Earth boring – well treating – and oil field chemistry – Well treating – Contains organic component
Reexamination Certificate
1998-12-11
2001-05-15
Tucker, Philip (Department: 1721)
Earth boring, well treating, and oil field chemistry
Well treating
Contains organic component
C507S239000, C507S276000, C507S277000, C507S921000, C507S922000, C507S925000, C166S300000
Reexamination Certificate
active
06232274
ABSTRACT:
The present invention relates to viscoelastic surfactant based gelling compositions for weltbore service fluids. More particularly it relates to viscoelastic surfactant based gelling compositions for selectively reducing the flow of subterranean aqueous fluids into a well while maintaining the hydrocarbon production.
BACKGROUND OF THE INVENTION
Various types of wellbore fluids are used in operations related to the development, completion, and production of natural hydrocarbon reservoirs. The operations include fracturing subterranean formations, modifying the permeability of subterranean formations, or sand control. Other applications comprise the placement of a chemical plug to isolate zones or complement an isolating operation. The fluids employed by those operations are known as drilling fluids, completion fluids, work over fluids, packer fluids, fracturing fluids, conformance or permeability control fluids and the like.
Of particular interest with regard to the present inventions are fluids for water control applications: During the life cycle of a hydrocarbon well, e.g., a well for extracting oil or natural gas from the Earth, the producing well commonly also yields water. In these instances, the amount of water produced from the well tends to increase over time with a concomitant reduction of hydrocarbon production. Frequently, the production of water becomes so profuse that remedial measures have to be taken to decrease the water/hydrocarbon production ratio. As a final consequence of the increasing water production, the well has to be abandoned.
In many cases, a principal component of wellbore service fluids are gelling compositions, usually based on polymers or viscoelastic surfactants.
Viscoelastic surfactant solutions are usually formed by the addition of certain reagents to concentrated solutions of surfactants, which most frequently consist of long-chain quaternary ammonium salts such as cetyltrimethylammonium bromide (CTAB). Common reagents which generate viscoelasticity in the surfactant solutions are salts such 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 behaviour.
Further references related to the use of viscoelastic surfactants as wellbore service fluids can be found for example in U.S. Pat. Nos.4,695,389, 4,725,372, and 5,551,516.
There has been considerable interest in the viscoelastic gels formed from the solutions of certain surfactants when the concentration significantly exceeds the critical micelle concentration. The surfactant molecules aggregate into worm-like micelles which can become highly entangled at these high concentrations to form a network exhibiting elastic behaviour. These surfactant gels are of considerable commercial interest, including application as oil well fracturing fluids.
The viscoelasticity of the surfactant solutions appears invariably to form rapidly on mixing the various components. The resulting high viscosities of the viscoelastic gels can make handling or placement difficult. For example, placement of a uniform surfactant gel in a porous medium is difficult since injection of the gel in the medium can lead to the separation of the surfactant from the solute by a filtration process. Any application of viscoelastic surfactant solutions which requires their transport or placement after their preparation would benefit from a method of controlling their viscosities and gel times.
The object of this present invention is therefore to provide improved compositions for wellbore service fluids based on viscoelastic surfactants. It is a specific object of the invention to provide means of controlling or delaying the build-up of viscosity in such compositions. It is a further specific object of the invention to provide such compositions for water control operations in hydrocarbon wells.
SUMMARY OF THE INVENTION
The objects of the invention are achieved by methods and compositions as set forth in the appended independent claims.
A composition in accordance with the present invention comprises viscoelastic surfactants and means of controlling the concentration of at least partially charged sites within the composition. For the purpose of this description, the term “partially charged sites” includes groups, molecules, or atoms, whether or not attached to larger molecules, of polar or ionic character. The concentration is used as a means to control or delay the onset of gelation in surfactant based viscoelastic fluids after the fluid has been mixed.
The control can be achieved by at least three different mechanisms:
the delayed release of a specific counter-ion such as the formation of the salicylate anion by ester hydrolysis;
the controlled removal of a hydrogen bonding modifier such as urea or guanidine hydrochloride in surfactant systems where hydrogen bonding provides a significant interaction between the entangled micelles; or
the controlled change in the ionic composition of the surfactant solution.
The use of an internal delayed release (removal) of a reagent which promotes (inhibits) the formation of viscoelastic gels from the surfactant solutions is seen as a novel feature of the present invention.
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Hughes Trevor L.
Jones Timothy Gareth J.
Tustin Gary J.
Nava Robin C.
Schlumberger Technology Corporation
Tucker Philip
Wang William L.
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