Search

EP-4063613-B1 - A DRAIN APPARATUS FOR A SUBSEA PIPELINE

EP4063613B1EP 4063613 B1EP4063613 B1EP 4063613B1EP-4063613-B1

Inventors

  • LIÉBANA YESTE, Laura
  • TREVELYAN THOMAS, Lee

Dates

Publication Date
20260506
Application Date
20170821

Claims (15)

  1. A drain apparatus (200) for use in a gas pipeline to remove liquid from a multiphase flow in the gas pipeline, the drain apparatus comprising: a first channel (20) for carrying a multiphase flow comprising liquid and gas phases; liquid extraction means (11; 12; 14; 16; 18) for extracting the liquid phase from the multiphase flow in the first channel; and a first storage tank disposed beneath the liquid extraction means, the first storage tank being arranged to receive liquid from the liquid extraction means; characterised in that the drain apparatus is for use in a subsea gas pipeline, such that the pipe arranged to carry the multiphase flow in the subsea gas pipeline is a subsea pipe, wherein the first channel further comprises curved sections between respective ends of the first channel and the liquid extraction means to accommodate a difference in height between the liquid extraction means and the subsea gas pipeline, such that, in use, the drain apparatus is configured to support the liquid extraction means a certain height above the seabed so as to accommodate the first storage tank without a need to excavate the seabed, and wherein a bend radius of each of said curved sections is greater than or equal to 3 times the internal diameter of the first channel, such that a pig travelling along the subsea pipe can pass through the drain apparatus including each of said curved sections.
  2. The drain apparatus of claim 1, comprising a plurality of storage tanks including the first storage tank, wherein the plurality of storage tanks are disposed beneath the liquid extraction means on opposite sides of the drain apparatus.
  3. The drain apparatus of claim 1 or 2, wherein the liquid extraction means is configured so as not to permit the multiphase flow to bypass the pig as the pig passes through the first channel, such that a pressure differential can be maintained across the pig.
  4. The drain apparatus of claim 3, wherein the liquid extraction means comprises at least one opening formed in a wall of the first channel to permit liquid to be extracted through the at least one opening, and wherein a distance between the furthest downstream point of the at least one opening and the furthest upstream point of the at least one opening is less than 1.5 times the internal diameter of the first channel.
  5. The drain apparatus according to any one of the preceding claims installed in the subsea gas pipeline, wherein the drain apparatus is disposed partway along a gradient in the subsea gas pipeline to reduce liquid holdup.
  6. The drain apparatus according to any one of the preceding claims, wherein the liquid extraction means comprises an inlet to receive liquid from the first channel, and a chamber in fluid communication with the inlet.
  7. The drain apparatus according to claim 6, wherein the drain apparatus further comprises a second channel configured to bypass part of the first channel, the liquid extraction means being disposed on the second channel, and further comprises at least one valve arranged to block the inlet in a first mode of operation and the first channel in a second mode of operation.
  8. The drain apparatus according to claim 6 or 7, wherein the liquid extraction means comprises an outlet in fluid communication with the chamber for removing liquid from the drain apparatus, and the drain apparatus further comprises: first and second inlets formed in a wall of the first channel along the longitudinal axis of the first channel; a baffle arranged to divide the chamber into first and second chambers, wherein the first inlet is arranged in the first chamber and the second inlet is arranged in the second chamber; and a conduit disposed outside the chamber and connected to the first and second chambers to fluidly connect the first chamber to the second chamber, wherein the outlet is arranged in fluid communication with the conduit.
  9. The drain apparatus according to claim 6, 7 or 8, wherein the liquid extraction means comprises a reservoir in fluid communication with an opening formed in the bottom of the chamber, wherein the opening has a diameter substantially equal to the diameter of the chamber, wherein the reservoir comprises an overflow outlet formed through a side surface of the reservoir for transporting gas to the chamber.
  10. The drain apparatus according to any one of claims 6 to 9, wherein the outlet is in fluid communication with a third channel, wherein the third channel is an internal conduit of a subsea umbilical line or a second subsea pipe, wherein the apparatus further comprises: at least one pump coupled to the outlet and configured to receive liquid from the outlet and pump the liquid to the surface, wherein the chamber or the reservoir further comprises a control mechanism configured to activate the at least one pump when a liquid level in the chamber or the reservoir exceeds a threshold.
  11. The drain apparatus according to any one of claims 1 to 5, wherein the liquid extraction means comprises: a first liquid extraction chamber comprising at least one first inlet to receive liquid from the first channel; a second liquid extraction chamber comprising at least one second inlet to receive liquid from the first channel, wherein the first channel is arranged to pass through the first liquid extraction chamber before the second liquid extraction chamber; and a second storage tank arranged to receive liquid from the second liquid extraction chamber, wherein the first storage tank is arranged to receive liquid from the first liquid extraction chamber.
  12. The drain apparatus according to claim 11, further comprising: a first gas conduit connecting the first storage tank to the first channel to permit gas flow between the first storage tank and the first channel; and/or a second gas conduit connecting the second storage tank to the first channel to permit gas flow between the second storage tank and the first channel.
  13. The drain apparatus according to claim 12, wherein the first gas conduit and the second gas conduit are connected to the first channel after the second liquid extraction chamber, or wherein the first gas conduit is connected to the first channel before the second liquid extraction chamber, and the second gas conduit is connected to the first channel after the second liquid extraction chamber.
  14. The drain apparatus according to any one of claims 11 to 13, wherein the first channel is configured such that when the drain apparatus is installed in the subsea gas pipeline the first and second liquid extraction chambers are raised above a level of the subsea pipe at either end of the first channel, such that the first and second storage tanks can be located at or above the level of the subsea pipe and below a level at which the first and second liquid extraction chambers are located.
  15. The drain apparatus according to any one of the preceding claims, further comprising: at least one injection port (24) in fluid communication with the first channel, the at least one injection port being configured to inject a hydrate inhibitor into the multiphase flow in the first channel on the dry side of the drain apparatus, wherein the injection port extends through an outer surface of the first channel where the first channel protrudes from the dry side of the chamber.

