Patent Application
20190024486
The field of the invention is screen construction for borehole use and more particularly end rings with a skive cut to allow fitment over the screen assembly built on base pipes with variable external dimension that further feature an end radial component directed toward the base pipe for welding the end ring to the base pipe.
Screens are used in borehole operations to control produced solids from the formation and to enable inflow through a surrounding pack of filtration material referred to as gravel when producing the formation. One common design used for such purposes is known as a wire wrap screen. In essence, a wire that has round or triangular cross-section with the flat side oriented outwardly is wrapped over a base pipe that features axially extending support members spaced about the periphery. A protective jacket which is commonly a rolled sheet with punched openings is put over the wire wrap to protect the assembly when running in the hole and during operations to protect the wire wrap from direct impingement by creating a tortuous path for the flow to reach the wire wrap. The base pipe is perforated under the wire wrap to allow the produced fluid to enter a tubing string, a part of which is formed by the base pipe.
The ends of the screen assembly need to be closed and this is done with end ring assemblies that are fitted around the base pipe and overlap the screen jacket and are welded or otherwise secured to a base pipe. Some examples of such designs are shown in U.S. Pat. No. 8,267,169; U.S. Pat. No. 8,127,447; U.S. Pat. No. 5,611,399; U.S. Pat. No. 6,305,468; U.S. Pat. No. 6,607,032; U.S. Pat. No. 6,478,092. One issue with assembling a variety of screens to meet different conditions is variation of screen jacket diameter due to tolerances of base pipe OD, wire dimensions and rib & wrap penetration. Typically the end ring assemblies had to be stocked in a variety of internal dimensions for a given size to fit over the base pipe outside diameter with clearance small enough to allow the end ring to slide over an end of the base pipe while leaving a gap that could be seal welded. Additionally the end ring assembly involved a base ring secured to the base pipe and an overlapping ring that went over an end of the screen jacket that was separately welded to the base ring secured around the outside of the base pipe. These overlapping rings could be purpose machined for a specific design and shrink fit into position over the screen jacket. Welding the overlapping ring to the screen jacket also created risks of screen gage openings that required manual correction which was not favored by the end user.
A compromise to address the dimensional variation of the screen assembly due to base pipe and other components' dimensional variations involved using two adjacent rings. The end ring was still custom machined for the application and the overlapping ring was skive cut to fit over the screen jacket. After fitting the overlapping ring and welding the skive cut in the overlapping ring, the overlapping ring had to be welded to the custom machined end ring that was in turn welded to the base pipe. Skive cuts in ring shaped objects are described in US 2005/0225037 and U.S. Pat. No. 4,840,379.
The present invention seeks to improve the manufacturing process particularly for screens for borehole use and in the process reduce manufacturing cost by using an end ring assembly that combines a radial segment that fits over the base pipe with an overlapping segment that spans over the screen outer jacket while incorporating a skive cut in the entire assembly. This construction maintains sand tight gap and allows a close fit of the overlapping segment while providing an undercut to allow the wire wrap screen end to contact an undercut defined by the end ring and integrated overlapping segment that are both skive cut. With the skive cut through the assembly, no part of the assembly needs to be slipped over an end of the base pipe and the internal dimensions of the overlapping assembly and the end ring can be modified to get a snug fit and the skive cut welded to hold the desired dimension. The end ring is then secured to the base pipe such as by welding. These and other aspects of the present invention will become more readily apparent to those skilled in the art from a review of the description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be determined from the appended claims.
A borehole screen such as one with a wire wrap/slip on screen on a base pipe with variable external dimensions features an end ring assembly that is one piece with a skive cut to allow fitment over a screen jacket that covers the wire wrap. The assembly has a cylindrically shaped component to go over the screen jacket and a radial component at one end oriented toward the base pipe. The assembly can be mounted over the base pipe without sliding the assembly over the end of a base pipe due to the skive cut. Relative sliding along the skive cut gets the desired dimension over the screen jacket to control sand inflow followed by the skive cut being sealed with a weld. The radial component is attached to the base pipe such that two welds complete the end assembly of the screen.
While the radial height of radial component 24 is fixed, its internal diameter is variable. Since the dimensions of the axial rods 16 and the wire wrap 18 along with any jacket that covers the wire wrap are typically well known and not subject to dimensional variability the undercut 38 is made to allow the cylindrical component 22 to fit snugly against the wire wrap 18 and a surrounding screen jacket as the inside diameter is varied with relative sliding movement of ends 32 and 34 until the inside surface 40 lands on the base pipe 12. At this point, the skive cut 26 which now has its gap nearly or completely closed can be welded between ends 28 and 30. When the skive cut 26 is welded after the relative sliding movement of ends 32 and 34, the weld 36 can be put down and the screen assembly 10 is completed at one end. The same procedure can be applied at an opposite end of the assembly 10.
The advantages can now readily be appreciated over a two piece system that required more welding and still needed a large end ring inventory to advance the right size over an end of a base pipe as a distinct cylindrical component is fitted over the screen and outer jacket assembly. Instead a single integrated design allows variability to place a radial component on or near an outer surface of the base pipe for a circumferential weld while providing an undercut for the known dimension of the screen assembly including the jacket so that the ends of the screen assembly are effectively sealed as a skive cut allows the radial component to approach the base pipe and the cylindrical overlapping component to fit snugly over the screen assembly as the skive cut is welded. Now two welds instead of three complete the end assembly for the screen and unique end ring inventory to account for outer wall dimension variability of the base pipe for a given size no longer is an issue. With the ability to make relative axial movements along the skive cut the desired dimension is obtained around the base pipe and an undercut offering a snug fit to the screen assembly is obtained at the same time. A skive weld and a circumferential weld to the base pipe of the radial component completes the operation.
The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below:
