Title:
METHOD AND DEVICE FOR DRILLING HOLES IN ICE
United States Patent 3680645
Abstract:
A method and apparatus for drilling holes in ice by melting the ice at the bottom of a drill hole to form a water reservoir and cooling the wall to re-freeze the upper portion of the water reservoir so that a continuous ice shell is maintained around the drill hole.
US Patent References:
Drilling wells through heaving or sloughing formations
Bowie et al. - March 1940 - 2193219
Combination cookstove and device for cutting holes through ice
Ostrowski - July 1954 - 2684669
Bottom hole pressure control in well drilling
Wells - March 1957 - 2786652
Coffer-dam
Perkins - April 1960 - 2931187
Nuclear reactor apparatus for earth penetration
Adams - December 1963 - 3115194
Drilling wells through heaving or sloughing formations
Bowie et al. - March 1940 - 2193219
Combination cookstove and device for cutting holes through ice
Ostrowski - July 1954 - 2684669
Bottom hole pressure control in well drilling
Wells - March 1957 - 2786652
Coffer-dam
Perkins - April 1960 - 2931187
Nuclear reactor apparatus for earth penetration
Adams - December 1963 - 3115194
Inventors:
Horbach Deceased., Edwin (LATE OF Stuttgart-Rohr, DT)
Horbach, Rita
Horbach, Yvonne
Horbach, Konstanze
Horbach, Rita
Horbach, Yvonne
Horbach, Konstanze
Application Number:
04/863176
Publication Date:
08/01/1972
Filing Date:
10/02/1969
View Patent Images:
Export Citation:
Primary Class:
Other Classes:
175/18
International Classes:
E21B7/15; E21B17/00; E21B7/14; F25C5/04
Field of Search:
175/16,17,11,18,213
US Patent References:
Primary Examiner:
Leppink, James A.
Assistant Examiner:
Favreau, Richard E.
Claims:
Having thus fully described my invention, what I claim as new and wish to secure by Letters Patent is
1. Method of drilling a hole in ice comprising melting said ice at the bottom of said hole to form at said bottom of said hole a water reservoir, cooling the wall of said hole at a certain distance from said bottom to such a low temperature that part of the previously melted ice is re-frozen to form an ice shell constituting the confines of said hole and the top of said water reservoir, and removing excess melted ice from said hole.
2. Method in accordance with claim 1, characterized by pressure-flush removal, of solid particles from the water reservoir where they have accumulated.
3. Drilling unit for drilling holes in ice comprising a hollow drill rod, an annular melting head adapted to be heated and positioned at the bottom end of said drill rod, a cooling means positioned above said melting head for keeping the outside face of said drill rod at a temperature of less than 0° centigrade, and a heat insulating material positioned on the inside of said hollow drill rod.
4. Drilling unit in accordance with claim 3, characterized by the fact that said melting head has a cutting edge at its bottom end.
5. Drilling unit in accordance with claim 3, characterized by heat insulation being provided between said melting head and said drill rod.
6. Drilling unit in accordance with claim 3, characterized by the fact that electric heating elements are arranged in said melting head and that electric lines leading to these heating elements are run through cavities of said drill rod which is double-walled.
7. Drilling unit in accordance with claim 3, characterized by the fact that, at the bottom end of said drill rod cooling means are provided which are fed with a coolant through lines, which are run through cavities of drill rod which, is doubled-walled.
8. Drilling unit in accordance with claim 3, characterized by the fact that, for heating said melting head and for cooling drill rod, a Peltier arrangement is used.
9. Drilling unit in accordance with claim 3, characterized by the fact that, at the bottom end of the drill rod, feelers for detecting the presence of melted ice are arranged.
10. Drilling unit in accordance with claim 3, characterized by the fact that the heat-insulating material completely fills said drill rod and that two pipes run through it, one of which is used for introducing a flushing fluid and the other for removing melted ice and/or solid particles of material included in the ice.
