NO20140769A1 - System and method for generating alerts and advice from automatically detected borehole fractures - Google Patents

Abstract

A method for generating an alert or drill bit for cutting a borehole which intersects a base formation comprises the steps of: receiving with a processor a borehole image from a downhole tool positioned on a borehole drilling the borehole; detecting a first fracture and a second fracture offset about 180 ° from the first fracture, if a fracture is present in the image, using a method for detecting fractures performed by the processor; and generate an alert or advice with the processor if the first and second violations are detected.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application takes priority from US application 13/357816 filed Jan. 25, 2012, which is a ClPav the non-provisional US application 13/191,016 filed July 26, 2011, which takes priority from US provisional patent application 61 /394,845 filed on 20 October 2010. The parent applications are incorporated as a reference here in their entirety.

BACKGROUND

1. The scope of the invention

[0002] The present invention generally relates to the drilling of boreholes, and in particular the identification of fractures therein.

2. Description of Related Art

[0003] Boreholes are drilled into the ground for many purposes, such as hydrocarbon production, geothermal production and sequestration of carbon dioxide. A borehole is drilled with a drill bit or a cutting tool placed at the far end of a drill string. A drill rig rotates the drill string and drill bit to cut through the formation rocks and thus drill the borehole.

[0004] Ideally, the drilled borehole is sufficiently smooth without interruptions that can cause instability of the borehole and make further drilling difficult. Lack of borehole stability can result in a reduction in the quality of well logs and thus difficulties in their interpretation. In addition, lack of wellbore stability can cause mechanical problems such as stuck pipe, high torque and back-reaming, which create further problems in casing setting and cuttings removal. One problem is that the drilling process can redistribute stresses in the formation around the borehole and result in instability of the borehole, which can cause parts of a borehole wall to fall out of the formation and cause notches or depressions in the borehole wall. This condition is referred to as a "breakout" or "wellbore break" (breakout). It would be well received within the drilling industry if drilling operators and field engineers could be notified of the occurrence of fractures during the drilling process to prevent further problems during drilling and completion.

SHORT SUMMARY

[0005] A method is described for generating a warning or advice for drilling a borehole that cuts through a basic formation, including: receiving with a processor a borehole image from a downhole tool placed on a drill pipe that drills the borehole; detecting a first break and a second break offset by about 180° from the first break if breaks are present in the image using a break detection method performed by the processor; and generate an alert or advice with the processor if the first and second violations are detected.

[0006] An apparatus for generating a warning or advice for drilling a borehole that cuts through a foundation formation is also described. The apparatus comprises: a processor adapted to: (i) receive a borehole image from a downhole tool mounted on a drill pipe drilling the borehole; (ii) detecting a first break and a second break offset by about 180° from the first break if breaks are present in the image using a break detection method performed by the processor; and (iii) generate an alert or advice with the processor if the first and second violations are detected.

[0007] It further describes a non-volatile computer-readable medium comprising computer-executable instructions for generating a warning or advice for drilling a borehole that intersects a foundation formation by performing a method that includes: receiving a borehole image from a downhole tool mounted on a drill pipe which drills the borehole; detecting a first break and a second break offset about 180° from the first break if breaks are present in the image; and generate an alert or advisory if the first and second violations are detected.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The descriptions that follow are not to be considered limiting in any way. In the attached drawings, similar elements are given similar reference numbers:

[0009] Figure 1 illustrates an example of the embodiment of a downhole imaging tool deployed in a borehole that cuts through the subsoil;

[0010] Figure 2 shows aspects of an image of a borehole that has fractures;

[0011] Figure 3 shows aspects of the processing and analysis of image data to detect the fractures;

[0012] Figure 4 shows aspects of dividing image sectors into angle segments;

[0013] Figure 5 shows aspects of rotation of the angle segments in relation to the breaks;

[0014] Figures 6A and 6B, collectively referred to as Figure 6, show aspects of rotation of angle segments having different angles;

[0015] Figure 7 shows aspects of creating fracture intervals from fractures shown in an image;

[0016] Figure 8 shows aspects of processed and analyzed image data illustrating fracture detection;

[0017] Figure 9 shows aspects of a pressure window for limiting drilling fluid pressure;

[0018] Figure 10 shows aspects of the automatic generation of alerts and advice based on detected borehole breaks;

[0019] Figure 11 shows aspects of one example of execution of alerts and associated advice shown by a display device; and

[0020] Figure 12 is a flow chart illustrating a method for generating a warning or advice for drilling a borehole that intersects a foundation formation.

DETAILED DESCRIPTION

[0021] A detailed description of one or more embodiments of the apparatus and method according to the invention will be given here by way of illustration, and not by way of limitation, with support in the figures.

[0022] Drilling boreholes causes the local rock stresses to redistribute themselves around the borehole. If the load applied by the annulus pressure from the drilling fluid against the borehole wall becomes too small and/or the temperature is increased sufficiently in the formation around the borehole, the redistributed shear stress will exceed the rock strength, whereupon parts of the borehole wall fall out of the formation and form a notch in the borehole wall. These notches are called breaks or outbreaks.

