Cup tool with three-part packoff for a high pressure mandrel

A cup tool for use with a high-pressure mandrel of a wellhead isolation tool has a three-part packoff assembly that slides over a cup tool tube from an unset position to a set position. The three-part pack off assembly includes an elastomeric cup, a rigid alignment ring located above the elastomeric cup and an elastomeric packoff element located above the rigid alignment ring. The rigid alignment ring helps ensure that the elastomeric cup remains correctly aligned in a casing or tubing that is not straight, is out of round or is washed, and helps ensure that the elastomeric packoff achieves a high-pressure seal in the set position, even under adverse downhole conditions.

FIELD OF THE INVENTION

This invention generally relates to well stimulation tools and, in particular, to a cup tool with a three-part packoff for a high-pressure mandrel of a well stimulation tool for isolating pressure-sensitive wellhead components during high-pressure fracturing and stimulation of oil and gas wells. The cup tool is of particular utility in adverse downhole conditions.

BACKGROUND OF THE INVENTION

Most oil and gas wells require some form of stimulation to enhance hydrocarbon flow to make or keep them economically viable. The servicing of oil and gas wells to stimulate production requires the pumping of fluids under high pressure. The fluids may be low temperature or caustic and are frequently abrasive because they are laden with abrasive propants such as sharp sand, bauxite or ceramic granules.

In order to protect the components which make up the wellhead, such as the valves, tubing hanger, casing hanger, casing head and blowout preventer equipment, wellhead isolation tools are used during well fracturing and well stimulation procedures. The wellhead isolation tools generally work on a principal of inserting a high-pressure mandrel through various pressure-sensitive valves and spools of the wellhead to isolate those wellhead components from elevated fluid pressures and from low temperature or corrosive and/or abrasive fluids used during the well stimulation treatment to stimulate production from the well. One example of those wellhead isolation tools is described in the Assignee's U.S. Pat. No. 6,626,245, entitled BLOWOUT PREVENTER PROTECTOR AND METHOD OF USING SAME. Another example of such a tool is described in the Assignee's U.S. Pat. No. 4,867,243, which issued Sep. 19, 1989 and is entitled WELLHEAD ISOLATION TOOL AND SETTING TOOL AND METHOD OF USING SAME. In those examples, a top end of the mandrel is connected to one or more high pressure valves through which the well stimulation fluids are pumped. A pack-off assembly is provided at a bottom end of the mandrel for achieving a fluid seal against an inside of a production tubing or well casing, so that the wellhead is completely isolated from the well stimulation fluids.

Various pack-off assemblies, commonly referred to as “cup tools”, provided at a bottom end of the mandrel of wellhead isolation tools are described in other prior art patents, such as U.S. Pat. No. 4,023,814, entitled A TREE SAVER PACKER CUP, which issued to Pitts on May 17, 1977; U.S. Pat. No. 4,111,261, entitled A WELLHEAD ISOLATION TOOL, which issued to Oliver on Sep. 5, 1978; U.S. Pat. No. 4,601,494, entitled A NIPPLE INSERT, which issued to McLeod et al. on Jul. 22, 1986; U.S. Pat. No. 5,261,487, entitled PACKOFF NIPPLE, which issued on Nov. 16, 1993 to McLeod, et al; Assignee's U.S. Pat. No. 6,918,441 entitled CUP TOOL FOR HIGH PRESSURE MANDREL which issued Jul. 19, 2005; and, Assignee's published United States Patent application 20040055742 entitled CUP TOOL FOR HIGH PRESSURE MANDREL which was published on Mar. 25, 2004. These pack-off assemblies include a cup tool and/or a packoff element that radially expands under high fluid pressures to seal against the inside wall of a production tubing or casing.

Although at least some of the prior art cup tools provide an adequate seal under most downhole conditions, they do not always provide a reliable seal in tubing or casing that is bent or out-of-round. They may also fail to provide a reliable seal when low temperature, very caustic or solvent-laden fluids are used for a well stimulation treatment. All low temperature, highly caustic and solvent-laden fluids stress the materials used to make elastomeric sealing cups and/or packoff elements used to achieve the high pressure seals. That stress can lead to seal failure, especially if a casing or tubing string into which the cup tool is inserted is not straight or is out-of-round.

There is therefore a need for a reliable cup tool for a high pressure mandrel used for injecting low temperature, caustic and/or solvent-laden well stimulation fluids.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a cup tool for a high pressure mandrel used for injecting well stimulation fluids into a well and, in particular, for injecting such fluids under adverse downhole conditions.

