Method Of Transporting Oil Or Gas In Frozen Tundra

Abstract

A method of preventing softening or thawing of the permafrost zone while producing or transporting hot oil or gas therethrough in which a liquefied hydrocarbon gas, preferably natural gas, is passed between the zone and the hot oil. The gas may be circulated in a suitable system.

Description

This invention relates to a method of oil and gas recovery from the earth and more particularly to a method of producing or transporting hot oil or gas through frozen tundra such as the Alaskan permafrost layer.

Substantial difficulty has been encountered when producing oil and gas at elevated temperatures from subsurface reservoirs in cold climates. As the hot oil or gas passes through the permafrost zone, its heat softens or melts the zone which may result in destruction of the oil or gas producing strings or buckling of the surface rigs used in producing oil or gas, or pipelines for transporting it, unless special precautions are taken.

I have invented a novel method for preventing the thawing or softening of the permafrost zone which surrounds the upper portion of the casing or string of oil and gas wells drilled, or oil, gas or oil product pipelines laid, in extremely cold climates, such as the Arctic region, where the permafrost zone extends to depths of 1,000 feet or more below the surface. In the case of wells, my method involves passing a liquefied hydrocarbon gas through suitable apparatus, preferably one which enables circulation of the gas, down through an annulus formed between two concentric strings of pipe or casing in an oil or gas well, and up through an annulus between the inner one of said strings and a third concentric string. The gas is circulated to that depth necessary to provide complete protection of the permafrost zone. In the case of oil or gas pipelines, the hot oil may be transported in the inner of two concentric pipes with the liquefied hydrocarbon gas being passed through an annulus between the pipes. In either case, the flow of the hydrocarbon gas is parallel to the flow of the oil or gas being produced or transported. Under some circumstances, it may be desirable to place insulation around the outer surface of the pipeline.

Although prior patents, for example, Balch U.S. Pat. No. 3,220,470, disclose certain refrigerants to be useful for maintaining earth in a frozen condition, I am not aware of any prior patent or publication which proposes a method such as mine utilizing liquefied hydrocarbon gases -- methane, ethane, butane, propane, ethylene, and others -- which are abundant in the Arctic region, as a means for maintaining the permafrost zone in a frozen condition in areas near oil and gas wells or pipelines. Such hydrocarbon gases include natural gas, which may be liquefied at temperatures down to -260.degree. F, substantially below any temperature envisioned by the prior art.

An understanding of my invention will be facilitated by the consideration of the following description taken with the accompanying drawings in which:

FIG. 1 is a diagrammatic elevation view partly in section of apparatus useful in carrying out my method;

FIG. 2 is a sectional view in reduced scale taken on lines II--II of FIG. 1; and

FIG. 3 is a sectional view of a portion of a transfer oil and gas pipeline between pumping stations which illustrates my invention.

In FIGS. 1 and 2, a part of a conventional oil producing string 1 extends from a reservoir (not shown) located below a permafrost zone 2 of the frozen tundra. The string 1 is suitably connected to an oil collecting means, such as a storage tank or to other equipment, e.g., a gas separator, for preliminary processing.

A suitable apparatus for performing my method in a well comprises jacketing the oil producing string 1 with a first pipe or casing 3 which is positioned concentrically with respect to string 1. A second pipe or casing 4 is positioned concentrically with respect to the string 1 and casing 3. The lower end of casing 4 is cemented in the well, as at 4a. Casings 3 and 4 are connected at the surface to conventional liquification equipment 5 and are of sufficient length to penetrate the earth to a depth greater than the depth of the permafrost zone, where they are suitably joined in fluid communication with one another to form a continuous circulation system.

Preferably, the gas is circulated as shown by the arrows in FIG. 1 and suitable check valves 6 are provided to prevent reversal of the cycle. Stated otherwise, referring to FIG. 1, a liquid hydrocarbon gas is circulated from liquefaction equipment 5 down through the annulus 7 between the wall of casing 4 and the wall of casing 3. Thereafter, the gas passes around the lower end of casing 3 and rises in the annulus 8 between the wall of casing 3 and the producing pipe 1.

