US2388416A - Casing centering device - Google Patents

Description

Nov. 6, 1945.

' M. c. JOHNSON 2,388,416

CASING CENTERING DEVICE Filed Sept. 17, 1943 Patented Nov. .6,

UNITED STATES PATENT: OFFICE CASING CENTERING DEVICE Mont 0. Johnson, Winterset, Iowa Application September 17, 1943, Serial No. 502,733

2 Claims.

This invention relates generally to centering devices used inconnection with the centering of a casing in an oil well or the like, and in particular to such a, device in which the casing is rotatable and axially movable and which is constructed to permit a free and positive flow of a cement material about the casing so that a uniformly thick layer of cement can be formed completely around the outside of the casing.

Casing centering devices now in common use for centering a casing in a well: hole for the purpose of forming a wall of cement about the casing. generally comprise ring members or the like fixed in an axially spaced relation on the casing and having springs' or yieldable members supported therebetween. These members are generally yieldable in a direction inwardly of the casing so as to.be capable of riding -'over any irregular surfaces" on the sides of the well hole in which the casing is being inserted. This action is generally objectionable because when the surfac irregularity is great the yleldable members at such surface irregularity are apt to be forced very close to the casing. As a result it is practically impossible to force any cement about the casing to provide allayer of cement of uniform thickness about the casing, since at the surface irregularity there may be very little or no space between the casing and the side wall of the well hole through which cement can be passed.

Other centering devices are of a construction such that they produce an obstruction between the casing and the sides of the well hole. Thus great difllculty is encountered in forcing any cement about the casing and through the centering device so that a defective cement wall is formed about the casing. A further disadvantage in many of the prior art centering devices is in the fact that they are assembled about the casing in a direction axially thereof by being slipped over the top or free end of the casing. The top end of the casing must, therefore, be kept free to permit the centering device to be slipped into an assembly position. This assembly is not only inconvenient but oftentimes results in much waste of time.

Yet another disadvantage in the prior art centering devices is found in the fact that they are welded or otherwise secured to the casing against movement relative to. the casing. It is common practice in well drilling to insert the casing in about thirty foot lengths within the well hole. Adjacent casing lengths are threaded and connected together by a usual pipe union. Where many lengths are thus threaded together appreciable tension or strain is produced in the casing tending to rotate the casing in a direction opposite to the direction of rotation used in threading the casing lengths together. As a result when it is necessary to raise the casing, the casing oftentimes rotates in such opposite direction to reduce the strain set up therein. Where the centering devices are secured to the casing this opposite rotation is apt to break or injure the centering devices within the well hole so as to destroy their centering function. Also with the centerin'g devices fixed on the casing, considerable force is required to raise the casing because of the .necessity of lifting the centering device with the casing through the well hole and against the side wall of the well hole.

It is an object of this invention, therefore, to provide an improved casing centering device or centralizer. w

Another object of this invention is to provide a casing centering device which is assembled about the casing in a direction laterally or radially of the casing. This eliminates the requirement in many of the prior art centering devices of the necessity for an end of the casing being free and over which end the centering deviceis axially moved into assembly position.

A further object of this invention is to provide a centering device adapted to maintain a uniform space between the casing and the sides of a well hole and constructed to form with the casing and well hole a plurality of open passages extended longitudinally or axially of the casing to permit a free flow of cement through the centralizer and around the casing.

A further object of this invention is to provide a centering device in which the casing is freely rotatable and axially movable.

A feature of this invention is found in the provision of a centralizer comprised of a pair of like arcuate units adapted to be loosely assembled about a casing in a direction radially of the easing and permitting rotation and axial movement of the casing relative thereto. The axial movement of thecasing relative to the centralizeris confined between a pair of stop members secured to the casing in an axially spaced relation, the centralizer being assembled on the casing between the stop members.

Further objects, features and advantages of this invention will become apparent from the following description when taken in connection withthe accompanying drawing in which: I

Fig. 1'is an elevational view of the centering device of this invention shown-in assembly position about the casing, with the casing being shown inserted in a well hole;

Fig, 2 is an enlarged transverse sectional view of the centering device as seen along the line 2--2 in Fig. 1;

Fig. 3 is an enlarged sectional view of the centering device as seen along the line 3-3 in Fig. 1; and

Fig. 4 is a plan perspective view of a half portion of a stop ring which is secured to the casing to, define the axial movement of the casing relative to the centering device.

