Subsea installation and process for processing gas from a subsea gas production field

Abstract

Installation and subsea method for processing gas from a subsea gas production field. The invention relates to an installation and method for processing gas (2) from a subsea gas production field, comprising a cooling module (6) supplied with a gas / liquid mixture directly from at least one subsea gas field (4), and a gas / liquid separation module (8) delivering treated gas to a gas export line (14) and liquid to a liquid export line (16), the gas / liquid separation module comprising a gas / liquid separator (18) and a coalescing filter separator (20) mounted in series, the gas / liquid separator having a gas outlet (18b) connected to an inlet (20a) of the coalescing filter separator and a liquid outlet (18c) connected to the liquid export line (16),The coalescing filter separator has a gas outlet (20b) connected to the gas export line and a liquid outlet (20c) connected to the liquid export line. Figure for the abbreviation: Fig. 1.

Description

Title of the invention: Subsea installation and process for processing gas from a subsea gas production field technical field

[0001] The present invention relates to the general field of subsea gas production. More specifically, it relates to the subsea processing of gas for export to offshore or onshore facilities. Previous technique

[0002] In current configurations, the export of gas from subsea production fields, and in particular from condensate gas fields, is carried out in part by long pipelines linking the production fields to the surface installations.

[0003] Gas export facilities used in practice generally do not include any treatment unit. The produced gas is typically exported via a pipeline without prior treatment (apart from the addition of chemicals to prevent solid deposits, limit corrosion, etc.). Publications WO 2015 / 181386, WO 2016 / 192813 and WO 2014 / 079515 are also known concerning gas export facilities that include, in particular, a cooling module supplied with a gas / liquid mixture directly from the gas fields, and a gas / liquid separation module that separates the gas from the liquid for transport to surface facilities via dedicated export lines.

[0004] This type of installation is subject to various problems that need to be addressed. One of the main problems encountered is the accumulation of liquid that can occur at low points in the gas export line. This problem arises when the gas velocity becomes insufficient to carry the liquid along, causing blockage in the gas export line. Another problem is ensuring that the pressure of the exported gas remains sufficient to allow efficient export to surface installations. It is also important to limit, or even prevent, the formation of solid deposits (hydrates, paraffins, etc.) in the gas export line. Description of the invention

[0005] The main object of the present invention is therefore to propose an underwater treatment installation which makes it possible to solve the problems mentioned above.

[0006] This objective is achieved through a gas processing installation for gas from a subsea gas production field, comprising: - a cooling module supplied with a gas / liquid mixture sourced directly from at least one subsea gas field to cool the gas to a temperature that allows the heavy hydrocarbons and water present in the mixture to condense; and - a gas / liquid separation module supplied with gas / liquid mixture from the cooling module and delivering treated gas to a gas export line and liquid to a liquid export line; - and in which, according to the invention, the gas / liquid separation module comprises a gas / liquid separator and a coalescing filter separator mounted in series, the gas / liquid separator having a gas outlet which is connected to an inlet of the coalescing filter separator and a liquid outlet which is connected to the liquid export line, the coalescing filter separator having a gas outlet which is connected to the gas export line and a liquid outlet which is connected to the liquid export line.

[0007] The gas processing plant according to the invention is notable in particular in that its gas / liquid separation module comprises a gas / liquid separator mounted in series with a coalescing filter separator, which gives it high separation performance. More generally, the plant according to the invention is based on lowering the dew point of the gas / liquid mixture by combining a cooling module and a high-performance gas / liquid separation module, which allows for passive gas export (i.e., without the need for a compressor). Such a plant is therefore particularly advantageously suited to deep-sea gas fields located far from the shore. Furthermore, the dew point of the gas / liquid mixture is lowered to a level that subsequently allows for gas export while the gas remains entirely (or almost entirely) in the gaseous phase throughout the export process.

[0008] More specifically, the cooling module of the installation according to the invention allows the heavy hydrocarbons and water present in the gas / liquid mixture, which would normally condense in the gas export line, to condense. The cooling also takes place at a lower temperature than that reached by the gas in the gas export line.

[0009] The cooling module may include a passive heat exchanger or an active heat exchanger. In the latter case, it may further include a Joule-Thomson effect valve or a turbo-expander installed downstream of the heat exchanger.

[0010] The gas / liquid separator of the gas / liquid separation module can be a gravity separator, a cyclone separator, or a centrifugal separator.

[0011] Preferably, the gas / liquid separation module further comprises a gas pretreatment unit disposed between the gas / liquid separator and the filter separator.

