Field of the Invention

The present invention relates to an apparatus for sand removal in a separator vessel and method thereof.

Background of the Invention

In hydrocarbons extraction process, drilling fluids or sludge containing a mixture of water, oil, gas and sand will be transported to a separator for separating the mixture. In the separator, sand would settle at the bottom of the vessel. In due course, the separator will need to be cleaned up to remove the accumulated sand. The removal process may be carried out manually by scooping the sand out of the separator. This cleaning method will require the operation of the separator to be stopped and it may take up to 10 days to complete the cleaning process.

Sand can be prevented from going into the vessel if a desander or filter is installed upstream of the separator. However it is observed that most of the desanders are not able to remove the sand completely from the drilling fluids. Typically, sand particle size under 45 micron will continue to flow through the system. It is important to prevent sand carry over that may damage the downstream equipment.

High pressure water jetting may be used to remove the accumulated sand in the separator vessel. The operation of the separator would need to be stopped to allow this cleaning process to be conducted. The following prior art discloses several water jetting systems used in vessels.

The Chinese patent publication no. CN106755922A discloses a water-jet spraying and iron sand spraying mixed system. The system comprises high-pressure liquid supplying system, iron sand jet generating system, iron sand spraying control system, iron sand recycling system and bracket system. The high-pressure liquid supplying system comprises water tank (1), water purification system (2), high-pressure pump (3), pressure adjusting valve (4) and high-pressure pipe (8). The iron sand jet generating system comprises iron sand tank (5), hydraulic motor (6), ejector (7), mixing tank, throttle valve and iron sand discharging valve. The Chinese patent publication no. CN106823204A discloses a system that includes a discharge valve (5) whose end is connected with a return gas tank (8). A discharge port of the return gas tank is with an end of a return pipeline (15). A sand blasting nozzle (9) is formed with the return pipeline. Another end of the return pipeline is connected with the return gas tank. A control system comprises a programmable logic controller (PLC) system (10) and a monitoring system (11). The valve, an air supply valve group (6) and a material level detecting device (7) are respectively connected to a receiving end of the PLC system. This method is not desirable, as it requires additional spray medium i.e. iron sand.

The PCT publication no. W0201369160 discloses a sand-removal apparatus for a ballast tank of a ship. The apparatus has several nozzles (19) which are provided near tank floor plate (8) of tank compartment (5). A water discharge pipeline (22) is provided to discharge muddy water that is washed away by water sprayed from nozzles. A water feed/discharge control unit (100) is provided, when mud and sand are discharged from a ballast tank (2). A starboard-side water injection drainage pump (11) is operated to feed water into water feed pipeline (13). A port-side water injection drainage pump (21) is operated to discharge muddy water from port-side water discharge pipeline.

The GB patent publication no. GB2509712 discloses a system for washing out sand, silt and mud in a marine vessel. The system has jets of high pressure water that are pumped by a pump (3) from the ducts distributed across the vessel's hull to remove seabed obstructions beneath the hull (1). An inlet pipe (2) is configured to provide water to the pump or battery of pumps. An outlet pipe (4) is configured to deliver water pressurized by the pump to the bottom duct. A valve (5) is arranged in the pipe to control forward flow of water. A duct section is attached into the vessel's hull to distribute pressurized water beneath the hull. A water jet nozzle (7) is fitted in the duct section.

It is observed that a huge amount of water is used to sufficiently remove the sand from the vessel using the existing water jetting systems. Typically, water is jet to the whole bottom area of the vessel to wash away the sand. However, in some instances, sand still remains inside the vessel after prolonged jetting due to inefficient fluidization of the sand. This may be due to ineffective spraying action or clogged nozzles. The nozzles may become clogged due to incorrect sizing of the nozzle. It is to be noted that the sand removal process requires the use of fresh or treated water and not of the sea water where the source of fresh water is scarce in the offshore facilities. When no water supply is available, manual sand removal would be carried out. It is also to be noted that not all separator vessels are equipped with a water jetting system and a desander. Therefore, when the sand accumulated, the operation of the separator or other related equipment need to be stopped to allow a manual sand removal. It is observed that no indication of sand deposit level inside of the separators to guide the spraying action of the jetting system.

In view of the above shortcomings, it is an object of the present invention to provide an improved apparatus for sand removal in a separator vessel. It is another object of the present invention to provide an improved method for sand removal in a separator vessel based on systematic cleaning operation that involves reading the distribution of sand accumulated in the vessel and initiating a sequential and directional spraying actions. The apparatus and method of the present invention provide advantages over the conventional method which includes a minimum water consumption to clean the vessel, a reduction in cleaning time during online and offline modes, increased separator performance, and a continuous operation for sand removal and hydrocarbons extraction processes.

