GB2174012A - Method and apparatus for producing oil-based drilling mud - Google Patents

Abstract

In a method for producing oil-based drilling mud, oil, water and emulsifiers are premixed in a first agitator tank 20 and, in a second agitator tank 22 in communication with this, mixed with bentonite and barium sulphate. The mixture in the second tank is stirred by means of disc agitators 30 with a powerful shearing action sufficient to breakdown the bentonite, and is circulated through the two agitator tanks by means of an impeller agitator 32. The second tank may be slightly heated to accelerate the breaking down of the bentonite by a heater accommodated in partition 28. <IMAGE>

Description

SPECIFICATION M lixod and apparatus for producing oil-based dllin sDUd The invention relates to a method of, and apparatus for, producing oil-based drilling mud.

Whereas water-based drilling mud is generally used in conventional oil wells, so-called oil-based drilling mud is used, particularly in the region of the North Sea, mainly because of the geological formations occurring there.

Oil-based drilling mud consists essentially of the components oil and water in a ratio in the region of about 80:20. In order to prevent coalescing of the dispersed water phase, emulsifiers are used which are based essentially on a soap base.

Furthermore, in order to adapt the density of the finished oil mud to the particular well depth, barium sulphate is added, which has a high specific gravity. In order to prevent the barium sulphate uniformly distributed in the oil mud from being precipitated, a substance which increases the mud viscosity, for example a bentonite, is added to the oil mud. Bentonites have the rheological property that they flow under shearing stress whereas they behave almost like solid bodies in the state of rest or without shearing.

In the accompanying drawing, Fig. 1 shows a known installation for the production of oil-based drilling mud, and Fig. 2 shows an installation according to the invention for the production of oil-based drilling mud.

In the known method as shown in Fig. 1, oil, water, emulsifiers, bentonite and barium sulphate are premixed in a tank 10 by means of an agitator 12. The premixed liquid is then fed, by means of a high-pressure pump 14, to a mixer 16 and is recycled from there into the tank 10 through a pipeline 18. In the course of this, the material is circulated and the mixer 16 is a so-called hopper in which beo jets of the premixed liquid impinge on one another and the oil is mixed with the water, the hopper being heated to a relatively high temperature of the order of magnitude of about 90"C in order to break up the bentonite.

Since the piston drilling-mud pump of the drilling plafform is generally used as the pump 14 during the preparation of the drilling mud, the oil drilling has to be stopped during this time. This is a great disadvantage because the production of about 400/m3 of drilling mud takes about 24 hours.

It is the object of the invention to avoid these disadvantages.

Its object is to develop further a method and an apparatus of the type mentioned at the beginning in such a manner that the drilling-mud pump used for the oil drilling is not necessary for the preparation of drilling mud and in particular, the expensive hopper can also be dispensed with.

According to the invention, this is achieved in that oil, water and emulsifiers are premixed in a first tank and are finish-mixed with the bentonite and barium sulphate with a powerful shearing action sufficient to break down the bentonite in a second tank in communication with this, while being circulated through the two tanks.

In this case, the mixing is advantageously effected in the first tank, but particularly also in the second tank, at room temperature.

The bentonite and the barium sulphate are preferably fed into the second tank.

The apparatus for carrying out the method appropriately comprises a first tank and a second tank in communication with this, at least one agitator for the premixing being disposed in the first tank and the second tank being provided with at least one agitator to produce a powerful shearing action and to circulate the mixture.

In the case of the agitator in the second tank, disc agitators, for example toothed discs for producing a powerful shearing action and an impeller agitator, for example, for conveying and circulating the mixture, are preferably disposed on a common shaft.

The volume ratio of the second tank to the first tank may appropriately be in the range from about 0.05 to 0.1.

For special applications, for example in the case where special bentonites are used, the second tank may additionally be slightly heated, for example to 4050 C, by means of a heating device in order to accelerate the break-up process.

Preferably the peripheral speed of the agitator in the second tank in which the powerful shearing action is achieved, is about S16 m per second and the external diameter of this agitator is about 30% of the diameter of the second tank.

One form of embodiment of the invention is described by way of example with reference to Fig 2.

It was expiained above that in the known method, heating of the mixer to about 90"C was considered necessary.

Extensive experiments have now shown, however, that the breaking down of bentonite can also be effected at room temperature by means of a powerful shearing action, the shearing action being achieved by means of an agitator which works with power levels of the order of magnitude of about S10 KW/m3.