11. Drilling unit in accordance with claim 10, characterized by said pipes being arranged concentrically one in the other.
12. A method of forming a hole in ice having a defined boundary comprising:
13. melting said ice in the region in which said hole is desired thereby forming a reservoir of water in the vicinity thereof,
14. re-freezing the upper portion of said reservoir of water to form a hole in said ice having said defined boundary, and
15. removing water from said water reservoir in excess of the amount required to form, upon re-freezing, said defined boundary.
16. An apparatus for forming a hole in ice comprising:
17. a hollow drill tube,
18. a melting head means, annularly arranged at the lower end of said hollow drill tube, for melting said ice,
19. a cooling means, positioned above said melting head means, for cooling the exterior surface of said drill tube to re-freeze the upper portion of the melted ice so that said hollow drill tube is encased by said ice,
20. an insulating means, located between said melting head means and said cooling means, for limiting the conduction of heat therebetween, and
21. a means, operatively arranged in the lower end of said hollow drill tube, for removing melting ice in excess of the amount required to form, upon re-freezing, the encasing ice.
1. Method of drilling a hole in ice comprising melting said ice at the bottom of said hole to form at said bottom of said hole a water reservoir, cooling the wall of said hole at a certain distance from said bottom to such a low temperature that part of the previously melted ice is re-frozen to form an ice shell constituting the confines of said hole and the top of said water reservoir, and removing excess melted ice from said hole.
2. Method in accordance with claim 1, characterized by pressure-flush removal, of solid particles from the water reservoir where they have accumulated.
3. Drilling unit for drilling holes in ice comprising a hollow drill rod, an annular melting head adapted to be heated and positioned at the bottom end of said drill rod, a cooling means positioned above said melting head for keeping the outside face of said drill rod at a temperature of less than 0° centigrade, and a heat insulating material positioned on the inside of said hollow drill rod.
4. Drilling unit in accordance with claim 3, characterized by the fact that said melting head has a cutting edge at its bottom end.
5. Drilling unit in accordance with claim 3, characterized by heat insulation being provided between said melting head and said drill rod.
6. Drilling unit in accordance with claim 3, characterized by the fact that electric heating elements are arranged in said melting head and that electric lines leading to these heating elements are run through cavities of said drill rod which is double-walled.
7. Drilling unit in accordance with claim 3, characterized by the fact that, at the bottom end of said drill rod cooling means are provided which are fed with a coolant through lines, which are run through cavities of drill rod which, is doubled-walled.
8. Drilling unit in accordance with claim 3, characterized by the fact that, for heating said melting head and for cooling drill rod, a Peltier arrangement is used.
9. Drilling unit in accordance with claim 3, characterized by the fact that, at the bottom end of the drill rod, feelers for detecting the presence of melted ice are arranged.
10. Drilling unit in accordance with claim 3, characterized by the fact that the heat-insulating material completely fills said drill rod and that two pipes run through it, one of which is used for introducing a flushing fluid and the other for removing melted ice and/or solid particles of material included in the ice.
11. Drilling unit in accordance with claim 10, characterized by said pipes being arranged concentrically one in the other.
12. A method of forming a hole in ice having a defined boundary comprising:
13. melting said ice in the region in which said hole is desired thereby forming a reservoir of water in the vicinity thereof,
14. re-freezing the upper portion of said reservoir of water to form a hole in said ice having said defined boundary, and
15. removing water from said water reservoir in excess of the amount required to form, upon re-freezing, said defined boundary.
16. An apparatus for forming a hole in ice comprising:
17. a hollow drill tube,
18. a melting head means, annularly arranged at the lower end of said hollow drill tube, for melting said ice,
19. a cooling means, positioned above said melting head means, for cooling the exterior surface of said drill tube to re-freeze the upper portion of the melted ice so that said hollow drill tube is encased by said ice,
20. an insulating means, located between said melting head means and said cooling means, for limiting the conduction of heat therebetween, and
21. a means, operatively arranged in the lower end of said hollow drill tube, for removing melting ice in excess of the amount required to form, upon re-freezing, the encasing ice.
