BI-MILL DEPLOYED WITH DUAL-ACTION HYDRAULICALLY OPERABLE ANCHOR AND METHODS OF OPERATION AND MANUFACTURE FOR WELLBORE DEPARTURE MILLING

Abstract

Sidetracking system including dual-action hydraulically operable anchor for positioning a whipstock in a wellbore and a bi-mill for milling an opening through a wellbore casing in a preplanned lateral drilling path in departure from the wellbore axis and through the wellbore casing or rock formation and in the direction of the drilling path. The anchor's upper and lower hydraulic pistons provide two compressive forces with a third mechanical force being applied from the attached whipstock and workstrin all forces being additive, to compressively set the floating mandrel. The three additive forces function to fix the anchor in the wellbore with extremely great force. The bi-mill mills an opening through a wellbore casing in a preplanned lateral drilling path in departure from the wellbore axis and through the wellbore casing or rock formation and in the direction of the drilling path. The bi-mill provides high-TFA fluid passages for increased fluid flow to the mill plateau, extremely dense cutting structure, and tuned debris removal channels for rapid milling with low torque. The synergistic operation of the anchor and buy mill function reduce rig time and ensure fast and reliable wellbore exit.

Claims

1. A wellbore departure system for deploying a dual-action hydraulically operable anchor in cooperation with a bi-mill for wellbore exit milling, comprising: a hydraulic anchor comprising a hydraulic anchor body, and an upper hydraulic piston and an opposing lower hydraulic piston, said upper hydraulic piston and said lower hydraulic piston for fixing an anchor in a wellbore to fixedly position whipstock in a wellbore, said whipstock for wellbore exit milling and for guiding lateral drilling outside the wellbore, said hydraulic anchor further comprising: an upper sub for slidably engaging and housing a floating mandrel, said upper sub also housing said upper hydraulic piston; a split clamp flexibly retaining said upper sub and fixedly retaining said hydraulic anchor body with confined movement toward and away from said upper sub and hydraulic anchor body; a lower cap fixedly coupled to said hydraulic anchor body and comprising a guide nose for guiding said hydraulic anchor within said wellbore, said lower cap and said hydraulic anchor body forming a fixed housing; a floating mandrel comprising a mandrel with threadably attached upper hydraulic piston and slidably moveable within said upper sub and said fixed housing and along the longitudinal axis of said fixed housing for transmitting a hydraulic fluid into said fixed housing or, alternatively, for transmitting compressive force from said upper hydraulic piston, or alternatively, for transmitting compressive force deriving from mechanical force applied to the work string and adjoining bottomhole assembly above and adjoining the hydraulic anchor; said lower hydraulic piston located below said upper hydraulic piston and operable from a first position to a second position along said floating mandrel using said transmitted hydraulic fluid; a T-slot adapter engaging said mandrel piston; a slip engaging said T-slot adapter and slidable within said fixed housing from a flush position along said fixed housing to an extended position along said fixed housing in response to movement of said T-slot adapter and said mandrel piston within said fixed housing, such that said slip firmly engages the wellbore to hold said hydraulic anchor and said whipstock in a fixed position within the wellbore, thereby providing a path for lateral drilling outside the wellbore: and a threaded ratchet nut attached to said lower hydraulic piston and slidably moveable along a threaded portion of the floating mandrel, said threaded ratchet nut mechanically locking said lower hydraulic piston in a second position, with said slips being retained mechanically in the extended position engaging the wellbore wall; and further comprising a bi-mill for milling an opening through a wellbore wall or casing in initiating a preplanned lateral drilling path in departure from the wellbore axis and through the wellbore casing or wellbore rock formation, and further continuing into underground rock formation outside the wellbore and in the direction of the preplanned lateral drilling path and as guided by a wellbore whipstock.

2. The wellbore departure system of claim 1, wherein said bi-mill further comprises: an assembly comprising a lead mill and a follow mill, said lead mill threadably attached to said follow mill, said lead mill comprising; a body forming a structural base for said lead mill, and further comprising: a smooth bore in the lead mill for receiving a circumferentially-grooved shear bolt, said shear bolt comprising a threaded end threadably attached to the wellbore whipstock and with the unthreaded end inserted into said smooth bore, said lead mill comprising a plurality of fluid passageways wherein said smooth bore comprises a sufficiently shallow depth so as to not intersect with internal fluid passageways and so as to not exit the distal side of said lead mill, said lead mill further comprising an external bore and a retaining pin inserted through said external bore for intersecting said smooth bore; and said shear bolt comprising a groove, wherein said retaining pin further inserts into said groove for retaining said shear bolt within said smooth bore; said lead mill further comprising a nose and wherein at least four fluid passageways lead from a central axial fluid passageway inside said lead mill and exit at a plateau defined as the end portion of said nose with an area perpendicular and obtuse in relation a central fluid passageway of said lead mill; a plurality of debris removal channels formed as recessed paths within said body and forming a plurality of exit paths for channeling milled debris away from said lead mill and in the direction of said follow mill; a plurality of milling inserts positioned on said lead mill and positioned in rows adjacent said debris removal channels for milling through said wellbore casing or wellbore rock formation and into said underground rock formation, with at least three rows of milling inserts originating contiguously from the center, and extending from the center, of said plateau down the side of said lead mill in continuity; said debris removal channels further formed in a helical configuration for guiding debris milled by said inserts along said debris removal channels and away from said lead mill and in the direction of said follow mill; said lead mill and said follow mill configured to follow a path defined by the wellbore whipstock to continue milling through said wellbore casing and into the underground rock formation a distance sufficient to initiate said preplanned drilling path.

3. The wellbore departure system of claim 1, further comprising a Belleville spring assembly for keeping said upper sub and said anchor body spread apart under normal, static conditions, wherein said split clamps retain said upper sub and said anchor body together.

4. The wellbore departure system of claim 3, wherein said Bellevile spring assembly provides a cushioning effect for aiding in helping said anchor body to absorb shocks as said anchor moves within the wellbore prior to setting.

5. The wellbore departure system of claim 1, further comprising a castellated top matching a similar form at the bottom portion of upper sub and for allowing smooth, slidable, torque resistant movement between said anchor body and a matching castellated lower portion of said upper sub.

6. The wellbore departure system of claim 1, wherein actuation of said lower piston forces said slips outward from said anchor body and concurrently advances said locking ratchet nut along a threaded portion of said floating mandrel.

7. The wellbore departure system of claim 1, wherein said upper piston and said lower piston apply forces in opposite directions for pushing said slips outward from said anchor body using said upper piston and pushing said floating mandrel downward and using said lower piston to advance slidably attached T-slot adapter upward advancing slidably attached slips outward, with compressive force applied from a surface rig pushing said floating mandrel downward concurrently with said piston forces, the three said forces being concurrently applied and additive.

8. The hydraulic anchor of claim 7, wherein said slips moving outward from said anchor body cause said slips to contact and engage the wellbore wall once the hydraulic anchor reaches a desired depth and circumferential orientation.

