I claim:
1. A radiant electric heater comprising:
a base of thermal insulation material having supported relative thereto at least two concentrically-arranged heating elements separated by a dividing wall of thermal insulation material to form an outer heating zone and an inner heating zone, the heater having a peripheral wall of thermal insulation material;
a tunnel formed of thermal insulation material extending between the peripheral wall and the dividing wall across the outer heating zone and such that at least one heating element of the outer heating zone is substantially absent from an area occupied by the tunnel;
a rod-like temperature-responsive device extending from a periphery of the heater through the tunnel and at least partly across the inner heating zone, through an aperture provided in the dividing wall;
at least one portion of at least one heating element of the inner heating zone extending into the tunnel; and
ventilation means provided for the tunnel intermediate the ends thereof to reduce temperature within the tunnel to a desired level.
2. A heater according to claim 1, wherein the ventilation means comprises at least one aperture extending into the tunnel from the outer heating zone.
3. A heater according to claim 2, wherein the at least one aperture is provided at a base region of side walls of the tunnel.
4. A heater according to claim 1, wherein the tunnel is of substantially inverted U-shaped cross section and supported on lower edges thereof.
5. A heater according to claim 4, wherein the tunnel is supported such that at least one aperture is provided between the tunnel and the base.
6. A heater according to claim 5, wherein the tunnel is supported on spaced-apart protrusions provided on the base.
7. A heater according to claim 6, wherein the protrusions are integral with the base.
8. A heater according to claim 5, wherein the tunnel has at least one lower edge of substantially castellated form.
9. A heater according to claim 5, wherein at least one pedestal region is formed by at least one lower region of the peripheral wall, the tunnel being spaced from the base at an end thereof by the at least one pedestal region.
10. A heater according to claim 5, wherein at least one pedestal region is formed by at least one lower region of the dividing wall, the tunnel being spaced from the base at an end thereof by the at least one pedestal region.
11. A heater according to claim 4, wherein at least one recess is provided in the base of thermal insulation material extending beneath at least one lower edge of the tunnel.
12. A heater according to claim 1, wherein the tunnel is integral with the dividing wall.
13. A heater according to claim 1, wherein the tunnel is integral with the peripheral wall.
14. A heater according to claim 1, wherein the tunnel comprises bound vermiculite.
15. A heater according to claim 1, wherein the at least one portion of the at least one heating element of the inner heating zone extends through the tunnel to a terminal region at the edge of the heater.
16. A heater according to claim 15, wherein the tunnel is provided with a laterally-extending portion proximate the peripheral wall to shield the at least one portion of the at least one heating element in the vicinity of the terminal region.
17. A heater according to claim 1, wherein the at least one heating element of the inner heating zone is energisable independently of the at least one heating element of the outer heating zone.
18. A heater according to claim 1, wherein the heating elements are of ribbon form.
19. A heater according to claim 18, wherein the heating elements are supported edgewise on the base.
20. A heater according to claim 1, wherein the base comprises microporous thermal and electrical insulation material.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A mill for running into a well bore comprising:
a substantially cylindrical mill body and at least one cutting or abrading element attached to said cylindrical mill body;
said cylindrical mill body having a recess defined therein for receiving a latch;
said latch received within said cylindrical body recess and movably attached to said cylindrical body between an open position and a closed position; and
an actuator for closing said latch against said cylindrical body to a closed position.
2. The mill of claim 1, further comprising:
an actuator for closing said latch radially inwardly against said cylindrical body to said closed position.
3. The mill of claim 1, further wherein said latch outer surface has substantially the same curvature as the substantially cylindrical mill body, such that when said latch is in said closed position, said substantially cylindrical mill body and said latch cooperate to form a cylindrical mill body surface.
4. The mill of claim 1, further wherein said actuator is controlled by a controller remote from said mill.
5. The mill of claim 1, further wherein said actuator is controlled by a controller on said surface of said well bore.
6. A mill for running a whipstock into a well bore comprising:
a substantially cylindrical mill body and at least one cutting or abrading element attached to said cylindrical mill body;
said cylindrical mill body having a recess defined therein for receiving a latch;
said latch received within said cylindrical body recess and movably attached to said cylindrical body between an open position and a closed position;
a whipstock having a top and a bottom and an angled face;
said whipstock further having a sleeve mounted along said angled face for receiving said latch;
wherein when said latch is inserted into said whipstock sleeve, said whipstock can be run into the wellbore attached to said mill; and
an actuator for closing said latch against said cylindrical body to said closed position.
7. The mill of claim 6, further comprising:
wherein said actuator closes said latch radially inwardly against said cylindrical body to said closed position.
8. The mill of claim 6, further wherein said latch outer surface has substantially the same curvature as the substantially cylindrical mill body, such that when said latch is in said closed position, said substantially cylindrical mill body and said latch cooperate to form a cylindrical mill body surface.
9. The mill of claim 6, further wherein said actuator is controlled by a controller remote from said mill.
10. The mill of claim 6, further wherein said whipstock angled face has a center and said sleeve is attached to said angled face substantially in said angled face center.
11. A method of running a whipstock into a well bore comprising:
providing a substantially cylindrical mill body having at least one cutting or abrading element attached to said cylindrical mill body;
providing walls on said cylindrical mill body defining a recess therein for receiving a latch;
providing a latch moveable attached within said cylindrical body recess;
providing an actuator for remotely selectively moving said latch between a first closed position adjacent said cylindrical body and a second open position outward from said cylindrical body, and for selectively returning said latch to said first closed position;
providing a whipstock having a top and a bottom and an angled face;
providing said whipstock with a sleeve mounted along said angled face for receiving said latch;
threading said latch on said mill body into said sleeve on said whipstock;
inserting said mill body and said whipstock in said wellbore.
12. The method of claim 11, further providing the step of:
actuating said actuator to move said latch into said closed position before inserting said mill body and said whipstock in said wellbore.
13. The method of claim 11, further providing the step of:
actuating said actuator to move said latch into said open position to release said latch from said sleeve and thereby release said whipstock from said mill body.
14. The method of claim 11, further providing the step of:
actuating said actuator to move said latch into said open position and rotating said mill body relative to said whipstock to release said latch from said sleeve and thereby release said whipstock from said mill body.