US3851704A - Method for insulating a borehole - Google Patents

Abstract

A method for insulating a wellbore penetrating a subterranean region and having positioned therein an inner well casing of a smaller diameter by placing in the space between the wellbore and the inner well casing a divided, solid, closed-cell material.

Description

United States Patent [1 1 Maxson et al.

[ Dec.3,1974

METHOD FOR INSULATING A BOREI-IOLE Inventors: Orwin G. Maxson; Gary D.

Achenbach, both of Ponca City,

Okla.

Assignee: Continental Oil Company, Ponca City, Okla.

Filed: June 28, 1973 Appl. No.: 374,439

U.S. Cl 166/292, 166/DIG. 1, 166/57, 166/315 Int. Cl E21b 33/13, E21b 43/00 Field of Search 166/D1G. 1, 302, 57, 315,

Primary ExaminerStephen J. Novosad Attorney, Agent, or FirmF. Lindsey Scott 5 7] ABSTRACT A method for insulating a wellbore penetrating a subterranean region and having positioned therein an inner well casing of a smaller diameter by placing in the space between the wellbore and the inner well casing a divided, solid, closed-cell material.

9 Claims, No Drawings BACKGROUND OF THE INVENTION This invention relates to a method for insulating boreholes penetrating subterranean formations.

A considerable need exists for an improved method for lining boreholes penetrating subterranean formations. Substantial benefits can be derived from the conservation of heat energy in steam injection wells for tertiary oil recovery, hot water injection, and production wells for the Frasch sulphur recovery process and wells for the recovery of geothermal steam by satisfactorily insulating such wells.

A particularly acute need for an improved method for lining boreholes with an insulating material occurs in the exploration for oil and production of oil in the artic regions. Major oil discoveries on the northern slope of Alaska and other artic areas occur in regions where permafrost may occur from the surface to a depth of 2,500 feet or more. The permafrost is largely made up of sand, gravel, soil, and other materials frozen in a matrix of solid ice. When a wellbore penetrates such a permafrost region, the circulation of relatively warm drilling mud in the drilling operation melts the permafrost in the area of the wellbore and when the well is put on production, movement of the relatively hot oil through the permafrost region melts the permafrost in the vicinity of the wellbore. Severe problems of enlargement of the wellbore with subsidence of material from the permafrost region have been encountered. This necessitates the use of extremely high strength casing materials and massive cementing jobs around the wellbore to maintain the integrity of the wellbore. One method for mitigating the problem of melting of permafrost in the region of a wellbore is to insulate the wellbore from the surrounding permafrost region. Various methods have been tried. For example, casing which is sheathed with polyurethane foam has been tried, however, beyond shallow depths, this is entirely unsatisfactory because the hydrostatic pressure at the lower levels of the permafrost region collapses the cell structure of the polyurethane foam and largely destroys its insulative properties. Attempts to form foam materi' als in the region of the wellbore employing foaming agents asshown by Chism US Pat. No. 3,379,253 and others are unsuccessful because the high hydrostatic pressure at the lower levels of the permafrost region prevents expansion of the gaseous foaming agents or contracts the foams formed before injection. Likewise, inclusion of foam materials such as expanded pearlite in conventional cements is not satisfactory because the high hydrostatic pressure crushes such materials and significantly destroys the insulating properties of such cements. Therefore, while such prior art methods have some utility for insulating boreholes in the permafrost regions near the surface, they are not at all satisfactory at greater depths where considerable hydrostatic pressure is encountered.

U.S. Pat. No. 3,722,591, issued Mar. 27, 1973, to Maxson, discloses a method for insulating and lining a borehole in permafrost by hardening in place a hardable, flowable composition containing microspheres. Such a method has the disadvantage that it is difficult to remove the insulating material when it is necessary to remove the inner casing from such wells for any reason since unless the insulation is friable, removable by heat, dissolution or the like the casing is locked in place in the wellbore. In certain cases it would be economically advantageous to remove the tubing, i.e., a dry hole.

An obvious need thus exists for an improved method for insulating boreholes penetrating permafrost regions, particularly at the lower levels of such formations where a considerable hydrostatic pressure is encountered and, more particularly, near the bottom of the permafrost region which is always near its melting point.

OBJECTIONS OF THE INVENTION An object of the present invention is to provide a method for insulating a borehole penetrating a subterranean region so that the insulating material is readily removed.

A further objective of the present invention is to provide a method for insulating a borehole so that the inner casing and the like is not bonded to the insulation and is readily removable from the wellbore.

These and other objects and advantages will appear from the following description of the embodiments of the invention.

SUMMARY OF THE INVENTION In one aspect, this invention discloses a method for insulating a borehole penetrating a subterranean region and having positioned therein an inner casing by placing in the annular space between the wellbore and the inner casing a divided, solid, closed-cell material.

