Patent Publication Number: US-2004050553-A1

Title: Tool method and system for flushing a vertical riser

Description:
[0001] The present invention relates to a system and a flushing device for cleaning of vertical risers at floating drilling rigs where the flushing device for internal cleaning of the vertical riser comprises a main body that is detachable connected to a cable. The invention also relates to a method for internal cleaning of a vertical riser, whereby the sludge pumps of the drilling rig circulate fluid through the riser.  
       [0002] In connection with drilling of oil-related wells, in particular from floating rigs, the opportunity to carry out a good internal cleaning of the riser during the drilling process is unsatisfactory. This cleaning is undertaken when mud types change and at the cleaning before the completion of the well is to be carried out. The cleaning before the last phase is particularly important in that poor cleaning can lead to a reduced production capacity for the well. Today, floating rigs use a tool which is fed down the riser with the aid of the drill string. By pumping seawater with the aid of the sludge pumps of the rig, a simple cleaning is carried out. Several of the large oil companies have let it be known that this type of cleaning is not good enough.  
       [0003] In many cases, the risers are not cleaned until after dismantling and being pulled up to the rig. This often leads to the riser being subjected to corrosion damage as a consequence of the brine that lies inside the riser. In addition, the cleaning on deck leads to a very high noise level while the work is being carried out. It is therefore important to clean the riser before it is pulled up.  
       [0004] It is an object of the present invention to provide a new system and a procedure for cleaning vertical risers which are cheap and simple, and where the cleaning process can be carried out in the riser before it is pulled up. It is also an object of the present invention to provide a tool for the cleaning system itself.  
       [0005] The present invention, relating to the cleaning of a vertical riser, is constructed from several main units: One ultra high-pressure pump unit, a hydraulic tubing and cable winch, and an internal flushing device.  
       [0006] The riser can be cleaned with ultra high-pressure, i.e., for example 830-950 bar. Experience has shown that this pressure is high enough to clean the riser to ensure that it does not lead to contaminations in the production well. Of course, other pressures can be used depending on the capacity of the flushing device, the amount of contaminating material, restrictions etc. In addition to cleaning, this system will at the same time carry out a visual inspection of the riser. This also leads to improved safety.  
       [0007] The oil companies can make great savings with respect to time, especially considering two simultaneous operations where, for example, two wells shall be drilled next to each other. Today, in this case, the rig must pull up the riser for inspection and cleaning. By using the new system, the rigs can, after having carried out cleaning and inspection, move the riser over to the next well without pulling it up.  
       [0008] The flushing device, according to the present invention, is characterised by comprising a number of spring loaded centring wheels around a body, one or more rotatively high-pressure jets in the body, collecting means for larger particles at the lower section of the body and a camera arranged on the underside of the tool.  
       [0009] Preferred embodiments of the flushing device are further characterised in that the spring loaded centring wheels are arranged to extend outwards from the body of the flushing device towards the inner wall of the riser and are arranged to lie against this with a force that is sufficient to centre the tool in the riser, and where the centring wheels are preferably arranged radially around the body in a number of wheel groups. A high-pressure jet is arranged rotatively in adapted apertures in the centre axis of the body and comprises a swivel with jets, through which cleaning fluid is forced under high-pressure. Furthermore, a collecting means is arranged in or at the lower section of the body and has an outer circular-cylindrical shape and having a size somewhat smaller than the inner diameter of the riser to allow passage of fluid between them, and with an inner opening adapted for collection of particles that are released from the inner wall of the riser by the flushing device.  
       [0010] The system, according to the present invention, is characterised in that it is comprised of the following main components: a high-pressure pump; an umbilical hose comprising a hydraulic tubing and an electric cable; a cable winch unit and an internal flushing device.  
       [0011] In a preferred embodiment of the system, the high-pressure pump functions as a pressure generator to provide an ultra high pressure from 700 to 1100 bar, preferably 830-950 bar, and for supply of fluid to an internal flushing device at a fluid flow from 5 m 3 /h to 20 m 3 /h, preferably from 10 m 3 /h to 15 m 3 /h, especially preferred about 12 m 3 /h to 14 m 3 /h. The winch unit is driven hydraulically, and the high-pressure tubing and the electric cable are constructed as one unit, in which the winch unit comprises equipment for reading of a load cell at the end of the cable and a digital meter counter to read the height level in the riser. The system also comprises a flushing device as described above.  
       [0012] According to the procedure for the cleaning of a vertical riser, a flushing device is fed into the riser and is thereafter lowered all the way down to a blow-out preventer (BOP) at the well head. A high-pressure unit supplies fluid down to the flushing device by way of an umbilical hose that is led down the riser with the aid of a hydraulic winch. At the same time as high pressure is supplied to the flushing device, the sludge pump of the drilling rig starts to feed a fluid stream into the riser to flush out particles which are released from the wall of the riser by the flushing device, whereupon the flushing device is pulled upwards in the riser until it reaches the top of the riser.  
       [0013] In a preferred embodiment of the procedure, the particles that are too large to be lifted by the fluid stream are caught by a trap or a collection means in or at the flushing device. 
     
