# Patent

## Title
System and method for generation of alerts and advice from automatically detected borehole breakouts

## Abstract

A method for generating an alert or advice for drilling a borehole penetrating an earth formation includes: receiving with a processor a borehole image from a downhole tool disposed at a drill tubular drilling the borehole; detecting a first breakout and a second breakout shifted approximately 180° apart from the first breakout if breakouts are in the image using a method for detecting breakouts implemented by the processor; and generating an alert or advice with the processor if the first and second breakouts are detected.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of U.S. non-provisional application Ser. No. 13/191,016 filed on Jul. 26, 2011, which claims priority to U.S. Provisional Patent Application No. 61/394,845 filed on Oct. 20, 2010. The parent applications are incorporated by reference herein in their entireties.


BACKGROUND
1. Field of the Invention
The present invention generally relates to drilling boreholes and, particularly, to identifying breakouts therein.
2. Description of the Related Art
Boreholes are drilled into the earth for many applications such as hydrocarbon production, geothermal production and carbon dioxide sequestration. A borehole is drilled with a drill bit or cutting tool disposed at the distal end of a drill string. A drilling rig turns the drill string and the drill bit to cut through formation rock and, thus, drill the borehole.
Ideally, the drilled borehole is somewhat smooth without interruptions that could cause borehole instability and impede further drilling. Lack of borehole stability can result in reduction in the quality of well log records and, consequently, difficulties in interpreting them. In addition, lack of borehole stability can cause mechanical problems such as stuck pipes, high torque and back-reaming, initiating further problems when setting the casing and removing cuttings. Unfortunately, the drilling process can re-distribute stresses in the formation around the borehole resulting in borehole instability, which can lead to parts of a borehole wall to breaking out of the formation and causing indentations in the borehole wall. This condition is referred to as a “breakout.” It would be well received in the drilling art if drilling operators and site engineers could be alerted to the occurrence of breakouts during the drilling process in order to prevent further drilling and completion problems.
BRIEF SUMMARY
Disclosed is a method for generating an alert or advice for drilling a borehole penetrating an earth formation includes: receiving with a processor a borehole image from a downhole tool disposed at a drill tubular drilling the borehole; detecting a first breakout and a second breakout shifted approximately 180° apart from the first breakout if breakouts are in the image using a method for detecting breakouts implemented by the processor; and generating an alert or advice with the processor if the first and second breakouts are detected.
Also disclosed is an apparatus for generating an alert or advice for drilling a borehole penetrating an earth formation. The apparatus includes: a processor configured to: (i) receive a borehole image from a downhole tool disposed at a drill tubular drilling the borehole; (ii) detect a first breakout and a second breakout shifted approximately 180° apart from the first breakout if breakouts are in the image using a method for detecting breakouts implemented by the processor; and (iii) generate an alert or advice with the processor if the first and second breakouts are detected.
Further disclosed is a non-transitory computer readable medium comprising computer executable instructions for generating an alert or advice for drilling a borehole penetrating an earth formation by implementing a method that includes: receiving a borehole image from a downhole tool disposed at a drill tubular drilling the borehole; detecting a first breakout and a second breakout shifted approximately 180° apart from the first breakout if breakouts are in the image; and generating an alert or advice if the first and second breakouts are detected.



BRIEF DESCRIPTION OF THE DRAWINGS
The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike:
FIG. 1 illustrates an exemplary embodiment of a downhole imaging tool disposed in a borehole penetrating the earth;
FIG. 2 depicts aspects of an image of a borehole having breakouts;
FIG. 3 depicts aspects of processing and analyzing image data to detect the breakouts;
FIG. 4 depicts aspects of dividing image sectors into angular segments;
FIG. 5 depicts aspects of rotating the angular segments with respect to the breakouts;
FIGS. 6A and 6B, collectively referred to as FIG. 6, depict aspects of rotating angular segments having unequal angles;
FIG. 7 depicts aspects of creating breakout intervals from breakouts shown on an image;
FIG. 8 depicts aspects of processed and analyzed image data illustrating detection of breakouts;
FIG. 9 depicts aspects of a pressure window for constraining drilling fluid pressure;
FIG. 10 depicts aspects of automatically generating alerts and advice based on detected borehole breakouts;
FIG. 11 depicts aspects of one exemplary embodiment of alerts and associated advice displayed by a display; and
FIG. 12 is a flow diagram illustrating a method for generating an alert or advice for drilling a borehole penetrating an earth formation.



