Method and multi-purpose apparatus for control of fluid in wellbore casing

This application claims priority from U.S. Provisional Patent Application, Ser. No. 60/132,044, filed Apr. 30, 1999.

This invention relates generally to equipment used in the drilling, completion and workover of subterranean wells and more specifically, to the control of drilling fluids, completion fluids, workover fluids, cement, and other fluids in a casing or other tubular string within a wellbore.

The process of drilling subterranean wells to recover oil and gas from reservoirs consists of boring a hole in the earth down to the petroleum accumulation and installing pipe from the reservoir to the surface. Casing is a protective pipe liner within the wellbore that is cemented into place to ensure a pressure-tight connection of the casing to the earth formation containing the oil and gas reservoir. The casing is run a single joint at a time as it is lowered into the wellbore. On occasion, the casing becomes stuck and is unable to be lowered into the wellbore. When this occurs, load must be added to the casing string to force the casing into the wellbore, or drilling fluid must be circulated down the inside diameter of the casing and out of the casing into the annulus in order to free the casing from the wellbore. To accomplish this, it has traditionally been the case that special rigging be installed to add axial load to the casing string or to facilitate circulating the drilling fluid.

When running casing, drilling fluid is added to each joint as it is run into the well. This procedure is necessary to prevent the casing from collapsing due to high pressures within the annulus inside the wellbore exterior to the casing. The drilling fluid acts as a lubricant which facilitates lowering the casing within the wellbore. As each joint of casing is added to the string, drilling fluid is displaced from the wellbore. The prior art discloses hose assemblies, housings coupled to the uppermost portion of the casing, and tools suspended from the drill hook for filing the casing. These prior art devices and assemblies have been labor intensive to install, required multiple such devices for multiple casing string sizes, have not adequately minimized loss of drilling fluid, and have not been multi-purpose. Further, disengagement of the prior art devices from the inside of the casing has been problematic, resulting in damage to equipment, increased downtime, loss of drilling fluid, and injury to personnel.

Circulating of the drilling fluid is sometimes necessary if resistance is experienced as the casing is lowered into the wellbore. In order to circulate the drilling fluid, the top of the casing must be sealed so that the casing may be pressurized with drilling fluid. Since the casing is under pressure, the integrity of the seal is critical to safe operation and to minimize the loss of the expensive drilling fluid. Once the casing reaches the bottom, circulating of the drilling fluid is again necessary to test the surface piping system, to condition the drilling fluid in the hole and to flush out wall cake and cuttings from the hole. Circulating is continued until at least an amount of drilling fluid equal to the volume of the inside diameter of the casing has been displaced from the casing and the wellbore. After the drilling fluid has been adequately circulated, the casing may be cemented into place.

The purpose of cementing the casing 500 (See FIG. 3 A through FIG. 3C) is to seal the casing to the wellbore formation. In order to cement the casing within the wellbore 502 , hereinafter the assembly to fill and circulate drilling fluid is generally removed from the drilling rig and a cementing head apparatus installed. This process is time consuming, requires significant manpower, and subjects the rig crew to potential injury when handling and installing the additional equipment to flush the mud out with water or other chemical hereinafter prior to the cementing step. A special cementing head or plug container is installed on the top portion of the casing being held in place by the elevator. The cementing head includes connections for the discharge line of the cement pumps, and typically includes a bottom hereinafter 506 and top wiper plug hereinafter 508 . Since the casing and wellbore are full of drilling fluid, it is necessary to inject a spacer fluid to segregate the drilling fluid from the cement to follow. The hereinafter bottom cementing plug hereinafter 506 is used to wiped the inside diameter of the casing and serve, in conjunction with the spacer fluid, to separate the drilling fluid from the cement as the cement is pumped down the casing string hereinafter 500 . Once the calculated volume of cement required to fill the annulus has been pumped, the top plug hereinafter 508 is released from the cementing head. Drilling fluid or some other suitable fluid is then pumped in behind the top plug, thus transporting both plugs and the cement contained between the plugs to an apparatus at the bottom of the casing known as a float collar hereinafter 510 . Once the bottom plug hereinafter 506 seals the bottom of the casing, the pump pressure increases, rupturing, for example, a diaphragm in the bottom of the plug hereinafter 506 and allowing the calculated amount of cement to flow hereinafter as indicated by flow lines 512 from the inside diameter of the casing to a certain level with the annulus hereinafter 504 being cemented. The annulus hereinafter 504 is the space within the wellbore between the inside diameter (“ID”) of the wellbore and the outside diameter (“OD”) of the casing string. When the top check valve closes, keeping the cement from flowing from the OD of the casing back into the ID of the casing.

