Chemistry of hydrocarbon compounds – Hydrate or production thereof
Reexamination Certificate
1999-10-01
2001-04-24
Howard, Jacqueline V. (Department: 1764)
Chemistry of hydrocarbon compounds
Hydrate or production thereof
C585S522000, C137S003000, C137S013000, C166S310000, C166S371000
Reexamination Certificate
active
06222083
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for inhibiting the formation of clathrate hydrates in a fluid. More specifically, the invention relates to a method for inhibiting the formation of gas hydrates in a pipe used to convey oil or gas.
BACKGROUND OF THE INVENTION
Petroleum fluids typically contain carbon dioxide and hydrogen sulfide, as well as various hydrocarbons, such as methane, ethane, propane, normal butane and isobutane. Water, present as a vapor and/or as a liquid phase, is also typically found mixed in varying amounts with such hydrocarbons. Under conditions of elevated pressure and reduced temperature, clathrate hydrates can form when such petroleum fluids contain water. Clathrate hydrates are water crystals which form a cage-like structure around “guest” molecules such as hydrate-forming hydrocarbons or other gases. Some hydrate-forming hydrocarbons include, but are not limited to, methane, ethane, propane, isobutane, butane, neopentane, ethylene, propylene, isobutylene, cyclopropane, cyclobutane, cyclopentane, cyclohexane, and benzene. Other gases which may form hydrates include, but are not limited to, oxygen, nitrogen, hydrogen sulfide, carbon dioxide, sulfur dioxide, and chlorine.
Gas hydrate crystals or gas hydrates are a class of clathrate hydrates of particular interest to the petroleum industry because of the pipeline blockages that they can produce during the production and/or transport of natural gas and other petroleum fluids. For example, at a pressure of about 1,000 kPa (145 psi), ethane can form gas hydrates at temperatures below 4 ° C.(39 ° F.), and at a pressure of 3,000 kPa (435 psia), ethane can form gas hydrates at temperatures below 14 ° C.(57 ° F.). Such temperatures and pressures are not uncommon for many operating environments where natural gas and other petroleum fluids are produced and transported.
As gas hydrates agglomerate, they can produce hydrate blockages in the pipe or conduit used to produce and/or transport natural gas or other petroleum fluids. The formation of such hydrate blockages can lead to a shutdown in production and thus substantial financial losses. Furthermore, restarting a shutdown facility, particularly an offshore production or transport facility, can be difficult because significant amounts of time, energy, and materials, as well as various engineering adjustments, are often required to safely remove the hydrate blockage.
A variety of measures have been used by the oil and gas industry to prevent the formation of hydrate blockages in oil or gas streams. Such measures include maintaining the temperature and/or pressure outside hydrate formation conditions and introducing an antifreeze such as methanol, ethanol, propanol, or ethylene glycol. From an engineering standpoint, maintaining temperature and/or pressure outside hydrate formation conditions often requires design and equipment modifications, such as insulated or jacketed piping. Such modifications are costly to implement and maintain. The amount of antifreeze required to prevent hydrate blockages is typically between 10% to 30% by weight of the water present in the oil or gas stream. Consequently, several thousand gallons per day of such antifreeze can be required. Such quantities present handling, storage, recovery, and potential toxicity issues. Moreover, these solvents are difficult to completely recover from the production or transportation stream.
Consequently, there is a need for a gas hydrate inhibitor that can be conveniently mixed at low concentrations in the produced or transported petroleum fluids. Such an inhibitor should reduce the rate of nucleation, growth, and/or agglomeration of gas hydrate crystals in a petroleum fluid stream and thereby inhibit the formation of a hydrate blockage in the pipe conveying the petroleum fluid stream.
As discussed more fully below, the inhibitors of this invention can effectively treat a petroleum fluid having a water phase, or a petroleum fluid containing water vapor that may condense to form a water phase, depending upon the operating environment.