Description

Field The present invention relates to a drain apparatus and a subsea pipeline. More particularly, the present invention relates to a drain apparatus for use in the subsea pipeline. Background When transporting production gas (which can be later processed into Liquefied Natural Gas (LNG)) along a subsea pipeline, water and other liquid components or mixtures precipitate out of the multiphase flow due to heat and pressure loss. This results in a reduction in pressure driving the system due to the gravitational effect on the condensing water, which means generally production gas cannot naturally flow more than about 80 - 140 km from a well head. Furthermore, the effect, known as "slugging", increases the back pressure on the well and shortens the production plateau, where it would have been much greater if liquids had not been in the system (in other words, a "dry gas" system). To solve this problem, both increasing and decreasing the bore of the main carrier pipe within the pipeline have been tried. However, increasing the bore was found to make the slugging worse due to an increase in gravitational pressure losses. Decreasing the bore was found to increase pressure loss due to friction. Therefore, it is necessary to remove as much liquid from the multiphase flow as possible, as early as possible. To that end, it is known to incorporate a single separator at the well head. However, this still does not produce a pseudo dry gas system. Moreover, it is known to use subsea drains (or, "Low Point Drains" (LPDs)), positioned at the lowest part of a gradient, to remove liquid flowing back down the pipe in the pipeline that precipitated out due to temperature and pressure variations. However, the particular designs of these LPDs, and their location, is shown not to have had a great effect on system efficiency, as indicated by comparing the plots represented by diamonds and squares in Figure 17. Moreover, present designs of LPDs do not allow continuous pigging operations, with subsequent negative effect on the system's integrity. Minimising the effect of gravitational pressure losses enables pipelines to have pipes with greater bore diameters, which in turn lowers the pressure drop per unit distance. Reducing the pressure drop also increases the production plateau and allows more resources to be extracted from the ground. Aspects of the present invention aim to address one or more of the aforementioned drawbacks inherent in prior art subsea pipelines, while still allowing continuous pigging operations. US 5,525,133 discloses a gas pipeline drip having two parts; a flow separator and a receptacle. GB2369787 A discloses a subsea separator comprising three compartments. WO2015/036041 A1 discloses a hydrocarbon separation apparatus with recirculation loop. US 7,516,794 B2 discloses a pipe separator for the separation of fluids, for example the separation of oil, gas and water. US 2008/0178915 A1 discloses an arrangement for the cleaning of a pipe separator. US2008/0156716 A1 discloses a device in connection with a separator for cleaning or reaming such a separator. WO2005/115583 A1 discloses apparatus for filtering of solids suspended in fluids, comprising a screen. US2005/0006086 A1 discloses an installation arranged on the sea bed for the separation of fluids, comprising at least one separator and a pipeline. Summary According to a first aspect of the present invention, there is provided a drain apparatus for use in a subsea gas pipeline to remove liquid from a multiphase flow in the subsea gas pipeline, according to claim 1. Advantageously, the first aspect provides a means for transporting gas greater distances by removing liquid from a subsea pipe in a subsea pipeline at any chosen point along the length of the subsea pipe. By being able to be positioned anywhere along the subsea pipe, rather than at the well head, more liquid can be removed from the system. The drain apparatus can be positioned anywhere along the subsea pipe by virtue of it being configured to allow pigging operations to continue uninterrupted between a well head and a terminal on the land. The liquid extraction means may be configured so as not to permit the multiphase flow to bypass the pig as the pig passes through the first channel, such that a pressure differential can be maintained across the pig. In some embodiments, the liquid extraction means comprises at least one opening formed in a wall of the first channel to permit liquid to be extracted through the at least one opening, and a distance between the furthest downstream point of the at least one opening and the furthest upstream point of the at least one opening is less than 1.5 times the internal diameter of the first channel. For example, in some embodiments the distance between the furthest downstream point of the at least one opening and the furthest upstream point of the at least one opening is less than 0.8 times the internal diameter of the first channel. The drain apparatus may b