Collection system for solid particles accumulating on the bottom of a subwater oil / water separation station, subwater water disposal facility and facility control process

Abstract

The present invention relates to a system for collecting solid particles that accumulate at the bottom of a subsea oil / water separation station (12) of a subsea wastewater disposal facility produced during the subsea production of hydrocarbons at great depths, comprising at least one vertical drainage channel (22) intended to discharge into a lower part of a horizontal body (14) of the oil / water separation station, an evacuation conduit (20) intended to be positioned horizontally under said horizontal body of the oil / water separation station and into which the drainage channel discharges, and a high-pressure liquid sludge ejector (28) having a suction orifice (26) connected to the evacuation conduit (20) by means of a feed valve.

Description

1 / 17 SYSTEM FOR COLLECTING SOLID PARTICLES THAT ACCUMULATE AT THE BOTTOM OF A SUBMARINE OIL / WATER SEPARATION STATION, SUBMARINE WATER DISPOSAL INSTALLATION AND INSTALLATION CONTROL PROCESS Technical expertise

[0001] The present invention relates to the general field of deep-sea subsea hydrocarbon production, particularly of oil and gas. It relates more precisely to the evacuation of solid particles that accumulate during the removal of water produced during such subsea hydrocarbon production. Previous technique

[0002] In current deepwater subsea hydrocarbon production configurations, the configuration generally chosen is that of connecting subsea production wells, directly or via a subsea manifold, to a floating production plant.

[0003] This plant is generally made up of a floating unit intended for the production, storage, and transfer of oil (called FPSO in English for “Floating production storage and offloading”) to an oil tanker that regularly moores at a fixed location on the sea surface, near the subsea production field, to collect the oil produced.

[0004] The FPSO, with primary production facilities on its bridge, routinely performs the separation and treatment of production fluids (gas, oil, and produced water). With regard to the latter fluid, the classic surface treatment facility consists of oil removal hydrocyclones, possibly supplemented by a degassing and / or flotation unit. Petition 870260077401, dated 04 / 08 / 2026, page 5 / 54 2 / 17 in order to allow its discharge into the sea with a reduced oil content (usually less than 30 ppm).

[0005] It is also known to use subsea systems for separating and treating produced water from production fields, especially at great depths and for high water contents of the produced oil, the produced water generally being injected into a rocky reservoir.

[0006] In fact, as opposed to a surface-produced water treatment setup, this subsea setup can substantially increase oil production by reducing wellhead pressure through the elimination of water column within the ascending column to the floating production unit (FPSO).

[0007] The reduction in wellhead pressure due to subsea water removal can be significant, and it is greater for greater water depths and higher water content in the produced oil. This condition of increased water content in the produced oil is quite frequent in most oil production fields, especially during the latter part of the exploration period, when the aquifer tends to reach the production wells.

[0008] However, allowing for increased production due to reduced pressure at the wellhead (which causes higher transfer pressure at the bottom) during the second half of the oil field's production life, when the water content of the oil exceeds 50%, the total flow rate (produced water and oil) from the wells increases and the drag forces around the well also increase, which can also cause an increase in the production of fine and solid particles that come from the formation (sand, silt, clay, etc. - referred to below as sand).

[0009] In practice, the flow from the production wells passes through an operating multiphase cyclone desander. Petition 870260077401, dated 04 / 08 / 2026, page 6 / 54 3 / 17 continuous (preferably with a ceramic lining) that removes most of the sand load, even in case of a sudden increase in sand, in a continuous manner. The low-pressure liquid sludge flow from the multi-stage desander is "pumped" by a liquid sludge ejector (which has an internal ceramic lining to increase erosion resistance), which is driven by a high-pressure water motor flow.

[0010] Any sudden increase in sand production can be managed by this multi-phase desander. Furthermore, a more persistent increase in sand load, due for example to sand retention problems within one of the wells producing for a long-ratio subsea oil / water separation station, can be compensated to some extent by forcing an increase in the flow rate of liquid mud to be rejected, thereby increasing the flow rate of high-pressure ejection water thanks to an increased opening of the control valve.

