US2370833A - Apparatus for cementing well bores - Google Patents

Description

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INVENTOR BY (y ,v 5?... @Maf/Lad ATTORNEY March 6, 1945. R. c. BAKER APPARATUS FOR CEMENTING WELL BORES Filed March 16, 1942 pfff. 1.

March 6, 1945. R. c. BAKER APPARATUS FOR EMENTlNG WELL BORES Filed Maron 1e, 1942 4: sheets-sheet 2 M EEE E?? Kfz/551V C`. i4/ese,

INVENTO R March 6, 1945. R. c. BAKER APPARATUS FOR CEMENTING WELL BORES Filed March 16, 1942 4 Sheets-Sheet 3 P aeg Kfz/35N C. Emea/e,

, INVENTOR @wilt/afm ATTORNEY March 6, 1945. R, Q BAKER APPARATUS FOR GEMENTING WELL BoREs Filed March 16, 1942 4 Sheets-Sheet 4 mail. .4 .Av

INVENTOR Arme/Vey Patented Mai'u 6. 1945 APPARATUS FOR CEMENTING WELL BORES Reuben C. Baker, Coalinga, Calif., assignor to Baker Oil Tools, Inc., Vernon, Calif., a corporation of California Application March 16, 1942, Serial No. 434,913

16 Claims.

This invention relates to the cementing of well bores, and is more particularly concerned with the cementing of long strings oi'- casing by ejecting separate charges of cementitious material from the casing at predetermined spaced points along the well bore.

In drilling a well, it is usual practice to cement the casing in the well bore along its entire length for the purpose of preventing migrant waters from contaminating the well fluid. Where the well is deep, it is diilicult to perform this operation with a single charge of slurry ejected from the lower end of the casing, because of the high pressures required to elevate the cement in the annulus around the casing to the desired level, and the time consumed, which might allow quick acting cements to set prematurely.

It has been proposed to avoid these difficulties by cementing the casing in the well bore by stages. That is, separate charges of cement are ejected from spaced predetermined points along the casing in upward sequence until the entire length of the casing is surrounded with the desired sheath of cement. The casing outlets above the lowermost of these predetermined points are initially closed, usually by a slidable sleeve valve, and plug devices are employed for opening them at the proper time and sequence. The plug devices not only serve to open the sleeve valves, but also as separating elements between each charge of cement slurry and mud, to prevent their commingling and consequent contamination of the slurry. The plug and sleeve valve arrangements heretofore used have been of such character and cooperate in such manner as to prevent circulation of washing fluid through the outlets of a particular stage prior to cementing of that stage, or they effect shifting of the sleeve valve of that particular stage to open position before a lower stage cementing operation has been completed.

Itis an object of the present invention to provide an improved multiple stage cementing apparatus which enables separate charges of cement to be displaced from the casing at vertically spaced stations along the casing, and which permits circulation to take place through the outlets of any stage for as long as desired prior to ejection of cement therethrough. By virtue of the present invention, it is only necessary to place one charge of cement in the casing at any-time for ejection from the particular station.

The invention further contemplates an rimproved multiple stage cementing apparatus having outlets at predetermined points or stations along the casing normally closed by sleeve valves which are shiftable to open position after the cement slurry for a'lower stage has been fully displaced to the desired extent around the casing, in which opening of the sleeve valve is independent of the displacement operation for the lower stage.

Another object of the invention is to provide an improved multiple stage cementing apparatus embodying a plug for preventing commingling between columns of cement slurry and mud, which is capable of readily passing through a materially restricted bore of a casing sleeve valve without shifting it to outlet opening position: so as to enable the valve to be opened later in dependently of the eementing operation in which the plug was employed.

The invention is also concerned with an improved top cementing plug capable of being forced without demage and at comparatively low pressures through a sleeve bore ofv much lesser diameter than the inside diameterv of a'casing with whose wall the plug slidably seals.

In lits general aspects, the invention contemplates a casing string or conduit provided with a sleeve valve initially closing lateral ports or' outlets through an upper cementing station of the casing. A charge of cement slurry is pumped ,down the casing witha flexible plug at its upper end to prevent commingling between the cement and the following mud column. The plug is so designed as to have slidable sealing contact with the wall of the casing and be pumped through the bore of the sleeve valve without shifting the latter to a position opening'its associated ports. despite the fact that the sleeve valve bore has a relatively small diameter. As soon as the plug is forced through the sleeve it expands to its .initial shape in order to continue .its slidable engagement with the casing in a downward direction on top of the cement column, until the desired quantity of slurry has been ejected from the casing at a predetermined exit point below the sleeve valve, to complete cementing of the lower stage.

