CA2773632A1

CA2773632A1 - Apparatuses and methods for cooling position sensor components while drilling gravity drainage wells in hot formations

Info

Publication number: CA2773632A1
Application number: CA2773632A
Authority: CA
Inventors: Troy Martin
Original assignee: 1669999 ALBERTA Ltd
Current assignee: 1669999 ALBERTA Ltd
Priority date: 2012-04-11
Filing date: 2012-04-11
Publication date: 2013-10-11

Abstract

A method is disclosed of drilling a second well in a formation that contains a first well and has been heated by a heat assisted gravity drainage operation, the method comprising:
monitoring the location of the second well using a position sensor having components in the first well; drilling the second well using the drill bit and signals from the position sensor; and cooling the components by supplying coolant through one or more supply lines from a ground surface to the components and returning coolant through one or more return lines from the components to the ground surface; in which one of the first well and the second well is a heat injection well and the other of the first well and the second well is a production well. A position sensor is also disclosed comprising: a housing; a sensor having components within the housing, the sensor being for monitoring the location of a second well during drilling of the second well while the housing is in a first well; one or more coolant supply lines extending between a coolant supply and the components; and one or more coolant return lines extending between the components and a coolant return.

Description

APPARATUSES AND METHODS FOR COOLING POSITION SENSOR COMPONENTS
WHILE DRILLING GRAVITY DRAINAGE WELLS IN HOT FORMATIONS
TECHNICAL FIELD
[0001] This document relates to systems and methods for cooling position sensor components while drilling gravity drainage wells in hot formations.
BACKGROUND

[0002] Wells used in heat assisted gravity drainage (HAGD) operations must be carefully positioned relative to one another to maximize production. For example, steam assisted gravity drainage (SAGD) operations generally use pairs of parallel horizontal wells (well pairs) aligned with 4-6 meters of vertical separation across kilometers of well length.

[0003] Position sensors such as magnetometers are used during drilling to ensure proper positioning of the second well relative to the first well. Many replacement position sensors may be required when drilling in a hot formation, such as a formation previously heated by a steam assisted gravity drainage (SAGD) operation, because the position sensors have a limited lifespan at such temperatures. Water may be injected into the formation to cool the formation and sensors to alleviate the number of replacement sensors used to drill or to reduce the temperature of the sensors until they are operating within their temperature specifications.
SUMMARY

[0004] A method is disclosed of drilling a second well in a formation that contains a first well and has been heated by a heat assisted gravity drainage operation, the method comprising: monitoring the location of the second well using a position sensor having components in the first well; drilling the second well using signals from the position sensor;
and cooling the components by supplying coolant through one or more supply lines from a ground surface to the components and returning coolant through one or more return lines from the components to the ground surface; in which one of the first well and the second well is a heat injection well and the other of the first well and the second well is a production well.

[0005] A position sensor is also disclosed comprising: a housing, for example made of one or both of ferrous or non ferrous material; a sensor having components within the housing, the sensor being for monitoring the location of a second well while drilling of the second well while the housing is in a first well; one or more coolant supply lines extending between a coolant supply and the components; and one or more coolant return lines extending between the components and a coolant return.

[0006] In various embodiments, there may be included any one or more of the following features: The components of the position sensor are contained within coiled tubing. The coiled tubing is coil in coil tubing. The one or more supply lines are defined by one or more inner coils of the coil in coil tubing, and the one or more return lines are defined by one or more inner coils of the coil in coil tubing. The one or more supply lines are defined by one or more inner coils of the coil in coil tubing, and the one or more return lines are defined by an outer annulus of the coil in coil tubing. The first well and the second well are a parallel well pair. The first well and the second well are an intersecting well pair.
Drilling the second well further comprises advancing the components towards a toe end of the first well. The first well and the second well are horizontal wells. The position sensor comprises a magnetometer. The components comprise the magnetometer. Carrying out a heat assisted gravity drainage operation, such as a SAGD operation, using the first well and the second well. The components are within a chamber defined by the housing and connected to receive coolant from the one or more coolant supply lines through one or more ports in a downhole end of the chamber. The downhole end and an uphole end of the chamber are each defined by a respective ported plate mounted within the housing. The components are mounted to one or both of the ported plate that defines the downhole end of the chamber and the ported plate that defines the uphole end of the chamber.
The components are located within coiled tubing, for example fixed to the end of the coil tubing, in one of a pair of horizontal wells used for heat assisted gravity drainage.