9. A method for operating a wellbore departure system comprising a dual-action hydraulically operable anchor cooperating with a bi-mill for wellbore exit milling, comprising the steps of: providing a hydraulic anchor comprising a hydraulic anchor body, and an upper hydraulic piston and an opposing lower hydraulic piston, said upper hydraulic piston and said lower hydraulic piston for fixing an anchor in a wellbore to fixedly position a whipstock in a wellbore, said whipstock for wellbore exit milling and for guiding lateral drilling outside the wellbore, said hydraulic anchor further comprising: engaging and housing a floating mandrel within an upper sub, said upper sub also housing said upper hydraulic piston; flexibly retaining said upper sub and said hydraulic anchor body using a split clamp to provide confined movement toward and away from said upper sub and hydraulic anchor body; guiding said hydraulic anchor within said wellbore using a lower cap fixedly coupled to said hydraulic anchor body and a guide nose, forming a fixed housing comprising said lower cap and said hydraulic anchor body; providing a floating mandrel comprising a mandrel with a threadably attached hydraulic piston slidably moveable within said upper sub and fixed housing and along the longitudinal axis of said fixed housing or, alternatively, for transmitting compressive force from said upper hydraulic piston using said floating mandrel, or alternatively, for transmitting compressive force deriving from mechanical force applied to the a workstring adjoining a bottom hole assembly adjoining said hydraulic anchor using said floating mandrel; operating said lower hydraulic piston located below said upper hydraulic piston from a first position to a second position along said floating mandrel using said transmitted hydraulic fluid; engaging said mandrel piston using a T-slot adapter; engaging said T-slot adapter within said fixed housing from a flush position along said fixed housing to an extended position along said fixed housing in response to movement of said T-slot adapter and said mandrel piston within said fixed housing using a slip for slidably, such that said slip firmly engages the wellbore to hold said hydraulic anchor and said whipstock in a fixed position within the wellbore, thereby providing a path for lateral drilling outside the wellbore; and slidably and movably attaching a threaded ratchet nut to said lower hydraulic piston along a threaded portion of the floating mandrel, and mechanically locking said lower hydraulic piston in a second position with said threaded ratchet nut, said slips being retained mechanically in the extended position engaging the wellbore wall; and further comprising the step of milling an opening through a wellbore casing in initiating a preplanned lateral drilling path in departure from the wellbore axis and through the wellbore casing or wellbore rock formation, and further continuing into underground rock formation outside the wellbore and in the direction of the preplanned lateral drilling path and as guided by a wellbore whipstock.

10. The method for operating a wellbore departure system of claim 9, further comprising the steps of: providing a bi-mill comprising an assembly, said assembly further comprising a lead mill and a follow mill, said lead mill threadably attached to said follow mill, said method further comprising the steps of; providing a structural base for said lead mill using a body, and further comprising the steps of; providing a smooth bore in the lead mill into which a circumferentially-grooved shear bolt is inserted, with a threaded end threadably attached to the wellbore whipstock and with the unthreaded end inserted into said smooth bore, said lead mill comprising a plurality of fluid passageways wherein said smooth bore comprises a sufficiently shallow depth so as to not intersect with internal fluid passageways and so as to not exit the distal side of said lead mill, said lead mill further comprising an external bore and a retaining pin inserted through said external bore for intersecting said smooth bore; and providing said shear bolt to comprise a groove, and further inserting said retaining pin into said groove for retaining said shear bolt within said smooth bore; providing a nose on said lead mill wherein at least four fluid passageways lead from a central axial fluid passageway inside said lead mill and exit at a plateau defined as the end portion of said nose with an area perpendicular and obtuse in relation a central fluid passageway of said lead mill; providing a plurality of debris removal channels formed as recessed paths within said body and channeling milled debris away from said lead mill and in the direction of said follow mill using a plurality of exit paths associated with said debris removal channels; milling through said wellbore casing or wellbore rock formation and into said underground rock formation using a plurality of milling inserts positioned on said lead mill, said plurality of milling inserts positioned in rows adjacent said debris removal channels for, with at least three rows of milling inserts originating contiguously from the center, and extending from the center, of said plateau down the side of said lead mill in continuity; guiding debris milled by said inserts along a plurality of debris removal channels and away from said lead mill and in the direction of said follow mill using debris removal channels formed in a helical configuration on said lead mill; directing said lead mill and said follow mill to follow a path defined by the wellbore whipstock to continue milling through said wellbore casing and into the underground rock formation a distance sufficient to initiate said preplanned drilling path.

11. The method of claim 9, further comprising the steps of keeping said upper sub and said anchor body spread apart under normal, static conditions using a Belleville spring assembly, and further retaining said upper sub and said anchor body together using said split clamps.

12. The method of claim 11, further comprising the step of providing a cushioning effect for aiding in helping said anchor body to absorb shocks as said anchor moves within the wellbore prior to setting using said Bellevile spring assembly.

13. The method of claim 9, further comprising the step using a castellated top matching a similar form at the bottom portion of upper sub allowing smooth, slidable, torque resistant movement between said anchor body and a matching castellated lower portion of said upper sub.

14. The method of claim 9, further comprising the step actuating said lower piston for forcing said slips outward from said anchor body and concurrently advances said locking ratchet nut along a threaded portion of said floating mandrel.

15. The method of claim 9, further comprising the step using said upper piston and said lower piston for applying forces in opposite directions for pushing said slips outward from said anchor body using said upper piston and pushing said floating mandrel downward using said lower piston.

16. The method of claim 15, further comprising the step of moving said slips outward from said anchor body for causing said slips to contact and engage the wellbore wall once the hydraulic anchor reaches a desired depth and circumferential orientation.

17. A dual-action hydraulically operable anchor for wellbore exit milling, comprising: a hydraulic anchor comprising a hydraulic anchor body, and an upper hydraulic piston and an opposing lower hydraulic piston, said upper hydraulic piston and said lower hydraulic piston for fixing an anchor in a wellbore to fixedly position whipstock in a wellbore, said whipstock for wellbore exit milling and for guiding lateral drilling outside the wellbore; and a bi-mill for milling an opening through a wellbore casing in initiating a preplanned lateral drilling path in departure from the wellbore axis and through the wellbore casing or wellbore rock formation, and further continuing into underground rock formation outside the wellbore and in the direction of the preplanned lateral drilling path and as guided by a wellbore whipstock, comprising: an assembly comprising a lead mill and a follow mill, said lead mill threadably attached to said follow mill, said lead mill comprising; a body forming a structural base for said lead mill, and further comprising: a smooth bore in the lead mill for receiving a circumferentially-grooved shear bolt, said shear bolt comprising a threaded end threadably attached to the wellbore whipstock and with the unthreaded end inserted into said smooth bore, said lead mill comprising a plurality of fluid passageways wherein said smooth bore comprises a sufficiently shallow depth so as to not intersect with internal fluid passageways and so as to not exit the distal side of said lead mill, said lead mill further comprising an external bore and a retaining pin inserted through said external bore for intersecting said smooth bore; and said shear bolt comprising a groove, wherein said retaining pin further inserts into said groove for retaining said shear bolt within said smooth bore; said lead mill further comprising a nose and wherein at least four fluid passageways lead from a central axial fluid passageway inside said lead mill and exit at a plateau defined as the end portion of said nose with an area perpendicular and obtuse in relation a central fluid passageway of said lead mill; a plurality of debris removal channels formed as recessed paths within said body and forming a plurality of exit paths for channeling milled debris away from said lead mill and in the direction of said follow mill; a plurality of milling inserts positioned on said lead mill and positioned in rows adjacent said debris removal channels for milling through said wellbore casing or wellbore rock formation and into said underground rock formation, with at least three rows of milling inserts originating contiguously from the center, and extending from the center, of said plateau down the side of said lead mill in continuity; said debris removal channels further formed in a helical configuration for guiding debris milled by said inserts along said debris removal channels and away from said lead mill and in the direction of said follow mill; said lead mill and said follow mill configured to follow a path defined by the wellbore whipstock to continue milling through said wellbore casing and into the underground rock formation a distance sufficient to initiate said preplanned drilling path.

18. The wellbore departure system of claim 17, wherein said plurality of milling inserts further comprise cylindrical inserts on both said lead mill and follow mill, said cylindrical inserts comprised of a tungsten carbide with a high percentage (10.5%-12%) of cobalt.

19. The bi-mill of claim 17, wherein said plurality of milling inserts further comprise cylindrical inserts on both said lead mill and follow mill, said cylindrical inserts comprised of a top layer of polycrystalline diamond (PCD) on an exposed cutting face.