The sleeve valve has a bore of much lesser diameter than the inside diameter of the casing, which allows a comparatively small diameter or size bridging member to gravitate or be otherwise lowered freely through the standing column of fluid in the casing above the sleeve, until it I seats on the sleeve valve to close its bore. Thereafter, the pressure of the standing fluid column in the casing can be increased to shift the sleeve downwardly to a position opening its associated ports or outlets, so as to permit establishment of free circulation down through the casing, the outlets, and up through the annulus around the casing. After sumcient circulation or washing has taken place, the next charge of cement can be sent down the casing for ejection through the open outlets of the upper cementing station and for upward passage around the casing.

This invention has other objects which will become apparent from a consideration of the apparatus shown in the drawings accompanying and forming part of the present specification. This apparatus will now be described in detail to illustrate the general principles of the invention, but it is to be understood that such detailed description is not to be taken in a limited sense, since the scope of the invention is best defined by the claims appended hereto.

Referring to the drawings:

Figure 1 is a longitudinal section through a well borewith'a casing string therein including the apparatus of the present invention, disclosed with a top cementing plug of the present invention positioned above a stage collar through which the plug is to pass Figure 21s a view similar to Figure 1, with the plug passing through the stage collar;

Figure 3 is a view similar to Figure 1, disclosing the plug after-it has passed through the stage collar;

Figure 4 is a view similar to Figure 1, disclosing the lower stage cemented and the upper stage in process of being cemented;

Figure 5 is a view of part of the apparatus shown in Figure 1 on an enlarged scale;

Figure 6 is a top plane view of a top cementing plug disclosed in vFigure 7;

Figure 'l is a. longitudinal section containing dimensions of an actual plug made and operated in accordance with the invention;

Figure 8 is a longitudinal section showing the dimensions of an actual sleeve valve made and used in conjunction with the plug disclosed in Figure 7; y

Figure 9 is a view similar to Figure 3, but disclosing the casing string as having more than one upper cementing stations;

Figure 10 is a view similar to Figure 9, illustrating the lowermost stage cemented and the intermediate stage being cemented; and

Figure 1l is a view similar to Figure 9, disclosing the uppermost stage beingcemented.

By referring to the drawings, it is to be noted that the casing string I0 is shown with the usual oat shoe I I at its lower end incorporating a back pressure ball l2 capable of engaging the valve seat I3 to prevent return iiow of fluids through the shoe into the casing. A stage collar I4 is included in the casing string at a predetermined point above the shoe, and this collar is provided with a plurality of outlets or ports I5 through which uids can be ejected. It is preferred to prevent return ow of such iiuids by any suitable means, such as a flexible sleeve valve I6 fixed at one end to the collar, but otherwise radially expandable to permit fluid passage from the interior of the casing to its surrounding annulus. This flexible or rubber sleeve valve I6 may be protected by a plurality of closely spaced leaf springs II whose lower ends are welded to the collar I4 and whose upper ends are free to iiex outwardly and permit opening of the valve member. The flexibility of the leaf springs I'I also assists in closing the rubber valve member I6 and keeping it in sealing engagement with collar in the region of the outlets I5. i

Passage of fluid through the outlets I5 is inltially prevented by a slidable sleeve valve I8 disposed over the outlet area of the casing string. Leakage between this sleeve valve I8 and the collar Il is prevented by opposed seals I9 on the sleeve engageable with the collar on opposite sides of its outlets I5. Downward movement of the sleeve I 8 is initially prevented by its seating upon a drillable, cast iron shear ring 20 attached to the collar by shear screws 2l threaded through the collar into an external groove 22 on the ring. The shear ring and screw arrangement 2li-22 prevents downward shifting of the slidable sleeve valve I8 and opening of the ports I5 until desired. Any other suitable frangible arrangement for preventing movement of the sleeve valve to port opening position can be employed.