[0023] In many cases, fractures appear in pairs approximately 180° apart on a borehole image. If the local stress around the borehole is anisotropic, so that the principal stresses have different magnitudes, the fractures develop in the direction of the smallest principal stress. The width of each fracture generally varies as a function of rock strength and the magnitude of the redistributed stresses.

[0024] Detection of fractures in images of the borehole wall provides a way to limit the magnitude and orientation of local rock stresses and determine rock strength, which are necessary prerequisites for predicting wellbore stability. Such a function is particularly relevant for long horizontal wells (where the vertical stress significantly exceeds the horizontal stress) and for drilling through unconsolidated sediments. Once fractures are identified, remedial measures can be taken to remove drilling risks. In addition, subsequent calibration of the local rock stresses will increase safety during continuous drilling by updating the pressure window used by drill operators and engineers.

[0025] Techniques are described here for detecting fractures by analyzing an image of a borehole wall that intersects a geological formation generally formed by rocks. The image is generally a data set of measurements of properties of the formation. Variations in the values from the measurements can be plotted to create a picture of the formation. In addition to fracture detection, the techniques include providing an automatic alert to drill operators and engineers if fractures are detected while drilling a borehole. Also in addition to fracture detection, the orientation and width of the detected fractures is provided as an output from the applied technique. In addition to providing the orientation and width of a single fracture at one specific depth position, an average width and orientation, averaged over a depth interval where fractures exist, can also be provided as an output from the applied technique.

[0026] Apart from providing the average width and orientation for a depth interval, the techniques presented here can be applied to a single image row at a particular depth, regardless of the number of sectors (pixel values) contained in the row. In this way, images from different data collection technologies and with different resolutions can be analyzed automatically. Providing the average width and orientation for a depth interval requires a depth-based analysis over more than one image row.

[0027] In one embodiment, the analysis is performed downhole in the downhole tool that acquires the image data. Since the acquired images can include a lot of data and a downhole telemetry system can have limited bandwidth, downhole analysis can make it possible to alert the drill operators and engineers to fractures more quickly than if the analysis was performed at the surface. For high-speed broadband telemetry embodiments, processing and analysis of the image data can also be performed on the surface.

[0028] Figure 1 illustrates an example of the embodiment of a downhole tool 10 placed in a borehole 2 that cuts through the soil 3, which includes a base formation 4. The formation 4 represents any subsoil material of interest that is cut through by the borehole 2. The downhole tool 10 is transported through the borehole 2 by a carrier 5. In the embodiment in Figure 1, the carrier 5 is a drill string 6 which includes a drill bit 7 in an operation referred to as logging-while-drilling (LWD). In one embodiment, the downhole tool 10 is placed in a bottom hole unit (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 out rock chips from the drill hole 2. In another embodiment, the carrier 5 be an armored cable in an operation referred to as cable logging. In cable logging, the cable carries the downhole tool 10 through the borehole 2 and can be a communication medium for communicating data or commands between the tool 10 and a communicator on the surface.

[0029] Still referring to Figure 1, the downhole tool 10 comprises downhole electronics 8 arranged to process data obtained by the downhole tool 10. Processed data can be sent to a data processing system 9 on the surface by means of a telemetry system 13. Non-limiting embodiments of the telemetry system 13 includes pulsed mud, cabled drill pipe having a broadband coaxial cable or a fiber optic cable, acoustic transmission and radio transmission. In one embodiment, the data processing system 9 on the surface is arranged 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 provide an image of the borehole wall as a function of depth is performed by engineering application software, which includes appropriate algorithms. The technical application software can be realized by the downhole electronics 8 and/or the data processing system 9 on the surface.

[0030] The engineering application software performs an automatic analysis of images of the borehole wall to monitor the existence or non-existence of borehole fractures (see Figure 2 for an example of fractures). If a fracture exists, a notification is given to a user in addition to relevant parameters, such as the measured depth of the fracture, fracture orientation and fracture width, which are delivered to a user for further processing and analysis, for example for calibration of local rock stresses or execution of ambient corrections, etc.

[0031] The downhole tool 10 is adapted 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 the circumferential direction around the borehole wall (i.e. radial measurements around the periphery) and at various depths in the borehole 2, generally while the downhole tool 10 is transported through the borehole 2. However, movement of the tool 10 can be stopped while a measurement is being performed.

The measurements are grouped in a data set. Variations in values for the measured property

in the datasets can be displayed as an image. The term "image", as used herein, can thus refer to a visual image or to the data set that can be used to form an image.

[0032] Figure 2, on the left, shows an example of a fracture in an image of the borehole wall. The borehole image is an azimuth/peripheral representation of a physical property of the formation in or near the borehole wall (depending on the penetration depth of a specific data acquisition technology). The value of the physical property at a specific location in the borehole is stored as a pixel value. The image is a graphical color-coded representation of the pixel values where different shades of color represent different pixel values, although it is shown here as a black and white image.

