Earth boring – well treating – and oil field chemistry – Well treating – Contains organic component
Reexamination Certificate
1999-07-29
2001-06-19
Tucker, Philip (Department: 1712)
Earth boring, well treating, and oil field chemistry
Well treating
Contains organic component
C507S267000, C507S922000, C585S003000, C516S029000, C166S308400
Reexamination Certificate
active
06248699
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to improved hydrocarbon gels useful in oil field applications including slurry pipeline transport of minerals, removal of solids produced during wellbore drilling operations, and for fracturing fluids and proppant transport. The present invention also relates to a method of using the hydrocarbon gels of the present invention as fracturing fluids.
In particular, the present invention relates to the use of salts Of C
6
to C
30
carboxylic acids, such as salts of 2-ethyl hexanoic acid, or polymeric fatty acid salts such as poly-oxo-metallic salts of fatty acids, as gelling agents for hydrocarbon liquids. Preferably, these salts of acids are utilized in combination with a gel activator which is a difunctional and/or trifunctional carboxylic acid, as a gelling system for hydrocarbon liquids.
BACKGROUND OF THE INVENTION
Gelled hydrocarbons have been used in petroleum producing subterranean formations as fracturing fluids to improve the recovery of oil and natural gas. The fracturing fluids are hydraulically injected into a wellbore which penetrates the subterranean formation, and are propelled against the formation strata by high pressure, forcing the strata to crack and fracture.
The fracturing fluids carry proppant particles to the fracture site. These proppant particles remain in the fracture thereby “propping” the fracture open when the well is in production. The proppant material is commonly sand, sintered bauxite, polystyrene beads, and so forth, and is generally suspended in the gelled fluid due to the insolubility of the particles in the fluid.
Fracturing fluids may be thickened or gelled through the use of various chemical agents which act to increase viscosity or induce the gel formation. It is in fact widely accepted that the viscosity of liquid hydrocarbon fracturing fluids can be increased by a variety of thickening agents including fatty esters, orthophosphate esters, and aluminum complexed fatty acids.
Fatty ester gelling systems are for the most part, no longer utilized in oil field operations. The problem which was associated with these systems was the failure to generate adequate viscosity within the required time, i.e. the time required to pump the gel to the fracture site, therefore requiring aging of the gel prior to use.
A second class of gelling agents are the phosphate based compounds, including alkyl phophates coupled with aluminum and iron such as aluminum salts of orthophosphate esters. Aluminum crosslinked or iron crosslinked orthophosphate esters are probably the most commonly used gelling agents available today. They may be utilized in either a batch-mix or a continuous-mix process, and gel times can be quite fast. Most service companies do utilize a continuous mix process for the phosphate ester systems. However, there is an increasing demand in the oil industry for non-phosphate based gelling agents because phophates are known to be detrimental to the refining process.
Problems exist with the currently available systems as well. U.S. Pat. No. 5,614,010 issued Mar. 25, 1997 to Smith et al. describes problems associated with the use of aluminum compounds. Smith et al. state that aluminum will not satisfactorily perform the desired crosslinking function in the presence of more than about 1200 ppm of water, nor where the pH is outside a relatively narrow range. Smith et al. overcame this problem by utilizing ferric salts, rather than aluminum compounds for combination with orthophosphate ester.
The aluminum complexed fatty acids include aluminum octoates and aluminum stearates. A specific compound is the aluminum soap of 2-ethylhexoic acid, also referred to as aluminum octoate.
U.S. Pat. No. 5,417,287 describes iron crosslinked phosphate gels which exhibit fast gelling times.