In cementing the lowermost stage around the casing, a quantity of cement slurry 23 at least suiiicient to ll the annular space A between the shoe I I and collar outlets I5 is introduced in the casing. This column of cement slurry and a flexible plug 24 forming part of the present invention placed at its top end are then pumped down the casing string with the aid of a follow ing column of mud, water or other fluid. The plug 24 makes slidable sealing contact with the wall of the casing to prevent contamination between the slurry and the following fluid column. However, when the plug reaches the slidable sleeve I8, the force of the uid above it and its coaction with the sleeve reduces its radial size and pushes it through the restricted bore 25 of the sleeve at a pressure that is too low to shear the screws 2| and shift the sleeve I8 downwardly to outlet opening position. After having been forced through the slidable sleeve valve, the plug 24 again expands to its original size and shape to continue its function as a normal top cementing plug in preventing admixture between the cement slurry and the following column of fluid.

The top cementing plug 24 is pumped down the. casing until sufficient cement slurry has been ejected through the shoe II (first cementing station), or until the plug 24 contacts the shoe (as disclosed in Figure 4), whereupon no further movement can occur. Thereafter, a, bridging member in the form of a ball 26 is placed in the casing and allowed to gravitate to its seat 2l on the slidable sleeve valve Il to close its central restricted bore 25. Pressure built up in the fluid column above the sleeve can then shear the screws 2| and shift the sleeve I8 downwardly to open the ports or outlets I5. Downward movement of the sleeve is limited by its engagement with a suitable stop, which in the present instance is disclosed as consisting of the end 28 of a lower casing section 29 threaded into the collar Upon opening of the outlets I5, circulating fluid can be pumped down the casing for passage through the outlets and upwardly through the annular space B around the casing. Any cement slurry from the lower stage above the collar I4 is removed by the circulating fluid, and this washing action is preferably continued until the well bore has been properly conditioned for receipt of the second charge of cement slurry. This charge is sent down the casing in a conventional manner, preferably with a top cementing plug 30 at its upper end, which has the usual flexible cups 3| slidable along the wall of the casing to prevent commingling between the cement slurry and the fluid above the plug I0. This cement slurry is ejected through the outlets I5 and passes upwardly around the casing to form an annular seal at the second cementing stage. Reverse ilow of the slurry in the casing is prevented by the flexible rubber sleeve valve I8 and spring elements I1. f

After the cement has set and hardened, the interior of the casing is drilled outto provide an unobstructed bore therethrough. For this reason, the slidable sleeve .valve I8, its shear ring 26, cementing plugs 24, 30, and interior of the casing shoey II are all preferably made of readily drillable materialy 'I'he passage or bore 25 through the slidable sleeve valve I8 is of much lesser diameter than the inside diameter of the casing, in order to permit employment of a bridging member 26 small enough in diameter to gravitate readily through the fluid in the casing to its companionseat 21. The flexible `plug 24 is designedto function as an eilcient top plug in forcing cement down through the casing, when positioned both above and below the sleeve valve I8, and still be capable of being forced through this latter member at a pressure sumciently low as to be incapable of disrupting the shear screws 2| holding the sleeve valve I8 in closed position across its outlets l5.

The flexible plug 24 is made of rubber or similar pliant, elastic material, and consists of a head or -body 35 having a tapered front or leading external surface 36 inclined downwardly toward the axis of the casing, and a rear or trailing tapered external surface 31 inclined upwardly toward the axis of the casing. These opposed, generally conical, conoidal, or similar shaped portions 36, 31 of the plug head or -body 35 are separated by or merged into a comparatively narrow casing engaging portion 38 of the body, having a leading wiper edge 39 for removing cement slurry from the wall of the casing, and a trailing, relatively short annular lip 40 adapted to be acted on by fluid under pressure above the plug to keep it expanded against the wall of the casing and prevent leakage between the casing and plug.'

The plug 24 is also provided with a. generally cylindrical nose 4I extending in advance of the body 35 and of much smaller diameter than that of the casing, and also with a generally cylindrical stem or tail piece 42 extending'from the tapered trailing portion 31 of the plug body. This tail piece 42 terminates ina guiding flange43 having a plurality of notches 44 forming intervening fingers 45 capable of upward deflection as tblug 24 passes through the sleeve I8. As further assistance lto the flexing of the guide flange 43, the upper end 46 .of the cylindrical.

stem or tail piece is relieved inl concave fashion. Similarly; the nose 4I and body 35 of the plug are relieved by a comparatively large central bore 41, which will permit compression of the plug body 35 inwardly more readily upon passing through the slidable sleeve valve I8.

