Abstract:
Devices and methods are described for evaluating tubulars installed in a wellbore, which permit detection of wellbore construction errors. Errors in the hardness or grade of the material installed, e.g., in critical wellbores, could potentially affect the integrity of the wellbore and lead to catastrophic effects with respect to well control, pipe connection failure while running casing down-hole, or pipe body failure due to buckling or axial/triaxial failure during stimulation and production. Once tubulars are installed, the devices and methods permit testing the hardness of the steel or other material forming the tubulars. Determining the hardness of the tubulars may provide assurances or indications that remedial action may be appropriate to secure the wellbore. The devices and methods can be implemented to deliver a down-hole Rockwell hardness test in connection with logging while drilling technologies, with wireline tools, or in connection with other deployment mechanisms.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Application No. 62/094,790 filed Dec. 19, 2014, entitled “Method for Rockwell Hardness Testing of Tubulars Post Wellbore Installation” the disclosure of which is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present disclosure relates generally to evaluating the integrity of structures installed in a wellbore, e.g., casing, liners and production tubing deployed in a hydrocarbon recovery wellbore. More particularly, embodiments of the disclosure relate to methods of hardness testing of metallic components subsequent to installing the metallic components in the wellbore. 
         [0004]    2. Background 
         [0005]    In the field of well construction in the oil at d gas industry, there has been occasion when one grade of the tubulars (casing, liner or completion tubing) has been mistaken for a different grade of tubular. This can occur through an error in material delivery from the vendor, poor casing design, lack of quality assurance/control (QA/QC) or a combination of all three. When wellbore conditions call for a particular grade of tubular, die result of installing a misidentified tubular can be that the weight or grade of steel being used is inadequate, or suspect at the very least. This may lead to a compromise in integrity of the tubular or premature failure during the lifecycle of the wellbore, particularly when the tubulars are installed in high-temperature-high-pressure (HTHP) wellbores and/or high hydrogen sulfide (H 2 S) or carbon dioxide (CO 2 ) environments. 
         [0006]    Often, tubulars are marked with color-coded bands, as set forth in API Spec 5CT, Section 11, marking, as an industry standard at one end that are intended to identify the grade of the tubulars and threaded connections or couplings. However, once the tubulars are installed in a wellbore, the color coded bands may not be visible, and the only recourse for determining the strength of the installed tubulars is to refer to the Mill Certificate. The Mill Certificate is a steel industry document that accompanies the shipments of tubulars when they depart the mill, and identify the tubulars by the manufacturing standards under which the tubulars were manufactured. Since the Mill Certificate may be separated from the tubulars before installation in the wellbore, or since the Mill Certificate may be inaccurate, reliance on the Mill Certificate is prone to error and is not a fail-safe method of establishing exactly what grade of tubulars are installed in the well. A need exists for devices and methods to test the hardness of the steel at any given point in the well while the pipe is in situ. The need exists, not necessarily for any specific well condition, rather in the event of a tubular failure, for assessing the failure mechanisms and for determining the appropriate hardness of down-hole steel structures. There may be both mechanical and geological reasons for assessing the hardness of down-hole steel structures, so a need exists for analysis tools for this type of analysis. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The disclosure is described in detail hereinafter on the basis of embodiments represented in the accompanying figures, in which: 
           [0008]      FIG. 1  is a partially cross-sectional side view of a drilling system including a down-hole hardness testing apparatus constructed in accordance With one or more exemplary embodiments of the disclosure; 
           [0009]      FIG. 2  is a partially cross-sectional schematic view of the down-hole hardness testing apparatus including an indenting member for engaging a structure to be tested in accordance with an example embodiment of the present disclosure; 
           [0010]      FIGS. 3A and 3B  are front views of tip members which may be installed on the indenting member of  FIG. 2  for evaluating different types of structures in accordance with other example embodiments of the present disclosure; 
           [0011]      FIG. 4  flow chart illustrating a process for evaluating down-hole structures including a plurality of indentation steps in accordance with example embodiments of the present disclosure; and 
           [0012]      FIGS. 5A, 5B and 5C  are cross-sectional schematic views of an indenting member illustrating the sequence of indentation steps of  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    In the following description, even though a Figure may depict an apparatus in a portion of a wellbore having a specific orientation, unless indicated otherwise, it should be understood by those skilled in the art that the apparatus according to the present disclosure may be equally well suited for use in wellbore portions having other orientations including vertical, slanted, horizontal, curved, etc. Likewise, unless otherwise noted, even though a Figure may depict an onshore or terrestrial operation, it should be understood by those skilled in the art that the apparatus according to the present disclosure is equally well suited for use in offshore operations. Further, unless otherwise noted, even though a Figure may depict a wellbore that is partially cased, it should be understood by those skilled in the art that the apparatus according to the present disclosure may be equally well suited for use in fully open-hole wellbores. 