[0012]

[0013]

[0014]

[0015]

[0016]

[0017]

[0018] coalescence in order to eliminate solid particles that could be carried along with the gas and also to reduce the liquid content before the coalescing filter separator, with the aim of extending the service life of the coalescing filter separator. The coalescing filter separator can be integrated into the gas / liquid separator. The gas export line can advantageously be devoid of gas compression means. As for the liquid export line, it can advantageously be equipped with liquid pumping means. Preferably, the gas / liquid separation module includes two coalescing filter separators installed in parallel to ensure redundancy in case of a problem on one of the separators and to ensure continuity of production during maintenance phases of the coalescing filters. Preferably, the installation also includes means for injecting a hydrate formation inhibitor upstream of the cooling module and / or means for injecting a paraffin inhibitor upstream of the cooling module. These injection means limit, or even prevent, the formation of solid deposits (hydrates, paraffins, etc.) in the installation as well as in the gas and liquid export lines. Correspondingly, the invention also relates to a method for the underwater treatment of gas from an underwater gas production field, comprising successively: - a stage of cooling the gas / liquid mixture directly from at least one subsea gas production field so as to condense heavy hydrocarbons and water and bring the gas / liquid mixture to a temperature lower than that of the gas in a gas export line; and - a subsea gas / liquid separation stage to deliver treated gas to a gas export line and liquid to a liquid export line; and in which - the gas / liquid separation stage includes a first gas / liquid separation stage followed directly by a second gas / liquid separation stage by coalescence in order to lower the dew point of the treated gas to a level allowing its export in single-phase form. The invention also relates to an application of the process as defined above to a condensate gas field in operation or to a condensate gas field not yet in operation. Brief description of the drawings

[0019] [Fig.1] Fig.1 is a schematic view of a subsea gas processing installation according to the invention.

[0020] [Fig.2] The [Fig.2] is a schematic view of an example of a coalescing filter separator of the installation according to the invention. Description of the implementation methods

[0021] The invention relates to the subsea processing of gas from a subsea gas production field. It finds a preferred (but not limited) application in subsea gas condensate fields located at great depths and far from the shore.

[0022] Fig. 1 represents an example of a subsea gas processing plant 2 according to the invention supplied by one or more subsea gas production fields 4.

[0023] Typically, this gas processing installation 2 includes a cooling module 6 which is supplied with gas / liquid mixture directly from the subsea gas field(s) 4, and a gas / liquid separation module 8 which is supplied with gas / liquid mixture from the cooling module.

[0024] The cooling module 6 has the particular function of cooling the gas / liquid mixture to bring it to a temperature enabling the heavy hydrocarbons and water present in the mixture to condense (and which would normally condense further downstream in the gas export line).

[0025] For this purpose, the cooling module 6 of the example embodiment of [Fig.1] includes a passive heat exchanger 10 whose inlet is directly connected to the outlet of the wellhead installations of the subsea gas field(s) 4, and a Joule-Thomson effect valve 12 positioned at the outlet of the passive heat exchanger 10.

[0026] The Joule-Thomson valve 12 is controlled to obtain a constant and predetermined pressure at the outlet of the gas export line (ordinarily, this type of valve is controlled to maintain a specific temperature at the valve outlet). By knowing the characteristics of the gas export line, it is thus possible to control the pressure downstream of the Joule-Thomson valve. Incidentally, by ensuring a certain gas pressure level at the outlet of the gas export line, a maximum temperature is ensured at the outlet of the Joule-Thomson valve 12.

[0027] As an alternative to the passive heat exchanger, an active heat exchanger may be provided, possibly associated with a downstream Joule-Thomson effect valve. This active heat exchanger may be a liquid / gas exchanger with seawater pumping, a gas / gas exchanger with reuse of the cold gas from the station outlet, a heat exchanger with heat transfer fluid and refrigeration loop, etc.

[0028] As an alternative to the Joule-Thomson effect valve, a turbo-expander can be provided installed downstream of the passive heat exchanger (or downstream of the active heat exchanger where applicable).

[0029] The gas / liquid separation module 8 receives the cooled gas / liquid mixture from the cooling module as input and delivers both treated gas to a gas export line 14 and liquid to a liquid export line 16.

[0030] According to the invention, the gas / liquid separation module 8 comprises a gas / liquid separator 18 and a coalescing filter separator 20 which are mounted in series.

[0031] More specifically, the gas / liquid separator 18 has a gas / liquid mixture inlet 18a which is connected to the outlet of the cooling module 6, a gas outlet 18b which is connected to an inlet of the coalescing filter separator 20 and a liquid outlet 18c which is connected to the liquid export line 16.

[0032] As for the coalescing filter separator 20, it has an inlet 20a which is connected to the gas outlet 18b of the gas / liquid separator 18, a gas outlet 20b which is connected to the gas export line 14 and at least one liquid outlet 20c which is connected to the liquid export line 16.

[0033] The gas / liquid separator 18 of the gas / liquid separation module can be a gravity separator, a cyclone separator, or a centrifugal separator. For example, a vertical separator with multiple pipes can be used.

[0034] In connection with [Fig.2], we will now describe an example of the architecture of the coalescing filter separator 20.

[0035] Coalescence is the process by which the fine liquid droplets of the gas / liquid mixture created by turbulence within the separator agglutinate to form larger droplets. This phenomenon allows for better gravitational separation of the liquid during its passage through the separator.