[0007] These and other aspects of the device and method are set out in the claims, which are incorporated here by reference.

BRIEF DESCRIPTION OF THE FIGURES

[0008] Embodiments will now be described with reference to the figures, which are not to scale, in which like reference characters denote like elements, by way of example, and in which:

[0009] Fig. 1 is a side elevation view, partially in section, of a coil-in-coil tubing rig being used to supply and return coolant to a position sensor in a production well while an injector well is being drilled.

[0010] Fig. 2 is a side elevation view, partially in section, of a position sensor contained in a housing with a sensor chamber, and with arrows illustrating coolant fluid movement through the housing.

[0011] Fig. 3 is a side elevation section view of a position sensor that has two coolant supply lines.

[0012] Fig. 4 is a section view taken along the 4-4 section lines from Fig. 3.

[0013] Fig. 5 is a side elevation section view of a position sensor that has one coolant supply line.

[0014] Figs. 6 and 7 are side elevation views illustrating uphole and downhole port assemblies, respectively, for use with the position sensors of Figs. 8 and 9.

[0015] Fig. 8 is a side elevation section view of another embodiment of a position sensor that has a single coolant supply line.

[0016] Fig. 9 is a side elevation section view of another embodiment of a position sensor that has a plurality of coolant supply lines.

[0017] Fig. 10 is a section view taken along the 10-10 section lines from Figs. 6 and 7.

[0018] Fig. 11 is a section view taken along the 11-11 section lines from Figs. 6 and 7.
DETAILED DESCRIPTION

[0019] Immaterial modifications may be made to the embodiments described here without departing from what is covered by the claims.

[0020] Steam-assisted gravity drainage (SAGD) is a hydrocarbon-producing process that is used to extract viscous hydrocarbons from hydrocarbon-producing reservoirs located under the ground surface. Conventional methods of hydrocarbon extraction, such as mining and/or drilling are generally ineffective or inefficient at extracting viscous hydrocarbons such as bitumen, crude oil, or heavy oil, and thus SAGD and other heat-assisted gravity drainage (HAGD) methods are used to add heat to the hydrocarbons to lower their viscosity to a point where they may be collected in a well for production. Examples of the type of hydrocarbon-producing reservoirs that contain these viscous hydrocarbons include oil sands located primarily in Canada and Venezuela.

[0021] The injection and production wells may be horizontally drilled wells that extend distances of several kilometers from heel-to-toe. Steam is injected into the reservoir along at least a portion of the length of the injection well, permeating the formation and forming a steam chamber throughout the reservoir around the injection well. In some cases other suitable species may be injected other than or in addition to steam, including heated solvent in the case of vapor extraction (VAPEX) or air in the case of toe heel air injection (THAI). Viscous hydrocarbons contained within the steam chamber are heated and reduce in viscosity enough to drain by gravity into the production well, where they are pumped to the surface. This process allows viscous hydrocarbons contained within large, relatively horizontal reservoirs under the ground surface to be effectively extracted.

[0022] Fig. 1 illustrates a horizontal well pair used for steam assisted gravity drainage (SAGD) operations. In some cases the methods disclosed herein may be carried out intersecting wells. The well pair comprises a production well 10 and an injection well 12 above the production well 10. There are no requirements as to which of wells 10 and 12 should be drilled first, but in the example shown the lower production well 10 is drilled first.
In some cases the wells 10 and 12 may be drilled simultaneously although one of the wells may be concurrently drilled ahead of the other.

[0023] SAGD wells may be shallow, and a slant rig (not shown) may be employed to drill the wells a few hundred meters deep. With a slant rig, the drill pipe enters the ground at an angle of about 45 angle, so that the well can build quickly to 90 , i.e.
horizontal. After being drilled in the desired zone, the first well 14, in this case production well 10, may be cased, for example with slotted or perforated liner (not shown) for stability.
In other cases, SAGD wells may be drilled from a vertical well.

[0024] Once the user is ready to drill the second well 16, in this case injection well 12, a wireless or wireline tool such as position sensor 18 described below may be deployed inside the tubing of first well 14. Such a tool is used because the relative distance between the injector and production wells may affect potential recovery. The wells should be located sufficiently near to one another such that heavy oil heated at the injector well may drain into the production well. If the wells are located too near to one another, steam or air from the injector well may shunt into the production well, and if the wells are located too far from one another, the heated heavy oil may not extend to the production well.

