Abstract:
A method of analyzing a core sample from a wellbore by creating a visual composite image of the core sample that is based on a scan of the core sample. The scan directs radiation at the core sample, such as a computerized tomography (CT) scan, and obtains scan data by estimating radiation absorbed by material in the core sample. The composite image is made up of an arrangement of voxels, where each voxel represents a designated volume of the core sample, and is are assigned a value that corresponds to a measured value of radiation absorbed in the designated volume of the core sample.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of Invention 
         [0002]    The present disclosure relates in general to a method and system for analyzing a core sample from a wellbore. More specifically, the present disclosure relates to a method and system for evaluating a core sample from a wellbore with computed tomography. 
         [0003]    2. Description of Prior Art 
         [0004]    Various techniques are currently in use for identifying the presence of hydrocarbons in subterranean formations. Some techniques employ devices that emit a signal from a seismic source, and receive reflections of the signal on surface. Others involve disposing logging devices downhole in a wellbore intersecting the subterranean formation, and interrogating the formation from within the wellbore. Example downhole exploration devices include seismic tools that can transmit and receive seismic signals, or ones that simply receive a seismic signal generated at surface. Other devices collect and sample fluid from within the formation, or from within the wellbore. Nuclear tools are also employed that direct radiation into the formation, and receive radiation that scatters from the formation. Analyzing the scattered radiation can provide information about fluids residing in the formation adjacent the wellbore, the type of fluid, and information about other materials next to the wellbore, such as gravel pack. 
         [0005]    Logging downhole also is sometimes done while the wellbore itself is being drilled. The logging devices are usually either integral with a drill bit used during drilling, or on a drill string that rotates the drill bit. The logging devices typically are either nuclear, seismic, can in some instances optical devices. In some instances, a core is taken from the wellbore and analyzed after being retrieved to the surface. Analyzing the core generally provides information about the porosity and/or permeability of the rock formation adjacent the wellbore. Cores are generally elongated cylindrical members and obtained with a coring tool having an open barrel for receiving and retaining the core sample. 
       SUMMARY OF THE INVENTION 
       [0006]    Disclosed herein is an example of a method of analyzing a core sample by obtaining information about characteristics of the core sample at discrete locations in the core sample, comparing the characteristics with one another, identifying a zone of interest in the core sample based on the step of comparing the characteristics with one another, and analyzing the zone of interest in the core sample. The step of obtaining information about characteristics of the core sample can include scanning the core sample with radiation, monitoring radiation scattered from the core sample, and estimating the amount of radiation absorbed in volumetric spaces of the core sample. The method can further include forming an image of the core sample that spatially represents characteristics of the core sample. In this example, the image has voxels that are strategically located to represent corresponding volumetric spaces of the core sample. Further, the voxels may be assigned a designated value to represent the corresponding characteristics of the volumetric space of the core sample. In an alternative, the designated value is an alpha-numeric attribute. The image can be segments that are coaxially arranged and that represent axial slices of the core sample, and wherein the step of identifying a zone of interest involves identifying changes in characteristics of the core sample represented by multiple segments. In this example, the multiple segments are adjacent one another. The step of comparing the characteristics with one another may include estimating an average value of a one of the characteristics. The zone of interest in the core sample can be identified where there is a change of a characteristic of the material in the core sample. Optionally, the step of analyzing the zone of interest in the core sample includes obtaining a plug from the core sample and scanning the plug with an amount of radiation that exceeds an amount of radiation that scanned the sample plug. 
