Boring or penetrating the earth – Processes
Reexamination Certificate
2002-03-23
2002-12-10
Bagnell, David (Department: 3672)
Boring or penetrating the earth
Processes
C166S376000, C166S243000, C166S098000
Reexamination Certificate
active
06491116
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to downhole tools for use in oil and gas wellbores and methods of drilling such apparatus out of wellbores, and more particularly, to such tools having drillable components made from metallic or non-metallic materials, such as soft steel, cast iron, engineering grade plastics and composite materials. This invention relates particularly to downhole packers and frac plugs.
In the drilling or reworking of oil wells, a great variety of downhole tools are used. For example, but not by way of limitation, it is often desirable to seal tubing or other pipe in the casing of the well, such as when it is desired to pump cement or other slurry down the tubing and force the slurry out into a formation. It thus becomes necessary to seal the tubing with respect to the well casing and to prevent the fluid pressure of the slurry from lifting the tubing out of the well. Downhole tools referred to as packers and bridge plugs are designed for these general purposes and are well known in the art of producing oil and gas.
The EZ Drill SV® squeeze packer, for example includes a set ring housing, upper slip wedge, lower slip wedge, and lower slip support made of soft cast iron. These components are mounted on a mandrel made of medium hardness cast iron. The EZ Drill® squeeze packer is similarly constructed. The Halliburton EZ Drill® bridge plug is also similar, except that it does not provide for fluid flow therethrough.
All of the above-mentioned packers are disclosed in Halliburton Services—Sales and Service Catalog No. 43, pages 2561-2562, and the bridge plug is disclosed in the same catalog on pages 2556-2557.
The EZ Drill® packer and bridge plug and the EZ Drill SV® packer are designed for fast removal from the wellbore by either rotary or cable tool drilling methods. Many of the components in these drillable packing devices are locked together to prevent their spinning while being drilled, and the harder slips are grooved so that they will be broken up in small pieces. Typically, standard “tri-cone” rotary drill bits are used which are rotated at speeds of about 75 to about 120 rpm. A load of about 5,000 to about 7,000 pounds of weight is applied to the bit for initial drilling and increased as necessary to drill out the remainder of the packer or bridge plug, depending upon its size. Drill collars may be used as required for weight and bit stabilization.
Such drillable devices have worked well and provide improved operating performance at relatively high temperatures and pressures. The packers and bridge plugs mentioned above are designed to withstand pressures of about 10,000 psi (700 kg/cm
2
) and temperatures of about 425° F. (220° C.) after being set in the wellbore. Such pressures and temperatures require using the cast iron components previously discussed.
However, drilling out iron components requires certain techniques. Ideally, the operator employs variations in rotary speed and bit weight to help break up the metal parts and reestablish bit penetration should bit penetration cease while drilling. A phenomenon known as “bit tracking” can occur, wherein the drill bit stays on one path and no longer cuts into the downhole tool. When this happens, it is necessary to pick up the bit above the drilling surface and rapidly recontact the bit with the packer or plug and apply weight while continuing rotation. This aids in breaking up the established bit pattern and helps to reestablish bit penetration. If this procedure is used, there are rarely problems. However, operators may not apply these techniques or even recognize when bit tracking has occurred. The result is that drilling times are greatly increased because the bit merely wears against the surface of the downhole tool rather than cutting into it to break it up.
In order to overcome the above long standing problems, the assignee of the present invention introduced to the industry a line of drillable packers and bridge plugs currently marketed by the assignee under the trademark FAS DRILL®. The FAS DRILL® line of tools consists of a majority of the components being made of non-metallic engineering grade plastics to greatly improve the drillability of such downhole tools. The FAS DRILL® line of tools has been very successful and a number of U.S. patents have been issued to the assignee of the present invention, including U.S. Pat. No. 5,271,468 to Streich et al., U.S. Pat. No. 5,224,540 to Streich et al., U.S. Pat. No. 5,390,737 to Jacobi et al., U.S. Pat. No. 5,540,279 to Branch et al., U.S. Pat. No. 5,701,959 to Hushbeck et al., U.S. Pat. No. 5,839,515 to Yuan et al., and U.S. Pat. No. 5,984,007 to Yuan et al. The preceding patents are specifically incorporated herein by reference.
The tools described in all of the above references typically make use of metallic or non-metallic slip-elements, or slips, that are initially retained in close proximity to the mandrel but are forced outwardly away from the mandrel of the tool to engage a casing previously installed within the wellbore in which operations are to be conducted upon the tool being set. Thus, upon the tool being positioned at the desired depth, the slips are forced outwardly against the wellbore to secure the packer, or bridge plug as the case may be, so that the tool will not move relative to the casing when for example operations are being conducted for tests, to stimulate production of the well, or to plug all or a portion of the well.
The FAS DRILL® line of tools includes a frac plug which is well known in the industry. A frac plug is essentially a downhole packer with a ball seat for receiving a sealing ball. When the packer is set and the sealing ball engages the ball seat, the casing or other pipe in which the frac plug is set is sealed. Fluid, such as a slurry, can be pumped into the well after the sealing ball engages the seat and forced into a formation above the frac plug. Prior to the seating of the ball, however, flow through the frac plug is allowed.
One way to seal the frac plug is to drop the sealing ball from the surface after the packer is set. Although ultimately the ball will reach the ball seat and the frac plug will perform its desired function, it takes time for the sealing ball to reach the ball seat, and as the ball is pumped downwardly a substantial amount of fluid can be lost through the frac plug.
The ball may also be run into the well with the packer. Fluid loss and lost time to get the ball seated can still be a problem, however, especially in deviated wells. Some wells are deviated to such an extent that even though the ball is run into the well with the packer, the sealing ball can drift away from the packer as it is lowered into the well through the deviated portions thereof As is well known, some wells deviate such that they become horizontal or at some portions may even angle slightly upwardly. In those cases, the sealing ball can be separated from the packer a great distance in the well. Thus, a large amount of fluid and time is taken to get the sealing ball moved to the ball seat, so that the frac plug seals the well to prevent flow therethrough. Thus, while standard frac plugs work well, there is a need for a frac plug which will allow for flow therethrough until it is set in the well and the sealing ball engages the ball seat, but that can be set with a minimal amount of fluid loss and loss of time. The present invention meets that need.
Another object of the present invention is to provide a downhole tool that will not spin as it is drilled out. When the drillable tools described herein are drilled out, the lower portion of the tool being drilled out will be displaced downwardly in the well once the upper portion of the tool is drilled through. If there is another tool in the well therebelow, the portion of the partially drilled tool will be displaced downwardly in the well and will engage the tool therebelow. As the drill is lowered into the well and engages the portion of the tool that has dropped in the well, that portion of the tool sometimes has a tendency to spin and thus
Berscheidt Kevin T.
Folds Don S.
Smith Donald R.
Stepp Lee Wayne
Vargus Gregory W.
Bagnell David
Rahhal Anthony L.
Walker Zakiya
Wustenberg John W.
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