Method and system for processing a fluid produced from a well

Abstract

A method of processing a fluid produced from a well, the produced fluid being a high pressure fluid, the method comprising: reducing the pressure of the fluid to a reduced pressure such that a gas phase and a liquid phase are formed; separating the gas phase from the liquid phase thus forming a gas product and a liquid product; and storing the liquid product in a storage tank at a pressure such that the liquid product remains in a stable liquid phase during storage, wherein the reduced pressure is greater than atmospheric pressure.

Claims

1. A system for processing a fluid produced from a well, the produced fluid being a high pressure fluid, the system comprising: means for reducing the pressure of the fluid to a reduced pressure such that a gas phase and a liquid phase are formed; means for separating the gas phase from the liquid phase thus forming a gas product and a liquid product; and a storage tank for storing the liquid product in a storage tank at a pressure such that the liquid product remains in a stable liquid phase during storage, the means for reducing pressure being configured such that the reduced pressure is greater than atmospheric pressure, the means for separating the gas phase from the liquid phase being configured such that the pressure of the liquid product is maintained at a pressure substantially equal to or greater than the reduced pressure during separation.

2. The system as claimed in claim 1, wherein the storage tank is configured such that the pressure of the liquid is maintained at a pressure substantially equal to or greater than the reduced pressure during storage.

3. The system as claimed in claim 1 comprising: a transfer means for transferring the liquid product from the storage tank to a liquid transporter; and a liquid transporter for transporting the liquid product to another location using the liquid transporter, the transfer means and the liquid transporter being configured such that the transferring and transporting may occur at a pressure such that the liquid product remains in a stable liquid phase during transfer and transportation.

4. The system as claimed in claim 3, wherein the transfer means is configured such that the pressure of the liquid product is maintained at a pressure substantially equal to or greater than the reduced pressure during transfer.

5. The system as claimed in claim 3, wherein the liquid transporter is configured such that the pressure of the liquid product is maintained at a pressure substantially equal to or greater than the reduced pressure during transportation.

6. The system as claimed in claim 3, wherein the well is an offshore well and the pressure reducing means, the separating means, the storage tank and/or the transfer means are offshore.

7. The system as claimed in claim 6, wherein the other location is an onshore location.

8. The system as claimed in claim 3 comprising: a second transfer means for transferring the liquid product from the liquid transporter to the other location, the second transfer means being configured such that the transferring may occur at a pressure such that the liquid product remains in a stable liquid phase during transfer; and another means for reducing the pressure of the liquid product to atmospheric pressure at the other location.

9. The system as claimed in claim 1, wherein the reduced pressure is greater than 2 bar.

10. A system for processing a fluid produced from a well, the produced fluid being a high pressure fluid, the system comprising: means for reducing the pressure of the fluid to a reduced pressure such that a gas phase and a liquid phase are formed; means for separating the gas phase from the liquid phase thus forming a gas product and a liquid product; and a storage tank for storing the liquid product in a storage tank at a pressure such that the liquid product remains in a stable liquid phase during storage, the means for reducing pressure being configured such that the reduced pressure is greater than atmospheric pressure, the storage tank being configured such that the pressure of the liquid is maintained at a pressure substantially equal to or greater than the reduced pressure during storage.

11. The system as claimed in claim 10, wherein the means for separating the gas phase from the liquid phase is configured such that the pressure of the liquid product is maintained at a pressure substantially equal to or greater than the reduced pressure during separation.

12. The system as claimed in claim 10 comprising: a transfer means for transferring the liquid product from the storage tank to a liquid transporter; and a liquid transporter for transporting the liquid product to another location using the liquid transporter, the transfer means and the liquid transporter being configured such that the transferring and transporting may occur at a pressure such that the liquid product remains in a stable liquid phase during transfer and transportation.

13. The system as claimed in claim 12, wherein the transfer means is configured such that the pressure of the liquid product is maintained at a pressure substantially equal to or greater than the reduced pressure during transfer.

14. The system as claimed in claim 12, wherein the liquid transporter is configured such that the pressure of the liquid product is maintained at a pressure substantially equal to or greater than the reduced pressure during transportation.

15. The system as claimed in claim 12, wherein the well is an offshore well and the pressure reducing means, the separating means, the storage tank and/or the transfer means are offshore.

