Method And System For Transporting Oil By Pipe Line

Abstract

System and method for transporting oil by pipe line under or over frozen ground, e.g., permanently frozen terrain, without melting or softening the ground by heat transfer from the oil, by passing oil through a pipe line supported by such frozen ground or terrain, placing a second pipe line for carrying a fluid refrigerant, particularly liquid natural gas, along and closely adjacent to the oil pipe line but spaced therefrom, the second pipe line also being supported by the frozen ground, and being disposed adjacent to the frozen ground, providing insulation between the oil and refrigerant, e.g., liquid natural gas, pipe lines, as by placing the oil pipe line in an excavation in the ground and positioning the liquid natural gas pipe line in such excavation below and parallel to the oil pipe line, with gravel, for example, filling the spaces in the excavation and between the two pipe lines, passing a liquid refrigerant such as liquid natural gas through the second pipe line at a temperature substantially below the temperature of the adjacent frozen ground, thereby maintaining the ground around the pipe lines frozen without cooling the oil in the oil pipe line down to a temperature which substantially retards flow of the oil in the oil pipe line. As a feature of the invention, a minor portion of the liquid natural gas at each pumping station can be used for operating both the oil pump or pumps and liquid natural gas pump or pumps at the respective stations. The result is that the ground supporting or surrounding the oil pipe line remains in permanently frozen condition to firmly support such pipe line at all times, and at the same time liquid natural gas can be transported to market and a portion thereof employed to operate the pumping stations.

Description

A particularly prolific oil field has been recently discovered and begun to be developed on the North Slope of Alaska. The most feasible way to transport such oil across Alaska to terminals in southern Alaska for transport to United States West Coast ports and to far eastern markets such as Japan, is by oil pipe line from the North Slope south across Alaska.

However, a substantial portion of the terrain in this region is tundra, which, if undisturbed, remains frozen most of the year but will melt if there is any activity in the vicinity. For this reason, the drilling rigs at the North Slope, town sites in the vicinity, and other activities of this nature, are all generally set upon a bed of gravel of the order of about 5 feet thick, in order to form a base that will allow for transportation and footings for structures without disturbing the tundra.

However, a considerable problem is involved in laying a pipe line over a large distance of several hundreds of miles over such tundra, particularly in establishing a suitable foundation for the oil pipe line, since as previously noted the danger exists of the tundra beneath the right of way melting and causing serious damage or collapse of the pipe line, resulting from such insecure base. For this reason various proposals have been made for supporting the oil pipe line passing through or across such generally frozen terrain. Thus, for example, it has been proposed to support the oil pipe line on a platform positioned several feet, for example, about 10 feet, above the ground by driving piles or stilts into the tundra to support a platform for the oil pipe line. However, this would result in a highly expensive system with the pipe line situated above the ground on a platform, thus providing obstructions for animals, and would still be subject to the danger of collapse of the tundra by the weight of the line and oil passing therethrough. While it has also been proposed to lay the oil pipe line on a gravel bed positioned on the surface of the tundra, here also there is a danger of possible melting of the tundra beneath the gravel bed, endangering the line, and the exposed line also presents an obstruction to animals, and objections from ecologists. The pumping of the oil through a pipe line, such as a proposed 48-inch oil pipe line requires that the oil be kept at temperatures above freezing and as a result the pipe line must be layed above ground, e.g., on a bed of gravel or tundra as previously noted. This is extremely expensive and still does not insure the stability of the permafrost areas. Thus, to date no acceptable or feasible system has been proposed, to applicant's knowledge, for constructing and properly supporting a pipe line across the above noted permafrost tundra without serious danger of collapse of the line as result of melting and instability of the frozen ground, and avoiding ecological objections.

The North Slope Alaskan oil field has also a very considerable amount of natural gas which requires shipment to market. However, the present practice is to flare the gas to the atmosphere, which is frowned upon by the authorities as a pollution hazard, and as a waste of natural resources, and in many areas of this region, the well operators are either penalized for this practice or made to reinject the gas into the formation, both of which are expensive and undesirable.