[0011] The hydrocarbon, water and gas effluents from the multiphase grit chamber - without most of the sand loads, which are removed by this device - are sent to a subsea oil / water separation station, for example to a modular liquid / liquid gravity separation device consisting of a plurality of tubes that form parallel loops (called spools) that can be installed on the seabed (separator called “SpoolSep” by the Applicant).

[0012] A portion of the residual solid particles, which were not removed by the multiphase desander and continue to move with the liquid, may eventually settle inside the pipes of the subsea oil / water separation station, due to the low fluid velocity within this equipment, which is required for good oil-water separation. Petition 870260077401, dated 04 / 08 / 2026, p. 7 / 54 4 / 17

[0013] The amount of sand likely to settle inside the pipes will probably be very small and will likely consist of very small particles, as the upstream multi-phase desander will remove most of the sand load and the larger particles. However, the oil / water separation station is expected to operate for several years during the duration of the seabed exploration, and even small amounts of tiny solid particles can form a significant layer at the bottom of the pipes if they are not removed periodically.

[0014] To solve this problem, it is known that systems for collecting sand accumulated at the bottom of the oil / water separation station pipes are used. For example, reference can be made to document US 9,359,878, which describes the use of sand traps placed along all the pipes of the oil / water separation station to periodically collect the sand accumulated at the bottom of these pipes. However, the collection system described in this document has several drawbacks, notably the need to multiply the sand traps and associated centrifugal evacuation devices, and its relatively complex implementation. Statement of the invention

[0015] The invention therefore has as its main objective to propose a system for collecting solid particles that accumulate at the bottom of a subsea oil / water separation station that does not present the aforementioned drawbacks.

[0016] According to the invention, this objective is achieved thanks to a system for collecting solid particles that accumulate at the bottom of a subsea oil / water separation station of a subsea wastewater disposal facility produced during the subsea production of hydrocarbons at great depths, comprising at least one vertical drainage channel intended to Petition 870260077401, dated 04 / 08 / 2026, page 8 / 54 5 / 17 discharges into a lower part of a horizontal body of the oil / water separation station, an evacuation conduit intended to be positioned horizontally under said horizontal body of the oil / water separation station and into which the drainage channel discharges, and a high-pressure liquid sludge ejector having a suction orifice connected to the evacuation conduit by means of a feed valve.

[0017] The collection system according to the invention is notable in that it features a passive network of pipes connected to a high-pressure liquid sludge ejector, which allows for the continuous and periodic removal of sand accumulated at the bottom of the oil / water separation station body. In particular, the collection system according to the invention has a simplified design and maintenance and is highly reliable, notably protected against failures. Furthermore, the collection system according to the invention allows for the independent cleaning of each pipe in the oil / water separation station body, thereby removing accumulated deposits, thus preventing the oil / water separation station from becoming completely inoperable during this cleaning.

[0018] In addition, this suction evacuation configuration via a dedicated liquid mud ejector increases the flexibility of the collection system with respect to evacuation flow rate (by activating the motive flow), which further improves the flexibility of this continuous sand removal configuration in the event of abnormal sand production from the wells.

[0019] Even if residual sand is deposited within the body of the oil / water separation station, the regular operation of the collection system according to the invention will ensure proper management of the sand bed that may eventually form within the oil / water separation station. This collection system, without moving parts Petition 870260077401, dated 04 / 08 / 2026, page 9 / 54 6 / 17 with no internal components, it is extremely reliable and, if functioning correctly, it should be used periodically to prevent highly concentrated sludge. Furthermore, the only valve used to enable this operation is remotely operated from the FPSO. The operating frequency is low (usually once a week or even less), which is not a problem; in addition, a connection of the rinse pipeline upstream of this valve can prevent the presence of sand near the valve just before its closure after a rinse operation.

