US3545543A - Casing apparatus and method for tensioning casing strings - Google Patents

Description

I United States Patent [1113,54

[72] Inventors Archer W. Kammerer, Jr. [56] References Cited Fullerton; UNITED STATES PATENTS in 52,523 2/1866 Bryson 166/206 [21] Appl. No. 778,403

2,050,970 8/1936 166/212 [22] Filed Nov. 25, 1968 2,297,415 9/1942 166/212 [45] Patented Dec. 8,1970

3,029,874 4/1962 166/212 [73] Asslgnee Rotary 01] Tool Company m h 3,055,424 9/1962 166/285 C 3,115,935 12/1963 Hooten 166/212 a corporation of California Primary Examiner-James A. Leppink Attorney-Bernard Kriegel ABSTRACT: A well-casing shoe or collar-forming part of a [54] agz gtg ggggg FOR casing string and having circumferentially spaced holding TENS) 6 D In m members or feet initially retracted within the external confines 30 Cum! 3 of the shoe or collar body. A piston member is shifted hydrau- [52] 11.8. CI. 166/212, lically downwardly in the body to engage and expand the hold- 166/224, 166/242 ing members laterally outwardly in underlying relation to a [51] Int." E2111 /00, preformed formation shoulder, allowing tension to be taken E2 1b 33/00, E21b 17/14 on the casing string, the piston member being disposed behind [50] Field of Search 166/212, the holding members to prevent the formation from returning the holding members to their retracted position.

CASING APPARATUS. AND METHOD FOR TENSIONING CASING STRINGS The present invention relates to casing anchoring apparatus adapted to be lowered in a well bore and a method of pretensioning the casing string and cementing it in place while its tensioned conditioned is retained.

Casing strings are run in well bores and cemented in place. Where the casing string is subject to temperature increases, it undergoes thermal expansion which may damage the annulus of cement surrounding it.

The present invention has i for its main purpose the attachment of the lower portion of a string of casing to the formation in such manner that the entire casing string may be placed in tension prior to its cementing. The invention contemplates a member-forming part of the lower end of the casing string having initially retracted holding elements which are expanded outwardly against the formation, and more particularly under a preformed formation shoulder, the holding members being retained in such outwardly expandedposition and engaging the downwardly'facing formation shoulder so that a substantial tensile pull can be taken on the string ofcasing. Thereafter, the casing may be cemented in place with the casing remaining in its prestretched condition. As a result, in the event that the casing is subjected to thermal expansion, as, for example, in connection with subsequent injection of steam into the formation, the extent to which it can further thermally expand is greatly limited, avoiding damage to the casing, the hardened cement surrounding the casing, and equipment that might be mounted in the casing: Theinternal portions of the apparatus used in pretensioning the casing are preferably made of readily drillable material, enabling them to be drilled or milled out for the purpose of leaving an unobstructed bore through the casing string. This invention possesses many other advantagesand has other purposes which may be made more clearly apparent fromja' consideration of several forms and methods embodying the'invention. These forms and methods are shown and described in the present specification and in.

the drawings accompanying and constituting a part thereof. They will now be described in detail, for the purpose of illustrating the general principles of the invention; but it is to be understood that such detailed description is not to be taken in a limiting sense, since the scope of the invention is best defined by the appended claims.

Referring to the drawings;

FIG. 1 is a longitudinal section of apparatus embodying the invention disposed me well bore havingan enlarged diameter portion to provide a downwardly facing formation shoulder, with the holding members of the apparatus in retracted position;

FIG. 2 is a longitudinal section similar to FIG. 1 of the lower portion of the apparatus, with the holding members in expanded position;

FIG. 3 is a cross section taken along the line 3-3 on FIG. 1;

FIG. 4 is a view similar to FIG. 1 of another form of the invention;

FIG. 5 is a view similar to FIG. 4 with the holding members in expanded position; and i FIG. 6 is an enlarged fragmentary section through the latch portion of the apparatus.

