US2937598A

US2937598A - Free piston

Info

Publication number: US2937598A
Application number: US620533A
Authority: US
Inventors: Brown Norman Fraser
Original assignee: US Industries Inc
Current assignee: US Industries Inc
Priority date: 1956-11-05
Filing date: 1956-11-05
Publication date: 1960-05-24
Anticipated expiration: 1977-05-24

Description

N. F. BROWN May 24, 1960 FREE PISTON 4 Sheets-Sheet 1 Filed Nov. 5, 1956 War/770m /'-T 5/0 w INVENTOR.

N. F. BROWN May 24, 1960 FREE] PISTON 4 Sheets-Sheet 3 Filed Nov. 5, 1956 Nor/77 0/; f? 5 0 W/7 BY M N. F. BROWN May 24, 1960 FREE PISTON 4 Sheets-Sheet 4 Filed NOV. 5, 1956 INVENTOR.

Jim

"nited States FREE PISTON Filed Nov. 5, 1956, Ser. No. 620,533

'3 Claims (Cl. 103-52) This invention relates to free pistons and more particularly to a free piston for use as a parafiin scraper or for use in gas lifting of oil wells in which the piston maintains a fairly sharply defined interface between the fluid being lifted and the driving gas.

It is common practice in the production of oil to raise it to the surface by the process known as gas lift. In one type of gas lift, a head of well fluid is permitted to accumulate in the production tubing above a gas lift valve. The valve is then opened and gas under pressure is introduced into the tubing to lift the column of well fluid. One problem encountered in this method of production is the tendency of the well fluid and gas to intermix at their interface and the Well fluid to fall back into the Well.

One form of apparatus for overcoming this difiiculty is the free piston which more or less effectively separates the gas from the Well fluid and prevents slippage.

This invention provides an improved form of free piston which has a long life and maintains a sliding seal with the tubing even though the tubing be out of round.

It is an object of this invention to provide an improved free piston having exceptionally long life which will conform to the inner contour of the pipe through which it passes.

Another object is to provide such a piston in combination with an actuator means for controlling flow through the piston bypass which is wholly carried by the piston.

Another object is to provide a piston packer of the type employing metal intermeshing segments to seal between the piston and a pipe in which the seal will conform to the variations in the shape of a pipe through which it is passed.

Another object is to provide a piston seal of the type employing metal intermeshing segments to seal between the piston and pipe in which the segments are free to move on one side of the piston while remaining stationary on the other side of the piston to conform to the shape of the pipe.

Another object is to provide a piston as in the preceding object in which each segment is movable independently of the remaining segments to permit better conformity of the segments to the inside of the pipe.

Other objects, features and advantages of this invention will be apparent from the drawings, the specification and the claims.

In the drawings, wherein like numerals indicate like parts and wherein there are shown illustrative embodiments of this invention:

Fig. 1 is a sectional view through a well equipped for gas lift production with a free piston'constructed in accordance with this invention shown in elevation in the lubricator of the Christmas tree;

Fig. 2A is a view partly in elevation and partly in vertical cross section through the upper end of a free piston constructed in accordance with this invention;

Fig. 2B is a continuation of Fig. 2A and shows the inatent ice termediate section of the free piston invertical cross section;

Fig. 2C is a continuation of Fig. 2B and shows the lower section of the free piston in vertical cross section;

Fig. 3A is a view in vertical cross section through the upper end of amodified form of free piston;

Fig. 3B is a continuation of Fig. 3A and shows'in vertical cross section thelower end of the modified form offree piston;

Fig. 4 is a cross sectional view along the lines 4-4 of Fig. 2C;

Fig. 5 is a schematic, fragmentary view of the seal member of the piston shown inFig. 33;

Fig. 6 is a schematic, inside view of the apparatus shown in Fig. 5;

Fig. 7 is a schematic view of one of the segments of the Fig. 3A3B form of seal; and

Fig. 8 is a schematic view of one of the segments of the Fig. 2A2B2C form of seal.

