US 4,589,434 A · Method and apparatus to prevent hydrate formation in full wellstream pipelines

Abstract

The apparatus and method disclosed prevents hydrate formation in subsea oil and gas pipelines including at least one marine riser. The invention reduces the pressure on the fluids in a shut in pipeline by displacing fluids in the system into a reservoir thereby reducing the height of the column of fluids in the riser. A pump may be used to remove additional fluid from the fluid reservoir and pipeline to ensure the hydrostatic pressure associated with the final fluid level is below the pressure where hydrates may form at shut in temperatures. During start-up, a pump removes fluids from the fluid reservoir at about the same rate as produced fluids are allowed into the pipeline. The pump is shut down and pipeline operations are resumed when the liquid full wellstream fluids in the pipeline warm to a temperature outside the range where hydrates may form.

Claims43

Dependent claims

Apparatus to prevent hydrate formation in a shut down pipeline system for transporting produced fluids, the pipeline system having at least one riser initially containing a column of produced fluids when the pipeline system is shut down, said apparatus comprising:

a fluid reservoir in fluid communication with the pipeline system for receiving produced fluids from the pipeline system when the system is shut down;
and
a fluid level controller adapted to transfer produced fluids from the pipeline system to the fluid reservoir when the pipeline system is shut down in an amount sufficient to reduce the height of the column of produced fluids in the riser, and the hydrostatic pressure in the pipeline system resulting therefrom, an amount sufficient to prevent hydrate formation in the produced fluids in the shut down pipeline system at the temperature of such fluids.

Apparatus to prevent hydrate formation in a pipeline system for transporting produced fluids when the pipeline system is shut down and during start-up, the pipeline system including at least one riser initially containing a column of produced fluids when the pipeline system is shut down and a source of a second fluid in which hydrates will not form at the conditions encountered during start up of the pipeline system, comprising:

a fluid reservoir in fluid communication with the pipeline system for receiving produced fluids from the pipeline system when the system is shut down;
a fluid level controller adapted to transfer produced fluids from the pipeline system to the fluid level control reservoir when the pipeline system is shut down in an amount sufficient to reduce the height of the column of produced fluids in the riser, and the hydrostatic pressure in the pipeline system resulting therefrom, an amount sufficient to prevent hydrate formation in the produced fluids in the shut down pipeline system;
and
a pump in fluid communication with the pipeline system and the source of the second fluid for circulating the second fluid into the pipeline system prior to start up of the pipeline system to prevent hydrate formation therein when operation of the pipeline system is resumed.

1 more element

An apparatus to prevent hydrate formation during start-up of a shut down pipeline system for transporting produced fluids having at least one riser, said pipeline system containing a quantity of fluid cooled to a temperature within the hydrate formation range at the operating pressure of the pipeline system and including a source of a second fluid in which hydrates will not form during start-up, said apparatus comprising:

a fluid reservoir in fluid communication with the pipeline system;
a pump for removing fluids from the fluid reservoir at a rate approximately equal to the rate that warm produced fluids are allowed to flow through the pipeline system during startup, whereby said pump maintains the fluid levels in the pipeline system and the fluid reservoir below the levels where the hydrostatic pressures resulting from such levels is outside the pressure range where hydrates may form.

Apparatus to prevent hydrate formation in a pipeline system for transporting warm produced fluids from a source thereof when the pipeline system is shut down and during start up, the pipeline system including at least one riser initially containing a column of produced fluids when the pipeline system is shut down and a shut off valve for controlling the flow of produced fluids from the source and through the pipeline system, comprising:

a fluid reservoir in fluid communication with the pipeline system for receiving produced fluids from the pipeline system when the shut off valve is closed and the pipeline system is shut down;
a fluid level controller adapted to transfer produced fluids form the pipeline system to the fluid reservoir when the pipeline system is shut down in an amount sufficient to reduce the height of the column of produced fluids in the riser, and the hydrostatic pressure in the pipeline system resulting therefrom, an amount sufficient to prevent hydrate formation in the produced fluids in the shut down pipeline system;
a conduit having a first end inside the fluid reservoir and a second end extending outside of the fluid reservoir for removing fluids from the fluid reservoir;
a pump having an inlet and an outlet in fluid communication with the conduit and adapted for removing produced fluids from the fluid reservoir when the shut off valve is opened during start up of the pipeline system in amounts sufficient to prevent hydrate formation in the fluid reservoir and the pipeline system.

1 more element

A method for prevention of hydrate formation in a pipeline system for transporting warm produced fluids, said pipeline system including at least one riser and having a fluid reservoir in communication with the pipeline system and containing a pressurized gas, said method comprising the steps of:

shutting off the flow of fluids in the pipeline system thereby placing a fixed amount of fluid in the pipeline system;
venting the pressurized gas in the fluid reservoir to reduce the pressure in the fluid reservoir to allow the produced fluids in the pipeline system to enter the fluid reservoir until the liquid levels in the pipeline system and the fluid reservoir settle to approximately the same level, wherein said level is a preselected level that is less than the level at which the corresponding hydrostatic head will cause hydrates to form in the pipeline system at the temperature of the produced fluids while the pipeline system is shut in.

Dependencies are inferred from the claim text.

Method and apparatus to prevent hydrate formation in full wellstream pipelines

Life of this patent

Method and apparatus to prevent hydrate formation in full wellstream pipelines

Life of this patent

Abstract

Claims43