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FIELD OF INVENTION 
       [0001]    This disclosure describes centralizers for drilling, and in particular centralizers having selectively deployable longitudinal bow springs. 
       BACKGROUND 
       [0002]    Centralizers are commonly used in oil and gas wellbore installations and generally serve to center a pipe or casing within a wellbore or previous casing string during run-in, installation, or cementing procedures. Conventional centralizers typically are characterized by a pair of opposed stop collars or stop rings with a number of outwardly-bowed springs extending longitudinally there between to contact the wellbore sidewalls and exert a centering force on the pipe or casing segment. Bow spring centralizer subs generally comprise a casing segment with pin and box connections and an integral bow spring centralizer. The centralizer sub is run as part of a casing string. 
         [0003]    In under-reamed applications, the casing string (with centralizers) is passed through a smaller casing string (restriction) before opening up to a larger hole. Significant force is required to compress a bow spring centralizer and push it through a restriction. As drilling projects push to greater and greater depths, increased drilling angles, and through a greater variety of geological formations, more challenging demands are placed on centralizers and other down- bore equipment. For example, deeper wells require more stages and passage of centralizers through a greater range and number of corresponding restrictions. 
         [0004]    Subjecting compressible bow strings to varied and varying pressures as it is passed down a well results in inconsistent, imperfectly predictable, and repeated strains. 
         [0005]    Conventional bow springs can therefore suffer from a number of disadvantages in such installations. As the bore restrictions become tighter, the starting or insertion force and running forces required to pass restrictions increase. Additionally, compression of the bow springs through particularly tight restrictions can exceed the elastic range of the material, can lead to deformation of bow springs, and compromise the ability of the bow springs to restore and to center. Similarly, damaged or forced centralizers can damage down-bore surfaces and down-bore equipment. The repeated compressions and decompressions of the bow springs of the centralizers compromise the integrity and reliability of the centralizer. 
         [0006]    Accordingly, the following discloses and enables improvements for reducing and controlling insertion forces and running forces and preserving centralizer integrity and down-bore surfaces and equipment against the increasing demands of deep-well drilling. 
       SUMMARY OF THE PREFERRED EMBODIMENTS 
       [0007]    The present disclosure describes and enables a centralizer with bow springs selectively deployable down a wellbore. The bows of the centralizer are elongated and compressed into a lower profile state and retained by a releasable locking mechanism. Maintaining a lower centralizer profile reduces frictional resistance and operational forces during tool insertion and run-in as the compressed centralizer bow springs more readily clear restrictions. The locking mechanism can then be selectively released to allow the restorative forces of the springs to centralize the casing within the bore. The locking mechanism can be released by controlled cyclical pressurization of the casing to actuate as described a rotational ratcheting release mechanism. 
         [0008]    In one preferred embodiment, a portion of a locking mechanism is affixed to one of the centralizer stop collars while an interlocking portion is affixed to the casing. The locking mechanism is released by alignment of a release notch defined in a ratcheting ring with the interlocking portion of the locking mechanism affixed to the casing. Rotational misalignment of the ratcheting ring release notch and locking mechanism maintains the locked engagement of the lock mechanism portions while alignment results in release of the lock mechanism and deployment of the centralizer. 
         [0009]    In another preferred embodiment, cyclical casing pressurization tensions one or more actuator bands wrapped about the casing with one actuator band end affixed to the casing and a free actuator band end acting on a ratcheting ring. Circumferential movement of the free end of the wrapped band during pressurization actuates the ratcheting band to decrease misalignment between the release notch and the lock mechanism and ultimately to release the lock mechanism and centralizer resulting in release of bow spring compression. 
         [0010]    Accordingly, a deployable centralizer is maintained in a low-profile configuration with elongated, compressed bow springs until cyclical casing pressurization is selectively used to release a lock mechanism and allow for deployment of the centralizer bow springs. 
         [0011]    A more complete understanding may be derived by referring to the detailed description and claims when considered in connection with the Figures, wherein like reference numerals refer to similar elements throughout the Figures, and 
         [0012]      FIGS. 1A, 1B and 1C  show a deployable centralizer embodiment with bows in a compressed configuration. 
         [0013]      FIGS. 2A, 2B and 2C  show a deployable centralizer embodiment with bows in a deployed configuration. 
         [0014]      FIG. 3  shows an exploded view of the centralizer of  FIGS. 1-2 , including enlarged Detail views of locking mechanism and ratcheting components. 
         [0015]      FIGS. 4A-4B  show side views of the ratcheting and locking mechanism components and Detail views of the locking mechanism used to secure and subsequently deploy the centralizer bows. 
         [0016]      FIGS. 5A-5B  show perspective views of the ratcheting components and a Detail view showing rotational misalignment of the release notch and locking mechanism used to deploy the centralizer bows. 
