Patent Application
20230065388
The invention relates to a dump bailer for being filled with a flowable material in a lubricator assembly and for depositing the flowable material in a wellbore. The invention also relates to a lubricator assembly configured to allow filling a flowable material into a dump bailer positioned within the lubricator assembly, and to a method for filling a flowable material into a dump bailer positioned within a lubricator assembly and for depositing the flowable material in a wellbore.
When permanently plugging hydrocarbon wells, there are certain regulatory requirements that must be complied with. Only when wells are properly plugged can well construction removal be performed. With today's technology, a lot of this activity is done with the drilling equipment. This equipment is very heavy and is operated by a large number of workers.
The plugging preparation work is usually done with lighter equipment such as wireline services. Coiled tubing can also be used, but due to the large scope of this equipment it is not appropriate. Typical preparation work performed with wireline is logging of the cement column in the annulus, inspection of production pipes, checking that plugging equipment can be installed at the desired depth, and checking condition of production pipes, for example corrosion and or degree of deposits on pipe wall. Preparation work may also involve removal of impurities so that mechanical barrier plugs can be installed at the desired depth.
Since wireline services are very cost-effective relative to drilling packages, it is desirable to carry out as much work as possible using wireline services. Several wireline tools exist for depositing a flowable material, such as cement slurry, in a wellbore. However, due to its large volume, placement of 50 meters of cement plug is still an activity only for coil tubing or drilling packages, as no wireline tools exist which can place such large volumes effectively (a 50 meters cement plug in 7 inches tubing is 970 litres). A single container for containing this volume would be too long for practical handling.
U.S. Pat. No. 4,696,343A discloses a wireline dump bailer for placing a cement slurry on a retainer in a wellbore, wherein the cement slurry is deposited by exploding a detonator. This will result in an uncontrolled deposition and reloading of the detonator at the surface will be time-consuming, since the operator would have to open the lubricator and release the pressure inside to reload.
US2019169955A1 discloses an apparatus for injecting a sealing mixture into a well, wherein the sealing mixture is released from the apparatus using compressed gas. This will also result poor control of the injection, and the apparatus will not be able to contain enough sealing mixture to set a cement plug of the required thickness.
WO2016053113A1 discloses a dump bailer arrangement with a displacement piston in the flow path. This arrangement has several disadvantages, especially the filling could only be done taking the system out of the well.
Displacement piston, wiper plug, swab plug, pipe dart etc, the arrangement dividing the substances preventing mixture inside the dump bailer arrangement has many names and embodiments but are in principle the same.
The dump bailer may also be sluiced into the well using a deployment BOP system, but this is a complex arrangement which is not advantageous to use.
The invention has for its object to remedy or to reduce at least one of the drawbacks of the prior art, or at least provide a useful alternative to prior art. The object is achieved through features, which are specified in the description below and in the claims that follow. The invention is defined by the independent patent claims, while the dependent claims define advantageous embodiments of the invention.
In a first aspect, the invention relates to a dump bailer for being filled with a flowable material in a lubricator assembly and for depositing the flowable material in a wellbore, wherein the dump bailer comprises:
This configuration of the dump bailer has several advantages. For example, it allows the dump bailer to be filled with flowable material while the dump bailer is positioned inside a complementary lubricator assemble which has a higher pressure than ambient pressure, typically at wellbore shut-in pressure. Filling of the dump bailer may thereby be performed while the lubricator assembly is connected to the wellbore and the dump bailer in completely positioned inside the lubricator assembly, i.e. without any portions of the dump bailer extending from the lubricator assembly. The means for orientation allows the dump bailer to be positioned and orientated such that the filling valve matches an inlet for injection the flowable materials through a wall of the lubricator assembly, whereby flowable material may be filled into the lower chamber via the filling valve. Before filling of the dump bailer, the wiper plug will be positioned at the bottom of the main chamber, whereby the lower chamber is non-existing or very small, and the upper chamber fills the entire or almost the entire main chamber. When filling of the bailer starts by flowable material being injected into the lower chamber through the filling valve, the wiper plug will be displaced upwards within the main chamber as flowable material is filling the lower chamber. The volume of the lower chamber thereby increases, while the volume of the upper chamber decreases. The content of the upper chamber, which is typically wellbore fluid, will be emptied through the first tensioned valve system. Since the pump is not active during filling of the dump bailer, liquid communication between the upper chamber and the surrounding is open. The force of the second tensioned valve system may be so large that it keeps the liquid communication between the lower chamber and the outlet closed during filling. The force may typically be several hundred kg. Alternatively, or additionally, the second tensioned valve system may include a locking mechanism for locking the second tensioned valve system in closed position during filling of the dump bailer. In this way the second tensioned valve system may be required to withstand a smaller pressure than it would have been required to without the locking mechanism, which therefore puts less requirements on the second tensioned valve system. The dump bailer is full when the wiper plug reaches the top of the main chamber. This results in an increase in filling pressure, which may be detected by e.g. an external pump used for filling of the dump bailer, and filling can be stopped.