DETAILED DESCRIPTION
A detailed description of one or more embodiments of the disclosed apparatus and method presented herein by way of exemplification and not limitation with reference to the Figures.
Drilling boreholes causes the in-situ Earth stresses to re-distribute around the borehole. If the load applied by the annular pressure of the drilling fluid against the borehole wall becomes excessively low and/or the temperature is sufficiently increased in the formation around the borehole, the re-distributed shear stress exceeds the rock strength by which parts of the borehole wall break out of the formation to form indentations in the borehole wall. These indentations are termed breakouts.
In many cases, breakouts occur in pairs approximately 180° apart on a borehole image. If the in-situ stress around the borehole is anisotropic, so that the principle stresses are of unequal magnitude, the breakouts develop in the direction of the least principle stress. The width of each breakout generally varies as a function of rock strength and the magnitudes of the re-distributed stresses.
Detection of breakouts on images of the borehole wall provides a way to constrain in-situ Earth stress magnitudes and orientation as well as the rock strength, which are necessary prerequisites to predict wellbore stability. Such a function is of particular relevance for long horizontal wells (where the vertical stress largely exceeds the horizontal stress) and for drilling through unconsolidated sediments. Once breakouts are identified, remedial actions can be performed to circumvent drilling hazards. In addition, the subsequent calibration of the in-situ Earth stresses improves the safety of continuous drilling by updating the pressure window used by drilling operators and engineers.
Disclosed herein are techniques for detecting breakouts by analyzing an image of a borehole wall penetrating a geologic formation generally formed of rock. The image is generally a data set of measurements of properties of the formation. Variations in the values of the measurements can be plotted to create an image of the formation. In addition to detecting breakouts, the techniques include providing an alert automatically to the drilling operators and engineers if breakouts are detected while drilling a borehole. Also in addition to detecting breakouts, the orientation and the width of the detected breakouts are delivered as an output of the applied technique. In addition to delivering the orientation and width of a single breakout at one particular depth location, an average width and orientation, averaged over a depth interval where breakouts exist can also be delivered as an output of the applied technique.
Except for delivering the average width and orientation for a depth interval, the techniques presented herein are applicable to one single image row at one particular depth, irrespective of the amount of sectors (pixel values) contained in the row. Hence, images from different acquisition technologies and with different resolutions can be automatically analyzed. Delivering the average width and orientation for a depth interval requires a depth-based analysis over more than one image row.
In one embodiment, the analysis is performed downhole in the downhole tool acquiring the image data. Because the acquired images can be data-intensive and a downhole telemetry system may have limited bandwidth, downhole analysis can provide for alerting the drilling operators and engineers of breakouts more quickly than if the analysis was performed at the surface of the earth. For embodiments with high-speed broadband telemetry, surface processing and analysis of the image data can also be performed.
FIG. 1 illustrates an exemplary embodiment of a downhole tool 10 disposed in a borehole 2 penetrating the earth 3, which includes an earth formation 4. The formation 4 represents any subsurface material of interest penetrated by the borehole 2. The downhole tool 10 is conveyed through the borehole 2 by a carrier 5. In the embodiment of FIG. 1, the carrier 5 is a drill string 6 that includes a drill bit 7 in an operation referred to as logging-while-drilling (LWD). The downhole tool 10 in one embodiment is disposed in a bottom-hole assembly (BHA) 12 behind the drill bit 7. Drilling fluid 11 is pumped through the drill string 6 and is used to lubricate and cool the drill bit 7, and to flush rock cuttings from the borehole 2. In another embodiment, the carrier 5 can be an armored wireline in an operation referred to as wireline logging. In wireline logging, the wireline conveys the downhole tool 10 through the borehole 2 and can provide a communications medium for communicating data or commands between the tool 10 and surface communicator.
Still referring to FIG. 1, the downhole tool 10 includes downhole electronics 8 configured to process data obtained by the downhole tool 10. Processed data can be transmitted to a surface computer processing system 9 by way of a telemetry system 13. Non-limiting embodiments of the telemetry system 13 include pulsed-mud, wired drill pipe having a broadband coaxial cable or a fiber optic cable, acoustic transmission, and radio transmission. In one embodiment, the surface computer processing system 9 is configured to store data in a database and prepare, process, and visualize data for subsequent analysis and interpretation. The analysis and interpretation of the acquired data to deliver an image of the borehole wall versus depth is performed by application engineering software, which includes appropriate algorithms. The application engineering software can be implemented by the downhole electronics 8 and/or the surface computer processing system 9.
The application engineering software performs an automatic analysis of images of the borehole wall to monitor the existence or non-existence of borehole breakouts (see FIG. 2 for example of breakouts). If breakouts exist, an alert is provided to a user in addition to relevant parameters such as the measured depth of the breakout, breakout orientation, and breakout width, which are delivered to a user for further processing and analysis, such as for the calibration of in-situ earth stresses or to perform environmental corrections, etc.
The downhole tool 10 is configured to measure a property of the formation 4. Non-limiting examples of the property include gamma ray emission, acoustic impedance, resistivity (or its inverse conductivity), density, or porosity. Measurements of the property are performed in circumferential direction around the borehole wall (i.e., radial measurements around the circumference) and at various depths in the borehole 2, generally while the downhole tool 10 is being conveyed through the borehole 2. However, movement of the tool 10 can be halted while a measurement is being performed. The measurements are grouped into a data set. Variations in values of the measured property in the data set can be displayed as an image. Accordingly, the term “image” as used herein can refer to a visual image or the data set that can be used to create an image.
FIG. 2 on the left shows an example of breakouts on an image of the borehole wall. The image of the borehole is an azimuthal/circumferential representation of a physical property of the formation at or close to the borehole wall (depending on the depth of penetration for a specific acquisition technology). The magnitude of the physical property at a specific borehole location is stored as a pixel value. The image is a graphical color-coded representation of the pixel values with different shades of color representing different pixel values, although shown herein as a black and white image.