         [0017]      FIGS. 6A-6B  show the interaction and operation of interlocking ratcheting rings and ratchet spring latch 
         [0018]      FIGS. 7A-7B  show side views of an alternative embodiment of the ratcheting and locking mechanism components and Detail views of the locking mechanism component used to secure and subsequently deploy the centralizer bows. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0019]    The following description is of exemplary embodiments, but is not intended to limit the scope, applicability or configuration of the claims. Rather, the following description provides a convenient illustration for implementing various embodiments. Various changes may be made in the function and arrangement of the elements described in these embodiments without departing from the scope of the claims as set forth hereafter. This detailed description may be adapted and employed with alternatively configured devices having different shapes, components, material, or mechanisms, and the like, and still fall within the scope of the present claims. Thus, this detailed description of preferred embodiments describes and enables the claimed inventions and is for purposes of illustration and not limitation. 
         [0020]    Therefore, reference in the specification to “one embodiment” or “an embodiment” indicates that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least an embodiment of the invention. The phrase “in one embodiment” or “an embodiment” do not necessarily refer to the same embodiment. 
         [0021]    In the following description, certain terminology is used to describe certain features of one or more embodiments of the invention. For example, a “bow spring” as described herein may include, but is not necessarily limited to, a distinct formed component assembled with a pair of stop collars or an integral component formed from the same material stock as the stop collars. The stop collars and bow springs may be constructed from a wide variety of materials including, but not necessarily limited to, spring steel, metal, composite materials, carbon fiber, plastics, or any combination thereof. Any number of bow springs or combination of bow spring profiles or bow spring positions may be used in accordance with various embodiments. 
         [0022]    Aspects of the invention provide mechanisms for a centralizer  10  to be run down-hole in a low-profile, compressed state, and then deployed upon reaching a desired position or after clearing a particular bore restriction. A bow spring centralizer  10  has longitudinal bows  12  and a ratchet/lock mechanism  14  selectively actuatable to deploy longitudinal bow springs  12  about casing  16  once said centralizer  10  is positioned down-hole. With reference to  FIGS. 1A, 1B and 1C , deployable centralizer  10  is shown in a compressed configuration prior to deployment of bows  12 .  FIGS. 2A, 2B and 2C  show bow springs  12  in a deployed configuration. A cover  18  protects a series of ratcheting components and lock/release mechanisms from impact, debris, and from potential premature bow spring deployment. One centralizer stop collar  20  and the ratcheting mechanism  14  are secured to casing  16  with the other stop collar  22  translating from the ratcheting mechanism  14  during preloading of the bow springs  12  and rebounding towards the other stop collar  20  upon release of ratcheting mechanism  14 . 
         [0023]    In some embodiments, longitudinal bow springs  12  extend between two collars  20 ,  22  secured about casing  16 . Collars  20 ,  22  are mechanically separated along the longitudinal axis of casing  10 , e.g., via compression, to retract bow springs  12  into a configuration adjacent casing  16 . Collars  20 ,  22  are maintained separated, and thereby bow springs  12  are in a retracted position via lock by ratcheting mechanism  14 . Ratcheting mechanism  14  is selectively actuatable to release or deploy bow springs. 
         [0024]    With reference now to  FIG. 3 , ratcheting mechanism  14  includes a series of ratcheting components configured such that retracted bow springs  12  are deployed by cyclical pressurization of casing  16 . In some cases, ratcheting mechanism/components are axially arranged to achieve a low-profile locking mechanism. 
         [0025]    In one such preferred embodiment the components of ratcheting mechanism  14  are stackably arranged as illustrated in  FIG. 3  as follows. Ratcheting mechanism  14  includes an outer ratchet band  24 , and inner ratchet band  26  with interlocking teeth, and compression/torsion springs  28  to urge outer and inner ratchet bands  24  and  26  into engagement. Two wrap band springs  30  are positioned under outer ratchet band  24  and attached to casing  16  and outer ratchet band  24 . Circumferential expansion of casing  16  during pressurization causes circumferential tensioning of wrap bands  30  and rotation of attached outer ratchet band  24 . Ratcheting mechanism  14  is protected by a cover  18  and end bands  32  to prevent damage during insertion and run-in. In some embodiments, wrap band springs  30  are removed and compression springs  28  cause rotation of outer ratchet band  24  in response to circumferential expansion of casing  16 . 
         [0026]    After centralizer  10  has reached a desired position or cleared a particular restriction, ratcheting mechanism  14  can be released to deploy bow springs  12 . While various embodiments are described in terms of pressure activation, release of ratcheting mechanism  14  can be accomplished also using any number or combination of mechanical actuators, thermal actuators, pressure actuators, or other suitable selective means for actuation of devices down-hole. 
         [0027]    When sufficient pressure is applied inside of casing  16 , the outside diameter of the casing  16  expands. A predetermined increase in pressure will result in a determinable expansion of the diameter of casing  16 . The extent of expansion depends on the casing size, its wall thickness, and materials used. The activation pressure may be measurably different for a 7″ casing, or a 16″ casing, or a 13⅜″ casing. Therefore target activation pressures can be determined and the locking mechanism designed to be activated by the predicted pressure at a predetermined depth or location. Designing the system around the casing expansion that will occur at a desired depth or location provides flexibility and reliability. As casing  16  expands, wrap band springs  30  are tensioned between casing  16  and outer ratchet band  24 , causing rotation of outer ratchet band  24  about casing  16 . Rotation of outer ratchet band  24 , in turn causes rotation of interlocking inner ratchet band  26 . (See  FIG. 6A  and detail AD). When this increased pressure is released, one or more compression/torsion springs  28  urge outer ratchet band  24  toward the original pre-pressurization position. (See  FIG. 6B  and detail AC). Wrap bands  30  can include any number of partial or full windings about casing  16  to achieve a desired circumferential tension and corresponding movement of a free end of wrap band  30  in response to a given pressurization and circumferential expansion of casing  16 . The latch or locking portion of ratchet mechanism  14  comprises numerous components that work together as illustrated in  FIGS. 3, 4A and 4B . 