         [0014]    Hardness is a characteristic of a material, not a fundamental physical property, Hardness may be defined as the resistance to indentation, and may be determined by measuring a permanent depth of an indentation created in a target structure by the application of known loads. Generally, when using a fixed force (load) and a given indenter, the smaller the indentation, the harder the target material. An indentation hardness value may be obtained by measuring the depth or the area of the indentation. The Rockwell hardness test method, as defined in ASTM E-18, is often employed in the well construction industry for characterizing steel and other metals. The Rockwell method measures the permanent depth of indentation produced by a force/load on an indenter, and may be implemented down-hole by employing devices and methods described herein. 
       1. Description of Exemplary Embodiments 
       [0015]    The present disclosure includes devices and methods for measuring and evaluating the hardness of downhole tubular members. Some of the devices and methods include a down-hole deployable probe with an indenting member thereon for applying minor and major loads to the target tubular member. A variance between depths of permanent indentations formed in the target tubular member by the applications of the minor and major loads may be measured to assess the hardness of the target tubular member. 
         [0016]      FIG. 1  is an elevation view in partial cross-section of a wellbore drilling system  10  utilized to produce hydrocarbons from wellbore  12  extending through various earth strata in an oil and gas formation  14  located below the earth&#39;s surface  16 . Wellbore  12  may be formed of a single bore or multiple bores (not shown), extending into the formation  14 , and may be disposed in any orientation, such as the horizontal, vertical, deviated and may include portions thereof any combination of different orientations. Wellbore drilling system  10  includes a testing apparatus  100  disposed at a lower end of a conveyance  18 . In the illustrated embodiment, the conveyance  18  comprises a drill string operable from the surface  16  to position the testing apparatus  100  within the wellbore  12 . In other embodiments, other types of conveyances are contemplated including coiled tubing, production tubing, other types of pipe or tubing strings, wirelines, slicklines, and the like. 
         [0017]    Drilling and production system  10  includes a drilling rig or derrick  20 . Drilling rig  20  may include a hoisting apparatus  22 , a travel block  24 , and a swivel  26  for raising and lowering the drill string  18 , another conveyance, and/or structure such as casing string. In  FIG. 1 , the conveyance  18  is a substantially tubular, axially extending drill string formed of a plurality of drill pipe joints coupled together end-to-end. Drilling rig  12  may include a kelly  32 , a rotary table  34 , and other equipment associated with rotation and/or translation of conveyance  18  within a wellbore  12 . For some applications, drilling rig  18  may also include a top drive unit  36 . 
         [0018]    Drilling rig  20  may be located proximate to a wellhead  40  as shown in  FIG. 1 , or spaced apart from wellhead  40 , such as in the case of an offshore arrangement (not shown) where the drilling rig  20  may be supported on an floating platform and coupled to a wellhead on the sea floor by a riser as appreciated by those skilled in the art. One or more pressure control devices  42 , such as blowout preventers (BOPs) and other equipment associated with drilling or producing a wellbore may also be provided at wellhead  40  or elsewhere in the wellbore drilling system  10 . 
         [0019]    A working or service fluid source  48 , such as a storage tank or vessel, may supply a working fluid  50  pumped to the upper end of the conveyance  18  or drill string and flow through conveyance  18 . Working fluid source  48  may supply any fluid utilized in wellbore operations, including without limitation, drilling fluid, cementous slurry, acidizing fluid, liquid water, steam or some other type of fluid. Subsurface equipment  52  may be disposed within the wellbore  12 , and may include equipment such as, for example, a drill bit  54  and bottom hole assembly (BHA)  56 , and/or some other type of wellbore tool. 