20. The wellbore departure system of claim 17, wherein said bi-mill attachably connects to the wellbore whipstock with a shearable fastener for enabling wellbore whipstock-setting and wellbore departure milling to be completed in a single trip into the wellbore.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The present subject matter will now be described in detail with reference to the drawings, which are provided as illustrative examples of the subject matter so as to enable those skilled in the art to practice the subject matter. Notably, the FIGUREs and examples are not meant to limit the scope of the present subject matter to a single embodiment, but other embodiments are possible by way of interchange of some or all of the described or illustrated elements and, further, wherein:

[0052] FIG. 1 depicts the bottom hole assembly (BHA) as it could be deployed in a wellbore departure operation, including dual=action hydraulically operable anchor and bi-mill ;

[0053] FIG. 2 depicts the dual-action hydraulically operable anchor in isometric view;

[0054] FIG. 3 depicts the dual-action hydraulically operable anchor in section view;

[0055] FIG. 4 depicts an isometric view of the exterior anchor body;

[0056] FIG. 5 presents a section view of the anchor body;

[0057] FIG. 6 highlights the castellated top portion of the anchor body;

[0058] FIG. 7 shows this anchor body castellated top portion in detail;

[0059] FIG. 8 shows an isometric view of the lower cap that attaches to the bottom of the anchor body;

[0060] FIG. 9 shows the upper sub with castellated lower portion that fits snugly and slidably with anchor body castellated top;

[0061] FIG. 10 shows the upper piston that fits inside an upper sub;

[0062] FIG. 11 shows two split clamps that fit over an upper sub and an anchor body;

[0063] FIG. 12 depicts an isometric exterior view of a single split clamp;

[0064] FIG. 13A through 13C shows operation of the dual-action hydraulically operable anchor; and

[0065] FIGS. 14A through 14C show a half section views of the various positions of a dual-action hydraulically operable anchor;

[0066] FIG. 15 shows a typical workstring configuration for wellbore departure milling, including dual-action hydraulically operable anchor and bi-mill ;

[0067] FIG. 16 shows a bi-mill comprised of a lead mill, a threaded tubular connection, and cylindrical inserts on both the lead mill and follow mill;

[0068] FIG. 17 shows the lead mill component of the bi-mill in the state of being attached to the upper portion of a whipstock;

[0069] FIG. 18 shows a more comprehensive isometric view of the bi-mill and adjoining whipstock;

[0070] FIG. 19 presents a section view of the lead mill and an upper portion of the whipstock, with the lead mill shown attached to the whipstock with a shear bolt;

[0071] FIG. 20A shows an isometric view of the bi-mill with follow mill, lead mill, and some capped shearable nozzles at the nose of the lead mill;

[0072] FIG. 20B shows a half section view of the bi-m ill, with the shear bolt cavity visible as well as capped shearable nozzles;

[0073] FIG. 21A shows an isometric view of the follow mill, lead mill, and the threaded connection that joins them together when assembled;

[0074] FIG. 21B shows a section view of the follow mill, lead mill, and threaded connection that joins them together when assembled;

[0075] FIG. 22A shows the lead mill in isometric representation, with capped shearable nozzles visible at the nose of lead mill;

[0076] FIG. 22B shows the lead mill in isometric representation, with capped shearable nozzles visible at the nose of lead mill;

[0077] FIG. 23 shows an isometric view of the lead mill with nozzle ports visible at the plateau of the nose of the lead mill;

[0078] FIG. 24 shows an enlarged view of a portion of lead mill, with a threaded break-off nozzle at the plateau of the nose of the lead mill; and

[0079] FIGS. 25A and 25B are graphical representations of the overlap of all the cylindrical inserts shown as if a 360-degree rotation were arranged in a single plane.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0080] Various embodiments of the dual-action hydraulically actuable anchor and bi-m ill and methods of use will now be described with reference to the accompanying drawings, wherein like reference numerals are used for like features throughout the several views. The detailed description set forth below in connection with the appended drawings is intended as a description of exemplary embodiments in which the presently disclosed subject matter can be practiced. The term exemplary used throughout this description means serving as an example, instance, or illustration, and should not necessarily be construed as preferred or advantageous over other embodiments. The detailed description includes specific details for providing a thorough understanding of the presently disclosed method and system. However, it will be apparent to those skilled in the art that the presently disclosed subject matter may be practiced without these specific details. In some instances, well-known structures and devices are shown in functional or conceptual diagram form in order to avoid obscuring the concepts of the presently disclosed method and system.

[0081] Certain terms are used throughout the following description and claims to refer to particular assembly components. This document does not intend to distinguish between components that differ in name but not function. In the following 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 . . . .

[0082] Reference to up or down will be made for purposes of description with up, upper, or upstream meaning toward the earth's surface or toward the entrance of a well bore; and with down, lower, or downstream meaning toward the bottom of the well bore. In the drawings, the cross-sectional side views of the expandable anchor should be viewed from top to bottom, with the upstream end at the top of the drawing and the downstream end at the bottom of the drawing.

[0083] In the present specification, an embodiment showing a singular component should not be considered limiting. Rather, the subject matter preferably encompasses other embodiments including a plurality of the same component, and vice-versa, unless explicitly stated otherwise herein. Moreover, the applicant does not intend for any term in the specification or claims to be ascribed an uncommon or special meaning unless explicitly set forth as such. Further, the present subject matter encompasses present and future known equivalents to the known components referred to herein by way of illustration.

[0084] One or more embodiments of the disclosure are described below. It should be noted that these and any other embodiments are exemplary and are intended to be illustrative of the disclosure rather than limiting. While the disclosure is widely applicable to different types of systems, it is impossible to include all the possible embodiments and contexts of the disclosure in this disclosure. Upon reading this disclosure, many alternative embodiments of the present disclosure will be apparent to the person's ordinary skill in the art. [0050]The benefits and advantages that may be provided by the present disclosure has been described above with regard to specific embodiments. These benefits and advantages, and any elements or limitations that may cause them to occur or to become more pronounced are not to be construed as critical, required, or essential features of any of any or all of the claims. As used herein, the singular forms a, an, and the are intended to include the plural forms as well, unless the context clearly indicates otherwise. It is further understood that the terms comprises and/or comprising or includes and/or including, or any other variation thereof, are intended to be interpreted as nonexclusively including the elements or limitations which follow those terms. Accordingly, a system, method, or other embodiment that comprises a set of elements is not limited to only those elements, and may include other elements not expressly listed or inherent to the claimed embodiment. These terms when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more features, regions, integers, steps, operations, elements, components, and/or groups thereof.

[0085] FIG. 1 depicts the bottom hole assembly (BHA) as it could be deployed in a wellbore departure operation, with this BHA including bypass valve 50, running tool 41, bi-mill 48, whipstock 42, hydraulic tubular 43, hinged connector 40 and dual-action hydraulically operable anchor 2 in an exterior isometric view, shown following actuation with the slips 4 having moved outward to protrude from the body of the anchor.

[0086] FIG. 2 depicts the dual-action hydraulically operable anchor 2 in isometric view, in its initial position with slips 4 not yet extended. The upper sub 12 is retained slidably with the anchor body 6 by the split clamps 14. The two split clamps 14 are held in place by screws (not shown) joining the two pieces together and by screws that externally pass through the lower circumference of the split clamps and thread into the anchor body 6. The slips 4 are depicted in their initial, unactuated position. The grooved pockets 18 in the anchor body 6 provide a guide along which the slips 4 can slide outward from the anchor body 6. The slips 4 have holes that contain cylindrical inserts (not shown) of a hard material that gain purchase on the wellbore wall, frictionally binding to it and slightly deforming it under extreme compressive force. Shear screw holes 10 receive shear screws (not shown) that hold the anchor body 6 and lower piston 22 in a fixed position until hydraulic force is applied, severing the screws connecting the anchor body 6 and lower piston 22 and enabling the lower piston 22 to travel upward. At the lower end of the hydraulic anchor 2, a threadably attached lower cap 8, with beveled leading edges, serves as a guide for anchor 2 and BHA during wellbore entry.

