Whipstocks with deflection surfaces

Abstract

An embodiment of a drilling system for forming a secondary borehole from a primary borehole is disclosed. The drilling system includes a casing extending along a central axis and a whipstock positioned within the casing. The casing has an outer diameter (OD150), an inner diameter (ID150), and a wall thickness (T150). The whipstock includes an uphole end, a primary ramp, and a deflection surface positioned between the uphole end and the primary ramp. The deflection surface has a thickness (T162) greater than a thickness of an immediately adjacent portion of the primary ramp and has an axial length (L162). The drilling system also includes a mill assembly having a lead mill and a follow mill spaced from the lead mill by a mill spacing (L104). A thickness ratio Formula (I) and length ratio Formula (II) are selected to promote controlled engagement with the casing during initiation of a window.

Description

PATENTAttorney Docket No.: WBRE / 0015PCWHIPSTOCKS WITH DEFLECTION SURFACES CROSS-REFERENCE TO RELATED APPLCIATIONS

[0001] This application claims priority to and the benefit of U.S. provisional patent application serial number 63 / 778,622, filed on March 27, 2025, and entitled “Whipstock with Sacrificial Entry Ramp,” the contents of which are incorporated by reference in their entirety and for all purposes.BACKGROUND

[0002] In the construction and completion of subterranean wells, it is sometimes desirable to form a secondary borehole that departs from an existing borehole. The existing borehole may be referred to as a primary borehole, and the secondary borehole may extend from the primary borehole at a non-zero angle relative to the primary borehole axis. Such a secondary borehole may be referred to as a deviated borehole, sidetracked borehole, or lateral borehole.

[0003] To initiate the secondary borehole, a departure device may be positioned within the primary borehole at a selected depth and orientation. One example of such a departure device is a whipstock. A whipstock generally includes an inclined surface or ramp configured to direct a cutting tool away from the primary borehole axis so that the cutting tool begins forming the secondary borehole. In some operations, the whipstock may be secured within the primary borehole, such as by an anchor, so that the ramp is maintained in a desired orientation during use.

[0004] A drilling assembly used with the whipstock may include a drill string and a bottomhole assembly carrying a cutting tool. Depending on the particular application, the cutting tool may be a mill, a drill bit, or a tool configured to perform both milling and drilling functions. For example, when the secondary borehole is initiated from a cased portion of the primary borehole, a mill may be guided by the whipstock to cut through the casing.SUMMARY

[0005] Some embodiments disclosed herein are directed to a drilling system for forming a secondary borehole from a primary borehole. In some embodiments, the drilling system includes a casing extending along a central axis, the casing having an outer diameter (OD150) and a wall thickness (Tiso). In addition, the drilling systemPATENTAttorney Docket No.: WBRE / 0015PCincludes a whipstock positioned within the casing and having an uphole end, a primary ramp, and a deflection surface positioned between the uphole end and the primary ramp, the deflection surface having a thickness (T162) that is greater than a thickness of a portion of the primary ramp that is immediately adjacent to the deflection surface, wherein a thickness ratio A is defined as A = — — — . The thickness ratio A is in a Ti 5oxOD150range of from about 0.270 to about 0.330.

[0006] In some embodiments, the drilling system includes a whipstock having an uphole end, a primary ramp, and a deflection surface positioned between the uphole end and the primary ramp. The deflection surface has a thickness that is greater than a thickness of a portion of the primary ramp that is immediately adjacent to the deflection surface. The deflection surface has an uphole end, a downhole end opposite the uphole end of the deflection surface, and an axial length L162 measured between the uphole end of the deflection surface and the downhole end of the deflection surface. In addition, the drilling system includes a mill assembly including a lead mill and a follow mill spaced from the lead mill by a mill spacing L104 along a longitudinal axis of the mill assembly. A length ratio B is defined as B = —. Thelength ratio B is in a range of from about 1.040 to about 1.560.

[0007] In some embodiments, the drilling system includes a casing extending along a central axis, the casing having an outer diameter (OD150) and a wall thickness (T150). In addition, the drilling system includes a whipstock positioned within the casing and having an uphole end, a primary ramp, and a deflection surface positioned between the uphole end and the primary ramp. The deflection surface has a thickness T162 that is greater than a thickness of a portion of the primary ramp that is immediately adjacent to the deflection surface. The deflection surface has an uphole end, a downhole end opposite the uphole end of the deflection surface, and an axial length L162 measured between the uphole end of the deflection surface and the downhole end of the deflection surface relative to the central axis. Further, the drilling system includes a mill assembly including a lead mill and a follow mill spaced from the lead mill by a mill spacing (L104) along the central axis. A thickness ratio A is defined as A = — — — . The thickness ratio A is in a range of from about 0.270 to about 0.330.TiPATENTAttorney Docket No.: WBRE / 0015PCA length ratio B is defined as B = The length ratio B is in a range of from about 1.040 to about 1.560.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] For a detailed description of various exemplary embodiments, reference will now be made to the accompanying drawings in which:

[0009] FIGS. 1 and 2 are schematic illustrations of a system for drilling a secondary borehole from a primary borehole according to one or more embodiments disclosed herein;

[0010] FIG. 3 is an enlarged perspective view of an uphole end of a whipstock of the system of FIG. 1 according to some embodiments disclosed herein; and

[0011] FIG. 4 is a side cross-sectional view of the whipstock and a mill of the system of FIGS. 1 and 2 inserted within a casing according to some embodiments disclosed herein.DETAILED DESCRIPTION

[0012] When a secondary borehole is initiated from a cased portion of a primary borehole, the cutting tool is generally guided by the whipstock into engagement with the casing so that a window can be formed in the casing before the secondary borehole is advanced further into the surrounding formation. In such operations, cutting the initial window in the casing may be a critical stage of the departure process because the cutting tool is transitioning from travel along the whipstock to lateral engagement with the casing wall.

