Patent Application
20120305259
This invention relates in general to production of oil and gas wells, and in particular to a wellhead system having a flow line for venting an annulus in the wellhead system that is heated by a production flow line also within the wellhead system.
Wellheads used in the production of hydrocarbons extracted from subterranean formations typically comprise a wellhead assembly attached at the upper end of a wellbore formed into a hydrocarbon producing formation. Wellhead assemblies usually provide support hangers for suspending production tubing and casing into the wellbore. The casing lines the wellbore, thereby isolating the wellbore from the surrounding formation. The tubing typically lies concentric within the casing and provides a conduit therein for producing the hydrocarbons entrained within the formation.
Wellhead assemblies also typically include a wellhead housing adjacent where the casing and tubing enter the wellbore, and a production tree atop the wellhead housing. The production tree is commonly used to control and distribute the fluids produced from the wellbore and selectively provide fluid communication or access to the tubing, casing, and/or annuluses between the tubing and casing. Valves assemblies are typically provided within wellhead production trees for controlling fluid flow across a wellhead, such as production flow from the borehole or circulating fluid flow in and out of a wellhead.
In
Generally, production tubing 26 is the inner most tubular within a wellhead assembly 10, thus the inner surface of the production tubing 26 defines the production bore 16. Circumscribing the production tubing 28 is casing 28 that generally extends down from the tree 21 and into the wellbore 28 to form a wellhead housing. An annulus 30 is defined between the tubing 26 and casing 28 which typically is in communication with the annulus line 24. Often, for access or for venting of the annulus 30, an annulus bleed line 32, which is schematically illustrated in
Fluids produced from within the wellbore 12 can include components that form hydrates when subjected to certain temperatures and pressures. When formed, hydrates are ice like solids made up of gases enclosed within a cage of hydrogen bonded water molecules. Because hydrate formation can occur when cooling a fluid having hydrate components, flow circuits that experience a sudden pressure drop, such as through a throttling valve, may induce hydrate formation. The ice like nature of hydrates typically impedes fluid flow through lines and valves of a flow circuit. Chemical injections can be useful for avoiding hydrate formation, but performing and maintaining the injections introduces added complexity to production of hydrocarbons.
Disclosed herein is an example of a wellhead assembly equipped with an annulus bleed line designed to prevent hydrate formation. In an example embodiment the wellhead assembly includes a wellhead housing mounted on a wellbore with a production tree connected on top of the wellhead housing. A production flow path is formed through the wellhead housing and production tree, where the production flow path is in fluid communication with the wellbore. Concentric tubulars are included with the wellhead assembly, both of which are registered with the wellbore. The concentric tubulars define an annulus therebetween. The annulus bleed line has an end in fluid communication with the annulus and has a portion routed so that it is in thermal communication with the production flow path. Thus when production fluid from the wellbore flows through the production flow path, and annulus fluid is in the bleed line, thermal energy from the production fluid transferred to bleed line heats the annulus fluid in the bleed line. Heating the annulus fluid that is in the bleed line prevents hydrate formation in the bleed line, even when the annulus fluid is throttled across a valve. In an example embodiment, the wellhead assembly further includes a cross over line for selectively providing fluid communication between the annulus and the production flow path; in this embodiment the bleed line has an end connected to the cross over line. In an example embodiment, the portion of the production tree having the production flow path defines a production wing block, and the bleed line is provided in the production wing block. In an example embodiment, a portion of the bleed line is adjacent a portion of the production flow path. In an example embodiment, a portion of the bleed line contacts a portion of the production flow path. In an example embodiment, a portion of the bleed line circumscribes a portion of the production flow path. In an example embodiment, the portion of the bleed line circumscribing the portion of the production flow path can be one or both of a helical line or a jacket. In an example embodiment the wellbore is subsea.
Also disclosed herein is a method of preventing hydrate formation in fluid produced from a wellbore. In an example embodiment, the method includes providing a wellhead assembly: where the wellhead assembly is made up of a wellhead housing mounted on the wellbore, a production tree connected on top of the wellhead housing, a production flow path formed through the wellhead housing and production tree and in fluid communication with the wellbore. An annulus is formed between concentric tubulars that are registered with the wellbore. Further included with the wellhead assembly is a bleed line having an end in fluid communication with the annulus and having a portion routed in thermal communication with the production flow path. The method further includes flowing production fluid from the wellbore through the production flow path, flowing annulus fluid from the annulus through the bleed line, and heating the annulus fluid by transferring heat from the production fluid to the annulus fluid so that the annulus fluid is at a temperature above that which hydrates are formed. In an example embodiment, after heating the annulus fluid, the annulus fluid is transferred to above sea surface while retaining sufficient thermal energy to remain above a hydrate forming temperature.
The apparatus and method of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. This subject of the present disclosure may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. For the convenience in referring to the accompanying figures, directional terms are used for reference and illustration only. For example, the directional terms such as “upper”, “lower”, “above”, “below”, and the like are being used to illustrate a relational location.
It is to be understood that the subject of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments of the subject disclosure and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. Accordingly, the subject disclosure is therefore to be limited only by the scope of the appended claims.
Referring now to
An annulus 62 is defined between the concentric production tubing 52 and casing 50. An annulus passage 64 is illustrated in
Still referring to
While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention.