16. The system as claimed in claim 15, wherein the other location is an onshore location.

17. The system as claimed in claim 12 comprising: a second transfer means for transferring the liquid product from the liquid transporter to the other location, the second transfer means being configured such that the transferring may occur at a pressure such that the liquid product remains in a stable liquid phase during transfer; and another means for reducing the pressure of the liquid product to atmospheric pressure at the other location.

18. The system as claimed in claim 10, wherein the reduced pressure is greater than 2 bar.

Description

(1) Certain preferred embodiments will now be described by way of example only with reference to the accompanying drawings in which:

(2) FIG. 1 shows a first embodiment of the present invention;

(3) FIG. 2 shows another embodiment of the present invention; and

(4) FIG. 3 shows another embodiment of the present invention.

(5) Regarding FIG. 1, this shows a wellhead 1 of a gas-condensate field on the sea bed 2. The pure well stream passes through riser 3 to unmanned wellhead platform (UWP) 4 on the sea surface 5. The pure well stream comprises a produced fluid, comprising water, natural gas and light liquid hydrocarbons, and sediments such as sand and mud. The sediments may be removed from the pure well stream at the UWP 4.

(6) The produced fluid passes from the UWP 4 to a means for creating a semi-stabilised liquid product 7 that is located on the seabed 2 via a flexible spool 6. A pure gas stream separated from the produced fluid may be output from the means for creating a liquid product 7 through a flexible spool 8. The flexible spool 8 delivers the purified gas stream to gas processing equipment 9 on the UWP 4. The gas processing equipment 9 may comprise a compressor or a pump and may be used to transport the gas to a host or onshore via a gas pipeline.

(7) A semi-stabilised liquid product stream separated from the produced fluid may be output from the means for creating a liquid product 7 through flexible spool 10. The liquid product comprises all non-gaseous components of the produced fluid, e.g. water, LPG and light oils, and may include some components that would be gaseous under atmospheric conditions. The flexible spool 10 delivers the semi-stabilised liquid product to a subsea storage tank 11. Since the storage tank 11 is subsea, it stores the liquid product under pressure, the pressure being generated by the hydrostatic pressure of the local environment. This hydrostatic pressure is used to maintain the semi-stabilised liquid product in a stable state. Between the means for creating a liquid product 7 and the storage tank 11 there may be a heat exchanger and/or a pump (not shown).

(8) A transfer conduit 12 connects the storage tank 11 to the sea surface 5. The transfer conduit 12 may be permanently present. However, the transfer conduit 12 need not always be present since the storage tank 11 can collect the liquid product over a period of days or weeks without being emptied. However, when it is desired to empty the storage tank 11, the transfer conduit 12 allows for transfer of the liquid product from the storage tank 11 to a vessel 13 on the sea surface 5.

(9) The vessel 13 maintains the semi-stable liquid product in a stable state by maintain the liquid product under pressure. The vessel 13 may be used to transfer the stable liquid onshore 14. Again, the liquid product may be maintained under pressure during this step such that it remains in a stable state. The liquid product can then be transferred to onshore processing equipment 15 which may reduce the pressure of the liquid product and perform further separation of the gas and liquid phases produced by the further pressure reduction, so as to form a fully stabilised liquid product at atmospheric pressure.

(10) Regarding FIG. 2, this shows a wellhead 1 of a gas-condensate field on the sea bed 2. The pure well stream passes from the wellhead 1 through riser 3 to unmanned wellhead platform (UWP) 4 on the sea surface 5. The pure well stream comprises a produced fluid, comprising water, natural gas and light liquid hydrocarbons, and sediments such as sand and mud. The sediments may be removed from the pure well stream at the UWP 4.

(11) The produced fluid passes to a means for creating a liquid product 7 that is located on UWP 4. A pure gas stream separated from the produced fluid may be output from the means for creating a liquid product 7 through a conduit 8′. The conduit 8′ delivers the pure gas stream to gas processing equipment 9 on the UWP 4. The gas processing equipment 9 may comprise a compressor or a pump and may be used to transport the gas to a host or onshore via a gas pipeline.

(12) A semi-stabilised liquid product stream separated from the produced fluid may be output from the means for creating a liquid product 7 through flexible spool 10. The liquid product comprises all non-gaseous components of the produced fluid, e.g. water, LPG and light oils, and may include some components that would be gaseous under atmospheric conditions. The flexible spool 10 delivers the semi-stabilised liquid product to a subsea storage tank 11. Since the storage tank 11 is subsea, it stores the liquid product under pressure, the pressure being generated by the hydrostatic pressure of the local environment. This hydrostatic pressure is used to maintain the semi-stable liquid product in a stable state. Between the means for creating a liquid product 7 and the storage tank 11 there may be a heat exchanger and/or a pump (not shown).

