WO2007147054A2

WO2007147054A2 - In-situ radiofrequency heating of fractured bedrock for removal or conversion of liquids gases and solids

Info

Publication number: WO2007147054A2
Application number: PCT/US2007/071216
Authority: WO
Inventors: Raymond S. Kasevich
Original assignee: Kasevich Raymond S
Priority date: 2006-06-14
Filing date: 2007-06-14
Publication date: 2007-12-21
Also published as: WO2007147054A3

Abstract

The present invention imparts heat to the targeted area through the application of carefully controlled radiofrequency transmissions. The technology is applied by inserting a flexible coaxial transmission line and applicator (antenna) system into multiple vertical or horizontal boreholes in the area to be treated. Radiofrequency generators supply energy through coaxial lines to multiple electromagnetically coupled down-hole antennas, and the subsurface material between the antennas rises in temperature as it absorbs radiofrequency energy radiating from the antennas.

Description

IN-SITU RADIOFREQUENCY HEATING OF FRACTURED BEDROCK FOR REMOVAL OR CONVERSION OF LIQUIDS, GASES, AND SOLIDS

FIELD OF THE INVENTION

[001] The present invention relates generally to the application of radiofrequency energy to fractured bedrock to facilitate the degradation or removal of liquids, gases, or solids such as environmental pollutants.

BACKGROUND OF THE INVENTION

[002] With the rise of the chemical and petrochemical industries, the introduction of toxic chemicals and other pollutants into the soil has become an ever growing problem. Various methods are used with more or less success to remove such pollutants from the soil.

[003] Removal of such pollutants is especially difficult when the contaminants enter bedrock fractures. For example, The heterogeneous distribution of residual 1,1,1- trichloroethane (TCA) dense nonaqueous phase liquid (DNAPL) within discrete, poorly connected bedrock fractures renders many remedial technologies inefficient or ineffective because the DNAPL cannot be physically removed or reached to treat in situ. Thermal resistivity heating and thermal conduction heating can treat a targeted volume of bedrock, overcoming the physical constraints of the bedrock fracture network, but can be prohibitively expensive to implement due to energy requirements for heating the rock mass. Thus, a system and method that facilitates the removal of such pollutants from bedrock fractures would be beneficial.

[004] The present invention applies radiofrequency energy to heat such contaminated areas. The radiofrequency energy will preferentially heat groundwater and residual chemicals within the bedrock fractures, instead of the surrounding bedrock mass, making this a cost-effective option for in situ thermal treatment in some geological media. BRIEF SUMMARY OF THE INVENTION

[005] The present invention applies radiofrequency energy to heat fractured bedrock contaminated with pollutants or other chemicals. Radiofrequency energy has advantages over the other current potential methods for remediating fractured bedrock sites. For example, radiofrequency energy, unlike other heating methods, preferentially heats bipolar molecules (e.g., water), which focuses the thermal energy on heating groundwater rather than the bedrock. Thus, radiofrequency energy is more efficient and cost effective. Also, radiofrequency energy heats water within a volume of bedrock independent of the degree of fracture interconnectivity. Furthermore, the hydrological characteristic of bedrock sites enhances the efficiency of radiofrequency heating. These include the low porosity of bedrock and the minimal flushing of groundwater through such areas.

[006] Radiofrequency energy prefers the dielectric properties of water over those of soil and bedrock and therefore targets water. As a result, the radiofrequency heating heats groundwater in bedrock fractures and the moisture within a bedrock matrix. The bedrock mass is not targeted by the radiofrequency energy, but undergoes secondary heating via conduction and convection from the heated groundwater. Groundwater migrates slowly through the poorly-connected fractures in bedrock. As a result of the relatively high groundwater residence time, less energy is required to heat the water.

[007] The present invention imparts heat to the targeted area through the application of carefully controlled radiofrequency transmissions. The technology is applied by inserting a flexible coaxial transmission line and applicator (antenna) system into multiple vertical or horizontal boreholes in the area to be treated. Radiofrequency generators supply energy through coaxial lines to multiple electromagnetically coupled down-hole antennas, and the subsurface material between the antennas rises in temperature as it absorbs radiofrequency energy radiating from the antennas. In one embodiment of the present invention, the treatment system includes a network of 100- foot deep boreholes, a radiofrequency generator and transmitter array, and a system to collect and remove an resulting soil vapors. Each radiofrequency treatment cell consists of four radiofrequency antennas that are operated at various treatment depths within the 100-deep boreholes. The RF antenna are positioned at two separate lifts located 35 and 50 feet below ground surface, and the total power output ranges from 12 to 16 kW, depending on the radiofrequency configuration.

[008] hi one embodiment of the invention, a system for remediating contaminated fractured bedrock sites is provided. The system comprises a borehole in a contaminated bedrock site, a radiofrequency antenna positioned within the borehole, a cable attached to the radiofrequency antenna to supply radiofrequency to the antenna, and a radiofrequency generator attached to the cable to generate radiofrequency to be supplied to the radiofrequency antenna.