[0013] This operation may become more difficult as casing designs move toward heavier weights, greater wall thicknesses, larger diameters, and stronger casing grades. In such casing strings, a greater volume of material may be removed in order to establish the window, and the forces and timing associated with initial engagement of the mill or other cutting tool with the casing may become more significant. As a result, window initiation that may be acceptable in lighter or thinner-walled casing may not reliably produce a desired cutout in heavier walled casing.

[0014] If the initial cutout is not initiated properly, the milling operation may fail to produce the intended window geometry. For example, the resulting window may be shorter than desired, may be formed at an undesired location, or may otherwise fallPATENTAttorney Docket No.: WBRE / 0015PCoutside operational specifications for the sidetracking operation. In some cases, an unsuccessful or incomplete initial cutout may require additional downhole operations or repeated trips in the borehole, thereby increasing operational time and cost. Accordingly, a need exists for systems and methods that improve initiation of a casing window, particularly in applications involving heavier walled or heavier gauged casing pipe.

[0015] Accordingly, embodiments disclosed herein are directed to drilling systems for forming a secondary borehole, the drilling systems including a whipstock having an additional deflection surface configured to reliably deflect a cutting tool, such as a mill, and thereby promote proper initiation of a window in casing. In some embodiments, the deflection surface is thicker than and positioned adjacent to a primary ramp of the whipstock. The deflection surface may be configured to engage and direct the mill during initiation of the casing window. The deflection surface may also be sized and shaped relative to one or more parameters of the mill and the casing so that the mill is directed into the casing in a controlled fashion during the initial cutout. In this manner, the disclosed whipstock configurations may improve initiation of the casing window, particularly in heavier walled or heavier gauged casing pipe, and may thereby promote initiation and formation of the window at a desired location toward the uphole end of the whipstock and with a desired geometry for subsequent drilling of the secondary borehole.

[0016] FIG. 1 illustrates a drilling system 100 according to some embodiments disclosed herein. The drilling system 100 may be configured to at least initiate the formation of a secondary borehole from a primary borehole. As a result, the drilling system 100 may include a whipstock 102 that is coupled to a delivery mechanism 103.

[0017] The delivery mechanism 103 may include various components, including a mill 104. As used herein, the mill 104 may, in some embodiments, include a drill bit, a mill, or a combination thereof. For example, the mill 104 may be configured as a window mill, a section mill, a drill bit, or a combination tool configured to perform both milling and drilling operations. In some embodiments, the mill 104 may be coupled to the whipstock 102 by a connector 106. The connector 106 may comprise a millable material.

[0018] FIG. 1 also depicts a primary borehole 108 extending into a subterranean formation 110. As used herein, a “primary borehole” refers to a borehole from whichPATENTAttorney Docket No.: WBRE / 0015PCa secondary borehole originates. A “secondary borehole” refers to a borehole extending at an angle, such as a non-zero angle, from a centerline or central axis of a primary borehole. For example, a secondary borehole may be a sidetracked borehole that branches off or otherwise deviates from a primary borehole. A primary borehole, such as the primary borehole 108 shown in FIG. 1, may be a borehole extending downwardly from the surface, or may itself be a secondary borehole extending from another borehole.

[0019] The primary borehole 108 may include a cased portion 112. The cased portion 112 may include a liner pipe or casing (see casing 150 shown in FIG. 4 and described later) configured to reinforce the primary borehole 108 against fluid pressure of the formation 110, to isolate the borehole 108 from fluids within the formation 110, or for other purposes. The casing may be manufactured from steel alloys or from lower-strength materials such as aluminum, fiberglass, or resin-reinforced composite materials. The length or presence of the cased portion 112 may vary depending on, for example, the formation 110 through which the primary borehole 108 is drilled or the intended function of the borehole 108. In some embodiments, the primary borehole 108 may also include an uncased or open-hole portion 114, which may extend through the formation 110 with little or no additional reinforcement. In some embodiments, the cased portion 112 may extend along substantially the full length of the primary borehole 108. In other embodiments, the open-hole portion 114 may extend along substantially the full length of the primary borehole 108. Other combinations of cased and uncased portions are also contemplated.

[0020] The whipstock 102 may be positioned in the cased portion 112 of the primary borehole 108 by use of the delivery mechanism 103. In some embodiments, the delivery mechanism 103 may include a drill string 116. The drill string 116 may include a tubular 118 and a bottomhole assembly 120. The tubular 118 may include drill pipe, coiled tubing, drill collars, transition drill pipe, heavy weight drill pipe, or similar components. In some embodiments, the tubular 118 may transmit torque and longitudinal force, such as tension or compression, to the bottomhole assembly 120. In some embodiments, the tubular 118 may also be used to transmit fluid to the bottomhole assembly 120. The bottomhole assembly 120 may include a mud motor, such as a turbine-powered motor or a positive displacement motor, to convert fluidPATENTAttorney Docket No.: WBRE / 0015PCflow into rotational force, which may be used to rotate the mill 104 or power other components of the bottomhole assembly 120.

[0021] The bottomhole assembly 120 may include the mill 104, which may be configured to cut or mill a window in the cased portion 112 (see window 115 in FIG.2). In some embodiments, the mill 104 may also be configured to at least partially drill a secondary borehole through the window in the cased portion 112 (see e.g., the secondary borehole 132 shown in FIG. 2). In some embodiments, the mill 104 may be used to form the window in the borehole 108, after which the tool string may be tripped to the surface and another cutting device, such as a drill bit, may be run into the borehole 108 to drill the secondary borehole 132 through the previously milled window.

[0022] In some embodiments, the bottomhole assembly 120 may include a directional mechanism used to guide or steer the bottomhole assembly 120 or the mill 104. For example, the directional mechanism may include a steerable portion 122 located on, near, or adjacent to the mill 104. The steerable portion 122 may direct the mill 104 during one or more stages of the borehole departure process, such as drilling, milling, orienting, anchoring of the whipstock 102, or combinations thereof. Example steerable portions 122 may include bent housings, point-the-bit systems, push-the-bit systems, or other directional mechanisms. In some embodiments, the steerable portion 122 may be omitted, and the whipstock 102 alone may direct the path of the mill 104.