When the dump bailer is filled with flowable material, it is ready to be lowered into the wellbore to deposit the flowable material at a desired depth. The wiper plug seals the content of the lower chamber from the upper chamber, the filling valve allows only flow into the lower chamber, and the second tensioned valve system is configured so that liquid communication between the lower chamber and the outlet is closed when the pump is inactive, so the flowable material inside the lower chamber of the dump bailer is completely sealed. Unwanted leakage of the flowable material, for example during the lowering of the dump bailer into the wellbore, is thereby avoided, and positive displaced on the flowable material by the pump is required. The depth of the dump bailer in the wellbore may be measured using e.g. equipment such as a gamma ray logging tool and/or casing collar locator. The flowable material may thereby be deposited at a very well-determined depth.
Deposition may be initiated by starting the pump in the dump bailer, which causes the first tensioned valve system to open for liquid communication between the pump and the upper chamber while closing for liquid communication between the upper chamber and the surroundings. The effect of starting the pump is thereby to pump liquid from the surroundings, typically wellbore fluid, into the upper chamber. The pressure in the upper chamber will be transferred to the lower chamber through the longitudinally displaceable and sealing wiper plug. Therefore, if the pump pressure increases sufficiently for the force of the second tensioned valve system to be overcome, liquid communication between the lower chamber and the outlet of the dump bailer will be allowed. The flowable material in the lower chamber will thereby flow out of the outlet and be deposited in the wellbore.
An advantage of the present configuration of the dump bailer is that there is a very large degree of control of the deposition of the flowable material, since it will only be deposited when the pump is active, and the rate of deposition is controlled by the pump. As soon the pump is stopped, deposition of the flowable material will also stop, and further leakage from the dump bailer is avoided.
The dump bailer according to the invention is therefore able to be filled with flowable material in the lubricator assembly at the surface, be lowered into the wellbore without leakage of the flowable material, accurately and controllably deposit the flowable material at the desired depth, be withdrawn to the lubricator assembly and refilled at wellbore shut-in pressure, i.e. without opening the lubricator assemble to the surroundings, and then continue the process with another round of deposition. Pressure tests of the different valves in the dump bailer may be performed at the surface before the dump bailer is refilled. In this way it is possible to deposit a very large amount of flowable material in the wellbore at a very specific depth with a relatively short period of time. By not having to open the lubricator assembly toward the surroundings and/or dissemble the lubricator assembly for refilling, the filling process will be much faster than prior art dump bailers. Therefore, the dump bailer on wireline will be able to compete in the speed and costs compared to using drilling equipment or coiled tubing for depositing large volumes of flowable material.
A typical application of the dump bailer will be plugging of a wellbore, where the flowable material is cement slurry or similar. For this application, several rounds of deposition of cement slurry using the dump bailer will typically be necessary, as a dump bailer able to contain the required volume of cement slurry is not possible, or at least not suitable for practical considerations, as deposition of a plug of 50 meters would require the dump bailer to be much longer than this. Using the dump bailer according to the invention, it will be possible to produce a plug within such a short time that it may be more cost-effective than using e.g. drilling equipment or coiled tubing. Wireline equipment is typically already in position on the oil or gas rig, whereas coiled tubing requires much time for transportation and installation. Since the dump bailer may be filled at shut-in pressure in the lubricator assembly, it can be refilled rapidly, and the subsequent round of deposition in the wellbore may be performed before the cement slurry of the previous round has cured. The result will thereby be a single plug without any weak interfaces between cement portions from different rounds.