         [0020]    Wellbore drilling system  10  may generally be characterized as having a pipe system  58 . For purposes of this disclosure, pipe system  58  may include casing, risers, tubing, drill strings, completion or production strings, subs, heads or any other pipes, tubes or equipment that attaches to the foregoing, such as conveyance  18 . In this regard, pipe system  58  may also include one or more casing strings  60  that may be cemented in wellbore  12 , such as the surface, intermediate and inner casings  60  shown in  FIG. 1 . An annulus  62  is formed between the walls of sets of adjacent tubular components, such as concentric casing strings  60  or the exterior of conveyance  18  and the inside wall of a casing string  60  or wellbore  12 , as the case may be. The testing apparatus  100  is disposed adjacent a casing string  60  for assessing a hardness of the casing string  60 . The conveyance  18  may be moved within to permit the drilling system  10  to perform other functions such drilling. 
         [0021]    Where subsurface equipment  52  is used for drilling and conveyance  18  is a drill string, the lower end of the conveyance  18  may support the BHA  56 , which may carry at a distal end the drill bit  54 . During drilling operations, weight-on-bit (WOB) is applied as drill bit  54  is rotated, thereby enabling drill bit  54  to engage formation  14  and drill wellbore  12  along a predetermined path toward a target zone. In general, drill bit  54  may be rotated with conveyance  18  from rig  20  with top drive  36  or rotary table  34 , and/or with a downhole mud motor  68  within BHA  56 . The working fluid  50  pumped to the upper end of conveyance  18  flows through the longitudinal interior  70  of conveyance  18 , through BHA  56 , and exit from nozzles formed in drill bit  54 . When the drill bit is positioned to rotate at a bottom end  72  of wellbore  12 , working fluid  54  may mix with formation cuttings, formation fluids and other downhole fluids and debris to form a drilling fluid mixture that may then flow upwardly through the annulus  62  to return formation cuttings and other downhole debris to the surface  16 . 
         [0022]    Bottom hole assembly  56  and/or drill conveyance  18  may include various other tools such as mechanical subs and directional drilling subs. The BHA illustrated in  FIG. 1  includes a power source  76 , and measurement equipment  80 , such as measurement while drilling (MWD) and/or logging while drilling (LWD) instruments, detectors, circuits, or other equipment to provide information about wellbore  12  and/or formation  14 , such as logging or measurement data from wellbore  12 . Measurement data and other information from tools  74  may be communicated using electrical signals, acoustic signals or other telemetry that can be converted to electrical signals at the rig  20  to, among other things, monitor the performance bottom hole assembly  56 , and associated drill bit  54 , as well as monitor the conditions of the environment to which the bottom hole assembly  56  is subjected. The measuring equipment  80  may also be communicatively coupled the testing apparatus  100 , and may be operable for receiving, processing, and/or communicating hardness data provided by the testing apparatus  100  as described in greater detail below. 
         [0023]    Although testing apparatus  100  is illustrated in a drilling system  10 , one skilled in the art will recognize that aspects of the disclosure may be practiced in other downhole environments including production systems. For example, where the conveyance  18  is a wireline or slickline, e.g., the conveyance  18  may be employed to position the testing apparatus  100  adjacent a tubular member such as production tubing in a completion assembly to assess the hardness thereof. 
