Liquid purification or separation – Processes – Making an insoluble substance or accreting suspended...
Reexamination Certificate
1998-02-13
2001-07-31
Barry, Chester T. (Department: 1724)
Liquid purification or separation
Processes
Making an insoluble substance or accreting suspended...
C210S734000, C210S735000, C210S758000, C507S226000
Reexamination Certificate
active
06267893
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for the flocculation of particulate solids, especially oil- contaminated particulate solids from completion and workover fluids or hydrocarbon fluids, the separation and removal of oil therefrom, and the prolonging of the useful life of the filter used with these fluids. This invention also has utility in flocculating finely divided solids and fatty acids from “Rule 66” solvents, halogenated hydrocarbon fluids, amine fluids and other gas processing fluids such as potassium carbonate and glycols.
2. Description of the Problems and the Prior Art
Contaminants in brines, such as completion and workover fluids, hydrocarbons and halogenated hydrocarbons disrupt the intended use of these fluids. The presence of small amounts of solids in the completion and workover fluids can directly affect completion effectiveness, and especially well productivity. Amounts as low as 500 ppm of solids in completion and workover fluids can be enough to cause total plugging in perforation tunnels, in channels behind pipe, in gravel packs and in propped fractures. Reduction in production due to plugging can be substantial and can also lead to multiple squeeze attempts required to successfully seal cement channels. In gravel packing and in fracturing, solids from the completion and workover fluid mix with the high-permeability gravel with a resulting mixture of gravel and fine solids which can be even less permeable than the fine solids alone. The smaller particles tend to fill the void spaces between the larger particles so that the permeability of the mixture is almost always less than the permeability of the smaller particulate matter. Thus, very few finely-divided solids are tolerated before the high permeability of the pack gravel is lost. There is a need to remove the finely-divided solids from the completion and workover fluids to eliminate these problems.
There is also a need to remove finely-divided solids from hydrocarbon such as naphtha and olefins as well as halogenated hydrocarbon fluids such as perchloroethylene (PERC). These fluids may contain finely divided solids or fatty acids. Hydrocarbons such as naphtha and olefins produced for the manufacture of polyolefins contain particulate impurities which must be removed before further processing. Processed hydrocarbons such as olefins collect metal and ceramic fines from catalyst or other sources. Halogenated hydrocarbon such as PERC, frequently used in dry cleaning operations, may contain fibers, sub-micron level particulate matter, oils and fatty acids. Although no individual particles may be visible to the naked eye, the presence of a color, such as a brown color in an olefin product, indicates the presence of extremely finely-divided solids. Restoring the olefin product to its clear color requires removal of the fines. Likewise, restoring a halogenated hydrocarbon to useful service requires the removal of particulate matter and fatty acids. There is a need to clean hydrocarbons such as olefins to create saleable product, purified feedstock or storage-ready fluids or to remove fine particles to permit flaring or incineration. There is a need to reduce contamination in halogenated hydrocarbons since contaminants cause the compounds to be discarded thus directly affecting operating costs and creating additional disposal problems as halogenated hydrocarbons are regulated.
It is, accordingly, the primary objective of this invention to fulfill these needs.
In U.S. Pat. No. 3,737,037 which issued on Jun. 5, 1973 to Lee Bone, III, there is described a process for treating drilling mud to remove substantially all of the suspended solids particles to provide a reusable mud. The method disclosed includes the addition of a flocculating agent to flocculate solids of size smaller than 20 microns. The flocculating agents disclosed include polyacrylates, polyacrylamides, polyamines, polyamides, partially hydrolyzed polyacrylamides, methylcellulose, carboxymethylcellulose, alkali metal carboxymethylcellulose, halides of aluminum, iron, nickel, and cobalt, aluminum sulfate, alkali metal aluminate, alum, bentonite, attapulgite, sepiolite, hydrous mica, and kaolin. There is no mention whatever, inter alia, within the metes and bounds of the Bone patent of treating clear brine, such as, completion and workover fluids.
Currently, removal of finely divided solids from hydrocarbon fluids and halogenated hydrocarbon fluids is attempted through the use of conventional filter techniques, if it is attempted at all. Frequently, the source of the problem is not recognized and when it is, the fluid is frequently disposed of as being unfit for further service. This is particularly true with fatty acid contamination.
A second objective of the current invention is to prolong the life of the conventional filter used to filter solid particles from drilling fluids, completion and workover fluids, hydrocarbon fluids, halogenated hydrocarbon fluids and amine streams as well as from other fluids. The speed of filtration and the length of time for a clean filter to accumulate a cake which disrupts flow are limiting factors in the recirculation of drilling fluids and completion and workover fluids. Traditionally, filter mesh size equals the size of the smallest particle to be screened. It is known that, and recent studies have shown that the accumulation of solids or “dirt” in a screen filter form a cake which provides a finer mesh than the original screen itself. Particles smaller than the original screen aperture can thus be retained improving the efficiency of the filter. The cake will continue to build on the filter until it reaches a point of maximum efficiency and then will begin to break down. This is due to the pressure differential created across the screen. The addition of filter aids like diatomaceous earth, while not necessary, can increase the incompressibility of the cake allowing longer filter use before the cake begins to break down. As a result, filters can attain a capturing ratio of 1:10 under certain conditions. (i.e. a 50 micron screen can provide removal of particles down to 5 microns). This allows the use of a less expensive larger mesh filter. The limiting factor associated with filter use continues to be the speed of filtration, the length of time before the cake begins to break down, and the presence of oil in the filter cake causing a disposal problem. This is true for hydrocarbon fluid and halogenated hydrocarbon fluid filtration as well as completion and workover fluid filtration. It is an objective of this invention to prolong the life of the conventional filter and address these limiting factors.
A further object of this invention is to separate oil from finely divided solids in the completion and workover fluids and to separate oil from those larger solids which will be or already have been separated from the drilling fluid or completion and workover fluid through conventional means such as shakers, which are vibrating screens canted at an angle from the horizontal, and centrifuges. These oil-contaminated solid particles are produced as a part of the drilling process and create an environmentally-sensitive disposal problem.
In rotary drilling, as practiced in oil and gas exploration, a well bore is formed which extends downwardly from the earth's surface to an oil or gas producing stratum. Formation of the well bore requires cutting into the earth with a rotating bit attached to the end of a drill string formed from joints of pipe sequentially attached as the well bore is extended downwardly. Various fluids are employed in a well bore formations, as for drilling, completions and workover operations. Exemplary of these are (1) drilling fluids, or “muds”, which are clay-based, and (2) brines which are clay-free, clear, heavy (dense) fluids. Drilling fluids, or muds, are generally circulated during the drilling process and clear fluids or brines are most often used for well completions and workovers. By definition, a workover is any operation in the well bo
Barry Chester T.
Bracewell & Patterson LLP
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