[0001] This application claims priority to U.S. Provisional Patent Application Serial Number 61/548,068 filed October 17, 2011.

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0002] The invention relates generally to the control of heating from adiabatic compression within pressurized vessels and components associated with a wellhead.

2. Description of the Related Art

[0003] When a gas is rapidly compressed within an enclosed chamber, the gas is adiabatically heated. Adiabatic heating can undesirably cause objects within the enclosed chamber to be melted or otherwise damaged by increased temperatures.

[0004] Wellheads typically include pressure control vessels, such as those that are used to equalize pressure across a wellhead valve prior to opening the valve. Undesirable adiabatic heating may occur within these vessels during operation.

SUMMARY OF THE INVENTION

[0005] The invention provides systems and methods for controlling and reducing adiabatic heating within pressure control equipment. Generally, the systems and methods of the present invention reduce adiabatic heating by venting the pressure control equipment either during or prior to compression of fluid within the pressure control equipment. The venting removes or substantially removes compressible gases from the pressure control equipment. In particular embodiments, venting is performed by a valve that is positioned to remove compressible gases at or near the upper end of

l the interior chamber of the pressure control equipment. In further particular embodiments, the valve components are formed of materials that are resistant to corrosive fluids, and in particular hydrogen sulfide (H ₂ S). Thus, corrosion-resistant plastics, thermoplastics, ceramic materials and nickel alloys are preferred.

[0006] According to one described embodiment, a wellhead for wireline run devices includes pressure control equipment in the form of a lubricator that is used to equalize pressure across the wellhead master valve prior to fully opening the wellhead master valve. A vent valve assembly is designed to remove compressible gases from the interior chamber of the lubricator prior to fully opening the master valve, In a described embodiment, the vent valve assembly removes compressible gases from the interior chamber during the time that the wellhead master valve is partially opened to pressurize the interior chamber. In a preferred embodiment, the valve assembly is positioned to remove compressible gases that reside within the upper portion of the interior chamber. Removed gases may be transmitted to a gas buster or similar device for incineration. In described embodiments, venting occurs until liquid effluent is expelled from the valve. Then the venting valve is closed. Thereafter, the wellhead master valve can be fully opened.

[0007] According to another embodiment, a venting system is associated with a coiled tubing injection arrangement to remove compressible gases from pressure control equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] For a thorough understanding of the present invention, reference is made to the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings, wherein like reference numerals designate like or similar elements throughout the several figures of the drawings and wherein:

[0009) Figure 1 is a side, cross-sectional view of an exemplary wellhead for the running of wireline tools and with pressure control equipment having a venting system constructed in accordance with the present invention.

[0010] Figure 2 is an external, isometric view of an exemplary vent valve assembly disposed between a lubricator and grease head in accordance with the present invention.

[0011] Figure 3 is a side, cross-sectional view of an exemplary vent valve assembly constructed in accordance with the present invention.

[0012] Figures 4A and 4B are schematic side cross-sectional views of portions of an exemplary chamber containing liquid and gas.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Figure 1 depicts an exemplary wellhead 10 for a wellbore into which it is desired to dispose one or more wireline tools. The wellhead 10 includes a "Christmas Tree" 12 of a type known in the art. The Christmas Tree 12 contains a master valve, which is shown schematically at 14. The master valve 14 is used to entirely shut off fluid flow through the wellhead 10. A lubricator 16 is affixed to the upper end of the Christmas tree 12. A grease head 22 extends upwardly from the lubricator 16 and includes flow tubes 24, as is known in the art.

[0014] As is known in the art, one or more wireline tools (not shown) are typically drawn up within the lower end of the lubricator 16 after being affixed to a wireline cable that is passed downwardly through the grease head 22 and through to the lubricator 16. These tools will be lowered into the wellhead 10 by wireline after the master valve 14 has been opened. It is noted that, for purposes of clarity, Figures 3, 4A and 4B do not show either a wireline cable or a wireline tool.

[0015] The lubricator 16 is a pressure control device that permits wireline tools to be inserted into and removed from the wellhead 10, which is under pressure. Pressure across the master valve 14 prior to opening can be on the order of around 15,000 psi. The lubricator 16 defines an interior chamber 28 that can be pressurized. The lower end of the interior chamber 28 is defined by the master valve 14. The upper portion 29 of the interior chamber 28 terminates at a vent valve assembly 30.

[0016] The vent valve assembly 30 is incorporated into the lubricator 16, preferably at or near the upper end of the lubricator 16 inside or integrated into the grease head 22. The vent valve assembly 30 is operable to selectively bleed compressible gases or fluids from within the interior chamber 28. It is preferred that the vent valve assembly 30 be associated with the interior chamber 28 so that compressible gases are removed from the upper portion 29 of the interior chamber 28.