Description:
The present invention relates to a method and a device for drilling holes in ice. Drilling in ice is of interest for the exploration of the Arctic and Antarctic ice caps as well as for the exploitation of oil fields underlying these ice caps. Practical experiments have shown that the drilling methods known to date do not lead to any satisfactory results. In the case of the Rotary Drilling Method, generally applied today, considerable heat is developed in the area of the drill point, which melts the ice and leads to uncontrollable hollows. The consequence of this is that the development of the hole is absolutely uncontrollable and that uncontrollable melting occurs, which continues up to the surface of the ice and even jeopardizes the stability of the drilling derrick anchored in the ice. So far no means is known by which these phenomena in Rotary Drilling could be prevented.
In addition to the Rotary Method, only the Percussion Drilling Method is known so far, in which, with the aid of a rope or a string of drill pipe, a sleeve is driven into the ice by repeated percussion. By this method only low drilling rates and comparatively shallow depths can be reached, so that this method is uneconomical and the achievable hole depths, in many cases, are insufficient. Not lastly because of the great hardness of the ice, it appears impossible that, by this method, better results could be achieved in ice than by the Rotary Method dealt with above.
Accordingly, the basis of the invention is the task of providing an ice drilling method permitting the drilling of satisfactory deep holes and which in addition is economical.
According to the present invention, this task is accomplished by melting of ice at the bottom of the hole by heat supply, so that at the bottom of the hole a kind of water reservoir is formed, and by cooling the wall of the hole at a certain distance from the bottom to such a low temperature that part of the previously melted ice is frozen again to form an ice shell constituting the confines of the drill hole and the top of the water reservoir, while redundant melted ice is removed from the hole.
By cooling the wall of the hole above the water reservoir being formed, it is ensured that this water reservoir does not expand uncontrollably, but remains confined to the area surrounding the bottom of the hole, whereby a controlled sinking of the floor, and thus a controlled drilling of the hole is guaranteed. By cooling the wall of the hole and by the freezing of part of the melted ice on the wall it can also be ensured that the hole has a smooth wall and a defined inside diameter. Removal of the redundant melted ice from the hole can be effected by having it displaced by solid particles, as formed by the necessary drilling unit, or else by means of compressed air or flushing liquids.
The method which is the subject of the present invention is economical too, for there is no need for complicated rotary equipment, requiring much power, for a drill bit and the drill rods carrying the bit, nor for complicated suspension means for the rotary drill; furthermore, it is no longer necessary to replace a bit which has become blunt, as is frequently required in the case of the Rotary Method, and which always requires extraction of the whole string of drill rods from the hole. The equipment required for melting practically does not wear out and the penetration rate mainly depends only on heat supply and on the possibility of partly freezing the melted ice, so that comparatively high drilling rates can be achieved. As no strings of rotary drill rods are needed and since there are no tools, frequently to be replaced, at the end of the bottom rod, the drill rods required for the method which is the subject of the present invention may remain in place as a casing of the hole, so that no additional string of casing, narrowing the hole, need be installed either. On the contrary, a hole of any diameter can be drilled, because the rods need not accommodate any torques, which become excessively high with the Rotary Method, when the working diameter of the bit exceeds certain limits. Moreover, for a rotary drilling unit, the drill rods must have a big cross section, in order that it can accommodate such torques, and, therefore, the strings of rods become extremely heavy in the case of great depths, for which reason the hole diameters are limited, too. As no such torques are produced by the method which is the subject of the present invention, the rods may be made with thin walls, so that larger diameters are possible also from the point of view of permissible weight. Nevertheless, when applying the method which is the subject of the present invention, a mainly vertical drilling of holes is achieved, because, during the melting of the ice, there do not occur any radial forces which might deflect the rod from the vertical direction.
