A method for characterizing azimuthal anisotropy using cross-dipole acoustic wave data

Abstract

A method for characterizing shear wave velocity anisotropy within a display for a wellbore region includes obtaining a shear wave velocity anisotropy magnitude and a shear wave velocity anisotropy azimuth, determining directed line segments (314, 316) to represent the anisotropy for each of a plurality of measured depth points (310) along the wellbore, and plotting the directed line segments (502, 504, 506) on the display to generate a one-dimensional anisotropy representation.

Description

Background Art

[0001] Acoustic well logs are commonly obtained from wellbores drilled in the oil and gas industry. They can be used to determine the direction of geological stresses, the orientation of microfractures, and to calibrate seismic wave propagation velocity models used in seismic imaging. The propagation velocity of acoustic and seismic waves can vary as a function of location within the Earth, and can also vary as a function of the propagation direction and polarization orientation. The variation in propagation velocity with respect to propagation direction and polarization is called anisotropy, and rocks that exhibit this variation in propagation velocity with respect to propagation direction and polarization are said to be anisotropic.

[0002] FIG1 illustrates various wave propagations that occur in an elastic material, such as rock. Figure 1A A compression wave 102 is shown with the direction of particle motion ("polarization") 104A aligned or nearly aligned with the direction of wave propagation 106A. Figure 1B and Figure 1C Shear waves 108A, 108B are shown. Shear waves have polarizations 104B, 104C that are orthogonal or nearly orthogonal to their propagation directions 106B, 106C. Unlike compressional waves, it is possible for two shear waves to propagate in the same direction with polarizations orthogonal to each other. Both compressional and shear waves can exhibit anisotropy. Summary of the Invention

[0003] This Summary is provided to introduce a series of concepts that are further described below in the Detailed Description. This Summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used to help limit the scope of the claimed subject matter.

[0004] In general, in one aspect, embodiments relate to a method for characterizing shear wave velocity anisotropy within a display for a wellbore region, the method comprising: obtaining a shear wave velocity anisotropy magnitude and a shear wave velocity anisotropy azimuth; determining a directed line segment to represent the anisotropy for each of a plurality of measured depth points along the wellbore, and plotting the directed line segments on the display as a plurality of directed line segments to generate a one-dimensional anisotropy representation.

[0005] In general, in one aspect, embodiments relate to a non-transitory computer-readable medium storing instructions executable by a computer processor. The instructions include functionality for obtaining a shear wave velocity anisotropy magnitude and an azimuth of the shear wave velocity anisotropy. Furthermore, the instructions include functionality for determining a directed line segment representing anisotropy for each of a plurality of measured depth points along a wellbore; and drawing the plurality of directed line segments on a display to generate an anisotropy representation.

[0006] Other aspects and advantages of the claimed subject matter will be apparent from the following description and appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The following is a description of the figures in the accompanying drawings. In the drawings, the same reference numerals identify similar elements or actions. The sizes and relative positions of the elements in the drawings are not necessarily drawn to scale. For example, the shapes and angles of various elements are not necessarily drawn to scale, and some of these elements may be arbitrarily enlarged and positioned to improve the legibility of the drawings. Furthermore, the particular shapes of the elements depicted are not necessarily intended to convey any information about the actual shapes of these particular elements but are chosen solely for ease of identification in the drawings.

[0008] FIG1 shows an example of elastic wave polarization.

[0009] Figure 2 Azimuth system definitions and line segments are shown in accordance with one or more embodiments.

[0010] Figure 3A and Figure 3B An anisotropic display is shown in accordance with one or more embodiments.

[0011] Figure 4 A flow chart is shown according to one or more embodiments.

[0012] Figure 5 An example of an anisotropic display is shown in accordance with one or more embodiments.

[0013] Figure 6 A computer system is shown in accordance with one or more embodiments. DETAILED DESCRIPTION

[0014] Now will be described in detail with reference to the accompanying drawings the specific embodiments of the present disclosure. For consistency, similar elements in the various drawings are represented by similar reference numerals.

[0015] In the following detailed description of the embodiments of the present disclosure, numerous specific details are set forth to provide a more thorough understanding of the present disclosure. However, it will be apparent to those skilled in the art that the present disclosure may be practiced without these specific details. In other cases, well-known features have not been described in detail to avoid unnecessarily complicating the description.