[0036] In the example embodiment of [Fig.2], the inlet 20a of the coalescing filter separator 20 is located in the lower part of the separator, the gas outlet 20b is located in the upper part of the separator, and two liquid outlets are provided, namely: an outlet in the lower part 20c-1, and an outlet in the intermediate part 20c-2.

[0037] The gas laden with liquid droplets that enters the separator through inlet 20a undergoes a first phase of gravity separation in the lower part 22 of the separator. Part of the liquid resulting from this separation is discharged through the liquid outlet in the lower part 20c-1.

[0038] The gas / liquid mixture then rises towards the upper part 24 of the separator, passing through one or more filter cartridges 26 in which the Liquid droplets clump together to form larger droplets. These droplets fall back down and collect at the bottom of the upper part 24 of the separator before being discharged through the outlet in the intermediate part 20c-2. The gas, now free of these liquid droplets, is discharged upwards through the gas outlet 20b.

[0039] It should be noted that the coalescing filter separator can be a separate device from the gas / liquid separator or it can be integrated into it.

[0040] It should also be noted that the gas / liquid separation module may advantageously include two coalescing filter separators installed in parallel to ensure redundancy in case of failure.

[0041] Preferably, the gas / liquid separation module 8 further comprises a gas pretreatment unit 27 which is disposed between the gas / liquid separator 18 and the coalescing filter separator 20 in order to remove solid particles which could be carried along with the gas and reduce the liquid content before the coalescing filter separator.

[0042] Preferably also, the liquid export line 16 is equipped with liquid pumping means, typically a submersible pump 29.

[0043] Conversely, the installation according to the invention can make it possible to avoid the gas export line 14 having to resort to means of gas compression.

[0044] Preferably, the installation further includes means for injecting a hydrate formation inhibitor 28 upstream of the cooling module 6. Similarly, the installation may also include means for injecting a paraffin inhibitor 30 upstream of the cooling module.

Claims

Demands

1. Subsea installation (2) for processing gas from a subsea gas production field, comprising: - a cooling module (6) supplied with gas / liquid mixture directly from at least one subsea gas field (4) in order to cool the gas to a temperature enabling the condensation of heavy hydrocarbons and water present in the mixture; and - a gas / liquid separation module (8) supplied with gas / liquid mixture from the cooling module (6) and delivering treated gas to a gas export line (14) and liquid to a liquid export line (16);- characterized in that the gas / liquid separation module (8) comprises a gas / liquid separator (18) and a coalescing filter separator (20) mounted in series, the gas / liquid separator having a gas outlet (18b) which is connected to an inlet (20a) of the coalescing filter separator and a liquid outlet (18c) which is connected to the liquid export line (16), the coalescing filter separator having a gas outlet (20b) which is connected to the gas export line and a liquid outlet (20c) which is connected to the liquid export line.;

2. Installation according to claim 1, wherein the cooling module (6) comprises a passive heat exchanger (10) or an active heat exchanger.

3. Installation according to claim 2, wherein the cooling module further comprises a Joule-Thomson effect valve (12) or a turbo-expander installed downstream of the heat exchanger (10).

4. Installation according to any one of claims 1 to 3, wherein the gas / liquid separator (18) of the gas / liquid separation module is a gravity separator or a cyclone separator or a centrifugal separator.

5. An installation according to any one of claims 1 to 4, wherein the gas / liquid separation module (8) further comprises a gas pretreatment unit (27) disposed between the gas / liquid separator liquid (18) and the coalescing filter separator (20) in order to remove solid particles that could be carried along with the gas and reduce the liquid content before the coalescing filter separator.

6. Installation according to any one of claims 1 to 5, wherein the coalescing filter separator is integrated with the gas / liquid separator.

7. Installation according to any one of claims 1 to 6, wherein the gas export line (14) is devoid of gas compression means.

8. Installation according to any one of claims 1 to 7, wherein the liquid export line (16) is provided with liquid pumping means (29).

9. An installation according to any one of claims 1 to 8, wherein the gas / liquid separation module comprises two coalescing filter separators installed in parallel.

10. Installation according to any one of claims 1 to 9, further comprising means for injecting a hydrate formation inhibitor (28) upstream of the cooling module (6).

11. Installation according to any one of claims 1 to 10, further comprising means for injecting paraffin inhibitor (30) upstream of the cooling module (6).

12. A subsea gas processing method for gas from a subsea gas production field, comprising successively: - a step of cooling the gas / liquid mixture directly from at least one subsea gas production field (4) so ​​as to condense heavy hydrocarbons and water and bring the gas / liquid mixture to a temperature lower than that of the gas in a gas export line; and - a subsea gas / liquid separation step to deliver treated gas to a gas export line and liquid to a liquid export line; - characterized in that the gas / liquid separation step comprises a first gas / liquid separation step followed directly by a second gas / liquid separation step by coalescence in order to lower the dew point of the treated gas to a level allowing its export in single-phase form.

13.

14. Application of the process according to claim 12 to an operating condensate gas field. Application of the process according to claim 12 to a gas condensate field not yet exploited.

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