[0087] FIG. 3 depicts the dual-action hydraulically operable anchor 2 in section view and in its initial position with slips 4 not yet extended. The upper piston 13 is visible inside the upper sub 12, with upper piston 13 attached to the upper end of mandrel 20. Split clamps 14 are attached to anchor body 6 with screws (not shown) inserted in split clamp attachment holes 17, with split clamps 14 slidably retaining upper sub 12. The lower face of upper piston 13 is spaced slightly above a ledge face in upper sub 12. This gap remains fixed by shear screws 15 that connect the anchor body 6 to the mandrel 20. During hydraulic actuation of the anchor, and following actuation of lower piston 22 described below, the shear screws 15 will shear and permit downward travel of the floating mandrel 20 due to force exerted by upper piston 13. The Belleville spring stack 16 is shown applying compressive force to keep upper sub 12 and anchor body 6 separated in the initial, static position. Upper piston 13 travels against the Belleville spring force upon actuation. T-slot adapters 24 are shown at the bottom edge of the slips 4, where they are slidably attached to the slips. The inner portion of locking ratchet nut 28, which includes internal threaded nut segments 30, is circumferentially disposed around the floating mandrel 20. The locking ratchet nut 28 is also connected to the lower piston 22 with shear screws (not shown) spaced around its circumference. Initially connected, the lower piston 22 and locking ratchet nut 28 travel upward together after actuating hydraulic force is applied and some separate shear screws in shear screw holes 10 are severed, permitting releasing the lower piston 22 to travel. However, after the locking ratchet nut has locked into place along the floating mandrel 20 threads, and the slips 4 are fully extended, it may be necessary, under certain conditions, to remove the anchor from the wellbore. In order to remove the anchor, a rig at the surface applies tension to the workstring and thereby to the BHA and floating mandrel 20, and the shear screws connecting the locking ratchet nut 28 and lower piston 22 sever, permitting the lower piston 22 to retract to a lower position, the T-slot adapters 24 to retract, and the slips 4 along with them, permitting the removal of the hydraulic anchor 2 and BHA from the wellbore. Note that at the lower end of the hydraulic anchor 2, a threadably attached lower cap 8, with central bore and beveled leading edges, serves as a guide for the anchor and BHA during wellbore entry. Additionally, lower cap 8 is shown with lower cap plug 9 threadably inserted into the bottom of the central bore in lower cap 8. This lower cap plug 9 seals the hydraulic anchor 2 so that hydraulic force can be used to set the anchor. The lower cap plug 9 may be omitted so as to permit different functions, such as flow through the anchor with use of a dropped ball (not shown) in place lower cap plug 9 to seal the anchor 2 and permit hydraulic setting.

[0088] Hydraulic anchor 2, therefore, provides opposing upper and lower hydraulic pistons 13 and 22 for extending slips 4 outward with considerable force in order to fixedly position a whipstock 42 in a wellbore. Whipstock 42 enables wellbore exit milling and initial guiding of lateral drilling outside the wellbore. Hydraulic anchor 2 includes an upper sub 12 for loosely retaining a floating mandrel 20 attached to a hydraulic upper piston 13. Upper sub 12 houses hydraulic upper piston 13 to hydraulically engage and advance floating mandrel 20. Managing Member with supplied hydraulic force, advancing mandrel 20 downward.

[0089] Belleville spring stack 16 abuts the lower external face of upper sub 12, forcing upper sub 12 upward to the point where it is retained by the inner face of the upper portion of split clamp assembly 14 in the absence of hydraulic or mechanical compressive force. Upper sub 12 houses hydraulic upper piston 13, attached to the upper end of floating mandrel 20, is retained at the upper end of upper sub 12 by a threaded male connection end of a hinged connector or similar adjacent sub. Split clamp assembly 14 loosely and slidably retains upper sub 12 to hydraulic anchor body 6. Lower cap 5 fixedly couples to anchor body 6 and provides a guide nose for guiding the hydraulic anchor within the wellbore, smoothing its travel around minor obstructions or uneven portions of the wellbore, with lower cap 8 and hydraulic anchor body 6 threadably connected, and the lower cap 8 central bore being closed with a plug, or open, depending on operational parameters. Floating mandrel 20 extends from inside upper sub 12 to inside lower cap 5 with slidably moveable axial engagement of a locking ratchet nut 29 within hydraulic anchor body 6.

[0090] Inside floating mandrel 20, along its longitudinal axis, a flow of hydraulic fluid originating from a piston inside a running tool travels through floating mandrel 20 to actuate lower piston 22 disposed in anchor body 6, forcing the mandrel 20 upward and advancing the slips. Hydraulic lower piston 22 located below upper piston 13 at the end of floating mandrel 20 distal from upper piston 13 actuates from a first position to a second position along floating mandrel 20 using hydraulic fluid supplied through the inner axial bore of floating mandrel 20. Lower piston 22 actuation forces slips 4 outward from anchor body 6 and concurrently advances locking ratchet nut 28 along a threaded portion of floating mandrel 20. Additionally, floating mandrel 20 receives compressive force from the upper piston 13 housed in upper sub 12 when hydraulic force is applied to upper piston 12, forcing it downward against floating mandrel 20 and serving to advance mandrel 20 slidably against locking ratchet nut 28. [0057]As needed, floating mandrel 20 can receive compressive force from mechanical force applied to the work string above and adjacent upstream BHA adjoining hydraulic anchor 2, providing yet more force to advance mandrel 20 slidably against locking ratchet nut 28. The two hydraulic forces and the mechanical force can be applied concurrently, making the forces additive, and thereby setting anchor 2 with extreme force. At the upper, uphole end of lower piston 22, T-slot adapter 24 engages mandrel 20 piston on the lower, downhole side of T-slot adapter 24. A slip slidably engages T-slot adapter 24 on the upper side of T-slot adapter 24 within the anchor housing. With standard-sized slips 4, slips 4 advance from a first flush-with-anchor housing 6 position through an opening in anchor housing 6 to a second, extended position extending outward from anchor housing 6 in response to movement of T-slot adapter 24 slidably engaged with the lower piston within anchor housing 6.

[0091] FIG. 4 depicts an isometric view of the exterior anchor body 6, with grooved pockets 18 for matching slips (not shown). FIG. 5 shows a section view of the anchor body 6, with grooved pockets 18 for matching slips (not shown).

[0092] Referring now to FIGS. 1 through 5, dual-action hydraulically actuated anchor 2 (hereinafter hydraulic anchor) sets, or engages the wellbore wall, so as to fixedly lock in place, when hydraulically-actuated bypass valve 50 located uphole in the BHA receives sufficient flow and pressure to actuate, passing flow and pressure to a piston (not shown) inside a running tool 41. Running tool 41 may be located downhole from bypass valve 50 and uphole adjacent to bi-mill 48. The piston inside running tool 50 is actuated, sending a pressurized clean fluid through the bi-mill 48, through the lead mill 44, through a tubular item attached to the lead mill 44 continuing through a hydraulic tubular 43 conductor in the whipstock 42 and to upper piston 13 and lower piston 22 inside the anchor body 6, actuating the pistons.

[0093] Lower piston 22, inside anchor body 6, initially attaches to anchor body 6 by shear screws inserted through shear screw holes 10. When hydraulic power is applied and the lower piston 22 is actuated, it shears the shear screws in shear screw holes 10 and advances upward. The shear screws that fasten the lower piston 22 to the anchor body 6 serve to prevent accidental upward travel of the lower piston. Lower piston 22 drives T-slot adapters 24, slidably attached to the lower portions of slips 4 and fixedly attached to the upper portions of lower pistons 22, in an upward direction, with the T-slot adapter 24 forcing the slips outward from grooved pockets 18. The outward movement of the slips 4 is facilitated by the angle of the top of the grooved pocket 18 and the grooves themselves, as well as, on the lower end of the slips, the angle of the T-slot adapter 24. [0061]As the lower piston 22 travels upward, a threaded locking ratchet nut 28 abuts a ledge inside the lower piston 22 to be secured to lower piston 22 by shear screws (not shown) spaced circumferentially around lower piston 22 and intersecting locking ratchet nut 28. The locking ratchet nut 28 is circumferentially grooved to accept shear screws and secures itself and lower piston 22 together in the initial, unactuated position, until hydraulic force is applied and the locking ratchet nut 28 and lower piston 22 advance upward together. As the locking ratchet nut 28 travels upward across a threaded portion of the floating mandrel 20, it locks in place on floating mandrel 20 and thereby mechanically locks T-slot adapters 24 and slips 4 in place.