The invention therefore provides a cup tool for providing a high-pressure fluid seal in an annulus between a high-pressure mandrel and a production casing or a production tubing in a wellbore, comprising: a cup tool tube having a threaded upper end for connection to the high-pressure mandrel; a three-part packoff assembly that slides over the cup tool tube from an unset position to a set position, the three-part pack off assembly including an elastomeric cup, a rigid alignment ring located above the elastomeric cup and an elastomeric packoff element located above the rigid alignment ring.

The invention further provides a cup tool for providing a high-pressure fluid seal in an annulus between a high-pressure mandrel and a casing or a production tubing in a wellbore, comprising: a cup tool tube having a threaded upper end for connection to the high-pressure mandrel; a three-part packoff assembly that slides over the cup tool tube from an unset position to a set position, the three-part pack off assembly including an elastomeric cup, a rigid alignment ring located above the elastomeric cup and an elastomeric packoff element located above the rigid alignment ring; and a gauge ring located above the elastomeric packoff element, the gauge ring comprising one of: at least two sloped shoulders; at least two right-angled shoulders; and, a single sloped shoulder.

The invention further provides a cup tool for providing a high-pressure fluid seal in an annulus between a high pressure mandrel and a casing or a production tubing in a wellbore, comprising: a first cup tool tube having a threaded upper end for connection to the high-pressure mandrel; a first three-part packoff assembly that slides over the first cup tool tube from an unset position to a set position, the three-part packoff assembly including an elastomeric cup, a rigid alignment ring located above the elastomeric cup and an elastomeric packoff element located above the rigid alignment ring; a second cup tool tube having a threaded upper end for connection to the first cup tool tube; and a second three-part packoff assembly that slides over the second cup tool tube from an unset position to a set position, the second three-part packoff assembly including an elastomeric cup, a rigid alignment ring located above the elastomeric cup and an elastomeric packoff element located above the rigid alignment ring.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention provides a cup tool for achieving a reliable high-pressure fluid seal in an annulus between a high pressure mandrel and a casing or production tubing in a wellbore under adverse downhole conditions. For example, when a casing or tubing in which the cup tool must pack off is not straight, is out-of-round or is “washed”, or when low temperature, caustic, or solvent-laden fluids are pumped into the wellbore. The cup tool includes a three-part packoff assembly that slides over a cup tool tube from an unset to a set position. The three-part packoff assembly includes an elastomeric cup, a rigid alignment ring located above the elastomeric cup and an elastomeric packoff element located above the rigid alignment ring. The rigid alignment ring helps ensure that the elastomeric packoff element achieves a reliable high pressure seal under adverse downhole conditions.

As shown inFIG. 1, a cup tool in accordance with one embodiment of the invention, generally indicated by reference numeral10, is attached to a bottom end of a high-pressure mandrel12and is inserted into a production tubing or production casing, hereinafter referred to simply as a production tubing14. The cup tool10includes a cup tool tube16which has an upper end18provided with pin threads20for connecting the cup tool tube16to the high-pressure mandrel12. The cup tool tube16terminates at its bottom end22in a bullnose26, which guides the cup tool10through a wellhead (not shown) and the production tubing14, and helps protect an elastomeric sealing element, such as elastomeric cup40operatively mounted to the cup tube16. In this embodiment, the bullnose26is a two-part element that is threadedly connected to the cup tool tube by box threads25that engage pin threads24provided on an outer surface of the bottom end22of the cup tool tube.

The bullnose26includes a tool guide28that guides the cup tool10down through the wellhead components and the production tubing14, as explained above. Only one diameter of tool guide28is required for any given diameter of cup tool tube16. Located above the tool guide28, and in this embodiment retained on the cup tool tube16by the tool guide28, is a cup guard30. The cup guard30is retained by a top end32of the tool guide28against an annular shoulder34formed on the cup tool tube16. The cup guard30has a diameter that is selected to be compatible with an internal diameter of the production tubing14, into which the cup tool10is being run. As understood by those skilled in the art, the internal diameter of the production tubing14is determined by an outer diameter and weight per linear unit of the production tubing14. The cup guard30includes an annular groove36in its top end that receives and protects a bottom end of the elastomeric cup40when the cup tool10is extracted from the production tubing14. The cup guard30also helps ensure that the cup tool tube16remains parallel with a production tubing14, which increases the probability of a successful pack-off.