The above problems and disadvantages can be overcome and a feasible and practical method and system are provided for transporting oil through a pipe line across the frozen terrain while maintaining such terrain or ground permanently frozen and providing a stable bed for the pipe line, in accordance with the concept of the present invention. In accordance with the present invention, by liquefying the natural gas at the well head, and transporting such liquid natural gas through a pipe line placed beneath the crude oil line and supporting such oil pipe line on a relatively thin gravel bed, for example, the cold from the liquid natural gas which is at a temperature, e.g., of the order of about -260.degree. F., can be used to maintain a below freezing temperature on the pipe line right-of-way, and maintaining a stable support for the pipe line. Thus, in accordance with the invention concept, the liquid natural gas line maintains the terrain along the right-of-way permanently frozen, but by providing suitable insulation between the liquid natural gas and oil pipe line, as by an intervening bed of gravel, the liquid natural gas line does not cool the oil in the oil pipe line to a point at which it substantially reduces the flow of the oil in the oil pipe line.

The oil pipe line is preferably placed below the surface of the ground or terrain, as by placing the pipe line in a relatively shallow excavation, with the liquid natural gas pipe line placed a short distance below the oil pipe line in the excavation, with gravel placed in the excavation and between the two pipe lines, according to certain preferred embodiments described below, and which can also include preferably an additional supporting member for the oil pipe line, in the form of a trough or cradle. This arrangement accomplishes the main objects of the invention, which are to maintain the supporting terrain or ground along the right-of-way permanently frozen, while permitting the oil to flow freely through the oil pipe line. Such preferred underground arrangement also has the advantages that the larger oil pipe line does not disturb the ecology, which would be the case if the line were laid over the ground, and is not subject to damage by animals, and is not a hazard to animals. Also, placement of the oil pipe line and liquid natural gas line below the ground surface has a further advantage that temperature variations due to change in climatic conditions are not nearly as severe when the pipes are laid underground as compared to being placed above the ground. Further, when the oil pipe line is placed above the ground, slack loops or expansion joints are required, which is expensive.

The crude oil pipe line pump stations are spaced at various distances along the line depending upon the pressure required to cross over the terrain between stations. The natural gas is liquefied at the well head and transported along the right of way according to the invention in the liquid natural gas pipe line or lines from one pumping station to the next in a manner allowing the temperature to be controlled so that the liquid natural gas maintains the desired ground temperature when it arrives at each of the successive stations. Due to rise of temperature of the liquid natural gas between stations, at each station means are provided, in the form of a small liquefaction installation, to again reduce the temperature of the liquid natural gas to that at the preceding station. As additional features of the invention, small amounts of natural gas can be bypassed at each station to operate the oil pump or pumps and also the liquid natural gas pump or pumps and any other auxiliary equipment, thereby reducing the cost of operation of the pipe line. Further, liquid natural gas can be bled from the liquid natural gas line at any desired locations along the line to serve communities or industry along the right-of-way.

Thus, the present invention accomplishes the following objects and achieves the following advantages:

It allows for the maintaining of a suitable soil or ground condition along the entire oil pipe line right-of-way, providing a stable support for the line at all times, thus reducing the oil pipe line construction costs and problems; it allows the pumping stations along the line to be operated economically and conveniently on natural gas; it provides a means to bring well head natural gas, presently being flared or reinjected, to tidewater and market along the same right-of way and together with the oil; it materially reduces the cost of construction of the liquid natural gas pipe line and indeed such liquid natural gas line can be installed at substantially no additional cost, since the savings effected by the method of pipe line construction for the oil line according to the invention, and the operation of pump stations on natural gas, will pay for the liquefaction of the natural gas and at least part of the cost of the liquid natural gas line.

The invention will be more readily understood by the description below of certain embodiments of the invention, taken in connection with the accompanying drawings wherein:

FIG. 1 is a cross sectional illustration of an oil pipe line and a liquid natural gas line positioned in an excavation in the ground, and insulated with gravel and by other means, in accordance with the invention;

FIG. 2 is a cross sectional illustration similar to FIG. 1, showing another embodiment of the invention; particularly applicable where detrimental permafrost is encountered;

FIG. 3 is a plan view of the embodiment illustrated in FIG. 2, partly broken away for clarity;

FIG. 4 is a cross sectional illustration similar to FIG. 1, of still another embodiment of the invention;

FIG. 5 illustrates a modification of the embodiment illustrated in FIG. 1;

FIGS. 6, 7 and 8 illustrate further embodiments of the invention concept, wherein the oil pipe line is disposed above the ground or terrain;

FIG. 9 is a schematic representation of the oil pipe line and liquid natural gas pipe line positioned along the same right-of-way, with the respective pumping stations for each line, and illustrating the bypassing of natural gas at each pumping station for operating the pumps and liquefaction apparatus; and

FIG. 10 is a schematic representation of a means for initially insuring a frozen terrain along the right-of-way, prior to commencing flow of oil in the oil pipe line, by recirculation of liquid natural gas between pairs of successive stations along the line.

The drawings are exaggerated for greater clarity.

Referring to FIG. 1 of the drawing, numeral 10 illustrates a system in which an excavation, e.g., about 8 feet deep and about 6 feet wide, as indicated at 12, is made in the ground, indicated at 14. A liquid natural gas line 16, e.g., from about 6 inches to about 1 foot in diameter, is placed centrally at the bottom of the excavation 12, and gravel, indicated at 18, is placed in the bottom of the excavation around the liquid natural gas pipe line up to the top of such line. A U-shaped member or trough 20, constructed of a lightweight insulation material of high strength, e.g., a lightweight chemical concrete construction material, and having a transverse dimension of about 50 inches to about 54 inches across the sides 21 of the trough, is placed centrally over the gravel bed 18 in the bottom of the trough and on the upper surface of the liquid natural gas line, so that the trough rests on such gravel and the liquid natural gas line.

The trough can be formed of any suitable material having high strength and which provides a high thermal barrier and is resistant to corrosion.

An oil pipe line 22, e.g., of about 48 inches in diameter, is then positioned within the trough so that it essentially rests on the bottom thereof, and gravel, indicated at 24, is placed within the trough and around the oil pipe line 22 and fills the crevices between the oil pipe line and the sides of the trough, up to ground level, as indicated at 26. Gravel is also placed within the excavation around the outer surfaces of the sides of the trough 20, as indicated at 28, up to ground level 26, thus substantially filling the excavation and the trough with gravel around the liquid natural gas and oil pipe lines 16 and 22, respectively. If desired, although not necessary, a cover indicated at 30 can be positioned over the upper end of the trough 20. Viewing FIG. 1, it will be seen that the liquid natural gas line withdraws heat from the surrounding ground 14 both below and around the sides of the excavation 12, serving to maintain such ground permanently frozen and provide a stable bed for the oil pipe line 22 along the right-of-way. However, as result of the assembly shown in FIG. 1, including the insulating gravel around and between the liquid natural gas and oil pipe lines, and the lightweight insulation trough 20 between the two lines, and which also tends to further support the pipe line 22 within the excavation, sufficient insulation is provided between the oil pipe line 22 and the liquid natural gas line 16 so that although the liquid natural gas cools the oil flowing in pipe 22 to some extent, the temperature of the oil is maintained at a desirable pumping temperature, e.g., of the order of about 30.degree. F.

Although gravel is a preferred insulation material, it will be understood that other bulk insulation materials such as earth (tundra) and sand can be employed for filling the trough 20 and excavation 12 around the oil and liquid natural gas pipe lines, as desired. Also ambient air can be used, e.g., for insulation within the trough around the oil pipe line, as noted below. Preferred insulation materials are gravel and earth (tundra).

Thus, for example, again viewing FIG. 1, after forming the excavation 12, and placing the natural gas pipe 16 in position as shown in FIG. 1, the bottom of the excavation can be filled with tundra at 18, which tundra was previously removed from the excavation, and the trough 20 and oil pipe 22 are placed in position as illustrated in FIG. 1, and the spaces around the trough at 28 and within the trough at 24 back filled with additional tundra previously removed from the excavation. Such replacement and maintenance of the tundra would be ecologically desirable. Further, if desired, tundra can be placed in the excavation around the outside of trough 20 and around the liquid natural gas (LNG) pipe 16, and gravel placed within the trough 20 and around the oil pipe 22, or vice versa.

Further, if desired, again viewing FIG. 1, trough 20 can be reduced to a cradle formed essentially only of the bottom portion 31 of the trough shown in FIG. 1, and not containing the vertical sides 21 above the dotted lines indicated at 33. Under these conditions the two gravel or tundra beds at 24 and 28 from a single insulation bed around the upper portion of the oil pipe 22 above the cradle.