[0023] In some embodiments, the drill string 116 may transmit torque from the surface. For example, a kelly 126 mated to a rotary table 128 may transmit torque to the drill string 116. The kelly 126 may also move longitudinally relative to the rotary table 128 to transmit longitudinal force to the drill string 116. In other embodiments, the drill string 116 may be rotated by another torque-transmitting device, such as a top drive. In still other embodiments, a downhole torque-transmitting device, such as a mud motor or turbine-powered motor, may be used. Although FIG. 1 illustrates a land-based drilling system 100, the disclosed systems and methods may also be utilized in offshore drilling systems.

[0024] FIG. 2 illustrates the drilling system 100 in which a secondary borehole 132 is formed departing from the primary borehole 108 with the assistance of the whipstock 102. Formation of the secondary borehole 132 may occur after thePATENTAttorney Docket No.: WBRE / 0015PCbottomhole assembly 120, including the mill 104, is released from the whipstock 102. In some embodiments, this release may occur after fully or partially removing the connector 106 that previously coupled the bottomhole assembly 120 to the whipstock 102, as shown in FIG. 1. The orientation of the whipstock 102 within the primary borehole 108 may at least partially determine the orientation of the secondary borehole 132. In some embodiments, the primary ramp 160 of the whipstock 102 may guide the mill 104 away from the axis of the primary borehole 108 and toward the inner wall of the cased portion 112 of the primary borehole 108 to cut a window 115 in the casing and initiate departure into the secondary borehole 132.

[0025] In some embodiments, the whipstock 102 may be coupled to a securing device, such as an anchor 136. After the whipstock 102 has been positioned at a selected depth and orientation within the primary borehole 108, the anchor 136 may be activated to secure the whipstock 102 in place. Activation of the anchor 136 may include moving expandable members 137 radially outward to engage an internal wall of the primary borehole 108 or casing, such as by expansion of a sealing element or by other anchoring techniques, thereby securing the anchor 136 at a selected axial position and orientation. In some embodiments, securing the whipstock 102 in place may also facilitate separation of the whipstock 102 from the mill 104. The secondary borehole 132 may be drilled, and the whipstock 102 may be placed, by the same drill string 116 used to drill the primary borehole 108, although in other embodiments a different drill string may be used.

[0026] FIG. 3 illustrates an enlarged perspective view of an uphole end 102a of the whipstock 102. With brief additional reference to FIGS. 1 and 2, the uphole end 102a of the whipstock 102 may be the upper most (or most uphole) portion of the whipstock 102 in a borehole (such as the primary borehole 108). Thus, the uphole end 102a may be initially connected to the mill 104 when inserting and positioning the whipstock 102 in the primary borehole 108 as previously described, and the uphole end 102a may be the end of the whipstock 102 that initially engages with the mill 104 when initiating formation of the secondary borehole 132 (such as by forming the window 115 in the cased portion 112 as previously described).

[0027] As shown in FIG. 3, the whipstock 102 includes a primary ramp 160 that extends downhole from a region near the uphole end 102a and is configured to deflect a cutting tool, such as the mill 104 described above, away from the longitudinal axisPATENTAttorney Docket No.: WBRE / 0015PCof the primary borehole and toward the casing wall during initiation of a secondary borehole. In some embodiments, the primary ramp 160 may comprise an arcuate surface that gradually increases in radial thickness in the downhole direction so as to progressively guide the mill 104 (FIGS. 1 and 2) during a milling or drilling operation.

[0028] A deflection surface 162 is defined on the whipstock 102 that is positioned uphole of the primary ramp 16. In the illustrated embodiment, the deflection surface 162 is adjacent to the primary ramp 160 and is positioned between the primary ramp 160 and the uphole end 102a of the whipstock 102.

[0029] The deflection surface 162 may include a first or uphole end 162a and a second or downhole end 162b that is opposite the uphole end 162a. The downhole end 162b is located near the upper end of the primary ramp 160. In some embodiments, the deflection surface 162 may have a greater thickness than the adjacent portion of the primary ramp 160. As a result, a chamfer 164 may be defined between the deflection surface 162 and the primary ramp 160. The chamfer 164 may provide a transition region between the thicker deflection surface 162 and the primary ramp 160. Thus, during operations, the deflection surface 162 may provide an initial, relatively thicker contact region for the mill 104 before the mill 104 progresses onto the primary ramp 160.

[0030] In some embodiments, the deflection surface 162 may have a substantially constant thickness between the uphole end 162a and the downhole end 162a. In other embodiments, the thickness of the deflection surface 162 may vary along its length, such as by increasing in the downhole direction. Accordingly, although identified herein as a deflection surface 162, this feature may also be regarded in some embodiments as a ramped deflection surface or region.

[0031] FIG. 3 further shows a lead ramp 166 extending between the uphole end 102a of the whipstock 102 and the uphole end 162a of the deflection surface 162. The lead ramp 166 may be configured to guide the mill 104 onto the deflection surface 162 as the mill 104 first engages the whipstock 102 during deployment and / or window initiation. In some embodiments, the lead ramp 166 may increase in thickness in the downhole direction toward the deflection surface 162. In some implementations, the lead ramp 166 may increase in thickness at a faster rate than the primary ramp 160, thereby providing a relatively aggressive initial pickup surface for the mill 104.PATENTAttorney Docket No.: WBRE / 0015PC

[0032] A recess 168 is also formed at the uphole end 102a and extends into the lead ramp 166 and partially into the uphole end 162a of the deflection surface 162. In the illustrated embodiment, the recess 168 comprises an arcuate, concave surface that opens through the uphole end 102a of the whipstock 102. A connection port 169 is defined in and along the recess 168. The connection port 169 may be configured to receive a shear pin or another suitable frangible or releasable connector for initially coupling the whipstock 102 to the mill 104 or to another component of the downhole assembly during run-in and positioning of the whipstock 102 within a primary borehole (such as borehole 108 shown in FIG. 1).