[0033] Fractures (ie expanded borehole in opposite positions) in an image become visible as a result of an increased distance between a sensor in the downhole tool 10 which measures the physical property and the borehole wall. If the distance becomes too great, the sensor is no longer able to determine the physical properties of the rock.

[0034] On the left side of Figure 2, the dark or shaded areas are the observed borehole fractures, while light areas represent intact formation rock. As indicated above, the fractures occur in pairs in most depth intervals, approximately 180 degrees apart.

[0035] Figure 2 shows on the right an example of normalized pixel values for one row in the image. Fracture in Figure 2 is represented by pixel value one (y-axis). In the image shown, each row of the image contains 120 sectors, i.e. 120 pixels, one pixel value for each sector (x-axis).

[0036] The techniques described herein present an algorithm for performing automatic analysis of borehole wall images to monitor the existence or non-existence of borehole fractures. If fractures are present, relevant parameters (fracture orientation and fracture width) are supplied for further processing and analysis, for example for calibrating the local rock stresses.

[0037] Figure 3 illustrates one example of a workflow for the technical application software. Presence or absence of fractures can be verified from images of the borehole wall. A prerequisite for the presented algorithm is therefore automatic monitoring of the borehole wall through the acquisition of images (process 31, Figure 3). For this workflow, any technology can be used to acquire images with any resolution, which of course affects the accuracy of the fracture analysis.

[0038] Figure 4 defines the terminology used to describe an algorithm, presented below, which is used for automatic detection of breaks. The lower figure shows a top view of a single row of pixels in a circle forming the image. The image sectors are represented by the dashed line (also shown as a straight line in the upper figure). Each dash represents one sector, to which one pixel value in the image is assigned. Paired breaks are highlighted as circle segments 40, 180 degrees apart. The fracture width (see also figure 2) is defined as the angle of each of the circle parts 40 where the fracture exists. Segments are defined as pieces or sectors of the circle, which are labeled as segments l-IV. The opening angles of the segments l-IV are denoted as angles a and (3, and the sum of the angle segments (2a + 2(3) in the circle is 360 degrees. Alternatively, the opening angles of the segments l-IV can all be slightly different from each other , as long as the sum of them is 360 degrees.

[0039] An algorithm will be described for the automatic detection of such paired breaks. The algorithm can be applied to any image, regardless of the technology used to acquire the image. Furthermore, the algorithm analyzes only one row of images at a given depth, regardless of the existence of breaks above the considered depth (ie analysis of only one row in Figure 2). This set-up means that the algorithm can be used with an implementation in firmware in the downhole tool 10. Such an implementation enables automatic monitoring of the borehole's status (i.e. break or no break) and automatic generation of alerts when breaks are detected. Compared to image analysis on the surface, where high-resolution image data must be transmitted via the telemetry system 13, this algorithm drastically reduces the amount of information that must be sent to the surface.

[0040] The algorithm includes the following steps, referring to Figures 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 in the image represent the resistivity of the borehole wall in the formation, the filter can be applied to the logarithm of the pixel values. Otherwise, the filter can be applied to the pixel values themselves. Filtering can also be applied automatically to the image, depending on the image quality. Image quality can be quantified by a statistical parameter, such as kurtosis. Step 2 - Divide the image row into four segments l-IV, including the angles a, (3. The angles diagonally opposite to each other are equal, and the sum of all the angles is 360 degrees. Step 3 - Depending on the subsequent methods used, normalize (and optionally invert) the pixel values between the largest and smallest pixel value. Inversion should be performed when the breaks are represented by low pixel values, compared to the places where there are no breaks. If breaks are represented by high pixel values in the image, inversion should not be applied. Step 4 - Starting with equal opening angles for the segments, a=[3=90 degrees, calculate the average of the physical property for each of the four segments l-IV. Different types of averages can be calculated, including harmonic, arithmetic, geometric, etc. averages. Step 5 - Stack ( stack) the averages of opposite segments, i.e. stack the average from segments I and III, and II and IV. Different methods can be used for stacking. Step 6 - Rotate the relative position between the image and the four segments (Figure 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 (for equal angles a=|3=90 degrees between the segments) or 180 degrees (for different angles ctf (3), find largest or smallest stack, depending on the methods used for normalization and inversion. Also find the angle of rotation at which the largest/smallest (ie largest or smallest) stack was found. Largest/smallest stack is found at the position of the break. Step 8 - Change the angles between the segments (Figures 6A and 6B) with a small amount (for example with one sector), so that a* (3, and repeat steps 1-6. However, repeat steps 2-7 until the relative position between the image and the segments becomes 180 degrees. Step 9 - Among all combinations of rotation (step 6) and angle changes (step 8), find the orientation and angle between the segments at which the stacks have a maximum/minimum.For the combination that produces the largest/smallest stack, the orientation of the segments defines the fracture positions around the boreholes, and the angle between se gments determine the width of the fractures (figure 5). Steps 6-8 can be performed in reverse order, i.e. first changing the angles between the segments and then rotating the image. Step 10 - If several breaks were detected in several image rows, these breaks are collected into a break interval as illustrated in Figure 7. If depth information is available, the break interval's position is assigned to the interval. Among other things, attributes such as a start depth, an end depth, a center depth, the lithology of the fracture interval where the fracture cluster is located, how long it has been since the depth at the fracture interval was drilled and the pressure range in the fracture interval are assigned to the fracture interval. Step 11 - If a fracture interval is identified, an average width and orientation is calculated from the widths and orientations of each fracture within this fracture interval, as illustrated in Figure 7. Different averaging methods can be used. In particular, one alternative is to use a weighted averaging function, which weights the fracture widths and orientations of each fracture by the stacking value. Step 12 - Assign an uncertainty to the parameters - width and orientation - of the fracture intervals, for example through statistical analysis of the widths and orientations of the fractures within each interval.