Breakouts (i.e., an enlarged borehole at opposite locations) on an image become visible due to an increased distance between a sensor in the downhole tool 10 that measures the physical property and the borehole wall. If the distance becomes too large, the sensor is not able to determine the physical property of the rock anymore.
In FIG. 2 on the left, the dark or shaded areas are the observed borehole breakouts, whereas light areas represent intact formation rock. As noted above, the breakouts appear in pairs in most depth intervals, approximately 180 degrees apart from each other.
FIG. 2 on the right shows an example of normalized pixel values for one row of the image. Breakouts in FIG. 2 are represented by a pixel value of one (y-axis). For the presented image, each row of the image contains 120 sectors, i.e., 120 pixels, one pixel value per sector (x-axis).
The techniques disclosed herein present an algorithm for performing an automatic analysis of images from the borehole wall to monitor the existence or non-existence of borehole breakouts. If breakouts exist, relevant parameters (breakout orientation and breakout width) are delivered for further processing and analysis, such as for the calibration of the in-situ Earth stresses.
FIG. 3 illustrates one example of workflow for the engineering application software. The presence or absence of breakouts can be verified from images of the borehole wall. A pre-requisite of the presented algorithm is therefore the automatic monitoring of the borehole wall by image acquisition (process 31, FIG. 3). For this workflow, any technology can be used for image acquisition of any resolution, which of course affects the accuracy of the breakout analysis.
FIG. 4 defines the nomenclature used to describe an algorithm, presented below, used for automatic detection of breakouts. The lower figure shows a top view of a single row of pixels in a circle that make up the image. The image sectors are represented by the dashed line (as also shown as a linear line in the upper figure). Each dash represents one sector, to which one pixel value of the image is assigned. Pair-wise breakouts are highlighted as circle sections 40, 180 degree apart from each other. The breakout width (see also FIG. 2) is defined as the angle of each of the circle sections 40 at which the breakout exists. Segments are defined as pieces or arcs of the circle, which are labeled segments I-IV. The included angles of segments I-IV are referred to as angles α and β, the sum of the segment angles (2α+2β) of the circle add up to 360 degrees. Alternatively, the included angles of segments I-IV may all slightly differ from each other, as long as they sum up to 360 degrees.
An algorithm is presented herein for the automatic detection of such pair-wise breakouts. The algorithm can be applied to any image, irrespective of the applied technology for image acquisition. Also, the algorithm analyzes only one image row at a particular depth, irrespective of the existence of breakouts above the depth under consideration (i.e., analysis of only one row in FIG. 2). This setup makes the algorithm applicable to an implementation into firmware in the downhole tool 10. Such an implementation allows for the automatic monitoring of the borehole status (i.e., breakout or no breakout), and the automatic generation of alerts whenever breakouts are detected. Compared to the image analysis at the surface for which high-resolution image data need to be transmitted via the telemetry system 13, this algorithm drastically reduces the amount of information that needs to be transmitted to the surface.
The algorithm includes the following steps with reference to FIGS. 4-7:
Step 1—Optionally, filter or smooth the image data by applying any filtering or smoothing algorithm to the image data. If the pixel values of the image represent the resistivity of the formation borehole wall, the filter may be applied to the logarithm of the pixel values. Otherwise, the filter may be applied to the pixel values themselves. Also, filtering may be applied automatically to the image, depending on the image quality. The image quality can be quantified by a statistical parameter such as kurtosis.
Step 2—Sub-divide the image row into four segments I-IV including the angles α, β. The angles diagonally opposed to each other are equal, and all angles sum up to 360 degrees.
Step 3—Depending on subsequently used approaches, normalize (and, optionally, invert) the pixel values between the maximum and minimum of pixel values. Inversion should be performed when the breakouts are represented by low pixel values, compared to the locations where no breakouts exist. If breakouts are represented by high pixel values on the image, inversion should not be applied.
Step 4—Beginning with equal angles included by the segments, α=β=90 degrees, calculate the average of the physical property for each of the four segments I-IV. Different types of averages can be calculated, including the harmonic, arithmetic, geometric, etc. averages.
Step 5—Stack the averages of opposed segments, i.e., stack the averages from segments I and III, as well as II and IV, respectively. Different methods can be used for stacking.
Step 6—Rotate the relative position between the image and the four segments (FIG. 5) by one or more sectors, keeping the angles between the segments constant. Then, repeat steps 2-5.
Step 7—After rotation by 90 degrees (in case of equal angles α=β=90 degrees between the segments) or 180 degrees (in case of unequal angles α≠β), find the maximum or minimum stack, depending on the applied approaches for normalization and inversion. Also, find the angle of rotation at which the maximum/minimum (i.e., maximum or minimum) stack was found. The maximum/minimum stack is found at the position of the breakout.
Step 8—Change the angles between the segments (FIGS. 6A and 6B) by a small amount (for example by one sector), so that α≠β, and repeat steps 1-6. However, repeat the steps 2-7 until the relative position between the image and the segments reaches 180 degrees.
Step 9—Out of all combinations of rotation (step 6) and angle changes (step 8), find the orientation and the angle between the segments at which the stacks become a maximum/minimum. At the combination that provides the maximum/minimum stack, the orientation of the segments defines the breakout positions around the boreholes, and the angle between the segments determines the width of the breakouts (FIG. 5). Steps 6-8 may be applied in reverse order, i.e., first changing the angles between the segments, and then rotating the image.
Step 10—If multiple breakouts were detected on multiple image rows, those breakouts are clustered into a breakout interval as illustrated in FIG. 7. If depth information is available, the location of the breakout interval is assigned to the interval. Among others, attributes such as a start depth, an end depth, a center depth, the lithology of the breakout interval wherein the breakout cluster resides, the time since drilling the depth of the breakout interval, and the pressure range of the breakout interval are assigned to the breakout interval.
Step 11—If a breakout interval has been identified, an average width and orientation is calculated from the widths and orientations of each breakout within that breakout interval as illustrated in FIG. 7. Different methods for averaging may be applied. In particular, one option is to use a weighting average function, which weights the breakout widths and orientations of each breakout by the stacking value.
Step 12—Assign an uncertainty to the parameters—width and orientation—for the breakout intervals, for example by statistically analyzing the widths and orientations of the breakouts within each interval.
Among others, the following methods can be used for normalization (norm) of each pixel value Isec where each pixel value relates to one sector as shown in FIG. 4.