DESCRIPTION OF PREFERRED EMBODIMENTS In the practice of the present invention, a wellbore penetrating subterranean formations is drilled to a desired depth. Typically an inner casing of a smaller diameter than the borehole is placed inside the wellbore so that fluids may be removed from or pumped into a desired formation. In many applications, it is desirable that the walls of the wellbore be insulated against heat transfer to or from the liquid in the inner casing. In the practice of the present invention, the wellbore is insulated by placing between the outer diameter of the wellbore and the inner casing a solid, closed-cell material, thereby providing insulation.

The method of the present invention will be found advantageous in wellbores used for steam injection for tertiary oil recovery, hot water injection in production wells for sulphur recovery processes, wells for recovery of geothermal steam, wells penetrating permafrost zones, and the like.

In a preferred embodiment, a wellbore is drilled to a desired depth, and thereafter an inner casing is placed inside the wellbore. The wellbore is then insulated by positioning between the wellbore and the inner casing a solid, closed-cell material. The closed cell material may be flowed into the well alone or suspended in a fluid. When suspended in a fluid, the closed cell material typically comprises from about 10 to about percent by volume of the mixture. Suitable fluids are selected from the group consisting of oil, water, thixotropic fluids, and volatile carriers. Some suitable thixotropic fluids are clay-water mixtures, asbestos-water mixtures, silica gel-water and silica gel-oil mixtures, alumina-water mixtures and the like. Some suitable volatile carriers are hydrocarbons having a boiling point below 200C at atmospheric pressure such as propane, butane, pentane, hexane, kerosene, gas oils, liquified natural gas, heptane, octane, naphtha and the like and water. When the closed cell material is positioned in the wellbore by the method described hereinbefore; the wellbore is insulated with an insulating material consisting essentially of a divided solid closed cell material and atleast one gas selected from the group consisting of the vapors of hydrocarbons having a boiling point below about 200C, water vapor and air. In many embodiments natural gas, propane, butane or water will be preferred because of their ready availability. As noted herein before, the closed-cell material may be introduced into the well alone or in suspension in a fluid. A preferred method for introducing the closed cell material is in suspension in crude oil, drilling fluid, water and the like. A further desired embodiment utilizes a thixotropic fluid. The closed cell material is suspended in a thixotropic fluid which is pumped into the wellbore and allowed to fill the wellbore, thereby providing an insulating layer between the wellbore and the inner casing. Such materials set and resemble solids upon standing yet are readily rendered fluid by imparting shear into the thixotropic mixture by agitation and the like.

It is readily seen that the closed-cell material of the present invention may be positioned in the wellbore by a number of methods well known to those skilled in the art. An important advantage of the present invention is that the closed-cell material is readily removed from the space between the wellbore and the inner casing. For instance, when the closed-cell material alone is present, it may readily be removed by pumping water into the lower portion of the wellbore and merely floating out the closed-cell material which is typically lighter than water. The closed-cell material may also be re.- moved by pneumatic methods such as air injection and the like. Of course, the thixotropic suspensions will require that shear be imparted by pressure, agitation, and the like but are readily removed by flushing and the like. It is therefore readily seen that by the method of the present invention, insulating material may be placed in position between a wellbore and an inner c'asing in such a manner that the insulating material is readily removed when desired such as in those instances when it is desired to remove the inner casing for repair salvage and the like.

The divided, solid, closed-cell materials of the instant invention include those materials which have a particular size diameter in the range of 1 micron to 2 centimeters; over 20 volume percent void space wherein the void space is present as closed cells; and a hydrostatic crush strength of at least 200 psi and preferably of about 200 to about 15,000 psi or more.

Presently preferred. are hollow microspheres having diameters in the range of about 1 16 to 1,000 microns which have wall thicknesses of from 0.5 to 30 percent of their diameters. The walls of such microspheres can be comprised of organic polymers such as polyurethane, surans, ceramic material such as galss and the like. Specific examples of suitable materials include certain fly ash floaters and the like. Also preferred are hollow,'siliceous microspheres having diameters in the range of to 200 microns, wall thicknesses of 2-l0 microns, and a bulk density from about 0.5 to about 0.75 gm/cc.

The divided, solid, closed-cell materials described herein are readily available from commercial sources.

While the invention has been described and discussed herein with reference to an uncased wellbore having positioned therein an inner casing the invention is by no means limited to this embodiment. For example the wellbore may be cased with a casing which may or may not be cemented into the wellbore in which case the insulating material is desirably placed between the inner casing and the outer casing; the inner casing may comprise tubing positioned inside an intermediate casing and the insulating material may be placed between the intermediate casing and the outer casing, between the intermediate casing and the tubing and the like. Many such variations and modifications are possible within the scope of the present invention.

It is noted that the embodiments described herein before are illustrative in nature, and many variations and modifications within the scope of the present invention are possible. In fact, it is expected that many such variations and modifications may appear obvious and desirable to those skilled in the art upon a review of the foregoing description of preferred embodiments and the following examples.

EXAMPLE 1 A 22-inch diameter borehole was drilled through a pennafrost region which is 2,435 feet thick into the strata below for a distance of an additional 2,000 feet. The wellbore is then cleaned of extraneous material and a 4-inch inner casing is positioned in the wellbore.