The cup tool10has a three-part pack-off assembly38that includes the elastomeric cup40, a rigid alignment ring42and an elastomeric packoff element44. The elastomeric cup40, the rigid alignment ring42and the elastomeric packoff element44are respectively annular elements that surround the cup tool tube16. In one embodiment, the elastomeric cup40and the elastomeric packoff element44are made of a polymer, e.g. a polyurethane having a consistent durometer of 80-90. In one embodiment, the rigid alignment ring42is made of steel or plated steel for sweet well service, and stainless steel for sour well service. The rigid alignment ring42is slidably received on the cup tool tube16and includes an annular groove46in its inner periphery. An O-ring48is received in the groove46and provides a fluid seal between the rigid alignment ring42and the cup tool tube16.

The elastomeric cup40further includes a depending skirt50, which extends downwardly from a cup body52and is formed integrally therewith. The depending skirt50has an outer diameter that is about the same as, or slightly larger than, the inner diameter of the production tubing14. The depending skirt50is open at its bottom end, and forms a sealed cavity around the cup tool tube16that is closed at a top end by an inwardly biased lip54, so that when the elastomeric cup40is exposed to fluid pressure the elastomeric cup40is forced to slide upwardly on the cup tool tube16.

The rigid alignment ring42separates the elastomeric cup40from the elastomeric packoff element44. All three parts of the pack-off assembly38slide freely over the cup tool tube16between the cup guard30and a gauge ring58, which respectively provide a lower and an upper travel limit for the three-part pack-off assembly38. In this embodiment, the rigid alignment ring42includes an annular V-shaped groove56in a bottom surface thereof. The V-shaped groove56provides an annular space into which a top edge of the elastomeric cup40extrudes when the elastomeric cup40is exposed to elevated fluid pressures. The groove56inhibits a top end of the elastomeric cup40from extruding into a space between the rigid alignment ring42and the production tubing14.

The packoff element44is located above the rigid alignment ring42and extrudes up over the gauge ring58when the elastomeric cup40is forced upwardly by fluid pressure, as will be explained below in more detail with reference toFIG. 3. In this embodiment, the gauge ring58includes a first upwardly-angled shoulder60and a second upwardly-angled shoulder62over which a top edge64of the packoff element44is forced when the packoff assembly38is exposed to high fluid pressures below the cup tool10within the production tubing14. In other embodiments of the cup tool10, the gauge ring58has square shoulders, as shown inFIG. 2, or a single-bevel shoulder as shown inFIG. 3.

The rigid alignment ring42helps ensure a reliable seal when the packoff assembly38is set in a production tubing14that is not straight, is out-of-round or is washed, i.e. has been eroded by abrasive propants pumped through it. Because the rigid alignment ring is located between the elastomeric cup40and the packoff element44, it inhibits distortion of those elastomeric elements when they are exposed to unbalanced stresses as they encounter in a tubing14that is not straight, is out-of-round or is washed. A more reliable fluid seal is thereby by achieved.

As well, the rigid alignment ring42is less affected by low temperatures than the elastomeric cup40or the elastomeric packoff element44. Consequently, when very low temperature fluids such as carbon dioxide, liquid nitrogen, liquid natural gas or the like is used as a well stimulation fluid the rigid alignment ring42provides a stable buffer between the elastomeric cup40and the elastomeric packoff element44that helps to reduce stress and inhibit low temperature induced cracking, which could cause the high pressure fluid seal to be lost.

Likewise, if very caustic or solvent-laden stimulation fluids are used for a well treatment, the rigid alignment ring42, which is unaffected or marginally affected by those fluids, provides a stable buffer below the elastomeric packoff element44that protects the elastomeric packoff element44even if an integrity of the elastomeric cup40is compromised by those stimulation fluids.

FIG. 2is a schematic diagram of a second embodiment of the cup tool10in accordance with the invention. The cup tool10shown inFIG. 2is identical to the cup tool10shown inFIG. 1with the exception that the gauge ring70has square rather than sloped shoulders. The gauge ring70shown inFIG. 2has a first square shoulder72and a second square shoulder74. As will be understood by those skilled in the art, the gauge ring70may have more than two square shoulders. The stepped shoulder gauge ring70guides the packoff element44to a set condition when the elastomeric cup40is subjected to high fluid pressures, as shown inFIG. 5.

Otherwise, the cup tool10shown inFIG. 2functions in the same way as described above a with reference toFIG. 1. The balance of the cup tool components shown inFIG. 2will therefore not be further described.

FIG. 3is a schematic diagram of yet another embodiment of the cup tool10in accordance with the invention. The embodiment of the cup tool10shown inFIG. 3is identical to the embodiment shown inFIGS. 1 and 2with the exception that the gauge ring80has a single sloped face82. The single sloped face82is inclined at an angle of about 30°-70° and guides the packoff element44to a set condition when the elastomeric cup14is subjected to high fluid pressures, as is shown inFIG. 6.