The first tensioned valve system of the dump bailer may for example comprise a first valve member which is spring-loaded towards the pump, whereby, when in passive position, the first valve member is blocking a port for liquid communication between the pump and the upper chamber, while another port for liquid communication between the upper chamber and the surroundings is open. When the pump is started, the pressure above the first spring-loaded valve member increases, which causes the first valve member to be disco placed in the direction opposite to the spring force, whereby it blocks a port for liquid communication between the upper chamber and the surroundings while at least partly opening the port for liquid communication between the pump and the upper chamber.
The second tensioned valve system may for example comprise a second valve member which is spring-loaded against the lower chamber. The force of the spring should be large enough to avoid that it opens under the weight of the flowable material inside the lower chamber, yet small enough to be overcome by the pump pressure. The area of the second valve member may be substantially equal to the area of the wiper plug for obtaining correct the pressure balance. When the second valve member is displaced against the spring force, a port towards the outlet is opened, for example one or more channels carved into a valve housing around the second valve member. In one embodiment, the second tensioned valve system comprises a locking mechanism for locking the second tensioned valve system in closed position during filling of the dump bailer. The locking mechanism may for example include a first pin extending from the filling valve and being configured to engage with a cap, a hole or similar of a second pin connected to the second valve member. In this way, when the filling valve is opened, the engagement of the first pin with the second pin thereby prevents the second valve member from being displaced downwards and allowing liquid communication between the lower chamber and the outlet of the dump bailer.
There is also disclosed a further dump bailer for depositing the flowable material in a wellbore, wherein the further dump bailer comprises:
The further dump bailer may be particularly beneficial in situations where pressure control equipment on the surface is not needed or is just a precaution. In these situations, the further dump bailer may be longer, whereby reduced number of runs are needed to deposit the required volume of flowable materials, for example to create a cement column. It may for example be possible to deploy the entire volume of flowable material into the well in one single run. Typically, the Down Hole Safety Valve (DHSV) will be a part of the well barrier in such scenarios. In one embodiment of the invention, the means for orientation of the dump bailer may comprise an inclined lower surface for orientating the dump bailer using a guide with a matching inclined surface. In this way the dump bailer will orient itself relative to the guide due to gravity. This is a very simple but effective means of orientation. The inclined lower surface may for example by due to a mule shoe, which is a piece of equipment already used for wireline tools. It may therefore be relatively easy and cheap to acquire.
In one embodiment of the invention, the filling valve may be configured to be opened with a dart. In this way it is assured that the filling valve is only opened when desired, and that no wellbore fluid bleeds into the lower chamber while the dump bailer is in the wellbore, e.g. due to pressure fluctuation. It may also ensure that the dump bailer has the correct orientation in the lubricator assembly. If the dump bailer does not have the correct orientation, the dart will encounter the wall of the dump bailer and will not be able to penetrate as deep into the lubricator assemble as required. Alternatively, the filling valve may be a check-valve with a large required opening pressure.
In one embodiment of either dump bailer, the pump may have an exact or a very high degree of control of the rate of the volume displaced by the pump. This will have the advantage that the operator will always know how much flowable material has been deposited. A suitable pump may be a positive displacement pump, for example a progressive cavity pump. In this type of pump one revolution of a shaft corresponds to a very well-determined displaced volume. Therefore, controlling the rotation speed and number directly controls the rate and total volume of displaced volume, corresponding to the rate and total volume of flowable material the deposited in the wellbore.
In either dump bailer a pressure sensor may be placed between the pump and the wiper plug for measuring pump pressure and the pressure of the surroundings as the pump displaces the flowable material out of the dump bailer. In this way the sensor will never come in contact with the flowable material due to its position above the wiper plug.
Either dump bailer may also comprise a propulsion mechanism for moving the dump bailer within the wellbore, for example a wireline tractor. Depositing the flowable material in the wellbore while simultaneously displacing the dump bailer upwards within the well using the tractor in reverse mode may lead to superior control of the displacement.