         [0024]      FIG. 2  is a partially cross-sectional schematic view of the down-hole hardness testing apparatus  100  including an indenting member  102  for engaging a target structure to be tested in accordance with an example embodiment of the present disclosure. The target structure is a tubular member  104  that extends within the wellbore  12  and is secured within the geologic formation  14  by a layer of cement  106 . In some exemplary embodiments, the target tubular member  104  is a steel casing member that forms part of casing string  60  ( FIG. 1 ). In some other embodiments (not shown), the target structures is production tubing, liner or other down-hole structure recognized in the art. The testing apparatus  100  includes a probe  108  operably coupled to conveyance  18 . As described above, conveyance  18  may include a drillstring, coiled tubing, electric line, wireline or other conveyance for deploying the probe  108  into the wellbore  12  and positioning the probe  108  adjacent the target tubular member  104 . As illustrated, the probe  108  can he deployed on BHA  56  including a drill bit  54  powered by circulation of a drilling fluid as described above. In embodiments where the target structures to be tested are completion tubulars, which may be disposed in open hole environments, the probe  104  may be deployed on slimmer equipment, e.g., on a wireline, to permit maneuverability of the testing apparatus  100  and/or the probe  108 . 
         [0025]    As illustrated, the probe  108  may be disposed on a lateral side of the testing apparatus  100 , and includes the indenting member  102  or other piston selectively extendable and retractable from the testing apparatus  100  and/or probe  108 . In some exemplary embodiments, the indenting member  102  is controlled by a hydraulic system  110  disposed within the testing apparatus  100 . As illustrated, the hydraulic system  110  includes a plurality of accumulators  114  that are controlled internally by a plurality of valves  116  such as solenoid valves. The valves  116  are operably coupled to a controller  120  that provides instructions to open and close the valves  116 . In some embodiments, the controller  120  provides instructions to the valves  116  with electrical or other types of signals. In some embodiments, the controller  120  may include a computer having a processor  122  and a computer readable medium  124  operably coupled thereto. The computer readable medium  124  can include a nonvolatile or non-transitory memory with data and instructions that are accessible to the processor  122  and executable thereby. In one or more embodiments, the computer readable medium  124  is pre-programmed with instructions for opening and closing the valves  116  appropriately to impart major and minor loads to the target tubular member  104 , as described in greater detail below, and to achieve other objectives. The controller  120  is also operable to receive feedback from hydraulic system  100  or other portions of the testing apparatus  100 . For example, the controller  120  may receive signals representative of a distance traveled by the indenting member  102 , readings from sensors (see inclination sensor  134  described below), or confirmation that certain steps have been completed. 
         [0026]    Appropriately opening and closing the valves  116  results in extension and retraction of the indenting member  102 , thereby forcing the indenting member  102  into the target tubular member  104  with predetermined minor and major forces as described in greater detail below. The accumulators  114  are attached to solenoids and are powered by a system pump (not shown), which may be disposed at the surface  16  (not shown). In some embodiments, the hydraulic system  110  of the testing apparatus  100  may be isolated from the flow of working fluid  50  ( FIG. 1 ) with a flow diverter valve  128  during normal circulating operations. When hydraulic power is needed the diverter valve  128  is opened such that working fluid  50  flowing through the conveyance  18  may be provided to the hydrauliuc system  110 . 
         [0027]    In other embodiments, where the probe  108  is deployed on a wireline for example, the hydraulic system  110  may be replaced with an electromechanical system (not shown), which may include electric motors or other electromechanical actuators for moving the indenting member  102 . When the probe  108  is deployed by slickline, a battery or other local power source may provide power to the actuator. When coiled tubing is used to deploy the probe  108 , either s hydraulic system  110  or an electromechanical system (not shown) may be employed for deploying the probe  108  and operating the indenting member  102 . 
         [0028]    Additionally, the testing apparatus  100  may include at least one stabilizer  132  extending laterally therefrom in some embodiments. The stabilizer  132  maintains the indenting member  102  in a generally perpendicular inclination with respect to the target tubular member  104 . In some embodiments, the stabilizer  132  is operable to maintain an inclination within 2 degrees of perpendicular to ensure precise loading of the target tubular member  104 . In addition, testing apparatus  100  or stabilizer  132  may include one or more inclination sensors  134  operably coupled to the controller  120  to verify an appropriate inclination. The inclination sensor  134  may comprise accelerometers or other devices for evaluating the inclination of the testing apparatus as recognized in the art. 