    Normalization Method 1—Normalize each pixel value according to minimum(min)/maximum(max) values:






  
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    Normalization Method 2—Normalize each pixel value according to min/max values and invert:






  
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    Normalization Method 3—Normalize each pixel value according to min/max values and invert, and then take the square (preferred method in one embodiment):






  
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    Normalization Method 4—Normalize each pixel value according to min/max values, and then take log10:






  
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    Normalization Method 5—Normalize each pixel value according to min/max values, and then take the square:






  
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Among others, the following methods can be used for averaging normalized pixel values for each of the four segments as shown in FIG. 4.

    Averaging Method 1—Average the normalized pixel values for each of the 4 segment:






  
    
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i=1, 2, 3, 4 where n=number of sectors in segment i

    Averaging Method 2—Average the logarithms of the normalized pixel values for each of the 4 segments:






  
    
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i=1, 2, 3, 4 where n=number of sectors in segment i

Among others, the following methods can be used for stacking the average of the normalized pixel values from opposite segments as shown in FIG. 4.

    Stacking Method 1—Stack averages from opposite segments, subtract the stacks, and take the absolute value:

stack=(av1+av3)−(av2+av4)

    Stacking Method 2—Stack averages from opposite segments, divide the two resulting stacks and determine the minimum (this method applies only to Normalization Methods 2 and 3):

stack1=(av1+av3)/(av2+av4)

stack2=(av2+av4)/(av1+av3)

stack=min(stack1, stack2)

    Stacking Method 3—Stack averages from opposite segments and determine the minimum (applies only to Normalization Methods 1, 4 and 5):

stack1=(av1+av3)

stack2=(av2+av4)

stack=min(stack1, stack2)

    Stacking Method 4—Stack averages from opposite segments and determine the maximum (applies only to Normalization Methods 2 and 3):

stack1=(av1+av3)

stack2=(av2+av4)

stack=max(stack1stack2)

    Stacking Method 5—Stack averages from opposite segments, divide the two resulting stacks and determine the minimum (applies to Normalization Methods 1, 4 and 5):

stack1=(av1+av3)/(av2+av4)

stack2=(av2+av4)/(av1+av3)

stack=max(stack1, stack2)