[0041] Among other things, 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 Figure 4.

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

Normalization method 2 - Normalize each pixel value according to (min/max) minimum/maximum values and invert:

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

Normalization Method 4 - Normalize each pixel value according to minimum/maximum values, then take the logarithm (logio):

Normalization Method 5 - Normalize each pixel value according to min/max values and then square:

[0042] Among other things, the following methods can be used for averaging normalized pixel values for each of the four segments as shown in Figure 4.

Averaging method 1 - Average the normalized pixel values for each of the 4 segments:

Averaging method 2 - Average the logarithms of the normalized pixel values for each of the 4 segments:

[0043] Among other things, the following methods can be used for stacking the average of the normalized pixel values from opposite segments as shown in Figure 4.

Stacking method 1 - Stack average (of) from opposite segments, subtract the stacks and take the absolute value:

Stacking method 2 - Stack average (off) from opposite segments, divide the two resulting stacks and find the minimum (this method is only applicable to normalization methods 2 and 3):

Stacking method 3 - Stack average (of) from opposite segments and find minimum (only applicable for normalization methods 1, 4 and 5):

Stacking method 4 - Stack average (off) from opposite segments and find maximum (only applicable for normalization methods 2 and 3):

Stacking method 5 - Stack averages from opposite segments, divide the two resulting stacks and find the minimum (applicable to normalization methods 1, 4 and 5):

[0044] Figure 8 shows the result of the automatic identification of borehole fractures using normalization method 3, averaging method 1 and stacking method 1 for a varying angle between the segments. The track on the far left shows the image with the borehole fractures and the orientation of the fractures (dots 70) on top of the image. The dots 71 show the average orientation of the two identified fracture zones. The second trace from the left shows the break intervals and widths of each break (dots 72), and average width for each break interval (dots 73). The third trace from the left shows the maximum from the stacking routine. A violation is identified when the maximum exceeds the threshold value of 0.8. which is an empirically determined value in one embodiment. The right trace shows the kurtosis for each image row. Kurtosis is one statistical parameter that can be used to automatically apply filtering/smoothing (step 1) when the kurtosis exceeds a predefined threshold.

[0045] Once a violation has been detected, different levels of alerts may be provided, depending on the design of the algorithm (process 33 in Figure 3). Level 1: an alert may be generated informing a user that a violation has been detected (no parameters are provided). Such an alert could be a trigger to change the telemetry setup to transmit higher resolution slides for more detailed analysis. If a fracture orientation is also provided (level 2 in process 33, Figure 3), subsequent fractures are monitored (stored or recorded) until a fracture zone (a depth interval) can be identified (process 34, Figure 3). The orientation of the fracture zone can then be used to calibrate the orientation of the local rock stresses. Level 3 triggers monitoring of subsequent alerts (process 35, Figure 3). If a fracture zone is identified, the pressure and temperature range that existed during the time period the zone was drilled must be determined (process 36, Figure 3) for use in calibrating the local rock stresses. Additionally, different levels of alerts can be generated based on the size of the detected breaches. Sizes for different breaches can be compared with different thresholds corresponding to the different warning levels. In one or more embodiments, three alert levels may be provided to an operator - no importance (continue drilling), minor importance (caution), and high importance (severe event expected). These are only examples, and the person skilled in the art can generate other alerts and alarms corresponding to equipment, methods and parameters of interest by applying the techniques explained here.

[0046] The automatic generation of alerts in addition to downhole analysis of image data includes monitoring of drilling status (either downhole by the tool 10 or on the surface by the surface data processing system 8 when a detected fracture is sent). Drilling status can include pressure and temperature at the detected fracture.

[0047] In addition to the features illustrated in Figure 3, the technical application system also provides the following applications for handling operational guidelines.

[0048] A first application is provided to deliver the geometry of the borehole (inclination, azimuth, degree of curvature (dogleg severity) and others), to avoid analysis of asymmetric images (images where one fracture is less pronounced than its counterpart) . In addition, the first application is able to predict whether formation layers are penetrated perpendicularly or at an angle. For the case where the borehole penetrates the formation layers at an oblique angle, a second application is provided which is able to perform de-sloping in the image, to avoid alerts due to sloping layers, but not fractures.

