Methods of demulsifying emulsions using carbon dioxide

Details Methods of demulsifying emulsions using carbon dioxide Methods of demulsifying emulsions using carbon dioxide

2000-06-21

2003-05-20

Metzmaier, Daniel S. (Department: 1712)

Colloid systems and wetting agents; subcombinations thereof; pro

Compositions containing an agent for breaking ; processes of...

Continuous liquid phase colloid system and discontinuous...

C516S138000, C516S194000, C208S045000, C208S188000, C210S708000, C585S812000, C585S838000, C507S921000

Reexamination Certificate

active

06566410

ABSTRACT:

FIELD OF THE INVENTION
The invention generally relates to demulsifying processes, and more particularly demulsifying processes involving water-in-oil emulsions.
BACKGROUND OF THE INVENTION
Extensive efforts have been made towards breaking, i.e., destabilizing, water-in-oil emulsions, particularly water-in-crude oil emulsions. Crude oil is often found in a reservoir in association with gas and saline formation water. As a reservoir becomes depleted, a time is typically reached when water is coproduced with oil. The number of wells now producing water with crude oil present therein is steadily increasing. Typically these immiscible fluids are readily emulsified by the simultaneous action of shear and pressure drop at the well head, chokes, and valves.
It has long been recognized that the resulting water-in-oil emulsions can be remarkably stable. Moreover, it is understood that asphaltenes are the predominant stabilizer of water-in-oil emulsions produced during the production, transportation, and refining of crude oil. Currently, the primary means by which these emulsions are destabilized is through the addition of polymeric demulsifying chemicals, usually based on phenol formaldehyde resin chemistry, as well as other water-soluble polymers. See e.g., U.S. Pat. No. 5,100,582 to Bhattacharyya; U.S. Pat. Nos. 5,460,750 and 5,525,201 to Diaz-Arauzo, and U.S. Pat. No. 2,446,040 to Blair, Jr.; “
The Efficiency of Polyalkylenepolyamines formaldehyde ethoxylates as Demulsifiers for Water
-
in
-
Crude Oil Emulsions”
, N. N. Zaki, Tensides Surfactants Detergents 34(1), pp. 12-17 (1997) and “
Polyoxyethylenated Bisphenol
-
A for Breaking Water
-
in
-
Oil Emulsions”
, Zaki, N. N., Polymers for Advanced Technologies, 7, pp. 805-808 (1996). These resins, particularly, comb polymers, often possess alkylated phenol hydrophobic moieties and ethoxylated hydrophilic moieties. These materials may be disadvantageous in that they pose potential environmental risks since they are believed to be endocrine disrupters. Moreover, such materials are often very costly.
Other means of destabilizing asphaltene-stabilized water-in-oil emulsions include thermal pressurization and rapid depressurization (see e.g., U.S. Pat. No. 5,948,242 to Ohsol), along with electrostatic droplet shattering and coalescence (see e.g., U.S. Pat. Nos. 5,607,574 to Hart and U.S. Pat. No. 5,746,908 to Mitchell). These methods tend to focus on efforts at “cracking” or “disrupting” the rigid, viscoelastic film of asphaltenes which form around the water droplets. One disadvantage of these techniques relates to the reforming of water droplets due to re-adsorption of displaced or “disrupted” asphaltenic film fragments in shear fields.
There is a need in the art for methods of destabilizing water-in-oil emulsions which address the problems discussed above.
SUMMARY OF THE INVENTION
In one aspect, the invention provides a method of demulsifying a water-in-oil emulsion. The water-in-oil emulsion comprises an oil phase and an aqueous phase. The oil phase comprises asphaltenes. The method comprises contacting a carbon dioxide containing fluid with the emulsion such that the carbon dioxide containing fluid enters the oil phase of the emulsion. Advantageously, the asphaltenes precipitate out of the emulsion and the emulsion destabilizes.
In another aspect, the invention provides a composition of matter. The composition of matter comprises a water-in-oil emulsion comprising an oil phase and an aqueous phase, as well as a carbon dioxide containing fluid. The oil phase comprises asphaltenes. The carbon dioxide containing fluid enters the oil phase of the emulsion, such that the asphaltenes precipitate out of the emulsion and the emulsion destabilizes.