The equipment specifically disclosed in the drawings, as exemplifying the apparatus invention, is adapted to form the lower part of a string of casing extending to the top of a well bore A in which the apparatus and casing string are lowered. As shown in FIGS. 1 to 3, inclusive, the apparatus includes a casing shoe 10, including altubular body member 11 having a threaded upper box 12 threadedly secured to the an adjacent lower pin 13 of the body 14 of a cement float collar 15, the upper end of which is threadedly secured to an adjacent casing section B, the casing section comprising a portion of the casing string extending to the top of the well bore. The float collar 15 can be of any form andis employed when it is desired to prevent the drilling mud, or other fluid, in the well bore from filling the well casing B during lowering of the latter in the well bore A. As disclosed, the interior 16,0f the collar is made of readily drillable material, such as concrete, having inner ribs 17 cast into companion grooves 18 in the collar body 19 and also having inner ribs 20 cast into grooves 21 in a drillable inner member 22 having a central passage 23 therethrough. A flapper'valve 24 is pivoted on a hinge pin 25 suitably secured to the lower end of the innermember 22, the flapper valve being movable upwardly into engagement with a downwardly facing valve seat 16 surrounding the. passage. The inner member 22 and flapper valve 24 may be made of cast iron or other suitable drillable material. If fluid entry into the casing string B during its lowering in the well bore is not be prevented, the float collar 15 can be omitted and the casing shoe 10 connected directly to a casing section thereabove.

The body 11 of the casing shoe elongate and has a concrete mass 27 in its lower portion provided with a tapered nose 28, so as to guide the shoe past any obstructions that might be encountered in the well bore during lowering of the casing string therein. The concrete body has ribs 29 cast into companion grooves 30 in a sleeve 31 suitably secured to the main body of the shoe, as by a plurality of screws 32. The concrete body has a central passage 33 therethrough defined by a drillable tube 34 made of fiber, or the like. The sleeve also has a plurality of axially extending clutching teeth 35, which have a purpose described hereinafter.

The main body 11 of the shoe is provided with a plurality of elongate circumferentially spaced slots 36, in each of which a holding member or anchor foot'37 is mounted. As disclosed,

the upper portion of each holding member pivotally mounted on a hinge pin 38 extending across the body slot and suitable secured to the body, as by welding or the like. The mainportion of the holding memberis T-shaped in cross section, including a central web 39 extending substantially inwardly of the body 11 when the holding member is in retracted position, this web being integral at its outer end with oppositely directed transverse arms 40 extending longitudinally along a substantial portion of the web. As disclosed in FIGS. 1 and 3, when the holding member 37 is in its retracted position within the peripheral confines of the main body of the shoe, the arms 40 are located within a companion slot 36, the lower main portion 41 of which is wider than the upper portion 42 of the slot in which only the web 39 extends and through which upper webportion the hinge pirl projects. When in retracted and held in their outward expanded condition by an expander member 46 which is hydraulically actuated and which functions as a piston. This piston 46 includes an outer sleeve 47 slidable along theinner wall of the main body member 11 of the shoe and disposed initially abodethe holding members, 37, being retained in such initial upper position by a releasable latch member 58 in the form of a split, inherently contractible ring mounted in an external groove 49 in the sleeve and also within an opposed internal groove 50 in the shoe body. The upper inner corner 51 of the ring is tapered in a downward direction and is engageable with a companion tapered side 52 of the sleeve groove, so that when sufficient downward force is imposed on the piston or expander member 46, the ring is cammed or expanded outwardly further into the body groove 50 and completely from the sleeve groove 49 to permit the expander 46 to move downwardly along the anchor dogs or holding members 37. f

As disclosed, the piston member 46 has a concrete body 53 therein anchored to the sleeveby the concrete ribs 54 cast within companion grooves 55 in the sleeve, there being a central passage 56 through the concrete defined by a suitable drillable hollow tube 57 of any suitable material, such as fiber, the

upper end of which engages an inner readily drillable tube 58 providing an upwardly facing valve seat 59, the upper end of the sleeve 47, concrete body 53 and the valve seat 59 being tapered in a downward direction to provide a guide surface toward the passage 56.

The body member 11 has a plurality of circumferentially spaced ports60 therein defined by radial openings extending through the body and communicating with upwardly opening grooves 61 in the main body. A sleeve 62 encircles the main body and is secured thereto, as by welding material 63, so as to close the grooves 61 and also the outer ends of the radial passages'60through the body in order to direct the fluid issuing through the ports, when open, in an upwarddirection. lnitially, a suitable side seal ring 64 is mounted on the body and seals against the periphery of the shifting sleeve 47 above the ports 60, 61 to prevent fluid leakage between the body 11 and sleeve 47. The lower end of the sleeve has a plurality of axial clutching teeth 65 companion to the clutching teeth 35 in the upper end of the lower sleeve 31, so as to lock the piston 46 to the lower sleeve against rotation, as described hereinbelow.

