Patent Number: 051911574
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENT A permanent storage or disposal well or borehole, generally designated 10, employed in the present invention, is illustrated in FIG. 1, that extends from the earth surface S into the earth's crust C. The borehole 10 may be formed by any suitable known method of drilling the crust C. The borehole 10 typically includes, in sequence from outside to inside, a tubular conductor casing 12, a surface casing 14, a protective casing 16, a protective liner 18 (supported from casing 16), and an inner casing 20. As is known, the various well tubular conduits are arranged concentrically and extend to various subsurface depths with the smaller conduits extending to the greater depths in the crust C. While the illustrated casing arrangement may be suitable for some locations, those skilled in the art will appreciate the casing program actually used will depend on numerous factors and may be varied from that disclosed without departing from the present invention. Part or all of the casing may be rendered permanent by cementing in place as illustrated. However, it will be understood that the fully cemented condition illustrated in FIG. 1 is not achieved until the hazardous waste has been properly placed or positioned using the bore hole 10. Disposed within the inner casing 20 are a plurality of substantially identical elongated closed containers, referenced from top to bottom 22, 24, 26, and 28 for receiving the hazardous material. Containers 24 and 26 are illustrated stacked vertically in tandem, but FIG. 1 is broken between containers 22 and 24 and containers 26 and 28 so as to schematically illustrate any desired number or plurality of containers 22, 24, 26, and 28 to be disposed or located in the casing 20. Those skilled in the art will also appreciate any suitable equivalent safe container for the hazardous waste to be disposed of in the borehole may be used. The material and configuration of the containers is a matter of design choice as long as they may be safely placed in the borehole 10 at the desired location by passing within the tubular casing. It is preferred that the containers be disposed concentric with the longitudinal axis of the inner casing 20 to aid in proper surrounding concentric encasement and storage of the containers 22, 24, 26 and 28 by concrete. Referring to lowermost container 28, a substantially concentric annulus is formed between the inwardly facing surface 30 of the inner casing 20 and the outwardly facing surface 32 of the container 28 which is filled with cement which then hardens in place. Various types of centralizers (not illustrated) may be used to hold the containers 22-28 in the concentric position during cementing. Turning now to FIG. 2, the elongated container 28, which is typical of the plurality of containers 22, 24, and 26, forms a waste material storage cavity or interior 34 and includes a sealing or closure cap 36. In the preferred embodiment the container 28 is vitrified to ensure that the container 28 will not rapidly decay with the passage of time. The seal cap 36 is threadedly secured at the upper end 38 of the container 28 and provides a fluid seal for preventing leakage of hazardous waste from the interior 34 of the container 28. In the preferred embodiment the seal cap 36 has outwardly facing helical pin threads 40 and the container 28 has complementary inwardly facing helical box threads 42 for securing the sealing the cap 36 with the container 28. The container 28 is preferably sealed with the seal cap 36 a the waste processing or generation site for safe transportation to the disposal well 10. The hazardous waste is sealed within the container 28 which is preferably formed in lengths of 30 ft to 60 ft and outside diameters of 5 to 6 inches. Such outside diameter allows the container 28 to be lowered into the borehole 10 through inner casing 20 which is somewhat larger in inside diameter to provide a desired radial clearance. The storage containers 28 are lowered in the borehole 10 until they are positioned or stacked for permanent safe disposal within a geopressured zone 48 which will be described in greater detail hereinafter. In FIG. 3 a fragmentary elevational view of the second embodiment of the hazardous waste disposal borehole of the present invention is illustrated which injects the hazardous material directly into the pores of the geopressured formation or zone. The hazardous waste may be entrained or in solution in the carrier hydraulic fluid. In the second embodiment, like reference characters, but increased by a factor of 100, will be used to designate like parts. The inner casing 120 is positioned in the borehole 110 similar to the bottom of inner casing 20 positioned in borehole 10 in FIG. 1, but the casing 120 is not cement filled to provide a flow passageway from the earth's surface. The inner casing 120 has a plurality of perforations 144 and 146 extending therethrough which communicate with the surrounding geopressured formation 148. The geopressured formation 148 is hydraulically split or fractured 150 by pressurized hazardous waste liquid directly injected through perforations 144 and 146 into the pores the geopressured formation 148. USE AND OPERATION In the use and operation of the preferred embodiment, a borehole 10 extending through a hydropressure zone 47 into geopressured formation 48 is formed or drilled and suitably cased. The present invention encompasses use of existing boreholes 10 drilled for oil, gas, or geothermal exploitation, which have been drilled through hydropressure zones 47 into geopressured formations 48. If needed, new boreholes or existing boreholes could be drilled deeper to provide the desired storage cavity in a geopressured zone 48. The hydropressure and geopressure formations 47 and 48 are separated by the mutation or transition zone 50 that forms the upper seal for the geopressure cell, formation or zone 48. The geopressure seal formed by the transition zone 50 is penetrated when forming the borehole 10, but care should be taken not to disturb any other seal of the geopressure formation or cell. The casing adjacent the transition zone 50 may be permanent or temporary (recoverable), but should not interfere with rescaling of the geopressure formation 48. While geopressured formations or zones are well known and easily recognized to those skilled in the art as abnormally high pressure zones, a brief explanation or review of such special formations may be useful to appreciating the present invention. Geopressured formations are characterized by abnormally high interstitial or pore fluid pressures