[0020] The body of the subsea oil / water separation station may be cylindrical and comprise in its lower part a plurality of holes spaced longitudinally from each other, each of which leads into a drainage channel. In this case, the holes formed in the lower part of the body of the subsea oil / water separation station are preferably aligned according to a longitudinal axis tangent to the cylindrical shape of the body.

[0021] In another embodiment, the body of the subsea oil / water separation station is cylindrical and comprises in its lower part a continuous longitudinal slit that opens into a drainage channel formed by two parallel plates. In this channel, the drainage channel advantageously comprises a plurality of crossbeams that connect the two plates to each other in order to stiffen the body of the subsea station and the drainage channel.

[0022] Preferably, the evacuation pipe has a diameter larger than the diameter of the drainage channel.

[0023] The suction orifice of the liquid sludge ejector can be connected to a longitudinal downstream end of the evacuation conduit.

[0024] Also preferably, the evacuation pipe is connected at one longitudinal end to a high-pressure water line. Petition 870260077401, dated 04 / 08 / 2026, page 10 / 54 7 / 17 pressure in order to allow rinsing with water of the evacuation duct.

[0025] The invention also relates to a subsea disposal plant for water produced during the subsea production of hydrocarbons at great depths, comprising a desander continuously fed with fluids coming directly from at least one hydrocarbon production well, a subsea oil / water separation station fed with fluids coming from the desander, and a system for collecting solid particles that accumulate at the bottom of the oil / water separation station as defined above.

[0026] Preferably, the oil / water separation station is a modular liquid / liquid gravity separation device whose body consists of a plurality of tubes forming parallel loops, the solid particle collection system comprising an evacuation conduit positioned horizontally under each tube of the oil / water separation station body and a high-pressure liquid sludge ejector common to the set of evacuation conduits.

[0027] The invention also relates to a process for controlling the installation as defined above, in which the desander, the oil / water separation station, and the solid particle collection system are put into continuous operation, the high-pressure liquid sludge ejector feed valve being periodically opened to allow cleaning of solid particle deposits within the evacuation conduit of the solid particle collection system. Brief description of the drawings

[0028] Figure 1 schematically and partially represents a subsea wastewater disposal system according to one embodiment of the invention. Petition 870260077401, dated 04 / 08 / 2026, page 11 / 54 8 / 17

[0029] Figure 2 is a view of a collection system that equips the installation in Figure 1.

[0030] Figure 3 shows a collection system according to another embodiment of the invention. Description of the modes of implementation

[0031] The invention applies to the subsea production and treatment of hydrocarbons, notably oil and gas, at great depths (i.e., greater than 700 meters) from oil fields that exhibit a growing increase in water content. It refers more precisely to the collection (or removal) of solid particles accumulated within the oil / water separation station of the subsea produced water disposal facility.

[0032] The increase in water content of produced oil has become very frequent in most oil production fields, especially during the latter part of the exploration period, when the aquifer tends to reach the production wells.

[0033] Figure 1 represents an example of a deep-sea subsea hydrocarbon production facility 2 from an oil production field 4.

[0034] Typically, a deep-sea oil production field is explored at a water depth of between 1000 m and 3000 m. It consists of a plurality of hydrocarbon production wells designed to collect oil and gas from an oil reservoir within the reservoir rock.

[0035] The extracted hydrocarbons are typically sent to a production unit 6 on the surface, for example a floating production, storage and offloading unit (FPSO). Petition 870260077401, dated 04 / 08 / 2026, page 12 / 54 9 / 17 storage and offloading”), via submarine pipelines and ascending columns (not shown).

[0036] Before going up to production unit 6, the hydrocarbons extracted from the oil reservoir are treated at seabed level to notably separate the produced oil from the water contained within the latter and eliminate fine and solid particles that come from the reservoir rock (sand, silt, clay, etc. - referred to below as sand).