[0094] Immediately following hydraulic actuation of the lower piston 22, upper piston 13 also actuates and travels a short distance in a downward, downhole direction. Upper piston 13 applies downward force to floating mandrel 20, in opposition to the force exerted by lower piston 22, forcing floating mandrel 20 against locking ratchet nut 28 from above at the same time as locking ratchet nut 28 is being forced upward by lower piston 22. This dual action ensures that slips 4 of hydraulic anchor 2 will be extended to maximum feasible distance and contact the wellbore wall with considerable force and mechanically lock into place. The mechanical lock provided by the locking ratchet nut 28 engagement with threads on floating mandrel 20 ensures that slips 4 remain in place, compressed against the wellbore wall with significant force, after the hydraulic anchor-setting operation has ceased.

[0095] Note that in this embodiment, at the lower end of hydraulic anchor 2, a threadably attached lower cap 8, with central bore and beveled leading edges, serves as a guide for the anchor and BHA during wellbore entry. Additionally, lower cap 8 is shown in FIG. 3 with lower cap plug 9 threadably inserted into the bottom of the central bore in lower cap 8. This lower cap plug 9 seals hydraulic anchor 2 so that hydraulic force can be used to set the anchor. Lower cap plug 9 may be omitted so as to permit different functions, such as flow through the anchor with use of a dropped ball (not shown) in place lower cap plug 9 to seal anchor 2 and permit hydraulic setting.

[0096] After hydraulic anchor 2 is set in place, whipstock 42 will resist significant compression, tension and torsion and remain fixed in the correct orientation for milling. At this point, the wellbore departure milling operation can begin.

[0097] An important feature of this embodiment is the shock absorbing aspects of the anchor body 6 and upper sub 12. This hydraulic anchor 2 has a stack of Belleville springs 16 that abut the lower end of its upper sub 12 and with the upper sub being attached to the BHA/workstring. Belleville springs 16 apply compressive force to keep the upper sub 12 and anchor body 6 spread apart under normal, static conditions, with the split clamps retaining the upper sub 12 and anchor body 6 together. The trip into the wellbore can produce unexpected difficulties. hydraulic anchor 2, the leading end of the BHA, can experience bumps and shocks along the way. If hydraulic anchor 2 experiences shocks as it travels downhole due to an uneven bore, debris, or other issues, the Belleville springs provide a cushioning effect that will help the anchor absorb shocks. On occasion, it may be necessary to utilize oversized slips in anchor 2 in order to accommodate a wellbore of larger inside diameter than the standard anchor slips are intended for. If such oversized slips were to be utilized, the slips and inserts could protrude from anchor body 6, even in the initial, unactuated position. In such a situation, the ability to absorb shocks can prevent damage to slips or inserts in the slips.

[0098] Hydraulic anchor 2 also makes use of three types of additive force in setting. The two opposing pistons 13 and 22 apply force in opposite directions, one pushing slips 4, via upward force on T-slot adapters 24, and the other pushing mandrel 20 downward, with both forces serving to advance locking ratchet nut 28 against mandrel 20 threads. These forces are applied concurrently following actuation. Yet a third force can be applied after the first two hydro-mechanical forces have been initialized and advanced slips 4 to gain initial pressure against the wellbore wall. The third force is mechanical force applied downward from the rig on surface through the workstring and BHA, reaching upper sub 12. Upper sub 12 may be used to mechanically force mandrel 20 downward after slips 4 have gotten the initial bite in the wellbore wall. This third force can be applied concurrently with the hydraulic force exerted by the opposing pistons 13 and 22, making these forces additive, and furthermore setting anchor slips 4 with extreme force. This feature is unprecedented in , unprecedented in prior art.

[0099] FIG. 6 highlights the castellated top portion of the anchor body 6 and FIG. 7 shows anchor body 6 castellated top 7 portion in detail. Castellated top 7 matches a similar form at the bottom portion of upper sub 12 and allows smooth, slidable, torque resistant movement between anchor body 6 castellated top 7 and the matching castellated lower portion of upper sub 12.

[0100] FIG. 8 shows an isometric view of the lower cap 8 that threadably attaches to the bottom of the anchor body 6.

[0101] FIG. 9 shows the upper sub 12 with castellated lower portion that fits snugly and slidably with anchor body castellated top 7.

[0102] FIG. 10 shows the upper piston 13 that fits inside upper sub 12 and attaches threadably to the end of mandrel 20 as seen in FIG. 3, ultimately applying downward force to mandrel 20 when hydraulic actuation occurs.

[0103] FIG. 11 shows two split clamps 14 that fit over portions of upper sub 12 and anchor body 6 so as to retain them together. The split clamps 14 are connected together by two screws (not shown) at their upper end and also connected to the anchor body 6 as in FIG. 3 with screws (not shown) inserted into split clamp attachment holes 17 screws spaced around the circumference of the lower end of the split clamps 14 and threading into anchor body 6, while slidably retaining upper sub 12 as seen in FIG. 3.

[0104] FIG. 12 depicts an isometric exterior view of a single split clamp 14.

[0105] FIG. 13A shows the exterior of the dual-action hydraulically operable anchor 2 in its initial, unactuated position with slips 4 not extended from the anchor body 6.

[0106] FIG. 13B shows the exterior of the dual-action hydraulically operable anchor 2 in a partially actuated position with slips 4 partially extended from the anchor body 6.

[0107] FIG. 13C shows the exterior of the dual-action hydraulically operable anchor 2 in an actuated position with slips 4 fully extended outward from the anchor body 6.

[0108] The effect of acute and obtuse angles on the outward movement of the slips 4 is clearly shown in FIGS. 14A, 14B, and 14C, where the initial position, partially actuated position, and actuated position of the slips 4 are depicted in stages. FIG. 14A shows a half-section view of the dual-action hydraulically operable anchor 2 in an unactuated position with slips 4 fully not extended from the anchor body 6. FIG. 14B shows a half section view of the dual-action hydraulically operable anchor 2 in a partially actuated position with slips 4 partially extended from the anchor body 6. FIG. 14C shows a half section view of the dual-action hydraulically operable anchor 2 in an actuated position with slips 4 fully extended outward from the anchor body 6.

[0109] Upon reaching its extended position, slips 4 firmly engage the wellbore to hold hydraulic anchor 2 and adjoining BHA components, including whipstock 42, in a fixed position. With the anchor fixedly secured against the wellbore casing or rock formation wall, a wellbore departure operation can be executed, subsequently providing a path for lateral drilling outside the main wellbore.

[0110] In summary, therefore, the present disclosure provides a dual-action hydraulically operable anchor 2 and methods of operation and manufacture for multilateral downhole drilling. The dual-action hydraulic anchor 2 includes hydraulic anchor body 6, and upper piston 13 and opposing lower piston 22. Upper piston 13 and lower piston 22 enable force slips 4 outward to fixedly position, or set, the hydraulic anchor 2 in a wellbore. The hydraulic anchor 2, when set, secures the whipstock 42 and makes possible wellbore departure milling and guiding lateral drilling outside the wellbore.

[0111] The hydraulic anchor 2 further includes an upper sub 12 for slidably engaging and containing a floating mandrel 20, as well a hydraulic upper piston 13 that threadably attaches to the floating mandrel 20. floating mandrel 20A split clamp 14 flexibly retains the upper sub and fixedly attaches to the hydraulic anchor body 6. The split clamp 14 permits confined movement of the upper sub 12 toward and hydraulic anchor body 6 toward and away from each other. A lower cap 8 fixedly couples to the hydraulic anchor body 6 and includes a guide nose for guiding the hydraulic anchor 2 within the wellbore and containing a threaded plug 9 to hydraulically seal the the hydraulic anchor body 6.

