Wellhead and control stack pressure test plug tool

A test plug tool for use in testing a pressure integrity of a pressure control stack mounted to a wellhead, including a joint between a casing and a casing support in the wellhead. The test plug tool includes a test plug of an appropriate diameter used to pressure test the pressure control stack as well as a joint between any one of a surface casing and the wellhead, an intermediate casing and an intermediate casing mandrel, and a production casing and a production casing mandrel. The pressure integrity of the wellhead is ensured at each stage of well drilling and well completion, and safety is improved. Optionally, a backpressure valve permits pressurized fluid that leaks below the test plug tool to flow upwardly through a central bore in a landing tool that is secured to the test plug tool to permit detection of the leak.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is the first application filed for the invention.

MICROFICHE APPENDIX

Not Applicable.

TECHNICAL FIELD

The invention relates generally to pressure-testing tools for pressure control stacks on wellheads and, in particular, to test plug tools for pressure-testing of those control stacks.

BACKGROUND OF THE INVENTION

Prior art pressure-test plug tools for testing the pressure integrity of pressure control stacks on wellheads are well known in the art. The pressure-test plug tools are used to test the pressure integrity of control stack components such as blowout preventers, valves, tees, etc., and joints between the components prior to drilling or stimulating a well.

While most prior art test plug tools are known to function well, they all suffer from a drawback in that they are only designed to test the pressure integrity of the stack above a casing joint, i.e., above a connection between a casing and a casing support. With prior-art devices, the pressure integrity of the casing joint cannot be verified. During well stimulation operations, where fluid pressures may spike to 20,000 PSI, this joint may be susceptible to leakage and/or failure, resulting in expensive repairs, cleanup, downtime and potential environmental damage.

Many configurations for pressure-test plug tools have been invented; For example, in U.S. Pat. No. 5,775,422 (Wong et al.) entitled TREE TEST PLUG, the test plug is lodged within the tubing hanger, i.e., above the connection between the surface casing and the wellhead. In this configuration, the pressure integrity of the stack beneath the tubing hanger cannot be verified.

In U.S. Pat. No. 4,121,660 (Koleilat) entitled WELL PRESSURE TEST PLUG, the test plug is seated in the bore of the wellhead. With the test plug in this configuration, the pressure integrity of the wellhead-to-casing joint cannot be tested.

Similarly, in U.S. Pat. No. 4,018,276 (Bode) entitled BLOWOUT PREVENTER TESTING APPARATUS, the test plug is positioned in the bore of the wellhead. The position of the test plug permits pressure-testing of the blowout preventer but does not permit pressure-testing of the wellhead or the casing connection.

Likewise, in U.S. Pat. No. 3,897,824 (Fisher) entitled BLOWOUT PREVENTER TESTING APPARATUS, the test plug is positioned in the bore of the wellhead beneath the blowout preventer. With the test plug in this location, it is not possible to verify the pressure integrity of the lower part of the wellhead, such as the joint between the wellhead and the well casing.

In U.S. Pat. No. 3,177,703 (Waters et al.) entitled METHOD AND APPARATUS FOR RUNNING AND TESTING AN ASSEMBLY FOR SEALING BETWEEN CONDUITS, the test plug is positioned in the bore of the wellhead above the joint between the wellhead and the casing. With the test plug in this location, it is not possible to pressure-test the wellhead-casing joint.

In U.S. Pat. No. 2,951,363 (Diodene) entitled TOOL FOR TESTING WELL HEAD EQUIPMENT, the test plug is also positioned above the wellhead and casing joint. Pressure-testing of the casing joint is not possible with the test plug located in that position.

There therefore exists a need for a test plug tool for pressure-testing wellhead control stacks that permits testing of the pressure integrity of a casing joint, i.e., the joint between a surface casing and a wellhead, the joint between an intermediate casing and an intermediate casing mandrel, or the joint between a production casing and a production casing mandrel.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a test plug tool for use in testing the pressure integrity of a pressure control stack mounted to a wellhead, together defining a wellhead stack assembly, including testing the pressure integrity of a joint between a casing and a casing support that secures the casing to the wellhead stack assembly, the test plug tool providing a fluid-tight seal with the casing beneath the joint between the casing and the casing support.

By constructing test plugs of appropriate diameters, the test plug tool may be used for testing the pressure integrity of a variety of casing joints, including the joint between a surface casing and a wellhead, the joint between an intermediate casing and an intermediate casing mandrel, and the joint between a production casing and a production casing mandrel.