         [0029]    In some embodiments, the probe  108  of the testing apparatus  100  may be deployed down-hole as a component of, or coupled to measurement equipment  80  ( FIG. 1 ), which may include a measure while drilling (MWD) or logging while drilling (LWD) system such as a modified GeoTap® IDS tool. The indenting member  102  could be operated, e.g., to perform a hardness test in a two-stage loading operation as described below, and the results of the hardness Lest could be communicated to the surface  16  with a communication unit  138  coupled to the controller  120 . The communication unit  138  may an MWD telemetry system provided as part of the measurement equipment  80 . In some embodiments, the communication unit  138  comprises a 2-way mud-pulse telemetry unit, operable to selectively deliver and receive information, and in some embodiments, the communication unit  138  comprises a wireless device such as a hydrophone or other types of transducers operable to selectively generate and receive acoustic signals. In some embodiments, the communication unit  138  can comprise other wired or wireless telemetry tools as will be appreciated by those skilled in the art. In other embodiments, the data obtained may be stored in a local memory  140  of the controller  120  until the testing apparatus  100  is removed from the wellbore  12 . 
         [0030]    As illustrated in  FIGS. 3A and 3B , for example, a variety of indenting members  150 ,  152  are contemplated for use within the probe  108 . A conical tip  154  ( FIG. 3A ) such as a conical diamond with a round tip may be employed for relatively harder target metals. In some embodiments, for relatively soft target metals, ball indenters ( FIG. 3B ) having a diameter “D” in the range from about 1/16 inch to about ½ inch may be employed. Generally, when selecting a Rockwell scale, a general guide is to select the scale that specifies the largest load and the smallest indenting member  102  ( FIG. 2 ),  150 ,  152  possible without exceeding defined operation conditions and accounting for conditions that may influence the test result. 
       2. Example Methods of Operation 
       [0031]      FIG. 4  is a flow chart illustrating a process  200  for evaluating down-hole target structures including a plurality of indentation steps in accordance with example embodiments of the present disclosure. As illustrated in  FIG. 4  and  FIGS. 5A-5C , and with continued. reference to  FIG. 2 , the process  200  exemplary embodiments of methods of evaluating down-hole structures such as the target tubular member  104  are illustrated. Initially at step  202 , an appropriate indenting member  102 .  150 ,  152  may be selected, and the testing apparatus  100  may be deployed down-hole on any of the conveyances  18  described above. Next at step  204 , a perpendicular inclination of the indenting member  102 ,  150 ,  152  with respect to the target tubular member  104  can be verified with the inclination sensor  134 . In some embodiments, when an inclination of greater than 2 degrees from perpendicular is detected, the conveyance  18  or testing apparatus  100  may be manipulated to urge the testing apparatus  100  into the proper inclination before proceeding. In some embodiments, e.g., where an inclination of greater than 2 degrees (or outside another predetermined threshold) may not be readily corrected, the inclination sensor  134  can provide an inclination data associated with the readings, so that an appropriate correction factor may be determined or estimated, or so the reliability of the data obtained may be assessed. In some embodiments, where an inclination of greater than 2 degrees is detected, the testing apparatus  100  may be repositioned at another point in the wellbore  12  where a more appropriate inclination is achievable. 
         [0032]    Once the desired inclination is verified, the controller  120  can command the hydraulic system  110  to urge the indenting member  102 ,  150 ,  152  to engage the target tubular member  104  and apply the minor load F 0  ( FIG. 5A ) thereto (step  206 ), In some embodiments, the hydraulic system  110  is operable to deliver minor loads F 0  in the range from about 3 kg f  to about 10 kg f  as specified in the “Regular” Rockwell scale, and in some embodiments minor loads F 0  of up to about 200 kg f  as specified in the macro scale (not part of ASTM E-18; see ASTM E-1) may be provided. The minor load F 0  may be a preliminary test force, commonly referred to as preload. The minor load F 0  causes the indenting member  102 ,  150 ,  152  to generate a minor indentation  302  (see  FIG. 5A ) in the target tubular member  104 , that breaks through any surface finishes on the target tubular member  104  to reduce the effects of the surface finish. An appropriate minor load F 0  may be pre-determined such that the minor load F 0  is sufficient to break through the particular surface finish on the target tubular member  104  or other down-hole structure such that the particular indenting member  102 ,  150 ,  152  engages a core material of the target tubular member  104 . The minor indentation  302  represents a zero datum or reference position from which subsequent positions are measured. At step  208 , a depth, area or other characteristic of the minor indentation  302  may be measured, e.g., by evaluating a distance the indenting member  102 ,  150 ,  152  extended from the probe  108 . Generally, it may be desirable to make measurements of indentations formed in flat perpendicular surfaces. However, since the target tubular member  104  is generally curved, the minor indentation  302  is formed in a concave surface. Because of the concavity, a predictably lower reading may be obtained than in a flat surface of the same material. Thus, a correction factor may be applied to the measurement of the depth, area or other measured characteristic of the minor cavity  302  (and other measurements described herein) by the controller  120  downhole, or by a processor (not shown) at the surface  16  in a post processing step. 