The leading face 43 of the sleeve valve -bore 25 diverges upwardly from its valve seat 21 or small-- est diameter 49, to leave a comparatively small shoulder 50 at its upper end. The smallest diam eter central portion 49 of the sleeve bore may be cylindrical or tapering slightly inan outward and downward direction, while the lower or trailing face I of the sleeve bore may diverge downwardly.

As the flexible plug 24 reaches the slidable sleeve valve I8, the inclined leading surface 36 of its body engages the inclined leading face 49 of the sleeve bore to compress the body member 35 inwardly. This compressiveaction is assisted by the fluids under pressure acting onfthe inclined trailing portion 31 of the body, which have radial thrust components exerted inwardly to decrease the diameter of the plug body 35 and enable the downward components of pressure to force the body and plug throughthe sleevevalve. passing through the most restricted portion 49 of the sleeve bore, the plug body 35 again expands to its initial shape. The inclined, trailing face 5I of the sleeve bore allows such expansion to occur gradually ratherthan suddenly, which might be the ease were the minimum bore through the sleeve to extend'cylindrica-lly throughout its re.

maining length.

- ,As the plug 24 is passing through the sleeve valve I8, the ngers ofA the guide flange 43 engage the inclined leading face 48 of the sleeve bore 2'5 and are deflected or stretched upwardly, while the fluid under pressure above the plug is pushing it through the'sleeve. However, upon leaving the sleeve,l the guideiiange 43 returns to its initial outward shape and position to continue its function of preventing material tilting of the plug as it moves through the casing string.

The nose 4I of the plug has an external diameter substantially equal to that of the minimum bore diameter 49.. This nose fits within the minimum boreportionof the sleeve to center the plug and prevent its tilting `or twisting as its inclined leading face 36 contacts the inclined leading face 48 of the sleeve bore. It should be noticed that the small shoulder 50 at the top of the sleeve is insumcient in extent to prevent lpassage of the plug into the sleeve bore. As a matter of fact, this shoulder could be eliminated' entirely by continuing the bore taper 46 upwardly to a further extent, 'but this is not essential. The cylin- I of the sleevey bore it is deflected upwardly and drical tail piece or stem 42 of the 4plug also has a diameter substantially equal to that of the minimum bore portion 49 so as to function as a piston after the body 35 of the plug has passed through the minimum bore section and has begun to expand to its initial position. The pressure of fluid acts on top of the tail piece 42 and pushes the entire plug through the sleeve. Ofcourse, as the guide flange 43 engages'the inclined face L48 inwardly until it passes through the sleeve, whereupon iti expands toits initial position, as was previously described.

After leaving the sleeve I8, the rubber plug 24 regains its initial shape to continue forcing the cement slurry down through the casing in as efflcient a manner as conventional top cementing Plugs.

Figures 'I and 8 are longitudinal sections through a flexible plug 24 and a sleeve valvel I8, respectively, designed to operate in 7", 24 pound casing, with all essential dimensions placed on the figures to enable an operable apparatus to be made from the data given. The plug 24 shown in Figure 7 is of a composite character.l Its neck 4I is molded from a rubbervhaving a 64 Shore hardness number, its body 35 from a rubber having a 32 Shore hardness number, and its cylindrical tailpiece or stem 42 and flange 43 from a rubber having a 64 Shore hardness number. These hardnesses of rubber were found to operate satisfactorily in pumping the rubber plug 24 yat low pressures through the sleeve; I8 whose dimensions appear in Figure 8. This latter sleeve .was

,Baker casting resin, to obtain readily drillable characteristics.

Upon

The collar device incorporating the sleeve valve and frangible connection is described and claimed in the application of Clarence E. Burt and William S. Althouse, Jr., Serial No. 437,548, filed April 3, 1942, entitled Well cementing apparatus, now Patent No. 2,330,267, granted Sept. 28, 1943.