         [0028]    A ratchet spring lock  31  engages inner ratchet  26  to ensure unidirectional rotation and prevent inner ratchet  26  from rotating backwards with the outer ratchet band  24  when the pressure is released. Ratchet spring lock  31  is protected from debris by ratchet spring lock cover  33 . Thus, selective cyclical pressurization of casing  16  causes outer ratchet band  24  to rotate back and forth, which in cooperation with spring lock  31  produces a ratcheting reaction between outer ratchet band  24  and inner ratchet band  26 . 
         [0029]    With reference to  FIGS. 4A and 4B , tab  44  affixed to casing  16  interfaces with a receptacle  46  integral with or welded to one collar  48  of centralizer  10 . In some embodiments, receptacle  46  includes an aperture for receiving tab  44 . Bow springs  12  of centralizer  10  are compressed until receptacle  46  engages with tab  44 . Ball bearings  48  are inserted into holes  50  defined in receptacle  46  and held in place by the nose  52  of tab  44 . In one preferred embodiment, ball bearings  48  protrude into recesses  54  defined in casing  16  to provide shear resistance between receptacle  46  and casing  16  to maintain centralizer bow springs  12  in a compressed state. 
         [0030]    Tab  44  is biased by a spring  56  to retract from receptacle  46  when aligned with release notch  58  defined on the inner ratchet band  26 . Upon predetermined rotation of inner ratchet band  26 , nose  52  of tab  44  retracts from receptacle  46  as tail  60  of tab  44  withdraws into release notch  58 . Upon withdrawal of nose  52  of tab  44  from receptacle  46 , ball bearings  48  are dislodged from recesses  54 , allowing centralizer bow springs  12  to deploy. 
         [0031]    With continued reference to  FIG. 4A , deployable centralizer  10  is preloaded for run-in with tab  44  seated within receptacle  46  and release notch  58  defined by inner ratchet band  26  rotationally offset a predetermined amount from tab  44 . When centralizer  10  has reached a desired position or depth down-hole, the casing pressure is selectively cycled or pulsed repeatedly until inner ratchet band  26  is positioned to align release notch  58  with tab  44 , as shown in  FIG. 4B . The number of pressure pulses required to deploy centralizer bow springs  12  can be customized or preset by selective positioning of release notch  58  relative to tab  44 . Stated otherwise, rotational offset between release notch  58  defined by inner ratchet band  26  and tab  44  can be selected to establish the number of pressure cycles required for subsequent alignment to thereby release tab  44 . For example, a ratchet tooth pitch and rotational offset can be selected to require ten pressurization cycles. 
         [0032]    Alternate embodiments include the use of multiple locking mechanisms to selectively release the bow spring centralizer. Such embodiments include a plurality of release notches  58  formed in inner ratchet ring  26 , a plurality of tabs  44 , and plurality of receptacles  46 , and related components. 
         [0033]    With reference to  FIGS. 7A and 7B , in one preferred embodiment, receptacle  72  includes two pivoting appendages  74  capable of engaging recesses  76 . Tab  44  maintains appendages  74  apart from each other and engaged with recesses  76 . Upon predetermined rotation of inner ratchet band  26 , nose  52  of tab  44  retracts from receptacle  72  as tail  60  of tab  44  withdraws into release notch  58 . Upon withdrawal of nose  52  of tab  44  from receptacle  72 , appendages  74  collapse and are dislodged from recesses  76 , allowing centralizer bow springs  12  to deploy. 
         [0034]    While various embodiments are described in the context of wellbore applications, centralizer  10  and ratcheting mechanism  14  described herein may provide similar advantages in other applications. Finally, while this description describes and enables various exemplary embodiments, many changes, combinations, and modifications may be made to any of the exemplary embodiments without departing from the scope of the claims. These alternatives can be suitably selected depending upon the particular application or in consideration of any number of factors associated with the operation of the device. These and other changes or modifications are intended to be included within the scope of the present claims.

Summary:
A centralizer sub, system, and method for enhanced access to subterranean zones from the surface as used in oil and gas wellbore installations to center a pipe or casing within a wellbore or previous casing string during run-in, installation, or cementing procedures. In under-reamed applications, casing strings and centralizers pass through a smaller casing string before opening up to a larger hole where repeated compressions and decompressions of bow strings of centralizers can compromise integrity and reliability. A centralizer sub, system, and method reduces and controls insertion and running forces to preserve centralizer integrity and down-bore surfaces and equipment.