FIG. 8 shows the result of the automatic identification of borehole breakouts using Normalization Method 3, Averaging Method 1, and Stacking Method 1 for a varying angle between the segments. The left-most track shows the image with the borehole breakouts and the orientation of the breakouts (the dots 70) on top of the image. The dots 71 show the average orientation of the two identified breakout zones. The second track from left shows the breakout intervals and the widths of each breakout (dots 72), as well as average widths for each breakout interval (dots 73). The third track from left shows the maximum of the stacking routine. A breakout is identified when the maximum exceeds the threshold value of 0.8, which is an empirically determined value in one embodiment. The right track shows the kurtosis for each image row. The kurtosis is one statistical parameter that can be used to automatically apply filtering/smoothing (Step 1) once the kurtosis exceeds a pre-defined threshold.
Once a breakout has been detected, different levels of alert can be provided, depending on the configuration of the algorithm (process 33 in FIG. 3). Level 1: an alert may be generated which informs a user that a breakout has been detected (no parameters delivered). Such an alert can be a trigger to change the telemetry configuration to transmit higher resolution images for more detailed analysis. If a breakout orientation is also delivered (level 2 in process 33, FIG. 3), subsequent breakouts are monitored (memorized or recorded) until a breakout zone (depth interval) can be identified (process 34, FIG. 3). The orientation of the breakout zone can then be used to calibrate the orientation of the in-situ Earth stresses. Level 3 triggers the monitoring of subsequent alerts (process 35, FIG. 3). If a breakout zone is identified, the pressure and temperature range prevailing in the time the zone was drilled needs to be determined (process 36, FIG. 3) for use in calibrating the in-situ Earth stresses. In addition, different levels of alerts can be generated based on the magnitude of the detected breakouts. Magnitudes of different breakouts can be compared to various thresholds corresponding to the different alert levels. In one or more embodiments, three alert levels can be provided to an operator—no significance (continue drilling), minor significance (caution), and major significance (serious incident expected). These are only examples as one skilled in the art can create other alerts and alarms corresponding to equipment, methods and parameters of interest using the techniques disclosed herein.
The automatic generation of alerts in addition to the downhole image data analysis includes monitoring the drilling status (either downhole by the tool 10 or at the surface by the surface computer processing system 8 once a detected breakout has been transmitted). The drilling status can include pressure and temperature at the detected breakouts.
In addition to the features presented in FIG. 3, the engineering application system also provides the following applications in order to handle operating constraints.
A first application is provided to deliver the geometry of the borehole (inclination, azimuth, dogleg severity and others), in order to circumvent the analysis of asymmetric images (images on which one breakout is less pronounced than its counterpart). Also, the first application is able to predict whether formation beds are penetrated perpendicular or inclined. If the borehole penetrates the formation beds in an inclined angle, a second application is provided which is able to perform dip removal on the image, in order to circumvent alerts arising from inclined beds but not from breakouts.
A third application is provided which is able to deliver the drilling status. That application can control the activation of the automatic image analysis, in order to exclude the analysis of images acquired while not drilling or re-logging.
A fourth application is provided to provide information related to detecting the breakouts for the purpose of calibrating a pressure window 91, which is represented in FIG. 9. The pressure window relates to a range of drilling fluid pressures having an upper bound (fracture gradient) and two lower bounds (shear failure gradient or pore pressure gradient) where the drilling fluid pressure is constrained between the upper bound and the higher of the two lower bounds as illustrated in FIG. 9. The shear failure gradient can be constrained by the breakout information and other drilling parameters associated with the breakout. Synonyms for the shear failure gradient are collapse gradient or collapse pressure.
The techniques disclosed herein have the benefit of being robust in a way that only significant, clearly visible breakouts are detected, which circumvents false alerts. In addition, the approach only alerts whenever breakouts occur as a pair, approximately 180 degrees shifted. This latter benefit circumvents the false detection of key seating.
As noted above, various levels or types of alerts can be automatically generated. The alerts may be automatically generated by the application engineering software. These alerts relate to the detection and/or quantification of borehole breakouts by the application engineering software as discussed above. The alerts can also include the condition where no breakouts are detected by the application engineering software. In addition, the alerts can be related to whether a detected breakout, a size of a breakout, or orientation of a breakout was expected or not. Once the alert is generated, it can be displayed to a drilling operator or other user. In one or more embodiments, the alert is presented as a description of events occurring downhole as related to breakouts if detected and if the events are expected or not. In one or more embodiments, the alert can be presented as a “traffic light” with colors such as green, yellow, and red representing the severity of the downhole breakout condition. In addition to or in lieu of automatically generating alerts, the application engineering software may also automatically generate advice to the drilling operator or other user based on the downhole conditions or events related to detected breakouts. The advice relates to suggestions in order to drill the borehole safely and efficiently.
FIG. 10 depicts aspects of automatically generating alerts and advice based on detected borehole breakouts. Application engineering software 90, which may include input from one or more modules for automatically generating the alerts and advice, may be implemented by the downhole electronics 8, the computer processing 9 or combination thereof. The alerts and advice may be presented to the drilling operator or user by a display 94. The display 94 may be located at or remote to a drilling rig drilling the borehole. The application engineering software 90 upon detecting and/or quantifying a downhole breakout pair from a borehole image of known depth or location may apply the one or more alert and advice generation modules. In order to determine if the detected breakouts are expected or not, the pressure window 91, a geomechanical model 92 of the formation 4 penetrated by the borehole 2, and/or measured formation and borehole parameters 93 may be input to the application engineering software 90. The application engineering software 90 by itself may be able to issue some alerts and associated advice. For example, the geomechanical model 92 may not be available when drilling a first exploratory borehole in a completely new area. In this situation, the software 90 by itself can detect and quantify breakouts and issue related alerts and advice. However, other alerts, such as whether a breakout condition is expected or not, may require use of the modules 91, 92, and/or 93.