In actual operations of the cementing apparatus in a well bore employing the plug and sleeve combination shown in Figures 'I and 8, the plug 24 was pumped slowly through the sleeve Il with a rise in pump pressure of only about 100 p. s. i. When pumped rapidly through the sleeve. no rise in pressure was noticed on the vpump gauge. Such low pressures required t move the plug through the sleeve are far below the shear values of the screws 2| holding the sleeve valve in closed position over its outlets i5. This last mentioned value can be of the order of 800 to 1000 p. s. i., which leaves a very large margin between the pressure necessary to pump the plug through the sleeve and that required to shear the screws after the bridging ball 26 has engaged the sleeve seat 21, thus ollering assurance that the sleeve will not be shifted prematurely or inadvertently as the dexible plug is forced through it in cementing the lower stage.

Figures 9. l0 and 11 disclose apparatus for performing more than two stages of cementing, In these iigures, another stage cementing collar lla, substantially the same as the lower collar device i4, has been incorporated in the casing string at a predetermined point above thelower collar device heretofore described. The minimum diameter 49a of the bore through the sleeve valve Ila of this upper device is greater than through the lower sleeve valve. As a matter of fact, it is large enough to permit the bridging ball 26 for the lower collar to pass through it freely, but this ball, of course,is larger than the minimum bore 49 through the lower collar sleeve it so as to engage its seat 21 and allow shifting of the sleeve to a position clear of its outlets i5.

The lowermost stage cementing operation is aardgas the same shear value as the lower set). Circulation can then be established through these open ports lia to wash the annulus C around the casing above the lower two stages: and a third charge of cement slurry ejected through the outlets of the second collar i4a by pumping it downwardly through the casing. preferably by use of any top cementing plug a. It is preferred that this and the flexible cementing plugs 24, 24a employed performed in exactly the same manner as previously described in connection with Figures 1 to 4. The ilexible cementing plug 24 employed on top of the charge of cement passes more readily through the upper cementing collar 4a than through the lower one i 4 since it does not have to compress radially to as great an extent. After the lowermost stage has been cemented, the lower bridging ball 26 dropped, and the lower sleeve valve Il moved to open position, circulation is established through the lower collar, and a sec ond, upper ilexible .cementing plug 24a is employed in forcing the secondcharge of cement through the lower collar I8 to perform the second stage of cementing. 'I'his second ilexible cementing plug 24a can be a duplicate of the rst cementing plug 24, and it passes readily through the upper sleeve valve ita without causing its shifting to open position.

After the upper plug 24a has moved downwardly suiilciently to eject its charge of cement from the casing, a second bridging ball 26a oi larger diameter than the minimum bore portion 49a through the upper sleeve is allowed to gravitate through the fluid in the casing until it engages its companion seat 21a on the upper sleeve, whereupon an increase inthe pressure of the iluid above the sleeve and ball to a suiiicient degree shears the second set of screws 2Ia and forces the second sleeve Ila downwardly to a'position opening its associated outlets or ports i511. (The second set of shear screws 2id may have about as top plug members for all lower stages. The only limitation is that the minimum diameter of the bores through the sleeve valves increase in upward sequence so as to permit free passage of bridging members adapted to seat upon lower sleeves.

' It is therefore apparent that a multiple stage well cementing apparatus has been described which permits circulation through and around the casing prior to the cementing oi each stage, while employing top cementing plugs which prevent contamination between the charge of cement slurry and the iluid following it. Such top cementing plug is made of such material and is ao designed as to pass through the sleeve valve without moving it to open position, andV this is true even though the minimum bore through the sleeve valve is much less in diameter than the inside diameter of the casing, so as to permit use of a bridging member to close the bore of the sleeve valve, which bridging member can gravitate to its companion seat without displacing the iluid above the sleeve valve and independently of the downward movement of the preceding flexible plug. It is after the top cementing plug has passed through the sleeve valve and continued on therebelow to complete the cementing of a lower stage that the bridging member is dropped to permit hydraulic opening of the ports or outlets through the upper stage collar.

I claim:

l. In combination, a string of well casing adapted to be positioned in a well bore, said casing string having lateral outlet means above its lower end, a sleeve valve in said casing string for closing said outlet means and provided with a central bore materially-less in diameter than the inside diameter of said casing string, frangible means for preventing movement of said sleeve valve to' outlet opening position, and a plug slidably engageable with the wall of said casing string and having a pliant, elastic central body portion normally larger than said central bore but adapted to compress inwardly to enable its complete passage through said central bore of said sleeve valve without disrupting said frangible means and moving said sleeve valve to outlet opening position, sad plug having a diameter when uncompressed substantially equal to the inside diameter of said casing.