When the piston 46 has beenshifted downwardly to its fullest extent, an upwardly facing latch shoulder 66 on the upper end of the sleeve 47, provided by a reduced diameter portion 67 of the sleeve, will bedisposed immediately below the latch ring 48 which will recontract across the shoulder 66 and prevent inadvertent upward shifting of the piston member 46.

*tWhen'the'pi'ston member is in this position, the cementing The shoe and collar are then secured to one another,

the collar being attached to an adjacent section of the casing B. At this time, the piston or expander member 46 is held in its upper position by the latch ring 48, and the holding members 37 are held in their retracted position by the breakable strap 45, the parts occupying the positions illustrated in FIGS. 1 and 3. The casing string is then lowered in the well bore A until the holding members 37, which are still in retracted position, are

located within the enlarged bore C of the well and below the preformed formation shoulder D.

Circulating fluid can now be pumped down through the casing string B and through the float collar 15, the flapper valve 24 being forced away from its companion valve seat 26, the circulating fluid continuing on down through the piston passage 56 and the lower passage 33 for discharge into the well bore C, A and for upward passage through its annulus 70 toward the top of the well bore. A suitable trip ball member 71 of a diameter smaller than the float collar passage 23, but greater than the passage 56 through the piston 46, is then dropped or is pumped down through the casing string B, moving throughthe float collar passage 23 and coming to rest upon the valve seat 59 of the piston. The pressure of the fluid in the casing is then increased slowly, the pressure exerting a downward force on the piston 46 until such downward force is sufficient to cam the latch ring 48 outwardly completely from the sleeve groove 49 and into the shoe body groove 50, the piston shifting downwardly and bringing its sleeve 47 down along the inner tapered expander surfaces 43 of the holding members 37, expanding them fully outwardly, as limited by engagement of stop fingers 72 on the holding members with a companion stop shoulder 73 on the body at the upper ends of the slots 36. The piston member 46 and its sleeve 47 slide downwardly along the inner webs 39 of the holding members until the sleeve 47 engages the lower sleeve 21 and concrete body 27, at which time the latch shoulder 66 is disposed below the latch 48, permitting the latter to contract inherently a ainst the reduced diameter portion 67 of the shifting sleeve above the latch to retain the piston 46 in a downward position, at which time the cementing ports 60, 61 are open. The fact that the holding members 37 have been shifted outwardly and locked in their outward condition is indicated to the operator at the top of the well bore by the opening of the ports 60, 61 and the resumption of fluid circulation down through the casing string and upwardly through the annulus 70 between the casing string B and the wall of the well bore A.

An upward pull is then taken on the casing string B, which will bring the holding members or feet 37 upwardly against the formation shoulder D. A desired amount of tension is imposed on the casing string, which tensile force can be very substan tial, and, in fact, may approach the joint strength of the casing sections. With the tension retained on the casing string, cement slurry is pumped down through the casing B and out through the cementing ports 60, 61 in the usual manner, using conventional cementing plugs (not shown), if desired, until the cement in the annulus 70 reaches the desired height. The tension on the casing string B is retained until the cement has set and hardened.

A drill bit or milling tool (not shown) is then lowered on a suitable string of drill pipe or tubing into the casing, and the internal parts of the collar and shoe 16, 22, 24, 53, 57, S8 of a lesser diameter than the inside diameter of the casing sections B are then drilled out. Drilling of the piston 46 if facilitated by the fact that its clutching teeth 65 interengage with the lower clutching teeth 35 to prevent rotation of the piston. Drilling is continued until all of the inwardly projecting parts of the collar and of the shoe within the confines of its shifting sleeve 47 and the lower sleeve 32 have been fully disintegrated or pushed to the bottom of the hole.

The casing string B is held in its tensioned condition by the cement bond between it and the formation. Subsequent increase in the temperature of the casingstring, such as resulting from the injection of steam into the casing string .and at producing formation, will not be-associated with significant elongation of the casing string, in view of its pretensioning, and

elongation. As a result, damage to the well bore, cement bond and casing string is avoided.