The method which is the subject of the present invention may also be used, when rock is included in the ice, because, on account of the melting of the ice, the rock material sinks with the floor of the hole. If required, it is possible to remove by pressure flushing the solid particles collecting in the water reservoir, such as particles from rock included in the ice.
As mentioned above, the present invention also covers a drilling unit for using the method which is the subject of the present invention. This drilling unit, justlike known drilling units, has a hollow drill rod, but an annular melting head which can be heated is mounted at the bottom end of the drill rod. Above this melting head, the drill rod is provided with a cooling device keeping its outside face at a temperature of less than 0° centigrade, and with a heat-insulating material on its inside.
The heated annular melting head mounted to the bottom end of the drill rod of this drilling unit melts the ice at the bottom of the drill rod, so that the water reservoir mentioned above is developed in the area surrounding the melting head. While the drill rod sinks farther down, the melted ice displaced by the drill rod rises within the drill rod and is removed continuously from the top end of the drill rod. The cooling device causes ice to form on the circumference of the drill rod at the upper edge of the water reservoir, thus closing and sinking the top of the water reservoir at a speed corresponding to the sinking of the reservoir's floor due to the melting of the ice. Thus, a hole develops which closely encompasses the drill rod and presents a continuous smooth surface. The weight of the drill rod ensures that the drill rod does not bind in the ice hole, and it would also be possible, if required, to provide the outside of the drill rod with a suitable sliding face, for instance with a coat of polytetrafluor ethylene.
In a further embodiment of the present invention, the melting head may present a cutting edge at its bottom end. By this one obtains a very high local contact pressure, which even alone leads to a melting of the ice and, therefore, favors good penetration of the melting head into the ice. To favor cooling of the drill rod above the melting head, heat insulation may be provided between the melting head and the drill rod. For heating the melting head, it is of advantage to arrange electric heating elements in the melting head. The electric lines leading to these heating elements may be run in a simple manner through cavities of the drill rod, which, as the case may be, may be double-walled. Simple cooling results from arrangement of cooling jackets or coiled cooling pipes at the bottom end of the drill rod which are fed with a coolant through lines run through cavities of the drill rod, which, as the case may be, may be double-walled.
It is conceivable, for example, to use means operating on the basis of the Peltier effect and the cooling elements of which are arranged in the drill rod's area to be cooled, while the elements giving up heat are located in the area of the melting head. Since, due to removal of melted ice by pumping, more ice is melted than melted ice must be frozen again by the cooling means, it is necessary, in spite of the cooling of the wall of the hole, to supply excess heat, for which the Joule heat may be used which is produced in the case of a Peltier arrangement. In any case, for the control of melting and freezing, feelers may be arranged at the bottom end of the drill rod, especially for temperature measuring and for measuring the expansion of the water reservoir.
In the case of a highly preferred embodiment of the invention, the heat-insulating material fills the drill rod completely, and two pipes preferably arranged concentrically one in the other pass through the insulating material, one of the pipes being used for the introduction of compressed air or of a flushing liquid and the other for removal of melted ice and/or solid particles originally included in the ice.
Further details and arrangements according to the present invention will be noted from the detailed description and explanations given hereinafter on the basis of an arrangement shown as an example on the drawing. The features shown on the drawing or mentioned in the description may be used individually or in any combination with each other for other arrangements in accordance with the present invention. The drawing schematically shows a longitudinal section of the bottom end of a drill rod of a drilling unit in accordance with the present invention, the drill rod being located in a hole formed in an ice layer.
The arrangement shown on the drawing comprises a double-walled hollow drill rod 1 projecting into hole 2 drilled into an icy mass 3. At the bottom end of drill rod 1 there is an annular hollow melting head 4, the bottom of which ends in a cutting edge 5 through which it is in contact with the bottom of the hole 2. Close to the cutting edge 5, inside melting head 4, there is an electric heating element 6 which is connected through line 7 to an electric power source arranged on the surface and not shown in the drawing. Line 7 extends through the hollow double wall of drill rod 1.