[0033] Turning now to FIG. 4, a side cross-sectional view is shown of the mill 104 and the whipstock 102 positioned within a casing 150 of a primary borehole, such as the borehole 108 described above with reference to FIGS. 1 and 2. FIG. 4 generally illustrates the relative positioning of the mill 104 and the whipstock 102 within the casing 150 during initiation of a window-forming operation, and further illustrates various dimensional features of the casing 150, the mill 104, and the whipstock 102 that may affect deflection of the mill 104 into engagement with the casing 150.

[0034] As shown in FIG. 4, the casing 150 may comprise a generally tubular member extending along a central axis 155 and defining an interior through which the mill 104 and whipstock 102 may be positioned. The casing 150 may include an inner diameter IDiso and an outer diameter OD150. The casing 150 may further include a wall thickness T150 measured in a radial direction between the inner wall and the outer wall of the casing 150. In some embodiments, the wall thickness T150 may be substantially uniform around the circumference of the casing 150 and along an axial length of the portion being engaged during the window-forming operation. In some embodiments, the wall thickness T150 may be defined as one-half of the difference between the outer diameter OD150 and the inner diameter IDiso (e.g., T150= - x (O£)150- Z£)15O)). Accordingly, the dimensions IDiso, OD150, and T150 may collectively define the size and structural characteristics of the casing 150 and may affect the manner in which the mill 104 is deflected into and engages the inner wall of the casing 150 during initiation of the window.

[0035] In some embodiments, the dimensions of the casing 150 (including the outer diameter OD150, inner diameter IDiso, and wall thickness Tiso) may be selected based on the intended well environment, pressure conditions, and mechanical loadingPATENTAttorney Docket No.: WBRE / 0015PCexpected within the primary borehole. For example, a casing 150 having a relatively larger wall thickness T150, a relatively larger outer diameter OD150, or both, may present a more substantial section of material to be cut during initiation of the window. As a result, the dimensional characteristics of the casing 150 may be considered in connection with the configuration of the whipstock 102 and the mill 104 to promote controlled engagement of the mill 104 with the casing 150 and reliable formation of a window having a desired location and geometry.

[0036] In some embodiments, the outer diameter OD150 of the casing 150 may be in a range of from about 7.000 inches to about 14.000 inches, such as from about 7.000 inches to about 13.375 inches, such as from about 7.625 inches to about 14.000 inches, such as from about 9.625 inches to about 14.000 inches, or such as from about 9.875 inches to about 10.125 inches. In some embodiments, the inner diameter ID150 of the casing 150 may be in a range of from about 5.875 inches to about 12.250 inches, such as from about 5.875 inches to about 8.500 inches, or such as from about 8.500 inches to about 12.250 inches. In some embodiments, the wall thickness T150 of the casing 150 may be a range of from about 0.750 inches to about 1.00 inches, such as from about 0.800 inches to about 0.900 inches, or such as from about 0.800 inches to about 0.875 inches. In some embodiments, the wall thickness T150 may be greater than 1.00 inches. Still other values and ranges are contemplated for each of the outer diameter OD150, inner diameter ID150, and wall thickness T150.

[0037] In some embodiments, the casing 150 may be manufactured from any suitable material or combination of materials selected to provide desired structural strength, pressure containment, corrosion resistance, wear resistance, drillability, millability, or other operational characteristics for use within the primary borehole. By way of example, the casing 150 may be formed from one or more metallic materials, metal alloys, non-metallic materials, composite materials, fiber-reinforced materials, or layered combinations thereof.

[0038] In some embodiments, the casing 150 may be formed from one or more high-strength materials selected to provide desired tensile yield strength for downhole use. By way of example, the casing 150 may comprise one or more alloy steels having tensile yield strengths of about 125 ksi to about 140 ksi or greater, which may exceed historically observed yield strengths of about 80 ksi to about 110 ksi. In some embodiments, one or more alloying elements, such as nickel, chromium, orPATENTAttorney Docket No.: WBRE / 0015PCcombinations thereof, may be included to increase strength, although such material selections may also increase the difficulty of creating and milling the window in the casing 150.

[0039] As further shown in FIG. 4, the mill 104 may comprise a plurality of milling sections or mills arranged and spaced along the central axis 155 of the casing 150. In the illustrated embodiment, the mill 104 may be configured as a “mill assembly” that includes a lead mill 104a and a follow mill 104b that are axially spaced from one another along the central axis 155. The lead mill 104a may be positioned downhole of the follow mill 104b such that, as the mill 104 is advanced downhole within the casing 150 and into engagement with the whipstock 102, the lead mill 104a contacts the whipstock 102 before the follow mill 104b. In this manner, the lead mill 104a may begin to ride along the uphole end 102a of the whipstock 102 and initiate radial deflection of the mill 104 toward the inner wall of the casing 150 prior to corresponding engagement of the follow mill 104b with the whipstock 102. In some embodiments, during initiation of the window, the lead mill 104a and the follow mill 104b may concurrently contact the inner wall of the casing 150. The relative axial positions of the lead mill 104a and the follow mill 104b may therefore affect the manner in which the mill 104 is progressively deflected into the casing 150 during initiation of the window-forming operation.