Referring first to Fig. 1, there is shown a free piston installation employing the free piston of this invention. At the top of the well a lubricator indicated generally at 10 is provided, for the insertion and removal of the piston. A latch mechanism indicated generally at 11 is provided and during normal operations, is locked in an out of the way position. The latch may be moved into operative position at any time it is desired to catch and hold the piston for putting ,it in or taking it out.

Fluid raised by the piston leaves the well head through outlet 12. Fluid reaches outlet 12'through holes 10a and 10b in the lubricator. When the piston reaches the top of its travel, it strikes the resiliently mounted stop 13 which absorbs the shock of the upwardly travelling piston and as will appear more fully hereinafter, actuates the re-setting rod to open the valve in the piston bypass.

After the piston bypass valve is open, the piston drops in the well, passing through any fluid accumulation therein, until it reaches a resiliently mounted stop 14 in the bottom of'the well. In striking this. stop, the bypass valve is closed as will appear more fully hereinafter. Thereafter, gasintroduced through gas lift valve 15 will force the free piston upwardly in the tubing, driving .before it the well fluid whichhad accumulated in the Well above the stop 14. V

Referringnow to Figs. 2A, 2B and 2C there is shown in more detail the piston in the lubricator of Fig. 1. This piston includes a body indicated generally at 16 which is tubular in form to provide a flow passageway 17 therethrough. This passageway is controlled by a valve in: dicated generally at 18 at the lower end of the piston. A closure is effected bythe nose piece 19 of the valve member striking the lower stop in the well and a re-opening is effected by the rod 20 striking the upper stop in the lubricator in the well. Arranged about the piston, there is provided one or more circumferentially expansible metal packers indicated generally at 21.

The body comprises a number of endwise arranged sections to facilitate assembly and to simplify manufacturing procedure. At the top of the body, into the uppermost body section 22 is fitted a head 23 adapted to be engaged by a wire line tool to permit manual removal of the piston from the hole if necessary. .The

screwed joint is locked mechanically by conventional ways 27 therein to permit flow of fluid through the bore in the body as the piston sinks through the fluid in the tubing on its way down the well.

Theadedly secured to the upper intermediate section 26 is a lower intermediate section 28 provided with a shoulder 29 which is engaged by the latch mechanism 11 in the lubricator.

Threadedly secured to the lower intermediate section 28 is the lower body section 30 which carries another packer assembly 21 and the counterbore 31 in the lower end thereof.

The valve assembly 18 comprises a nose piece 19 screwed to the threaded end of the rod 20 and locked thereto by a pin 34 secured by a snap ring 34a. Mounted above the nose piece 19 is a U-type seal 33 backed up against washer 32 and accompanied by inner seal ring 320. The seal 33 cooperates with the counterbore 31 to close the passageway 17.

In order to re-open the valve 18 when the piston reaches the lubricator, the re-setting rod 20 extends upwardly through the passageway 17 for the full length of the free piston and extends beyond it by an amount equal to the valve travel in order to cooperate with the pad 13 shown in Fig. 1. At vertically spaced points, guide pins 35 are carried by the re-setting rod 20 to centralize it in the bore 17.

In the upper section 22 of the body, the re-setting rod is provided with a detent carrier 36 in which there is mounted a plurality of detents 25a. The detents are urged outwardly by resilient means such as springs 37. At the upward limit of travel of valve member 33, the detents 25a engage an annular groove 38 in the wall of bore 24 and at the lower limit, engage a similar groove 39. The shoulders of each

groove

38 and 39 are formed with conical surfaces diverging inwardly and the heads of the detents 25a are correspondingly conically formed so that, upon the exertion of a sufficient axial force on the re-setting rod, the detents will retract radially permitting the rod to reciprocate in the piston body.

Referring now to the packer assemblies 21, reference is made to Fig. 8 in which the shape of one of the component segments of packer 21 is better shown. Reference is also made to Fig. 7. Functionally, the segments of Fig. 7 are similar to the segments of packer 21 except for the mounting of the segments.