Melting head 4 is connected to the bottom end of drill rod 1, a ring 8 consisting of heat-insulating material being arranged between the rod end and the melting head. Above this heat-insulating ring 8, in space 9 between the walls of drill rod 1, there is a cooling jacket 10 which preferably is of annular formation and which is directly in contact with the inside of outer wall 11 of drill rod 1. This cooling jacket is divided by a partition 12 into two compartments 13 and 14 arranged concentrically one in the other and communicating with each other at their bottoms. The cooling jacket's (10) compartment 13 bordering on the outer wall 11 of drill rod 1 is fed through a line 15 with a coolant, which after passing through outer compartment 13 runs through inner compartment 14, which it leaves through line 16. Lines 15 and 16, too, are installed in the space between the two walls of drill rod 1 and are connected to a refrigerating machine, not shown in the drawing, which may be arranged on the surface or at a suitable point of the drill rod.
The interior of drill rod 1 is filled with heat-insulating material 17, and two pipes 18 and 19 placed concentrically one within the other and extending approximately down into melting head 4 are arranged concentrically with hollow drill rod 1.
As shown in the drawing, the heat supply to the melting head by means of heating element 6 causes a water reservoir 20 to develop at the bottom end of drill rod 1, this reservoir surrounding melting head 4 and the bottom end of drill rod 1 in a certain area. Redundant melted ice rises within pipes 18 and 19 and may be removed from the upper ends of these pipes. It is also possible, by introducing compressed air for example into outer pipe 19, to press the water through inner pipe 18 out of hollow drill rod 1. The water contained in reservoir 20 is communicating with the water contained in drill rod 1 through openings 21 provided for this purpose in melting head 4. Expansion of water reservoir 20 is prevented by refreezing the water surrounding drill rod 1 at the upper edge of reservoir 20 by means of cooling jacket 10 at a rate corresponding to that of the sinking of melting head 4 into icy mass 3, so that above reservoir 20 an ice layer is produced again which forms tightly around the outside 11 of drill rod 1.
Therefore, by controlled melting of ice and controlled refreezing of melted ice and without any mechanical force being exerted, a hole is developed which, due to the absence of lateral mechanical forces, can be drilled in a very straight line, and thus without considerable deviations from a vertical line, and the diameter of which may be selected at will within wide limits, because the factors involved in other current drilling methods and limiting the hole diameter are inexistent in this case. Solid particles collecting in water reservoir 20 may readily be removed from the water reservoir by pressure flushing, which is used in a similar manner as in Rotary Drilling. Furthermore, if required, drill rod 1 can be left as a casing in the hole after completion of same, although the frozen annular ice layer which surrounds drill rod 1 forms a smooth undisturbed casing, which in many cases permits dispensing with a casing anyway. The possibility of making holes of a large diameter, on the other hand, is important for introducing petroleum extraction lines, if these lines are to be firmly concreted in place and, as the case may be, surrounded with heat-insulating material. On the other hand, especially if the petroleum to be extracted is very warm, it may be of advantage to leave the double-walled drill rod in the holes as a casing and to provide it, all over its length, with cooling means which ensure that the wall of the hole remains frozen and thus keeps its stability, while at least one of pipes 18 and 19 embedded in insulating material within the drill rod, can be used as a petroleum extraction line.
It is understood that the present invention is not limited to the arrangement presented as an example, but that variations from same are possible without exceeding the scope of the present invention. Thus it is possible to install the electric lines and the cooling lines as well as pumping pipe 18 inside drill rod 1 and to dispense with the double-wall formation of the drill rod 1. Installation of these lines within the drill rod may possibly be of advantage for mounting couplings. Furthermore, it is possible to provide coiled cooling pipes instead of a cooling jacket, such coiled cooling pipes being attached to the inside of the drill rod or to the outside of same. Such cooling pipes may then extend all over the length of the drill rod, possibly having a pitch increasing with height. It is also conceivable to use burner units instead of electric heating elements. Moreover, there is a possibility, as shown on the right half of the drawing, to use instead of the separate heating and cooling elements or in addition to such, a Peltier arrangement 22, 23 the cooling elements 22 of which are arranged at the bottom end of drill rod 1 and the heating elements 23 of which are in the area of melting head 4. Feelers 24 serve to monitor the temperature in the area of water reservoir 20 and in the melting zone and/or to measure the expansion of the water reservoir and to control the rate of heating and cooling to be provided.