[0017] In one embodiment, the interior vent valve assembly components are formed of or protected by corrosion-resistant materials (i.e., plastics, thermoplastics, ceramics or nickel-based alloys) in order to protect the valve assembly 30 from corrosion and damage resulting from corrosive well bore-related chemicals. In particular, the vent valve assembly 30 should preferably be protected from damage and corrosion resulting from hydrogen sulfide (H ₂ S) which makes the valve operable in an environment that includes hydrogen sulfide. In particular embodiments, it is preferred that at least the valve member 48 be either formed of a corrosion-resistant material of protected by a coating or overlay of such material. [0018] An exemplary vent valve assembly 30 is shown in greater detail in Figure 3. An exhaust line or conduit 32 extends outwardly from the vent valve assembly 30 and is used to transmit compressible gases from the interior chamber 28 away from the valve assembly 30 for disposal. In one embodiment, the exhaust line 32 transmits removed gases to a gas buster, of a type known in the art that incinerates the gases, or to a pit.

[0019J The vent valve assembly 30 is an engineered solution which provides a valve assembly that is selectively moveable between a closed position, wherein the valve assembly 30 does not permit compressible gases or fluids within the interior chamber 28 to flow into the exhaust line 32, and an open position, wherein compressible gases or fluids within the interior chamber 28 will vent into the exhaust line 32. In accordance with one embodiment of the invention, the vent valve assembly 30 is actuated hydraulically between its open and closed positions. Figure 1 shows an exemplary hydraulic line 34 which supplies hydraulic fluid to the valve assembly 30 from pump 18. The valve assembly 30 may be controlled by a conventional hydraulic console or interpack unit or in other ways known in the art.

[0020] The cross-sectional view of Figure 3 depicts an exemplary vent valve assembly 30 as having an outer valve housing 36 and an adapter 38. The adapter 38 is provided with threaded portions 40, 42 which permit it to be affixed directly in-line between the lubricator 16 and the first flow tube of the grease head 22. Axial passage 44 is defined within the adaptor 38 so that the wireline can be contained therein. The upper portion of the axial passage 44 forms the upper portion 29 of the interior chamber 28. Those of skill in the art will understand that the presence of a wireline cable (not shown) tightly retained under pressure within the grease head 22 prevents fluid from flowing or migrating above the upper portion 29. A lateral passage 46 extends from the axial passage 44 to the valve housing 36. The valve housing 36 defines a flowpath 47 between the lateral passage 46 and exhaust line 32. The valve housing 36 also houses valve member 48 which is biased by spring 50 toward the closed position wherein fluid from the lateral passage 46 cannot pass into the exhaust line 32. Hydraulic fluid within hydraulic line 34 will selectively open the valve assembly 30 by urging the valve member 48 to an open position (Fig. 4B) by axial I y compressing the spring 50 to open the flowpath 47 to fluid flow therethrough. In embodiments where nickel-based alloys are used, a weld overlay may be used to protect the valve member 48 and the interior portions of the valve housing 36 and adapter 38. When hydraulic fluid is no longer flowed into the vent valve assembly 30, the spring 50 will urge the valve member 48 back to the closed position (fig. 4A).

[0021] To insert a tool into the well, the wellhead master valve 14 is closed below the lubricator 16, and pressure within the interior chamber 28 is removed. A wireline tool (not shown) is disposed within the interior chamber 28 of lubricator 16 with an affixed wireline cable (not shown) passing upwardly through the grease head 22. The lubricator 16 is then affixed to the Christmas Tree 2, and the interior chamber 28 is now sealed off. Prior to opening the master valve 14, the vent valve assembly 30 is opened to bleed compressible gases from the interior chamber 28. The vent valve assembly 30 is opened and the master valve 4 is partially opened until all or substantially all compressible gases are removed from the interior chamber 28. An operator will typically monitor the exhaust line 32 to determine when liquid is beginning to be removed from the chamber 28, which indicates that compressible gases have been removed. Then the vent valve assembly 30 is closed. Thereafter, the master valve 14 can be fully opened to dispose the wireline tool into the wellhead 10. Figures 4A and 4B depict the upper portion 29 of the interior chamber 28. In Figure 4A, the vent valve assembly 30 is closed. The interior chamber 28 contains liquid 52 and compressible gases 54, which are resident within the upper portion 29 of the chamber 28. The liquid 52 resides below the gases 54. Typical liquids used are fresh water, brine, gun barrel water or formation fluids. In Figure 4B, the vent valve assembly 30 has been opened, and the compressible gases 54 have been removed via the exhaust line 32. Liquid 52 is now resident within the upper portion 29 of the chamber 28.

[0022] A vent valve assembly similar to vent valve assembly 30 described above could be incorporated into a coiled tubing injection assembly or another arrangement that is associated with a well valve.

[0023] It should be understood that the invention provides systems and methods for controlling adiabatic heating within a pressure control device that is associated with a well valve, such as master valve 14 wherein the pressure control device is used to substantially equalize a pressure differential across the well valve. In described embodiments, a vent valve assembly, such as vent valve assembly 30, is associated with the pressure control device in order to remove compressible gases from an upper portion of the interior chamber of the pressure control device. In accordance with methods of the present invention, compressible gases are removed or substantially removed from at least a portion of the interior chamber during pressurization of the interior chamber to equalize pressure across the well valve and prior to fully opening the well valve. In a described embodiment, compressible gases are removed from the upper portion 29 of the interior chamber 28.

[0024] Those of skill in the art will recognize that numerous modifications and changes may be made to the exemplary designs and embodiments described herein and that the invention is limited only by the claims that follow and any equivalents thereof,