A modified form of apparatus is illustrated in FIGS. 4 and 5, in which the apparatus 10a containing the holding members or feet 37 is constituted as a collar, the upper end of which is threadedly secured to a lower casing section 80. The apparatus 10a is essentially the same as disclosed in FIGS. 1 to 3, inclusive, the lower concrete body 27a being cast in the lower portion of the collar body 11a immediately below its slots 36 'and has a readily drillable inner member 34a provided with a central passage 33a opening into side ports 81 extending to the exterior of the body 11a below its slots 36. If desired, the ports 81 could be omitted and the central passage 33a coritinued completely through the concrete body 27a to discharge fluid into the casing section therebelow for continued movement to the lower end of the casing string and thence into the well bore A, C.

The upper piston member 46 member 46 and latch device 48-50, 66 are essentially the same as in the other form of the invention, except that there are no side ports in the main body of the collar initially closed by the outer shifting sleeve 47, An inner sleeve 83 is slidably mounted within the readily drillable inner member 570 of the piston, this sleeve 83 initially occupying a lower position in which its upper flange 84 engages shoulder 85 of the inner member 57a, at which time side ports 86 through the upper part of the inner sleeve are in closed position, the inner sleeve extending substantially below the lower end of the concrete body 53 and of the inner drillable member 57a.

The operation of the apparatus disclosed in FIGS. 4 and 5 is essentially the same as in the other form of the invention. The collar 10a is connected to the float collar 15, which, inturn, is connected to the casing section B thereabove, or the collar We may be connected directly to the casing section thereabove in the event that a bac pressure valve, provided by the float collar 15, is not neede 1 The lower end of the collar a is connected to the lower casing section 80, or other suitable member. The casing string B is lowered in the well bore -A until the anchor feet or holding members 37 are disposed in the enlarged well bore C below the formation shoulder D. Fluid may be circulated down through the apparatus to condition the well bore. When the anchor feet 37 are to be expanded outwardly, the trip ball 71 is dropped or pumped down through the casing string, passing through the float collar and coming to rest on the upper end 59a of the shifiable sleeve 83 to close the central passage 56a through the latter. Fluid pressure is then increased in the casing string above the ball 71, exerting a downward force on thepiston 46 to expand the latch ring 48 outwardly to a position released from the piston, whereupon the piston shifts downwardly, engaging the inclined surfaces 43 of the holding members 37 and expanding 'them laterally outwardly. The piston or expander member 46 moves downwardly until it contacts the lower concrete body 27a, at which time it is disposedbehind the holdingmembers to retain them in their outward expanded condition, the latch ring 48 snapping back over the upper portion 67 of the sleeve 47 and above its shoulder 66 to retain the piston member in its lower position (FIG. 5). As the piston 46 moves downwardly toits lowermost position, the lower end 88 of the shifting sleeve 83;.engages the drillable inner member 34a in the lower cement body 27a which prevents its further downward movement, allowing the remainder of the piston to move downwardly along the sleeve 83 to its final position and placing the upper end of the inner drillable member of the piston below the ports 86, which are then in the open condition illustrated in FIG. '5. i

With the holding members 37 expanded and locked in their lateral outward position, the casing string B is elevated to bring the holding members upwardly against the shoulder D and an appropriate pull taken on the casing string. Fluid circulation can now take place through the casing string.B,.the fluid passing throughtheflpat collar 15 into the lower collar 10a, passing inwardly through the ports 86 in the upper portion of Y the shiftable sleeve 83 into its .central passage 56a, and thence downwardly therethrough and through the'central passage 56a, and thence downwardly therethrough and through the central passage 33a of the lower cement body 27a and through its ports 81 to the exterior of the casing string. Cement slurry,

or other cementitious' material, can also be pumpeddown through the casing string' tofollow the path just described, continuing on upwardly through the annulus 70 surrounding the casing string toward the top of the hole. During the ce' menting operation, tensionlis maintained on the casing string,

its prestressing beingretained until the cement sets and hardens. 1

We claim:

1. ln apparatus for use with a pipe string to be disposed in a well bore having a downwardly facing formation shoulder: a tubular body adapted to be secured to an adjacent pipe string member; initially retracted holding members pivotally mounted on said'body for lateral expansion outwardlyof said body for engagement with the formation shoulder; and expanding member shiftable in said body and slidable along the inner wall of said body against said holding members to swing said members about their pivot axes and expand said holding members laterally; and'means for shifting said expanding memberin said body.

