Earth boring – well treating – and oil field chemistry – Earth boring – Contains organic component
Reexamination Certificate
2001-07-30
2004-07-13
Tucker, Philip C. (Department: 1712)
Earth boring, well treating, and oil field chemistry
Earth boring
Contains organic component
C507S141000, C507S145000, C507S135000, C507S134000, C507S240000, C507S241000, C507S244000, C507S252000, C507S259000, C507S267000, C507S276000, C507S277000, C507S922000, C507S927000, C166S308400, C166S278000, C166S312000
Reexamination Certificate
active
06762154
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to the drilling, completion, and stimulation of hydrocarbon wells and in particular to fluids and methods for gravel packing, cleanup or drilling in a subterranean formation.
BACKGROUND OF THE INVENTION
Viscous fluids play many important roles in oilfield service applications. The viscosity of the fluids allows them to carry particles from one region of the formation, the wellbore, or the surface equipment to another. For instance, one of the functions of a drilling fluid is to carry drilling cuttings from around the drilling bit out of the wellbore to the surface. Fluid viscosity also plays an essential role for instance in gravel packing placement. Gravel packing essentially consists of placing a gravel pack around the perimeter of a wellbore across the production zone to minimize sand production from highly permeable formations.
Solid suspension properties are also an important requirement for fracturing fluids. For a well to produce hydrocarbons from a subterranean geologic formation, the hydrocarbons have to follow a sufficiently unimpeded flow path from the reservoir to the wellbore. If the formation has relatively low permeability, either naturally or through formation damages resulting for example from addition of treatment fluids or the formation of scales, it can be fractured to increase the permeability. Fracturing involves literally breaking a portion of the surrounding strata, by injecting a fluid directed at the face of the geologic formation, at pressures sufficient to initiate and/or extend a fracture in the formation. A fracturing fluid typically comprises a proppant, such as ceramic beads or sand to hold the fracture open after the pressure is released. It is therefore important for the fluid to be viscous enough to carry the proppant into the fracture.
The fluid viscosity is most commonly obtained by adding water-soluble polymers, such as polysaccharide derivatives. Recently, viscoelastic surfactants have been used as thickeners. Unlike the polymers, viscoelastic surfactants based fluids do not lead to reduction of permeability due to solid deposits, and exhibit lower friction pressure. In addition, the viscosity of the fluid is reduced or lost upon exposure to formation fluids such as for instance crude oil thereby ensuring better fracture clean-up.
Viscoelastic surfactant fluids are normally made by mixing in appropriate amounts suitable surfactants such as anionic, cationic, nonionic and zwitterionic surfactants. The viscosity of viscoelastic surfactant fluids is attributed to the three dimensional structure formed by the components in the fluids. When the concentration of surfactants in a viscoelastic fluid significantly exceeds a critical concentration, and in most cases in the presence of an electrolyte, surfactant molecules aggregate into species such as micelles, which can interact to form a network exhibiting elastic behavior. In the remaining part of this description, the term “micelle” will be used as a generic term for the organized interacting species.
Cationic viscoelastic surfactants—typically consisting of long-chain quaternary ammonium salts such as cetyltrimethylammonium bromide (CTAB)—have been so far of primarily commercial interest in wellbore fluid. Common reagents that generate viscoelasticity in the surfactant solutions are salts such as ammonium chloride, potassium chloride, sodium salicylate and sodium isocyanate and non-ionic organic molecules such as chloroform. The electrolyte content of surfactant solutions is also an important control on their viscoelastic behavior. Reference is made for example to U.S. Pat. Nos. 4,695,389, No. 4,725,372, No. 5,551,516, No. 5,964,295, and No. 5,979,557. However, fluids comprising this type of cationic viscoelastic surfactants usually tend to lose viscosity at high brine concentration (10 pounds per gallon or more). Therefore, these fluids have seen limited use as gravel-packing fluids or drilling fluids, or in other applications requiring heavy fluids to balance well pressure.