         [0033]    After measuring the minor indentation  302 , at step  210 , an additional load, called the major load F 1  is applied to the target tubular member  104  to reach the total required test load or combined load F 0 +F 1  (see  FIG. 5B ). In some embodiments, a major load F 1  may be provided such that the combined load F 0  +F 1  (including the minor and major loads F 0  and F 1 ) may be in the range of about 15 kg f  to about 150 kg f , and in some embodiments the combined load F 0 +F 1  may be in the range of about 500 kg f  to about 3000 kg f  (macro hardness). This combined load F 0  +F 1  may be maintained for a predetermined amount of time (dwell time) at step  212  to allow for elastic recovery. The major load is then released at step  214  and a permanent or persisting major indentation  304  (see  FIG. 5C ) is defied in target tubular member  104 . At step  216 , the depth, area or other characteristic of the major indentation  304  may be measured against the position, depth, area or other characteristic of the minor indentation  302  derived from the minor load F 0 . In some embodiments, the variance “E” between the depth of the major indentation  304  and the minor indentation  302  may then be determined. 
         [0034]    The variance “E” can be used to calculate a hardness value for the target tubular member  104  at step  218 . For example, the variance “E” between minor indentation  302  and the major indentation  304  can be converted to a dimensionless hardness number, noted as HRA. Indentation hardness also correlates linearly with tensile strength (the penetration depth and hardness are inversely proportional), so verification or evaluation of the tensile strength of the target tubular member  104  may also be made by the preceding methodology. 
         [0035]    In some embodiments of the procedure  200 , one or more of the steps described above may be automatically executed in response to a sequence of instructions stored on the computer readable medium  124 . For example, the controller  120  may execute the sequence of instructions to induce the application of the minor and major loads F 0 , F 1  and the associated measurements described in steps  206  through  216  without any input from a user. In other embodiments, the user may transmit a distinct signal to the communication unit  138  to prompt the controller  120  to selectively apply each of the major and minor loads F 0 , F 1  individually, In this manner, a user may select a desired force, indentation depth or other characteristic associated with the minor and major loads F 0 , F 1 , and may selectively or manually instruct the testing apparatus  100  to apply the minor and major loads F 0 , F 1  at any time by manually sending instructions to the communication unit  138 . 
       3. Aspects of the Disclosure 
       [0036]    The aspects of the disclosure described in this section are provided to describe a selection of concepts in a simplified form that are described in greater detail above. This section is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject 
         [0037]    According to one aspect, the disclosure is directed to a method of evaluating down-hole structures. The method includes (a) conveying a testing apparatus having an indenting member into a wellbore to position the testing apparatus adjacent a target down-hole structure, (b) applying a major load to the down-hole structure with an indenting member of the testing apparatus to permanently form a major indentation in the target down-hole structure (c) measuring a characteristic of the major indentation, and (d) determining a hardness value for the target down-hole structure from the characteristic of the major indentation. 
