Patent Application
20060096761
1. Field of the Invention
Embodiments of the present invention generally relate to a wellscreen, more particularly, to a slip-on screen with an expanded base pipe.
2. Description of the Related Art
The problem of reliably removing particulates from liquids or gasses (production fluids) exists in many types of wells including oil and gas wells, water wells, geothermal wells, and wells for ground remediation. Typical particulates needing to be filtered out are sand and clay including unconsolidated particulate matter, also known as “formation sand”. A major problem in producing hydrocarbon fluids from unconsolidated formations is the intrusion of formation sand, which is typically very fine, into production fluid and equipment. The presence of sand in production fluid often leads to the rapid erosion of expensive well machinery and hardware.
Subterranean filters, also known as “sand screens” or “wellscreens”, have been used in the petroleum industry for years to remove particulates from production fluids. They are generally tubular in shape, comprising a perforated inner member or pipe, at least one porous filter layer wrapped around and secured to the pipe, and an outer cover. The wellscreens are used where fluid enters a production string. For example, a common way to achieve the filtration is to mount a wellscreen in the production string near the area of fluid production such that the produced fluid must pass through the filter layers and into the perforated pipe prior to entering the production string and being pumped to the surface.
One type of filter is a screen manufactured from wrapped wire. Two typical types of wire wrap screens are slip-on screens and direct-wrap screens. A slip-on screen is manufactured by wrapping a screen jacket on a precisely machined mandrel. Then the jacket is later slipped on the base pipe and the end of the jacket is attached to the base pipe. The slip-on screen allows for a precise slots to be constructed, but is inherently weaker than direct-wrap screen because of an annulus between the screen jacket and the base pipe. Differential pressure usually exists across the screen when in service. This pressure, if sufficient, will cause the wires and the rods to be bent inwardly into contact with the base pipe. Such a collapse will result in a shifting of the coils of wire forming the screen and reduce or destroy the ability of the screen to serve its intended purpose.
The direct-wrap screen is constructed by wrapping the screen directly on the perforated base pipe, resulting in a stronger screen by eliminating the annulus between the screen jacket and the base pipe. Variations in the base pipe, however, result in a less precise screen slots.
Therefore, there exists in the art a need for a wellscreen that has the mechanical properties of a direct-wrap wellscreen and the precise slot tolerance of a slip-on wellscreen.
To wrap the wire 14 on the mandrel 10 and rods 12, relative rotation between the mandrel and rods and the wire feeding means is necessary. Usually, the wire feeding means is fixed and the mandrel 10 and rods 12 are rotated. At the same time the mandrel 10 and rods 12 are moved longitudinally at a speed which along with the speed of rotation provides the desired spacing between the adjacent coils of wire 14. This spacing is commonly referred to as the “slot”. Alternatively, as shown in the Smith Patent, the wire feeding means can be moved longitudinally of the pipe and rods while the pipe and rods are rotated.
Welding electrode 16 is positioned to engage the wire 14 as it is wrapped on the mandrel 10 and provide a welding current that causes the wire and the rod it engages to fuse together. The welding electrode 16 is disc-shaped and rolls along the wire 14. To complete the circuit, means are provided to connect the rods 12 to ground a short distance ahead of the wrapped wire 14.
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Means are provided to resiliently urge the contact surface 22c of each contact 22 toward the rod 12 it engages to hold the rod in contact with the mandrel 10. In the embodiment shown, coil spring 30 is positioned between the back of U-shaped housing 24 and engages leg 22b adjacent its upper end. The spring urges the contact 22 to pivot around pin 32, which mounts the contact in the housing 24. This in turn urges contact surface 22c of the contact 22 into firm engagement with the rod 12 it engages and, in turn, holds the rod in groove 26 and against the outside surface of mandrel 10. As the mandrel 10 and rods 12 are rotated, the rods tend to move and flop around. So the contacts 22 through the resilient force of springs 30 and grooves 26 also serve to hold the rods 12 from lateral movement and guide the rods as they move under the wire 14 and welding electrode 16 so that they will have the proper spacing under the wire.
Ground electrode assembly 18 including contacts 22 should be made of a material having good electrical conductivity, such as brass. This reduces the tendency for any welding to occur between the contacts 22 and the rods 12. The rods 12 are generally of steel, often stainless steel. Housing 24 for the contact assembly 20 as well as the mounting plate 28 should also be made of a material having good electrical conductivity. The ground electrode assembly 18 is mounted for rotation with the mandrel 10 and the rods 12. A commutator or the like (not shown) connects the ground electrode assembly 18 to ground.
The best welds are obtained between the wire 14 and the rod 12 by providing an electrical welding circuit wherein the major resistance in the circuit is the contact between the wire and the rod to which it is to be welded. The circuit between there and ground should be substantially lower in resistance. Therefore, preferably ground electrode assembly 18 is positioned so that contact surface 22c on each individual contact 22 is positioned as close to the welding electrode as possible to reduce the distance the electrical current has to flow down the rod to the ground contact. Also, the contacts 22 can do a better job of guiding the rods 12, the closer the contacts are to the point of welding the wire to the rods. Preferably, the contacts 22 are spaced less than one inch from the welding electrode.
Mounted on the back of mounting plate 28 of the ground electrode assembly 18 are means for engaging the outside surface of the mandrel 10 to hold the contacts 22 of the ground electrode 18 equally spaced from the longitudinal axis of the pipe. In the embodiment shown, four wheels 36 are positioned at 90 degree angles from each other to extend between the rods and engage the surface of the mandrel 10. These wheels 36 serve to hold the individual contacts 22 of the ground electrode assembly 18 equally spaced from the mandrel 10, i.e. the electrode is centered relative to the mandrel.
The present invention provides a method for manufacturing a wellscreen and a wellscreen that have the mechanical properties of a direct-wrap wellscreen and the precise slot tolerance of a slip-on wellscreen.
In one embodiment, a method for manufacturing a wellscreen for use in a wellbore is provided. The method includes disposing a filter subassembly on a base pipe sized so that there is annulus between the base pipe and the filter subassembly. The filter subassembly includes a length of wire wrapped and welded along a plurality of rods so that a slot is defined between adjacent coils of wire. The method further includes expanding the base pipe so that the slot is not substantially altered, thereby substantially reducing or eliminating the annulus.
In another embodiment, a wellscreen for use in a wellbore is manufactured by a method. The method includes disposing a filter subassembly on a base pipe sized so that there is annulus between the base pipe and the filter subassembly. The filter subassembly includes a length of wire wrapped and welded along a plurality of rods so that a slot is defined between adjacent coils of wire. The method further includes expanding the base pipe so that the slot is not substantially altered, thereby substantially reducing or eliminating the annulus.
So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
After manufacture, the filter subassembly 215 is removed from the mandrel 10 and disposed on the perforated base pipe 210. The base pipe 210 is sized so that there is an annulus 220 between the base pipe 210 and the filter subassembly 220. The filter subassembly 215 may be temporarily coupled to the base pipe 210 so that the filter subassembly does not move axially or radially relative to the base pipe prior to expansion of the base pipe. The base pipe 210 may then be placed in a press (not shown) where a first end would be supported for expansion and a second end would receive the expansion tool 100.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
