Method For Insulating And Lining A Borehole In Permafrost

Abstract

A borehole penetrating a subterranean region is insulated and lined by hardening in place a hardenable, flowable composition consisting essentially of a hardenable, flowable, adhesive cement and a divided, solid, closed-cell material wherein the closed-cell material can comprise as much as about 80 volume percent of the hardenable, flowable composition and wherein the hardened material forming the liner has a hydrostatic crush strength of about 200-5,000 psi, or more. More particularly, syntactic foams are formed in situ to line boreholes penetrating permafrost.

Description

BACKGROUND OF THE INVENTION

The invention relates to a method for lining boreholes penetrating subterranean formations.

A considerable need exists for an improved method of lining boreholes penetrating subterranean formations. Thus, substantial benefits can be derived from a conservation of heat energy in steam injection wells for tertiary oil recovery, hot water injection and production wells for the Frasch sulfur recovery process, and wells for the recovery of geothermal steam can be insulated satisfactorily with insulating liners.

A particularly acute need for an improved method for lining boreholes with an insulating liner occurs in the exploration for and production of oil in Arctic regions. Major oil discoveries on the northern slope of Alaska and other Arctic areas occur in regions where permafrost may occur from the surface to depths 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 circulation of relatively warm drilling mud in the drilling operation melts the permafrost in the area of the wellbore. When a 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 to mitigate the problem of melting of permafrost in the region of a wellbore is to insulate the wellbore from the surrounding permafrost region. Various expedients have been tried. For example, casing which is sheathed with polyurethane foam has been tried. However, beyond shallow depths this is entirely unsatisfactory because hydrostatic pressure at lower levels of the permafrost region crushes the cell structure of the polyurethane foam and largely destroys its insulative properties. Attempts to form foamed materials in the region of the wellbore employing foaming agents as taught by Chism, U. S. Pat. No. 3,379,253, and by 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 foamed materials such as expanded perlite 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. Thus, a clear cut need exists for an improved method of insulating boreholes penetrating through permafrost regions, particularly at the lower levels of such formations where considerable hydrostatic pressure is encountered and more particularly near the bottom of the permafrost region which is always near its melting point.

OBJECTS OF THE INVENTION

An object of the instant invention is to provide a method for insulating and lining a borehole penetrating a subterranean region whereby a liner is formed in situ by hardening in place a hardenable, flowable composition consisting essentially of a hardenable, flowable, adhesive cement and a divided, solid, closed-cell material.

These and other objects and advantages will appear from the following description of the embodiments of the invention, and the most novel features will be particularly pointed out hereinafter in connection with the appended claims.

SUMMARY OF THE INVENTION

In one aspect, this invention discloses a method for insulating and lining a borehole penetrating a subterranean region wherein a liner is formed in situ by hardening in place a hardenable, flowable composition consisting essentially of a hardenable, flowable, adhesive cement and a divided, solid, closed-cell material.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A liner for a borehole penetrating a subterranean region is formed in situ by hardening in place a hardenable, flowable composition consisting essentially of a hardenable, flowable, adhesive cement and a divided, solid, closed-cell material, the closed-cell material comprising as much as about 80 volume percent of the hardenable, flowable composition and the hardened material forming the liner having a hydrostatic crush strength of at least about 200 psi, and more particularly of about 200- 15,000 psi, or more.

According to one presently preferred embodiment, a wellbore is drilled through the subterranean region to be lined, such as a permafrost region. This wellbore should be somewhat larger than the wellbore desired for the final well. Residual materials are removed from the wellbore or are displaced by a composition consisting essentially of a hardenable, flowable, adhesive cement and a divided, solid, closed-cell material. The composition is admixed and flowed into the wellbore to entirely fill the wellbore throughout the region to be lined. The material is then allowed to harden. A wellbore of smaller diameter is then drilled through the center of the hardened material leaving a liner formed in situ lining the original borehole.

Alternatively, according to another presently preferred embodiment, a wellbore is drilled through a subterranean region to be lined, such as a permafrost region. A second liner such as a steel pipe is hung so that it extends substantially through the region to be lined. The hardenable, flowable composition of the instant invention consisting essentially of a hardenable, flowable, adhesive cement and a divided, solid, closed-cell material is then injected between the second liner and the inner surface of the borehole. Upon hardening, an insulating lining is formed in situ which bonds the steel liner to the formation.

