Sealing assembly

1. A pressure containment device for sealing around rotating drill string during drilling of a well bore, comprising an actuator assembly and a seal assembly, the actuator assembly being operable to engage with the seal assembly to prevent significant rotation of the seal assembly with respect to the actuator assembly and to force the seal assembly into sealing engagement with a drill string mounted in the pressure containment device, the seal assembly comprising:

a tubular seal sleeve having a radially inward portion made from a non-elastomeric polymer, and a radially outward portion made from an elastomer,

wherein,

the radially inward portion of the seal sleeve contains a plurality of apertures, and

elastomeric parts of the radially outward portion of the seal sleeve extend into the plurality of apertures of the radially inward portion.

2. A pressure containment device according to claim 1 wherein the actuator assembly includes an annular packing unit and an actuator operable to reduce the internal diameter of the annular packing unit.

3. A pressure containment device according to claim 2 wherein the seal sleeve is in use positioned generally centrally of the packing unit so that the packing unit surrounds at least a portion of the seal sleeve.

4. A pressure containment device according to claim 2 wherein the actuator comprises a piston movable generally parallel to a longitudinal axis of the pressure containment device by a supply of pressurised fluid to the pressure containment device.

5. A pressure containment device according to claim 1 wherein the radially inward portion of the seal sleeve is made from one of polytetrafluoroethylene (PTFE), a PTFE-based polymer or ultra-high molecular weight polyethene (UHMWPE).

6. A pressure containment device according to claim 1 wherein the radially inward portion of the seal sleeve contains an additive or filler.

7. A pressure containment device according to claim 6 wherein the additives or filler comprises at least one of fibreglass, molybdenum disulphide, tungsten disulphide or graphite.

8. A pressure containment device according to claim 1 wherein the radially outward portion of the seal sleeve is made from one of polyurethane or hydrogenated nitrile butadiene rubber.

9. A pressure containment device according to claim 1 further comprising a second actuator assembly and seal assembly, the second actuator assembly being operable to engage with the second seal assembly to prevent significant rotation of the second seal assembly with respect to the second actuator assembly and to force the second seal assembly into sealing engagement with a drill string mounted in the pressure containment device, the second seal assembly also comprising a tubular seal sleeve having a radially inward portion made from a non-elastomeric polymer, and a radially outward portion made from an elastomer.

10. A pressure containment device according to claim 9 further comprising means to direct lubricating fluid to the region around the drill string between the first and second seal assemblies.

11. A pressure containment device according to claim 1 wherein the actuator assembly is operable to force the seal assembly into sealing engagement with a drill string mounted in the pressure containment device whilst allowing rotation of the drill string relative to the pressure containment device.

12. The pressure containment device as recited in claim 1 , wherein the radially inward portion of the seal sleeve is formed as a cylindrical tube.

13. The pressure containment device as recited in claim 12 , wherein the plurality of apertures of the radially inward portion of the seal sleeve are arranged so as to have a honeycomb mesh structure.

14. A method of containing pressure in a well bore, a drill string extending into the well bore, the method comprising mounting a pressure containment device around the drill string, the pressure containment device comprising an actuator assembly and a seal assembly, the seal assembly comprising a tubular seal sleeve having a radially inward portion made from a non-elastomeric polymer, and a radially outward portion made from an elastomer, wherein the radially inward portion of the seal sleeve contains a plurality of apertures, elastomeric parts of the radially outward portion of the seal sleeve extend into the plurality of apertures of the radially inward portion, and the method comprises:

operating the actuator assembly to engage with the seal assembly to prevent significant rotation of the seal assembly with respect to the actuator assembly and to force the radially inward portion of the seal sleeve into sealing engagement with the drill string, whilst allowing rotation of the drill string relative to the pressure containment device.

15. The method of claim 14 wherein the step of operating the actuator assembly comprises supplying pressurised fluid to the pressure containment device.

16. The method of claim 15 further comprising varying the force exerted on the drill string by the seal sleeve by varying the pressure of fluid supplied to the actuator assembly.

17. A pressure containment device for sealing around rotating drill string during drilling of a well bore, comprising an actuator assembly and a seal assembly, the actuator assembly being operable to engage with the seal assembly to prevent significant rotation of the seal assembly with respect to the actuator assembly and to force the seal assembly into sealing engagement with a drill string mounted in the pressure containment device, the seal assembly comprising:

a tubular seal sleeve having a radially inward portion made from a non-elastomeric polymer, and a radially outward portion made from an elastomer,

wherein,

the radially inward portion of the seal sleeve contains a plurality of radially-extending apertures, and

elastomeric parts of the radially outward portion of the seal sleeve extend into the plurality of radially-extending apertures of the radially inward portion.