2. ln apparatus as defined in claim 1: said expanding member having retaining surface means shiftable and retained behind said holding members to prevent retraction of said holding members from their expanded position, said retaining surface means being parallelto the axis of said tubular body.

3. In apparatus as defined in claim 1: means engaging said expanding member to .releasably retain said expanding member in its initial position prior to expanding said holding members.

4. ln apparatus as defined in claim 1: means engaging said expanding member to releasably retain said expanding member in its initial position prior to expanding said holding .6 members; and means engaging said expanding member to retain said expanding member in its final position after expanding said holding members.

5. ln apparatus as defined in claim 1: said expanding member being shiftable and retained behind said holding members to prevent retraction of said holding members from their expanded position; and means engaging said expanding member to releasably retain said expanding member in its initial position prior to expanding said holding members.

6. ln apparatus as defined in claim 1: said expanding member being shiftable and retained behind said holding members to prevent retraction of said] holding members from their expanded position; means engaging said expanding member to releasably retain said expanding member in its initial position prior to expanding said holding members; and

means engaging said expanding member to retain said expand-.

ing member in its final position behind said holding members.

7. ln apparatus as defined in claim 1: said expanding member having a fluid passage; and said shifting means comprising a trip member movable through the pipe string into engagement with said expanding member to close said fluid passage and enable fluid pressure to be built up in the pipe string to hydraulically shift said expanding member in said body to expand said holding members.

8. In apparatus. as defined in claim 1: said expanding member having a fluidpassage; said shifting means comprising a trip member movable through the pipe string into engage ment with said expanding member to close said fluid passage and enable fluid pressure to be built up in the pipe string to hydraulically shift said expanding memberin said body to expand said holding members; and means for opening said fluid passage after said expanding member has expanded said holding members. a i

9. ln apparatus as defined in claim 1: said expanding member having a fluid passage; said shifting means comprising means for restricting fluid flow through said fluid passage to enable fluid pressure to. be built up in the pipe string to hydraulically shift saidexpanding member in said body to expand said holding members; and means for opening said fluid passage after said expanding member has expanded said holding members.

10. In apparatus as defined in claim 1:.said expanding member having a fluid passage; said shifting means comprising means for restricting fluid flow through said fluid passage to enable fluid pressure .to be built up in the pipe string to hydraulically shift said expanding member in said body to expand said holding members; and means responsive ,to downward movement of said expanding member in said body for opening said fluid passage.

11. Inapparatus as defined in claim 1: a sleeve-shiftable in said expanding member and having a fluid passage and a port communicating therewith and initially closed by said expanding member; said shifting means comprising means engageable with said sleeve to close said fluid passage .and enable fluid pressure to be built up in the pipe string to hydraulically shift said expanding member in said body to expand said holding members; and means engageable with said sleeve in response to downward movement 'of said expanding member and sleeve in said body for relatively elevating said sleeve in said expanding member to open said port.

12. in apparatus as defined in claim 1: said body having side ports; and said shifting means shifting said expanding member to a position in which said side ports are opened.

13. in apparatus for use with a pipe string to be disposed in a well bore having a downwardly facing formation shoulder: a tubular body adapted to be secured to an adjacent pipe string member andhaving circumferentially spaced slots; initially retracted holding members carried by said body in said slots and having portions extending inwardly of said body, said holding members being expandable laterally outwardly of said body to underlie the formation shoulder in engagement wall of said tubular body; means releasably retaining said expanding member in said initial position; and means for shifting said expanding member downwardly in said body along said inner wall to release said retaining means and to engage said inwardly extendingjportions to expand said holding members laterally outwardly.

14. In apparatusas defined in claim 13: said expanding member having retaining surface means shiftable downwardly behind said inner portions to prevent retraction of said holding members from their expanded position, said retaining surface means being parallel to the axis of said tubular body.

15. ln'apparatus as defined in claim 13: said expanding member being shiftable downwardly behind said inner portions to prevent retraction of said holding members from their expanded position; and said retaining means reengaging said expanding member to retain said expanding member said portions of said holding members,

16. In apparatus asdefined in claim 13: said retaining means comprising an inherently contractible latch member engaging a lower shoulder of said expanding member and expandable from engagement with said shoulder in response to downward from engagement with said shoulder in response to downward force imposed on said expanding member; and said expanding member having an upper shoulder across which said latch member contracts upon downward shifting of said expanding member to prevent upward movement of said expanding member in said body.