[0037] For this purpose, the subsea hydrocarbon production facility 2 notably comprises a desander 8 that is fed with fluids from the hydrocarbon production wells 4. For example, the desander is a multiphase cyclone desander (preferably having a ceramic lining) that operates continuously in order to remove most of the sand load, including in the event of a sudden increase in sand.

[0038] The low-pressure liquid sludge flow from the desander 8 is continuously drawn in by a liquid sludge ejector 10 (which preferably has an internal ceramic lining to increase erosion resistance), which is driven by a high-pressure water motor flow controlled by the feed valve (on or off) 34. The liquid sludge flow is then sent to the production unit 6 for treatment.

[0039] The hydrocarbon, water and gas effluents from the desander 8 (without most of the sand loads, which are removed by this device) are sent to a subsea oil / water separation station 12.

[0040] Different types of subsea oil / water separation stations can be used. In the embodiment shown in Figure 1, it will be possible in particular to use a modular separation device. Petition 870260077401, dated 04 / 08 / 2026, page 13 / 54 10 / 17 gravitating liquid / liquid body consisting of a plurality of cylindrical tubes 14, without internal elements, forming parallel loops (called coils, four in number in the example in figure 1) that can be installed on the seabed due to the fact that their reduced diameter provides high resistance to external / internal differential pressure.

[0041] An example of such a modular liquid / liquid gravity separation device (called “SpoolSep”) is described in publication WO 2011 / 161343 on behalf of the Applicant. The large length and circular cross-section of the tubes in this separation device allow for high differential pressure resistance in a relatively small weight configuration. On the other hand, its modular configuration allows for flexible installation conditions, even for high-capacity systems (high inlet flow rate). Thus, this device allows for the primary separation of bulk raw water at any desired pressure, especially at low pressure, regardless of the surrounding pressure (water depth).

[0042] As represented in figure 1, this subsea oil / water separation station 12 also comprises a hydrocarbon inlet 12a, an oil and gas outlet 12b which is connected to the production unit 6 on the surface by means of an ascending column by means of a pump 51, and a water outlet 12c which is for example intended to be connected by means of a high pressure pump 52 to a preferably flat gravity oil / water separation reservoir 18 resting on the seabed.

[0043] A portion of the residual solid particles that were not removed by the desander 8 and that continue to move with the liquid may eventually settle inside the conduits, due to the low velocity of the fluids within this equipment, which Petition 870260077401, dated 04 / 08 / 2026, p. 14 / 54 11 / 17 is required for good oil-water separation.

[0044] For this purpose, according to the invention, it is planned to install a system for collecting the solid particles that accumulate at the bottom of the oil / water separation station.

[0045] More precisely, an evacuation conduit 20 is positioned horizontally under the body of the oil / water separation station 12. In the example of an oil / water separation station of the type illustrated in figure 1, an evacuation conduit 20 is positioned under each pipe 14 that forms the parallel loops.

[0046] For each evacuation conduit 20, the collection system according to the invention also comprises a plurality of vertical drainage channels 22, each of which is intended to discharge into a lower part of the pipes 14 of the oil / water separation station and to open into the evacuation conduit.

[0047] As represented more precisely in figure 2, the lower longitudinal axis T that is tangent to the cylindrical body of the tubes 14 of the oil / water separation station has a plurality of holes 24 that are spaced longitudinally from each other and that each of them leads into a drainage channel 22.

[0048] Drainage channels 22 (and holes 24) have a diameter d that depends on the diameter of pipe 14 of the oil / water separation station, and is designed to drain liquid sludge at low speed. Typically, this diameter d is on the order of about 2 to 8 mm.

[0049] Drainage channels 22 are devoid of internal elements and vortex breakers at the top, meaning pieces of small-diameter vertical pipes that open at the bottom of pipes 14. This configuration aims to prevent any device that could be obstructed by liquid mud.