[009] hi another embodiment of the invention, a method for remediating contaminated fractured bedrock sites is provided. The method comprising the steps of positioning a radiofrequency antenna in a borehole in a contaminated bedrock site, generating radiofrequency energy, and applying the radiofrequency energy to the contaminated bedrock site with the antenna to heat water and contaminants in the contaminated bedrock site to the degradation point of the contaminants. [010] While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the invention. As will be realized, the invention is capable of modifications in various obvious aspects, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

[011] Fig. 1 is an overhead plan view of the system according to the invention.

[012] Fig. 2 shows the system of the present invention from a sub-surface perspective. DETAILED DESCRIPTION

[013] The present invention applies radio frequency energy to heat such contaminated areas. The radiofrequency energy will preferentially heat groundwater and residual chemicals within the bedrock fractures, instead of the surrounding bedrock mass, making this a cost-effective option for in situ thermal treatment in some geological media.

[014] Fig. 1 is an overhead plan view of the system according to the invention.

Li the embodiment of the invention that is pictured, four boreholes 20 are drilled in targeted bedrock area 10. The depth of the boreholes will be dictated by the characteristics of the targeted bedrock area 10; for example, the boreholes should be deep enough that the radiofrequency antennas can be placed in proximity to the contaminated area to be treated. A radiofrequency antenna 22 for the application of radiofrequency energy to the targeted area is placed within each borehole 20. The antennas 22 can be placed in boreholes 20 that are wet, dry, or filled with materials depending upon the application. The antennas 22 do not require electrical contact with the targeted bedrock area 10. The dielectric heating produced by the radiofrequency antennas 22 extends elliptically and horizontally away from the antennas 22 and into the target formation 10. The radial extent of the heating pattern will vary as a function of the operating frequency, the length of the antennas 22, and the electrical conductivity and dielectric constant of the target formation 10.

[015] A variety of radiofrequency antennas that are known in the art are suitable for this application. For example, the antennas described in U.S. Patent Application 60/645154, U.S. Patent No. 5,065,819, or J. Bridges, et al, "RF Heating of Utah Tar Sands," Final Report, HT Research Institute, may be utilized. [016] The radiofrequency antennas are connected to radiofrequency generator

30 by coaxial cable 32. The radiofrequency generator 30 generates radiofrequency, which is carried to the antennas 22 by coaxial cable 32. The antennas 22 then apply radiofrequency energy to the targeted area 10, heating the water and chemicals in bedrock fractures, thereby degrading the pollutants and remediating the site. [017] In the event that contaminants are vaporized, a soil vapor extraction system may be used to collect and store the materials to prevent the escape of harmful pollutants. This may be effected by drilling in the bedrock in the targeted area 10 a soil vapor extraction well 42. A soil vapor collector 42 may be placed at the mouth of well 42 to collect and store any soil vapors that are generated by the application of radiofrequency energy to the targeted area.

[018] Fig. 2 shows the system of the present invention from a sub-surface perspective. Boreholes 20 are drilled into targeted bedrock area 10. Radiofrequency antennas 22 are placed within the boreholes 20 in the vicinity of the pollutants that are targeted. Radiofrequency antennas 22 are connected to radiofrequency generator 30 by coaxial cable 32. The radiofrequency current that is generated by radiofrequency generator 30 is then transmitted to antennas 22 by coaxial cables 32. The antennas 22 then apply radiofrequency energy to targeted area 10, thereby heating the water and contaminants in the targeted area 10 and degrading the pollutants. To collect and store any soil vapors that are generated, a soil vapor extraction well 40 is drilled in the vicinity of boreholes 20, and a soil vapor collector 42 is placed at the mouth of well 40. [019] In operation, a user of an embodiment of the present invention would position radiofrequency antennas in boreholes in a contaminated fractured bedrock site. The user would connect the antennas to a radiofrequency generator via coaxial cable. The user would then apply radiofrequency energy using the radiofrequency generator to the antennas, thereby applying the radiofrequency energy to the bedrock. High power radiofrequency transmitters of 50,000 watts may be used with frequencies in the 12 to 16 MHz frequency range. The user would also drill a soil vapor extraction well in the targeted area and use a soil vapor collector to collect and store any soil vapor generated by the system.

Claims

CLAIMS What is claimed is:

1. A system for remediating contaminated fractured bedrock sites, said system comprising: a borehole in a contaminated bedrock site;

a radiofrequency antenna positioned within the borehole;

a cable attached to the radiofrequency antenna to supply radiofrequency to the antenna; and

a radiofrequency generator attached to the cable to generate radiofrequency to be supplied to the radiofrequency antenna.

2. The system of claim 1 wherein the applicator is an antenna array.

3. The system of claim 1 wherein said applicator is a solenoid antenna.

4. The system of claim 1 wherein the applicator is a helical antenna.

5. The system of claim, further comprising: a soil vapor extraction well in the contaminated bedrock site; and

a soil vapor collector at the mouth of the soil vapor extraction well.

6. The system of claim 5 wherein the applicator is an antenna array.

7. A method for remediating contaminated fractured bedrock sites, the method comprising the steps of: positioning a radiofrequency antenna in a borehole in a contaminated bedrock site;

generating radiofrequency energy; and applying the radiofrequency energy to the contaminated bedrock site with the antenna to heat water and contaminants in the contaminated bedrock site to the degradation point of the contaminants.

8. The method of claim 6, further comprising the steps of: collecting soil vapors generated by the application of radiofrequency energy to the contaminated bedrock site.