Abstract:
A method for transitioning a rigid or semi-rigid tool around a whipstock having a curved internal guide channel. The apparatus and method entail the tool meeting specific proportion criteria relative to the narrowest part of the curved guide channel through which it must pass and relative to the length and width of the tool. In lateral borehole related applications, if the wider ends portions of the tool are of approximately the same diameter of the borehole, the tool can be stabilized as it travels through the guide channels and creates and transitions a lateral borehole. The disclosure is particularly suited to tools that are rotated through the curved whipstock and in certain applications offers such tools the benefit of a reduced number of segments or links and hence reduced costs and failure points. The method described herein can be used with a variety of tool types and for a variety of purposes and may increase the applicability of tools otherwise only feasible on wellbores of a larger diameter.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority to U.S. Provisional Application No. 61/465,074 filed Mar. 15, 2011. 
     
    
     FIELD 
       [0002]    The present invention relates to an apparatus and method for transitioning a rigid or semi-rigid tool segment, meeting specific proportion criteria, around a whipstock having an internal guide channel with an inner and outer curve. Additionally, in lateral borehole related applications, if the end portions of the tool (which are wider than the midsection) are of approximately the same diameter as the borehole, the tool segment can be centralized and stabilized as it travels through the lateral borehole. 
       BACKGROUND 
       [0003]    The present invention generally relates to a method and apparatus for use in downhole applications, wherein a tool is guided around an internal curve of a whipstock and toward the wellbore casing and/or earthen formation of interest. This disclosure has specific applicability to ultra-short radius lateral drilling and procedures that rely upon such lateral boreholes. This concepts disclosure herein can be used with cased or open-hole completed wells. 
         [0004]    A large number of wells have been drilled into earth strata for the extraction of oil, gas, and other material there from. In many cases, such wells are found to be initially unproductive, or may decrease in productivity over time, even though it is believed that the surrounding strata still contains extractable oil, gas, water or other material. In order to establish greater communication between the wellbore and strata, methods have been developed to create boreholes in the strata radiating outward from the primary wellbore. Typically, such methods entail high pressure jetting or cutting systems, but they may also include laser and spallation technologies. Howsoever created, other tools, such as measuring or diagnostic devices, may be transitioned around the whipstock and moved through the newly created borehole. Known methods utilize a whipstock with internal guide channel that directs tools or tool segments from the primary wellbore toward the wellbore casing, if present, and earthen formation of interest. Typically, the internal guide channels of the whipstock has an inner and outer curve (often defined by radii of circles) used to guide the tools around the curved path. The difference between the inner and outer surfaces of the guide channel define the width of the guide channel, and hence limit the maximum width of any tool that must transition through the guide channel. 
         [0005]    Obviously, a whipstock sweeping out 90 degrees in a 5½″ diameter wellbore must complete its transition with a smaller radius than one that is able to sweep out the same 90 degrees in a larger 9″ wellbore casing. Said in other words, a smaller diameter wellbore necessitates a tighter smaller guide path radius or curve in the whipstock in order to sweep out the same number of degrees. 
         [0006]    In certain well completion and stimulation applications, a hole in the well casing is created, such as by a rotating mechanical cutter, an abrasive jetting system or other means. These tools are often transitioned around the radius or curve in the internal guide channel of a whipstock. 
         [0007]    Regardless of whether a wellbore is cased hole or open hole completed, certain tools are transitioned around the curved guide paths of a whipstock and toward the earthen formation. For example, the tools may be used for cutting or jetting or otherwise forming the lateral borehole itself, or they may be used for measuring and diagnostic purposes, or for other procedures performed in the lateral borehole themselves (e.g. injection of chemicals, placement of another whipstock in the lateral borehole, etc.). 
         [0008]    By the nature of the whipstock—namely, one sweeping out an arc with a short curve (of less than 18 inches in diameter), any rigid or semi-rigid tool that is to be transitioned around the curved guide path of such a whipstock is severely limited in its length and diameter combination. Flexible tools like hoses or springs may readily transition around such a curve, but long, rigid or semi-rigid tools may not be able to pass through a given channel at all. While the obvious solution to transitioning such a tool around the tight guide path curve is to reduce the length and/or width of the tool, sometimes this is not possible—such as when the components cannot be made of a smaller size and still perform their function. 