U.S. Pat. No. 3,799,267 issued Mar. 26, 1974 to Ely et al. describes “a method whereby the viscosity of a liquid hydrocarbon, having an aluminum soap of an oil soluble aliphatic carboxylic acid solvated therein, is unexpectedly increased by dissolving benzoic acid in the hydrocarbon liquid.” Ely et al. go on to state that “the addition of benzoic acid to a liquid hydrocarbon having an aluminum soap of an oil soluble aliphatic carboxylic acid solvated therein, has been found to further increase the viscosity of the liquid hydrocarbon by as much as 100 times the viscosity produced by an equivalent concentration of the aluminum soap solvated therein.” See column 1, lines 39 to 50.
U.S. Pat. No. 4,981,608 issued Jan. 1, 1991 to Gunther describes the use of a gelling agent for a hydrophobic organic liquid comprising the solid reaction product of a poly-oxo-aluminum stearate and 2-ethyl hexanoic acid. Gunther states at column 2, lines 62 to 65 that “gelling occurs within a comparably very short time, such as one hour upon spraying or intermixing the gelling agent into the liquid to be gelled.” Furthermore, many of the fatty acid systems are solids, while many end users prefer liquid based systems.
The present invention has overcome the aforementioned problems through the use of a hydrocarbon based gel which comprises at least one salt of a carboxylic acid having from about 6 to about 30 carbon atoms. Preferably, the salt is an aluminum tri-salt of 2-ethylhexanoic acid, and preferably at least one activator is utilized whereby the gelling can be controlled by the addition of the activator, and gelation can occur very quickly. The present invention utilizes a continuous mix gel process.
SUMMARY OF THE INVENTION
The present invention relates to a gelling system useful in hydrocarbon based fracturing fluids comprising at least one salt of a carboxylic acid having from about 6 to about 30 carbon atoms. Preferably, the salt is an aluminum tri-salt of 2-ethylhexanoic acid, and preferably at least one activator is utilized to control gelation to preferably less than about 5 minutes, and more preferably less than about 3 minutes. The rate of gellation will further depend on the hydrocarbon fluid to be gelled, the other ingredients added, and the combinations of the ingredients utilized, and the concentration of each component as well as on the activator. The activator is a difunctional and/or trifunctional acid, or a mixture thereof. Preferably, the activator is a dimer-trimer fatty acid, or a polymeric fatty acid. The salt may also be a metal alkoxide dicarboxylate salt.
The resultant hydrocarbon gels have thermal stability of greater than about 200° F. (about 93.3° C.) as exhibited by maintenance of a viscosity which is adequate for particle, i.e. proppant, suspension for instance
The present invention further relates to a continuous mix gel method for preparing the hydrocarbon gels of the present invention.
The present invention further relates to a method of fracturing a subterranean formation comprising the steps of providing the hydrocarbon gel of the present invention through a wellbore to a subterranean formation at a pressure sufficient enough to fracture the formation.
DETAILED DESCRIPTIONS OF THE PREFERRED EMBODIMENTS
The gelling agents useful to the present invention are salts of carboxylic acids having from about 6 to about 30 carbon atoms, and preferably from about 8 to about 20 carbon atoms.
These gelling agents may be prepared by heating the carboxylic acid with a multivalent metal compound. These metals are preferably divalent or trivalent, and may be complexed with anions including halides, hydroxides, sulfates, sulfonates, nitrates, carboxylates, and other oxo anions, and so forth. Preferably, this is accomplished in a ratio of about two or three carboxylic acid equivalents to one metal, and preferably, the salts formed are di and tri-salts having the following general formula:
(CH
3
—(CH
2
)
y
—COO)
n
X
wherein y is 6 to 28, and preferably 6 to 18; n is 2 or 3; and X is a multivalent metal such as aluminum, boron, zinc, copper, iron, magnesium, calcium, barium, titanium, zirconium, tin, cobalt and so forth, and mixtures thereof, or a metal alkoxide, complexed to carboxylic acid groups. Aluminum is one of the preferred multiv
Bunting Charles R.
Stewart RoseMarie E.
Subramanian Shankar
Zhu Yun-peng
Crompton Corporation
Ma Shirley S.
Tucker Philip
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