In general, the insulating liner of this invention can be formed in situ by injecting into place a hardenable, flowable composition consisting essentially of a hardenable, flowable, adhesive cement, and a divided, solid closed-cell material by any method known to the art for injecting a conventional fluid hydraulic cement into place. Such techniques are disclosed in U. S. Pat. No. 3,379,253 and in various literature distributed by oil well cementing companies. Such techniques are well known to the art.

The hardenable, flowable, adhesive cement of this invention can include any substantially fluid material which can be injected into the borehole with conventional oil well cementing equipment and which will harden upon standing to a solid material having sufficient cohesive strength and adhesive strength to the divided, solid, closed-cell material to form a material having sufficient mechanical strength to substitute for conventional wellbore lining cements. Examples of suitable hardenable, flowable, adhesive cements include: hydraulic cements, epoxy resin, phenolformaldehyde resin, polyurethane, and polysulfide resin. When a liner is formed in a permafrost region, a hardenable, flowable, adhesive cement should be employed which is flowable but yet hardenable at the temperatures encountered.

The hydraulic cement is admixed with a conventional amount of water, and includes any of the conventional hydraulic cements employed in oil well cementing. In addition, suitable additives can be incorporated including retarders, accelerators, low water loss additives, lost circulation additives, friction reducers, and the like.

When the terms epoxy resin, phenolformaldehyde resin, polyurethane, or polysulfide are employed in the instant application to describe examples of a hardenable, flowable, adhesive cement, it is to be understood that these terms are used in conformity with a wide general useage among those skilled in the art. Actually, these terms, as they are employed here, refer to the precursor mixtures for the various resins which harden to form the actual solid adhesive cement by chemical reaction. These materials and their mode of action are well known to those skilled in the art. Considerable information on such adhesive cement systems can be found in Skeist, Handbook of Adhesives, Reinhold Publishing Corp., (1962). In essence, any of such hardenable, flowable, adhesive cements which meet the criteria defined above can be employed according to this invention.

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 10 cm, which have over 20 volume percent void space, which have the void space present as closed-cells, and which have a hydrostatic crush strength of at least about 200 psi, and preferably of about 200 to 15,000 psi, or more.

Presently preferred are hollow microspheres having diameters in the range of about 1 to 1,000 microns which have wall thicknesses of 0.5 to 10 percent of their diameters. The walls of such microspheres can be comprised of an organic polymer such as polyurethane or a ceramic material such as glass. Specific examples of suitable materials include certain fly ash floater products.

Even more presently particularly preferred are hollow siliceous microspheres having diameters in the range of 10 to 100 microns and wall thicknesses of 1 to 5 percent of their diameters.

The hardenable, flowable compositions of this invention can be prepared by admixing the hardenable, flowable, adhesive cements and the divided, solid, closed-cell materials of this invention by any means conventionally known for the admixing of particulate solids and liquids.

The divided, solid, closed-cell material comprise as much as 80 volume percent of the hardenable, flowable composition, and often comprises 10 to 80 volume percent of the hardenable, flowable composition.

The materials sued to prepare the hardenable, flowable compositions of this invention are readily available from commercial sources.

EXAMPLES

Example 1

A 22 inch diameter wellbore is drilled through a permafrost region which is 2,480 feet thick and into the strata below for a distance of an additional 50 feet. The wellbore is then cleaned of extraneous material. A hardenable, flowable composition containing 80 volume percent of a product which is comprised of hollow siliceous spheres having a diameter range of 1 to 1,000 microns and a wall thickness of 0.5 to 10 microns, 15 volume percent Portland cement, 5 volume percent of water and air is admixed on the surface and injected into the borehole penetrating the permafrost region and portion of the stratum below. The material is allowed to harden for 24 hours. Upon substantial hardening of the hardenable material, a wellbore having a diameter of 18 inches is drilled through the center of the hardened material filling the original borehole. An insulative liner is thus formed in situ which has good mechanical strength and excellent insulating properties due to the voids in the closed-cell material which remain open even under the high hydrostatic pressure found at the bottom of the borehole.