In a second aspect, the invention relates to a lubricator assembly configured to allow filling a flowable material into a dump bailer positioned within the lubricator assembly, wherein the lubricator assembly comprises:
wherein the inlet sealing mechanism and the guide are operable from the outside of the lubricator assembly.
A lubricator with such a configuration will allow a complementing dumb bailer, e.g. the dump bailer according to the first aspect of the invention, to be filled with flowable material while the lubricator assembly is at wellbore shut-in pressure. The dump bailer may thereby be inserted into the lubricator assembly before filling of the dump bailer, which may make the filling procedure easier and more secure. Filling of the dump bailer may thereby be performed while the lubricator assembly is connected to the wellbore and the dump bailer in completely positioned inside the lubricator assembly, i.e. without any portions of the dump bailer extending from the lubricator assembly. Additionally, the dump bailer may be pressure-tested before filling to assure that all valves are tight and working properly. The risk of leakage of flowable material inside the lubricator is therefore decreased. Another major advantage of the lubricator assembly is that, after the flowable material has been deposited in the wellbore, the dump bailer may be refilled in the lubricator without opening the lubricator assembly to the surroundings. This will greatly speed up the refilling process between subsequent deposition rounds of the dump bailer compared to if the lubricator assembly had to be opened toward the surrounding as in prior art lubricators. This therefore speeding up deposition of flowable material in the wellbore. The lubricator assembly is only required to be opened after the desired number of deposition rounds have been accomplished.
In one embodiment, the guide may comprise an inclined surface for matching an inclined lower portion of the dump bailer. The normal of the inclined surface may for example form an angle relative to a longitudinal axis of the lubricator assembly for matching a mule shoe on the dump bailer, as mule shoes on dump bailers are already used and therefore easy to acquire. Using an inclined surface is a simple and efficient way to provide the correct position and orientation to the dump bailer. When the dump bailer is to be filled, it is lifted inside the lubricator assembly to a height such that it is ensured that the lower portion of the dump bailer is above the guide. Then, operated from the outside of the lubricator assembly, the inclined surface of the guide is displaced into the centre of the lubricator assembly, and the dump bailer is slowly lowered on the inclined surface. The dump bailer will thereby automatically orient itself correctly on the inclined surface, whereby the filling valve of the dump bailer will match the inlet of the lubricator assembly.
In addition to the inclined surface, the lubricator assembly may further comprise a wash line inlet and a wash line outlet for washing at least a portion of the dump bailer by injecting a cleaning liquid through the wash line inlet and letting the cleaning liquid out of the wash line outlet, wherein the inclined surface is configured for guiding the cleaning liquid towards the wash line outlet. This may be particularly advantageous when the dump bailer is refilled with flowable material between two deposition rounds in the wellbore, as any residue from the previous round may be washed off the dump bailer before the subsequent round. In this way the risk of contamination or the deposited flowable material is decreased. Using the inclined surface to guide the cleaning liquid towards the outlet ensures that no residues from the cleaning process is left in the lubricator assembly after cleaning, thereby assuring that no unwanted chemicals are transferred to the wellbore by the dump bailer.
The inlet sealing mechanism may comprise a seal cup which is displaceable within the inlet of the lubricator assembly towards the filling valve of in the dump bailer. In this way, when the dump bailer is correctly positioned and orientated within the lubricator assembly, the seal cup can be displaced towards the filling valve to seal the communication between the inlet of the lubricator assembly and the filling valve of the dump bailer. If the filling valve is a tensioned check valve, filling of the dump bailer may be initiated simply by providing a filling pressure which is large enough to overcome the tension of the check valve. The lubricator assembly may further comprise a dart through the inlet for opening the filling valve of the dump bailer, which is advantageous if the filling valve is configured to be opened with a dart. The dart may be operated from the outside of the lubricator assembly and may function to ensure that the dump bailer indeed has the correct position and orientation. The dart may for example be screwed toward the centre of the lubricator assembly. Since the dart functions to open the filling valve, a lower filling pressure is required than if the filling valve is a tensioned check valve.