The embodiments described above and illustrated in FIG. 1 are preferred embodiments:

Referring now to FIG. 2, here again excavation 18 is provided in the ground 14, and a liquid natural gas pipe line 16 is also placed centrally in the bottom of the excavation, and an insulation material such as gravel, indicated at 32, is then placed in the excavation around and above the liquid natural gas line, e.g., for a height of about 1 to 11/2 feet above the liquid natural gas line. The oil pipe line 22 is then placed on such gravel bed and held in position in the gravel bed by means of river weights 34, e.g., of concrete, placed around the oil pipe line at intervals along the line, as further illustrated in FIG. 3. The excavation is then back filled with insulation material such as gravel, indicated at 36, up to the ground level 26 within the excavation, so that the oil pipe line 22 is completely embedded in gravel within the excavation below the upper surface of the gravel bed 36. The river weights 34 not only maintain the oil pipe line 22 in position in the gravel bed, but in the event of the presence of any water flowing into or formed in the excavation around the pipe 22, which would cause it to float upward, and forming a detrimental permafrost, the river weights prevent this from occuring.

As in the embodiment illustrated in FIG. 1, in the present modification of FIGS. 2 and 3, liquid natural gas passing through line 16 maintains the ground 14 below the excavation and around the excavation permanently frozen, but as result of the gravel insulation between liquid natural gas pipe line 16 and the oil pipe line 22, the oil flowing through line 22 is maintained in a free flowing condition.

Now referring to FIG. 4, illustrating a further modification of the system of FIG. 1, the liquid natural gas line and lightweight insulation trough 20 are placed within the excavation 12 and gravel or earth (tundra) indicated at 18 and at 28 are placed within the excavation around the liquid natural gas line 16 and the outer surfaces of the trough 20, up to the ground level 26, as in the case of FIG. 1.

However, in the embodiment of FIG. 4, a supporting insulating block 38 is positioned at intervals along the bottom of the trough 20, and the oil pipe line is supported on such blocks, with the sides of the line 22 substantially in contact with the inner surfaces of the trough 22, to maintain the oil line in fixed position within the trough.

However, no solid insulation material such as gravel is placed within the trough 20, but rather ambient air is permitted to enter the space 40 with the trough and around the oil line 22, to function as an insulation medium. In this embodiment, the cover within is preferably placed over the top of the open trough 20, to close same and prevent debris from falling into the trough around the pipe line, and also to prevent danger to animals, humans and the like from falling into the trough and being injured.

The embodiment of FIG. 4 functions similarly to that of FIG. 1 in that the cold from the liquid natural gas line withdraws heat from the surrounding ground and terrain 14, maintaining same permanently frozen, and the insulation means including the gravel beds 18 and 28, trough 20 and the air within the space 40 prevent undue lowering of the oil temperature in line 22 and permits free flow thereof.

Now referring to the modifications of FIG. 5, this embodiment is substantially the same as that of FIG. 1, except that in place of employing a single centrally disposed natural gas pipe line 16 positioned at the bottom of the excavation below the oil pipe 22, there are disposed two liquid natural gas pipe lines 16 positioned adjacent opposite corners of the excavation 12. This arrangement gives more effective and widespread cooling of the adjacent ground 14 by both of the liquid natural gas lines 16, to maintain the adjacent ground permanently frozen, while the oil line 22 is still sufficiently insulated from both of the liquid natural gas lines 16 by the intervening gravel indicated at 18 and 28 and the insulating trough 20, so that the oil is maintained at a sufficiently high temperature to be readily pumped.

In FIGS. 1, 4 and 5, it will be understood that the trough 20 or cradle supporting the oil pipe line can have any desired shape, e.g., rectangular, with a simple horizontal bottom portion and vertical sides as at 21, without the sloping sides of bottom portion 31 of trough 20.

FIGS. 6, 7 and 8 illustrate further modifications of the invention principles, wherein the oil pipe line is positioned above the surface of the ground. In FIG. 6, the liquid natural gas pipe line 16 is placed on the surface 26 of the ground 14 along the pipe line right-of-way, and a gravel bed indicated at 42 is then positioned over the right-of-way, covering and embedding the liquid natural gas line 16. There is placed on the top of the gravel bed 42, which can be, for example, about 3 to about 4 feet high, the oil pipe line 22 which is disposed directly above the liquid natural gas line 16. Suitable supports, indicated at 44 in FIG. 6, can be disposed at intervals along the gravel bed 42 to maintain the pipe line 22 in position on the gravel bed. It will be understood that any other suitable and conventional means can be employed to maintain the oil pipe line 22 in position on the gravel bed.