The prior art typically discloses separate devices and assemblies for (i) filling and circulating drilling fluid; and (ii) cementing operations. The prior art devices for filling and circulating drilling fluid disclose a packer tube, which requires a separate activation step once the tool is positioned within the casing. The packer tubes are known in the art to be subject to malfunction due to plugging, leaks, and the like, leading to downtime. Since each step in the well drilling process is potentially dangerous, time consuming, labor intensive and therefore expensive, there remains a need in the art to minimize any downtime. One advantage in this art is described in U.S. Pat. No. 5,735,348, issued on Apr. 7, 1998 to Samuel P. Hawkins for “Method and Multi-Purpose Apparatus for Dispensing and Circulating Fluid in Wellbore Casing,” some of the components of which can be used, as but one example, in using the present invention.

FIG. 1 A: Illustrates hereinafter the initial effects of a sequence hereinafter of dropping a pair of balls from the earth's surface into the downhole apparatus according to the present invention.

FIG. 1B Illustrates separation of an upper mandrel and lower mandrel such that lower mandrel drops into the wellbore.

FIG. 1C Illustrates opening passageway in lower mandrel and initial steps of launching upper mandrel to drop into the wellbore

FIG. 2 : Illustrates the sleeve which is moved down by dropping the first of two balls from the earth's surface and increasing the pump pressure.

FIG. 3A Illustrates initial configuration of typical cementing operation. hereinafter

FIG. 3B Illustrates lower cement wiper plug pumped to top of float shoe or collar.

FIG. 3C Illustrates upper cement wiper plug pumped to top of lower cement wiper plug.

Referring now to FIG. 1 ( a ), there is illustrated an upper cylindrical mandrel 320 , having an upper sub-mandrel 322 , the upper end 324 of the sub-mandrel 322 comprising an externally flared, contractible collet. The invention contemplates the use of two balls, one being referred to as a small ball, and one as a larger ball. The upper sub-mandrel 322 has three progressively smaller axial bores, commencing at the collet end 324 with axial bore 326 followed by axial bores 327 and 328 , axial bore 328 being sized to allow passage of a smaller ball, but not a larger ball. A first section 330 of the external side wall of the sub-mandrel 322 is threaded and of reduced diameter of the remainder of the sub-mandrel 322 . A second section 332 of the external side wall is threaded and of an even smaller diameter than that of section 330 . The section 330 has a male thread, around which a shoulder ring 334 is threadedly connected.

Referring further to FIG. 1 ( a ), a lower sub-mandrel 340 , being part of the upper mandrel 320 , has a first axial bore 342 , the upper end of which has a female thread 344 to accept the male thread of section 332 . The axial bore 342 tapers inwardly to a reduced diameter axial bore 346 , through which a smaller ball can pass.

The external wall of the sub-mandrel 340 has a reduced diameter section 350 and a larger diameter section 352 on its end. The transition between the sections 350 and 352 forms a shoulder 351 . A conventional elastomeric cement plug 356 is sized to fit over the section 350 and is locked into place between the shoulder 351 and the shoulder ring 334 .

The section 352 has a larger diameter axial bore, approximately the same diameter as axial bore 327 . The interior side wall of the axial bore 352 has a circular groove 354 for accepting a plurality of round balls, preferably of glass, ceramic or other drillable materials. In the preferred embodiment, four such balls (not illustrated) are used in the groove 354 . One or more threaded holes hereinafter 353 are in the side wall of section 352 and which feed into the groove 354 . After the four balls are fed into the groove 354 , a plug (not illustrated) is threadably connected into each of the holes hereinafter 353 to block them off and keep the balls captured in the groove 354 .

Referring further to FIG. 1 ( a ), a lower mandrel 360 comprises a cylindrical lower-sub-mandrel 362 and a cylindrical upper sub-mandrel 364 . The sub-mandrel 362 has a first axial bore 366 size to accept the sleeve 300 of FIG. 2, but has a reduced diameter axial bore 368 which will initially block the flared, contractible collet end 306 of sleeve 300 . The side wall 370 around the axial bore 377 has a plurality of holes 372 therethrough, preferably four holes in which the glass or plastic balls can reside while also in the groove 354 . A plurality of shear pins, preferably four, are threaded through the sidewall 370 of the axial bore 368 to ride in the longitudinal slots in sleeve 300 , illustrated in FIG. 2. A pair of grooves 308 and 310 are formed in the exterior side walls and around axial bores 366 and 368 , respectively, and are used to house o-rings (not illustrated) for preventing fluid loss between the sub-mandrel 364 and the sub-mandrel 340 .

The sub-mandrel 362 has a raised shoulder 392 and a threaded (female) portion to threadedly engage a threaded (male) lower end 394 of the upper sub-mandrel 364 . The lower sub-mandrel 364 has a raised shoulder 396 . A conventional, elastomeric cement plug 355 is sized to fit over the threaded connection between the shoulders 392 and 396 and is secured to the lower mandrel 360 by such shoulders.

The lower sub-mandrel 362 has a plurality of holes hereinafter 400 through its sidewall below the shoulder 396 , and also has an end cap hereinafter 402 at its lowermost end with an opening through the cap hereinafter 402 of a diameter less than the axial bore hereinafter 404 to which the holes hereinafter 400 are connected. The cap hereinafter 402 has a slot in its lower side to assist in making up the various threaded connections. The bore hereinafter 404 is sized to accept the sleeve 300 all the way down to the cap hereinafter 402 , against which the sleeve 300 comes to rest.