[0025] The wireline tool determines the location of second well 16 relative to first well 14. This information is then used to steer the second well 16 parallel or within sufficient proximity to first well 14. The bottom hole assembly 20 in second well 16 may include a steering mechanism (not shown), such as a steerable motor with bent sub or a rotary steerable system, for steering a drill bit 22. Position sensor 18 may use measurement while drilling technology such as magnetic ranging or nuclear ranging. There are several magnetic ranging techniques that may be used, including active and passive ranging.

[0026] Active techniques generally involve the production of a magnetic field in the first well 14 or second well 16, followed by detection in the other of wells 14 or 16 by a sensor such as a magnetometer. For example, the tool 18 may contain a solenoid (not shown) that produces a magnetic field, with known strength and field pattern, that is then detected by a sensor (not shown) in the second well 16. The tubing and slotted casing may affect the magnetic field but these effects can be removed by calibrating the solenoid inside the same size tubing and casing on the surface. The magnitude of the measured magnetic field indicates the separation of the two wells 10, 12 and the direction of the magnetic field indicates their relative positions. In another example, the second well 16 generates the magnetic field using one or more permanent magnets mounted in a near-bit sub (not shown), or on the mud motor (not shown) in some cases. The permanent magnets rotate with the drill bit 22 thus producing an oscillating magnetic field that is detected by a magnetometer in the position sensor 18 as the drill bit 22 passes by the position sensor 18. The distance between the wells 14, 16 is deduced from the variation in the magnetic field with measured depth of the drill bit. In yet another example of an active technique, a wire (not shown) is used in first well 14 to carry a current to the toe 24 of first well 14 where the wire is grounded to the casing 26. Most of the current returns to the surface through the casing 26 but a small amount of current leaks into the formation 28 at each foot along its length.
The leakage current varies from foot to foot depending on the properties of the casing, the cement, and the formation resistivity. The net current produces an azimuthal magnetic field around the wellbore that can be measured with a magnetometer in the second well 16. Other sensors and sensing techniques may be used.

[0027] Passive ranging techniques are generally less effective than active techniques.
For example, permanent magnets may be installed inside the steel casing and alternately magnetized N-S and S-N to create a discernable magnetic field pattern. The magnetic field is measurable within the second well 16 and the information employed to steer drill bit 22.
Afterwards, the permanent magnets may be recovered from the cased well.

[0028] Once a SAGD field is up and running, the formation 28 may be pumped with heat for a suitable amount of time, such as years. Often a single formation 28 will be injected with heat from plural well pairs, in order to heat the entire formation.
However, a user may desire for a variety of reasons to drill additional wells in the formation 28 after heating. For example, a user may want to re-drill an injection well to replace an existing injection well that is not properly aligned with the corresponding production well, or to replace an injection well that has been damaged. In other cases, a user may desire to place an additional well pair at a location in the formation 28 where the steam chamber has not adequately penetrated. A
user may also simply wish to provide a denser matrix of well pairs in order to facilitate maximum draw from the formation 28. In some cases a wedge well may be drilled.

[0029] Components used in the position sensors described above are generally electrical components and include microprocessors, accelerometers, magnetomers, or transducers for example. A limitation on the use of such components may be the high temperatures that are often present and associated with a formation 28 made hot from the SAGD process. Downhole ambient temperatures can approach those of saturated steam and many electrical components that are commercially available cannot operate reliably with such conditions.

[0030] As a result of the temperature limitations on these tools, drilling wells in such hot formations 28 is made more difficult than conventional drilling of these wells. For example, one approach taken is to have in stock a plurality of replacement position sensors that are used one at a time in the first well 14 until inevitable failure of the sensor. Upon failure, the old sensor is withdrawn and a new sensor is inserted. This process is continued until the second well 16 is drilled. This approach is expensive because it requires the purchase of a plurality of replacement sensors, as well as the additional labor and tool rental time required to change out and calibrate each new sensor. This approach may not be possible in wells that are above a certain temperature.

[0031] Another approach is to cool off the formation 28 in the vicinity of the first well 14. This approach involves the injection into first well 14 of coolant such as water.
Again, this approach is also expensive for various reasons. Firstly, it requires large amounts of water, due to the large volume of formation 28 that must be cooled, and due to other factors such as non uniform dispersal into the formation resulting in lingering hot spots that can only be cooled by continual pumping of coolant. Most or all of the injected water must then be recovered and removed from produced bitumen once operations begin again.
Secondly, the injected water cools the formation, meaning that SAGD operations cannot be immediately resumed after the well 16 is drilled because the formation 28 temperature must be raised again by additional and costly steam injection. In addition, the heat plants supplying steam to the formation 28 must be shut down months in advance in order to assist this method. It generally takes months after drilling to get the temperature back up to sufficient levels. Thirdly, this approach imparts a temperature shock on the casing of the first well sufficient to strain and sometimes damage the casing, which may be difficult or impossible to repair.