         [0007]    Also disclosed herein is an example of a method of analyzing a core sample that includes measuring a value of radiation absorption at discrete volumetric spaces in the core sample, estimating a physical characteristic of the core sample at each of the discrete volumetric spaces based on the step of measuring the radiation absorption, identifying differences between physical characteristics of proximate discrete volumetric spaces, designating a zone of interest in the core sample to be where the differences between physical characteristics of proximate discrete volumetric spaces exceed a threshold value, and analyzing the zone of interest in the core sample. Voxels may be created that are assigned a location that correlates to the discrete volumetric spaces, and which are assigned a value that represents the physical characteristics of the corresponding discrete volumetric spaces. The method can further include forming a visual image based on the voxels. The method can further include obtaining plugs from the zone of interest. The plugs may be scanned with a computerized tomography scan, or optionally can be analyzed with a spectroscopy. One alternative involves further designating a multiplicity of zones of interest in the core sample and analyzing the zones of interest. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0008]    Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which: 
           [0009]      FIG. 1  is a plan partial sectional view of an example of a system for analyzing a core sample. 
           [0010]      FIG. 2  is an overhead view of an example of a cabinet for housing a scanning unit for a core sample. 
           [0011]      FIG. 3  is an axial sectional view of the cabinet of  FIG. 2  and taken along lines  3 - 3 . 
           [0012]      FIG. 4  is a perspective view of the cabinet of  FIG. 2 . 
           [0013]      FIG. 5  is a perspective view of an example of scanning the core sample of  FIG. 1 . 
           [0014]      FIG. 6  is an example of a composite image formed from the step of scanning of  FIG. 5 . 
           [0015]      FIGS. 7A-7D  are axial views of segments of the composite image of  FIG. 6 . 
       
    
    
       [0016]    While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims. 
       DETAILED DESCRIPTION OF INVENTION 
       [0017]    The method and system of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The method and system of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout. In an embodiment, usage of the term “about” includes +/−5% of the cited magnitude. In an embodiment, usage of the term “substantially” includes +/−5% of the cited magnitude. 
         [0018]    It is to be further understood that the scope of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. 
         [0019]    Shown in a plan partial sectional view in  FIG. 1  is one example of a core analysis system  10 , which includes first, second and third mobile enclosures. In the example of  FIG. 1 , the first mobile enclosure is a scan trailer  12 , the second mobile enclosure is a handling trailer  14 , and the third mobile enclosure is an analysis trailer  16 . In one example, each of the enclosures may be part of a tractor trailer and which are movable by a tractor trailer. Schematically illustrated in the scan trailer  12  is a scan system  18 , and substantially all of which is housed within a cabinet  19 . In the illustrated example, cabinet  19  is specially designed to shield any radiation within, generated, inherent, or otherwise, from making its way to outside of the cabinet  19 . Thus, cabinet  19  is in compliance with 21 C.F.R. 1020.40. Further shown in cabinet  19  is a scan source  20 , which in one embodiment includes a device for emitting radiation, such as but not limited to an X-ray. A scan receiver  22  is also shown provided within cabinet  19  and combined with scan source  20 , in one example, forms a computerized topography (CT) scanner. 
         [0020]    An elongate and cylindrical core sample  24  is shown axially inserted within scan system  18 . Core sample  24  is disposed into scan system  18  through a loading assembly  26 , which is shown coupled to one end of the scan system  18  and projecting through an opening in a side wall of handling trailer  14 . In an example, core sample  24  is taken from a subterranean formation below system  10 , and is retrieved via a wellbore  27  shown adjacent system  10 . Thus the wellbore  27  intersects the subterranean formation. Embodiments exist where the system  10  is “onsite” in the field and where the distance between the wellbore  27  to system  10  can range from less than one hundred yards up to five miles, and any distance between. Accordingly, real time analysis while drilling the wellbore  27  can take place within the system  10 . Feedback from the analysis can be used by the drilling operator to make adjustments or changes to the drilling operation. 