In a third aspect, the invention relates to a method for filling a flowable material into a dump bailer positioned within a lubricator assembly and for depositing the flowable material in a wellbore, wherein the method comprises the steps of:
Using this method allows the dump bailer to be filled with the flowable material while positioned inside the lubricator. Filling of the dump bailer may thereby be performed while the lubricator assembly is connected to the wellbore and the dump bailer in completely positioned inside the lubricator assembly, i.e. without any portions of the dump bailer extending from the lubricator assembly. In this way the filling process will be easier, and the risk of spilling of the flowable material will be decreased. The method is therefore particularly suitable for deposition of hazardous chemicals. Typically, during filling of the dump bailer, an equal volume of wellbore fluid is bled off from the lubricator assembly to maintain a correct pressure.
The step of filling the dump bailer with flowable material while the dump bailer is within the lubricator assembly may for example be performed at wellhead shut-in pressure, but it may also be performed at ambient pressure, where the lubricator pressure is bled down to ambient.
In one embodiment, the method may additionally comprise the step of testing at least one valve of the dump bailer while the dump bailer is within the lubricator assembly. This has the advantage that correct function of the valves of the dump bailer may be ensured before filling, whereby the risk of leakage of flowable material inside the lubricator assembly is decreased. If one or more of the valves are not tight, the dump bailer may be removed from the lubricator assembly for further testing and maintenance. This step is typically performed while the pressure of the lubricator assembly is at wellhead shut-in pressure.
In one embodiment, the method may additionally comprise the step of washing at least a portion of the dump bailer while the dump bailer is within the lubricator. This step ensures that the dump bailer is clean before use.
In one embodiment, the step of depositing the flowable material in the wellbore may comprise simultaneously displacing the dump bailer upwards within the well at controlled speed, for example by hoisting the dump bailer using the wireline cable or by driving a wireline tractor that is connected to or forms part of the dump bailer in reverse. In this way the outlet of the dump bailer may be kept close to the upper surface of the deposited material, thereby preventing that the flowable material falls too long a distance at the beginning of the deposition, and/or that the deposited material rises up too high around the dump bailer during deposition. Advantageously, the dump bailer may comprise a pump with control of the rate for depositing the flowable material in a controlled manner, and the speed of displacement of the dump bailer may be selected to match the deposit rate of the flowable material so that the relative distance between the upper surface of the deposited flowable material and the dump bailer is substantially constant during the step of depositing the flowable material in the wellbore while simultaneously displacing the dump bailer upwards within the well. The fall of the flowable material will thereby be substantially constant during deposition. The method may additionally comprise the step of depositing a first portion of the flowable material until the outlet of the dump bailer is covered by the flowable material before the step of depositing the flowable material in the wellbore while simultaneously displacing the dump bailer upwards within the well. In this way, apart from during deposition of the first portion, deposition of the flowable material from the outlet will happen below the surface of the already deposited flowable material, whereby the risk of contamination of the deposited material with contents from the wellbore fluid is decreased. If the speed of displacement of the dump bailer matches the rate of deposition of flowable material, it is ensured that the outlet of the dump bailer is always below the surface of the flowable material.
In one embodiment, the method may additionally comprise the step of pulling the dump bailer into the lubricator assembly after the flowable material has been deposited at the desired depth; and repeating the preceding method steps. This has the advantage that repeated rounds of deposition in the wellbore may be performed without opening the lubricator assembly towards the surroundings, for example if the pressure of the lubricator is maintained substantially at wellhead shut-in pressure when repeating the filling step. As opening of the lubricator assembly is a time-consuming process, not having to do this step saves a lot of time. Deposition of large volumes of flowable material using the method according to the invention, for example when plugging a well, will be much faster than previously possible using wireline. In terms of time and costs, the method may be more efficient than, or at least comparable to, using drilling equipment or coiled tubing. For every time the step of lowering the dump bailer containing the flowable material into the wellbore at a desired depth is repeated, the dump bailer may be lowered so that the outlet of the dump bailer is immersed into the previously deposited flowable material to such an extent that the outlet of the dump bailer is covered by the previously deposited flowable material, before the step of depositing the flowable material in the wellbore while simultaneously displacing the dump bailer upwards within the well. This may ensure that the flowable material is deposited as a single homogenous matter even though it has been deposited over multiple rounds, and that contaminants from the wellbore fluid are not mixed into the deposited flowable material. For example, if the flowable material is cement slurry for forming a plug in the wellbore, immersing a portion of the dump bailer which comprises the outlet will prevent formation of interfaces between each consecutively deposited volumes of flowable material. This process is made possible by the rapid refilling of the dump bailer in the lubricator assembly, typically at wellbore shut-in pressure, since the subsequent deposition can be initiated before the deposited cement slurry cures.