The pressure window 91 is a software package or module that includes a range of drilling fluid pressures having a fracture gradient as an upper bound and shear failure gradient (or collapse pressure) and pore pressure gradient as two lower bounds. In general, the downhole annular pressure (resulting from drilling fluid) is attempted to be maintained within the range of pressures in the pressure window 91. By inputting the downhole annular pressure for the depth at which the borehole image was obtained into the application engineering software 90, the software 90 will be able to determine whether a detected breakout pair at that depth was expected or not. For example, if a breakout was detected and the annular pressure was less than the shear failure gradient, then the breakout was expected. If a breakout was detected and the annular pressure was greater than the shear failure gradient, then the breakout was not expected because the annular pressure always exceeded the predicted collapse pressure.
The geomechanical model 92 includes at least some of the following parameters or values relating to the formation 4 and the borehole 2:
an in-situ stress tensor of the Earth containing the magnitudes of the three principle or orthogonal stresses and an orientation of this stress tensor;
formation pore pressure, among others to calculate effective stresses by subtracting the formation pore pressure from the absolute stresses;
orientation of the borehole with respect to the in-situ stress tensor or with respect to another reference system so that the relative orientation between the stress tensor and he borehole trajectory can be calculated;
size and/or diameter of the borehole;
predicted and/or measured attributes such as temperature, pressure, chemical composition of the formation and drilling fluid, and drilling fluid additives;
a sub-model describing the compressive strength of the formation rock under in-situ and/or surface conditions; and
a sub-model describing the deformation behavior of the formation rock under stress (e.g., linear elastic, non-linear elastic, poroelastic, plastic).
From the in-situ earth stress tensor, the geomechanical model 92 can calculate the re-distributed stresses around the borehole due to the borehole being drilled and compare the re-distributed stresses (specified in units of pressure) against the compressive formation rock strength (also specified in units of pressure). If the stresses exceed the formation rock strength, the borehole may collapse creating the breakouts. The circumferential extent to which the re-distributed stresses exceed the formation rock strength determines the width of the breakouts. The orientation of the breakouts depends on the orientation of the in-situ Earth stresses and how they are distributed around the borehole. Hence, the application engineering software 90 using the geomechanical model 92 can predict the expected width and the expected orientation of breakouts for a downhole annular pressure and/or temperature condition. In general, the annular pressure (i.e., borehole fluid pressure) in the borehole at the depth where the borehole image was obtained is input into the geomechanical model 92 in order to determine whether breakouts are expected or not, and, in case they are expected, their width. For the downhole annular pressure and/or temperature conditions, the expected width and the expected orientation of the breakouts can then be compared with the detected width and the detected orientation of the breakouts. If they agree, then the geomechanical model 92 is validated. If they don't agree, then an alert can be generated noting the disagreement and advice can be generated to re-calibrate or update the appropriate sections of the geomechanical model 92. For example, if breakouts are detected but not expected, then the geomechanical model 92 needs to be updated. If the detected widths of breakouts are greater than or less than the expected widths, then the model for the in-situ earth stresses and/or the model for the formation rock strength need to be updated. If the detected orientation of the breakouts does not agree with the expected orientation of the breakouts, then the re-distributed stress orientations need to be updated. The geomechanical model 92 can be obtained from formation and borehole measurements performed while measurements for the borehole images are performed. Alternatively or in combination, the formation and borehole measurements for the geomechanical model can be performed in nearby boreholes penetrating the same formation and/or from surface seismic measurements. In addition, formation samples can also be obtained from the nearby boreholes for laboratory analysis to determine formation lithologies and relevant rock mechanical properties.
The measured formation and borehole parameters 93 are input into the application engineering model 90, the pressure window 91, and/or the geomechanical model 92. The measured parameters 93 include the latest measured parameters that may be substituted for previously assumed parameters. Non-limiting embodiments of the measured parameters 93 include: annular pressure or drilling fluid pressure at various borehole depths where the borehole images were obtained such as sensed by a pressure sensor (not shown) disposed in the BHA 12; borehole temperature at various borehole depths where the borehole images were obtained such as sensed by a temperature sensor (not shown) disposed in the BHA 12; borehole caliper measurements; formation pore pressure measurements obtained by a formation tester disposed at the bottom hole assembly in proximity to the downhole tool 10 such that the pore pressure is representative of the formation where the borehole images were obtained; additionally, the pore pressure from the formation tester may be used as a measurement against which a pore pressure in model 91/92 can be calibrated; and borehole trajectory such as inclination (from vertical) and azimuth obtained using a borehole trajectory determining system. In general, the borehole trajectory determining system includes a downhole tool or sensor combination, which is able to measure the orientation or direction of the bottom hole assembly with respect to North (magnetic or geographic, both of which can be converted to the other), giving the azimuthal direction with respect to the vertical (giving the inclination).
In addition to determining the widths of the detected breakouts, the application engineering software 90 may also categorize the widths for providing the alerts and advice. In one or more embodiments for vertical boreholes, the widths can be categorized as small, large, or extra-large where small breakouts have widths less than 75 degrees, large breakouts have widths between 75 to 90 degrees, and extra-large breakouts have widths greater than 90 degrees. In one or more embodiments for horizontal boreholes, small breakouts have widths less than 20 degrees, large breakouts have widths between 20 and 30 degrees, and extra-large breakouts have widths greater than 30 degrees. In general, a borehole with an inclination of 15 degrees or less can be considered vertical. For other inclinations, the categories can be interpolated between the two extreme (vertical and horizontal) cases. It can be appreciated that a geomechanical engineer may at the time of drilling suggest other criteria based on local environmental conditions. For example, a very thick mud cake or excellent hole cleaning practices may strengthen the borehole requiring an increase in the general values listed above.
FIG. 11 depicts aspects of one exemplary embodiment of alerts and associated advice displayed by the display 94. Also depicted in FIG. 11 is a “traffic light” configured to display green, yellow, and red colors to indicate general levels of alert in increasing levels of severity, respectively. If no breakouts are observed, the green light is displayed with the advice to continue drilling