This has the advantage that the very expensive piston pump and hopper, which are used in the known method, can be replaced by an agitator tank having an agitator with a powerful shearing action. This agitator tank is in communication with another agitator tank which is stirred considerabFy more lightly, however, and in which a premixing is effected.

The experiments have shown that a satisfactory quality of mud is achieved without any problems at room temperature with such an installation.

As Fig. 2 shows, the apparatus according to the invention consists of a first agitator tank 20 and a second agitator tank 22 in communication with this. The two tanks 20 and 22 may be constructed separately and be connected to one another by pipes but they may also be parts of a larger tank, as illustrated, which are separated from one another by a partition 28 and are in communication with one another through connecting passes 34, 36.

Oil, water and emulsifiers are fed into the first agitator tank 20, preferably from above, and are premixed by ordinary commercial agitators 24 which run slowly. The agitator tank 20 may be divided into a plurality of portions and an agitator 24 may be allocated to each portion.

The second agitator tank 22 is provided with at least one agitator 26 by means of which a powerful shearing action is produced in the material to be mixed. Disc agitators 30, for example, particularly agitators with so-called toothed discs, are suitable for this. The agitator 26 is further provided with an impeller agitator 32 which projects into a guide tube 38 and serves to convey the mixture or to circulate it in the direction of the arrows so that it flows through the upper passage 34 from the agitator tank 20 into the agitator tank 22 and flows back through the lower passage 36 from the agitator tank 22 into the agitator tank 20.

The disc agitators 30 and the impeller agitator 32 are preferably mounted on one and the same shaft of the agitator 26, the impeller agitator 32 appropriately forming the lowest agitator stage.

The peripheral speed of the agitator 26, that is to say in particular of the disc agitators 30, is preferably in the range from 8 to 16 second and the external diameter of the agitator 26, that is to say particularly of the disc agitators 30, is preferably in the region of 30% of the diameter of the agitator tank 22.

The power is in the region of p10 KW/m3 and the mixing time is about 24 hours.

The addition of the bentonite and of the barium sulphate is effected in the second agitator tank 22.

Thus only a premixing by means of slow-speed agitators is effected in the first agitator tank 20, practically without any shearing action, while in the second agitator tank 22 into which the bentonite and the barium sulphate are fed, the material is stirred and mixed with a powerful shearing action and circulated through the two agitator tanks 20, 22 by the impeller agitator 32.

In many cases, for example if special bentonites are used, the agitator tank 22 may be slightly heated, for example to temperatures of 40--50"C, in order to accelerate the breaking down process of the bentonite. A suitable heating device may be accommodated in the partition 28 for example.

Claims (10)

1. A method of producing oil-based drilling mud wherein oil, water, emulsifiers, bentonite and barium sulphate are mixed, characterised in that the oil, water and emulsifiers are premixed in a first agitator tank and are finish-mixed with the bentonite and barium sulphate with a powerful shearing action sufficient to break down the bentonite in a second agitator tank in communication with this, while being circulated through the two tanks.

2. A method as claimed in claim 1, characterised in that the mixing in the two agitator tanks is effected at room temperature.

3. A method as claimed in claim 1 or 2, characterised in that the bentonite and the barium sulphate are fed into the second agitator tank.

4. An apparatus for carrying out the method as claimed in claim 1, characterised in that a first agitator tank and a communicating second agitator tank are provided, and that the first agitator tank is provided with at least one agitator for the premixing and the second agitator tank is provided with at least one agitator for producing the powerful shearing action and for circulating the mixture.

5. An apparatus as claimed in claim 4, characterised in that, in the case of the agitator in the second agitator tank, disc agitators for producing a powerful shearing action and an impeller agitator for circulating the mixture are disposed on a common shaft.

6. An apparatus as claimed in Claim 4 or 5, characterised in that the volume ratio of the second agitator tank to the first is substantially in the range from 0.05 to 0.1.

7. An apparatus as claimed in one of the claims S6, characterised in that the second agitator tank is provided with a heating device.

8. An apparatus as claimed in one of the claims Q7, characterised in that the peripheral speed of the second agitator is about 8-16 m/sec and its external diameter is about 30% of the diameter of the second agitator tank.

9. A method of producing oil-based drilling mud substantially as described.

10. Apparatus for producing oil-based drilling mud substantially as described with reference to Fig. 2.