Preferably, the test plug tool includes a test plug hanger and a test plug, the test plug being positioned below the casing joint.

Preferably, the test plug of the test plug tool comprises a cup tool with flange supporting a gauge ring, a sealing element and a cup for providing a fluid-tight seal between the test plug and the casing.

The invention further provides a method for testing the pressure integrity of seals and joints in a pressure control stack mounted on a wellhead, together defining a wellhead stack assembly, including testing the pressure integrity of a joint between a casing and a casing support, the method comprising the steps of inserting a test plug tool into the wellhead stack assembly with a landing tool; landing the test plug in the casing beneath the joint between the casing and the casing support; locking the test plug tool in position; detaching the landing tool from the test plug tool; retracting the landing tool from the wellhead stack assembly; pressurizing the wellhead stack assembly to an estimated operating pressure; and inspecting the seals and joints of the wellhead stack assembly, including the joint between the casing and the casing support, to ascertain that the seals and joints have withstood the estimated operating pressure.

The method can be applied to the testing of various casing joints, including the joint between a surface casing and a wellhead, the joint between an intermediate casing and an intermediate casing mandrel, and the joint between a production casing and a production casing mandrel.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In general, and as will be explained below, a test plug tool can be used for testing the pressure integrity of a wellhead having a pressure control stack mounted thereto. The wellhead and the pressure control stack will be referred to hereinafter as a “wellhead stack assembly”. The test plug of the test plug tool is designed to be landed below a casing joint formed between a casing and a casing support so that this casing joint and all joints above it in the pressure control stack can be pressure-tested. The expression “casing joint” as used in this specification means a joint between a casing and a casing support. A “casing”, as persons skilled in the art will understand, includes a surface casing, an intermediate casing and a production casing. A “casing support” means a component of the wellhead stack assembly that holds and/or secures the casing to the wellhead stack assembly, and suspends the casing in a well bore. Persons skilled in the art will understand that where the casing is surface casing, the casing support is typically a wellhead. Where the casing is an intermediate casing, the casing support is generally an intermediate casing mandrel. Where the casing is production casing, the casing support is generally a production casing mandrel.

By constructing test plugs of suitable diameter, the test plug tool can be used to pressure-test the surface casing, the intermediate casing or the production casing. The test plug tool includes a test plug hanger with fluid passages to permit test fluids to pass therethrough, a test plug leg that extends downwardly from the test plug hanger to support a test plug. In one embodiment, the test plug is a cup tool that includes a cup sleeve which terminates in a bullnose, the cup sleeve supports, above an annular abutment, a gauge ring, an elastomeric sealing element and an elastomeric cup. The gauge ring, sealing element and cup are dimensioned to provide a high-pressure fluid seal against an inside of the casing. During operation, the valves of the pressure control stack are closed, the side ports are plugged and the stack is pressurized to at least an estimated operating pressure to verify that all seals and joints, including the casing joint, are able to withstand the estimated operating pressure.

FIG. 1illustrates what is known in the art as a pressure control stack10[hereinafter the “stack”] which is configured for pressure integrity testing. The expression “pressure integrity testing” as used in this specification means a testing procedure during which the stack is pressurized to at least an estimated operating pressure and the joints and seals are inspected to verify that they have withstood the test pressure.

At the base of the stack10, and dug into the ground12, is a conductor14. The conductor14is installed, or “stuffed”, into a “rat-hole” that is typically bored 60 to 80 feet deep, depending on subsurface conditions. The conductor14supports a conductor ring16on the upper lip of the conductor. The conductor ring16is beveled to form a bowl-shaped receptacle18for receiving a bottom beveled portion of a wellhead22. A surface casing20is connected to the wellhead22below the side ports24of the wellhead. The side ports24are sealed during pressure-testing.

The surface casing20is joined to the wellhead22at a wellhead-to-casing joint26. The wellhead-to-casing joint26is formed between an upper portion of the surface casing20and a lower portion of the wellhead22, as illustrated inFIG. 1.

As shown inFIG. 1, mounted atop the wellhead22is a drilling flange30which is secured to an upper portion of the wellhead22by a wing nut32. The drilling flange30has transverse bores in a flanged portion34that house locking pins36. Each locking pin has a head38. Mounted atop the drilling flange30is a blowout preventer40, well known in the art.