If a breakout is observed, then the associated advice includes monitoring drill rig parameters derived from both surface and downhole parameters such as hydraulic parameters, drilling dynamics (e.g., vibrations), weight on bit, drill tubular torque, and drill tubular drag. If the breakout is quantified as small, then the yellow traffic light is displayed. The yellow traffic light is also displayed if a small breakout was expected, but did not occur. In this case, the advice includes re-calibrating the shear-failure gradient. In addition, the yellow traffic light is displayed if observed and expected breakout orientations coincide or do not coincide. If they do not coincide, then the advice includes re-calibrating the shear-failure gradient. Further, the yellow traffic light is displayed if the detected breakout orientation coincides with a change in drilling direction. In this case, the advice includes: monitoring for cavings, such as by percent, size, or shape; warning that breakout enlargements due to drill string dynamics are possible; ensure cleaning of borehole; and/or warning that a stuck drill tubular is possible due to key seating.
If large or extra-large breakouts are detected, then the red traffic light is displayed. The red traffic light is also displayed if rotating breakout orientations are detected without a change in drilling direction. The advice for this situation includes monitoring for faults, cautioning that a stuck drill tubular is possible, monitoring for drilling fluid losses, and ensure borehole cleaning If a large breakout is detected but not expected or if a detected breakout width is larger than expected, then the red traffic light is displayed and the advice includes re-calibrating the shear failure gradient, ensure borehole cleaning, increase downhole annular pressure, and/or consider drilling fluid changes.
If a very large breakout is observed, then the associated advice includes ensure borehole cleaning, increase downhole annular pressure, consider mud changes, and/or pull out of the borehole.
Superscript 1 in FIG. 11 relates to alarms and advice that can be generated alone from the automatic breakout detection algorithm (i.e., application engineering software 90) such as: breakouts exist/do not exist (time/depth); breakouts are oriented in . . . direction (time/depth); breakouts have . . . width (time/depth); and/or breakout intervals (depth). Superscript 2 in FIG. 11 relates to potential alarms that can be generated from the automatic breakout detection algorithm in combination with a pressure window model (e.g., inputs: image data and shear failure gradient) such as: existence/non-existence of breakouts and whether expected or not; detected and expected breakout orientation coincide or do not coincide; and/or detected and expected breakout width coincide or do not coincide. Superscript 3 in FIG. 11 relates to potential alarms that can be generated from the automatic breakout detection algorithm if additional formation evaluation and drilling data are available (e.g., inputs: image data, inclination, azimuth, dogleg, gamma radiation data, formation lithology) such as: breakout orientation coincides with drilling directional change and/or breakouts in different lithologies.
It can be appreciated that the alerts and advice can be presented in various ways. In one or more embodiments, only the current alert, traffic light, and associated advice are displayed. Alternatively, in one or more embodiments, all of the potential alerts and advice are displayed together and the current alert and associated advice is highlighted or blinking. In addition to the visual display, an alert and associated advice can be presented acoustically. A recorded voice can be used to actually say what the alert and advice are or a sound can alert the drilling operator to look at the display 94.
FIG. 12 is a flow diagram illustrating a method 110 for generating an alert or advice for drilling a borehole penetrating an earth formation. Block 111 calls for receiving with a processor a borehole image from a downhole tool disposed at a drill tubular drilling the borehole. Block 112 calls for detecting a first breakout and a second breakout shifted approximately 180° apart from the first breakout if breakouts are in the image using a method for detecting breakouts implemented by the processor. Block 113 calls for generating an alert or advice with the processor if the first and second breakouts are detected. The method 110 can also include issuing an alert indicating that no breakouts are detected with associated advice to continue drilling. The method 110 can also include determining if a breakout, breakout width, or breakout orientation is expected or not and generating associated alerts and advice.
In support of the teachings herein, various analysis components may be used, including a digital and/or an analog system. For example, the downhole electronics 8 or the surface computer processing system 9 may include the digital and/or analog system. The system may have components such as a processor, storage media, memory, input, output, communications link (wired, wireless, pulsed mud, optical or other), user interfaces, software programs, signal processors (digital or analog) and other such components (such as resistors, capacitors, inductors and others) to provide for operation and analyses of the apparatus and methods disclosed herein in any of several manners well-appreciated in the art. It is considered that these teachings may be, but need not be, implemented in conjunction with a set of computer executable instructions stored on a non-transitory computer readable medium, including memory (ROMs, RAMs), optical (CD-ROMs), or magnetic (disks, hard drives), or any other type that when executed causes a computer to implement the method of the present invention. These instructions may provide for equipment operation, control, data collection and analysis and other functions deemed relevant by a system designer, owner, user or other such personnel, in addition to the functions described in this disclosure.
Further, various other components may be included and called upon for providing for aspects of the teachings herein. For example, a power supply (e.g., at least one of a generator, a remote supply and a battery), cooling component, heating component, magnet, electromagnet, sensor, electrode, transmitter, receiver, transceiver, antenna, controller, optical unit, electrical unit or electromechanical unit may be included in support of the various aspects discussed herein or in support of other functions beyond this disclosure.
The term “carrier” as used herein means any device, device component, combination of devices, media and/or member that may be used to convey, house, support or otherwise facilitate the use of another device, device component, combination of devices, media and/or member. Other exemplary non-limiting carriers include drill strings of the coiled tube type, of the jointed pipe type and any combination or portion thereof. Other carrier examples include casing pipes, wirelines, wireline sondes, slickline sondes, drop shots, bottom-hole-assemblies, drill string inserts, modules, internal housings and substrate portions thereof.
Elements of the embodiments have been introduced with either the articles “a” or “an.” The articles are intended to mean that there are one or more of the elements. The terms “including” and “having” are intended to be inclusive such that there may be additional elements other than the elements listed. The conjunction “or” when used with a listing of at least two terms is intended to mean any term or combination of terms. The terms “first,” “second,” and “third” are used to distinguish elements and are not used to denote a particular order.
It will be recognized that the various components or technologies may provide certain necessary or beneficial functionality or features. Accordingly, these functions and features as may be needed in support of the appended claims and variations thereof, are recognized as being inherently included as a part of the teachings herein and a part of the invention disclosed.
While the invention has been described with reference to exemplary embodiments, it will be understood that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications will be appreciated to adapt a particular instrument, situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