[0016] Throughout this application, ordinal numbers (e.g., first, second, third, etc.) may be used as adjectives for elements (i.e., any noun in this application). Unless explicitly disclosed, such as with the terms "before," "after," "single," and other such terms, the use of ordinal numbers does not imply or create any particular order of elements, nor does it limit any element to only a single element. Rather, the use of ordinal numbers is intended to distinguish between elements. As an example, a first element is distinct from a second element, a first element may contain more than one element, and may be ranked after (or before) a second element in the ordering of elements.

[0017] In general, embodiments of the present disclosure relate to a method for characterizing azimuthal anisotropy using cross-dipole acoustic wave data. Two shear waves with orthogonal polarizations can propagate at different propagation velocities in anisotropic materials (e.g., rock). An important characteristic of anisotropic rock may be the difference between the shear wave propagation velocities. This difference may be referred to as the anisotropy intensity. Another important characteristic of anisotropic rock may be the polarization angle of the shear wave. This angle may be referred to as the anisotropy azimuth. The shear wave propagation velocity anisotropy azimuth is between 0 degrees and 180 degrees. The anisotropy azimuth has 180-degree symmetry. For example, the anisotropy intensity for an anisotropy azimuth of 210 degrees is the same as the anisotropy intensity for an anisotropy azimuth of 30 degrees. Although there may be two shear waves with different polarizations, the polarizations are always orthogonal, so a single angle (e.g., the angle between the polarization of the shear wave with the fastest velocity and a reference direction at the Earth's surface) may be sufficient to characterize the shear wave propagation velocity anisotropy azimuth.

[0018] Acoustic logging tools typically have an acoustic source in the form of orthogonal dipoles that can excite shear waves of orthogonal polarizations. They also typically have an acoustic receiver in the form of orthogonal dipoles that can receive orthogonally polarized shear waves from multiple acoustic source dipoles. Such acoustic logging tools are often referred to as cross-dipole acoustic logging tools, and the data recorded by them is often referred to as cross-dipole acoustic data.

[0019] In one or more embodiments, the anisotropic property is represented by a line at each measured depth along the wellbore. The slope of the line corresponds to the anisotropy azimuth or fast shear wave azimuth (FSA), and its length represents the strength of the shear wave propagation velocity anisotropy. By repeating the same process for all depths along the wellbore, a new map is obtained as a new method for characterizing anisotropy. In one or more embodiments, the present disclosure provides a method for simultaneously characterizing the strength and azimuth of the shear wave propagation velocity anisotropy in the near-wellbore region within a one-dimensional map. Compared to traditional anisotropy maps, this method provides a meaningful and intuitive representation for characterizing and understanding subsurface geological / rock physical anisotropic characteristics (such as the location and direction of stresses and fractures along the wellbore).

[0020] In this disclosure, display means a representation printed on paper, microfilm, or other printable material, as well as a representation displayed using digital media (e.g., a computer monitor, laptop monitor, workstation monitor, television screen) or projected onto a screen in a temporary manner (whether digitally or analog).

[0021] Figure 2 An embodiment is shown in which paired combinations of shear wave propagation velocity anisotropy strengths and shear wave propagation velocity anisotropy azimuths are represented on the display as directed line segments 202. In one or more embodiments, the lengths of the directed line segments 202 are monotonically related to the values ​​of the shear wave propagation velocity anisotropy strengths, such that smaller values ​​of the shear wave propagation velocity anisotropy strengths correspond to shorter directed line segments 202, and larger values ​​of the shear wave propagation velocity anisotropy strengths correspond to longer directed line segments 202. In some embodiments, the shear wave propagation velocity anisotropy strengths are proportional to the lengths of the directed line segments, such that a first anisotropy strength that is twice the second anisotropy strength is represented by a directed line segment 202 that is twice the length of the directed line segment 202 representing the second anisotropy strength. In other embodiments, the relationship between the shear wave propagation velocity anisotropy strength and the lengths of the directed line segments 202 may not be proportional, for example, the relationship may be quadratic, logarithmic, or have the form of another mathematical function.