Before the stack is pressurized, a test plug tool50is inserted into the bore of the stack10. The test plug tool50includes a test plug hanger51and a test plug53which are interconnected by a test plug leg58.

The test plug hanger51of the test plug tool50includes a landing joint connector, which is a box threaded socket52for receiving one of a pin threaded landing joint150as illustrated inFIG. 1a, a drill pipe, or a production tubing. In operation, the drill pipe, the production tubing or the landing tool150is threaded to the socket52and then the test plug tool50is lowered into the stack10and the test plug is landed inside the casing, as shown inFIG. 1a.

The test plug hanger51includes a hanger flange54that extends laterally from the socket52to an outer radius of the test plug hanger51. The hanger flange54has a beveled top edge that is locked in place by the locking pins36, so that the test plug hanger51is restrained from upward movement. In addition, the bottom surface of the hanger flange54rests on an annular abutment31in the drilling flange30, which prevents the test plug hanger51from moving downwardly through the wellhead control stack. Since the hanger flange54is locked between the annular abutment31and the heads38of the locking pins36, the test plug tool50cannot be displaced during pressurization of the stack10.

The hanger flange54also includes at least one fluid passage56that are extends through the test plug hanger. During pressurization of the stack, pressurized fluid flows through the fluid passage56. The fluid passage56thus permits pressure to equalize on both sides of the hanger flange54.

The test plug tool50has a test plug leg58integrally formed with the hanger flange54and extending downwardly from the underside of the hanger flange54to a test plug53. A bottom end59of the test plug leg58is threaded to an upper end61of a cup tool60. The test plug leg58is preferably hollow to reduce a weight of the test plug tool50. As illustrated inFIG. 1, the cup tool60includes a bullnose60aat the bottom and a cup sleeve60bwith an outer diameter less than that of the bullnose60a. Because the bullnose60ahas a greater outer diameter than that of the cup sleeve60b, the top surface of the bullnose60aforms an annular shoulder60c. The annular shoulder60cextends in the radial direction but does not contact the surface casing20. A small annular gap60dremains between the annular shoulder60cand the surface casing20.

Supported directly above the annular shoulder60cis a metal gauge ring62. The gauge ring62is dimensioned to support an elastomeric sealing element64and to inhibit the elastomeric sealing element64from extruding between the casing and the bullnose60cwhen the test plug tool50is exposed to elevated fluid pressures. The elastomeric sealing element64forms a fluid seal with the surface casing20when compressed by an elastomeric cup66that is supported directly above the elastomeric sealing element64. The elastomeric cup66is preferably made of nitrile rubber, although persons skilled in the art will appreciate that other elastomers or polymers, such as polyethylene or polystyrene, may also be used. The elastomeric cup66is also dimensioned to form a fluid seal against the surface casing20. The elastomeric cup66is bonded to a steel ring that slides over the cup sleeve60b. The steel ring includes a pair of radial grooves for seating two O-rings68. The O-rings68provide a fluid seal between the elastomeric cup66and the cup sleeve60b.

During pressure-testing, pressurized fluid flows through the fluid passages56in the test plug hanger51to pressurize an annular space55. The annular space55is a generally annular volume defined between the test plug leg58and the stack10. The annular space is pressurized to at least an estimated operating pressure, which may be as high as 20,000 PSI (or about 140 MPa). Since the cup66is below the wellhead-to-casing joint26, this joint is subjected to the test pressure. Thus, with the test plug tool50, it is possible to test the pressure integrity of the wellhead-to-casing joint26.

As illustrated inFIG. 2, the test plug50can be designed and constructed with a smaller outer diameter for use in testing the pressure integrity of a stack10configured with an intermediate casing70in addition to the surface casing20. As is known by persons skilled in the art, industry regulations in certain jurisdictions require that intermediate casing be run into the well as a safety measure when exploiting a deep, high-pressure well.

As shown inFIG. 2, the wellhead22is seated on the bowl-shaped receptacle18of the conductor ring16which, in turn, is mounted on the conductor14. The surface casing20is joined to the wellhead22below the side ports24at a wellhead-to-surface casing joint26. (These components are configured in the same way as those shown inFIG. 1.)

The wellhead22supports an intermediate casing mandrel72which is threadedly fastened to the intermediate casing70to form a joint with a frusta-conical interface which will be referred to below as an intermediate casing-to-mandrel joint75.

The drilling flange30is secured to an upper end88of an intermediate head spool80by the wing nut32. The drilling flange30includes lockdown pins36in the upper flanged portion34. A blowout preventer40is mounted to the upper flanged portion34, as described above.