[0049] A third application is provided which is capable of delivering drilling status. This application can control the activation of the automatic image analysis, to prevent analysis of images acquired while not drilling or relogging.

[0050] A fourth application is provided to provide information related to the detection of the fractures for the calibration of a pressure window 91, which is represented in Figure 9. The pressure window is a variation range of drilling fluid pressure that has an upper limit (fracture gradient) and two lower limits (shear failure gradient or pore pressure gradient), where the drilling fluid pressure is limited between the upper limit and the higher of the two lower limits as illustrated in Figure 9. The shear failure gradient can be limited by the fracture information and other drilling parameters related to the fracture. Synonyms for shear failure gradient are collapse gradient or collapse pressure.

[0051] The techniques described here have the advantage that they are robust in such a way that only significant, clearly visible breaches are detected, so that false alerts are avoided. In addition, the method only alerts when breaks appear as a pair, approximately 180 degrees offset. This last advantage prevents false detection of wear grooves (key seating).

[0052] As indicated above, different levels or types of alerts can be generated automatically. The alerts may be generated automatically by the technical application software. These notifications relate to the detection and/or quantification of borehole ruptures by the technical application software mentioned above. The alerts may also include the condition that no breach has been detected by the technical application software. In addition, the notifications can be linked to whether a detected breach, a size of a breach or an orientation of a breach was expected or not. As soon as the alert is generated, it can be shown to a drilling operator or other user. In one or more embodiments, the notification is presented as a description of events occurring downhole related to breaches, if detected, and whether the events are expected or not. In one or more embodiments, the alert may be presented as a "traffic light" with colors, such as green, yellow, and red, representing the severity of the downhole failure condition. In addition to or instead of automatically generating alerts, the engineering application software may also automatically generate advice to the drill operator or other user based on downhole conditions or events related to detected fractures. The council concerns proposals for drilling the borehole safely and efficiently.

[0053] Figure 10 shows aspects of the automatic generation of alerts and advice based on detected borehole breaches. The technical application software 90, which may include input from one or more modules for automatically generating the alerts and advice, may be realized by the downhole electronics 8, the data processing system 9 or a combination thereof. The alerts and advice may be presented to the drilling operator or user by a display device 94. The display device 94 may be located on or remote from a drilling rig that is drilling the borehole. The technical application software 90, when it detects and/or quantifies a fracture pair downhole from a borehole image of known depth or position, can use the one or more warning and advice generation modules. To determine whether the detected fractures are expected or not, the pressure window 91, a geomechanical model 92 of the formation 4 intersected or penetrated by the borehole 2 and/or measured formation and borehole parameters 93 can be fed into the engineering application software 90. The technical application software 90 may be able to provide some alerts and associated advice on its own. For example, the geomechanical model 92 may be unavailable when drilling a first exploratory hole in a completely new area. In this case, the software 90 can independently detect and quantify violations and provide associated alerts and advice. However, other alerts, such as whether or not a break condition is expected, may require the use of modules 91, 92 and/or 93.

[0054] The pressure window 91 is a software package or module that includes a range of variation of drilling fluid pressure having a fracture gradient as an upper limit and shear failure gradient (or collapse pressure) and pore pressure gradient as two lower limits. In general, the annulus pressure downhole (as a result of drilling fluid) is tried to be kept within the pressure range in the pressure window 91. By inputting the annulus pressure for the depth where the borehole image was obtained to the technical application software 90, the software 90 will be able to determine whether a detected fracture pair on this the depth was expected or not. If, for example, a fracture was detected and the annulus pressure was lower than the shear failure gradient, the fracture was expected. If a fracture was detected and the annulus pressure was higher than the shear failure gradient, the fracture was not expected since the annulus pressure always exceeds the predicted collapse pressure.

[0055] The geomechanical model 92 includes at least some of the following parameters or values regarding the formation 4 and the borehole 2: a local stress tensor for the ground containing the magnitude of the three main stresses or orthogonal stresses and an orientation of this stress tensor; formation pore pressure, including to calculate effective stresses by subtracting the formation pore pressure from the absolute stresses; orientation of the borehole relative to the local stress tensor or relative to another reference system so that the relative orientation between the stress tensor and the borehole trajectory can be calculated;

the size and/or diameter of the borehole;

predicted and/or measured attributes such as temperature, pressure, chemical composition in the formation and drilling fluid, and additives in the drilling fluid;

a partial model that describes the compressive strength of the formation rock under local conditions and/or surface conditions; and

a partial model that describes the deformation behavior of the formation rock under stress (e.g. linear elastic, non-linear elastic, poroelastic, plastic).