         [0021]    A hatch assembly  28  is schematically illustrated which provides the coupling interface between trailers  12 ,  14  and includes sealing around the loading assembly  26 . While in scan system  18 , core sample  24  rests on a core carrier  30 . Core carrier  30  is part of a manipulator system  31 , which further includes a manipulator arm  32  that telescopingly moves along a manipulator base  34 . As shown, an end of manipulator arm  32  distal from manipulator base  34  couples onto an end of core carrier  30 , so that core carrier is basically cantilevered on an end of the manipulator arm  32 . Manipulator arm  32  is shown in an extended position over manipulator base  34 . Manipulator arm  32  axially moves with respect to manipulator base  34  via a motor  36  shown having a shaft  38  that couples to manipulator arm  32 . In one example, motor  36  is a linear direct current motor. A gear (not shown) on an end of shaft  38  distal from motor  36  engages a gear rack  40  that is provided on manipulator arm  32 . Accordingly, selectively operating motor  36  urges manipulator arm  32 , core carrier  30  and core sample  24  in an axial direction with respect to scan source  20 . Moving manipulator arm  32  into a refracted position onto manipulator base  34  positions the entire length of core sample  24  in scan system  18 , so that all of core sample  24  may be analyzed by the scan system  18 . In one example, the scan source  20  and scan receiver  22  orbit around the core sample  24  and so that when in combination of axial movement of core sample  24  within system  18 , a scan is taken of core sample  24 . Further optionally, motor  36 , or additional motors not shown, may manipulate and selectively move manipulator arm vertically and/or laterally to thereby better position core sample  24  into a designated orientation and/or spatial position during the scanning process. 
         [0022]    Further shown in  FIG. 1  are a series of work surfaces  42  provided within handling trailer  14 . In one example of operation, before or after core sample  24  is scanned, it may be broken into sections for further analysis and analyzed on surfaces  42 . Examples of the surfaces  42  include a crusher, sample divider, and mortar grinder. Additional analysis may take place within analysis trailer  16 . Schematically illustrated within analysis trailer  16  is a nanotom  44 , which can include a scanning system for scanning the internals of core sample  24 , or parts of the core sample. Further shown in the analysis trailer  16  is a laser induced spectroscope  46 , a Raman spectroscope  48 , and near infrared spectroscope  49 . 
         [0023]    Referring now to  FIG. 2 , shown in an overhead view is an example of the scan system  18  and an upper surface of cabinet  19 . Further illustrated in this example is a conditioning vent  50  on an upper end of the cabinet  19 , where conditioning vent  50  provides a path for airflow and that is used in conditioning the inside of the cabinet  19 . An advantage of the conditioning vent  50  is that conditioned air at proper temperature and humidity may be injected into the inside of cabinet  19  so that the sensitive device is housed within the cabinet  19  may be maintained in proper operating conditions to ensure normal operating functionality. A power distribution panel  52  is shown provided at an aft end of cabinet  19 , and which includes buses (not shown) and other devices for distributing power through cabinet  19  into scan system  18 . A control panel  54  is shown adjacent power distribution panel  52  and includes hardware and software for managing control of the operation of the systems house within cabinet  19 . Projecting outward past the forward end of cabinet  19  is the loading assembly  26  in an open configuration. In the illustrated example, the loading assembly  26  includes a loading cover  56  and loading basin  58 , where the loading cover  56  is shown swung open from a loading basin  58 . As shown the core sample  24  has been inserted into open loading assembly  26  and onto the core carrier  30 . As will be described in more detail below, safety features are included with the system that prevent operation of the manipulator system  31  when the loading assembly  26  is in the open position of  FIG. 2 . 
         [0024]      FIG. 3  shows an example of the cabinet  19  in a sectional view and taken along lines  3 - 3  of  FIG. 2 . This view which is taken along the axial portion of manipulator system  31  shows one example of a wiring track  60 ; which has cross members for organizing the control and power wires needed for use in the scan system  18  and as the manipulator arm  32  axially moves with respect to manipulator base  34 . Wiring track  60  maintains the wires in a designated location and position with use of wiring track  60  during operation of the manipulator system  31 . Further in the example of  FIG. 3  is a shroud  62  shown mounted on an upper end of manipulator system  31  and which covers a portion of the upper end and shields components within the manipulator system  31 . Manipulator base  34  (and thus manipulator arm  32 ) is supported on a vertical mounting pedestal  64 , which has a generally rectangular cross section along its axis, and has a lower end mounted on the floor of cabinet  19 . Shown housed within shroud  62  is a wiring bus  66  which extends axially along the manipulator assembly. 