[0022] In some embodiments, the orientation of the directed line segment 202 measured relative to a reference direction on the display is equal to the shear wave propagation velocity anisotropy azimuth measured relative to a reference direction on the surface of the Earth. For example, in some embodiments, the angle 206 measured in a clockwise direction between the depth axis 204 on the display and the directed line segment 202 can be equal to the shear wave propagation velocity anisotropy azimuth measured in a clockwise direction from true north. In other embodiments, the shear wave propagation velocity anisotropy azimuth can be measured in a clockwise direction from magnetic north at the wellbore location. In alternative embodiments, the reference direction on the display can be selected to be orthogonal to the depth axis 204. Figure 2 , defines the reference north direction, and also specifies whether the azimuth angle increases in a clockwise or counterclockwise direction. In the embodiment disclosed in this specification, the positive vertical direction is taken as the true north direction, and the azimuth angle increases in a clockwise manner. Figure 2 An azimuth system definition is shown, where the directions due north (vertical y-axis) and due east (horizontal x-axis) fall at azimuths of 0 and π / 2 (radians), respectively.

[0023] Those skilled in the art will readily appreciate that there are other reference directions on the Earth's surface from which the shear wave propagation velocity anisotropy azimuth may be measured, and other directions on the display from which the directed line segment 202 may be drawn.

[0024] Figure 3A and Figure 3B A plurality of directed line segments 302 corresponding to a plurality of pairwise combinations of anisotropy intensity and shear wave propagation velocity anisotropy azimuths measured at a plurality of depth sampling points 310 along the wellbore are shown. Figure 3A A directed line segment 302 is shown displayed in accordance with some embodiments, wherein the directed line segment 302 extends symmetrically on either side of a point 312A designated as a point of zero shear wave velocity anisotropy strength. Some directed line segments 314 in the plurality of directed line segments are short and drawn at a constant display angle, corresponding to low shear wave velocity anisotropy strength and a constant shear wave velocity anisotropy azimuth. Other directed line segments 316 in the plurality of directed line segments have long directed line segments and varying display angles, corresponding to high anisotropy strength and varying shear wave velocity anisotropy azimuth.

[0025] Figure 3B An embodiment is shown in which a plurality of directed line segments 318 are displayed asymmetrically about a point 312B designated as a zero anisotropy intensity point. In some embodiments, one end of the directed line segment is juxtaposed with the zero anisotropy intensity point 312B. In other embodiments, other asymmetrical arrangements of directed line segments about the zero anisotropy intensity point 312B may be used.

[0026] Figure 4 A flow chart according to one or more embodiments is shown. In block 402, cross-dipole acoustic data related to anisotropy intensity and shear wave propagation velocity anisotropy azimuth at a plurality of points is obtained. The anisotropy intensity and anisotropy azimuth at the plurality of points may be obtained from a database, or directly from an acoustic logging tool or another source. More specifically, in one or more embodiments, Figure 4 The inputs to the method are the anisotropy intensity and the anisotropy azimuth. The anisotropy intensity is obtained by the difference (measured as a percentage) between the fast shear wave slowness and the slow shear wave slowness. To further suppress the effects of noise or inaccurate estimates, the anisotropy intensity is smoothed. In one or more embodiments, the effective range of the shear wave propagation velocity anisotropy azimuth should be [0 to π].

[0027] In block 404 , fast and slow shear wave velocities and corresponding polarization directions of the fast and slow shear waves may be determined for a plurality of measured depth points along the wellbore.

[0028] In block 406, the anisotropic strength may be calculated based on the difference between the fast shear wave velocity value and the slow shear wave velocity value. In some embodiments, the anisotropic strength may be calculated by subtracting the slow shear wave velocity value from the fast shear wave velocity value. In other embodiments, a different mathematical function may be used to calculate the anisotropic strength. For example, it may be determined as the square or logarithm of the difference between the fast shear wave velocity value and the slow shear wave velocity value.

[0029] In block 408, a directed line segment is determined according to one or more embodiments. In some embodiments, the length of the directed line segment is monotonically related to the value of the anisotropy strength. For example, in some embodiments, the anisotropy strength is proportional to the length of the directed line segment. In other embodiments, the relationship between the anisotropy strength and the length of the directed line segment can take a different mathematical form. For example, the length of the directed line segment can be related to the square of the anisotropy strength, or the length of the directed line segment can be related to the logarithm of the anisotropy strength.

[0030] In other embodiments, in block 408 , the anisotropy strength may be determined by dividing the difference between the fast shear wave velocity and the slow shear wave velocity by the sum of the fast shear wave velocity and the slow shear wave velocity.

[0031] Additionally, in block 408, according to some embodiments, an angle at which the directed line segment is drawn on the display may be determined. In some embodiments, the orientation of the directed line segment measured relative to a reference direction on the display is equal to the shear wave propagation velocity anisotropy azimuth measured relative to a reference direction on the surface of the Earth. For example, in some embodiments, the angle measured clockwise between the depth axis on the display and the directed line segment may be equal to the shear wave propagation velocity anisotropy azimuth measured clockwise from true north. Thus, the coordinates of the starting point of the directed line segment on the display may be given by:

[0032] (x1, z1)=(-L sinθ,-Lcosθ+z D ), Formula (1)

[0033] And the coordinates of the endpoints of a directed line segment on the display can be given by:

[0034] (x2, z2)=(Lsinθ, coSθ+z D ), Formula (2)

[0035] where L is the anisotropy strength, θ is the anisotropy azimuth measured clockwise from true north on the Earth's surface and plotted clockwise from the depth axis on the display, and zD is the position on the displayed depth axis corresponding to the depth of the sample point.

[0036] In other embodiments, other reference directions on the earth's surface may be used, such as magnetic north at the wellbore location. In other embodiments, the reference direction on the display may be selected to be orthogonal to the depth axis.

[0037] In block 410, multiple directed line segments may be drawn on the display according to one or more embodiments. That is, step 408 is repeated for all available depth ranges in the borehole. By placing the coordinate origin of each line segment at its corresponding measured depth, a new anisotropy representation map may be generated, as follows: Figure 5 As shown. Each directed line segment can correspond to a paired combination of anisotropy intensity and shear wave propagation velocity anisotropy azimuth measured at a depth sampling point, and the directed line segments can be drawn on the display so that the directed line segments intersect the depth axis of the display at the point representing the depth sampling point. In some embodiments, the directed line segments can be arranged symmetrically about the depth axis. In other embodiments, the directed line segments can be arranged asymmetrically about the depth axis.

[0038] Figure 5 An example of a plurality of paired combinations of anisotropy intensities and shear wave velocity anisotropy azimuths measured for a plurality of depth sampling points plotted on a display according to one or more embodiments is shown. The directed line segments are arranged symmetrically about a line of zero anisotropy intensity, and the anisotropy azimuths are measured with the depth axis direction as the reference direction for the display and true north as the reference direction for the earth's surface. The top of the display shows a region 502 of high anisotropy intensity and an east-northeast-east shear wave velocity anisotropy azimuth. Immediately below 502 is a wellbore section 504 having a moderate anisotropy intensity and an east-southeast-east anisotropy azimuth. Below 504 is a long wellbore section 506 having a moderate anisotropy intensity. The bottom of the display shows a region 508 of low anisotropy intensity.

[0039] like Figure 5 As shown, the simultaneous representation of anisotropic properties in a single one-dimensional diagram can create a new perspective that simplifies the interpretation of formation anisotropy and greatly facilitates the evaluation and comparison of anisotropy. Figure 5 The diagrams shown in [1] provide an improved representation of subsurface anisotropy (e.g., anisotropy variation, direction, and transitions). This new method for characterizing and displaying anisotropy using cross-dipole acoustic data has broad applications in formation characterization, such as identifying the location and direction of stresses and fractures along a wellbore.

[0040] The embodiments may be implemented on a computer system. Figure 6is a block diagram of a computer system 602 for providing computing functionality associated with the algorithms, methods, functions, processes, flows, and programs as described in the present disclosure, according to a specific implementation. The computer 602 shown is intended to encompass any computing device, such as a server, desktop computer, laptop / notebook computer, wireless data port, smart phone, personal data assistant (PDA), tablet computing device, one or more processors within such devices, or any other suitable processing device, including physical or virtual instances of computing devices (or both). In addition, the computer 602 may include a computer that includes: an input device, such as a keypad, keyboard, touch screen, or other device that can accept user information; and an output device that transmits information associated with the operation of the computer 602, such information including digital data, visual or audio information (or a combination of information), or a GUI.

