily attributed to the peak of the direct signal between the transmitter and receiver when the instrument is located in a 1 Ohm-m deposit.

In yet another example, an apparent incidence angle of 0 _arr (1) can be used to generate a shaped log. On the right side of FIG. 63, a coaxial tool is seen approaching a highresistive formation at an angle of incidence of approximately 30 °. The response of the apparent angle of incidence is shown on the left side of FIG. 63. As noted earlier, the time at which the response of the apparent angle of incidence occurs characterizes the distance to the formation. When the responses for different distances are plotted together, a curve can be drawn that characterizes the response when the instrument reaches the deposit, as shown on the left side of FIG. 63.

Thus, an image of the formation can be created using apparent conductivity / resistivity and dip angle without the additional processing required to invert and highlight information. This information is able to ensure the sequence of control of drilling parameters, as well as the ability to profile underground formations.

The present invention has been set forth in relation to specific embodiments, which in all aspects are illustrative and not limiting. Alternative embodiments that do not go beyond the scope of the present invention will become apparent to those skilled in the art.

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 sub-combinations. They are considered and are within the scope of the claims.

Claims (13)

CLAIM 1. A method of creating an image of a subterranean formation intersected by a borehole using a tool comprising a transmitter for transmitting electromagnetic signals through the formation and a receiver for detecting response signals, the method comprising the following steps: (a) inserting a tool into a first position within the borehole; (b) initiating a transmitter to propagate an electromagnetic signal into the formation; (c) detecting a response signal that propagates through the formation; (6) calculating the derived value for the reservoir based on the detected response signal for the reservoir; (e) plotting the derivative value for the reservoir over time. (D) moving the tool to at least one more position within the well and repeating steps from (b) to (e), followed by step (d) or (e); (e) creating an image of the formation within the subterranean formation based on the graphs resulting from step (e). 2. The method of claim 1, wherein step (e) involves plotting a derivative of the value for the reservoir calculated with respect to the tool, at least in yet another position on the same graph as the derivative value for the reservoir, calculated relative to the tool in the first position, and in which imaging the characteristics of the formation of step (e) involves identifying one or several inflection points on each constructed curve of the derived quantity and fitting the curve to one or more points ne egiba. - 20 010068 3. The method according to claim 1 or 2, wherein after step (e) there follows a step ()) of moving the tool to at least one more position inside the borehole and repeating steps (b) to (e), followed by a step (D) or (e). 4. A method according to any one of the preceding claims, in which, after excitation, a change is made in the transmitted electromagnetic signal, and in which the construction of the derivative curve for the formation versus time comprises constructing the derivative curve for the formation depending on the time that has elapsed after the change. 5. The method according to claim 4, in which the change made to the transmitted electromagnetic signal contains the end of the signal. 6. A method according to any one of the preceding claims, in which the derived quantity is one of: apparent conductivity, apparent resistivity, apparent dip angle, and apparent azimuth angle. 7. The method according to any one of the preceding claims, wherein the image of the formation represents one or more layers of the formation, each of which represents a feature of the formation that is different from the others. 8. The method according to claim 7, in which for each position of the tool inside the borehole determines the distance from the tool to at least one layer of the reservoir. 9. The method according to claim 7, wherein determining the distance comprises determining a point in time at which one of the apparent conductivity and apparent resistivity begins to deviate from the corresponding one of the apparent conductivity and apparent resistivity of the formation in which the device is located. 10. The method according to any one of the preceding claims, wherein the detection of the response signal comprises the detection of the induced voltage response signal. 11. The method of claim 10, wherein calculating the derived value includes converting the induced voltage signal to the derived value. 12. The method according to any one of the preceding claims, in which the detection of the response signal comprises detecting the transient response signal as a function of time, and in which the derivative value for the formation is calculated as a function of time from the transient response signal. 13. The method according to claim 4 or 5, in which the response signal is detected depending on the time after the change.