## Claims

1. A method for generating an alert or advice for drilling a borehole penetrating an earth formation, the method comprising:
receiving with a processor a borehole image from a downhole tool disposed at a drill tubular drilling the borehole;
detecting a first breakout and a second breakout shifted approximately 180° apart from the first breakout if breakouts are in the borehole image using a method for detecting breakouts implemented by the processor comprising receiving with the processor a drilling fluid pressure for a borehole depth where the borehole image was obtained and comparing the drilling fluid pressure to a shear-failure gradient in a drilling pressure window; and
generating an alert or advice with the processor if the first and second breakouts are detected.

2. The method according to claim 1, wherein the alert comprises no breakout observed and the advice comprises to continue drilling if no breakouts are detected in the borehole image by the method for detecting breakouts implemented by the processor.

3. The method according to claim 2, wherein the alert further comprises breakout not observed but expected and the advice further comprises re-calibrating the shear-failure gradient if the drilling fluid pressure is less than the shear-failure gradient.

4. The method according to claim 1, wherein the alert comprises breakout observed and the advice comprises monitoring drill rig parameters, drilling dynamics, drill tubular torque, and drill tubular drag if the first and second breakouts are detected.

5. The method according to claim 4, wherein the alert further comprises breakout observed but not expected and the advice further comprises re-calibrating the shear-failure gradient if the drilling fluid pressure is greater than the shear-failure gradient.

6. The method according to claim 4, further comprising determining orientations of the first and second breakouts from the borehole image using the method for detecting breakouts implemented by the processor.

7. The method according to claim 6, further comprising receiving with the processor a stress orientation from a formation stress model of the earth formation for the borehole depth where the borehole image was obtained, wherein the alert further comprises observed and breakout orientations coincide and the advice further comprises re-calibrating the stress orientation in the formation stress model if the stress orientation in the formation stress model does not coincide with the orientations of the first and second breakouts.

8. The method according to claim 6, further comprising receiving with the processor a drilling direction.

9. The method according to claim 8, wherein the alert further comprises breakout orientations coincide with a drilling direction change and the advice further comprises at least one of: monitoring for borehole caving, breakout enlargements, ensure borehole cleaning, and possible stuck drill tubular due to key seating if the drilling direction change coincides with the orientations of the first and second breakouts.

10. The method according to claim 8, wherein the alert further comprises rotating breakout orientation with no drilling direction change and the advice further comprises at least one of: monitor for faults, possible stuck drill tubular, monitor for drilling fluid losses, and ensure borehole cleaning if the received orientations of the first and second breakouts rotate with increasing borehole depth and there is no drilling direction change.

11. The method according to claim 4, further comprising determining a width of the first and second breakouts from the borehole image using the method for detecting breakouts implemented by the processor.

12. The method according to claim 11, further comprising determining that a widest of the determined widths of the first and second breakouts is within a first range of breakout widths and the alert further comprises large breakout observed and the advice further comprises at least one of: ensure borehole cleaning, increase downhole annular pressure, and consider a drilling fluid change.

13. The method according to claim 12, wherein the first range of breakout widths is 75 to 90 degrees. age.

14. The method according to claim 12, further comprising determining that the widest of the determined widths of the first and second breakouts is outside of the first range of breakout widths and in a second range of breakout widths, and the alert further comprises very large breakout observed and the advice further comprises pull out of borehole.

15. An apparatus for generating an alert or advice for drilling a borehole penetrating an earth formation, the apparatus comprising:
a downhole tool disposed at a drill tubular drilling the borehole; and
a processor configured to: (i) receive a borehole image from the downhole tool disposed at the drill tubular drilling the borehole; (ii) detect a first breakout and a second breakout shifted approximately 180° apart from the first breakout if breakouts are in the borehole image using a method for detecting breakouts implemented by the processor; (iii) receiving a drilling fluid pressure for a borehole depth where the borehole image was obtained; (iv) comparing the drilling fluid pressure to a shear-failure gradient in a drilling pressure window; and (v) generate an alert or advice with the processor if the first and second breakouts are detected.

16. The apparatus according to claim 15, further comprising a display device coupled to the processor and configured to display the alert or the advice.

17. The apparatus according to claim 16, wherein the alert comprises a color related to a significance of a drilling condition, the drilling condition being related to a presence or non-presence of breakouts in the borehole image.

18. The apparatus according to claim 17, wherein the downhole tool is configured to sense at least one of gamma ray emission, acoustic impedance, resistivity conductivity, density, or porosity.

19. A non-transitory computer readable medium comprising computer executable instructions for generating an alert or advice for drilling a borehole penetrating an earth formation by implementing a method comprising:
receiving a borehole image from a downhole tool disposed at a drill tubular drilling the borehole;
detecting a first breakout and a second breakout shifted approximately 180° apart from the first breakout if breakouts are in the borehole image;
receiving a drilling fluid pressure for a borehole depth where the borehole image was obtained;
comparing the drilling fluid pressure to a shear-failure gradient in a drilling pressure window; and
generating an alert or advice if the first and second breakouts are detected.