In addition to the Rotary Method, only the Percussion Drilling Method is known so far, in which, with the aid of a rope or a string of drill pipe, a sleeve is driven into the ice by repeated percussion. By this method only low drilling rates and comparatively shallow depths can be reached, so that this method is uneconomical and the achievable hole depths, in many cases, are insufficient. Not lastly because of the great hardness of the ice, it appears impossible that, by this method, better results could be achieved in ice than by the Rotary Method dealt with above.
Accordingly, the basis of the invention is the task of providing an ice drilling method permitting the drilling of satisfactory deep holes and which in addition is economical.
According to the present invention, this task is accomplished by melting of ice at the bottom of the hole by heat supply, so that at the bottom of the hole a kind of water reservoir is formed, and by cooling the wall of the hole at a certain distance from the bottom to such a low temperature that part of the previously melted ice is frozen again to form an ice shell constituting the confines of the drill hole and the top of the water reservoir, while redundant melted ice is removed from the hole.
By cooling the wall of the hole above the water reservoir being formed, it is ensured that this water reservoir does not expand uncontrollably, but remains confined to the area surrounding the bottom of the hole, whereby a controlled sinking of the floor, and thus a controlled drilling of the hole is guaranteed. By cooling the wall of the hole and by the freezing of part of the melted ice on the wall it can also be ensured that the hole has a smooth wall and a defined inside diameter. Removal of the redundant melted ice from the hole can be effected by having it displaced by solid particles, as formed by the necessary drilling unit, or else by means of compressed air or flushing liquids.
The method which is the subject of the present invention is economical too, for there is no need for complicated rotary equipment, requiring much power, for a drill bit and the drill rods carrying the bit, nor for complicated suspension means for the rotary drill; furthermore, it is no longer necessary to replace a bit which has become blunt, as is frequently required in the case of the Rotary Method, and which always requires extraction of the whole string of drill rods from the hole. The equipment required for melting practically does not wear out and the penetration rate mainly depends only on heat supply and on the possibility of partly freezing the melted ice, so that comparatively high drilling rates can be achieved. As no strings of rotary drill rods are needed and since there are no tools, frequently to be replaced, at the end of the bottom rod, the drill rods required for the method which is the subject of the present invention may remain in place as a casing of the hole, so that no additional string of casing, narrowing the hole, need be installed either. On the contrary, a hole of any diameter can be drilled, because the rods need not accommodate any torques, which become excessively high with the Rotary Method, when the working diameter of the bit exceeds certain limits. Moreover, for a rotary drilling unit, the drill rods must have a big cross section, in order that it can accommodate such torques, and, therefore, the strings of rods become extremely heavy in the case of great depths, for which reason the hole diameters are limited, too. As no such torques are produced by the method which is the subject of the present invention, the rods may be made with thin walls, so that larger diameters are possible also from the point of view of permissible weight. Nevertheless, when applying the method which is the subject of the present invention, a mainly vertical drilling of holes is achieved, because, during the melting of the ice, there do not occur any radial forces which might deflect the rod from the vertical direction.
The method which is the subject of the present invention may also be used, when rock is included in the ice, because, on account of the melting of the ice, the rock material sinks with the floor of the hole. If required, it is possible to remove by pressure flushing the solid particles collecting in the water reservoir, such as particles from rock included in the ice.
As mentioned above, the present invention also covers a drilling unit for using the method which is the subject of the present invention. This drilling unit, justlike known drilling units, has a hollow drill rod, but an annular melting head which can be heated is mounted at the bottom end of the drill rod. Above this melting head, the drill rod is provided with a cooling device keeping its outside face at a temperature of less than 0° centigrade, and with a heat-insulating material on its inside.