[0040] The lead mill 104a and the follow mill 104b may be separated by a mill spacing L104. In some embodiments, the mill spacing L104 may be defined axially, relative to the central axis 155, between the lead mill 104a and the follow mill 104b. Thus, the mill spacing L104 may also be defined axially between the lead mill 104a and the follow mill 104b along a longitudinal axis (not shown) of the mill 104 (or mill assembly as previously described). In some embodiments, the mill spacing L104 may be defined axially (e.g., along axis 155) between a widest or gauge diameter of the lead mill 104a and a widest or gauge diameter of the follow mill 104b. Thus, the mill spacing L104 may characterize the axial offset between the principal cutting regions of the lead mill 104a and the follow mill 104b. Each of the lead mill 104a and the follow mill 104b may include one or more blades each carrying a hard coating and / or one or more cutter elements that are configured to engage and remove material from the casing 150. Accordingly, when the mill 104 is rotated and deflected radially outward into engagement with the inner wall of the casing 150, the lead mill 104a and the followPATENTAttorney Docket No.: WBRE / 0015PCmill 104b may cooperatively shear, cut, or otherwise remove casing material to initiate the formation of a window in the casing 150. In some embodiments, selection of the mill spacing L104 may influence the timing with which the lead mill 104a and the follow mill 104b engage the casing 150, which may in turn affect the location, length, and overall geometry of the resulting window.

[0041] As further shown in FIG. 4, the deflection surface 162 may have a thickness T162 measured radially relative to the axis 155 of the casing 150. In some embodiments, the thickness T162 of the deflection surface 162 may be greater than the thickness T o of the axially adjacent portion of the primary ramp 160, such that the deflection surface 162 presents a relatively enlarged outer profile for initial engagement with the mill 104. In some embodiments, the thickness T 2 may be about 0.25 inches to about 0.50 inches, or more, greater than the thickness Two of the axially adjacent portion of the primary ramp 160.

[0042] In this manner, the deflection surface 162 may initially urge the lead mill 104a and the follow mill 104b radially outward within the casing 150 before the mills progress further along the primary ramp 160. As previously described, the increased thickness of the deflection surface 162 relative to the primary ramp 160 may define the chamfer 164 therebetween and may provide a transition that promotes controlled redirection of the mill 104 into engagement with the inner wall of the casing 150 during initiation of the window-forming operation. In some embodiments, and as previously described, the thickness Tw2 may be substantially constant between the uphole end 162a and the downhole end 162b. In other embodiments, the thickness Tw2 may vary along the deflection surface 162, such as by increasing in the downhole direction (that is from the uphole end 162a to the downhole end 162b), such that the deflection surface 162 may itself provide a ramped deflection profile.

[0043] In some embodiments, the thickness Tw2 of the deflection surface 162 may be in a range of from about 2.000 inches to about 4.000 inches. In some embodiments, the thickness Tw2 may be in a range of from about 2.000 inches to about 3.500 inches, such as from about 2.000 inches to about 3.000 inches, such as from about 2.250 inches to about 3.750 inches, such as from about 2.250 inches to about 3.250 inches, such as from about 2.375 inches to about 4.000 inches, such as from about 2.375 inches to about 3.500 inches, such as from about 2.500 inches to about 3.500 inches, or such as from about 2.500 inches to about 3.000 inches. InPATENTAttorney Docket No.: WBRE / 0015PCsome embodiments, the thickness T162 may be about 2.000 inches, about 2.250 inches, about 2.375 inches, about 2.500 inches, about 3.000 inches, about 3.500 inches, or about 4.000 inches. Still other values are contemplated.

[0044] The deflection surface 162 may further have an axial length L162 measured along the axis 155 of the casing 150 between the uphole end 162a and the downhole end 162b. The axial length L162 may therefore define the extent of the deflection surface 162 over which the mill 104 is engaged and redirected before the mill 104 transitions fully onto the primary ramp 160. In some embodiments, and as is described in more detail herein, the axial length L162 may be selected in coordination with the configuration of the mill 104, including the relative spacing of the lead mill 104a and the follow mill 104b, so that the mills are supported and deflected in a controlled manner during initial contact with the whipstock 102. As a result, the dimensions of the deflection surface 162, including the thickness T162 and the axial length L162, may be selected to influence the timing and manner in which the lead mill 104a and the follow mill 104b engage the inner wall of the casing 150, thereby promoting formation of a window at a desired location and with a desired geometry.

[0045] In some embodiments, the axial length L162 of the deflection surface 162 may be in a range of from about 14.000 inches to about 34.000 inches. In some embodiments, the axial length L162 may be in a range of from about 14.000 inches to about 30.000 inches, such as from about 14.000 inches to about 26.000 inches, such as from about 16.000 inches to about 34.000 inches, such as from about 18.000 inches to about 32.000 inches, such as from about 20.000 inches to about 30.000 inches, such as from about 22.000 inches to about 28.000 inches, such as from about 24.000 inches to about 30.000 inches, or such as from about 26.000 inches to about 34.000 inches. In some embodiments, the axial length L162 may be about 14.000 inches, about 16.000 inches, about 18.000 inches, about 20.000 inches, about 22.000 inches, about 24.000 inches, about 26.000 inches, about 28.000 inches, about 30.000 inches, about 32.000 inches, or about 34.000 inches.

[0046] As previously described, in some embodiments, the thickness T162 of the deflection surface 162 may be selected relative to one or more other dimensional parameters of the system so that the lead mill 104a and the follow mill 104b are urged into the inner wall of the casing 150 in a controlled and repeatable manner during initiation of the window-forming operation. For example, the thickness T162 may bePATENTAttorney Docket No.: WBRE / 0015PCselected relative to the wall thickness T150 and outer diameter OD150 of the casing 150 such that the deflection surface 162 provides sufficient radial displacement of the mill 104 to initiate the window (window 115 in FIG. 2) relatively close to the uphole end 102a of the whipstock 102. In some embodiments, a thickness ratio A may be defined by Equation 1 as follows:A = — — (1).Ti5oxor)15Q

[0047] In some embodiments, the thickness ratio A may be in a range of from about 0.270 to about 0.330. In some embodiments, the thickness ratio A may be in a range of from about 0.285 to about 0.315. In some embodiments, the thickness ratio A may be about 0.300. Selection of the thickness T162 such that the thickness ratio A falls within one or more of these ranges may promote reliable initial engagement of the mill 104 with the casing 150 and may assist in initiating a window at a desired depth and with desired dimensional characteristics.