Referring now to FIG. 2, there is illustrated a cylindrical sleeve 300 having a first axial bore 302 of a diameter sized to accept a first dropped ball, i.e., 1⅝,″ and a second axial bore 304 sized to stop the first dropped ball. The upper end 306 comprises an externally flared, contractible collet.

External grooves 308 , 310 and 312 , perpendicular to the longitudinal axis of the sleeve 300 , with grooves 308 and 310 at collet end 306 , and groove 312 at the opposite end of the sleeve 300 , use o-rings (not illustrated) to provide a fluid seal in the operation of the sleeve 300 , described hereinbelow.

Four equally spaced longitudinal slots, of which only slots 406 and 408 are illustrated, are spaced about the periphery of the sleeve 300 , parallel to the longitudinal axis of the sleeve 300 , within which a pair of shear pins hereinafter 409 and a pair of shear pins 410 , respectively, can ride and are protected until the sleeve has moved sufficiently to shear the shear pin pairs hereinafter 409 and 410 .

In making up the tools illustrated in FIGS. 1 and 2, the lower mandrel 360 can be rotated with respect to the upper mandrel 320 to align the holes 372 and hereinafter 353 to feed the small “marble sized” balls into the groove 354 . The holes hereinafter 353 are then plugged up. The sleeve 300 keeps the small balls in place within the groove 354 and holes 372 , thus locking the upper mandrel 320 to the lower mandrel 360 , while allowing rotation between the two mandrels.

In the operation of the system described herein, with the equipment ready to be run into the interior of the casing string, whether to circulate fluid, fill-up the casing, to cement the casing to the earth formation walls, or otherwise control fluid according to the preferred embodiment of the invention, the system requires that a pair of balls be dropped, a first smaller ball, i.e., having a 1⅝″ diameter, and then a larger ball, i.e., having a 1⅞″ diameter. The balls should be a drillable material in the event of malfunction requiring the entire apparatus to be drilled out. The balls can be dropped manually, or can be dropped sequentially through the use of various ball-drop mechanisms known in the art.

As soon as the smaller ball enters the top end of the upper mandrel 320 of FIG. 1 ( a ), it passes all the way down to the sleeve 300 residing in the upper end of lower mandrel 360 . By increasing pump pressure at the earth's surface and hence, by increasing differential fluid pressure across the first dropped ball 70 , the sleeve 300 shears the first set of shear pins hereinafter 409 , at a predetermined pressure, i.e., 1,000 psi. This causes the sleeve 300 to move down and uncover the small balls in the groove 354 and holes hereinafter 357 , allowing the small balls to drop out and the lower mandrel to separate from the upper mandrel, as illustrated in FIG. 1 ( b ). As the now separated lower mandrel 360 is pumped down after being separated from the upper mandrel 320 , it comes to rest against a float collar or other plug landing surface commonly used in this art at or near the bottom of the casing string. As a special feature of the present invention, means are provided for bending over and holding the ball 70 from falling out of its seating arrangement within the sleeve 300 . By further increasing pump pressure at the earth's surface, the differential fluid pressure across the first dropped ball increases to a predetermined value, i.e., to 1,250 psi, shearing a second set of shear pins 410 , and forcing the collet end of the sleeve to be forced through the axial bore 368 , resulting in the sleeve 300 coming to rest against the end cap 402 . When the sleeve 300 bottoms out, this causes the plurality of holes 400 to be uncovered, allowing fluid to be pumped out of the holes 400 , either to fill up the casing, to circulate fluid, to cause cement to exit out of the casing, or to otherwise control fluid in a casing string.

When the operator desires to separate the top mandrel, the second, largest ball is dropped. The second dropped ball reaches the narrowed-down opening 327 to axial bore 328 , and seals off that opening. By increasing pump pressure to a predetermined amount, i.e., 1,500 psi, the collet end 324 of the upper mandrel is pulled out of a fill-up and circulation tool or whatever other tool or apparatus is located immediately above the upper mandrel, shearing any shear pins as necessary and thus, the top cement plug can be pumped down the interior of the casing string. As a final step, the top mandrel is pumped down until it settles over the lower mandrel and the job is completed, usually by drilling out the lower and upper mandrels with their respective cement plugs.

In an alternative embodiment of using the apparatus according to the present invention, when it is desired to circulate fluids or fill up the casing with fluids, and it is not necessary, nor desired, to have the cement plugs be separated from the apparatus as contemplated by FIG. 1, the entire assembly comprised of the first and second cement plugs can be separated as a unit merely by dropping the second, large ball without having dropped the first, smaller ball, or upper mandrel 320 and the lower mandrel 360 can be bolted securely together, resulting in the ability to move the sleeve 300 down to uncover the holes 400 without separating the lower mandrel 360 from the upper mandrel 320 .