17. In apparatus as defined in claim 13: said expanding memberbeing shiftable downwardly behind said inner portions to prevent retraction of said holding'members from their expanded position; said retaining means comprising an inherently contractible latch member engaging a lower shoulder of said expanding member and expandable from engagement with said shoulder in response to downward force imposed on said expanding member; and said expanding member having an upper shoulder across which said latch member contracts to retainsaid'expanding member behind said inner portions of said holding members.

18, In apparatus for use with a pipe string to be disposed in a well bore having a downwardly facing formation shoulder: a tubular body adapted to be secured to an adjacent pipe string member and having circumferentially spaced slots; initially retracted holding members pivotally carried by said body in said slots and having portions extending inwardly of said body, said holding members being expandable laterally outwardly of said body to underlie the formation shoulder in engagement therewith; said body having ports above said holding members; anexpanding member in and slidable along the inner wall of said body and disposed initially across said ports to close the same and above said holding members, said expanding memberhaving a fluid passage; means releasably retaining said expanding member in said initial position; and means for closing said passage to enable fluid pressureinthe pipe string to release said retaining means and shift said expanding member downwardly in said body against said inwardly extending portions to swing said members about their pivot axes and expand said holding members laterally outwardly, said expanding member being shifted in said body to a position opening said ports.

19. in apparatus as defined in claim 18: said expanding member being shiftable downwardly behind said inner portions to prevent retraction of said holding members from their expanded position.

20. lnapparatus as defined in claim 18: said expanding member being shiftable downwardly behind said inner portions to prevent retraction of said holding members from their expanded position; and said retaining means reengaging said expanding member to retain said expanding member behind said portions of said holding members.

21. In apparatus as defined in claim 18: said retaining means comprising an inherently contractible, latch member engaging a lower shoulder of said expanding member and expandable from engagement with said shoulder in response to downward force imposed on said expanding member; and said expanding member having an upper shoulder across which said latch member contracts upon downward shifting of said expanding member to prevent upward movement of said expanding member in said body.

22. In apparatus as defined in claim 18: said expanding member being shiftable downwardly behind said inner portions to prevent retraction of said holding members from their expanded position; said retaining means comprising an inherently contractible latch member engaging a lower shoulder of said expanding member and expandable from engagement with said shoulder in response to downward force imposed on said expanding member; and said expanding member having an upper shoulder across which said latch member contracts to retain said expanding member behind said portions of said holding member and in a position in which said ports are open.

23. A method of cementing a well casing string in a well bore, the casing string having expandable holding members carried by its lower portion, comprising forming a downwardly facing shoulder in the well bore formation, running the casing ing string to bear the holding members against the shoulder and applying a desired tension to the casing string to prestretch the casing string, and maintaining the tension on the casing string while cementing the casing string in the well bore.

24. A method as defined in claim 23: maintaining thetension on the casing string to retain the casing string in its prestretched condition until the cement sets and hardens.

25. A method of tensioning a tubular string in a well bore, comprising forming a downwardly facing shoulder in th well bore formation, locating the tubular string in the well bore and expanding holding members on the tubular string laterally outwardly to underlie the formation shoulder, and applying a desired tension to the tubular string with its holding members engaging the formation shoulder, whereby to prestretch the tubular string.

26. A method as defined'in claim 25: securing the tubular string in the well bore in its stretched condition.

27. A method as defined in claim 25: maintaining the tension on the tubular string while cementing the tubular string in the well bore v 28. A method as defined in claim 25: maintaining the tension on the tubular string while cementing the tubular string in the well bore; and maintaining the tension on the tubular string to retain the tubular string in its prestretched condition while the cement sets and harden's.

29. in apparatus as defined in claim 1: said expanding member being made of readily drillable material to allow said expanding member to be disintegrated by a drilling tool to leave the tubular body passage substantially unobstructed.

30. In apparatus as defined in claim 13: said expanding member being made of readily drillable material to allow said expanding member to be disintegrated by a drillingtool to leave the tubular body passage substantially unobstructed.

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