It is also known from International Patent Publication WO 98/56497, to impart viscoelastic properties using amphoteric/zwitterionic surfactants and an organic acid, salt and/or inorganic salt. The surfactants are for instance dihydroxyl alkyl glycinate, alkyl ampho acetate or propionate, alkyl betaine, alkyl amidopropyl betaine and alkylamino mono- or di-propionates derived from certain waxes, fats and oils. The surfactants are used in conjunction with an inorganic water-soluble salt or organic additives such as phthalic acid, salicylic acid or their salts. Amphoteric/zwitterionic surfactants, in particular those comprising a betaine moiety are useful at temperature up to about 150° C. and are therefore of particular interest for medium to high temperature wells. However, like the cationic viscoelastic surfactants mentioned above, they are not compatible with high brine concentration.
SUMMARY OF THE INVENTION
This invention provides a viscoelastic fluid, useful as a thickener for the suspension of particles, in particular useful as thickener for wellbore fluids, which retain viscosity at high brine concentrations.
According to a first embodiment, this invention specifically relates to a fluid comprising a high brine carrier fluid having a density of at least 10 ppg (10 pounds per gallon or 1.198 g/cm
3
], a member selected from the group consisting of organic acids, organic acid salts, inorganic salts and combination of one or more organic acids or organic acid salts, an amount of a zwitterionic surfactant represented by the formula:
wherein R
1
is an alkyl, alkylarylakyl, alkoxyalkyl, alkylaminoalkyl or alkylamidoalkyl group, containing from about 12 to about 24 carbon atoms, branched or straight chains, saturated or unsaturated, and R
2
and R
3
are independently hydrogen or an aliphatic chain having from 1 to about 30 carbon atoms, and R4 is a hydrocarbyl radical having from 1 to 4 carbon atoms and a co-surfactant.
The co-surfactant increases the gel strength of the viscoelastic-based fluid, if desired. A preferred co-surfactant is a salt of an alkyl benzene sulfonate, most preferred salts being sodium dodecylbenzenesulfonate (SDBS) and sodium dodecylsulfate (SDS). Alkyl phosphonates and alkylcarboxylates may also be used. The concentration of the co-surfactant in the fluid is preferably about 0.1 wt % to about 1 wt %. More preferably, the concentration of the co-surfactant in the fluid is about 0.29 wt % to about 0.5 wt %. The compositions of the invention are also compatible with mineral and organic acids.
According to a second embodiment, this invention specifically relates to a fluid comprising a high brine carrier fluid having a density of at least 10 ppg (10 pounds per gallon or 1.198 g/cm
3
), a member selected from the group consisting of organic acids, organic acid salts, inorganic salts and combination of one or more organic acids or organic acid salts, an amount of a zwitterionic surfactant represented by the formula:
wherein R
1
is an alkyl, alkylarylakyl, alkoxyalkyl, alkylaminoalkyl or alkylamidoalkyl group, containing from about 12 to about 24 carbon atoms, branched or straight chains, saturated or unsaturated, and R
2
and R
3
are independently hydrogen or an aliphatic chain having from 1 to about 30 carbon atoms, and R4 is a hydrocarbyl radical having from 1 to 4 carbon atoms and a chelating agent.
The chelating agents are typically hydroxyethylaminocarboxylic acids. Preferably, the hydroxyethylaminocarboxylic acid is selected from hydroxyethylethylene-diaminetriacetic acid (HEDTA), hydroxyethyliminodiacetic acid (HEIDA), or a mixture thereof or analogous materials hydroxyalkyl, allyl or aryl-aminocarboxylic acids. Hydroxyethylaminocarboxylic acids are used essentially to remove drilling fluids deposits from the wellbore, in particular to remove filter cake. They are also used to prevent precipitation of iron species and in the removal of carbonate and sulfate scales. Ethylenediaminetetra-acetate (EDTA) is not preferred, as such a chel
Brady Mark E.
Daniel Sylvie
Lungwitz Bernhard
Morris Elizabeth
Parlar Mehmet
Echols Brigitte L.
Mitchell Thomas O.
Nave Robin
Schlumberger Technology Corporation
Tucker Philip C.
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