With reference to the drawing the centering device or centralizer of this invention is illustrated in Figs. 1 and 2 in assembly relation with a casin l and is seen to include a pair of integrally constructed elongated arcuate units H of like construction. Each arcuate unit H (Figs. 1, 2 and 3) includes a plurality of longitudinally or axially extended frame members l2, four being illustrated in the drawing, supported in an angularly spaced'relation at their corresponding ends by an arcuate connecting member or strap l5 integral with the members l2. Each frame member I! has an outer peripheral surface I! of arouate contour for contacting the side wall of a well hole I and tapers inwardly toward its inner side l6 which contacts the outer periphery of the easing Ill. The inner sides I6, when the centering device is assembled about the casing ill, define a circle which corresponds substantially to the circular contour of the casing III while the outer sides l3 are spaced from the casing Ill and define a circle having a diameter greater than the diameter of the casing l0 and equal substantially to the diameter of the well hole H.

In the assembly of the centralizer about the casing in an arcuate unit II is positioned axially of the casing with the inner sides iii of the members 12 adjacent to the casing. The second unit His then arranged about the casing II) in a mating relation with the first unit, so that the two units H together completely encircle the casing Ill. At this mating position of the units II the adjacent ends of the connecting straps l5 are substantially in abutting engagement so that together the arcuate straps constitute an annular band or ring which extends about the casing Ill.

As shown in Fig. 2 the adjacent ends of the connecting straps I! are of a tapered construction so as to form a V-shaped recess or notch 20 extended axially of the assembled connecting straps It. By virtue of this notch 20 an enlarged welding surface is provided at which the members l5, and in turn the units H, are welded together to complete the assembly of the units about the casing I0. It is seen, therefore, that the units II are connected together at the connecting members l5 and are entirely free of the casing It. The members I! are of a size to loosely fit about the casing in so that the casing is free to rotate and move axially relative to the centralizer for a purpose which will be noted later.

Since the units l l are assembled about the casing III by merely positioning them in mating relation about the outer periphery of the casing it is obvious that this assembly can be made at any place along the length of the casing without regard to the location of any union connections between adjacent casing lengths, or to the location of the free or upper end of the casing above the top of the well hole H.

In the operation of inserting the casing in a well hole a casing length, to be inserted, is threadably connected through a union connection with a previously inserted casing length. When each new casing length is thus connected it is necessary to lift the entire string of casing lengths previously inserted to a height of about two or three feet. During this lifting operation the prior art centralizers, which are fixed to the casing, are lifted with the casing so as to appreciably increase the lifting force, due to their being pulled upwardly against the walls of the well hole. Also, as has been previously explained above, the casing on being lifted has a tendency to rotate in a direction opposite to that in which the casing lengths are rotated to thread them into connecting unions. Thus with the centering devices secured to the casing this rotation at times breaks the centering devices free of the casing, or at least partially destroys them, so as to impair their centering function.

In the present invention the casing is free to rotate and move axially relative to the centralizer as was above explained. As a result when the casing is lifted, prior to connecting another casing length thereon, the centralizer remains stationary while the casing is free to rotate and move axially relative to the casing. The objections encountered by the use of the prior art centralizers are thus completely eliminated.

In order to accomplish an insertion of the centering devices in the well hole with the casing, and to maintain the centering devices in a spaced relation axially of the casing, without interfering with a free relative movement between the casing and the centering device, each centering device is associated with a pair of stop rings l1 spaced axially of the casing (Figs. 1 and 4). Each ring I! is comprised of a pair of semi-circular segments l8 adapted to be fitted in an encircling position about the casing HI. When in this position adjacent ends of the segments I! are welded together, as indicated at 25, and the-segments welded to the casing at weld holes I!) angularly spaced in a segment. The rings 11 are usually spaced about 18 inches to 36 inches apart. depending upon the axial movement desired for the casin relative to the centering device, with the centering device being assembled about the easing and between the stop rings H. To facilitate passage of the stop rings in a well hole H the top edge of the upper ring I! and the bottom edge of the lower ring II, as viewed in Fig. 1, are of a tapered construction.

As clearly appears in Fig. 1 the connecting members l5 and stop rings I! have substantially the same outside diameter and are located entirely within the confines of the circle defined by the outer sides ll of the frame members l2. The outer sides I3 are tapered inwardly to the outer periphery of the connecting members Hi to provide for a gradual change in the diameter of the units I I so as to eliminate sharp shoulder portions.

