Patent Application
20160290093
The field of the invention is plugs that disintegrate and more particularly plugs with compression set sealing elements that disintegrate and that further have a shortened mandrel to the top of a slip cone to facilitate the disintegration.
Fracturing is a process to enhance hydrocarbon delivery from a formation to a surface location. The fracturing is frequently a sequential process where a plug is set and a perforating gun that was run in with the plug is released from the plug and shot into the formation to create fractures. These fractures are then extended with high pressure slurry of proppant or typically mostly sand to open the perforation and hold them open by remaining in the perforation after the high pressure flow is cut off. The zone with the recently produced fractures from the perforating gun is sometimes isolated by dropping a ball on the seat of the plug to close off a passage through the plug so that pressure into the formation can be built up to deliver the proppant and further open or propagate the initially made fractures with the perforating gun. In general the process repeats until the entire formation is fractured at which time the completion for production is undertaken. However, before producing the plugs in aid of the fracturing need to be removed. The traditional way this was done was with a milling trip into the borehole to mill up all the plugs. This took a long time and required the milling debris to be removed from the borehole with circulation and/or with various debris retention devices.
Over time, various components of the plugs were made from materials that would disintegrate or otherwise fail over time after their purpose was served. This partial construction with disintegrating components still required a milling trip before production could start but the benefit was that the duration of the milling trip could be shortened as fewer components needed to be milled. For example U.S. 2011/0048743 had anchors that disintegrated with a seal assembly that needed milling out. In U.S. 2014/0318761 a lock for a hydrostatically set packer disintegrated to allow the packer to set. In U.S. Pat. No. 7,487,678 o-ring piston seals needed to disintegrate to enable some functions of a downhole valve. In U.S. 2007/0051521 a frack ball dropped onto a frack plug would disintegrate in an application of a retrievable frack packer. Disintegrating slips are shown in use with a ramp expanded sealing element are shown in U.S. 2013/0299185 and U.S. Pat. No. 8,959,504. In that same family a swage expanded seal that has a disintegrating agent in it is used as shown in FIGS. 9A and 9B of U.S. 2013/0300066. A seal that has a degradable layer is shown in U.S. 2013/0025849. For high pressure application the common approach to sealing has been pushing a seal assembly up a ramp into contact with a surrounding tubular as shown in U.S. Pat. Nos. 8,109,340 and 7,748,467.
Slips made from disintegrating materials are described in U.S. 2014/0262327. Grit applied to a slip with a smooth outer surface is discussed in U.S. 8,579,024. Slips that bite with an exterior surface roughness are described in WO2014170685A2.
What is needed and provided by the present invention is a packer or plug design that has degrading metallic components preferably made with controlled electrolytic materials (CEM) and sold under the brand In-tallic by Baker Hughes Incorporated of Houston Tex. and described in U.S. 2011/0136707 and related applications filed the same day. The sealing element is preferably 85A-95A TDI-Ester Polyurethane that is axially compressed to increase in radial dimension. These materials can be used in a compression set packer assembly such as a Model D packer sold by Baker Hughes with modifications such as CEM anti extrusion rings and locking system for the set. The mandrel is shortened to support the top of the cone for the slips so that there is less bulk to the plug and it can disintegrate faster. The inventors have discovered that sealing in fracking applications can be achieved with a compression set packing element that disintegrates. This goes contrary to the prevailing thinking that has focused on pushing sealing elements up ramps to get a seal or radially expanding rings from within with swage assemblies. Instead, the present invention combines the reliability of known plug designs that push slips out on a cone and then axially compress a sealing element and lock the set in a combination with materials that degrade to reduce or eliminate subsequent drilling out. To aid the disintegration process the mandrel is shortened to not go under the slip cone but instead to support the slip cone by its upper end so that there is less mandrel bulk to disintegrate with no sacrifice in structural integrity. Moreover, incorporating a disintegrating feature into a familiar and reliable basic plug layout gives confidence that the plug will set and properly anchor and seal without undue component complication or the need for high setting forces as would be needed in radial expansion with swages or axially forcing a seal assembly up a ramp to a sealing position. A slip ring is provided with external irregular surface that is coated with grip enhancing grit as part of a slip assembly that can disintegrate. The application technique takes into account the sensitivity of disintegrating slip material to heat when the grit coating is adhered to the slip body. These and other aspects of the present invention will be more readily apparent to those skilled in the art from a review of the description of the preferred embodiment and the associated drawing while recognizing that the full scope of the invention is to be determined by the appended claims.