    
    
     [0014] The invention shall now be further explained in more detail with reference to the enclosed figures, in which:  
     [0015]FIG. 1 shows a principle drawing of a floating drilling rig comprising the system and device according to the present invention.  
     [0016]FIG. 2 shows parts of the cable winch system according to the invention.  
     [0017]FIG. 3 shows a preferred embodiment of a flushing device according to the invention. 
    
    
     [0018]FIG. 1 shows a floating drilling rig  10  which is used for petroleum-related drilling operations. A riser  12  is arranged between the drilling rig  10  and the ocean bed. Normally, the riser will be connected to a blow-out preventer (BOP)  14  which in turn is fitted to the well head. Placed on the drilling rig  10  is a high-pressure unit  16 , which is classified for placing in zone  2 . This high-pressure unit  16  comprises an ultra high-pressure pump and a power-supply unit to drive the pump and a cable winch system  18 . The cable winch system is further comprised of a hydraulic tubing for supply of fluid to a flushing device  20  which is led down into the riser. Both the high-pressure unit and the cable winch system are in themselves known units which will be known to a person skilled in petroleum related drilling.  
     [0019] The system according to the invention comprises further a runner  22  that is suspended by the aid of a suspension means  24 , normally a top drive, which is above the vertical riser  12 . The hydraulic cable or umbilical hose, comprising an electric cable, shown by  26 , is led from the cable winch system  18  over the runner  22  and down to the flushing device  20  that is lowered into the riser  12 .  
     [0020]FIG. 3 shows a preferred embodiment of the flushing device  20 . The device  20  is connected to a reinforced umbilical hose  28 , which is comprised of the electric and the hydraulic cables. Furthermore, suspended between the body  31  of the flushing device  20  and the umbilical hose  28  load cells  30  can be arranged for connection to the umbilical hose and to register load impacts on the cable.  
     [0021] To guide the flushing device  20  in the riser  12 , a number of mutually separate load bearing centring wheels  32  are fitted around the body  31 . The centring wheels  32  are preferably extending, outwards towards the inner wall of the riser and are arranged to abut against the riser, thereby to be forced or held against this by a force sufficient to centre the tool in the riser, without the upwardly or downwardly movement of the flushing device being hampered. The centring wheels  32  are preferably arranged radially around the body  31  in a number of wheel groups  32   a,    32   b.    
     [0022] A rotable high-pressure jet  34  is arranged below the centring wheels  32 . In an alternative embodiment, the high-pressure jet  34  can be arranged above the centring wheels, or a high-pressure jet  34  can be arranged both above and underneath the wheels. In addition, in a further embodiment, a high-pressure jet can be arranged between the centring wheels  32   a,    32   b.  As mentioned, the high-pressure jet  34  can rotate and function according to known principles for such a rotary swivel that rotates because of pressure exerted by a medium. The swivel with the jets, will rotate at great speed, due to the feeding of cleaning fluid under pressure, and will correspondingly spray cleaning fluid against the inner wall of the riser at great speed for cleaning it.  
     [0023] The flushing device  20  also comprises a camera  40  fitted at the lower section of the body  30 , for visual inspection of the riser  12 . The camera sends signals to a screen on the drilling rig by way of the cable  28 . The camera can, for example, be a colour camera that is designed for ocean depths of 1000 metres (with the possibility for up to 5000 m) and can rotate 360 degrees as well as tilt 180 degrees.  