[0048] In some embodiments, the axial length L162 of the deflection surface 162 may likewise be selected in relation to the configuration of the mill 104, including the spacing between the lead mill 104a and the follow mill 104b. More particularly, the axial length L162 may be selected so that the deflection surface 162 supports the mill 104 over a sufficient axial distance to coordinate engagement of the lead mill 104a and the follow mill 104b with the casing 150 during the initial window formation stage. In some embodiments, a length ratio B may be defined by Equation (2) as follows:B =(2).L162

[0049] In some embodiments, the length ratio B may be in a range of from about 1.040 to about 1.560. In some embodiments, the length ratio B may be in a range of from about 1.170 to about 1.430. In some embodiments, the length ratio B may be in a range of from about 1.235 to about 1.365. In some embodiments, the length ratio B may be in a range of from about 1.2 to about 1.4. In some embodiments, the length ratio B may be about 1.300. Selection of the axial length L162 such that the length ratio B falls within one or more of these ranges may improve the timing with which the lead mill 104a and the follow mill 104b enter cutting engagement with the casing 150 during initiation of the window.

[0050] Without being bound by theory, selection of the thickness T162 and the axial length L162 of the deflection surface 162 such that one or both of the thickness ratio APATENTAttorney Docket No.: WBRE / 0015PCand the length ratio B are within the foregoing ranges may allow the lead mill 104a and the follow mill 104b to contact the inner wall of the casing 150 at approximately the same time during the initial window-forming operation. Such coordinated engagement may promote more consistent formation of the window in casings which have a greater strength and wall thickness (T162) to optimize the window profile, to reduce the likelihood that the initial cutout is misplaced or formed outside of a desired specification, and to thereby provide a window having dimensions suitable for subsequent formation of the secondary borehole 132.

[0051] In some embodiments, the deflection surface 162 and / or the lead ramp 166 at the uphole end 102a of the whipstock 102 may together define a sacrificial entry ramp or sacrificial cutout ramp. In such embodiments, at least a portion of the material of the whipstock 102 in this region may be intentionally configured to be removed by the mill 104 during initiation of the window in the casing 150. Stated differently, the uphole ramp region of the whipstock 102 may be dimensioned not only to redirect the mill 104, but also to provide a controlled amount of sacrificial material that may be milled away as the lead mill 104a and the follow mill 104b begin cutting into the casing 150. This sacrificial interaction may assist in establishing the initial cutout and in directing the mill 104 outward into the wall of the casing 150 in a controlled manner.

[0052] In some embodiments, the sacrificial entry ramp defined by the deflection surface 162 and / or lead ramp 166 may provide sufficient material at the uphole portion of the whipstock 102 to allow the mill 104 to engage and begin cutting the whipstock 102 early in the window initiation process, thereby creating a foundation for outward cutting into the casing 150. The amount of sacrificial material may be selected to be adequate to promote timely engagement of the mill 104 with the casing 150, while avoiding an excessive amount of material that could delay cutout initiation or undesirably alter the resulting window geometry. Accordingly, the geometry of the deflection surface 162 and the lead ramp 166 may be selected such that the mill 104 achieves a relatively quick cutout, which in turn may permit formation of a longer fullgage window for a given overall whipstock length. In this regard, the disclosed configurations may improve the usable length of the completed window without requiring a corresponding increase in the overall length of the whipstock 102.

[0053] In some embodiments, selection of the sacrificial entry ramp geometry may be particularly beneficial in applications involving relatively large-diameter casing,PATENTAttorney Docket No.: WBRE / 0015PCrelatively thick-walled casing, relatively high-weight casing, relatively high-strength casing grades, or combinations thereof. As the size, wall thickness, or strength of the casing 150 increases, greater material removal may be involved in establishing the initial cutout, and the dimensions of the uphole ramp region of the whipstock 102 may be selected accordingly to promote proper initiation of the window. In some embodiments, the axial extent of the sacrificial entry ramp may be sufficient to allow each active cutting section of the mill 104, including the lead mill 104a and the follow mill 104b, to participate in the cutout operation as the mill 104 advances along the whipstock 102. By coordinating the sacrificial ramp geometry with the cutting profile of the mill 104 and the characteristics of the casing 150, the disclosed whipstock 102 may promote more reliable window initiation and improved consistency in the resulting window dimensions.

[0054] As explained above and reiterated below, the present disclosure includes, without limitation, the following Examples.

[0055] Example 1: A drilling system for forming a secondary borehole from a primary borehole, the drilling system comprising: a casing extending along a central axis, the casing having an outer diameter (OD150) and a wall thickness (Tiso); and a whipstock positioned within the casing and having an uphole end, a primary ramp, and a deflection surface positioned between the uphole end and the primary ramp, the deflection surface having a thickness (T162) that is greater than a thickness of a portion of the primary ramp that is immediately adjacent to the deflection surface, wherein a thickness ratio A is defined as A = — — — , and wherein the thickness Ti 5oxOD150ratio A is in a range of from about 0.270 to about 0.330.

[0056] Example 2: The drilling system of any of the Examples, wherein the thickness ratio A is in a range of from about 0.285 to about 0.315.

[0057] Example 3: The drilling system of any of the Examples, wherein the thickness ratio A is about 0.300.

[0058] Example 4: The drilling system of any of the Examples, wherein the wall thickness of the casing is in a range of from about 0.750 inches to about 1.00 inches.

[0059] Example 5: The drilling system of any of the Examples, wherein a chamfer is defined between the deflection surface and the primary ramp.

[0060] Example 6: The drilling system of any of the Examples, wherein the whipstock includes a lead ramp extending between the uphole end of the whipstockPATENTAttorney Docket No.: WBRE / 0015PCand an uphole end of the deflection surface, and wherein a recess is formed at the uphole end of the whipstock and extends into the lead ramp and partially into the uphole end of the deflection surface.