[0041] Computer 602 can act as a client, a network component, a server, a database or other persistent storage, or any other component (or combination of roles) in a computer system for performing the subject matter described in this disclosure. Computer 602 is shown communicatively coupled to network 630. In some implementations, one or more components of computer 602 can be configured to operate within an environment including a cloud-based environment, a local environment, a global environment, or other environment (or a combination of environments).

[0042] At a high level, computer 602 is an electronic computing device that is operable to receive, transmit, process, store, or manage data and information associated with the described subject matter. According to some specific implementations, computer 602 may also include an application server, an email server, a web server, a cache server, a streaming data server, a business intelligence (BI) server, or other server (or combination of servers), or be communicatively coupled to any of the above servers.

[0043] Computer 602 may receive requests from client applications (e.g., executing on another computer 602) via network 630 and respond to the requests by processing the received requests in a suitable software application. Additionally, requests may be sent to computer 602 from internal users (e.g., from a command console or through other suitable access methods), external or third parties, other automated applications, and any other suitable entity, individual, system, or computer.

[0044] Each component of computer 602 can communicate using system bus 603. In some implementations, any or all components of computer 602 (hardware or software (or a combination of hardware and software)) can interact with each other or with interface 604 (or a combination of both) over system bus 603 using application programming interface (API) 612 or service layer 613 (or a combination of API 612 and service layer 613). API 612 may include descriptions of routines, data structures, and object classes. API 612 may be independent of or dependent on the computer language and may refer to a complete interface, a single function, or even a set of APIs. Service layer 613 provides software services to computer 602 or other components communicatively coupled to computer 602 (whether or not shown). The functionality of computer 602 is accessible to all service consumers using the service layer. Software services (such as those provided by service layer 613) provide reusable, defined business functionality through defined interfaces. For example, the interface may be software written in Java, C++, or another suitable language that provides data in Extensible Markup Language (XML) or other suitable formats. Although shown as an integrated component of the computer 602, alternative implementations may show the API 612 or service layer 613 as a separate component relative to or communicatively coupled to other components of the computer 602 (whether shown or not). Furthermore, any or all portions of the API 612 or service layer 613 may be implemented as a sub-module or sub-module of another software module, enterprise application, or hardware module without departing from the scope of the present disclosure.

[0045] Computer 602 includes interface 604. Although Figure 6 602, two or more interfaces 604 may be used depending on the particular needs, desires, or implementation of the computer 602. The interface 604 is used by the computer 602 to communicate with other systems in a distributed environment connected to a network 630. Generally speaking, the interface 604 includes logic encoded in software or hardware (or a combination of software and hardware) and operable to communicate with the network 630. More specifically, the interface 604 may include software supporting one or more communication protocols associated with the communication so that the network 630 or the hardware of the interface is operable to transmit physical signals within and outside the illustrated computer 602.

[0046] Computer 602 includes at least one computer processor 605. Although Figure 6A single computer processor 605 is shown in FIG6 , but two or more processors may be used depending on the particular needs, desires, or implementation of the computer 602. In general, the computer processor 605 executes instructions and manipulates data to perform the operations of the computer 602 and any algorithms, methods, functions, procedures, flows, and programs described herein.

[0047] The computer 602 also includes a memory 606 that stores data for the computer 602 or other components that may be connected to the network 630 (or a combination of both). For example, the memory 606 may be a database that stores data consistent with the present disclosure. Figure 6 602, two or more memories may be used depending on the particular needs, desires, or implementation of the computer 602 and the functionality being described. Although the memory 606 is shown as an integral component of the computer 602, in alternative implementations, the memory 606 may be external to the computer 602.