There is also disclosed a further method for depositing a flowable material in a wellbore, wherein the further method comprises the steps of:
The step of depositing the flowable material in the wellbore while simultaneously displacing the dump bailer upwards within the well at a controlled speed may for example be performed by hoisting the dump bailer using a wireline cable or by driving a wireline tractor that is connected to or forms part of the dump bailer in reverse. In this way the outlet of the dump bailer may be kept close to the upper surface of the deposited material, thereby preventing that the flowable material falls too long a distance at the beginning of the deposition, and/or that the deposited material rises up too high around the dump bailer during deposition. Advantageously, the dump bailer may comprise a pump with control of the rate for depositing the flowable material in a controlled manner, and the speed of displacement of the dump bailer may be selected to match the deposit rate of the flowable material so that the relative distance between the upper surface of the deposited flowable material and the dump bailer is substantially constant during the step of depositing the flowable material in the wellbore while simultaneously displacing the dump bailer upwards within the well. The fall of the flowable material will thereby be substantially constant during deposition. The further method may additionally comprise the step of depositing a first portion of the flowable material until the outlet of the dump bailer is covered by the flowable material before the step of depositing the flowable material in the wellbore while simultaneously displacing the dump bailer upwards within the wellbore at a controlled speed. In this way, apart from during deposition of the first portion, deposition of the flowable material from the outlet will happen below the surface of the already deposited flowable material, whereby the risk of contamination of the deposited material with contents from the wellbore fluid is decreased. If the speed of displacement of the dump bailer matches the rate of deposition of flowable material, it is ensured that the outlet of the dump bailer is always below the surface of the flowable material.
The further method may additionally comprise the step of pulling the dump bailer to the surface after the flowable material has been deposited at the desired depth; and repeating the preceding method steps. This may be particularly advantageous if the filling step can be performed relatively quickly. The further method may thereby be used for deposition of large volumes of flowable material, for example when plugging a well. For every time the step of lowering the dump bailer containing the flowable material into the wellbore at a desired depth is repeated, the dump bailer may be lowered so that the outlet of the dump bailer is immersed into the previously deposited flowable material to such an extent that the outlet of the dump bailer is covered by the previously deposited flowable material, before the step of depositing the flowable material in the wellbore while simultaneously displacing the dump bailer upwards within the well at a controlled speed. This may ensure that the flowable material is deposited as a single homogenous matter even though it has been deposited over multiple rounds, and that contaminants from the wellbore fluid are not mixed into the deposited flowable material. For example, if the flowable material is cement slurry for forming a plug in the wellbore, immersing a portion of the dump bailer which comprises the outlet will prevent formation of interfaces between each consecutively deposited volumes of flowable material.
In the following is described an example of a preferred embodiment illustrated in the accompanying drawings, wherein:
a and b show cross-sectional views of a portion of the lubricator assembly and dump bailer during filling of two embodiments of the dump bailer with flowable material; and
In the drawings, the reference numeral 1 indicates a dump bailer according to the invention. Identical reference numerals indicate identical or similar features in the drawings. The drawings are presented in a simplified and schematic manner, and the features therein are not necessarily drawn to scale.
The chamber section 11 also comprises a first tensioned valve system 31 and a second tensioned valve system 33. The first tensioned valve system 31 comprises a first valve member 35 which is tensioned with a first spring 36 towards the pump 9. In
The second tensioned valve system 33 comprises a second valve member 41 which is tensioned against the lower chamber 29 with a second spring 43. The area of the second valve member 41 is substantially equal to the area of the wiper plug 25. In
When the wiper plug 25 reaches the bottom of the main chamber 23, as in
A typical operation for plugging a wellbore with a cement plug may be:
It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb “comprise” and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article “a” or “an” preceding an element does not exclude the presence of a plurality of such elements.
The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20191237 | Oct 2019 | NO | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/NO2020/050246 | 10/9/2020 | WO |