         [0009]    In one known device, a series of links connected by joints, such as universal joints or ball-and-socket style connectors, have been designed in an attempt to allow a specialized toolstring to transition the guide path curve of a whipstock so as to cut the casing. This tool is problematic as it requires many segments to transition the radius of the whipstock with each joint or segment creating a failure point in the system. That is, due to the width/length limitation imposed by the tight curve in the whipstock, the flexible links must be relatively short and hence a large number of them are required, unnecessarily adding complexity, costs and additional failure points. 
         [0010]    While the above example highlights shortcomings for a particular drill-string, the width-length combination limitations imposed by the tight guide path curve or radius of the whipstock can affect rigid or semi-rigid tools of many sorts. For example, the cutting or jetting heads commonly used to forming the lateral borehole must first make it around the radius of the whipstock and hence are severely limited in their length and width combinations. Similarly, tools used for measuring and diagnostic function or other lateral borehole treatments, have similar sizing limitations. Oftentimes, in practice, certain tools are simply precluded altogether from performing their intended purposes on wellbores requiring a whipstock with too small of an internal guide path curve. In effect, the failure of industry to address this problem has limited the commercial potential of certain tools and relegated them to usage only on larger wellbore, which can accommodate whipstocks with the requisite large guide path radii. 
         [0011]    A further shortcoming of certain known tools that are able to make transition around the guide path curve of the whipstock is that they do so by being sub-optimally narrow. For example, a tool that cannot be made any shorter and yet perform its function is often reduced in width so as to allow it to transition around the radius of the whipstock. In applications, however, this often creates the unintended problem that the tool is then very poorly centralized when it traversing the larger diameter guide channel of the whipstock or when in the lateral borehole itself. 
         [0012]    In view of the above, it would be desirable to have a method for transitioning relatively long rigid or semi-rigid tools around the tight internal radius of a whipstock. It would also be desirable if such tools could be centralized when in the lateral borehole. 
       SUMMARY 
       [0013]    The present invention addresses the shortcomings of known devices that transition around the tight internal guide channel curve of a whipstock. Specifically, by utilizing the disclosure described herein one may increase the length/width combinations of rigid or semi-rigid tools (of whatever nature), that can transition around the tight radius of a whipstock. This disclosure can help improve the efficacy and speed of tools used to cut a hole in wellbore casing by reducing the number of segments in such a tool. In addition, it can allow wide and long tools to transition around the radius of whipstock and yet have good centralization when in the lateral borehole. 
         [0014]    The disclosure entails having at least one segment of the tool having at least two end portions being greater than 80% of the minor width of the guide channel in the whipstock through which the tool must transition. Additionally, it entails at least one segment of the tool being longer than it is wide by in excess of 1.25 to 1. Additionally, it entails the mid-section of the tool segment to have a smaller width or diameter than its ends, thereby allowing the tool to transition around a radius of the whipstock when it otherwise could not, due to interference. To accomplish this, the segment of the tool may comprise an “hourglass”, “barbell” or “dogbone” profile. Furthermore, the frontal or rear-facing end of the segment of the tool may be tapered or have a radius to allow that respective portion of the tool to better transition around the tight radius of a whipstock without jamming; and, in the process allowing for a tool with an longer overall length to make the transition. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0015]      FIG. 1 : Illustrates an example of the maximum length limitation of a rigid tool capable of transitioning around the tight radius of a whipstock; the maximum length is the point at which both the ends are in contact with the outer curve while the midsection is in contact with the inner curve. 
           [0016]      FIG. 2 : Illustrates the maximum width limitation of a rigid tool capable of transitioning through a whipstock; essentially, the width limitation is the distance between the inner and outer curve of the whipstock&#39;s guide channel. 
           [0017]      FIG. 3 : Illustrates examples of maximum width and length combinations a rectangular-profiled tool can have and yet still transition around the tight curve of a whipstock; it further shows that a narrow width allows for a longer tool to transition around the radius. 
           [0018]      FIG. 4 : Illustrates the disclosure having an “hourglass” shaped profile, which allows it to transition around the tight internal radius of a whipstock, whereas if it had a rectangular profile it could not make this transition. 
           [0019]      FIG. 5 : Illustrates the disclosure having a “dumbbell” or “dogbone” shaped profile, which allows it to transition around the tight internal radius of a whipstock, whereas if it had a rectangular profile it would become jammed in the guide channel. 