[0112] A floating mandrel 20 within the hydraulic anchor body 6 includes an upper piston 13 threadably attached at the floating mandrel's 20 upper end and slidably moving within the upper sub 12 and along the longitudinal axis of the hydraulic anchor body 6. A hydraulic lower piston 22 with locking ratchet nut 28, upon anchor actuation, travels upward along the floating mandrel 20 and applies a first force to move slips 4 outward from the anchor body 6. Additionally, following the hydraulic lower piston's 22 upward travel, the hydraulic upper piston 13 applies compressive force to drive the floating mandrel 20 downward to advance in opposition to the movement of the hydraulic lower piston 22 and locking ratchet nut 28. Additionally further, the floating mandrel 20 transmits additional downward compressive force deriving from mechanical force applied from a surface rig to the workstring and BHA components uphole and adjoining the hydraulic anchor 2.

[0113] The hydraulic lower piston 22 is located below the hydraulic upper piston 13 and operates from a first position to a second position along the floating mandrel 20 using transmitted hydraulic fluid. A T-slot adapter 24 engages the hydraulic lower piston 22. A slip 4 engages the T-slot adapter 24 and may slide within the hydraulic anchor body 6 from a flush position along the hydraulic anchor body 6 to an extended position along the hydraulic anchor body 6 in response to movement of the T-slot adapter 24 and the lower piston 22 within the hydraulic anchor body 6. In response, the slip 4 firmly engages the wellbore to hold the hydraulic anchor 2 and the whipstock 42 in a fixed position within the wellbore, thereby providing a path for lateral drilling outside the wellbore. A threaded locking ratchet nut 28 attaches to the lower hydraulic piston 22 and slidably moves along a threaded portion of the floating mandrel 20. The locking ratchet nut 28 mechanically locks the lower hydraulic piston 22 in a second position, with the slips 4 being retained mechanically in the extended position engaging the wellbore wall.

[0114] The foregoing description of embodiments is provided to enable any person skilled in the art to make and use the subject matter. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the novel principles and subject matter disclosed herein may be applied to other embodiments without the use of the innovative faculty. The claimed subject matter set forth in the claims is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. It is contemplated that additional embodiments are within the spirit and true scope of the disclosed subject matter.

[0115] Referring to details of the other key component of the disclosed system, the bi-mill, provided is a description of a bi-mill having a lead mill and follow mill configured to follow a path defined by the whipstock to continue milling through the wellbore casing or wellbore rock formation wall and into the rock formation a distance sufficient to initiate the preplanned drilling path. However, it should be understood that the description is by way of example only and is not to be construed in a limiting sense. It is contemplated that all such changes and additional embodiments are within the spirit and true scope of this disclosure, as claimed below.

[0116] This disclosure facilitates the exit from the casing, or rock formation, in the absence of casing, and creation of an initial bore over a short distance into the rock formation. In a main wellbore that is either open hole, i.e., without casing cemented in the wellbore, or cased hole, i.e., with casing cemented in the wellbore, a wellbore departure system requires an assembly that includes a few key components. An anchor, such as the dual-action hydraulically actuable anchor disclosed above, is deployed on a workstring and located below, i.e. farther downhole, from a whipstock on the same workstring.

[0117] After the anchor is set in place, a milling operation can begin. The mill(s) used for wellbore departure milling may be comprised of various components and configurations known in the art, usually an arrangement of two or three mills connected in close proximity. The milling system in this disclosure is a bi-mill, that is to say, a two-mill system. This bi-mill is comprised of a lead mill that is threadably connected to a follow mill, with the lead mill being positioned farther downhole.

[0118] In this disclosure, the bi-mill is attachably connected to the whipstock with a shearable fastener known as a break bolt or shear bolt. Attaching the bi-mill to the whipstock with a shearable item enables the whipstock-setting and wellbore departure milling operation to be completed in a single trip into the wellbore. After the anchor has been set in place as described above, and thereby the connected whipstock has been set in place, force, such as tension or compression from the workstring, is used to shear the shear bolt so that the connection between the whipstock and bi-mill is severed. Incidentally, the hydraulic tubular, an expendable item, connected to the mill, is destroyed at this stage or in the following initiation of milling. At this point, rotation of the bi-mill begins, and downhole compressive force is applied, forcing the bi-mill down the whipstock ramp and against the wellbore's internal casing wall or rock formation, as the case may be. In a cased well, the bi-mill creates an opening in the wellbore casing and a bore through any cement and into rock formation. When no casing is present, the bi-mill begins immediately boring into rock formation. The opening and new adjoining bore, separate from the main wellbore, are enlarged to a desired maximum diameter, or enlarged to full gage, in common oilfield terminology. The bi-mill bores a short distance in the new adjoining bore, forming a rathole in the rock formation in which the lateral bore will be drilled, and then ceases its operation and is withdrawn from the well. A drilling system designed for boring in rock formations is then tripped into the new adjoining bore in order to extend that bore a comparatively great distance. [0087]A bi-mill assembly has a lead mill, which mills through the casing or rock formation wall ahead of the adjoining follow mill. Although follow mills may be of different types and forms, and may be relied upon to perform a large or small part of the milling operation in terms of material removed, the lead mill in this disclosure performs the bulk of the milling, leaving mostly smoothing or cleanup work for the follow mill in most situations.

[0119] However, the lead mill may experience some wear and breakage as it leads the milling operation, contacting, milling and penetrating the casing ahead of the follow mill. Significant wear on the lead mill, should it occur, can cause the lead mill's diameter to decrease from the desired full gage. The follow mill, which has been engaged in relatively light duty compared to the lead mill, helps to ensure that full gage is achieved in the main wellbore opening and in the adjoining bore created beyond the main wellbore. After creating the opening in the main wellbore and departing into the new, adjoining bore, the bi-mill bores a short distance in rock formation before being withdrawn from the well.

[0120] Referring now to FIG. 15 which shows a typical workstring configuration for wellbore departure milling, including the bi-mill 108, flex groove 107, whipstock 114, and hydraulic anchor 116, with the hydraulic anchor 116 located distal and downhole from the bi-mill 108, as well as ancillary components. The bypass valve 102 located uphole in the workstring receives sufficient flow and pressure to actuate, passing along flow and pressure to a piston (not shown) inside a running tool 106 downhole from the bypass valve 102 but uphole and in close proximity to the bi-mill 108. The piston inside the running tool 106 is actuated, sending a pressurized clean fluid through the bi-mill 108, to and through the lead mill 112, through a hydraulic tubular 118 item attached to the lead mill 112 continuing through a tubular item (not shown) in the back of the whipstock 114, through a hinged connector 120 and into the hydraulic anchor 116 to pistons (not shown) inside the hydraulic anchor 116, actuating the pistons sequentially. When the pistons in the anchor are actuated, they drive slips 122 into the wellbore wall and an internal locking mechanism (not shown) within hydraulic anchor 116 holds the slips 122 in place.

[0121] FIG. 16 shows a bi-mill 108 comprised of a lead mill 112 at the lower end connected, by a threaded connection 121, to a follow mill 110 at the upper end. The flex groove 107 is located at the end of bi-mill 108 distal from lead mill 112. This uphole location of a flex groove 107 allows most of the downhole portion of bi-mill 108 to remain relatively stiff during milling operations, with flex occurring uphole at flex groove 107, enabling smooth, low torque milling and extremely robust cutting structure. Also seen in FIG. 16 are cylindrical inserts 130 on both the lead mill 112 and follow mill 110. These cylindrical inserts 130 are comprised of a hard material, such as tungsten carbide with a high percentage (e.g. 10.5%-12%) of cobalt or may be comprised of carbide with a top layer of polycrystalline diamond (PCD) on the exposed cutting face. Such inserts are designed to be wear and break resistant as well as useable with significant heat. On lead mill 112, wear insert holes 133 are shown at the rear portion of the cutting structure, but no wear inserts are shown inserted in these holes. Wear inserts are an optional item that may be utilized for protecting the mill body and preventing wear.