FIG. 7 shows an arrangement similar to that of FIG. 6, except that in the modification of FIG. 7, the liquid natural gas line 16 is buried in the ground 14 so that the upper surface of the liquid natural gas line is about at the level of the surface 26 of the ground.

In the modification of FIG. 8, the liquid natural gas line 16 is first buried in the ground along the right-of-way, e.g., about 2 to about 21/2 feet below the ground level 26. A gravel bed 45 is placed in a shallow excavation 47, above pipe line 16, and the oil pipe line 22 is positioned along the top 49 of the gravel bed at ground level 26, with suitable supporting means 44, noted above, or other equivalent means, employed to maintain the pipe line 22 in position along the right-of-way.

In all of the embodiments of FIGS. 6, 7 and 8, the liquid natural gas pipe line provides sufficient cold to maintain the adjacent terrain below the oil pipe line 22 permanently frozen, while the gravel bed 42 in the embodiments of FIGS. 6 and 7, and the gravel bed 45 in FIG. 8, between the liquid natural gas line 16 and the oil pipe line 22, provides sufficient insulation to prevent undue reduction of the temperature of the oil pipe line 22, and to permit such oil to flow freely.

In all of the embodiments of FIGS. 1 to 8 described above, it will of course be understood, and as illustrated in FIG. 9 below, that the liquid natural gas pipe line or lines 16 are positioned parallel to the oil pipe line 22 along the same right-of-way.

Now referring to FIG. 9, there is illustrated a pipe line arrangement 46 comprising an oil pipe line 22 and a liquid natural gas pipe line system 16, insulated from each other, as illustrated by any of the embodiments of FIGS. 1 to 8 described above, along the same right-of-way. Thus, oil and gas are both produced at the well head indicated at 48, and the oil, generally at a temperature ranging from about 150.degree. F. to about 200.degree. F. is conducted via pipe 50 to the oil pipe line 22. The natural gas is gathered and liquefied at a location near the terminus of the oil pipe line indicated at 52, and is then conducted via conduit 54 to the liquid natural gas pipe line 16.

The oil in line 22 is pumped at successive pumping stations A, B, C, D, etc. along the entire right-of-way, the pumping stations being suitably placed depending upon the pressure required to traverse the terrain between successive stations. The liquid natural gas in the liquid natural gas line 16 traverses the same right-of-way, as noted above, there being a series of successive liquid natural gas pumping stations A', B', C', D', etc., corresponding to, and at the same corresponding locations as the pumping stations A, B, C, D, etc. of the oil line 22. At each oil pumping station and at each liquid natural gas pumping station, it will be understood that there can be one or more pumps.

At station A, the oil from the well head is pumped to a suitable pressure to traverse the terrain between stations A and B, e.g., to a pressure of about 1,000 p.s.i., and at each successive pumping station B, C, D, etc. the oil is again pumped up to suitable pressure, e.g., of the order of about 1,000 p.s.i., to permit continuous uniform flow of the oil through the entire line.

The liquid natural gas in line 16 is generally operated at higher pressures to balance heat loss and maintain the gas in an essentially liquid condition between stations, e.g., at pressures of the order of about 1,500 to about 2,000 p.s.i., and which is at a temperature say of about -258.degree. F. at the initial station A', and which temperature is controlled so that it will still maintain a desired ground temperature such as to maintain the ground frozen between stations A and B, and A' and B', and will have its temperature raised, say about 100.degree. F. to about -158.degree. F., by heat transfer from the ground, when it reaches the station B'. Thus, the liquid natural gas between two successive pumping stations can range from about -200.degree. to about -275.degree. F. at one station, and being heated during passage from such station up to about -125.degree. to about -175.degree. F. at the next station. At the same time, during traversal of the oil from station A to B, the oil in line 22 will be cooled down say to about 30.degree. F., the latter temperature still permitting free flow and pumpability of the oil. At station B, the oil is pumped up again say to about 1,000 p.s.i., such pumping increasing the temperature of the oil somewhat, and the oil traverses the next stretch of distance between stations B and C.