The packer assembly 21 includes a plurality of oppositely facing

intermeshing segments

41 and 42 mounted on the body with limited freedom of movement to enable them collectively to expand and contract with changes in the bore of the tubing through which the piston is passed. The group of segments 41 is mounted on the body with the free ends facing upwardly and the identical group 42 is mounted on the body with the free ends facing downwardly. The components of each group are evenly spaced circumferentially about the body and each group intermeshes with the other.

These segments are mounted with some freedom of movement in carriers 43. Resilient means such as springs 44 acting through split rings 45 urge the component segmtgnts of each group toward the components of the er.

The rings 45 are split to permit flexibility and individual movement of component segments on one side of either group without corresponding movement of the component segments on the other side. The splits of the rings 45 are such as to prevent them from cocking within the carrier 43 and preferably are 120 apart. When the piston is in a round section of the tubing, the springs 44 will exert a fairly constant force on each component of the

groups

41 and 42 and the assembly will be concentric with the tubing. In the event the piston passes through an out-of-round section of the tubing, these springs will permit individual components of both groups to move relatively in varying amounts in order to produce resultant radial movements relatively which,

in turn, enable the assembly collectively to maintain close contact circumferentially with the inside walls of the pipe.

A ring 46 is positioned circumferentially about the body and underlies both

segments

41 and 42. Each of the segments has an internal conical surface 47 which cooperates with a corresponding conical surface 48 on the ring 46, and the

surfaces

47 and 48 act as wedge surfaces. The ring 46 is approximately triangular in cross section with the inside diameter floating on the body and sealed by sliding seal ring 46a. Its other two conical faces 48 engage alternately the opposite conical surfaces 47 of both groups of segments. Thus, it will be seen that as the segments move toward the ring, they will swing radially outward while preserving continuous contact between

surfaces

47 and 48.

In order to provide a seal between segments regardless of their lateral position, each adjacent pair of

intermeshing segments

41 and 42 have side faces 51 and 52 respectively in sliding engagement with each other. These side faces extend at an angle to the axial center line and all are identical so that the angle on a segment 41 is exactly complementary to the adjacent angle on a segment 42. The side wall faces 51 and 52 being on planes truly perpendicular to the axis of the assembly, also converge inwardly as best shown in Fig. 7. These wall faces 51 and 52 should be portions of helical surfaces but, in practice, are substantially flat, and as the departure from the ideal is extremely small, they can satisfactorily move relatively and sufliciently while preserving sealing contact. The wall faces 51 and 52 intersect the conical surfaces 47 at the same point at which the latter are intersected by the ring faces 48 and therefore a nearly perfect continuity of contact and seal is maintained between adjacent segments and between the segments and ring, independent of relative segment movements.

From the above, it will be seen that the several segments may move relative to each other so that some of the segments on one side of the body may move while segments on the other side of the body do not move or move in different amounts or in opposite directions to accommodate an out-of-round pipe.

Referring now to the Figs. 3A, 3B, 5, 6 and 7, there is shown another form of piston. The body of the piston of Figs. 3A and 3B is made-up of an upper section and a lower section 101. The body is again generally tubular in form and has an internal bore 102 therethrough. The lower end of the upper section 100 of the body is beveled at 103 to provide a valve seat and a valve member 104 cooperates with the valve seat to close the passageway and stop flow through the bore in the body.

When the piston is moveing downwardly in a well, fluid enters the bore through inlets 105 and exits from the bore through outlets 106 in its upper end and

side outlets

107 and 108, which together permit free flow of well fluid through the piston commensurate with reasonable travelling velocities.

The upper end of the piston is guided through tubing by a group of annular ribs 109.

The valve member 104 has a stem 111 which, when the valve is open, projects below the valve body by an amount equal to the valve travel and strikes the lower stop in the well to close the valve. A multiple ball detent, indicated generally at 112, cooperates with

grooves

113 and 114 in stem 111 to releasably latch the valve member in open or closed position. An O-ring 115 inside lower body section 101 acts as a wiper to prevent dirt from interfering with the free sliding fit of valve stem 111. When the free piston falls through gas and strikes a liquid surface at high speed, the danger of accidental and premature closure of the valve 104 is eliminated by thus restricting the impact effect to the com paratively small area of the end of stem 111.