The test plug tool50is inserted with a landing tool150(shown inFIG. 1a) which connects to the box threaded socket52. The test plug tool50is inserted into the stack10and positioned at the location shown inFIG. 2, such that the test plug53is beneath the intermediate casing-to-mandrel joint75. The test plug53shown inFIG. 2has a smaller outer diameter than the test plug shown inFIG. 1. To ensure a fluid-tight seal, the cup tool60, the gauge ring62, the sealing element64and the cup66are constructed with diameters appropriate for the size and weight of the intermediate casing, as is understood by persons skilled in the art.

The test plug hanger51is secured in place by the locking pins36in the upper flanged portion34of the drilling flange30, as already explained above. The heads38of the locking pins36engage the annular shoulder54of the test plug hanger51to prevent the test plug from moving upward during pressurization. As also explained above, the fluid passages56serve to equilibrate pressure on each side of the test plug hanger51during pressurization of the annular space55.

As illustrated inFIG. 2, because the test plug tool50may be inserted beneath the intermediate casing-to-mandrel joint75, this joint (and all the joints and seals above it in the stack) may be pressure-tested to ensure that they are able to withstand at least the estimated operating pressure.

FIG. 3illustrates another embodiment of the test plug tool50′ which is designed to be used in testing the pressure integrity of a production casing90which is run inside an intermediate casing70for deep well production.

As illustrated, the test plug53′ of the test plug tool50′ resembles the test plug53of the test plug tool50except that the test plug53′ has a solid cup sleeve60b′, whereas the test plug53has tubular cup sleeve60b. The reason for this design is explained below. Other than the solid cup sleeve60b′, the test plug53′ resembles the test plug53in that the cup tool60′ which supports a metal gauge ring62′, a sealing element64′ and an elastomeric cup66′, each of which have a smaller outer diameter than the outer diameter of the test plug ofFIG. 2, so as to fit the smaller bore of the production casing90. The test plug50′ also has O-rings68′ to provide a fluid seal between a steel ring that supports the elastomeric cup60bof the cup tool60.

The production casing90is fastened to a production casing mandrel92to form a production casing-to-mandrel joint95. A flared bottom portion of the production casing mandrel92is seated in a bowl-shaped portion94of the intermediate spool80. The intermediate spool80is secured to the wellhead22by a wing nut82as described above with reference toFIG. 2.

A tubing head spool100is mounted to a top of the intermediate spool80. The tubing head spool100includes flanged side ports114and further includes a top flange116which has transverse bores for housing locking pins118for securing a tubing mandrel (commonly referred to as a tubing hanger or a “dognut”). A flanged Bowen union120is mounted to a top of the top flange116. The flanged Bowen union120has a box threaded socket124for receiving a pin threaded upper end50aof the test plug tool50. The flanged Bowen union120also has a pair of annular grooves125for seating O-rings for providing a fluid-tight seal between the upper end of the test plug and the flanged Bowen union120. The flanged Bowen union120has at its uppermost end a threaded union126, a type of connection that is well know in the art for connecting high-pressure lines, or the like. The flanged Bowen union120includes an axial passage127.

The test plug50′ has a differently shaped test plug hanger51′ than the test plug hanger51of the embodiment shown inFIGS. 1 and 2. The test plug hanger51′ shown inFIG. 3includes a hanger flange54′ with beveled shoulders dimensioned to fit snugly in the bore of the tubing head spool100. The lower beveled shoulder is machined to rest against a bowl-shaped abutment in the tubing head spool100, which prevents the test plug50′ from descending further into the wellhead stack assembly. Three peripheral grooves57are machined into the hanger flange54′. Three O-rings are seated in the grooves57to provide a fluid-tight seal between the test plug hanger51′ and the tubing head spool100, because the tubing head spool100above the tubing hanger bowl is normally not subjected to elevated fluid pressure and the tubing head spool100is not necessarily constructed to withstand high fluid pressures.

A fluid passage58ais machined through a sidewall of the test plug leg58′ to permit pressurized fluid to flow through the central bore127of the flanged Bowen union120, through the fluid passage in the sidewall of the test plug leg58′ and into the annular space55, i.e., the annulus between the test plug leg58′ and the wellhead stack assembly10. Since pressurized fluid flows below the production casing mandrel joint95, this joint can be pressure-tested.