         [0025]      FIG. 4  provides in perspective view of one example of the cabinet  19  and having hinged panel  68  along its outer surface. As indicated above, the structure of cabinet  19  is in compliant with 21 C.F.R. 1020.40. Thus proper protective shielding is provided in the panel  68  and along the hinged interface. An additional safety feature is a door assembly  70  which includes a barrier (not shown) that slides axially across the opening shown at the base of the loading assembly  26  and in a forward wall of cabinet  19 . The barrier thus provides a radiation shield from the inside to the outside of cabinet  19 . An interlock connector  72  is shown provided on the loading cover  56  and loading basin  58 . The interlock connectors  72  thus may recognize when the cover  56  is in the open position of  FIG. 4  and in combination with controller  74  may prevent operation of the manipulator assembly. However, the control system associated with the scan system  18  that allows for motion of the manipulator assembly when the cover  56  is in the closed position and interlock connectors are adjacent one another 
         [0026]    Shown in  FIG. 5  are curved supports  76 ,  78  that provide a mounting assembly for scan source  20  and scan receiver  22 . The combination of support  76  and support  78  define a gantry system  80  that when rotated puts the scan source  20  and scan receiver  22  at an orbiting rotation around the core sample  24  and provides the scanning capabilities of the scan system  18 . Curved arrows A R  provide one example direction of rotation of the gantry system  80  for orbiting the scan source  20  and scan receiver  22  around the sample core  24 . Further in this example, the manipulator system  31  ( FIG. 1 ) selectively moves the core sample  24  bi-directionally along axis A Z . As the gantry system  80  orbits the scan source  20  and scan receiver  18  around the axially moving core sample  24 , radiation R is emitted from the scan source  20  into the core sample  24 . Some of the radiation R scatters from the core sample  24  to create scattered radiation R S , which can be received by the scan receiver  22 . 
         [0027]    The scan receiver  22  collects the radiation R and scattered radiation R S  at multiple angular locations about axis A X  of the core sample  24 . In the example illustrated in  FIG. 6 , the data collected by the scan receiver  22  is used to create a composite image  82  that represents the core sample  24 , and that also visually depicts physical characteristics of the core sample  24 . The embodiment of the composite image  82  illustrated substantially replicates the form of the core sample  24  of  FIG. 5 . In an example, the composite image  82  is made up of voxels, where each voxel represents a volume of the core sample  24 , and where each voxel has a characteristic or value that relates back to the volume of the core sample  24  it represents. Embodiments exist where the characteristic or value of the voxel represents a physical characteristic of the volume of the core sample  24  relating to the voxel. In the example of  FIG. 6 , the composite image  82  is made up of a series of disk like segments  84   1 - 84   n  shown coaxially aligned along axis A Zi . In an alternative, each of the segments  84   1 - 84   n  is created by one orbit of the scan source  20  scan receiver  22  around the core sample  24 . Alternatives exist wherein each of the segments  84   1 - 84   n  represents about a 5 mm wide axial slice of the core sample  24 . Portions  86  of the composite image  82  are shaded to reflect different physical characteristics in locations of the core sample  24  that spatially correspond to locations in the composite image  82 . In an example, the image  82  is formed to emulate the core sample  24 . Moreover, optional X-Y-Z axes are provided with both  FIGS. 5 and 6  so that characteristics of a point or region in the core sample  24  can be identified in a point or region of the composite image  82  using corresponding X, Y, Z values, or range of values, from the X-Y-Z axes. 