[0032] Referring to Fig. 1, a method of drilling a second well 16 in a formation 28 that contains a first well 14 and has been heated by a heat assisted gravity drainage operation is illustrated. In the example shown the second well 16 is the upper injector well 12, but this orientation may be reversed and the second well 16 may be the production well 10. The location of the second well 16 is monitored using a position sensor 18 having components 30 in the first well 14. The location of the second well 16 may be indirectly monitored by monitoring the position of the drill bit 22 or the drill string.

[0033] The second well 16 is drilled using the drill bit 22 and signals from the position sensor 18. Such signals may be used in various ways in order to aid in the steering of drill bit 22. In one example the signals are routed to a controller (not shown) that is set to automatically steer drill bit 22 in order to achieve a predetermined distance and alignment with the first well 14. In another example the signals are sent wirelessly or by wire to a console (not shown) where a user interprets the signals or data from the signals in order to manually guide steering of the drill bit 12.

[0034] Referring to Figs. 1 and 2, the components 30 are cooled by supplying coolant through one or more supply lines 32 from a ground surface 36 to the components 30 and returning coolant through one or more return lines 34, such as a coil annulus, from the components to the ground surface 36. Fig. 2 illustrates an exemplary position sensor 18 in greater detail than shown in Fig. 1. Position sensor 18 has a housing 54, components 30 of a sensor 56, one or more coolant supply lines 32 and one or more coolant return lines 34.
Components 30 are located within housing 54 (Fig. 1), the sensor 56 being for monitoring the location of a drill bit 22 (Fig. 1) during drilling of second well 16 while the housing or flask 54 is in first well 14.

[0035] The components 30 contained within housing 54 may include a magnetometer as sensor 56. Other components 30 may be used, such as accelerometers, e-magnets, transducers, wired or wireless transmitters and receivers, and other suitable electronic components. In some cases components 30 may include a magnetic field generator (not shown) instead of a magnetometer. In this case, the position sensor 18 may incorporate other components, such as a magnetometer, that are to be located during drilling in the second well 16. In general when components are mounted in the second well 16, such components may be sufficiently cooled by drilling fluid and may not require a coolant system such as the one used in first well 14 described herein.

[0036] Referring to Fig. 2, the components 30 may be housed within a chamber 58 defined by the housing 54. Chamber 58 may be connected to receive coolant from the one or more coolant supply lines 32 through one or more ports 60 in a downhole end 62 of the chamber 58. The components 30 may be immersed in coolant in use. The downhole end 62 and an uphole end 64 of the chamber 58 may be each defined by ported plates 66 and 68, respectively, mounted within the housing 54. As shown, the components 30 may be mounted to one or both downhole ported plate 66 and uphole ported plate 68. Housing 54 may be designed to allow the one or more supply lines 32 to bypass components 30 in a downhole direction 72, so that coolant from the one or more supply lines 32 may reverse direction and wash over components 30 in an uphole direction 74. Thus, the portion of components 30 that are situated furthest downhole receive the coolest of coolant supply fluid.
This direction of flow may be reversed. The lines 32 and 34 may be oriented as shown to ensure that fluid is circulated through the chamber 58 in one direction only, in this case from downhole end 62 to uphole end 64. Such a circulation loop reduces the possibility of stagnant coolant being retained and overheated in chamber 58 as may occur if fluid were directly supplied to and removed from chamber 58 from the same ported plate. The supply lines 32 may supply coolant to chamber 58 by passing through one or more ports 60 of ported plate 66 into a secondary chamber 76 downhole of the chamber 58, and then reversing direction and entering the chamber 58 by passing through one or more ports 60 in the same ported plate 66 as shown. In other embodiments ported plate 66 is a manifold that combines plural supply lines 32 and directly supplies fluid to chamber 58. A wireline 70 may be used to communicate signals between components 30 and ground surface 36 (Fig. 1).