The heated annular melting head mounted to the bottom end of the drill rod of this drilling unit melts the ice at the bottom of the drill rod, so that the water reservoir mentioned above is developed in the area surrounding the melting head. While the drill rod sinks farther down, the melted ice displaced by the drill rod rises within the drill rod and is removed continuously from the top end of the drill rod. The cooling device causes ice to form on the circumference of the drill rod at the upper edge of the water reservoir, thus closing and sinking the top of the water reservoir at a speed corresponding to the sinking of the reservoir's floor due to the melting of the ice. Thus, a hole develops which closely encompasses the drill rod and presents a continuous smooth surface. The weight of the drill rod ensures that the drill rod does not bind in the ice hole, and it would also be possible, if required, to provide the outside of the drill rod with a suitable sliding face, for instance with a coat of polytetrafluor ethylene.
In a further embodiment of the present invention, the melting head may present a cutting edge at its bottom end. By this one obtains a very high local contact pressure, which even alone leads to a melting of the ice and, therefore, favors good penetration of the melting head into the ice. To favor cooling of the drill rod above the melting head, heat insulation may be provided between the melting head and the drill rod. For heating the melting head, it is of advantage to arrange electric heating elements in the melting head. The electric lines leading to these heating elements may be run in a simple manner through cavities of the drill rod, which, as the case may be, may be double-walled. Simple cooling results from arrangement of cooling jackets or coiled cooling pipes at the bottom end of the drill rod which are fed with a coolant through lines run through cavities of the drill rod, which, as the case may be, may be double-walled.
It is conceivable, for example, to use means operating on the basis of the Peltier effect and the cooling elements of which are arranged in the drill rod's area to be cooled, while the elements giving up heat are located in the area of the melting head. Since, due to removal of melted ice by pumping, more ice is melted than melted ice must be frozen again by the cooling means, it is necessary, in spite of the cooling of the wall of the hole, to supply excess heat, for which the Joule heat may be used which is produced in the case of a Peltier arrangement. In any case, for the control of melting and freezing, feelers may be arranged at the bottom end of the drill rod, especially for temperature measuring and for measuring the expansion of the water reservoir.
In the case of a highly preferred embodiment of the invention, the heat-insulating material fills the drill rod completely, and two pipes preferably arranged concentrically one in the other pass through the insulating material, one of the pipes being used for the introduction of compressed air or of a flushing liquid and the other for removal of melted ice and/or solid particles originally included in the ice.
Further details and arrangements according to the present invention will be noted from the detailed description and explanations given hereinafter on the basis of an arrangement shown as an example on the drawing. The features shown on the drawing or mentioned in the description may be used individually or in any combination with each other for other arrangements in accordance with the present invention. The drawing schematically shows a longitudinal section of the bottom end of a drill rod of a drilling unit in accordance with the present invention, the drill rod being located in a hole formed in an ice layer.
The arrangement shown on the drawing comprises a double-walled hollow drill rod 1 projecting into hole 2 drilled into an icy mass 3. At the bottom end of drill rod 1 there is an annular hollow melting head 4, the bottom of which ends in a cutting edge 5 through which it is in contact with the bottom of the hole 2. Close to the cutting edge 5, inside melting head 4, there is an electric heating element 6 which is connected through line 7 to an electric power source arranged on the surface and not shown in the drawing. Line 7 extends through the hollow double wall of drill rod 1.
Melting head 4 is connected to the bottom end of drill rod 1, a ring 8 consisting of heat-insulating material being arranged between the rod end and the melting head. Above this heat-insulating ring 8, in space 9 between the walls of drill rod 1, there is a cooling jacket 10 which preferably is of annular formation and which is directly in contact with the inside of outer wall 11 of drill rod 1. This cooling jacket is divided by a partition 12 into two compartments 13 and 14 arranged concentrically one in the other and communicating with each other at their bottoms. The cooling jacket's (10) compartment 13 bordering on the outer wall 11 of drill rod 1 is fed through a line 15 with a coolant, which after passing through outer compartment 13 runs through inner compartment 14, which it leaves through line 16. Lines 15 and 16, too, are installed in the space between the two walls of drill rod 1 and are connected to a refrigerating machine, not shown in the drawing, which may be arranged on the surface or at a suitable point of the drill rod.