[0050] The distance between the holes 24 on the bottom of the tubes Petition 870260077401, dated 04 / 08 / 2026, page 15 / 54 12 / 17 of the oil / water separation station, meaning the distance between two consecutive drainage channels 22 is variable and calculated (by fluid dynamics analysis software) based on the actual conditions of a special route in order to limit the maximum height of the sand layer at the bottom of the pipe. Typically, this distance is about 1 m.

[0051] Each drainage channel 22 that leaves the pipe 14 of the oil / water separation station descends within the same horizontal evacuation conduit 20 (which has a diameter D larger than that of the drainage channels - generally on the order of 5 to 10 cm in diameter).

[0052] Furthermore, as shown in Figure 1, the downstream end of each horizontal evacuation conduit 20 is connected to the suction port 26 of a high-pressure liquid slurry ejector 28 by means of a feed valve 30 (of the on / off type).

[0053] In order to facilitate the periodic cleaning of sand deposits at the bottom of the oil / water separation station's pipes 14, each of them can have a corresponding feed valve 30 opened at a time and the slurry from the bottom of that pipe is suctioned through several vertical drainage channels 22 connected to the corresponding evacuation conduit 20.

[0054] The suction speed control is done by injecting high-pressure water into the liquid sludge ejector 28 via the adjustment of the opening of a modulating regulating valve 32 (or by adjusting a narrowing adjustable by a plateau). This operation allows the controlled suction of a portion of the liquid from the oil / water separation station tube 14 in order to avoid the formation of drainage vortices inside the tube so as not to disturb its operation.

[0055] This elimination of water at the bottom of the station's pipes Petition 870260077401, dated 04 / 08 / 2026, page 16 / 54 13 / 17 Oil / water separation will transport solid particles (sand, silt, etc.) that will eventually settle at the bottom of the exhaust pipes. Even if a small amount of solid particles remains at the bottom of the pipes after the suction operation, between two adjacent holes 24 at the bottom of the pipe, the height of this sand layer is limited because the next suction period will drag the particles from the top to fall, where they will be replaced by new ones.

[0056] Thus, this repeated process prevents any eventual compaction of the particle layer by periodically forcing its release through the vertical drainage channels. No increase in the residual sand layer is expected, the fluid dynamics within the oil / water separation station body during rinsing being designed to prevent this phenomenon, in accordance with an appropriate collection system design.

[0057] The diameter d of the vertical drainage channels 22 may eventually vary depending on their distance to the liquid sludge ejector 28. This optimized configuration can be determined during the design phase, taking into account specific routing data, and will be established in order to obtain appropriate suction through the different vertical drainage channels.

[0058] Alternatively, a study using fluid dynamics analysis software can show that, for a specific route (data referring to the particle size distribution of solid particles), solid particles also having a selective size distribution can only settle a certain length from the inlet of the oil / water separation station pipes (the larger solid particles remaining close to the inlet). This is likely in a widely dispersed particle size distribution. In this case, the collection system according to the invention can be equipped with a conduit diameter configuration of Petition 870260077401, dated 04 / 08 / 2026, page 17 / 54 14 / 17 non-uniform evacuation, in order to optimize the removal of sand along the pipes of the oil / water separation station.

[0059] On the other hand, a high-pressure water line connection 36 (used to feed the high-pressure liquid sludge ejector 28, see figure 1) can also be connected (by means of a valve 38) to each of the upstream ends of the horizontal evacuation conduits 20 of the collection system or immediately upstream of the corresponding feed valve 30, in order to allow rinsing of the evacuation conduits. This offers the advantage of great operational flexibility in case of system malfunction, or to avoid the absence of residual solid particles at the level of the feed valve perforation.