. asst-ji s The valve member is unseated at the limit of the free pistons upward travel by the re-setting rod 116 which is provided with guide pins 117' at. spaced points along its length to centralize it in the body.

The re-setting rod has at its upper end a head'118 which normally projects from the upper end of the body and engages the upper stop 13 in the lubricator.

The re-setting rod is urged upwardly by a spring 119 whose thrust is in excess of the weight of rod116 to insure that this weight willihave nov eifect on the re-opening of the valve member other than when the piston strikes the lubricator. stop in spite-of the dynamic effectof a temporary deceleration of the free piston while travelling upwards.

The head 118 is limited in its upward travel by stop ring 11811 locked in place by. snap ring 118b and the mass of the rod 116 sub/assembly'is normally held at rest against ring 118a by the spring 119.

Thefree piston is here shown provided with a modified form of'metal' packer assembly. similar to that shown in Figs. 28 and'Z'C except that eachofthe segments is provided with an individual spring to. assist it to-move independently of all the other segmentsof the seal.

As in the case of the segments of the Fig. 2A-2B-2C piston, the segments indicated generalIy at 120 are mounted with their free ends extending downwardly and the segments indicated generally at 121 are mounted with their free ends extending upwardly. These segments are all identical and'are provided with internal conical surfaces 122 which engage complementary conical surfaces 123 on the ring indicated generally at 124 which surrounds the body and underlies the. seal segments. Each of the segments is provided with side walls having faces 12S and 126 which extend at an angle to the axial center line of the segments but whose planes, at the intersection of the axis of the packer assembly, are perpendicular to that axis. These faces 125 and 126 on each segment again maintain contact with like faces of oppositely facing adjacent segments while permitting relative movements therebetween.

The mounting for each group of the segments comprises a two-piece ring having an inner section 127 over which an outer section 127a has a sliding fit.

The two rings may be secured to the body in any desired manner. Preferably, a pin 128 penetrates a hole 129 in the inner ring and is received in a bore in the free piston body. It is assembled through a slot 130 in the outer ring. The pin 128 has a step-like recess at its outer end which permits the outer ring 127, after the pin has been put in, to move over that recess. The thrust of the packer segment springs holds rings 127 in this position and locks the pin in position as well as itself. Three or more of these pins are preferably employed in securing each pair of mounting

rings

126 and 127 to the body.

The inner ring 126 is provided withspaced groves 131 in which the slotted legs 132 of the

segments

120 and 121 are mounted freely for reciprocation. As best shown in Fig. 6, the outer ring is provided with lugs 133 which project into the slots 134 within legs 132 to limit the axial travel of the segments and also provide moorings for the segment springs. The clearance between each segment and its groove is loose enough to permit free axial and some lateral, radial and rotational movement of the free end of the segments to appropriate extents respectively.

In order to bias the segments toward the ring 124, each segment is provided with a resilient means such as spring 135 having one end bearing against one lug 133 inside the outer ring 127 and the other end bearing against the inner end 136 of slot 134. These compres sion springs will independently urge each segment toward the ring yet will yield to superior forces in the opposite direction and thus the seal assembly may assume the internal shape of any out-of-round tubing through which it passes and simultaneously maintain contact on all the, radially disposed faces 125, 126. and all the axially disposed conicalfaces 122 on the segments and 123 on the ring 124.

The thrustof'one packer segment spring is in excess of the total weight of the free pistondivided by the effective area of the pipe multiplied by the effective area closed" oh by that segment, or

where St=Spring thrust in pounds F=Allowance for friction, pounds W=Wt. of free piston'in' pounds Ap=Eifective area of pipe I.D., sq. inches As=Eflective area closed off by the segment considered sq. inches An excess of 10% to 20% has been found satisfactory.

Intheory, the greater the number of segments employed, the better the seal but in practice, the number has been reduced with economy to 8 per packer assembly, i.e., 4 a side, without any appreciable loss of efiiciency in oil well practice.

The'angle of the sides of the inner seal ring is a function of the angle of the

faces

51 and 52 to the segment axial center line in Fig. 8.