[0061] Example 7: The drilling system of any of the Examples, further comprising a mill assembly including a lead mill and a follow mill that is axially spaced from the lead mill along the central axis of the casing.

[0062] Example 8: The drilling system of any of the Examples, wherein a length ratio B is defined as a ratio of an axial length of the deflection surface to a mill spacing axially between the lead mill and the follow mill along the central axis, and wherein the length ratio B is in a range of from about 1.040 to about 1.560.

[0063] Example 9: A drilling system for forming a secondary borehole from a primary borehole, the drilling system comprising: a whipstock having an uphole end, a primary ramp, and a deflection surface positioned between the uphole end and the primary ramp, wherein the deflection surface has a thickness that is greater than a thickness of a portion of the primary ramp that is immediately adjacent to the deflection surface, wherein the deflection surface has an uphole end, a downhole end opposite the uphole end of the deflection surface, and an axial length L162 measured between the uphole end of the deflection surface and the downhole end of the deflection surface; and a mill assembly including a lead mill and a follow mill spaced from the lead mill by a mill spacing L104 along a longitudinal axis of the mill assembly, wherein a length ratio B is defined as B =and wherein the length ratio B is in a range offrom about 1.040 to about 1.560.

[0064] Example 10: The drilling system of any of the Examples, wherein the length ratio B is in a range of from about 1.2 to about 1.4.

[0065] Example 11: The drilling system of any of the Examples, wherein the whipstock includes a lead ramp extending between the uphole end of the whipstock and the uphole end of the deflection surface, and wherein a recess is formed at the uphole end of the whipstock and extends into the lead ramp and partially into the uphole end of the deflection surface.

[0066] Example 12: The drilling system of any of the Examples, further comprising a casing extending along a central axis and having a wall thickness in a range of from about 0.750 inches to about 1.00 inches.PATENTAttorney Docket No.: WBRE / 0015PC

[0067] Example 13: The drilling system of any of the Examples, wherein the casing has an outer diameter (OD150), wherein the thickness of the deflection surface is represented by T162, wherein a thickness ratio A is defined as A = — — — , and ’T'ISOXOAISO wherein the thickness ratio A is in a range of from about 0.270 to about 0.330.

[0068] Example 14: The drilling system of any of the Examples, wherein the thickness ratio A is in a range of from about 0.285 to about 0.315.

[0069] Example 15: The drilling system of any of the Examples, wherein the thickness ratio A is about 0.300.

[0070] Example 16: A drilling system for forming a secondary borehole from a primary borehole, the drilling system comprising: a casing extending along a central axis, the casing having an outer diameter (OD150) and a wall thickness (Tiso); a whipstock positioned within the casing and having an uphole end, a primary ramp, and a deflection surface positioned between the uphole end and the primary ramp, wherein the deflection surface has a thickness T162 that is greater than a thickness of a portion of the primary ramp that is immediately adjacent to the deflection surface, and wherein the deflection surface has an uphole end, a downhole end opposite the uphole end of the deflection surface, and an axial length L162 measured between the uphole end of the deflection surface and the downhole end of the deflection surface relative to the central axis; and a mill assembly including a lead mill and a follow mill spaced from the lead mill by a mill spacing (L104) along the central axis, wherein a thickness ratio A is defined as A = —— — , wherein the thickness ratio A is in a TISOXOD15Qrange of from about 0.270 to about 0.330, wherein a length ratio B is defined as B = and wherein the length ratio B is in a range of from about 1.040 to about 1.560.

[0071] Example 17: The drilling system of any of the Examples, wherein the thickness ratio A is about 0.300.

[0072] Example 18: The drilling system of any of the Examples, wherein the length ratio B is in a range of from about 1.2 to about 1.4.

[0073] Example 19: The drilling system of any of the Examples, wherein the wall thickness of the casing is in a range of from about 0.750 inches to about 1.00 inches.

[0074] Example 20: The drilling system of any of the Examples, wherein the whipstock includes a lead ramp extending between the uphole end of the whipstock and an uphole end of the deflection surface, and wherein a recess is formed at thePATENTAttorney Docket No.: WBRE / 0015PCuphole end of the whipstock and extends into the lead ramp and partially into the uphole end of the deflection surface.

[0075] Embodiments disclosed herein are directed to drilling systems for forming a secondary borehole, the drilling systems including a whipstock having an additional deflection surface configured to reliably deflect a cutting tool, such as a mill, and thereby promote proper initiation of a window in casing. In some embodiments, the deflection surface is thicker than and positioned adjacent to a primary ramp of the whipstock. The deflection surface may be configured to engage and direct the mill during initiation of the casing window. The deflection surface may also be sized and shaped relative to one or more parameters of the mill and the casing so that the mill is directed into the casing in a controlled fashion during the initial cutout. In this manner, the disclosed whipstock configurations may improve initiation of the casing window, particularly in heavier walled or heavier gauged casing pipe, and may thereby promote initiation and formation of the window at a desired location toward the uphole end of the whipstock and with a desired geometry for subsequent drilling of the secondary borehole.

[0076] The preceding discussion is directed to various embodiments. However, one of ordinary skill in the art will understand that the examples disclosed herein have broad application, and that the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to suggest that the scope of the disclosure, including the claims, is limited to that embodiment.

[0077] The drawing figures are not necessarily to scale. Certain features and components herein may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in interest of clarity and conciseness.

[0078] In the preceding discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection of the two devices, or through an indirect connection that is established via other devices, components, nodes, and connections. In addition, as used herein, the terms “axial” and “axially” generally mean along or parallel to a given axis (e.g., central axis of aPATENTAttorney Docket No.: WBRE / 0015PCbody or a port), while the terms “radial” and “radially” generally mean perpendicular to the given axis. For instance, an axial distance refers to a distance measured along or parallel to the axis, and a radial distance means a distance measured perpendicular to the axis. Further, when used herein (including in the claims), the words “about,” “generally,” “substantially,” “approximately,” and the like, when used to refer to a stated value, mean within a range of plus or minus 10% of the stated value.