These and other aspects and advantages of the invention are set forth in detail herein.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention now will be described more fully hereinafter with reference to the accompanying specification and examples, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
In one aspect, the invention relates to a method of demulsifying a water-in-oil emulsion comprising an oil phase and an aqueous phase. The oil phase comprises asphaltenes. The method comprises contacting a carbon dioxide containing fluid with the emulsion such that the carbon dioxide containing fluid enters the oil phase of the emulsion, wherein the asphaltene precipitates out of the emulsion and the emulsion destabilizes. Although not intending to be bound by theory, it is believed that when the asphaltenes precipitate, they begin to flocculate and agglomerate from the oil phase. Additionally, it is believed that the carbon dioxide containing fluid diffuses into the oil phase of the emulsion to render the asphaltenes interfacially inactive, i.e., the state of the phase of the asphaltenes changes, such that the emulsion destabilizes.
For the purposes of the invention, the term “water-in-oil” emulsion has a meaning that is conventionally known in the art, and refers to an emulsion in which the oil phase is the continuous phase and the aqueous phase is the dispersed phase. In a preferred embodiment, the emulsion comprises at least about 20 percent by volume of the oil phase, and more preferably from about 20 to about 90 percent by volume of the oil phase. In another embodiment, the oil phase comprises from about 1 to about 10 volume percent of the aqueous phase, i.e., about 90 to 99 percent of the oil phase.
The oil phase which is present contains a number of hydrocarbon materials that are typically present in water-in-oil emulsions, the selection of which is known to those skilled in the art. In a preferred embodiment, the oil phase includes mineral oils, particularly in the form of petroleum oil or petroleum-derived oil (e.g., Petroleum Refinery Products). Petroleum oil preferably encompasses aliphatic or wax-base oil, aromatic or asphalt-base oil, or mixed base oil. Crude oil, particularly heavy or light oil is particularly preferred. The term “heavy oil” refers to crude oil having an API gravity less than 20 and a viscosity higher than 100 cp and up to 10,000 cp at 20° C. In a typical embodiment, heavy crude oil has a relatively high asphaltene content with a relatively low H/C ratio. The term “light oil” refers to crude oil having an API gravity higher than 20 and a viscosity less than 100 cp at 20° C. In a typical embodiment, light crude oil has a relatively low asphaltene content with a relatively high H/C ratio. See e.g.,
The Chemistry and Technology of Petroleum
, 2
nd
Ed., James G. Speight, (1991), pp. 3-5. Preferred crude oils that are employed in the method of the invention includes, but is not limited to, Arab Berri, Hondo, and B6 crude oils.
For the purposes of the invention, the term “asphaltenes” is defined to be components of the high boiling point fraction of the crude oil which are composed of polynuclear aromatic hydrocarbons of molecular weights ranging from 500 to 2000 or greater and aggregate molecular weights of up to 20,000 joined by alkyl chains. See e.g.,
Hawley's Condensed Chemical Dictionary,
12
th
Ed., Richard J. Lewis, Sr., Editor, (1993), p. 101. Various amounts of asphaltenes may be present in the emulsion. For example, in a preferred embodiment, the emulsion may include from about 0.2 or 15 to about 25 or 30 percent (w/w) of asphaltenes. In another embodiment, the emulsion may include from about 25 to about 30 percent (w/w) of asphaltenes. In another embodiment, the emulsion may include greater than about 25 percent (w/w) of asphaltenes. It should be appreciated that other amounts are encompassed by the invention.
The aqueous phase includes water. For the purposes of the invention, the term “water” is to be broadly construed and ma

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