(13) A transfer conduit 12 connects the storage tank 11 to the sea surface 5. The transfer conduit 12 may be permanently present. However, the transfer conduit 12 need not always be present since the storage tank 11 can collect the liquid product over a period of days or weeks without being emptied. However, when it is desired to empty the storage tank 11, the transfer conduit 12 allows for transfer of the liquid product from the storage tank 11 to a vessel 13 on the sea surface 5.

(14) The vessel 13 maintains the semi-stabilised liquid product under pressure in a stable state and may be used to transfer the semi-stable liquid onshore 14. Again, the semi-stabilised liquid product may be maintained under pressure during this step such that it remains in a stable state. The semi-stabilised liquid product can then be transferred to onshore processing equipment 15 which may reduce the pressure of the liquid product and perform further separation of the gas and liquid phases produced by the further pressure reduction, so as to form a fully stabilised liquid product.

(15) Regarding FIG. 3, this shows in more detail the means for creating a semi-stabilised liquid product 7. The produced fluid enters a first separator 102 through a first conduit 101.

(16) The produced fluid exiting the well typically is at high pressure and temperature. The produced fluid comprises gas and liquid components (i.e. components that would be gas and liquids at atmospheric conditions), but due to the high pressure the produced fluid is a liquid. Upstream of the first separator 102, the produced fluid is cooled and has its pressure reduced. This forms a gas phase and a liquid phase upstream of the first separator 102. The first separator 102 separates the gas phase of the reduced-pressure produced fluid from the liquid phase of the reduced-pressure produced fluid, thus forming a first gas product and a first liquid product.

(17) The gas product is output through a second conduit 103 and passes to a cooler 104 that cools the gas, thus allowing any remaining heavy hydrocarbons to liquefy. The cooled gas product is then fed into a second separator 105 that separates the gas from the liquefied remaining hydrocarbons. The purified gas product is output from the second separator 105 through conduit 106 to an ejector 108. The remaining heavy hydrocarbons are output from the second separator 105 though conduit 107.

(18) The liquid product of the produced fluid separated in the first separator 102 is output from the first separator 102 through conduit 109. Conduit 107 joins conduit 109 upstream of a choke or expander 110. Thus, substantially all liquid components of the produced fluid are fed into the choke or expander 110. The choke or expander 110 is used to reduce the pressure of the liquid. Further, reducing the pressure of the liquid allows for any remaining gas components in the liquid to evaporate out of the liquid. The reduced-pressure liquid and gas combination passes into a third separator 111. The pressure at this stage is low, but above atmospheric pressure, such as 1 to 10 bar.

(19) The third separator 111 outputs the evaporated gas as a second gas product through conduit 112. The gas passes through conduit 112 to the ejector 108. The ejector combines the low pressure gas in conduit 112 with the high pressure gas in conduit 106. The combined gas leaves the ejector through flexible spool 8 or conduit 8′, as seen in FIGS. 1 and 2. Alternatively to an ejector, a compressor could be used to compress the gas product in conduit 112.

(20) The third separator 111 outputs the purified liquid product through flexible spool 10. The liquid in the flexible spool 10 is at a low pressure in comparison to the well pressure, but is at a pressure greater than atmospheric pressure. The liquid product is maintained at a pressure such that it is in a stable liquid phase.

(21) Further, due to the two-stage separation and feedback of the gas stream and the liquid stream, the gas product output from the ejector 108 comprises substantially all of the gas components in the produced fluid and the liquid output from the third separator 111 comprises substantially all of the liquid components in the produced fluid.

(22) The unstable liquid product output from third separator 111 is stored in storage tank 11 where it is maintained in a stable state by being stored under pressure generated by the hydrostatic pressure of the surrounding sea environment. In order for the low pressure liquid product exiting the third separator 111 to be able to enter the pressurised storage tank 11, a pump may be provided between the third separator and the storage tank 11. Further, in order to store the liquid product at the correct temperature (e.g. in order to maintain the semi-stable liquid product in a stable state) a heat exchanger may be provided between the third separator 111 and the storage tank 11. The heat exchanger may heat or cool the liquid product as necessary.