[0079] While exemplary embodiments have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teachings herein. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the systems, apparatus, and processes described herein are possible and are within the scope of the disclosure. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims. Unless expressly stated otherwise, the operations in a method claim may be performed in any order. The recitation of identifiers such as (a), (b), (c) or (1 ), (2), (3) before operations in a method claim are not intended to and do not specify a particular order to the operations, but rather are used to simplify subsequent reference to such operations.

Claims

PATENTAttorney Docket No.: WBRE / 0015PCWhat is claimed is:

1. A drilling system for forming a secondary borehole from a primary borehole, the drilling system comprising:a casing extending along a central axis, the casing having an outer diameter (OD150) and a wall thickness (T150);a whipstock positioned within the casing and having an uphole end, a primary ramp, and a deflection surface positioned between the uphole end and the primary ramp, wherein the deflection surface has a thickness T162 that is greater than a thickness of a portion of the primary ramp that is immediately adjacent to the deflection surface, and wherein the deflection surface has an uphole end, a downhole end opposite the uphole end of the deflection surface, and an axial length L162 measured between the uphole end of the deflection surface and the downhole end of the deflection surface relative to the central axis; anda mill assembly including a lead mill and a follow mill spaced from the lead mill by a mill spacing (L104) along the central axis,wherein a thickness ratio A is defined asA = — — — ,TISOXOD15Qwherein the thickness ratio A is in a range of from about 0.270 to about 0.330, wherein a length ratio B is defined asB = andL162wherein the length ratio B is in a range of from about 1.040 to about 1.560.

2. The drilling system of claim 1 , wherein the thickness ratio A is about 0.300.

3. The drilling system of claim 2, wherein the length ratio B is in a range of from about 1.2 to about 1.4.

4. The drilling system of claim 3, wherein the wall thickness of the casing is in a range of from about 0.750 inches to about 1.00 inches.PATENTAttorney Docket No.: WBRE / 0015PC5. The drilling system of claim 4, wherein the whipstock includes a lead ramp extending between the uphole end of the whipstock and an uphole end of the deflection surface, and wherein a recess is formed at the uphole end of the whipstock and extends into the lead ramp and partially into the uphole end of the deflection surface.

6. A drilling system for forming a secondary borehole from a primary borehole, the drilling system comprising:a casing extending along a central axis, the casing having an outer diameter (ODi5o) and a wall thickness (Tiso); anda whipstock positioned within the casing and having an uphole end, a primary ramp, and a deflection surface positioned between the uphole end and the primary ramp, the deflection surface having a thickness (T162) that is greater than a thickness of a portion of the primary ramp that is immediately adjacent to the deflection surface, wherein a thickness ratio A is defined asA = — — — , andT150XOD|5Qwherein the thickness ratio A is in a range of from about 0.270 to about 0.330.

7. The drilling system of claim 6, wherein the thickness ratio A is in a range of from about 0.285 to about 0.315.

8. The drilling system of claim 6, wherein the thickness ratio A is about 0.300.

9. The drilling system of claim 6, wherein the wall thickness of the casing is in a range of from about 0.750 inches to about 1.00 inches.

10. The drilling system of claim 6, wherein a chamfer is defined between the deflection surface and the primary ramp.

11. The drilling system of claim 6, wherein the whipstock includes a lead ramp extending between the uphole end of the whipstock and an uphole end of the deflection surface, and wherein a recess is formed at the uphole end of the whipstockPATENTAttorney Docket No.: WBRE / 0015PCand extends into the lead ramp and partially into the uphole end of the deflection surface.

12. The drilling system of claim 11 , further comprising a mill assembly including a lead mill and a follow mill that is axially spaced from the lead mill along the central axis of the casing.

13. The drilling system of claim 12, wherein a length ratio B is defined as a ratio of an axial length of the deflection surface to a mill spacing axially between the lead mill and the follow mill along the central axis, and wherein the length ratio B is in a range of from about 1.040 to about 1.560.

14. A drilling system for forming a secondary borehole from a primary borehole, the drilling system comprising:a whipstock having an uphole end, a primary ramp, and a deflection surface positioned between the uphole end and the primary ramp, wherein the deflection surface has a thickness that is greater than a thickness of a portion of the primary ramp that is immediately adjacent to the deflection surface,wherein the deflection surface has an uphole end, a downhole end opposite the uphole end of the deflection surface, and an axial length L162 measured between the uphole end of the deflection surface and the downhole end of the deflection surface; and a mill assembly including a lead mill and a follow mill spaced from the lead mill by a mill spacing L104 along a longitudinal axis of the mill assembly, wherein a length ratio B is defined asB = andL162wherein the length ratio B is in a range of from about 1.040 to about 1.560.

15. The drilling system of claim 14, wherein the length ratio B is in a range of from about 1.2 to about 1.4.PATENTAttorney Docket No.: WBRE / 0015PC16. The drilling system of claim 15, wherein the whipstock includes a lead ramp extending between the uphole end of the whipstock and the uphole end of the deflection surface, and wherein a recess is formed at the uphole end of the whipstock and extends into the lead ramp and partially into the uphole end of the deflection surface.

17. The drilling system of claim 15, further comprising a casing extending along a central axis and having a wall thickness in a range of from about 0.750 inches to about 1.00 inches.

18. The drilling system of claim 17, wherein the casing has an outer diameter (OD150),wherein the thickness of the deflection surface is represented by T162, wherein a thickness ratio A is defined asA _ — Tie? — ,and’T'ISOXOAISOwherein the thickness ratio A is in a range of from about 0.270 to about 0.330.

19. The drilling system of claim 18, wherein the thickness ratio A is in a range of from about 0.285 to about 0.315.

20. The drilling system of claim 18, wherein the thickness ratio A is about 0.300.

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