           [0020]      FIG. 6 : Illustrates a relatively long tool having a “dogbone” shape (narrower midsection) that is both able to transition around the radius of the whipstock and yet remain well centralized in the lateral borehole. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    As used herein, the term “lateral” or “laterally” refers to a borehole deviating from the wellbore and/or a direction deviating from the orientation of the longitudinal axis of the wellbore. The orientation of the longitudinal axis of the wellbore in at least one embodiment is vertical, wherein such a wellbore will be referred to as a vertical wellbore or substantially vertical wellbore. However, it should be understood that the orientation of the longitudinal axis of the wellbore may vary as the depth of the well increases, and/or specific formations are targeted. As used herein, the term “strata” refers to the subterranean formation also referred to as “earthen formation.” The term “earthen formation of interest” refers to the portion of earthen formation chosen by the operator for lateral drilling. Such earthen formation is typically chosen due to the properties of the formation relating to hydrocarbons, liquids, gasses or other materials. 
         [0022]    The specifications disclosed in this invention address the specific shortcomings of known rigid or semi-rigid devices that transition around the tight internal guide channel radius of a whipstock. Specifically, by utilizing the disclosure described herein one may increase the length/width combinations of rigid or semi-rigid tools (of whatever nature), that can transition around the tight radius of a whipstock. This disclosure can help improve the efficacy and speed of certain multi-segmented tools used to cut a hole in wellbore casing by reducing the number of segments in such a tool. In addition, it can allow wide and long tools to transition around the radius of whipstock and yet have good centralization when in the lateral borehole. 
         [0023]    The apparatus entails having at least one segment or tool-body with at least two end portions being greater than 80% of the minor diameter of the guide channel in the whipstock (e.g. the smallest distance between the inner and outer radius of the guide channel). Optionally the apparatus entails having at least one segment or tool-body with at least two end portions being greater than 85% of the minor diameter of the guide channel in the whipstock, optionally greater than 90%, optionally greater than 95%. Additionally, it entails at least one segment of the tool having an overall length in proportion to its overall width of at least 1.25 to 1; that is the tools is longer than it is wide. Optionally the tool has an overall length in proportion to its overall width of at least 1.30 to 1, optionally at least 1.40 to 1, optionally at least 1.50 to 1. Additionally, it entails the mid-section of the tool segment having a smaller width (or if it is a generally cylindrical tool, a smaller diameter) than its ends thereby allowing the tool to transition around a radius of the whipstock when it otherwise could not. That is, by having a narrower mid-section the tool avoids becoming jammed in the guide channel precisely because the mid-section is not interfering with the inner guide channel surface when the end portions of the tool are in contact with the outer guide channel surface. To accomplish this, the segment of the tool may comprise an “hourglass”, “barbell” or “dogbone” type profile. Furthermore, the frontal or rear-facing end of the segment of the tool may be tapered or have a radius to allow that respective portion of the tool to better transition around the tight radius of a whipstock without jamming; and thereby potentially further increasing the effective length of tool that can be transitioned around a given radius of the whipstock. 
         [0024]    Notably, since the main tool body can continue without interference from the whipstock (or with minimal friction), increased transfer of torque and weight may also occur. This aspect is of particular importance for those using a segment or flexible link system to mill through casing, cement and/or into earthen formation. The benefit of using the tool profile of this disclosure for the aforementioned purpose(s) is that it will allow for significantly longer segments or links to transition the whisptock&#39;s radius, while allowing those segments or links to also be very large relative to the width of the guide channel (i.e. over 80% of the guide channel width). By allowing a longer flexible segment to transition the whipstock curve, one can reduce the number of links required and in the process allow for improved weight and torque transference. With more efficient weight and torque transference, faster and/or more efficient cutting results, reducing the wear on the whipstock, flexible links, and/or cutting head. 
         [0025]    Turning now to the Figures,  FIG. 1  illustrates a cross-sectional view illustration depicting a whipstock ( 1 ) with internal guide channel ( 2 ) with tight inner curve ( 3 ) having minimum distance (W), shown by dotted line, to nearby outer curve ( 4 ) . Evident from the illustration is the fact that the length limitation of a rigid tool ( 5 ) that can transition through the entire internal guide channel ( 2 ) is a very narrow tool whose mid-section (M) is in contact with the inner curve ( 3 ) and whose opposing-side lower and upper end portions (L and U, respectively) are in contact with the outer curve ( 4 ). 
