Classifying – separating – and assorting solids – Precedent preparation of items or materials to facilitate...
Reexamination Certificate
1999-05-03
2002-05-07
Matecki, Katherine A. (Department: 3653)
Classifying, separating, and assorting solids
Precedent preparation of items or materials to facilitate...
C209S010000, C209S012100
Reexamination Certificate
active
06382423
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method for dividing the volume of a mass of solid fine particles containing Naturally Occurring Radioactive Materials (“NORM”) according to activity levels, thereby reducing the amount of material requiring treatment, and the treatment of the material requiring it. The invention is particularly applicable to industries involved in the extraction of hydrocarbons and minerals from the earth where NORM-containing soil and precipitates generated during the extraction, processing, and storage of hydrocarbons and minerals must be treated. More specifically, the invention relates to a method for extracting and/or segregating materials containing NORM components from materials generated during the process of hydrocarbon or mineral recovery. In one application of the invention, NORM is separated from bulk solids, then placed in solution, and injected into a formation similar to the subterranean formation from which the material was originally extracted.
BACKGROUND OF THE INVENTION
Naturally Occurring Radioactive Materials (“NORM”) include isotopes of uranium and thorium, and their decay chain daughters such as radium, radon, and lead. All of them are present in the earth's crust in immobile and mobile forms. NORM can be released from the earth's crust due to naturally occurring disturbances or human activity such as, for example, hydrocarbon recovery processes.
From a regulatory standpoint, only Technologically Enhanced Natural Radioactive materials (“TENR”) require remediation. Technological enhancement is considered to be the concentration of radioactive substances through a process not intended to produce radioactive substances. As used herein, the term “NORM” will be understood to include TENR. In sufficient quantities and concentrations, NORM may present a health risk due to radiation exposure by its increasing the background levels of radiation. Consequently, the disposal of such materials is subject to regulation.
Water recovered or utilized in the process of extracting of hydrocarbons and other materials from substrates almost invariably includes alkaline metal ions of Group I-III elements of the Periodic Table such as cations of barium, strontium, calcium, and magnesium. Also present in the water, along with radioactive substances, are anions such as sulfate, bicarbonate, carbonate, phosphate, fluoride, chloride, and the like. Concentrations of anions and cations in the water, which exceed the solubility of salts formed from the anions and cations, will result in the precipitation of solid salts that may entrap accompanying radioactive substances.
Thus, a problem associated with the emergence of solids in many hydrocarbon and other production operations is the inclusion of NORM in those materials. For instance, NORM species are generated in significant quantities during many oil well drilling and hydrocarbon recovery processes. These NORM materials are present in the earth's crust as water soluble or insoluble constituents. The majority of water insoluble U
238
and Th
232
forms of NORM, remains in the earth's crust or substrate, while waiter soluble NORM materials such as Ra
226
, Ra
228
and R
222
may be transported to ground level along with water produced during the oil drilling process.
For example, in the hydrocarbon recovery industry, and in various oil field operations, difficulties are often encountered in dealing with NORM contained in complex form in mineral materials including magnesium sulfate, barium sulfate, strontium sulfate, radium salts and the like. Most notably, the solid, barium sulfate, which has properties making it extremely difficult to treat, retains NORM. The most commonly encountered NORM materials associated with hydrocarbon drilling and recovery processes are isotopes of radium and radon. Uranium and thorium, themselves present in rocks and shales, are insoluble in reservoir fluids, and therefore largely immobile. On the other hand, Radium (
226
Ra and
228
Ra) and Radon (
222
Rn), radioactive species, components of NORM, are soluble in water.
During oil drilling operations or other hydrocarbon recovery processes, radioactive substances noted may be present in water associated with processes. During the transportation of fluids, these radioactive nucleotides may be encapsulated into a solid matrix. The encapsulation of these radioactive substances occurs with the precipitation of salts from the fluids as the physical or chemical conditions change. Such changes include a decrease in the proportion of water, thus an increase in the concentration of various ions, pressure decrease, and temperature decrease. Precipitation of these salts involves the formation of crystal structures that may encapsulate or entrap radioactive substances as impurities in mineral scales. The radioactive materials are entrapped during the crystal formation process.
Since NORM materials are typically encapsulated in a complex soil or mineral matrix, cost-effective removal and disposal of NORM materials require techniques to penetrate the soil and mineral matrix and extract the radioactive materials prior to release of the solid material. Treating NORM-containing waste material, especially in the case of waste material generated in hydrocarbon recovery, can present additional problems. Often such materials include debris, oil, water, grit, scale and dirt. In some cases, NORM-containing solids are entrained in water-oil emulsions. Thus, the composition of the NORM-containing waste material can present difficulties which must be overcome to treat the material.
SUMMARY OF THE INVENTION
Current disposal techniques are directed to treating the entire NORM-containing mass. However it has been found that radioactive substances may, in many cases, be segregated from bulk masses of materials generated, for example, in oil and gas production. It has also been determined that in many such cases NORM-containing materials may be segregated from the bulk of the materials, treated and injected or otherwise disposed of.
Research into the mechanisms for encapsulation and generation of NORM materials has revealed that the distribution of NORM within the solid materials of interest is governed or affected by two factors: (1) physical characteristics such as particle size and (2) the particular type of mineral matrix of the solid materials. In order for NORM to be encapsulated in a precipitate, the matrix must be porous, not an impervious crystal structure. Particle growth, resulting in NORM encapsulation, involves a nucleation process and the type of matrix being formed. A likely location of encapsulated NORM materials is in precipitates such as BaSO
4
, CaCO
3
, CaSO
4
. These materials may be differentiated from, for example, sand, on the basis of various physical characteristics such as density, particle size distribution, and porosity. Further analysis has demonstrated that these forms of solid and mineral matrices can be segregated on the basis of physical characteristics such as particle size distribution and/or density.
It has been discovered that through the use of one or more appropriate solids classification and separation techniques, materials containing higher levels or concentrations of NORM can be separated from the bulk of the materials, thereby reducing the volume of the contaminated, e.g., radioactive, material. In the practice of the invention, it has been found that the majority of contaminated material may be isolated, to form a greatly reduced volume of solid material requiring treatment.
In one embodiment, the invention provides a process for separating a material including a mass of solid fine particles, including particles incorporating NORM. The mass of solid fine particles is classified into samples based upon one or more preselected criteria The level of radioactivity associated with one or more of the samples is determined, enabling separation of the mass into fractions based upon levels of radioactivity associated with the fractions. The term “fine” as used herein refers generally to a mass of
Bush John G.
Gaur Siddhartha
BPF, Incorporated
Burr Matthew E.
Gardere Wynne & Sewell LLP
Matecki Katherine A.
Warren, Jr. Sanford E.
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