Hazardous or toxic waste destruction or containment – Containment – Solidification – vitrification – or cementation
Reexamination Certificate
1999-10-22
2001-07-31
Suchfield, George (Department: 3672)
Hazardous or toxic waste destruction or containment
Containment
Solidification, vitrification, or cementation
C175S066000, C588S259000
Reexamination Certificate
active
06267716
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for in situ treatment of drill cuttings to remove free hydrocarbons, including heavy crude oil and/or bitumen from the cuttings.
BACKGROUND OF THE INVENTION
During the drilling of oil and/or gas wells, a drill bit at the end of a rotating drill string, or at the end of a drill motor, is used to penetrate through geologic formations. During this operation, drilling mud is circulated through the drill string, out of the bit, and returned to the surface via the annular space between the drill pipe and the formation. Among other functions, the drilling mud provides a washing action to remove the formation cuttings from the wellbore. The mud returns to the surface along with entrained drill cuttings and typically flows through “shale shakers,” desanders, desilters, hydrocyclones, centrifuges, and/or other known devices to separate the cuttings from the mud. The shale shaker(s), which typically sit above the mud storage area, essentially are screens that are used to separate the drill cuttings from the drilling mud. The drilling mud falls through the screens by gravity and the cuttings pass over the end of the screens.
The disposal of the drill cuttings after separation from the drilling mud can present a problem. One way to dispose of the cuttings would be to discharge the cuttings directly at the drilling site. An even more economically efficient way to dispose of drill cuttings would be to “recycle” the cuttings as components of building materials, such as concrete. Unfortunately, the cuttings may contain environmentally undesirable “free hydrocarbons,” defined herein as hydrocarbons derived either from the drilling mud, from the rock formation, or both.
One approach that has been used to reduce potential environmental contamination by drill cuttings has been to minimize the toxicity of the oil-base fluids used to make drilling muds, and more recently, to use base fluids that are more biodegradable. Unfortunately, this approach does not eliminate contamination by the free hydrocarbons which originate in the rock formation rather than in the drilling fluid.
Methods are needed to treat cuttings, preferably in situ, to reduce the quantity of free hydrocarbons discharged into the environment upon subsequent use or disposal of the cuttings.
SUMMARY OF THE INVENTION
The invention provides a method comprising: providing cuttings produced during drilling operations comprising a first quantity of free hydrocarbons comprising bitumen; mixing with the cuttings a buffer solution comprising a buffer agent effective to activate at least one natural surfactant in the bitumen, thereby converting the solution into an emulsion comprising bitumen droplets having a mean average particle size of about 5 microns or less; mixing with the emulsion an emulsifier effective to stabilize the emulsion; and, thereafter adding to the emulsion an encapsulating material comprising an aqueous solution of a water soluble silicate under conditions effective to form silica shells around the droplets.
DETAILED DESCRIPTION OF THE INVENTION
According to the present invention, drill cuttings are treated, preferably in situ, to minimize their environmental impact upon subsequent use or disposal. The free hydrocarbons in the cuttings preferably are converted into “isolated hydrocarbons,” preferably using emulsification and encapsulation techniques. The converted cuttings comprising the isolated hydrocarbons may be disposed of in a variety of ways. In a preferred embodiment, the converted cuttings either are discharged into the environment, preferably at the drilling site in order to reduce costs, or the converted cuttings are reused to make concrete.
The conversion to “isolated hydrocarbons” reduces the hydrocarbon content in the cuttings, as determined using standard techniques, such as liquid/liquid extraction or solid-phase extraction followed by gas chromatography or QFT fluorescence. Preferably, the free hydrocarbons are reduced to at least about 1 wt. % or less, preferably at least about 0.1 wt. % or less.
Isolated hydrocarbons may be formed in a number of ways, including but not necessarily limited to a preferred method in which free hydrocarbons are encapsulated with an encapsulating material which renders the hydrocarbons wholly or partially inaccessible for a prolonged period of time. In a most preferred embodiment, the free hydrocarbons in the drilling mud are non-toxic and biodegradable.
The cuttings may be treated using any suitable system of equipment. After separation from the drilling mud, the contaminated cuttings typically pass through a holding bin into an inlet hopper. The cuttings preferably are treated directly in a batch mixer equipped with an appropriate inlet for the relevant solutions, and an apparatus for low shear mixing, such as a paddle mixer.
The preferred conditions for forming isolated hydrocarbons will vary depending upon the upon the types of free hydrocarbons in the cuttings. Many types of hydrocarbons may be converted into isolated hydrocarbons in a first preferred embodiment, in which the cuttings are sprayed with an emulsifying solution effective to transform the free hydrocarbons in the cuttings into an oil-in-water emulsion with very low droplet size. The emulsion thereafter is treated with an encapsulating material to encapsulate the emulsified hydrocarbons.
The composition of the emulsifying solution will vary depending upon the type of free hydrocarbons found in the drilling mud and/or in the cuttings, and may be similar to the emulsifiers used in U.S. Pat. No. 5,076,938, incorporated herein by reference. However, the following emulsifiers are superior because of (a) environmental compatibility, and (b) stability of the emulsion. The emulsifying solution may be a blend of organic acids, inorganic acids, and emulsifiers. Preferred emulsifying solutions are as non-toxic as possible, and the components of the emulsifying solution have an ionic nature selected from the group consisting of cationic, anionic, non-ionic, and combinations thereof. In a preferred embodiment, the emulsifying solution comprises at least a non-ionic surfactant and most preferably a combination of a non-ionic and an anionic emulsifier. Although compounds called “emulsifiers” herein typically are referred to as surfactants, their function in the present solution is to act as emulsifiers. The emulsifying solution lowers the interfacial tension between the oil and water to produce a droplet size—or an average mean diameter of the oil droplets in the continuous water phase—which is sufficiently small to form a stable emulsion but sufficiently large to generate a total surface area that can be encapsulated using an acceptably low concentration of chemical additives. Preferably, the droplets have a mean average diameter of from about 1 micron to about 20 microns, preferably about 15 microns or less, more preferably about 10 microns or less, even more preferably about 5 microns or less, and most preferably about 2 microns or less.
Because the operator will know the composition of the oil in the rock formation to be drilled, whether bitumen will be encountered, and also the composition of the base oil in the drilling system to be used, emulsifier selection initially is based on the properties of the oil to be encountered, such as its hydrophobicity. Candidate emulsifiers initially may be chosen based on their hydrophilic/lipophilic balance. Preferably, the HLB of the emulsifier or the emulsifier combination is substantially the same as the required HLB for oil-in-water emulsification with the oil to be encountered. “HLB of Nonionic Surfactants,”
Nonionic Surfactants Physical Chemistry
. Schick Martin J., ed., Surfactant Series V. 23 (Marcell Dekker, Inc. 1987; “Recent Progress on HLB System in Organized Solutions,”
Organized Solutions, Surfactants in Science and Technology
, Friberg, S. and B. Lindman, ed., Surfactant Series V. 44 (Marcel Dekker, Inc. 1992), both incorporated herein by reference. Emulsifier selection also is determined by whether or
Baker Hughes Incorporated
Paula D. Morris & Associates
Suchfield George
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