In respect of functioning of either of the packer assemblies described but referring for illustration to Figs. 8'and 2B, it is to be noted that when the unit is assembled and at rest inside aroundpipe of the correct nominal diameter, all the sealing faces'will be pressed into engagement. The shoulders 41a will then be clear of the ledges 43a inside the housings 43 by an amount that will allow axial movement of opposite segments towards each other suflicient to produce an overall increase in the efi'ecive circumference of the assembled unit to suit the maximum increase in pipe diameter anticipated.

When this assembly moves through a pipe, say downwards relative to Fig. 2B, all the segments will be moved up relatively by friction. Thereafter the shoulders 41a of the lower group will rest against the ledge 43:: and all the segments of that group will trail past high spots in the pipe which will bear first on the gently sloping conical faces 41b. These lower segments will not move axially but only radially.

Meanwhile the upper segments can be moved singly or collectively against spring 44 and are capable of yielding both axially and radially to possible high spots while otherwise maintaining continuity of effective seal.

Thus it is arranged that the leading components of the sealing assemly, in either direction of travel, are the trailers and the onus of maintaining the seal rests with the followers.

This form of seal has more freedom of individual seg ment movement than the Fig. 2A--2B2C form, but may be slightly more expensive to fabricate.

Either of the free pistons described may be utilized in conventional free piston gas lift with the time cycle of the free piston travel being controlled in any conventional manner.

From the foregoing it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth, together with other advantages which are obvious and which are inherent to the apparatus.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.

As many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

The invention having been described, what is claimed 1. A free piston comprising; a cylindrical body; a laterally expansible metal seal surrounding the body including a ring surrounding the body, a plurality of intermeshing alternately facing segments mounted, on the body for axial and radial movement, each of said segments overlying the ring and havinga wedge surface engaging a wedge surface on the ring, said segments having engaging side walls extending at identical angles to the axial center lines of the segments and lying on planes otherwise perpendicular to the central axis of the body to provide engaging surfaces between adjacent segments at relatively varied axial and radial positions of the segments, and means carried by the body and engaging and urging the segments toward the ring and permitting movement of one or more of the segments independently of each other and of the remainder of the segments.

2. A free piston comprising; a cylindrical body; a laterally expansible metal seal surrounding the body including, a ring surrounding the body, a plurality of intermeshing alternately facing segments mounted on the body for axial and radial movement, each of said segments overlying the ring and having a wedge surface engaging a wedge surface on the ring, said segments having engaging side walls extending at identical angles to the axial center line of the segments and lying on planes otherwise perpendicular to the axis of the assembly to provide engaging surfaces between adjacent segments at relatively varied axial and radial positions of the segments, and resilient means carried by the body and engaging and independently urging each segment toward the ring and permitting movement of one or more of the segments independently of each other and of the remainder of the segments.

3. A free piston having a body and a metal seal, the seal comprising a wedge ring surrounding the body, a plurality of mutually interengaging, alternately oppositelydispbsed wedge-shaped segments arranged around the body overlying the ring'and eachhaving a wedge surface engaging a wedge surface on the ring, whereby said seal will be expanded radially of the body by axial movement of alternate segments in opposite directions relative to the body and resilient means carried by the body and engaging and independently urging each segment, in a direction to laterally expand the seal.

References Cited the file of this patent UNITED STATES PATENTS 1,819,994 Claytor Aug. 18, 1931 1,919,529 Ricker July 25, 1933 1,919,548 Fletcher July 25, 1933 1,932,451 Evans Oct. 31, 1933 2,001,012 Burgher May 14, 1935 2,016,433 Humason Oct. 8, 1935 2,246,577 Davis June 24, 1941 2,642,002 Knox et al June 16, 1953 2,674,951 Zaba Apr. 13, 1954 2,676,547 Knox Apr. 27, 1954 2,684,633 Knox July 27, 1954 2,714,855 Brown Aug. 9, 1955 2,757,614 Spalding Aug. 7, 1956 2,762,310 Eklund Sept. 11, 1956