Example 2

A wellbore having a diameter of 22 inches is drilled through a permafrost region having a depth of 2,400 feet to a total hole depth of 2,500 feet. A steel casing having an outside diameter of 18 inches is hung so that it extends nearly to the bottom of the borehole. A hardenable, flowable composition containing 38 volume percent of epoxy resin precursors and 62 percent by volume of hollow siliceous microspheres is admixed on the surface and injected into the annulus between the steel pipe and the outside of the borehole. The epoxy resin precursors include 95 volume percent of EPON 8- 28 (a trademark) epoxy resin (which is a reaction product between bis-phenol A and epichlorohydrin), and 5 percent of DETA (diethylene triamine). This hardenable, flowable composition is allowed to harden for 24 hours. The syntactic foam which is thus formed in the annulus between the steel casing and the borehole is a liner which has excellent mechanical strength and excellent insulating properties due to the high closed-cell void content of the resulting syntactic foam. The high hydrostatic crush strength of the microsphere material and the resulting syntactic foam insures that excellent thermal properties are present in the insulating liner thus formed, even at lower depths.

Example 3

The run of Example 2 is repeated, except that 1, 3, 6-hexane trithiol is substituted for about 80 mole percent of the diethylene triamine. Cure is affected more rapidly at the relatively low downhole temperature to produce a liner of improved strength.

Claims

I claim:

1. A method for insulating and lining a borehole penetrating a subterranean region comprising forming a liner in situ by hardening in place a hardenable, flowable composition consisting essentially of a hardenable, flowable, adhesive cement and a divided, solid, closed-cell material, wherein the divided, solid, closed-cell material comprises as much as about 80 volume percent of the hardenable, flowable composition, and wherein the hardened material forming the liner has a hydrostatic crush strength of at least about 200 psig; wherein the subterranean region is a permafrost region; wherein the liner is formed in situ by centering a well casing of smaller diameter with the borehole, injecting the hardenable, flowable composition consisting essentially of a hardenable, flowable, adhesive cement and a divided, solid, closed-cell material into the annulus between the well casing and the interior surface of the borehole, and allowing the hardening, flowable composition to harden in the annulus to form the insulating layer; wherein the hardenable, flowable composition contains about 10 to 60 volume percent of hollow microspheres whose diameters are in the range of 1 to 1000 microns having wall thicknesses of 0.5 to 10 percent of their diameters, and the remainder comprises a hardenable, flowable, adhesive cement, said hardenable, flowable, adhesive cement comprising a hydraulic cement, an epoxy resin, a phenolformaldehyde resin, a polyurethane resin, or a polysulfide; and wherein the hollow microspheres are siliceous microspheres.

2. A method for insulating and lining a borehole penetrating a subterranean region comprising forming a liner in situ by hardening in place a hardenable, flowable composition consisting essentially of a hardenable, flowable, adhesive cement and a divided, solid, closed-cell material, wherein the divided, solid, closed-cell material comprises as much as about 80 volume percent of the hardenable, flowable composition, and wherein the hardened material forming the liner has a hydrostatic crush strength of at least about 200 psi; wherein the hardenable, flowable composition contains about 10 to 60 volume percent of hollow siliceous microspheres whose diameters are in the range of 1 to 1000 microns having wall thicknesses of 0.5 to 10 percent of their diameters, and the remainder comprises a hardenable, flowable, adhesive cement, said hardenable, flowable, adhesive cement comprising a hydraulic cement, an epoxy resin, a phenolformaldehyde resin, a polyurethane resin, or a polysulfide.

3. A method for insulating and lining a borehole penetrating a permafrost region comprising drilling a borehole through the permafrost region, removing extraneous material from the borehole, flowing a hardenable, flowable composition consisting essentially of a hardenable, flowable, adhesive cement and a divided, solid, close-cell material into the borehole filling said borehole, hardening the hardenable, flowable composition in the borehole, and drilling a smaller diameter borehole through the hardened material to complete the formation of the insulating liner in the original borehole; wherein the divided, solid, closed-cell material comprises as much as about 80 volume percent of the hardenable, flowable composition; and wherein the hardened material forming the liner has a hydrostatic crush strength of at least about 200 psi.

4. A method for insulating and lining a borehole penetrating a permafrost region comprising forming a liner in situ by hardening in place to form hardened matter a hardenable, flowable composition consisting essentially of a hardenable, flowable, adhesive cement consisting essentially of an epoxy resin plus a hardening agent plus a divided, solid, closed-cell material; wherein the divided, solid, closed-cell material comprises as much as about 80 volume percent of a hardenable, flowable composition; wherein about 10 to 60 volume percent of the hardenable, flowable composition is hollow, siliceous, microspheres having diameters in the range of 1 to 1000 microns and wall thicknesses of 1 to 5 percent of their diameters; and wherein the hardened matter of the liner has a hydrostatic crush strength of about 200 to 15,000 psig.