         [0028]    In an embodiment, the radiation absorption of the material making up the core sample  24  is estimated by the radiation received by the scan receiver  22 . Portions  86  in the example composite image  82  are shaded based on the amount of radiation absorption estimated in corresponding locations in the core sample  24 . For the purposes of simplicity, the composite image  82  is shown to have only shaded and non-shaded areas. However, the image  82  could have a multiplicity of colors to reflect how the core sample  24  has many different segments with varied characteristics. In an example operation, values of radiation absorption measured in discrete spaces in the core sample  24  are compared with radiation absorption values measured in other discrete spaces in the core sample  24 . In one example step of determining which spaces to represent with shading is based on relative values of measured radiation absorption within the core sample  24  rather than comparing measured radiation absorption values with historical data. The step of determining what spaces or voxels to shade can alternatively involve estimating an average value of the radiation absorption measured in the spaces within the core sample  24 , and then shading spaces or voxels in the composite image  82  depending on the value of the radiation absorption in the corresponding space in the core sample  24 . For example, shading can be assigned if the radiation absorption value is above or below the average radiation absorption value, or if the specific radiation absorption value of the space in the core sample  24  is offset a threshold percentage or deviation from the average radiation absorption value. In one alternate embodiment, radiation attenuation of the core sample  24  is measured, which can be one or a combination of radiation absorption, radiation transmission, and radiation scattering. 
         [0029]      FIGS. 7A-7D  are axial views of side surfaces of a series of adjacent segments  84   i - 84   i+3  where the shape and location of the portions  86  of different characteristics may vary between the adjacent segments  84   i - 84   i+3 . As shown in  FIGS. 7A and 7B , the example segments  84   i ,  84   i+1  are substantially non-shaded. As such, it can be deduced that the portions of the core sample  24  represented by segments  84   i - 84   i+1  are substantially homogenous without changes in their material properties. In contrast, segments  84   i+2  and  84   i+3  have portions  86  that are shaded, and where the portions  86  in those adjacent segments  84   i+2  and  84   i+3  have different shapes and locations. In an example it is estimated that the material characteristics changes in the portions of the core sample  24  represented by segments  84   i+2  and  84   i+3 . In an example embodiment, zones of interest  88  ( FIG. 5 ) are identified based on where material characteristics of the core sample  24  are estimated to be changing based on scan data as described above. Optionally, a change in an average value reflected within voxels or other values assigned to locations in a specific segment  84  can identify the presence of a zone of interest  88 . In yet another alternative, a zone of interest  88  is identified when particular values represented in a specific segment  84  are outside of a designated range, or when particular values represented in a specific segment  84  exceed a designated spread. 
         [0030]    Identifying the zones of interest  88  from the scan process described above, and from correlating the spatial reference coordinate systems (i.e. X-Y-Z axes), can pinpoint what portions of the core sample  24  to analyze with further detail. For example, plugs can be extracted from the zone of interest  88  of the core sample  24  for additional analysis, such as in the nanotom  44  or by spectroscopy as described in relation to  FIG. 1  above. An example plug can have a cylindrical shape with a diameter and or length that ranges in the centimeters, and is therefore substantially smaller than core sample  24 , which can have a length that exceeds one meter. Alternatively, embodiments of plugs can have any shape and any size, which can be obtained by slicing, scraping, granulating and the like. A significant advantage exists by focusing plug extraction to the zone of interest  88  rather than random locations on the core sample  24 , as more information can be obtained from plugs taken from zone(s) of interest  88  in the core sample  24  over those taken from locations in the core sample  24  with characteristics that are substantially homogeneous. As plug preparation can be time consuming, an additional advantage is realized in the time savings gained by a focused approach of obtaining a few plugs in the zone(s) of interest  88  instead of many plugs over the entire core sample  24 . 
         [0031]    In examples where constituents throughout the core sample  24  have physical characteristics with a range of multiplicity of values, sections in the composite image  82  that represent the core sample  24  can be assigned alpha-numeric values that correlate to those physical characteristics. Examples of the physical characteristics include homogeneity, density, average density, and median density of the material in the core sample  24 . 
         [0032]    The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. In an example embodiment, the zone of interest  88  is strategically chosen so that the formation adjacent wellbore  27  can be represented by analyzing the zone of interest  88 . In another embodiment, clays, minerals, and other elements in the zone of interest  88  are identified. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.