Summary of the Invention

The present invention provides an improved apparatus for sand removal in a separator vessel. The apparatus comprises a jetting system which includes one or more tiers of piping or manifolds to sequentially fluidize and displace sand accumulated in the vessel and discharge the same from the vessel. In one embodiment, the jetting system operation is guided by a probe which provides information on level of medium inside the vessel which includes sand level. In another embodiment the jetting system operates based on the profile of sand accumulated in the vessel, predicted by empirical equations or software. Several methods of determining accumulated sand volume in the vessel includes predictive method based on known sand production rate. This can be based on manual sand sampling and online sand monitoring device. Acoustic sand detectors may be used to determine sand volume entering the vessel. Direct measurement method using a density profiler, and calculation based on the actual sand collected during manual sand removal may also be used. The manifold includes one or more openings to allow a pressurized fluid to be sprayed onto the sand. The opening may include a nozzle or header for discharging a jet of fluid. The spraying or jetting of the fluid from the jetting system is based on one or more readings of the sand distribution in the vessel. A control system is provided to regulate the spraying or jetting actions. The control system includes the use of a probe for reading the sand distribution and concentration or density in the vessel. Based on the reading, the system will initiate one or more spraying/jetting actions from the piping at one or more tiers. Preferably, the spraying/jetting action is performed in sequential and directional manners to fluidize and displace the sand from its settling location to a preferred location that allows sand evacuation from vessel. Preferred evacuation of sand include vessel drain points and/or any other suitable mechanism which include via dedicated eductor piping. In an embodiment, the jetting system may operate automatically based on the readings of the probe or a profiler which is run by a computer system. The profiler may indicate the sand settling profile that can be monitored.

The present invention also provides an improved method for sand removal in a separator vessel comprising the step of sequentially spraying or jetting the sand based on the level and profile of the sand accumulated in the vessel. The method also includes the step of spraying the sand in directional manner. The method further includes the step of reading the sand distribution and concentration or density in the vessel. The steps for initiating the sequential and directional spraying/jetting actions will be based on one or more readings of the probe or a sand settling profile where one or more readings activate the spraying actions of the jetting system.

The spraying or jetting action of the jetting system may be initiated either from one or more manifolds at a tier and followed by one or more manifolds at another tier. The spraying or jetting action of the jetting system may also be initiated by sequencing the operation of jetting nozzles on the manifold. The spraying or jetting action of the jetting system may be initiated when the level of the sand substantially reaches half of a weir height provided in the vessel or when it matches a predetermined reading. A subsequent spraying or jetting action may be initiated when the level of the sand substantially reaches a quarter of the weir height or when it matches one or more predetermined readings.

The method of the present invention allows the removal of sand to be conducted effectively and efficiently as the sequential and directional spraying actions will facilitate the fluidization of the sand which result in the sand that can be easily displaced towards one or more evacuation points. The use of liquid such as water in stages for spraying or jetting the sand would result in a lesser consumption of water compared to a continuous and prolonged spraying/jetting action.

According to the present invention, optimal spray nozzle count and sand evacuation locations/points are correlated to the vessel’s dimension and sand settling profile inside the vessel. The sizing of the nozzles and their orientation are correlated to sand particle size distribution, predicted / actual sand settling profile inside vessel, mixture liquid and solid density difference, and evacuations locations. A low pressure zone is created for the evacuation points at the bottom of the vessel to actively discharge the slurry.

According to the present invention, the sequential jetting or spraying action in the vessel can be operated during online and offline modes of the separator. The online mode means that the vessel is in operation whereas the offline mode means that the vessel is not in operation. With this online jetting facility, continuous operation of the separator and all related equipment in the hydrocarbon extraction process is possible.

Brief Description of the Drawings

The present invention will be described by way of example with reference to the accompanying drawings, in which:

Fig. 1 shows a side view of a diagram of an example of an existing a sand removal system; Fig. 2a shows a plan view of a diagram of an example of a sand removal system according to an embodiment of the present invention;

Fig. 2b shows a side view of the diagram shown in Fig. 2a;

Fig. 3a shows a perspective view of an example of an assembly of a sand removal system according to an embodiment of the present invention; Fig. 3b shows a nozzle arrangement for the sand removal system shown in Fig. 3a;

Fig. 3c shows a piping arrangement for the sand removal system according to an embodiment.