In summary, the test plug tools50,50′ shown inFIGS. 1,2and3may be dimensioned for use in testing the pressure integrity of pressure control stacks attached to wellheads. As described and illustrated above, the test plug tools may be used to test the pressure integrity of the wellhead-to-surface casing joint (FIG. 1), the intermediate casing mandrel joint (FIG. 2), and the production casing mandrel joint (FIG. 3). In each of these three applications, the test plug tool is also useful for testing the various joints and seals above the wellhead surface casing joint, the intermediate casing mandrel joint, or the production casing mandrel joint, as the case may be, including the rams of blowout preventer(s) located above the wellhead stacks, and any control valves mounted to the wellhead stack10.

As shown inFIG. 4, the test plug tool50may further include a backpressure valve200which communicates with an axial passageway220in the test plug hanger51. The backpressure valve is a one-way valve used to ensure that a fluid-tight seal is provided by the test plug tool. If the test plug tool fails to provide a fluid-tight seal, pressurized fluid can leak past the test plug53, causing backpressure to build up downhole of the test plug tool. Such downhole backpressure may damage the casing or cause other problems.

As shown inFIG. 4, the backpressure valve200is a generally annular body202with pin threads for engaging a box thread in a test plug hanger51. The backpressure valve200also has a spring-loaded ball valve, which includes a ball216that is forced downwardly against an annular shoulder by a spring218. The spring is retained by an annular retainer cap224that threads onto the annular body202. The structure of the backpressure valve will be described in greater detail below with regard toFIG. 6. In operation, if the test plug tool leaks and backpressure builds up beneath the test plug53, pressurized fluid will travel up a central bore50bof the test plug tool50and up the axial passageway220. If the backpressure is more than a few pounds per square inch (PSI), the spring-loaded ball valve will be displaced upwardly against the spring, thereby permitting pressurized fluid to flow up a central bore of the landing tool150, thereby alerting an operator of the leak.

FIG. 5illustrates another embodiment in which the test plug tool50employs another embodiment of a backpressure valve200, the structure of which is illustrated in greater detail inFIG. 6. The backpressure valve200shown inFIG. 6also has a spring-loaded ball valve which is displaced upwardly when the backpressure exceeds the compressive resistance of the spring.

As shown inFIG. 6, the backpressure valve200includes a generally annular body202which has threads203for connecting to an annular anchor that in turn threadedly engages (via threads208) to the test plug hanger51. A gasket210sits in an annular groove to provide a fluid-tight seal between the test plug hanger51and a lower portion206of the annular anchor204.

The backpressure valve includes a ball216which is forced downwardly by a compression spring218against an annular gasket214which sits on annular shoulder of the anchor204. The annular shoulder defines an aperture through which pressurized fluid may flow. In other words, the backpressure valve is a one-way spring-loaded ball valve in which the spring exerts a downward force on the ball for obstructing the aperture defined by the annular shoulder.

In operation, if a leak occurs and the backpressure exceeds the compressive resistance of the spring, then the ball is displaced upwardly, thereby permitting pressurized fluid to flow from the axial passageway220to an upper passageway222and upwards through a central bore151of the landing tool150.

Depicted inFIG. 7is a set-up for pressurizing the wellhead and control stack. The test plug tool50is inserted into the stack using the landing tool150and is locked into place by locking pins36in the drilling flange30. Mounted atop the drilling flange30is the blowout preventer40. Secured atop the blowout preventer40is the tubing head spool100having flanged side ports102for injection of pressurized fluids for testing the pressure integrity of the wellhead and stack. Secured atop the tubing head spool100is a tubing adapter250. The tubing adapter250is flanged to the tubing head spool and is sealed thereto with a ring gasket which is housed in an annular groove252. The tubing adapter250has threads255for connection to a retainer nut260. The tubing adapter also has a radially inward annular cavity known as a stuffing box. The stuffing box houses a packing retainer ring266, a chevron packing264and a packing nut262. Accordingly, with the stack configured as shown inFIG. 7, the annular space55can be pressurized to test the pressure integrity of the wellhead and stack. If pressurized fluid leaks past the test plug, backpressure will force open the backpressure valve200, thereby permitting fluid to flow up the central bore151of the landing tool150.

Persons skilled in the art will appreciate that these test plug tools may be modified to suit similar pressure-testing applications. The embodiments of the invention described above are therefore intended to be exemplary only. The scope of the invention is intended to be limited solely by the scope of the appended claims.