         [0026]      FIG. 2  is a cross-sectional view illustration depicting a whipstock ( 1 ) with internal guide channel ( 2 ) with tight inner curve ( 3 ) and nearby outer curve ( 4 ). Evident from the illustration is the fact that the width limitation of a rigid tool ( 5 ) that can transition through the entire internal guide channel ( 2 ) is a very short but wide tool ( 5 ) that is of approximately the same width as the guide channel ( 2 ) and whose mid-section (M) is in contact with the inner curve ( 3 ) and whose opposite-side lower and upper end portions (L and U, respectively) are in contact with the outer curve ( 4 ). In this case, the tool ( 5 ) is being moved by positioning means ( 50 ). 
         [0027]      FIG. 3  is a cross-sectional view illustration depicting a whipstock ( 1 ) with internal guide channel ( 2 ) with tight inner curve ( 3 ) and nearby outer curve ( 4 ). A rigid tool ( 5 ) with a generally rectangular profile is being lowered through the guide channel ( 2 ) by positioning means ( 50 ). Evident from the illustration is the fact that a rigid tool ( 5 ) of this profile cannot be made any longer and still be capable of transitioning the entire guide channel ( 2 ) unless it were made narrower (as shown by dotted line figure) as the tool ( 5 ) would become jammed when its middle section (M) was in contact with the inner curve ( 3 ) and its opposing-size lower and upper ends (L and U, respectively) were in contact with the outer curve ( 4 ). 
         [0028]      FIG. 4  is a cross-sectional view illustration depicting a whipstock ( 1 ) positioned in an wellbore ( 16 ) in which there is casing ( 17 ) and cement ( 18 ), but that is openhole completed ( 19 ) in an earthen formation of interest ( 20 ). The whipstock ( 1 ) has an internal guide channel ( 2 ) with tight inner curve ( 3 ), in this case defined by an arc of a circle, and nearby outer curve ( 4 ) through which a toolstring ( 21 ) is being lowered. A rigid segment ( 5 ) of the toolstring ( 21 ) has a barbell-like profile (see item  5 ) wherein the center area (M) of the segment ( 5 ) is of a smaller width than the width of the segment&#39;s lower and upper ends (L and U, respectively), thereby allowing the member ( 22 ) to transition through the entire internal guide channel ( 2 ). Evident from this illustration, as shown by dashed line (A) is the fact that if the segment ( 5 ) did not have the narrower mid-section (M) it would be unable to transition through the entire guide channel ( 2 ) because of interference with the guide channel&#39;s inner curve ( 3 ). 
         [0029]      FIG. 5  is a cross-sectional view illustration depicting a whipstock ( 1 ) positioned in a wellbore ( 16 ) in which there is casing ( 17 ) and cement ( 18 ) in the earthen formation of interest ( 20 ). The whipstock ( 1 ) has an internal guide channel ( 2 ) with tight inner radius ( 3 ) and nearby outer radius ( 4 ) through which a segmented but interconnected toolstring ( 21 ) is attached to rotational source ( 51 ). The lower end of the toolstring ( 21 ) has a cutting head ( 31 ). A segment ( 5 ) on the toolstring ( 21 ) has a dogbone-shaped profile (see item  5 ) wherein its midsection (M) is of a smaller width than its lower and upper ends (L and U, respectively), thereby allowing the member ( 5 ) to transition through the entire internal guide channel ( 2 ). Evident from this illustration, as shown by dashed line (A) is the fact that if the member ( 5 ) did not have the narrower mid-section (M) it would not be able to transition through the entire guide channel ( 2 ) because of interference with the inner radius ( 3 ). 
         [0030]      FIG. 6  is a cross-sectional view illustration depicting the cutting head ( 31 ) on a rigid segment ( 5 ) of a toolstring ( 21 ) positioned in a borehole ( 32 ) in an earthen formation of interest ( 20 ). The segment ( 5 ) has been able to transitioned through the guide channel ( 2 ) of a whipstock ( 1 ) because of its “hourglass” profile with narrow mid-section (M); and yet, the segment ( 5 ) is stabilized and centralized in the borehole ( 32 ) by virtue of its upper (U) and lower (L) end portions being of approximately the same width as borehole ( 32 ). 
         [0031]    Depending on the context, all references herein to the “invention”, “tool” or “method” may in some cases refer to certain specific embodiments only. In other cases it may refer to subject matter recited in one or more, but not necessarily all, of the claims. While the foregoing is directed to embodiments, versions and examples of the present invention, which are included to enable a person of ordinary skill in the art to make and use the inventions when the information in this patent is combined with available information and technology, the inventions are not limited to only these particular embodiments, versions and examples. Other and further embodiments, versions and examples of the invention may be devised without departing from the basic scope thereof and the scope thereof is determined by the claims that follow.