Fig. 4 shows a side view of an exemplary assembly of the sand removal system as shown in Fig. 3a in a separator vessel.

Detailed Description of the Invention

Fig. 1 shows an example of a sand removal system in a separator vessel (110). The system is used to determine the optimal jetting actions for displacing and discharging the accumulated sand in the vessel. As shown in Fig. 1, the system includes a jetting system for discharging a pressurized fluid such as water and drain outlets for discharging slurry from the vessel. The jetting system is connected to a fluid/water supply (160). The jetting system includes nozzles or jetting headers. In this example, the vessel may be provided with one or more drain outlets or evacuation points. As shown in Fig. 1, the vessel is provided with three drain outlets (120).

Figs. 2a and 2b show another example of a sand removal system. The system includes a piping indicated as Manifold A (210) that is arranged next to another piping indicated as Manifold B (230). Manifold A is closer to a water inlet and Manifold B is closer to a drain outlet at the bottom of the vessel. In this example, each pipe includes 8 spray nozzles. Flat-V type of spray nozzles are used as to provide a flat triangle jetting/spraying profile. In this example, the nozzles are arranged in a 45 degree position from the horizontal axis of the piping. In this example, the sand removal system is used in a vessel with two drain outlets (VI 030) and a vessel with three drain outlets (VI 020).

In determining the optimal jetting actions for displacing and discharging the accumulated sand in the vessel, pressure distribution and spray profile are iterated using computer system.

To determine an improved jetting system for the vessel, the following conditions are considered. a) Water usage for jetting should be minimized. The effective diameter of the nozzle is determined. b) The jetting process will not interfere and upset normal separation process within the vessel; c) Pressurized water for the jetting is higher than the separator vessel operating pressure; d) Water inlet flowrate is maintain such that to ensure volumetric flow balance to outlet flowrate to maintain liquid level inside the vessels. The flowrate will be governed by various factor i.e. erosion rate; e) Sufficient number of evacuation points for discharging sand slurry; f) Minimal intervention by the production operators to control the operation of the jetting system; g) Discharged sand or slurry can be disposed properly to the environment or to be collected safely; and h) Either both manifolds to be operated simultaneously or one manifold to be operated at a time.

It is observed that the spraying/jetting action of the jetting system may be initiated when sand has occupied vessel to a certain sand level which may include a level setting in accordance to weir height, vessel height, or time based operation. Weir (140) with 1.6 m height may be used. For instance, a duration of 30 - 40 seconds is required for jetting when the bed height is half or of 50% of the weir with a volume of 0.605 m ³ . The spraying action of the jetting system to be stopped when the outflow concentration limit of 5% is reached.

It is observed that in order to effectively discharge the slurry (i.e. a mixture of sand and water), Manifold B, the piping which is located at a distal end of the vessel where a drain outlet is located need to be operated. The distal end of the vessel is defined as a point that is far away from the entry point of the drilling fluids. The point that is adjacent to the said drilling fluid entry point may be defined as a proximal end.

A sequence of jetting operation comprising a number of steps. During the online mode, the steps may include: i. Checking the sand level or height. In one example, If sand volume lesser than 0.3% of vessel volume or sand level is lesser than 0.05566m the jetting system will not be operated. The jetting can be initiated when sand has reached the volume of 0.6m ³ or height of 0.125m (50% of the weir height) ii. Initiating a spraying action from the top tier to fluidize the sand when the sand level reaches the said predetermined parameter. During this step, the drain outlet is closed. The jetting may be performed for 30 seconds, depending on the flowrate and liquid level. Liquid level in the separator need to be controlled during the jetting. iii. Opening a selected evacuation point to initiate outflow of the slurry. iv. Initiating a spraying action from the bottom tier to continue fluidization when the sand level lower than 24% of the weir height or 60mm. Liquid level in the separator need to be controlled during the jetting. v. Checking the sand level after jetting operation is performed. Sand level is checked if it is below predetermined level for sand jetting to stop, or in another embodiment, based on measured concentration in outflow. Sand concentration can be measured by densitometer or by measuring sand sampling during the discharge. The jetting may be stopped when sand outflow concentration is about 5%. vi. Controlling liquid level inside the vessel. If liquid level remains unchanged, the drain outlet will be closed. If liquid level increases, slurry discharging will be continued until the desired liquid level is obtained or normal.

During the jetting process, the liquid level in the separator need to be controlled so that the rate of liquid flowing into the vessel is matched by the rate out of the vessel. For instance is one piping/manifold is used, one or more drain outlets/valves are opened. If two pipings/manifolds are used, all drain outlets/valves may need to be opened.