At station B' along the liquid natural gas line 16, the liquid natural gas is passed through a liquefaction plant 56 to liquefy vapors of natural gas generated in the run between stations A' and B', and the liquid natural gas, again reduced in temperature, e.g., down to about -258.degree. F., is pumped up if necessary at station B' to the desired pumping pressure, e.g., of about 1,500 to about 2,000 p.s.i. The liquid natural gas as result of rise in temperature in passing from station A' to B' and some resultant vaporization, expands and generates at least some of the power required for pumping the liquid natural gas to the next station, but generally some mechanical pumping at station B' is necessary for the run between stations B' and C'.

As previously noted, the oil will be cooled down to some extent by the liquid natural gas, but this is balanced to a degree by the line friction in the oil line, and the temperature of the liquid natural gas will be raised to some extent by the oil during traversal of the oil and liquid natural gas from stations A to B and A' to B', respectively. This transfer of heat between the oil and liquid natural gas should be minimized as much as possible. This heat transfer mechanism can be balanced so that the oil will be maintained at the most desirable temperature for pumping, e.g., about 30.degree. F., while the liquid natural gas is maintained at as low a temperature as possible, e.g., varying between -140.degree. to about -260.degree. F., in which event the cold from the liquid natural gas line will stabilize the soil along the right-of-way by maintaining it at a below freezing temperature so that it remains permanently frozen, as described above.

At each station a small amount of liquid natural gas is bypassed, as indicated at 58, to operate the oil pump at the station, and starting at station B', and at successive station C', D', etc. a minor portion of liquid natural gas is bypassed from the line 16, as indicated at 60, to operate the liquid natural gas liquefaction plant 56 and the liquid natural gas pump at each such station. If desired, liquid natural gas can be bled from any place along the liquid natural gas line 16, as indicated at 62, to serve a community or an industry in the area.

Referring to FIG. 10, there is illustrated a system for initially reducing the temperature of the ground adjacent the oil and liquid natural gas pipe lines 22 and 16, prior to pumping of oil in line 22. In this arrangement another liquid natural gas line 64 is provided, and adjacent to successive stations, branch lines 66 and 68 are provided to form a closed circulation loop 16, 66, 64 and 68 between successive liquid natural gas stations, e.g., between A' and B', to provide circulation of liquid natural gas through each such loops for a period of time sufficient to reduce the temperature of the ground along the right-of-way between each pair of successive liquid natural gas stations the desired amount.

In each of these loops, the returning liquid natural gas is passed to the liquefaction plant, e.g., 52 or 56, and then again pumped as at A' for passage again to the next station, e.g., B'. A small amount of liquid natural gas is bypassed at 70 and 72 from the return line 68 for operation of the initial gas liquefaction plant 52 and the liquid natural gas pump at that station, e.g., station A'. A system of valves 74, 76 and 78 is provided in each circulation loop to control circulation of the liquid natural gas through each of such loops, as desired. Similar closed loops are provided between the successive pairs of stations such as between B' and C', for circulation of liquid natural gas between such stations. After the ground or terrain along the right-of-way has reached the desired reduced temperature to maintain the ground frozen to form a stable support for the oil line, circulation of the liquid natural gas through the respective closed loops illustrated in FIG. 10 is terminated, and the oil and liquid natural gas flow through lines 22 and 16 is commenced, as described above and illustrated in FIG. 9.

It will be understood that although the principles of the invention have been described particularly in relation to the use of liquid natural gas as fluid refrigerant to maintain the oil pipe line right-of-way permanently frozen to support the oil line, other fluid refrigerants having suitable boiling points such as, for example, Freon 12 (boiling point, -28.degree. C.) or other suitable refrigerants such as, for example, suitable brine solutions, can be passed through line 16, the refrigerant being chosen such that it can be maintained at sufficiently low temperatures to maintain a permanently frozen ground condition between successive stations for the above described purpose, while minimizing the cooling down of the oil between stations, to permit facile pumping of the oil.

As previously indicated, the arrangements of FIGS. 1 to 5, with the oil pipe line and liquid natural gas pipe line both positioned below the ground are preferred arrangements while the embodiments of FIGS. 6, 7 and 8, wherein the oil pipe line is disposed above the ground, although functioning to obtain the intended results, are not preferred, for reasons previously noted.