A solid, closed-cell material is injected in the form of a suspension of the closed-cell material in propane wherein the closed-cell material comprises percent by volume of the suspension. The suspension is passed into the space between the wellbore diameter and the inner casing until the well is substantially full, and thereafter the propane is allowed to vaporize off. An insulative liner is thus formed in situ which has excellent insulating properties due to the voids in the closedcell material even under the high hydrostatic pressure found at the bottom of the borehole. This insulation could then be loosened or removed as desired to permit retrieval of the 4-inch casing.

It is clearly illustrated that the method of the present invention is effective in forming insulating layers between wellbore diameters and inner piping as discussed hereinbefore.

Having thus described the invention, I claim:

1. A method for insulating a wellbore penetrating a subterranean region and having positioned therein an inner casing of a smaller diameter than the borehole by placing in the annular space between the wellbore and said inner casing an insulating material consisting essentially of a divided, solid, closed-cell material, having a particular size diameter in the range of 1 micron to 2 cm and at least 20 volume percent void space and at least one gas selected from the group consisting of the vapors of hydrocarbons having a boiling point below about 200C, water vapor and air.

2. The method of claim 1 wherein said closed-cell material consists essentially of hollow microspheres having a diameter in the range of l to about 1,000 microns, a wall thickness of from about 0.5 to about 30 percent of their diameter, a crush strength of about 200 to about 15,000 psi and a bulk density from about 0.5 to about 0.75 g/cc.

3. The method of claim 2 wherein said subterranean region comprises permafrost.

4. The method of claim 2 wherein said closed-cell material comprises fly ash floaters.

'5. The method of claim 2 wherein said wellbore is cased and wherein said closed-cell material is placed between said wellbore casing and said inner casing.

6. The method of claim 1 wherein said insulating material is placed in said annular space by placing in said annular space a mixture of said closed-cell material with at least one volatile solvent selected from the group consisting of hydrocarbons having a boiling point lower than 200C and water and thereafter allowing said volatile solvent to evaporate.

7. A method for insulating a wellbore penetrating a subterranean region and having positioned therein an inner casing of a smaller diameter than the borehole by placing in the annular space between the wellbore and said inner casing a mixture of a divided, solid, closedcell material having a particulate size diameter in the range of 1 micron to 2 cm and at least 20 volume percent void space with a thixotropic fluid.

8. The method of claim 7 wherein said closed cell material is present in said mixture in an amount equal to from about 10 to percent by volume of the mixture.

9. The method of claim 7 wherein said thixotropic fluid is selected from the group consisting of clay-water mixtures, asbestos-water mixtures, silica gel-water mixtures, silica gel-oil mixtures and alumina-water mixtures.

Claims (9)

1. A METHOD FOR INSULATING A WELLBORE PENETRATING A SUBTERRENEAN REGION AND HAVING POSITIONED THEREIN AN INNER CASING OF A SMALLER DIAMETER THAN THE BOREHOLE BY PLACING IN THE ANNULAR SPACE BETWEEN THE WELLBORE AND SAID INNER CASING AN INSULATING MATERIAL CONSISTING ESSEENTIALLY OF A DIVIDED, SOLID, CLOSED-CELL MATERIAL, HAVING A PARTICULAR SIZE DIAMETER IN THE RANGE OF 1 MICRON TO 2 CM AND AT LEAST 20 VOLUME PERCENT VOID SPACE AND AT LEAST ONE GAS SELECTED FROM THE GROUP CONSISTING OF THE VAPORS OF HYDROCARBONS HAVING A BOILING POINT BELOW ABOUT 200*C, WATER VAPOR AND AIR.

2. The method of claim 1 wherein said closed-cell material consists essentially of hollow microspheres having a diameter in the range of 1 to about 1,000 microns, a wall thickness of from about 0.5 to about 30 percent of their diameter, a crush strength of about 200 to about 15,000 psi and a bulk density from about 0.5 to about 0.75 g/cc.

3. The method of claim 2 wherein said subterranean region comprises permafrost.

4. The method of claim 2 wherein said closed-cell material comprises fly ash floaters.

5. The method of claim 2 wherein said wellbore is cased and wherein said closed-cell material is placed between said wellbore casing and said inner casing.

6. The method of claim 1 wherein said insulating material is placed in said annular space by placing in said annular space a mixture of said closed-cell material with at least one volatile solvent selected from the group consisting of hydrocarbons having a boiling point lower than 200*C and water and thereafter allowing said volatile solvent to evaporate.

7. A method for insulating a wellbore penetrating a subterranean region and having positioned therein an inner casing of a smaller diameter than the borehole by placing in the annular space between the wellbore and said inner casing a mixture of a divided, solid, closed-cell material having a particulate size diameter in the range of 1 micron to 2 cm and at least 20 volume percent void space with a thixotropic fluid.

8. The method of claim 7 wherein said closed cell material is present in said mixture in an amount equal to from about 10 to 80 percent by volume of the mixture.

9. The method of claim 7 wherein said thixotropic fluid is selected from the group consisting of clay-water mixtures, asbestos-water mixtures, silica gel-water mixtures, silica gel-oil mixtures and alumina-water mixtures.