The condition of the hydrocarbon gas at any point in its cycle is a function of its temperature and pressure. As the gas circulates in the system, it may gradually change from liquid to vapor state due to its close proximity to the hot oil which is produced through pipe 1. If the gas is cooled to a sufficiently low temperature prior to pumping it into the well, it may be maintained in the liquid state throughout the cycle; however, the extent to which the gas can be cooled is limited by the cost of liquefying it and because excessive heat transfer from the hot oil to the gas would tend to impede the flow of the oil being produced. Since the temperature of the oil may be in the range of 150.degree.-180.degree. F, but for the protection afforded by the circulation of the liquefied gas, it is certain that the permafrost zone would be softened or melted, leading to the complications previously described, by heat transfer from the high temperature oil produced.

In a second embodiment, shown in FIG. 3, a laterally extending pipeline for transferring hot oil and gas comprises a transfer pipe 10 having a concentrically disposed jacket or pipe 11. Hot oil flows through the transfer pipe 10 while a liquefied hydrocarbon gas is passed through annulus 12 formed by the walls of pipe 10 and pipe 11 to protect the frozen permafrost zone 13 from the effects of the substantially higher temperature of the hot oil. Where desirable, insulation 14 is placed on the outer surface of pipe 11. An additional advantage of such a pipeline is that not only may the oil be transported, but the gas itself may be moved considerable distances in the pipeline, for example, from Alaska to the United States.

Hydrocarbon gases, preferably liquefied natural gas, comprise the medium for protecting the permafrost from the softening effect of the hot oil being produced or transferred. While any hydrocarbon gas may be used, for instance, propane, ethylene, etc., the large supply of natural gas in the Arctic region suggests its use for economic reasons. In addition, liquefaction of natural gas may be accomplished in accordance with known techniques with a minimum of specialized equipment.

Although refrigerants have been used before to maintain soil in frozen condition, to my knowledge, liquefied hydrocarbon gases have not been used in oil and gas producing and transporting operations in which the oil or gas is at such a high temperature as to effect softening or even melting of the permafrost zone. The extremely low temperatures of the liquefied hydrocarbon gases virtually insure complete protection of the permafrost layer during production and transportation of oil or gas at elevated temperatures.

Claims

I claim: pg,6

1. A method of transporting oil or gas at elevated temperatures in a pipeline through a permafrost zone of earth comprising:

A. surrounding that part of a first pipe which extends through the permafrost zone with a second pipe to form an annulus between said pipes;

B. passing a liquified hydrocarbon gas through said annulus in a path parallel to the path of oil or gas passing through said first pipe; and

C. maintaining the temperature of said hydrocarbon gas sufficiently low to prevent heat transfer from said oil or gas to said permafrost zone.

2. A method as set forth in claim 1 in which the hydrocarbon gas is one of methane, ethane, butane, ethylene, and propane.

3. A method as set forth in claim 1 in which the hydrocarbon gas is natural gas.

4. A method of protecting a permafrost zone from softening under the influence of heat from oil or gas being transported in a pipeline therethrough comprising:

A. extending a length of pipe to form a part of the pipeline substantially horizontally in said zone;

B. surrounding the pipe with a jacket to provide an annulus between the pipe and the jacket;

C. passing a liquified hydrocarbon gas through said annulus in a path parallel to the path of oil or gas passing in the pipe; and

D. maintaining the temperature of the hydrocarbon gas sufficiently low to prevent the permafrost zone adjacent the pipe from softening.

5. A method as set forth in claim 4 in which the temperature of the liquid natural gas is maintained by passing it through pumping stations located along the pipeline.

6. A method as set forth in claim 4 in which a plurality of lengths of pipe are disposed end to end to provide a continuous pipeline.