[0122] FIGS. 17, 18 and 19 show the lead mill 112 component of the bi-mill in the state of being attached to the upper portion of a whipstock 114. FIG. 17 shows an isometric view of a portion of the lead mill 112 and whipstock 114, as these parts are connected and in the assembled position for tripping downhole. A hydraulic tubular 118 conveys fluid from the running tool (not shown in FIG. 17) that passes through the lead mill to a hydraulic anchor (not shown in FIG. 17). One of the nozzle ports 134 is shown at the plateau of the nose of the lead mill 112. FIG. 18 shows a more comprehensive isometric view of the bi-mill 108 and adjoining whipstock 114. In FIG. 19, a section view of the lead mill 112 and section view of a portion of the whipstock 114 are seen, with the lead mill 112 shown attached to the whipstock 114 with a shear bolt 124. FIG. 19 also shows the shear bolt 124 being threaded into the whipstock 114 and retained in the lead mill 112 inside a shear bolt cavity 123 by a recessed threaded retaining pin 126 that interferes with a circumferential groove in the shear bolt 124. A hydraulic tubular 118, used for actuating the hydraulic anchor 116 (shown in FIG. 15), is threaded into a port at the nose or plateau of the lead mill. Capped, shearable nozzle 128 assemblies are also threaded into the plateau of the lead mill.

[0123] FIG. 20A shows an isometric view of the bi-mill 108 with follow mill 110, lead mill 112 and some capped shearable nozzles 128 at the plateau of the nose of lead mill 112. FIG. 20B shows a section view of the bi-mill 108, with the shear bolt cavity 123 visible as well as capped shearable nozzles 128.

[0124] FIG. 21A shows an isometric view of the follow mill 110 and lead mill 112 and the threaded connection 121 that joins them together when assembled. FIG. 21B shows a section view of the follow mill 110 and lead mill 112 and the threaded connection 121 that joins them together when assembled.

[0125] FIG. 22A shows the lead mill 112 in isometric representation, with capped shearable nozzles 128 visible at the plateau of the nose of lead mill 112, the shear bolt cavity 123, and cylindrical inserts 130 visible. FIG. 22B shows the lead mill 112 in isometric representation, with capped shearable nozzles 128 visible at the plateau of the nose of lead mill 112, the shear bolt cavity 123, and cylindrical inserts 130 visible.

[0126] FIG. 23 shows an isometric view of the lead mill 112 with nozzle ports 134 visible at the plateau of the nose of the lead mill 112. Nozzles have not been threaded into the nozzle ports 134 in this view. Notable in nozzle ports 134 are the smooth circumferential spaces in the inside diameter just above and adjacent to the threaded area in the inside diameter. These smooth recesses are designed to receive the hex heads of threaded items such as capped shearable nozzles 128. This allows the hex head to be recessed below the surface, with only the grooved break-off portion of a capped shearable nozzle 128 exposed even with the surface. The end result of this is a flush-with-surface breaking off of capped shearable nozzles 128 or other shearable items. By breaking off flush with the lead mill 112 debris removal channels 138, better flow paths and better, more efficient removal of debris is enabled. The increase in flow path and debris removal efficiency leads to less wear and longer cutting life of lead mill 112.

[0127] FIG. 24 shows an enlarged view of a portion of lead mill 112, with a threaded break-off nozzle 137 at the plateau of the nose of the lead mill 112. The lower grooved portion of threaded break-off nozzle 137 illustrates the low breaking off point that permits better debris removal and longer lead mill 112 life as described in previous FIG. 23. Note that the hex head of this nozzle is not visible, as it is submerged below the surface of the debris removal channel. Again, breaking off flush with the upper edge of nozzle port 134 permits the enhanced debris removal and longer lead mill life as described in FIG. 23.

[0128] FIGS. 25A and 25B are graphical representations of the overlap of all the cylindrical inserts 130 shown as if arranged in a single plane. This graphical representations indicate that strategic design has left no gaps in the spacing of cylindrical inserts 130, or cutting structure, and that many inserts share similar cutting loads, reducing torque and increasing insert and mill life. Little breakage occurs with such complete insert coverage and rate of progress (ROP) is markedly increased.

[0129] The disclosed invention is an apparatus for milling an opening in wellbore casing or wellbore rock formation and creating a bore beyond the casing that is discrete from the main wellbore. The subject matter of this disclosure is a bi-mill 108. The bi-mill 108 is comprised of a lead mill 112 with a single follow mill 110. Each of these mills, lead mill 112 and follow mill 110, is comprised of a body with an arcing cutting structure in relief from debris removal channels 138 that includes an arrangement of rows of cylindrical inserts 130 of a hard material brazed into pockets in the body, and recessed debris removal channels 138 formed between the rows of inserts. The lead mill 112 has a body with recessed debris removal channels 138 and fluid delivering orifices, potentially including three nozzle ports and a tubular connection port for flushing debris, with these ports being located on the plateau, or nose, of the lead mill. When used in conjunction with a hydraulic anchor, the nozzle ports are capped with capped shearable nozzles 128 so that fluid will not escape through these ports and may be supplied under pressure through one port connected to a hydraulic tubular 118 for hydraulic anchor 116 actuation.

[0130] The nozzle ports 134 are designed with threaded connections recessed below the surface of the mill body and shear points or circumferential grooves positioned at or below the surface of the mill body so that the nozzles break off flush with the surface of the adjacent area. A smoothly bored area within the upper inside diameter of the nozzle ports 134 is sized to accept the hex head portion of a threaded nozzle. This smoothly bored area may exceed the diameter of the threaded area of the nozzle port 134 if necessary. The smoothly bored portion of nozzle port 134 permits the hex head portion of the threaded nozzle to be fully submerged below the surface of the debris removal channel 138 or other surface area of lead mill 112. This leaves the shear groove of the capped shearable nozzle 128 or threaded break-off nozzle 137 in position to break off flush with the upper edge of nozzle port 134. Flush breaking off of the nozzles permits the enhanced debris removal, smoother cutting and longer lead mill life as detailed in FIG. 23 and FIG. 24.

[0131] Placement of a recessed shear bolt cavity 123 that is bored to a shallow depth in the lead mill body, i.e. not bored to the central axial fluid carrying bore within the lead mill 112 or bored through to exit the other side of the lead mill, and held by a threaded retaining pin 126, preserves sufficient internal space at the plateau of the lead mill 112. This is sufficient to enable efficient geometric placement of three nozzles and a tubular connection, or alternatively, two large diameter nozzles and a tubular connection, or four nozzles at the plateau of the lead mill 112. Regardless of the number of orifices at the plateau, these orifices can be of larger diameter than in the prior art due to the novel use of the lead mill's internal space. The ability to place more nozzles at the plateau, and to increase total flow area (TFA) at the plateau, is critical in achieving efficient debris removal, reducing required torque and reducing potential for slip-stick. Slip-stick occurs when a mill or bit binds during workstring rotation, stores energy until it releases, and then releases with unwanted rotational acceleration, causing vibratory and potentially destructive effects.

[0132] In this embodiment, cylindrical inserts 130 with a diameter of 13.437 mm are used, with the inserts being composed of a sintered carbide with a polycrystalline diamond (PCD) layer on top of the cylinder at its cutting face, or, alternatively, utilizing no PCD layer but simply tungsten carbide containing cobalt of 10.5% for improved breakage resistance and longer wear. The portion of the milling operation in which the bi-mill contacts steel casing involves significant vibration and interrupted, inconsistent contact with the casing. Such conditions necessitate employing a breakage-resistant carbide that must be somewhat softer, i.e., contain more cobalt, than a normal machining grade of carbide insert.

