Downhole servicing compositions having high thermal conductivities and methods of using the same

Abstract

A downhole servicing composition comprising from about 15 percent to about 80 percent by weight of a clay, and from about 10 percent to about 75 percent by weight of a carbon source is disclosed. The invention includes a downhole servicing composition comprising from about 15 percent to about 45 percent by weight of a first clay, from about 15 percent to about 45 percent by weight of a second clay, from about 10 percent to about 35 percent by weight of a filler, and from about 10 percent to about 75 percent by weight of a carbon source. The invention also includes a downhole servicing composition comprising an aqueous base and from about 10 percent to about 75 percent by weight of flaked graphite, wherein the downhole servicing composition has a thermal conductivity not less than about 0.8 BTU / hr-ft-° F.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This is a continuation application claiming priority to U.S. patent application Ser. No. 11 / 422,277, filed Jun. 5, 2006, now published as U.S. Patent Publication 2006-0243166 A1, and entitled “Downhole Servicing Compositions Having High Thermal Conductivities and Methods of Using the Same,” which claims priority to U.S. patent application Ser. No. 10 / 767,690 filed Jan. 29, 2004, now issued as U.S. Pat. No. 7,067,004, and U.S. patent application Ser. No. 11 / 099,023 filed Apr. 5, 2005, now published as U.S. Patent Publication 2005-0205834 A1, which are incorporated by reference as if reproduced in their entirety.FIELD OF THE INVENTION[0002]This invention generally relates to thermally conductive downhole servicing compositions. More specifically, the invention relates to grout compositions having relatively high thermal conductivities and low hydraulic conductivities and methods of using the same to install a heat transfer loop in the earth....

AI Technical Summary

Benefits of technology

The composition provides a cost-effective, flexible, and efficient thermally conductive seal with high thermal conductivity and low hydraulic conductivity, reducing heat transfer inefficiencies and equipment wear, while minimizing environmental impact and labor costs.

Problems solved by technology

Further, the grout may form a seal that is substantially impermeable to fluids that could leak into and contaminate ground water penetrated by the hole in which it resides.

In an attempt to achieve such properties, two types of grouts containing sand to enhance their thermal conductivity, i.e., bentonite-based grout and cement-based grout, have been developed that are extremely labor intensive to prepare.

In particular, conventional grouts often require several hundred pounds of sand to render them suitably thermally conductive.

Unfortunately, the thermal conductivity that may be achieved by these conventional grouts is limited by the amount of sand that can be incorporated into and properly suspended in the grout.

Also, the preparation of such grouts is inflexible in that the concentrations of the components and the mixing procedures must be precise to avoid problems in the field.

Further, cement-based grout has the limitation of being very expensive.

However, the capabilities of such installations are limited by the ability of the installations to dissipate heat generated by the flow of electrical power through the equipment.

If the thermal resistivity of the environment surrounding the buried equipment is unsatisfactorily high, the heat generated during functioning of the equipment can cause an increase in the temperature of the equipment beyond tolerable limits resulting over time in the premature failure or destruction of the equipment.

At the very least, the equipment's life expectancy is decreased, which is an economic disadvantage.

Without sand, bentonite grout does not have high thermal conductivity properties.

Typical thermal conductivity values for bentonite grouts range from about 0.4 to about 0.6 BTU / hr-ft-° F. The addition of sand of an appropriate size can increase such thermal conductivity to a range of about 1.0 to about 1.2 BTU / hr-ft-° F. However, the sand can cause placement problems and high pump pressures when positioning as the thermally conductive grout.

In horizontal heat loops, high pump pressures can lead to a “frac out” situation where the material induces fractures in the soil through which the material can break through to the surface.

Use of sand can also lead to excessive friction, prematurely wearing out pumps and their various parts.

For example, in the case of a pipe bundle containing cables, such friction from sand can result in pulling forces that can exceed the strength of the bundle causing the bundle to separate during installation.

Backfilling soil with sand added after the pipe installation might be used to avoid such installation friction but backfilling may not always be possible or effective for the full length of the installation.

Further, additional wear caused by the sand to pumps and pump parts remains a concern.

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