[0056] From the local rock stress tensor, the geomechanical model 92 can calculate the redistributed stresses around the borehole as a result of the borehole being drilled and compare the redistributed stresses (specified in pressure units) against the compressive strength of the formation rock (also specified in pressure units). If the stresses exceed the strength of the formation rock, the borehole may collapse and create the fractures. The circumferential extent over which the redistributed stresses exceed the strength of the formation rock determines the width of the fracture. The orientation of the fracture depends on the orientation of the local rock stresses and how they are distributed around the borehole. The technical application software 90, using the geomechanical model 92, can thus predict the expected width and the expected orientation of fractures for given annulus pressure and/or temperature conditions downhole. Generally, the annulus pressure (ie, pressure in borehole fluid) in the borehole at the depth where the borehole image was acquired is fed into the geomechanical model 92 to determine whether or not fractures are expected and, if expected, their width. For the annulus pressure and/or temperature conditions downhole, the expected width and the expected orientation of the fracture can then be compared with the detected width and the detected orientation of the fracture. If they match, the geomechanical model 92 is validated. If they do not match, an alert can be generated indicating the discrepancy and advice can be generated to recalibrate or update the relevant parts of the geomechanical model 92. If, for example, fractures are detected but not expected, the geomechanical model 92 must be updated. If the detected fracture widths are greater than or less than the expected widths, the model for the local rock stresses and/or the model for the strength of the formation rock must be updated. If the detected orientation of the fractures does not match the expected orientation of the fractures, the orientations of the redistributed stresses must be updated. The geometric model 92 can be obtained from formation and borehole measurements performed at the same time as measurements for the borehole images are performed. Alternatively or in combination, the formation and borehole measurements for the geomechanical model can be carried out in nearby boreholes that intersect the same formation and/or obtained from seismic measurements from the surface. In addition, formation samples can also be obtained from the nearby boreholes for laboratory analysis to determine formation lithologies and relevant mechanical rock properties.

[0057] The measured formation and borehole parameters 93 are fed into the technical application software 90, the pressure window 91 and/or the geomechanical model 92. The measured parameters 93 include the most recently measured parameters that can replace previously assumed parameters. Non-limiting embodiments of the measured parameters 93 include: annulus pressure or drilling fluid pressure at various borehole depths where the borehole images were acquired, for example sensed by a pressure sensor (not shown) placed in the downhole unit 12; borehole temperature at different borehole depths where the borehole images were obtained, for example sensed by a temperature sensor (not shown) placed in the bottom hole unit 12; borehole gauge measurements; measurements of formation pore pressure obtained by a formation tester placed on the downhole unit in the vicinity of the downhole tool 10 so that the pore pressure is representative of the formation where the borehole images were obtained; in addition, the pore pressure from the formation tests can be used as a measurement against which a pore pressure in the model 91/92 can be calibrated; and borehole trajectory as inclination (from the vertical) and azimuth found using a borehole trajectory determination system. Generally, the system for determining borehole trajectory includes a combination of downhole tools or sensors, capable of measuring the orientation or direction of the downhole unit relative to north (magnetic or geographic, either of which can be converted to the other), which provides the azimuth direction relative to the vertical (which gives the slope).

[0058] In addition to determining the widths of the detected breaches, the technical application software 90 may also categorize the widths to provide the alerts and advisories. In one or more vertical borehole embodiments, the widths may be categorized as small, large, or extra large, where small fractures have widths less than 75 degrees, large fractures have widths between 75 to 90 degrees, and extra large fractures have widths greater than 90 degrees. In one or more embodiments of horizontal boreholes, small fractures have widths less than 20 degrees, large fractures have widths between 20 and 30 degrees and extra large fractures have widths greater than 30 degrees. Normally, a borehole with an inclination of 15 degrees or less can be considered vertical. For other slopes, the categories can be interpolated between the two extremes (vertical and horizontal). It will be understood that a geomechanical engineer at the time of drilling may propose other criteria based on local environmental conditions. For example, a very thick mud cake or excellent hole cleaning practices may strengthen the borehole and with it require an increase of the general values listed above.

[0059] Figure 11 shows aspects of one example of execution of warnings and associated advice shown by the display device 94. Also shown in Figure 11 is a "traffic light" arranged to display green, yellow and red colors to indicate general warning levels in increasing severity. If no breaks have been observed, the green light is displayed with advice to continue drilling.

[0060] If a breach is observed, the associated advice includes monitoring rig parameters derived from both surface and downhole parameters, such as hydraulic parameters, drilling dynamics (eg vibrations), bit pressure, drill pipe torque and drill pipe drag. If the violation is quantified as minor, the yellow traffic light is displayed. The yellow traffic light is also shown if a small violation was expected, but did not occur. In this case, the advice includes recalibrating the shear failure gradient. In addition, the yellow traffic light is displayed if observed and expected break orientations coincide or do not coincide. If they do not coincide, the advice includes recalibrating the shear failure gradient. Furthermore, the yellow traffic light is displayed if the detected fracture orientation coincides with a change in drilling direction. In this case, the advice includes: monitor for erosion, for example in percentage, size or shape; a warning that fracture extensions due to drill string dynamics are possible; ensure borehole cleaning; and/or a warning that wedging of drill pipe is possible as a result of wear grooves.