[0133] The lead mill's recessed debris removal channels 138 benefit from three shearable nozzles 128 and a tubular connection hole 132 at the plateau of the lead mill 112. Three shearable nozzles 128 with nozzle ports 134, in addition to a tubular connection hole 132 located at the plateau provide for significantly increased total flow area (TFA) at the plateau when compared to the prior art. The increased TFA provides for maximal upflow of milled debris, and a resultant reduction in required torque, producing a smoother milling operation. The greater TFA and torque reduction provides less opportunity for vibration destructive slip-stick. Slip-stick occurs when a mill or bit binds during workstring rotation, stores energy until it releases, and then releases with unwanted rotational acceleration, causing vibratory and potentially destructive effects.

[0134] The lead mill 112 possesses a novel geometry that makes efficient use of space and enables greater TFA at the nose of the mill. The lead mill 112 employs a recessed, blind cavity, not through-bored to opposite side of the lead mill as in prior art, nor bored to the fluid-carrying axial bore inside the lead mill, but rather with shear bolt cavity 123 bored transverse to the lead mill's axial plane, and with the shear bolt 124 is held in place by retaining pin 126. The internal space saved by utilizing a short, shallow, blind bore in the shear bolt cavity 123 leaves enough internal space to bore three fluid nozzle ports 134 and a tubular connection hole 132 to exit on the plateau of the nose of the lead mill 112. Furthermore, the fluid-delivering orifices, in this embodiment fluid nozzle ports 134 and tubular connection hole 132 are of larger diameter than similar prior art orifices. This use of space both concentrates and increases flow at the plateau. All exterior connecting parts, such as shearable nozzles 128 or hydraulic tubular 118, are fastened with recessed bolt heads and with shear points flush with the adjoining area of the lead mill 112. These parts break off flush when the milling operation begins, leaving no obstruction to milling or debris flow paths, and thereby providing maximum flow efficiency for removal of milled debris.

[0135] The lead mill 112 body, when machined, leaves substantial insert cutting structure after creation of the debris removal channels 138. Improving upon prior art cutting structure, the lead mill 112 body has three complete rows of inserts from the center plateau of the nose of the lead mill 112 and extending completely down along the side of the lead mill 112. The extra insert cutting structure at the plateau is achieved by recessing the hex heads and shear points of all shearable nozzles 128 or hydraulic tubular 118 parts, as described above in this disclosure. Recessing these hex heads allows more body to remain in place, i.e. leaving more body in relief as debris removal channels 138 are milled in manufacturing, providing sufficient strength to increase body area that may be utilized as insert cutting structure. The lead mill 112 body has six complete rows of inserts 130 from the nose (including the three rows from plateau, above) and extending completely down the side of the lead mill 112. Three additional segments of the lead mill 112 body along the side of the lead mill 112 offer additional insert cutting structure. Altogether, the lead mill 112 body in this embodiment contains nine rows of inserts 130.

[0136] The lead mill and follow mill inserts 130 are made of a hard material designed to resist wear and breakage, while still maintaining the ability to mill through steel and bore at least a short distance in rock formation to create a rat hole for accepting a rock drilling assembly following the milling operation. The hard insert material may be a polycrystalline diamond (PCD) sintered as a layer on top of a given type of carbide, or what is commonly known as a polycrystalline diamond compact (PCD) insert. Alternatively, a type of sintered carbide, such as tungsten carbide or a tungsten carbide insert (TCI) material containing cobalt content of at least 10.5% may be utilized. Additionally, PCD inserts may be used in conjunction with carbide inserts, such as TCI inserts, in a varied array of different material inserts placed into the lead mill 112.

[0137] When executing a milling operation to create an opening in casing, the lead mill's nose, the narrower portion of the lead mill 112 that is less than full gage, travels along a whipstock 114, initially contacting the whipstock 114 as the full gage and near-full gage portions of the lead mill 112 engage the casing without engaging the whipstock 114. The novel features of this lead mill 112 are its efficient use of space at its nose so as to create concentrated fluid passageways for fluid orifices, such as three nozzle ports 134 and tubular connection hole 132 at the plateau and large recessed debris removal channels 138 to accommodate the flow of debris from those orifices. Key to making efficient use of space is the lead mill shear bolt cavity 123 that is not bored through from one side of the lead mill to the other, nor is it bored into the axial fluid-carrying bore inside the lead mill 112.

[0138] An additional novel feature is that the lead mill and follow mill bodies may have their recessed debris removal channels 138 timed to match each other, enabling a more efficient milling and debris removal operation. In other words, the lead mill and follow mill may have the same number of debris removal channels and furthermore these debris channels may be aligned, such that debris channels of the lead and follow mills are the same in number and furthermore the trailing ends of debris channels from the lead mill align with leading ends of debris channels from the follow mill for improved flow of debris and for smoother milling.

[0139] In summary, therefore, the present disclosure provides for a wellbore departure system including a hydraulic anchor for securing a whipstock in place and a bi-mill for milling an opening through a wellbore casing in initiating a preplanned lateral drilling path in departure from the wellbore axis and through the wellbore casing or wellbore rock formation, and further continuing into underground rock formation outside the wellbore and in the direction of the preplanned lateral drilling path and as guided by a wellbore whipstock. The bi-mill includes an assembly having a lead mill and a follow mill. The lead mill threadably attaches to the follow mill. The lead mill includes a body forming a structural base for the lead mill, and further includes a smooth bore in the lead mill into which a circumferentially-grooved shear bolt is inserted. A threaded end threadably attaches to the wellbore whipstock and with the unthreaded end inserts into the smooth bore. The lead mill further includes a plurality of fluid passageways wherein the smooth bore has a sufficiently shallow depth so as to not intersect with the internal fluid passageways and so as to not exit the distal side of the lead mill. The lead mill further includes an external bore and a retaining pin inserted through the external bore for intersecting the smooth bore.

[0140] The shear bolt includes a groove, wherein the retaining pin further inserts into the groove for retaining the shear bolt within the smooth bore. The lead mill further includes a nose and at least four fluid passageways leading from a central axial fluid passageway inside the lead mill and exiting a plateau defined as the end portion of the nose with an area perpendicular and obtuse in relation a central fluid passageway of the lead mill. A plurality of debris removal channels form recessed paths within the body and a plurality of exit paths for channeling milled debris away from the lead mill and in the direction of the follow mill. A plurality of milling inserts positioned on the lead mill and in rows adjacent the debris removal channels for milling through the wellbore casing or wellbore rock formation and into the underground rock formation. At least three rows of milling inserts extend from the center of the plateau down the side of the lead mill in continuity.

[0141] The debris removal channels further form in a helical configuration for guiding debris milled by the inserts along the debris removal channels and away from the lead mill and in the direction of the follow mill. The lead mill and follow mill are configured to follow a path defined by the wellbore whipstock to continue milling through the wellbore casing and into the underground rock formation a distance sufficient to initiate the preplanned drilling path.

[0142] The disclosed bi-mill is of a rigid, robust, flex-resistant construction from the lead mill to the uphole portion of the follow mill. The lead mill has a box connection that threads onto the pin connection of the thick-walled follow mill. A flex groove is machined into the upper, uphole portion of the follow mill to permit flex. Thus the robust construction from the distal end of the lead mill to the flex groove maintains a proportionally long downhole axial portion of the bi-mill in a relatively rigid state during milling operations. This construction reduces vibration and enables smooth milling at low torque, providing the additional benefit of enabling placement of a large number of cutting inserts onto the lead mill, in turn ensuring faster milling. The robust construction virtually eliminates the risk of shearing off the lead mill under the most difficult milling conditions.

[0143] The foregoing description of embodiments is provided to enable any person skilled in the art to make and use the subject matter. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the novel principles and subject matter disclosed herein may be applied to other embodiments without the use of the innovative faculty. The claimed subject matter set forth in the claims is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. It is contemplated that additional embodiments are within the spirit and true scope of the disclosed subject matter.