1. Field of the Invention
The present invention pertains to a method for disposing of slurried and sometimes toxic solids wastes in hydraulically fractured subterranean earth formations and in such a way that the waste material is confined in the fracture.
2. Background
Certain types of solid waste material may be permanently stored or disposed of by forming a slurry of solids particulates of the waste with a carrier liquid, reducing the particle size of the solids and then injecting the slurry into a subterranean earth formation. U.S. Pat. No. 5,129,469 to J. E. Jackson, issued Jul. 14, 1992, assigned to the assignee of the present invention, and incorporated herein by reference describes a system for disposing of drill cuttings from drilling wells in earth formations by combining the cuttings with a carrier liquid, grinding the cuttings to a predetermined particle size and injecting the viscous slurry of cuttings and carrier liquid which results from the grinding operation into a subterranean earth formation zone.
Certain problems arise, however, with respect to the disposal of certain types of wastes wherein the containment of the waste material in a particular portion of an earth formation zone is required. In the production of oil and gas, for example, a significant amount of naturally occurring radioactive material (NORM) may accumulate in the conduits and processing vessels associated with the production wells and related fluid handling facilities. The radioactive parts of these naturally occurring radioactive materials are usually Radium.sup.226 and/or Radium.sup.228. These radioactive substances are usually bound within the structure of scales and other produced solids. Typically, the composition of the scale is in the form of barium sulfate which is particularly hard and cannot be dissolved by most naturally occurring fluids. Accordingly, this barium sulfate scale, as well as other materials which are mixed with the scale, presents a disposal problem because of its radioactivity.
Certain techniques for disposing of solids-laden slurries in subterranean formations are described in U.S. patent application Ser. No. 08/032,951 filed Mar. 17, 1993, by Thomas K. Perkins, et. al now U.S. Pat. No. 5,314,265, issued May 24, 1995, and assigned to the assignee of the present invention. This application describes a method of disposing of slurries of relatively fine particles of solid wastes into disposal zones which have a lower in situ compressive stress than that of an overburden zone and an underburden zone adjacent to the disposal zone. The disposal zone preferably has a permeability greater than the overburden and underburden zones. This technique is advantageous in that it is common to find earth formations having one or more relatively permeable zones of substantial thickness which are located below a formation zone comprising overburden of relatively impermeable material and which may exhibit in situ compressive stresses generally greater than the more permeable zone.
U.S. patent application Ser. No. 08/043,323 filed Apr. 6, 1993, by Joseph H. Schmidt, et. al now U.S. Pat. No. 5,387,737, issued Feb. 7, 1995, and assigned to the assignee of the present invention describes a method of disposing of particulate solids in a subterranean formation by injecting a quantity of substantially solids-free liquid into a predetermined disposal zone having a predetermined porosity such that the injection of the solids-free liquid disaggregates at least part of the disposal zone, and then injecting a slurry of particulate solids into the disaggregated part of the disposal zone to place the solids in the pore spaces of the disaggregated part of the disposal zone. Other techniques which are of interest but which are not suitable for disposing of toxic wastes in accordance with the present invention are disclosed in U.S. Pat. No. 3,292,693 issued Dec. 20, 1966 to G. A. Hill, et. al, which describes a technique of disposing of liquid wastes into a low pressure zone in an earth formation which is between higher pressure zones and wherein liquids in the higher pressure zones tend to migrate toward the low pressure zone.
Still further, Australian Patent 233,971, published Mar. 3, 1960 by J. J. Reynolds, et al, describes a method of underground disposal of radioactive liquids or slurries wherein a substantially horizontal fracture is created in a shale or nominally non-porous rock formation by opening the fracture with a suitable fracturing fluid and then injecting a radioactive waste material and propagating the fracture by injecting the radioactive fluid at a pressure greater than the formation breakdown pressure. Although generally horizontal fractures were thought to be the type of fracture typically formed in a subterranean earth formation according to the state of the art in 1960, it is generally accepted presently that fractures tend to extend in generally vertical planes under the urging of hydraulic or similar fluid injections. Moreover, totally non-porous or non-permeable formations may exist but they are difficult to locate and are usually not readily accessible for disposal operations.
Notwithstanding the foregoing methods for disposing of slurries of waste materials, the present invention provides a method for disposing of toxic wastes, including radioactive materials, in an improved way which substantially satisfies the requirement of containment of the waste in a predetermined earth formation zone.