[0061] If large or extra large breaks are detected, the red traffic light is displayed. The red traffic light is also displayed if rotating fracture orientations are detected without a change in drilling direction. Advice for this scenario includes monitoring for faults, a warning that drill pipe wedging is possible, monitoring for loss of drilling fluid and ensuring borehole cleaning. If a large fracture is detected but not expected, or if a detected fracture width is greater than expected, the red traffic light is displayed and the advice includes recalibrating the shear failure gradient, ensuring borehole cleaning, increasing annulus pressure downhole and/or considering changes in drilling fluid.

[0062] If a very large fracture is observed, the associated advice includes ensuring borehole cleaning, increasing annulus pressure downhole, assessing mud change and/or pulling out of the borehole.

[0063] Superscript 1 in Figure 11 relates to alarms and advisories that can be generated solely from the automatic breach detection algorithm (ie the technical application software 90) such as: breach present / not present (time / depth); fracture is oriented in... direction (time / depth); break has... width (time / depth); and/or fracture intervals (deep). Raised index 2 in figure 11 relates to possible alarms that can be generated from the automatic fracture detection algorithm in combination with a pressure window model (e.g. inputs: image data and shear failure gradient) such as: existence / non-existence of fractures and whether expected or not; detected and expected fracture orientation coincide or do not coincide; and/or detected and expected fracture width coincide or do not coincide. Superscript 3 in Figure 11 relates to possible alarms that can be generated from the automatic fracture detection algorithm if additional formation evaluation and drilling data are available (e.g. inputs: image data, slope, azimuth, borehole kink, gamma radiation data, formation lithology) such as: fracture orientation coincides with change in drilling direction and/or fractures in different lithologies.

[0064] It will be understood that the notifications and advice can be presented in different ways. In one or more embodiments, only the current warning, traffic lights and associated advice are displayed. Alternatively, in one or more embodiments, all of the possible alerts and advisories may be displayed together and the applicable alert and associated advisories are highlighted or flashed. In addition to visual display, a warning and associated advice can be presented acoustically. A voice recording can be used to actually say what the warning and advice is or a sound can alert the drilling operator to take a look at the display device 94.

[0065] Figure 12 is a flowchart illustrating a method 110 for generating a warning or advice for drilling a borehole that intersects a bedrock formation. Step 111 includes receiving with a processor a borehole image from a downhole tool positioned on a drill pipe drilling the borehole. Step 112 includes detecting a first break and a second break offset by approximately 180° from the first break, if breaks are present in the image, using a break detection method performed by the processor. Step 113 includes: generating an alert or advice with the processor if the first and second violations are detected. The method 110 may also include sending out a notification indicating that no breach has been detected with an associated advice to continue drilling. The method 110 may also include determining whether or not a fracture, a fracture width, or a fracture orientation is expected and generating associated alerts and advisories.

[0066] In support of the ideas here, different analysis components can be used, including a digital and/or an analog system. For example, the downhole electronics 8 or data processing system 9 on the surface may include the digital and/or analog system. The system may have components such as a processor, storage media, memory, input, output, communication links (cable-based, wireless, pulsed-slam, optical or other), user interfaces, computer programs, signal processors (digital or analog) and other such components ( such as resistors, capacitors, inductors and the like) to enable use and analysis with the apparatus and methods shown herein in any of several possible ways well known to those skilled in the art. It is believed that these ideas may, but need not, be realized in connection with a set of computer-executable instructions stored on a non-volatile computer-readable medium, including memory (ROM, RAM), optical (CD-ROM), or magnetic (disk storage, hard disks) or any other type, which when executed, cause a computer to perform the method of the present invention. These instructions may provide for equipment activation, management, collection and analysis of data and other functions deemed relevant by a developer, owner or user of the system and other such personnel, in addition to the functions described in this description.

[0067] Furthermore, various other components can be incorporated and used to enable aspects of the ideas 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 unit, antenna, control unit, optical device, electrical device or electromechanical device is incorporated in support of the various aspects discussed here or in support of other functions beyond this description.

[0068] With a "carrier", as the term is used here, is meant any device, device component, combination of devices, media and/or elements that can be used to transport, contain, support or otherwise facilitate the use of other devices, device components, combinations of devices, media and/or elements. Other non-limiting examples of carriers include coiled tubing type drill strings, extension tubing type, and any combination or proportion thereof. Other examples of carriers include casing, cables, cable probes, wireline probes, drop shots, downhole assemblies, drill string inserts, modules, inner casings and portions thereof.

[0069] Elements in the embodiments have been introduced with indefinite singular forms. The singular form is intended to be understood as one or more of the elements. Words such as "include", "comprise" and "have" are intended to be inclusive so that there may be additional elements beyond the specified elements. The conjunction "or", when used with a listing of at least two elements, is intended to mean any one of the elements or any combination of those elements. Numerals such as "first", "second" and "third" are used to separate elements and are not used to indicate a particular order.

[0070] It will be understood that the various components or technologies can enable certain necessary or useful functions or features. Accordingly, these functions and features, which may be necessary in support of the appended claims and variations thereof, shall be understood as naturally incorporated as part of the ideas herein and part of the disclosed invention.