         [0038]    In some exemplary embodiments, the characteristic of the major indentation is a depth of the major indentation. In other embodiments, the characteristic of the major indentation is an area of the major indentation. In some embodiments, the method further includes applying, prior to applying the major load, a minor load to the indenting member to urge the indenting member to engage the target down-hole structure and to permanently form a minor indentation in the target down-hole structure. The method may include measuring a depth of the minor indentation, and determining a variance between the depth of the major indentation and the depth of the minor indentation to thereby determine the hardness value for the target down-hole structure. In some embodiments, the method further includes communicating at least one of the depth or other characteristic of the major indentation, the depth or other characteristic of the minor indentation, the variance between the depths or other characteristics of the major and minor indentations and the hardness value to a surface location from the testing apparatus in the wellbore. In some embodiments, the method further includes pre-determining the minor load such that the minor load is sufficient to break through a surface finish on the target down-hole structure such that the indenting member engages a core material of the target down-hole upon application of the preload. 
         [0039]    In one or more embodiments, the method further includes maintaining the major load for a predetermined dwell Lime, wherein the dwell tune is predetermined to permit elastic recovery of the target down-hole test structure. The method may further include orienting the testing apparatus in the wellbore such that the indenting member engages the target down-hole structure in a generally perpendicular manner In some embodiments, the testing apparatus is oriented to engage the target down-hole structure within 2 degrees of perpendicular. In some embodiments the indenting member engages a concave surface of the target down-hole structure, and wherein determining the hardness value for the target down-hole structure comprises applying a correction factor to accommodate for the concave surface. 
         [0040]    According to another aspect, the disclosure is directed to a method of evaluating tubular members disposed in a wellbore. The method includes (a) conveying a testing apparatus into the wellbore to position the testing apparatus adjacent a target tubular member. (h) measuring a characteristic of the target tubular member with the testing apparatus, and (c) determining a hardness value for the target tubular member from the measured characteristic of the target tubular member. 
         [0041]    In some embodiments, the method further includes applying minor and major loads to the target tubular member with the testing apparatus, and in some embodiments the measured characteristic of the target tubular member is a variance between depths of permanent indentations formed in the target tubular member by the applications of the minor and major loads. In some embodiments, the major load is in the range of about 500 kg f  to about 3000 kg f . The major and minor loads may be sequentially applied to the target tubular member in a generally perpendicular direction at the same location on the target tubular member, In some embodiments, determining the hardness value includes determining a Rockwell hardness value in accordance with ASTM E-18. 
         [0042]    According to another aspect, the disclosure is directed to a down-hole testing apparatus for determining a hardness of tubular members deployed in a wellbore. The down-hole test apparatus includes a probe deployable on a conveyance into the wellbore. An indenting member of the testing apparatus is operable to selectively extend from the probe and to form permanent indentations a target tubular member. A controller including instructions for obtaining measurements of a minor indentation and a major indentation formed in the target tubular member by the respective application of a minor load and a major load with the indenting member to the target tubular member is provided, a communication unit of the down-hole testing apparatus is operable to transmit a signal indicative of the measurements from the probe. 
         [0043]    In some embodiments, the controller includes a processor operable to determine a hardness value from the measurements of the minor indentation and the major indentation. In some embodiments, the down-hole testing apparatus further includes an inclination sensor operably coupled to the controller, and the controller may be operable to verify a perpendicular inclination of the indenting member with respect to the target tubular member. In some embodiments, the indenting member includes at least one of a ball indenter tip and a conical indenter tip. The down-hole testing apparatus may further include a hydraulic actuator operably coupled to the indenting member and selectively operable to impart the minor load and the major load to the target tubular member through the indenting member. In one or more exemplary embodiments, the down-hole testing apparatus further includes a conveyance coupled to the probe, wherein the conveyance comprises at least one of a drill string, coiled tubing and wireline. 
         [0044]    Moreover, any of the method steps described herein may be embodied within a system including electronic processing circuitry to implement any of the methods, or a in a computer-program product including instructions which, when executed by at least one processor, causes the processor to perform any of the methods described herein. 
         [0045]    The Abstract of the disclosure is solely for providing the United States Patent and Trademark Office and the public at large with a way by which to determine quickly from a cursory reading the nature and gist of technical disclosure, and it represents solely one or more embodiments. 
         [0046]    While various embodiments have been illustrated in detail, the disclosure is not limited to the embodiments shown. Modifications and adaptations of the above embodiments may occur to those skilled in the art. Such modifications and adaptations are in the spirit and scope of the disclosure.