From the foregoing, it is seen that the invention provides a simple, economical and effective means for transporting oil, particularly in combination with the transport of liquid natural gas, along the same right-of-way, with the chief advantage that the cold from the liquid natural gas maintains the ground in a permanently frozen and stable condition. Although the invention has particular merit in transporting oil from the Alaskan oil fields, it will of course be obvious that these same principles can be employed for transporting oil across any other regions, e.g., of the United States, Canada, the Scandinavian countries, Siberia or other regions of the earth where a permanently Siberia, ground condition is desirable or required to provide a suitable stable base for oil pipe lines.

While I have described particular embodiments of my invention for purposes of illustration, it will be understood that variations and modifications will occur to those skilled in the art and the invention is not to be taken as limited except by the scope of the appended claims.

Claims

I claim:

1. A method for transporting oil by pipe line across frozen ground without melting or softening the ground by heat transfer from the oil, which comprises passing oil through a pipe line supported by frozen ground, said oil being at a temperature substantially above the temperature of said ground, placing a second pipe line along and closely adjacent to said oil pipe line but spaced therefrom, said second pipe line also being supported by said frozen ground, and being disposed adjacent to said frozen ground, providing insulation between said oil and second pipe lines, and passing liquid natural gas through said second pipe line at a temperature substantially below the temperature of the adjacent frozen ground, thereby maintaining said last mentioned ground frozen but without cooling the oil in the oil pipe line down to a temperature which would substantially reduce the flow of said oil in said oil pipe line, including providing said oil and said natural gas in gaseous form from a common source, and liquefying said natural gas prior to passage thereof through said second pipe line.

2. A method as defined in claim 1, said insulation including a substance selected from the group consisting of gravel, earth, sand and air.

3. A method as defined in claim 1, said insulation including a substance selected from the group consisting of gravel and earth, and comprising placing said substance around said oil pipe line.

4. A method as defined in claim 1, including pumping said oil at a plurality of stations along said oil pipe line and pumping said liquid natural gas at a plurality of stations along said second pipe line, the temperature of said liquid natural gas increasing from one liquid natural gas pumping station to the next liquid natural gas pumping station by removal of heat from said ground adjacent said oil pipe line between said last mentioned pumping stations, and reducing the temperature of the natural gas at said next pumping station substantially to the temperature of said natural gas at said preceding pumping station.

5. A method as defined in claim 4, a portion of said liquid natural gas being vaporized during passage thereof from said one liquid natural gas pumping station to said next liquid natural gas pumping station, and including liquefying said vaporized natural gas at said next liquid natural gas pumping station for said reducing said temperature of said liquid natural gas substantially to the temperature of said liquid natural gas at said preceding pumping station.

6. A method as defined in claim 5, said oil pipe line pumping stations and said liquid natural gas pipe line pumping stations being respectively positioned at adjacent locations along said respective pipe lines, including bypassing a minor portion of liquid natural gas from said liquid natural gas pipe line at each station thereof to the adjacent oil pipe line pumping station for operation of the pump at said last mentioned pumping station and to the pump at said liquid natural gas pumping station, for operation of said respective pumps.

7. A method as defined in claim 5, wherein the temperature of said liquid natural gas between two successive liquid natural gas pumping stations ranges from about -200.degree. to about -275.degree. F. at one station, and being heated during passage from said one station up to about -125.degree. to about -175.degree. F. at the next station.

8. A method as defined in claim 1, including initially circulating liquid natural gas through said liquid natural gas pipe line in a closed loop between a pair of successive liquid natural gas pumping stations to reduce the temperature of the adjacent ground to insure that said ground is initially in a frozen condition, prior to passing oil through said oil pipe line.

9. A method for transporting oil by pipe line across frozen ground without melting or softening the ground by heat transfer from the oil, which comprises passing oil through a pipe line supported by frozen ground, said oil being at a temperature substantially above the temperature of said ground, placing a second pipe line along and closely adjacent to said oil pipe line but spaced therefrom, said second pipe line also being supported by said frozen ground, and being disposed adjacent to said frozen ground, providing insulation between said oil and second pipe lines, and passing cold natural gas through said second pipe line at a temperature substantially below the temperature of the adjacent frozen ground, thereby maintaining said last mentioned ground frozen but without cooling the oil in the oil pipe line down to a temperature which would substantially reduce the flow of said oil in said oil pipe line, including providing said oil and said natural gas from a common source.