On insertion of the casing 10, with the centering device thereon, in the well hole ll the upper ring I], as viewed in Fig. 1, engages the connecting members I! at the upper end of the centering device whereby the centering device is moved into the well hole with the casing in. The frame members I! are of a substantially rigid construction so as to be unyielding in a direction radially of the casing when the casing ill, with the centering device thereon, is lowered into the well hole I4. As a result the centering device spaces the casing I0 away from the side walls of the hole It by at least a distance corresponding to the thickness of a frame member I! in a direction radially of the casing. The surfaces II, by virtue of their curvature inwardly and away from the side walls of the well hole ll, permit the centering device to be angularly moved within the hole well hole, is accomplished by the provision of the tapered connection between the frame members I! and connecting members l5.

On lifting of the casing Hi, the casingis axially moved independently of the centering device until the lower ring H, as viewed in Fig. l, is moved into engagement with the lower connecting members l5. As a result appreciable free movement of the casing relative to the centering device is permitted before the centering device is lifted, and while the centering devices are still retained in a spaced relation axially of the casing. If during the lifting operation the casing i should rotate, such rotation takes place independently of but within the centering device so that any possibility of the centering device being broken is entirely eliminated.

Because of the assembled connecting members I! and stop rings ll being within the peripheral confines of the frame members l2, cement for forming a wall about the casing I0 is able to pass between these parts and the side wall of the well hole H, and through the passages 30 formed longitudinally of the centering device by the side wall and the spaces 2| between adjacent frame members I2 (Figs. 1 and 2). In order that the cement can more readily pass through the longitudinal passages 30 the connecting members l5 are formed with tapered recess portions 22 opposite the spaces 2| and connected therewith. Thus on the forcing of a cement material, as is common practice, downwardly through the casing ill around its lower end and upwardly about the outside of the casing, the cement is free to flow about the rings l1, connecting members l5 and through the passages 30 completely through the centering device and about the casing at the centering device so as to form a layer of cement of substantially uniform thickness about'the casing.

By virtuelof the tapered cross section construction of the frame members l2 and their arrangement in an angularly spaced relation a relatively large wall area of the cement layer is directly against the side of the hole I4 and the outer periphery of the casing I0. Thus while the centering device is supported in centering position with the casing III, the layer of cement is able to substantially completely enclose the casing at those portions of the casing within the confines of the centering device, and also above and below the centering device.

From a consideration of the above description it is seen that the centering device of this invention is of a simple design and rugged in construction and comprised of a plurality of like parts capable of being assembled anywhere along the length of a casing and in a free encircling relation with the casing. The relative construction of the frame members I2 and connecting members I I, in conjunction with the relative arrangement of these members in an arcuate unit ll, provides for a free angular and axial movement of the centering device in the well hole I4 and for open passages extending longitudinally of the centering devices so that cement is free to flow about the casing and through the centering device. Further the mounting of the centering device on the casing for free rotation, and axial movement between defined limits, provides for a movement of the casing independently of the centering device after a. centering device has been positioned within a, well hole, whereby to avoid any damage or breaking of the centering device during the setting of the casing III in the well hole.

Although the invention has been described with respect to a preferred embodiment thereof it is to be understood that it is not to be so limited since modifications and changes can be made therein which are within the full intended scope of this invention as defined by the appended claims.

I claim:

1. A device for centering a casing in an oil hole comprising a pair of elongated mating frame units of a semi-circular contour adapted to be assembled in an encircling position about the casing, each said frame units being of a preassembled construction and comprised of a pair of oppositely arranged semi-circular ring members, a plurality of frame members of straight form connected between said semi-circular ring members in a circumferentially spaced relation, each of said frame members being of a substantially triangular shape in cross section having a base of an areuate contour adapted to contact the side wall of the oil hole, and the apex thereof adapted to contact the outer periphery of the casing, with the base of each frame member at the opposite ends thereof being inclined inwardly for Junction with the outer peripheries of the semi-circular ring members.

2. A device for centering a casing in an oil hole comprised of a pair of mating semi-circular frame units adapted to encircle the casing, each said frame units including a plurality of circumferentially spaced longitudinal frame members integrally formed with a semi-circular ring member at each of the opposite ends thereof, each of said frame members having an outer peripheral surface of an arcuate contour adapted to contact the side wall of the oil hole, with the high points on said peripheral surfaces defining a half circle concentric with but having a radius greater than the outer radius of said semi-circular ring members, said peripheral surfaces, at corresponding ends of said frame members, being inclined inwardly for Junction with a semi-circular ring member, and each frame member being tapered inwardly from its outer peripheral surfaceto' provide for the inner surface thereof being in a substantially single line contact with the outer periphery of the casing. MONT C. JOHNSON.

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