A compression set sealing element preferably 85A-95A TDI-Ester Polyurethane is compressed axially and retained against extrusion by CEM anti-extrusion rings. The compressed state of the sealing element is locked in by a degradable lock ring assembly. The mandrel is secured to an upper end of a slip cone and a breakable slip ring is secured by a wireline setting tool until the set position is reached. The slip ring breaks into segments that are pulled up the slip cone as the setting tool pushes on a sleeve to axially compress the sealing element and lock in the set. The sealing element is retained against extrusion by CEM anti-extrusion rings. When the setting tool is removed a ball seat is exposed for delivery of a ball to build pressure into the formation for fracturing. The entirety of the plug then disintegrates from well fluid exposure. A slip ring has external wickers and a coating of grit is applied in a manner that preserves the strength of the disintegrating slip body for enhancement of grip.
Referring to the
Preferably the mandrel 50 including the lock ring assembly 34, the cone 12, the slips 14, internal ring 44, seal rings 49 and the anti-extrusion rings 38 and 40 as well as the bottom sub 26 are all made of a disintegrating material that is preferably CEM or another material that responds to existing or added well fluids or exposure over time to thermal or chemical inputs. Similarly the sealing assembly 32 is preferably made of 85A-95A TDI-Ester Polyurethane or a material that disintegrates under similar conditions as the balance of the plug or packer. Notably the mandrel 50 that stays in the hole is made short by ending it at the top of the cone 12 so that there is less of it to degrade so that the overall disintegration time is reduced.
In essence the slips 14 are not supported by the mandrel 50 but instead when set are wedged between the borehole wall that is not shown and the cone 12.
Those skilled in the art will appreciate that what is presented is a compression set plug that can be used in fracturing or other applications such as stimulation or acidizing, for example, by simply dropping a ball that is not shown onto a seat 60 that becomes exposed on removal of the setting tool 16. What was unexpected is the fact that degradable materials can be used in the context of a compression set sealing element with opposed degradable anti-extrusion rings and provide a reliable seal along with the degradability feature. After years of experimentation with designs that form as seal in place that degrades as well as designs that push seals up wedges or radially expand such seals while encountering a variety of issues that made such designs problematic for cost or operational reliability reasons, the present invention is in a sense back to the future in that the basic elements of a compression set packer have been fitted into an assembly that can reliably seal and disintegrate. Modifications have been further made to minimize the bulk of the packer or plug while retaining structural integrity to promote more rapid disintegration. The shorter mandrel also promotes the use of a larger bore through the plug or packer and exposes more surface area to well fluids to accelerate the disintegration process. Those skilled in the art will appreciate that the terms disintegrate, degrade, fail, dissolve or other terms are meant to be used interchangeably to connote an end to functional utility of the structure in the process of coming apart in pieces and ultimately disappearing or being circulated out to the surface.
Slip ring 10 is preferably made from magnesium but other materials such as chrome steel alloys nickel alloys; stainless alloys; carbide alloys; copper alloys; bronze; brass; aluminum and zinc to name some examples.
Ring 10 has a surface roughness 60 that can have a grit coating 62 for enhanced grip. The application process utilizes two wires of desired materials in a spray gun which facilitates a high current between them. The current causes the wires to melt while an air channel pushes the resulting grit onto the surface of the base metal. Parameters are set such that the particles create a rigid surface capable of producing an anti-slip feature, rather than a smooth, wear-resistant surface. This coating may be additive to provide a thicker layer ranging from, but not limited to, 0.010″-0.060″.
The benefit of this process for the magnesium material is that this process does not create excessive surface temperature, which would typically burn the magnesium.
The ring 10 has scores 46 that allow the ring to break into segments as the swage 12 advances to then push the segments out further radially to engage the surrounding tubular.
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:
This application is a continuation in part of application Ser. No. 14/677,415 filed on Apr. 2, 2015.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 14677415 | Apr 2015 | US |
| Child | 14954525 | US |