[0060] This high-pressure water rinse could be carried out during the final suction process of the lower part of the oil / water separation station pipes, in order to avoid the accumulation of sand upstream of the corresponding feed valve 30. It is worth noting that during this high-pressure water rinse, an increase in water flow is provided within the horizontal evacuation conduit during the rinsing process, thus facilitating the drainage of the liquid sludge. In normal operation, the expected deposited sand layer is quite reduced and the rinsing process of the conduits should be frequent enough to only generate low-concentration liquid sludge and avoid any increase in height and compaction of the deposited layer, so that no blockage of the rinsing piping network is possible if such operation of this system is carried out.

[0061] Figure 4 represents another embodiment of the collection system according to the invention.

[0062] This mode of implementation differs from that described Petition 870260077401, dated 04 / 08 / 2026, page 18 / 54 15 / 17 previously noted by the fact that each tube 14 of the oil / water separation station comprises in its lower part a continuous longitudinal slit 40 that opens into a vertical drainage channel 22' formed by two parallel plates 42, 44, this drainage channel opening into a suction conduit 20.

[0063] With this method of implementation, it is virtually impossible to have a growing layer of sand on the underside of the oil / water separation station body.

[0064] On the other hand, in order to stiffen the drainage channel 22' and thus reduce the thickness of the plates 42, 44, the drainage channel comprises a plurality of crossbeams 46 that connect the two plates to each other.

[0065] The process of collecting solid particles must be repeated for each of the oil / water separation station tubes in order. The duration of this operation, as well as its frequency, will be determined operationally based on the amount of solid particles present at the bottom of the tubes, which should be very small due to the desander 8 that operates continuously upstream, as already explained.

[0066] The determination of the quantity of solid particles can be carried out with the aid of a surveillance system (sonar type, for example) or by a sand bed surveillance system, or even directly evaluated by the operator by aligning the flow produced by the subsea system at a separation test station located on the FPSO (for the rinsing time) in order to allow the evaluation of the quantity of solid particles. Once the frequency of operation has been determined, it can be automated via the main control system. In this case, acoustic detectors of solid particles should be installed in the collection system in order to provide immediate information in the event of certain sudden arrivals of Petition 870260077401, dated 04 / 08 / 2026, page 19 / 54 16 / 17 solid particles (e.g., accidental sand production). Based on this information, the exploration team could examine the required frequency of rinsing operations in order to optimize the functioning of the collection system.

[0067] It will be noted that even if residual sand is deposited inside the oil / water separation station pipes, the regular operation of the collection system according to the invention will ensure proper management of the sand bed that may eventually form inside the pipes.

[0068] This collection system, with no moving parts or internal components, is extremely reliable and, if functioning correctly, is used periodically to prevent highly concentrated sludge. Furthermore, the single on-or-off valve (one per sludge evacuation conduit) used to enable this operation is remotely operated from the FPSO. The operating frequency is low (usually once a week or even less), which is not a problem; moreover, a connection of the collection system upstream of this valve can prevent the presence of sand near the valve just before its closure after a rinsing operation.

[0069] The increased flexibility, reliability and robustness of the collection system according to the invention result in: - Regarding the possibility of managing sudden and large arrivals of sand, as well as a permanent increase in sand production, due to a problem located in one of the production wells. The desander has this characteristic of handling sudden and large arrivals of sand and the possibility of increasing the evacuation flow rate - by increasing the water flow rate of the suction ejector - which allows for handling a permanent increase in the sand load. - Ducts with open pipes in order to gently eliminate Petition 870260077401, dated 04 / 08 / 2026, page 20 / 54 17 / 17 the sand layer, through a flow of diluted mud injected continuously into a multi-phase pipeline (diluted further with production) using a dedicated mud ejector - no moving parts or internal elements required - virtually nothing goes wrong. - Limited number of on / off feed valves required (one per coil of the oil / water separation station). - Possibility of rinsing these feed valves after each operation (thus avoiding any sand residue immediately upstream / downstream of the valves). - No interruption of normal separation within the coils of the oil / water separation station, even during the periodic process of removing sand from the tubes. - Possibility of regulating the flow of excess water produced by the sand evacuation process, modulating the time required for the suction process, thus minimizing the impact on surface production activities. - No mud runoff due to sand in active pumping systems, as the liquid mud ejectors are designed to send mud runoff downstream of the multiphase pump, directly into the multiphase pipeline. - An economical solution based solely on pipes, a reduced number of on / off feed valves, and passive elements (sand ejectors with a ceramic core that resists erosion). Petition 870260077401, dated 04 / 08 / 2026, page 21 / 54