     [0024] In the embodiment that is shown in FIG. 3, a collecting means  38  or a trap is arranged between the high-pressure jet  34  and the camera  40  for larger particles, which are released from the wall of the riser. A spring loaded safety valve  36  can also be arranged to or at the collecting means  38 . Associated with there being a flow of fluid directed upwards in the riser during the cleaning operation, the safety valve  36  will ensure that the flushing device will not travel upwards in the riser at a speed greater than that which is desired.  
     [0025] In an alternative embodiment (not shown), the collecting means can be arranged underneath the flushing device  20  itself with the aid of, for example, a cable system, at a desired distance from the tool. Correspondingly, the collecting means can comprise a safety valve which, because of the upwardly directed fluid flow, ensures that the collecting means does not travel upwards in the riser at a speed greater than that of the flushing device  20 . In this embodiment, the camera  40  will be placed, for example, on a plate which is fitted underneath the high-pressure jets.  
     [0026] The ultra high-pressure pump unit functions both as a high-pressure generator and as a fluid supplier to an internal flushing device. The supply pressure can, for example, be from 700-1100 bar, preferably 830-950 bar, with a fluid flow of, for example, 13 m 3 /h. The unit is composed of in itself known technology, and is designed and built according to current regulations for the offshore industry.  
     [0027] To transfer high pressure/signals/hoisting to an internal flushing device, a hydraulic winch unit is used as mentioned. This can, for example, have a pulling capacity of about 3T, but is not restricted to this load. The high-pressure tubing itself and the electric cable will be constructed as one unit. This unit is also in itself known technology, and is designed and built according to current regulations for the offshore industry. In addition, this winch unit has facilities for reading of a load cell at the end of the cable and a digital metre counter to read the height level in the riser.  
     [0028] As mentioned, the flushing device consists of several parts. It has, as mentioned, spring loaded centring wheels which ensure that the tool lies stably in the riser. It has a rotary swivel for the spraying jets. It has a colour camera that is designed for depths of up to 1000 metres (with the possibility of up to 5000 m) which can rotate 360 degrees and tilt 180 degrees. It has a load cell at the top to ensure that the counter-current flow in the riser does not lead to the device being lifted. In addition, the device has a lower section that catches large particles and ensures that these do not fall down into the well during cleaning.  
     [0029] The procedure, according to the invention, aims at cleaning the riser in the following way; the flushing device is led into the riser and is thereafter led all the way down to the blow-out preventer (BOP). Thereafter, the ultra high-pressure pump starts and feeds fluid down to the flushing device by way of the high-pressure tubing which is led down in the riser with the help of the hydraulic winch. At the same time as the high pressure is brought about, the sludge pump of the rig starts. This leads to a fluid flow which, for example, can be 2000 litres/min by way of the kill-line, to flush out particles that are released from the wall of the riser with the help of the ultra high-pressure tool. If there are larger particles than the fluid flow can lift, these are caught by a trap or a collecting means at the lower part of the flushing device. The flushing fluid with particles is fed out in the flow pipe that leads to tanks/screening machine/or overboard. The flushing device is then gently pulled upwards in the riser until it reaches the top. With the help of the camera that is fitted at the bottom of the flushing device, a visual inspection of the riser can also be carried out. When the flushing device has reached the top of the riser, it is pulled out by way of the rotation table and the work is done.