[0071] Although the invention has been described with support in examples of embodiments, it will be understood that various changes can be made and that equivalents can be used instead of elements therein without departing from the scope of the invention. In addition, many modifications will be seen to adapt a given instrument, scenario or material to the ideas in the invention without removing themselves from its framework. It is therefore intended that the invention should not be limited to the specific embodiment described as the expected best way to realize this invention, but that the invention should include all embodiments that fall within the framework of the appended claims.

Claims (20)

1. Method for generating an alert or advice for drilling a borehole intersecting a foundation formation, the method comprising the steps of: receiving, with a processor, a borehole image from a downhole tool positioned on a drill pipe drilling the borehole; detecting a first break and a second break offset by about 180° from the first break, if breaks are present in the image, using a break detection method performed by the processor; and generate an alert or advice with the processor if the first and second violations are detected. 2. Method according to claim 1, comprising the step of generating a warning comprising no fractures observed or an advice comprising continuation of drilling if no fractures are detected in the image by the method for detecting fractures performed by the processor. 3. Method according to claim 2, further comprising the step of receiving, with the processor, a drilling fluid pressure for a borehole depth where the image was acquired, and comparing the drilling fluid pressure with a shear failure gradient in a drilling pressure window, where the warning includes breaks not observed, but expected, and advised further includes recalibration of the shear failure gradient if the drilling fluid pressure is lower than the shear failure gradient. 4. Method according to claim 1, where the warning comprises fracture observer, and the advice comprises monitoring of drilling rig parameters, drilling dynamics, torque on drill pipe and traction force on drill pipe if the first and second fractures are detected. 5. Method according to claim 4, further comprising the step of receiving, with the processor, a drilling fluid pressure for a borehole depth where the image was acquired, and comparing the drilling fluid pressure with a shear failure gradient in a drilling pressure window, wherein the warning includes fractures observed but not expected, and advised further includes recalibration of the shear failure gradient if the drilling fluid pressure is higher than the shear failure gradient. 6. Method according to claim 4, further comprising the step of determining orientations for the first and the second breaks from the image using the method for detecting breaks performed by the processor. 7. Method according to claim 6, further comprising the step of receiving, with the processor, a stress orientation from a formation stress model of the formation for a borehole depth where the image was obtained, wherein the warning comprises that observed and expected fracture orientation coincide, and the advice comprises recalibration of 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 fractures. 8. Method according to claim 6, further comprising the step of receiving, with the processor, a drilling direction. 9. Method according to claim 6, where the warning includes that fracture orientation coincides with a change in drilling direction, and the advice further includes at least one of: monitoring after drilling boreholes, expansion of fractures, securing borehole cleaning and possible wedged drill pipe as a result of wear furrows if a change in the received drilling direction coincides with the orientations of the first and second fractures. 10. Method according to claim 8, where the warning includes rotation of the fracture orientation without a change in drilling direction, and the advice includes at least one of: monitoring for faults, possible wedged drill pipe, monitoring for loss of drilling fluid and ensuring borehole cleaning if the received orientations to the first and the second fracture rotates with increasing borehole depth and there is no change in the drilling direction. 11. Method according to claim 4, further comprising the step of determining a width for the first and the second break from the image using the method for detecting breaks performed by the processor. 12. Method according to claim 11, further comprising the step of determining that a largest of the widths is within a first range of fracture widths, and the warning includes observing large fractures, and the advice includes at least one of: ensuring borehole cleaning, increasing annulus pressure downhole and assessment of changes in drilling fluid. 13. Method according to claim 12, where the first range of fracture widths is 75 to 90 degrees. 14. Method according to claim 12, further comprising the step of determining that the largest of the widths is outside the first range of fracture widths and within a second range of fracture widths, and the warning comprises very large fracture observers, and the advice further comprises pulling out from boreholes. 15. Apparatus for generating an alert or advice for drilling a borehole intersecting a foundation formation, the apparatus comprising: a processor adapted to: (i) receive a borehole image from a downhole tool mounted on a drill pipe drilling the borehole; (ii) detecting a first break and a second break offset by about 180° from the first break, if breaks are present in the image, using a break detection method performed by the processor; and (iii) generate an alert or advice with the processor if the first and second violations are detected. 16. Apparatus according to claim 15, further comprising a device connected to the processor and arranged to display the warning or advice. 17. Apparatus according to claim 16, where the warning comprises a color related to an importance of a drilling condition, where the drilling condition is linked to the existence or non-existence of breaks in the image. 18. Apparatus according to claim 15, further comprising the downhole tool. 19. Apparatus according to claim 17, wherein the downhole tool is arranged to sense at least one of: gamma ray release or emission, acoustic impedance, resistivity, conductivity, density or porosity. 20. Non-volatile computer-readable medium comprising computer-executable instructions for generating a warning or advice for drilling a borehole intersecting a bedrock formation by performing a method comprising the steps of: receiving a borehole image from a downhole tool positioned on a drill pipe that drills the borehole; detecting a first break and a second break offset about 180° from the first break, if breaks are present in the image; and generate an alert or advice if the first and second violations are detected.