During the offline mode, liquid level control in the vessel is not necessary. The steps for cleaning the vessel during the offline operation, may include the steps of: i. Closing all drain outlet and initiate the jetting; ii. Opening selected drain point and initiate slurry outflow; and iii. Closing drain outlet after the jetting is complete or when no sand in the sampling.

The jetting process will not interfere and upset normal separation process within the vessel. The jetting pressure is higher than separator operating pressure.

Fig. 3 a shows a perspective view of an example of a sand removal system according to an embodiment of the present invention. The sand removal system includes a piping or manifold (510) at a first tier located at the top and a piping or manifold (520) at a second tier locate at the bottom. The top piping (510) is in communication with the bottom piping (520). The top piping (510) includes a transverse pipe (511) that is connected to a first longitudinal pipe (512) and a second longitudinal pipe (514). The transverse pipe (511) is also connected to the bottom piping (520). The transverse pipe (511) is connected to a first longitudinal pipe (612) and a second longitudinal (614) of the bottom piping (520). The top and bottom pipings (510, 520) includes a plurality of nozzles (430). The top piping or bottom piping is connected to a water inlet/water supply. The nozzles are orientated in a slanting position to improve jetting time with increase slurry concentration. The transverse pipe is to provide a transverse jet to facilitate slurry drain. The nozzle may be positioned to be in 45 degree from a vertical axis pointing to the centre of the vessel as shown in Fig. 3c where one or more evacuation points (410) are provided. A flat- V type nozzle with 4.61mm opening is used to provide a flat-triangular spraying profile (590). A corresponding piping assembly may be arranged next to the piping assembly as shown in Fig. 3a. For instance, the operation of the piping assembly at the distal end of the vessel (i.e. a portion away from the entry point of the drilling fluids) will be followed by the piping assembly at the proximal point (i.e. a portion adjacent to the entry point of the drilling fluids). Sand level is typically higher at the proximal end i.e. at the entry point than sand level at the distal end of the vessel

In another embodiment, a pipe-in-pipe system is provided. An internal pipe i.e. the top piping is disposed within a pipe i.e. the bottom piping to form a co-axial arrangement as shown in Fig. 3b. In operation, the spraying action may begin from the internal pipe (310) and followed by the external pipe (320).

Fig. 4 shows a side view of an exemplary assembly of the sand removal system as shown in Fig. 3a in a separator vessel.

According to the present invention, the spraying action of the jetting system may be initiated either from one or more manifolds at a tier and followed by one or more manifolds at another tier, or by sequencing the operation of jetting nozzles in the tier or based on one or more reading of the sand distribution and/or concentration in the vessel.

When drilling fluids enter into the separator vessel i.e. via schoepentoeter (440), sand will settle at the bottom of the vessel and retained by a weir plate. The height of the weir plate will depend on the capacity of the vessel. In this example, a weir plate of 250 mm of height is used. In an operation, a water jetting will be initiated from the piping/manifold at a first tier located at the top and followed by piping/manifold at a second tier located at the bottom. The initiation for the spraying action of the jetting system for fluidizing and displacing the accumulated sand is dependent on the level or height of the sand bed in the vessel. The piping/manifold at the first tier provides a water jetting to displace a top layer of the sand when the height of the sand reaches a first predetermined parameter or reading. Preferably, when the sand bed reaches a first reading e.g. 50% of weir height or 125mm of the 250mm weir height, the piping at the top tier will be activated and discharge a jet to start fluidizing and displacing the sand. The piping/manifold at the second tier provides a water jetting to displace a subsequent layer of the sand when the height of the sand is lower than or reaches a second predetermined parameter. Preferably, when the sand bed level is less than or substantially reaches a second reading e.g. 25% of the weir height or 60mm of the 250mm weir height, the bottom piping/manifold will then be activated and discharge a jet. The jet stream form the top tier is discharged from the transverse manifold (611), first longitudinal manifold (612) and second longitudinal manifold (613). The jet is slanting in its trajectory coming from the nozzle that is orientated at 45 degree and pointing toward the bottom centre where a drain outlet is provided will direct more slurry to evacuate the vessel via the drain outlet. A higher concentration of 55% -60% of sand in water can be discharged via the drain outlet. By sequential and directional spraying actions, the sand is easy to be fluidized and displaced, and less water need to be used. The sequential spraying action that are performed at different tiers may reduce 30% to 50% of water consumption compared to a conventional spraying action from a single level. Discharged sand or slurry from the vessel can and be collected safely and disposed properly to the environment