Otherwise, the cup tool10shown inFIG. 3functions in the same way as described above a with reference toFIG. 1. The balance of the cup tool components shown inFIG. 3will therefore not be further described.

FIG. 4is a schematic diagram of the cup tool shown inFIG. 1in a set condition. As is well understood in the art, the function of the cup tool10is to move to the set condition after the cup tool10has been inserted into a production tubing14and fluid under high pressure is pumped into the production tubing14, such as is performed during a well stimulation treatment. When subjected to high fluid pressures, the elastomeric cup40traps fluid pressure beneath the inwardly biased lip54and the elastomeric cup40is forced upwardly over the cup tool tube16. Upward movement of the elastomeric cup40forces the rigid alignment ring42upward over the cup tool tube16, which in turn compresses the packing element44and forces the packing element44upwards over the inclined shoulders60and62of the gauge ring58. When the packing element44is forced over the first inclined shoulder60, a fluid seal is obtained between the cup tool10and the production tubing14. If the fluid pressure is high enough, the packing element44continues to be extruded upwardly over the second shoulder62and into a space between the gauge ring58and the production tubing14.

FIG. 5is a schematic diagram of the cup tool10shown inFIG. 2in the set condition. All of the elements of the cup tool10shown inFIG. 5have been described above with reference toFIGS. 1 and 2, and they will not be described again. As will be understood by those skilled in the art and described in Applicant's above-referenced U.S. Pat. No. 6,918,441, the substantially right-angled stepped shoulders a72,74over which the elastomeric packoff element44is forced inhibits extrusion past the stepped shoulder72during insertion of the mandrel into the production tubing14, thereby reducing a risk of damaging the packoff element44before the mandrel12is fully inserted through the wellhead.

FIG. 6is a schematic diagram of the cup tool10shown inFIG. 3in a set condition. All the elements of the cup tool10shown inFIG. 6have been described above with reference toFIGS. 1 and 3. As will be understood by those skilled in the art, the gauge ring80with the single sloped face82guides the packoff element44to the set condition as shown when the cup tool10is subjected to elevated fluid pressures within the production tubing14.

FIG. 7is a cross-sectional schematic diagram of an alternate embodiment of a bullnose26ain accordance with the invention. In this embodiment, a tool guide28ais identical to the tool guide the28described above with reference toFIGS. 1-3, except that a cup guard30ais configured differently and is threadedly secured to the tool guide28aby pin threads27on an outer circumference of the tool guide28a. The pin threads27mate with complementary box threads29on an inner periphery of the cup guard30a. An annular groove36aformed between a top surface of the cup guard30aand the cup tool tube16receives a bottom end of the elastomeric cup40shown inFIGS. 1-3. The bullnose26ais particularly useful when tolerances do not permit the formation of the shoulder34on the cup tool tube16shown inFIGS. 1-3.

FIG. 8is a cross-sectional schematic diagram of a further embodiment of a bullnose26bhaving a configuration useful for applications where high fluid flow rates are required. The bullnose26bis similar to the bullnose26adescribed above with reference toFIG. 7, with the exception that the tool guide28bis longer than the tool guide28ashown inFIG. 7, and an interior wall31of the tool guide at28bis outwardly flared towards the bottom end to permit high pressure fluids to expand before they enter the production tubing14.

The bullnoses26a,26bshown inFIGS. 7 and 8can be used on any of the cup tools described above with reference toFIGS. 1-3, as well as with a double cup tool described below with reference toFIG. 9.

FIG. 9is a cross-sectional view of yet another embodiment of a cup tool in accordance with the invention. In this embodiment, a double cup tool80is provided. The double cup tool80has the advantage of providing a redundant backup packoff and places an elastomeric seal in two spaced-apart locations in the production tubing14. The cup tool80is made up from any combination of the embodiments shown inFIGS. 1-3. In this exemplary embodiment, two of the cup tools shown inFIG. 1are connected together using a connecting collar82after the tool guide28is removed from the first cup tool10a. The second cup tool10bis secured to a bottom end of the connecting collar82by pin threads20(FIG. 1) that engage complementary box threads84in the connecting collar82. In all other respects, the double cup tool80is the same as the cup tool described above with reference toFIG. 1and the other components will not be redundantly described.

As will be understood by those skilled in the art, the embodiments of the invention described above are intended to be exemplary only. The scope of the invention is therefore intended to be limited solely by the scope of the appended claims.