The use of polymeric inhibitors has been proposed, however, these materials have a tendency to precipitate out of solution at higher temperatures. This is an undesirable characteristic, since the inhibitor must stay in solution under a wide range of temperatures to be most effective. The monomers described herein yield homopolymers and copolymers with good inhibition properties as well as better solubility at higher temperatures.
SUMMARY OF THE INVENTION
According to the invention, there is provided a method for inhibiting the formation of clathrate hydrates in a fluid having hydrate-forming constituents. One embodiment of the method comprises contacting the fluid with an inhibitor comprising a polymer or copolymer which has been made from esters or amides of N-acyldehydroalanine. In an alternative embodiment, the fluid is treated with a copolymer of such N-acyldehydroalanine monomers copolymerized with a comonomer that is known, when polymerized with itself, to exhibit hydrate inhibition.
The polymers and copolymers of the invention can be classified as N-acyldehydroalanine derivatives, and are characterized by the general formula:
&Brketopenst;A&Brketclosest;
x
&Brketopenst;B&Brketclosest;
y
where the sum of x and y is an average number sufficient to produce a number average molecular weight between about 1,000 and about 1,000,000.
In one embodiment, A is the following “mer-unit” produced from an ester of an N-acyldehydroalanine:
where,
R
1
is a hydrogen atom or a hydrocarbon group having one to six carbon atoms,
R
2
is a hydrogen atom or a methyl group,
R
3
is a hydrocarbon group having one to six carbon atoms, and
x is an average number of repeating monomeric units for producing an average molecular weight for said polymer between about 1,000 and about 1,000,000.
Preferably, R
1
and R
2
are, independently, a hydrogen atom or a methyl group, and R
3
is an alkyl group with zero to two heteroatoms.
In another embodiment, A is the following “mer-unit” produced from an amide of an N-acyldehydroalanine:
where,
R
1
is a hydrogen atom or a hydrocarbon group having one to six carbon atoms,
R
2
is a hydrogen atom or a methyl group,
R
3
is a hydrocarbon group having one to six carbon atoms, and
x is an average number of repeating monomeric units for producing an average molecular weight for said polymer between about 1,000 and about 1,000,000.
Preferably, R
1
and R
2
are, independently, a hydrogen atom or a methyl group, and R
3
is an alkyl group with zero to two heteroatoms.
The term “mer-unit” is used to describe both the monomers that are reacted to form polymers, and the polymer units that result from the conversion of one type of polymer units into another type of polymer units, by some reaction or conversion which occurs subsequent to the polymerization reaction.
B may be an N-acyldehydroalanine derivative mer-unit that is the same as, or a variant of, A. For example, the inhibitor may comprise a copolymer of two mer-units derived from two different esters of an N-acyldehydro-alanine, or a copolymer of one mer-unit derived from an ester of an N-acyldehydroalanine with another mer-unit derived from an amide of an N-acyldehydroalanine. Alternatively, B is a monomer or mer-unit that is known, when polymerized with itself, to exhibit hydrate inhibition.
For example, B may be an N-vinyl amide, an N-allyl amide, an acrylamide or methacrylamide, an N-vinyl lactam, a maleimide, or a vinyl oxazoline (a ring-closed cyclic imino ether).
The A and B mer-unit proportions, or mole ratio of x to y, can vary. The mole ratio m:n may vary from about 5:95 to about 95:5, or from about 25:75 to about 75:25,or from about 45:55 to about 55:45. Ratios which provide the most effective inhibitors for a given system are preferred.
Some preferred inhibitors derived from ester monomers include, but are not limited to, homopolymers and copolymers of methyl 2-acetamidoacrylate and ethyl 2-acetamidoacrylate. Some preferred inhibitors derived from amide monomers i
ExxonMobil Upstream Research Company
Howard Jacqueline V.
Wolfs Denise Y.
LandOfFree
Method for inhibiting hydrate formation does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for inhibiting hydrate formation, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for inhibiting hydrate formation will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2505479