[0037] The example in Fig. 1 illustrates a coiled tubing rig 38 used to contain and position the components 30 of the position sensor 18 within coiled tubing 40, in this case coil in coil tubing. Coiled tubing has the advantage of allowing the position sensor 18 to be =
precisely repositioned in an inclined well such as a directional or horizontal well without requiring additional components. For example, the injection rate of coiled tubing 40 at rig 38 may be controlled to advance the components 30 towards a toe end 24 of the first well 14 at the desired rate and temperature without dumping unwanted fluid in the well bore. By contrast, conventional wireline sensors may require additional components such as tractors or hydraulic tubing to reposition the sensors in a directional or horizontal well.

[0038] As shown in Fig. 1, coil in coil tubing 40 may be used to contain the components 30 of position sensor 18. The one or more supply lines 32 may be defined by one or more inner coils 42 of the coil in coil tubing, and the one or more return lines 34 may be defined at least in part by an outer annulus 44 of the coil in coil tubing.
Pumping return coolant up the annulus provides a shielding effect to coolant being supplied through the supply lines 32, because the return coolant insulates the supply coolant from heat from the formation 28. This effect will be realized to some extent with the use of a return line 34 in general. In the example shown, a pump 46 may be used to pump coolant from a coolant supply such as a reservoir 48, down supply line 32 to components 30, up return line 34, and into a coolant return such as a reservoir 52 at ground surface 36. In some embodiments, the one or more supply lines 32 are defined by one or more inner coils of the coil in coil tubing, and the one or more return lines 34 are defined by one or more inner coils of the coil in coil tubing. Reservoirs 48 and 52 may be independent, linked, or may be the same reservoir in some cases. A cooling system (not shown) may be used to cool reservoir fluid.
Coolant may be recycled by these or other methods. Although coil in coil tubing is illustrated by concentric coil in coil tubing, other coil in coil tubing may be used, such as coil in coil tubing with plural inner tubes.

[0039] Referring to Figs. 3-5 embodiments of a position sensor 18 are illustrated that have a single supply line 32 (Fig. 5) or plural supply lines 32 (Fig. 3).
Other numbers of lines 32 or 34 may be used. In both Figs. 3 and 5, each supply line 32 passes through a series of ported plates 78 en route to secondary chamber 76 at the end of the sensor 18.
Each line 32 may be secured within a port 60 in the ported plates 78 by a suitable mechanism such as one or more set screws 80. Gaskets (not shown) such as 0-rings may be used to seal the space between each plate 78 and each line 32. In the multi supply example of Figs. 3 and 4, two supply lines 32 provide coolant to chamber 76, which then supplies coolant to sensor chamber 58 through two open ports 61 in the two most downhole plates 79.
Coolant is then returned from chamber 58 up the annulus 59 and around supply lines 32 within coiled tubing

40. In the single supply example of Fig. 5, supply line 32 supplies coolant to chamber 76 through the most downhole plate 81 shown, which then supplies coolant to chamber 58 through ports 63 in the two most downhole plate 81 and 83. Coolant leaves chamber 58 through return line 34, which connects to chamber 58 through another port 65 in the plate 83 that defines the uphole end 81 of chamber 58 as shown.
[0040] Figs. 6-11 show various parts that make up the chamber 58 in another embodiment of a position sensor 18 housing 54. Figs. 6 and 7 illustrate the uphole and downhole ported plate assemblies 82, 84, respectively. The uphole assembly 82 may have a pin 90 and the downhole assembly 84 may have a box 92 for mounting the components 30 (not shown) within chamber 58 (not shown) when the tool is assembled. Figs. 10 and 11 illustrate the two types of ported plates 86 and 88 used in both assemblies 82, 84. Figs. 8 and 9 illustrate the assemblies 82 and 84 connected to give a single supply embodiment (Fig. 8) and a plural supply embodiment (Fig. 9).

[0041] A test was carried out using a housing 54 at the end of two 1900 meters of coiled one way coolant line within a steam truck. Thus, there was no return line washing over the coil as would be present in the examples shown in the drawings. The removal of the return line represents a worst case scenario, i.e. if the return line 34 failed in a real life application of using the tool. Steam was injected into the apparatus until all the components reached a temperature above 240 C. The temperature was held at 240 C for two hours before coolant was pumped into both coils at a combined flow rate of 19 liters/minute (0.019 cubic meters/min) and 1145 psi. The temperature of the tool dropped below the target temperature of 120 C. Note that the flow rate can be brought up substantially by adding additional coolant. In a downhole environment the returning fluid would add an additional barrier insulating the injection fluid from the formation temperature. This test illustrated that the sensors could be adequately cooled using a fraction of the amount of water used previously to cool down the formation, even if the coolant did not return to the surface.