Claims

1 / 3 CLAIMS 1. A system for collecting solid particles that accumulate at the bottom of a subsea oil / water separation station (12) of a subsea disposal facility for water (2) produced during the subsea production of hydrocarbons at great depths, characterized in that it comprises at least one vertical drainage channel (22) intended to discharge into a lower part of a horizontal body of the oil / water separation station, an evacuation conduit (20) intended to be positioned horizontally under said horizontal body of the oil / water separation station and into which the drainage channel (22) discharges, and a high-pressure liquid sludge ejector (28) having a suction orifice (26) connected to the evacuation conduit (20) by means of a feed valve (30),wherein the oil / water separation station is a modular liquid / liquid gravity separation device whose body consists of a plurality of tubes (14) forming parallel loops; and wherein the feed valve (30) is of the all or nothing type.

2. System according to claim 1, characterized in that the body of the subsea oil / water separation station is cylindrical and comprises in its lower part a plurality of holes (24) spaced longitudinally from each other and each of which leads into a drainage channel (22).

3. System according to claim 2, characterized in that the holes (24) formed in the lower part of the body of the subsea oil / water separation station are aligned according to a longitudinal axis (T) tangent to the cylindrical shape of the body.

4. System according to claim 1, characterized in that the body of the submarine oil / water separation station Petition 870260077401, dated 04 / 08 / 2026, page 22 / 54 2 / 3 is cylindrical and comprises in its lower part a continuous longitudinal slit (40) that leads into a drainage channel (22') formed by two parallel plates (42, 44).

5. System according to claim 4, characterized in that the drainage channel (22') comprises a plurality of crossbeams (46) that connect the two plates (42, 44) to each other in order to stiffen the drainage channel.

6. System according to any one of claims 1 to 5, characterized in that the evacuation conduit (20) has a diameter (D) greater than the diameter (d) of the drainage channel (22).

7. System according to any one of claims 1 to 6, characterized in that the suction orifice (26) of the liquid sludge ejector (28) is connected to a longitudinal downstream end of the evacuation conduit.

8. System according to any one of claims 1 to 7, characterized in that the evacuation conduit (20) is connected at one longitudinal end to a high-pressure water line (36).

9. Subsea water disposal installation (2) produced during subsea hydrocarbon production at great depths, characterized in that it comprises a desander (8) continuously fed with fluids coming directly from at least one hydrocarbon production well (4), a subsea oil / water separation station (12) fed with fluids coming from the desander, and a system for collecting solid particles that accumulate at the bottom of the oil / water separation station as defined in any one of claims 1 to 8, wherein the oil / water separation station is a modular liquid / liquid gravity separation device of which the body is Petition 870260077401, dated 04 / 08 / 2026, page.23 / 54 3 / 3 consisting of a plurality of tubes (14) that form parallel loops and the solid particle collection system comprises an evacuation conduit (20) positioned horizontally under each tube of the oil / water separation station body and a high-pressure liquid sludge ejector (28) common to the set of evacuation conduits.

10. Installation control process as defined in claim 9, characterized in that the desander, the oil / water separation station, and the solid particle collection system are put into continuous operation, the high-pressure liquid sludge ejector feed valve being periodically opened to allow cleaning of solid particle deposits within the evacuation conduit of the solid particle collection system. Petition 870260077401, dated 04 / 08 / 2026, page 24 / 54

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