DRILLING MUD COLLECTOR FOR A SLIP JOINT OF A RISER

A DEVICE FOR A DRILLING MUD COLLECTOR

This invention concerns a drilling mud collector. More particularly, it concerns a drilling mud collector for a slip joint of a riser, the slip joint comprising an outer pipe and an inner pipe and also at least one first seal between the inner pipe and the outer pipe. A second seal encloses the inner pipe. Between the seals there is provided a collector compartment communicating with receiving equipment for drilling mud.

Due to wear and tear in a slip joint seal, drilling mud leakages have proven to occur in a slip joint during operation. Usually such leakages have a modest extent, which may be corrected by increasing somewhat the pressure in the seal packer, or by activating a secondary packer normally located below the primary packer of the seal .

When employing oil-based drilling mud, a build-up of relatively dry drilling mud may occur in the annulus between the inner and outer pipes of the slip joint. When replacing oil-based drilling mud with water-based drilling mud, at least a portion of said relatively dry drilling mud remains in the annulus.

By allowing this oil-based drilling mud to contact the water- based drilling mud, the consistency of the oil-based drilling mud is changed. The oil-based drilling mud adheres to the inner pipe and lumps may also form, potentially causing sudden discharge of drilling mud to the environment when the inner pipe is displaced in the seal .

During a discharge of this type, most of the drilling mud located at a level above the seal will discharge. Normally, discharges in the order of 5000 litres are involved.

The object of the invention is to remedy or reduce at least one of the disadvantages of the prior art.

The object is achieved by virtue of features disclosed in the following description and in the subsequent claims.

According to the invention, a drilling mud collector for a slip joint of a riser is provided, the slip joint comprising an outer pipe and an inner pipe and also at least one first seal between the inner pipe and the outer pipe, characterized in that a second seal encloses the inner pipe, and wherein a collector compartment is provided between the seals. Typically, the collector compartment communicates with receiving equipment for drilling mud.

The second seal is located at an upper portion of the first seal. Drilling mud unintentionally discharging via the first seal may be caught by the collector compartment and the second seal .

Typically, the collector compartment is provided with a first level switch at a first level and advantageously also with a second level switch at a second level located higher up than the first level.

Advantageously, the receiving equipment comprises a drilling mud collector tank, a pump and necessary valves. Advantageously, the liquid discharging via the first seal is allowed to collect in a separate receptacle so as to be able 5 to determine the type of liquid discharged.

Normally, the second seal is inactive in the initial position thereof. Should drilling mud, or possibly other liquids, discharge via the first seal, the liquid level rises within the collector compartment. By means of a control, at least o one of the level switches is arranged in a manner allowing at least activation of the second seal, starting of the pump or activation of a warning.

In a preferred embodiment, the second level switch is arranged to output a signal which, via the control, activates s the second seal so as to seal around the inner pipe, starts the pump so as to pump fluid in the collector compartment to the collector tank, and also that the control activates a warning to the effect that an unintentional leakage is ongoing .

o The first packer of the first seal may be tightened in order to stop the leakage. If required, also the second packer of the first seal must be activated.

When the leakage is stopped, the liquid level drops below the first level switch, whereby the first level switch, via the 5 control, at least stops the pump, deactivates the second seal or discontinues the warning.

A device in accordance with the invention protects against unintentional discharge of drilling mud to the environment, which implies a significant reduction in pollution danger and o also in loss of relatively costly drilling mud.

Hereinafter ¹ , an example of a preferred embodiment is described, the embodiment of which is depicted in the accompanying drawings , where :

Fig. 1 schematically shows a drilling mud collector according to the invention in the initial position thereof, and

Fig. 2 shows the drilling mud collector of fig. 1 in the activated position thereof.

In the drawings, reference numeral 1 denotes a drilling mud collector connected to a slip joint 2 of a riser 4. The slip joint 2 comprises an outer pipe 6 connected to the riser 4, an inner pipe 8 connected to an upper riser arrangement known per se (not shown) , and a first seal 10.

The first seal 10 comprises a first seal housing 12 sealingly connected to the upper end portion of the outer pipe 6, the seal housing surrounding the inner pipe 8. The seal 10 further comprises an upper first packer 14 and a lower second packer 16, wherein the packers 14 and 16 are arranged in a manner allowing them to bear sealingly against the inner pipe 8.

The bearing pressure of the first packer 14 against the inner pipe 8 is controlled by regulating the air pressure in a first control pipe 18, whereas the bearing pressure of the second packer 16 against the inner pipe 8 is controlled by regulating the air pressure in a second control pipe 20. Upon experiencing insufficient overpressure in the control pipes 18, 20, the packers 14, 16 will not seal against the inner pipe 8.

During normal operation, when the inner pipe 8 may be displaced axially in the outer pipe 6, the first packer 14 is

activated, whereas the second packer 16 forms an auxiliary packer should the first packer 14 fail.

The outer pipe 6 with the first seal 10 and also the riser 4 are supported by a support ring 22 in a manner known per se.

A second seal 24 comprises a second seal housing 26 connected concentrically and sealingly to an upper portion of the first seal housing 12. The second seal housing 26 is provided with a third packer 28 arranged in a manner allowing it to seal, when in the activated position thereof, against the inner pipe 8. The third packer 28 is activated by opening a compressed-air valve 30 for supply of compressed air.

In the second seal housing 26, and between the first seal 10 and the third packer 28, there is provided a collector compartment 32 that surrounds the inner pipe 8, and which is arranged in a manner allowing it to receive and collect fluid discharging between the first seal 10 and the inner pipe 8.

In the collector compartment 32 there is provided a first level switch 34 and a second level switch 36 located at a level higher up than the first level switch 34. The level switches 34, 36 communicate with a control 38 via wires 40. The control 38 controls the compressed-air valve 30 via a wire 42 and a pump 44 and also a warning (not shown) via connections (not shown) .

The collector compartment 32 communicates with a drilling mud collector tank 50 via a pipe connection 46, valves 48 and the pump 44.

During normal operation, see fig. 1, the third packer 28 is not activated.

Should a leakage occur in the first seal 10, the liquid level

in the collector compartment 32 will rise to the second level switch 36, see fig. 2.

Thereby, the second level switch 36 outputs a signal to the control 38, which activates the third packer 28 by opening the compressed-air valve 30 simultaneous with starting the pump 44 and outputting a warning.

The third packer 28 is arranged in a manner allowing it also to withstand the pressure from the drilling mud while the pump is pumping the discharging drilling mud onwards to the collector tank 50.

The pipe connection 46, the valves 48, the pump 44 and the collector tank 50 form components in receiving equipment 52 for drilling mud.

Having repaired the leakage, the level in the collector compartment 32 will drop ^' to below the first level switch 34. The first level switch 34 outputs a signal to the control 38, which stops the pump 44 and controls the compressed-air valve 30 to vent the third packer 28 and thus to deactivate it.

Upon having determined the type of liquid that has discharged, the collector tank 50 may be drained to a drilling mud facility (not shown) via a drainage pipe 54.