[0042] A well pair may originate from two separate mother wells, or from a single multilateral mother well to reduce environmental impact. A magnetometer may be a three axis magnetometer, which allows the direction of the second well 16 to the casing to be deduced from the three orthogonal components of the magnetic field. Although described above for use in drilling horizontal SAGD well pairs, the methods and apparatuses can be used for other HAGD methods that require precise positioning of one well next to another, for example cross SAGD (X-SAGD), THAI, and VAPEX methods. More than one sensor or component may be carried within the housing 54. The housing 54 may be threaded or otherwise modified so as to allow the coupling of additional lengths of housing 54 that have a similar thread or coupling modification, to increase or decrease the length of chamber 58.
The housing 54 may be threaded or otherwise modified so as to allow coupling with a coiled tubing drill string, drill pipe or well bore tractor. The number of supply and return lines do not need to be equal, and include one, two, or a plurality of lines. The coolant does not need to directly contact the components 30, but may indirectly cool the components 30 by passing sufficiently adjacent the components 30. Suitable coolants may be used, including water, nitrogen, propane, hydrocarbons, and other suitable fluids, including gases or liquids. The plates 66 and 68 may centralize the components 30 within chamber 58. The temperature in the chamber 58 may be monitored directly or indirectly and a coolant characteristic such as flow or coolant temperature adjusted in order to maintain the chamber 58 within a predetermined range of temperatures. The actual sensor may be located in the second well, while other related components are located within the first well. One, two, or a plurality of ports may be provided in each ported plate.

[0043] In the claims, the word "comprising" is used in its inclusive sense and does not exclude other elements being present. The indefinite articles "a" and "an"
before a claim feature do not exclude more than one of the feature being present. Each one of the individual features described here may be used in one or more embodiments and is not, by virtue only of being described here, to be construed as essential to all embodiments as defined by the claims.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of drilling a second well in a formation that contains a first well and has been heated by a heat assisted gravity drainage operation, the method comprising:
monitoring the location of the second well using a position sensor having components in the first well;
drilling the second well using signals from the position sensor; and cooling the components by supplying coolant through one or more supply lines from a ground surface to the components and returning coolant through one or more return lines from the components to the ground surface;
in which one of the first well and the second well is a heat injection well and the other of the first well and the second well is a production well.

2. The method of claim 1 in which the components of the position sensor are contained within coiled tubing.

3. The method of claim 2 in which the coiled tubing is coil in coil tubing.

4. The method of claim 3 in which the one or more supply lines are defined by one or more inner coils of the coil in coil tubing, and the one or more return lines are defined by one or more inner coils of the coil in coil tubing.

5. The method of claim 3 in which the one or more supply lines are defined by one or more inner coils of the coil in coil tubing, and the one or more return lines are defined by an outer annulus of the coil in coil tubing.

6. The method of any one of claim 2 - 5 in which the first well and the second well are a parallel well pair.

7. The method of claim 6 in which drilling the second well further comprises advancing the components towards a toe end of the first well.

8. The method of any one of claim 1 - 7 in which the first well and the second well are horizontal wells.

9. The method of any one of claim 1 - 8 in which the position sensor comprises a magnetometer.

10. The method of claim 9 in which the components comprise the magnetometer.

11. The method of any one of claim 1 - 10 further comprising carrying out a steam assisted gravity drainage operation using the first well and the second well.

12. A position sensor comprising:
a housing;
a sensor having components within the housing, the sensor being for monitoring the location of a second well during drilling of the second well while the housing is in a first well;
one or more coolant supply lines extending between a coolant supply and the components; and one or more coolant return lines extending between the components and a coolant return.

13. The position sensor of claim 12 in which the components are within a chamber defined by the housing and connected to receive coolant from the one or more coolant supply lines through one or more ports in a downhole end of the chamber.

14. The position sensor of claim 13 in which the downhole end and an uphole end of the chamber are each defined by a respective ported plate mounted within the housing.

15. The position sensor of claim 14 in which the components are mounted to one or both of the ported plate that defines the downhole end of the chamber and the ported plate that defines the uphole end of the chamber.

16. The position sensor of any one of claim 12 - 15 in which the components are located within coiled tubing in one of a pair of horizontal wells used for heat assisted gravity drainage.

17. The position sensor of claim 16 in which the coiled tubing is coil in coil tubing.

18. The position sensor of any one of claim 12 - 17 in which the components comprise a magnetometer.

19. The method of any one of claims 1-11 in which monitoring the location of the second well comprises monitoring the location of a drill string.