2. In combination, a string of well casing adapted to be positioned in a well bore, said casing string having lateral outlet means above its lower end, a sleeve valve in said casing string disposed over said outlet means to close the same and provided With a central bore materially less in diameter than the inside diameter of said casing string, frangible means for resisting movement of said sleeve valve to outlet opening position, a

plug having a normal unrestrained diameter of' such size as to have slidable sealing contact with the wall oi' said casing string and having a pliant, elastic central body portion normally larger than said central bore but adapted to compress inwardly to enable its complete passage through said central bore of said sleeve valve without disrupting said frangible means and moving said sleeve valve to outlet opening position, and means movable downwardly through said casing string without displacing the column of iluid above said sleeve valve for closing said central bore. to enable said sleeve valve to be subjected to the pressure of the iluid column thereabove to disrupt said frangible means and shift said sleeve to outlet opening position.

3. In combination, a string of well casing adapted to be positioned in a well bore and provided with lateral outlet means above its lower end, a sleeve valve in said casing string for closing said outlet means and provided with a central bore of materially less diameter than the inside diameter of said casing string, a cementing plug having a, normal unrestrained diameter substantially equal to the inside diameter of said casing string and adapted to pass through said central bore of said sleeve valve Without shifting it to outlet opening position, and means adapted to be introduced in said casing string and movable downwardly therethrough Without displacing the column of ilud above said sleeve valve for closing said central bore` to enable said sleeve valve to be shifted hydraulically to outlet opening position.

4. ln combination, a string of well casing adapted to be positioned in a well bore and provided with lateral outlet means at spaced points therealong above its lower end, sleeve valves slidable along the inner wall of said casing string and adapted to close said outlet means, each of said sleeve valves being provided with a central bore of materially less diameter than the inside diameter of said casing string, with the bore through a lower sleeve valve having a lesser diameter than the bore through an upper sleeve valve, a cementing plug slidably engageable with the wall of said casing string and adapted to pass through the central bores of said sleeve valves without shifting them to outlet opening positions, means movable downwardly through said casing string and upper sleeve valve without displacing the column of uid above said lower sleeve valve for closing its central bore, to enable said lower sleeve valve to be shifted hydraulically to outlet opening position. a second cementing plug slidably engageable with the wall of said casing string and adapted to pass through the central bore of said upper sleeve valve without shifting it to outlet opening posit'on, and means movable downwardly through `said casing string without displacing the column of fluid above said upper sleeve for closing its central bere, to enable said upper sleeve valve to be shifted hydraulically to outlet opening position,

4said plugs having normal unrestrained diameters of such size as to have slidable sealing contact with the wall of the casing.

5, In combination, a string of well casing adapted to be positioned in a well bore and provided with lateral outlet means at spaced points therealong above its lower end. sleeve valves in said casing string for closing said outlet means, each of said sleeve valves being provided with a central bore of materially less diameter than the inside diameter of said casing string, with the bore through a lower sleeve valve having a lesser diameter than the bore through an upper sleeve valve, a top cementing plug slidably engageable with the wall of said casing string and having a pliant, elastic central body portion normally larger than the bore through said lower sleeve valve but adapted to compress inwardly to enable its complete passage through the bores of said sleeve valves without moving them to outlet opening positions, a bridging ball of lesser diameter than said upper sleeve valve bore adapted to be sent down said casing string to close the central bore of said lower sleeve valve, to enable said lower sleeve valve to be shifted hydraulically to outlet opening position, a second top cementing plug slidably engageable with the wall of said casing string and having a pliant. elastic central body portion normally larger than the bore throughvsaid upper sleeve valve but adapted to compress inwardly to enable its complete passage through said central bore of said upper sleeve valve without moving said upper sleeve valve to outlet .opening position, and a larger ball than said first mentioned ball adapted to be sent down said casing string for closing the bore of said upper sleeve, to enable said upper sleeve to be shifted hydraulically to outlet opening position,

vided with a central bore of materially less diameter than the inside diameter of said conduit, 1

and a plug having a pliant, elastic body portion engageable with the surface of the central bore of said sleeve valve to be compresstd thereby inwardly to an extent suilicient to enable passage of the plug through said valve, said plug having a diameter when uncompressed substantially equal to the inside diameter of said conduit.