[0048] Application 607 is an algorithmic software engine that provides functionality, particularly with respect to the functionality described in the present disclosure, as specifically needed, desired, or tailored to the particular implementation of computer 602. For example, application 607 may be implemented as one or more components, modules, applications, etc. Furthermore, although illustrated as a single application 607, application 607 may be implemented as multiple applications 607 on computer 602. Furthermore, although illustrated as being integral to computer 602, in alternative implementations, application 607 may be external to computer 602.

[0049] There may be any number of computers 602 associated with or external to the computer system containing computer 602, with each computer 602 communicating over network 630. Furthermore, the terms "client," "user," and other suitable terminology may be used interchangeably where appropriate without departing from the scope of this disclosure. Furthermore, this disclosure contemplates that many users may use one computer 602, or that one user may use multiple computers 602.

[0050] Although only a few exemplary embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications may be made in the exemplary embodiments without departing substantially from the present invention. Therefore, all such modifications are intended to be included within the scope of this disclosure as defined by the appended claims.

[0051] In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and their equivalents. Similarly, any means-plus-function clauses in the claims are intended to cover the actions described herein as performing the recited function and their equivalents. It is not the applicant's express intention to invoke Section 112(f) of the U.S. Patent Act to impose any limitations on any claim in this specification except where a claim expressly uses the phrase "means for" or "step for" in conjunction with an associated function.

Claims

1. A method for characterizing shear wave propagation velocity anisotropy within a display for a wellbore region, the method comprising: Obtaining the anisotropy intensity and azimuth of shear wave propagation velocity; determining a directed line segment to represent anisotropy for each of a plurality of measured depth points along the wellbore; as well as A plurality of directed line segments are drawn on the display to generate a one-dimensional anisotropy representation.

2. The method according to claim 1, in, The shear wave propagation velocity anisotropy intensity and the shear wave propagation velocity anisotropy azimuth are obtained from cross-dipole acoustic wave data.

3. The method according to claim 1 or 2, in, The shear wave propagation velocity anisotropy intensity is obtained from the difference between the propagation velocity of the fast shear wave and the propagation velocity of the slow shear wave.

4. The method according to claim 1, in, The shear wave propagation velocity anisotropy azimuth is obtained from the orientation of the polarization of the shear wave.

5. The method according to claim 1, in, The length of the directed line segment is a monotonic function of the anisotropy strength.

6. The method according to claim 1 or 5, in, The length of the directed line segment is proportional to the anisotropy strength.

7. The method according to claim 1, in, The orientation of the directed line segment measured relative to the displayed depth axis is equal to the anisotropy azimuth measured relative to a fixed direction on the Earth.

8. The method according to claim 7, in, The fixed direction on the Earth is selected from the group consisting of true north and magnetic north.

9. A non-transitory computer-readable medium storing instructions executable by a computer processor, the instructions comprising: a device for obtaining the anisotropy intensity and azimuth of the shear wave propagation velocity; means for determining a directed line segment to represent anisotropy for each of a plurality of measured depth points along the wellbore; as well as Means for drawing, by the computer processor, a plurality of directed line segments on a display to generate an anisotropic representation.

10. The non-transitory computer-readable medium of claim 9, wherein: The instructions also include: means for obtaining the shear wave propagation velocity anisotropy intensity and the shear wave propagation velocity anisotropy azimuth from cross-dipole acoustic wave data.

11. The non-transitory computer-readable medium of claim 9, wherein: The instructions also include: means for obtaining the shear wave propagation velocity anisotropy intensity from the difference between the propagation velocity of the fast shear wave and the propagation velocity of the slow shear wave.

12. The non-transitory computer-readable medium of claim 9, wherein: The instructions also include: means for deriving said shear wave propagation velocity anisotropy azimuth from the orientation of the polarization of the shear wave.

13. The non-transitory computer-readable medium of claim 9, wherein: The instructions also include: Means for determining the length of the directed line segment as a monotonic function of the anisotropy strength.

14. The non-transitory computer-readable medium of claim 9, wherein: The instructions also include: means for determining a length of the directed line segment to be proportional to the anisotropy strength.

15. The non-transitory computer-readable medium of claim 9, wherein: The instructions also include: Means for determining that the orientation of the directed line segment measured relative to a depth axis of the display is equal to the anisotropy azimuth measured relative to a fixed direction on the earth.

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