10. A system for transporting oil by pipe line across frozen ground without melting or softening the ground by heat transfer from the oil, which comprises an oil pipe line supported by frozen ground, a second liquid natural gas pipe line disposed closely adjacent to and substantially parallel to said oil pipe line, but spaced therefrom, said second pipe line also being supported by said frozen ground, insulating means positioned between said oil and second pipe line, means for pumping oil through said oil pipe line and including a plurality of oil pumping stations along said oil pipe line, a plurality of liquid natural gas pumping stations along said liquid natural gas pipe line, each of said oil pumping stations being positioned adjacent corresponding liquid natural gas pumping stations, means for initially liquefying natural gas to provide said liquid natural gas and means for supplying said liquid natural gas to said second liquid natural gas pipe line, a well head supplying oil and natural gas, means for supplying said oil to said oil pipe line and means for supplying said natural gas to said initial liquid natural gas liquefying means, and means for maintaining the temperature of said liquid natural gas pumped through said second pipe line substantially below the temperature of the adjacent frozen ground supporting said oil pipe line, to thereby maintain said last mentioned ground frozen.

11. A system as defined in claim 10, said insulating means including a substance selected from the group consisting of gravel, earth, sand and air.

12. A system as defined in claim 11, said insulating means also including a supporting member for said oil pipe line.

13. A system as defined in claim 10, having a substantially smaller diameter than said oil pipe line, said oil pipe line and said second liquid natural gas pipe line being disposed in an excavation below the surface of said ground, said oil pipe being positioned above said second liquid natural gas pipe line.

14. A system as defined in claim 13, said insulating means including a substance selected from the group consisting of gravel and earth, and said substance surrounding a substantial portion of the periphery of said oil pipe line.

15. A system as defined in claim 14, including means anchoring said oil pipe line in position in said excavation and supported on said gravel or said earth therein.

16. A system as defined in claim 13, said insulating means including an insulating trough or cradle member positioned in said excavation, said oil pipe line being positioned within said member adjacent the bottom thereof, said second liquid natural gas line being positioned below said member and adjacent the bottom of said excavation.

17. A system as defined in claim 16, said insulating means also including a substance selected from the group consisting of gravel and earth positioned within said member, and said substance also positioned in said excavation around said member and around said liquid natural gas pipe line.

18. A system as defined in claim 16, said insulating means also including a substance selected from the group consisting of gravel and earth positioned in said excavation around said member and around said liquid natural gas pipe line, a block member positioned within said member on the bottom thereof, said oil pipe line being positioned on said block in said member, a space in said member around said oil pipe line, and ambient air in said space and further insulating said oil pipe line from the adjacent ground.

19. A system as defined in claim 10, said second pipe line having a substantially smaller diameter than said oil pipe line, said insulating means comprising a gravel bed positioned on the surface of said ground, said oil pipe line being supported on said gravel bed and said liquid natural gas line being positioned within said gravel bed below said oil pipe line and adjacent the surface of said frozen ground.

20. A system as defined in claim 10, said second pipe line having a substantially smaller diameter than said oil pipe line, said insulating means comprising a gravel bed positioned on the surface of said ground, said oil pipe line being supported on said gravel bed and said liquid natural gas line being positioned in said ground jest below the surface thereof and below said gravel bed supporting said oil pipe line.

21. A system as defined in claim 10, including liquid natural gas liquefying means at each liquid natural gas pumping station for liquefying vaporous natural gas formed in said liquid natural gas during passage thereof from one liquid natural gas pumping station to the next liquid natural gas pumping station, for reducing the temperature of said liquid natural gas at said next station, means for bypassing a minor portion of natural gas at each liquid natural gas pumping station and using same to operate the adjacent corresponding oil pumping station, and means for bypassing an additional minor portion of liquid natural gas at each liquid natural gas pumping station for operating said last mentioned pumping station.

22. A system as defined in claim 10, including a third liquid natural gas pipe line, means connecting said second liquid natural gas pipe line to said third liquid natural gas pipe line at each of said liquid natural gas pumping stations, and valve means in said second and third liquid natural gas pipe lines to provide closed loops between successive liquid natural gas pumping stations for circulating liquid natural gas through said loops for initially freezing said ground.