'1. In combination, a well conduit provided with lateral outlet means, a sleeve valve slidable along the inner wall of said conduit and adapted to close said outlet means, said sleeve valve having a central borel portion of materially less diameter than the inside diameter of said conduit and a leading bore surface diverging in an upward direction from said portion, and a plug having a pliant, elastic body portion engageable with said diverging surface to be compressed thereby inwardly to an extent suiiicient to enable downward passage of the plug through the less di.. ameter portion of said sleeve valve, said plug having a diameter when uncompressed substantially equal to the inside diameter of said conduit.

8. In combination, a well conduit provided with lateral outlet means, a sleeve valve in said conduit for closing said outlet means, said sleeve valve having a central bore diverging in an upward direction from a sleeve bore portion of materially less diameter than the inside diameter of said conduit, and a plug having an upwardly diverging, pliant, elastic body portion engageable with said diverging bore to be comconduit.

9. In combination, a well conduit provided with lateral outlet means, a sleeve valve slidable along the inner wall of said conduit and adapted to close said outlet means, said sleeve valve having a central bore diver-ging in an upward direction from a `sleeve bore portion of materially less diameter than the inside diameter of said conduit, and a plug having a pliant, elastic body of a diameter when uncompressed substantially equal to the inside diameter of said conduit, said body having an upwardly diverging leading surface and an upwardly converging trailing surface, whereby said leading surface is engageable with said diverging bore and said trailing surface is acted on by iluid under pressure in said conduit above said plug to effect compression of said body inwardly to an extent suillcient to enable downward pumping of the plug `through said sleeve valve.

10. In combination, a weil conduit provided with lateral outlet means, a sleeve valve slidable along the inner wall of said conduit, frangible means for preventing shifting of said sleeve valve to outlet opening position, said sleeve valve having a central bore diverging in an upward direction from a sleeve bore portion of materially less diameter than the inside diameter of said conduit, and a top cementing plug having a pliant,

elastic body slidably engageable with the inner pumping of the plug through said sleeve valve r:

without disrupting said frangible means, and a bridging member adapted to be introduced in said conduit for seating in the bore of said sleeve to close the same and enable said frangible means to be disrupted hydraulically and said sleeve valve shifted to outlet opening position.

11. A plug, including a pliant, elastic and inwardly collapsible body provided with a portion adapted to engage the wall of a well casing, said body having an outer leading surface converging downwardly from said wall engaging portion, and an outer trailing surface converging upwardly from said wall engaging portion.

12. A plug, including a pliant. elastic and inasvoss wardly compressibie body provided with a portion adapted to engage the wall of a well casing. said body having an outer leading surface converging downwardly from said wall engaging p0rtion, an outer trailing surface converging upwardly from said wall engaging portion, and said body being relieved centrally thereof to reduce its resistance to inward compression.

13. A plug, including a pliant, elastic and inwardly collapsible body provided with a portion adapted to engage the wall of a well casing, said body having an outer leading surface converging downwardly from said wall engaging portion, an outer trailing surface converging upwardly from said wall engaging portion, and a tail piece extending upwardly from the trailing surface of said body.

14. A plug, including a pliant, elastic body provided with a portion adapted to engage the wall of a well casing, said body having an outer leading surface converging downwardly from said wall engaging portion, an outer trailing surface converging upwardly from said wall engaging portion, an elastic tail piece extending upwardly from the trailing surface of said body, and an elastic guide flange projecting radially from said tail piece.

15. A plug, including a pliant, elastic and inwardly collapsible body provided with a portion having anupwardly facing lip adapted to engage the wall of a well casing, said body having an outer leading surface converging downwardly from said portion, and an outer trailing surface converging upwardly from said lip.

16. A plug, including a pliant, elastic body provided with a relatively narrow portion adapted to engage the wall of a well casing and having an upwardly facing wall engaging lip, said body having an outer leading surface converging down- 'wardly from the lower end of said narrowr portion, an outer trailing surface converging upwardly from said lip, an elastic generally cylindrical tail piece extending upwardly from the trailing surface of said body, and an elastic guide i ilange projecting radially from said t'ail piece,

said body having a central bore extending upwardly from its lower end.

REUBEN C. BAKER.

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