The interior of drill rod 1 is filled with heat-insulating material 17, and two pipes 18 and 19 placed concentrically one within the other and extending approximately down into melting head 4 are arranged concentrically with hollow drill rod 1.
As shown in the drawing, the heat supply to the melting head by means of heating element 6 causes a water reservoir 20 to develop at the bottom end of drill rod 1, this reservoir surrounding melting head 4 and the bottom end of drill rod 1 in a certain area. Redundant melted ice rises within pipes 18 and 19 and may be removed from the upper ends of these pipes. It is also possible, by introducing compressed air for example into outer pipe 19, to press the water through inner pipe 18 out of hollow drill rod 1. The water contained in reservoir 20 is communicating with the water contained in drill rod 1 through openings 21 provided for this purpose in melting head 4. Expansion of water reservoir 20 is prevented by refreezing the water surrounding drill rod 1 at the upper edge of reservoir 20 by means of cooling jacket 10 at a rate corresponding to that of the sinking of melting head 4 into icy mass 3, so that above reservoir 20 an ice layer is produced again which forms tightly around the outside 11 of drill rod 1.
Therefore, by controlled melting of ice and controlled refreezing of melted ice and without any mechanical force being exerted, a hole is developed which, due to the absence of lateral mechanical forces, can be drilled in a very straight line, and thus without considerable deviations from a vertical line, and the diameter of which may be selected at will within wide limits, because the factors involved in other current drilling methods and limiting the hole diameter are inexistent in this case. Solid particles collecting in water reservoir 20 may readily be removed from the water reservoir by pressure flushing, which is used in a similar manner as in Rotary Drilling. Furthermore, if required, drill rod 1 can be left as a casing in the hole after completion of same, although the frozen annular ice layer which surrounds drill rod 1 forms a smooth undisturbed casing, which in many cases permits dispensing with a casing anyway. The possibility of making holes of a large diameter, on the other hand, is important for introducing petroleum extraction lines, if these lines are to be firmly concreted in place and, as the case may be, surrounded with heat-insulating material. On the other hand, especially if the petroleum to be extracted is very warm, it may be of advantage to leave the double-walled drill rod in the holes as a casing and to provide it, all over its length, with cooling means which ensure that the wall of the hole remains frozen and thus keeps its stability, while at least one of pipes 18 and 19 embedded in insulating material within the drill rod, can be used as a petroleum extraction line.
It is understood that the present invention is not limited to the arrangement presented as an example, but that variations from same are possible without exceeding the scope of the present invention. Thus it is possible to install the electric lines and the cooling lines as well as pumping pipe 18 inside drill rod 1 and to dispense with the double-wall formation of the drill rod 1. Installation of these lines within the drill rod may possibly be of advantage for mounting couplings. Furthermore, it is possible to provide coiled cooling pipes instead of a cooling jacket, such coiled cooling pipes being attached to the inside of the drill rod or to the outside of same. Such cooling pipes may then extend all over the length of the drill rod, possibly having a pitch increasing with height. It is also conceivable to use burner units instead of electric heating elements. Moreover, there is a possibility, as shown on the right half of the drawing, to use instead of the separate heating and cooling elements or in addition to such, a Peltier arrangement 22, 23 the cooling elements 22 of which are arranged at the bottom end of drill rod 1 and the heating elements 23 of which are in the area of melting head 4. Feelers 24 serve to monitor the temperature in the area of water reservoir 20 and in the melting zone and/or to measure the expansion of the water reservoir and to control the rate of heating and cooling to be provided.