existing in subsurface formations. Geopressure formations or zones come into being due to geostatic compaction by overlaying sediments which action eventually produces a pressure seal transition zone that prevents fluids from leaving the geopressure cell or formation, thereby resulting in abnormally high interstitial or pore fluid pressure from the geostatic pressure. The geopressure seals are extremely old and unlikely to be disturbed by natural geological changes such as earthquakes. Abnormally high interstitial pressure is defined in relation to normal or hydrostatic pressures for the location or depth of the subsurface formation. Normal pressures are those exerted by a column of naturally occurring water between the surface of the earth and the depth at which the pressure is being measured (the hydrostatic head). A hydropressure formation system with normal pressure is termed an open system that enables migration of the liquid to normalize pressure. Naturally occurring waters vary in density equivalent ranging from 0.433 psi/ft to 0.465 psi/ft. Thus a normal hydrostatic pressure, in a hydropressure formation will vary with depth (the hydrostatic head). Hazardous waste, if composed of heavy dense metal molecules, as with nuclear waste, tend to segregate to levels lower than the natural interstitial water. In a sealed geopressure cell or zone, the lower geopressure seal will contain that internal migration since the lower or bottom seal is not disturbed in forming the borehole 10. At any rate, assuming a geopressure zone seal 50 is penetrated or breached at 7,000 ft, and further assuming escaped water does actually migrate towards the surface of the earth, the driving gradient would be quickly dissipated, and very little real movement of the hazardous waste would occur. Furthermore, since the radiation level of the nuclear waste declines to harmless levels within 400 years (McGraw Hill Encyclopedia of Engineering, 1982, Parker, Cybil, Editor, page 885) danger of contamination from escaping radiation is virtually non-existent. Additionally if the hazardous waste is contained within a steel and concrete cased borehole below the reestablished upper geopressure seal, as disclosed in the present invention, there would be a further assurance against leakage. At the well or borehole 10, the waste filled elongated containers 22, 24, 26, 28 are moved down lowered individually into the borehole 10 by wireline until positioned within the geopressured formation 48. The containers are stacked or placed in a tandem relationship concentric with the casing 20 as shown in FIG. 1. In most deep boreholes, approximately 14,000 to 25,000 ft. in depth, 5,000 ft to 10,000 ft of elongated containers 22, 24, 26, and 28 may be lowered into the borehole 10 and still remain within the geopressured formation. The containers 22, 24, 26 and 28 are then encased within the borehole 10 by cementing the interior of casing 20 back to the surface S of the earth. The metal casing adjacent the geopressure zone seal 50 is preferably removed prior to encasement to avoid forming a leak path when the metal corrodes. This encasement would be performed to insure permanent safety in the permanent disposal of the hazardous waste. This encasement also restores the seal 50 of the geopressure zone 48 to prevent migration up the borehole 10. The preferred embodiment uses a cement mixture to encase the containers 22, 24, 26 and 28 but other types of encasing mixtures or compositions could be used. The resultant relatively small column of containers 22, 24, 26 and 28 enables heat and radiation to dissipate into the relative large volume of sediments and trapped non-migrating salt water to provide a final or safe permanent disposal of the hazardous waste. The second embodiment for a method for disposal of hazardous waste as illustrated in FIG. 3 is especially well suited for low permeability geopressure zones. A well casing 120 in the borehole 110 is perforated at 144 and 146. By pressurizing the hydraulic waste including entrained or suspended solids to move down the bore of casing 120 from the surfaces through the perforations 144 and 146 the hazardous waste is forced to flow into and thereby fracture the geopressured formation 148. When the injection pressure on the hazardous waste is reduced, the fractures close and the solid and liquid waste material is trapped in the geopressured formation 48. The waste fluid bleed into local sections increasing the pressure within the geopressure zone slightly and the entrained solids are trapped and held permanently within the formation. Thus the hydraulic fracture technique can be used for emplacement of both liquid waste and sand grain sized solid waste. Hydraulic fracture technology has been used in the oil industry for enhancement of recovery of hydrocarbons. Such procedures create formation fractures through very intense hydraulic pressure applied by pumps at the surface S of the earth's crust C and transmitted to the geopressure formation 50 through the casing 120 in the borehole 110. The resulting hydraulic formation fractures are of small width, usually 2 inches or less, which grow in vertical height, 100 ft to 1000 ft, and radial penetration of 200 ft to 2000 ft from the point of fracture initiation at the perforations 44 and 46, but can hold relatively large volumes of fluids and entrained solids. After injection of the hazardous material into the geopressure zone 148 the borehole is sealed with concrete to reestablish the geopressure zone seal 50 and prevent migration up the borehole 10. It will be appreciated that to maximize the disposal in a particular geopressure cell or formation, that both disclosed embodiments may be employed sequentially to dispose of the hazardous waste. By sequentially it should be understood that the containers may be placed in the borehole before or after disposal by pumping. This is preferably accomplished by filling the entire borehole with cement (FIG. 1), but suitable monitoring passages may be provided above the transition zone. If desired a radioactive barrier of any suitable material such as lead may be used to help reestablish the seal. Various modifications and alterations in the described apparatus and methods will be apparent to those skilled in the art of the foregoing description which does not depart from the spirit of the invention. For this reason, these changes are desired to be included in the appended claims. Dependent claims recite the only limitation to the present invention and the descriptive manner which is employed for setting forth the embodiments and is to be interpreted as illustrative and not limitative.