Earth boring – well treating – and oil field chemistry – Earth boring – Contains organic component
Reexamination Certificate
1998-09-18
2001-02-27
Tucker, Philip (Department: 1712)
Earth boring, well treating, and oil field chemistry
Earth boring
Contains organic component
C507S136000, C507S131000, C516S058000, C516S900000
Reexamination Certificate
active
06194354
ABSTRACT:
The invention relates to concentrates for use in preparing structured surfactant drilling fluids, and especially drilling fluid for use in offshore locations.
The term “Drilling Fluid” is used herein to refer to fluids used in the drilling of bore holes in rock to lubricate and cool drill bits, and to transport rock cuttings away from the rock face. The term is also used herein to include “Spacer Fluids”, which are used to clean the sides of bore holes prior to cementing. Drilling Fluids are used in the construction of deep wells and bore holes, and especially oil and gas wells. For convenience the term Drilling Fluid as used herein also embraces “Completion Muds”, which are used in civil engineering and the construction industry to stabilise holes and excavations by preventing the breakdown of shales on exposure to water. The term Drilling Fluid is also used herein to include “Packing fluids” which are used in drilling operations to fill the space between concentric, downhole tubing used in the well casing.
“Electrolyte” is used herein to denote those ionic compounds which dissociate at least partially in aqueous solution to provide ions, and which at the concentrations present tend to lower the total solubility (including micellar concentration) of surfactants in such solutions by a “salting out” effect. References herein to the Electrolyte content or concentration refer to the total dissolved Electrolyte, but excludes any suspended solid.
“Micelle” refers to a particle, which is either spherical, disc or rod shaped, formed by aggregation of surfactant molecules and having a radius, or minor dimension less than twice the mean length of the surfactant molecules. The molecules in a Micelle are typically arranged such that their hydrophilic (“head”) groups lie on the surface of the Micelle and the lipophillic (“tail”) groups are in the interior of the Micelle.
“Bilayer” includes a layer of surfactant approximately two molecules thick, which is formed from two adjacent parallel layers, each comprising surfactant molecules which are disposed such that the lipophillic portions of the molecules are located in the interior of the Bilayer and the hydrophilic portions are located on its outer surfaces. “Bilayer” is also used herein to include interdigited layers, which are less than two molecules thick. An interdigited layer may be regarded as a Bilayer in which the two layers have interpenetrated allowing at least some degree of overlap between the tail groups of the molecules of the two layers.
“Spherulite” means a spherical or spheroidal body having maximum dimensions of from 0.1 to 50 microns. Spherulites may sometimes be distorted into prolate, oblate, pear or dumbell shapes. “Vesicle” means a Spherulite containing a liquid phase bounded by a Bilayer. “Multiple Vesicle” means a Vesicle which contains one or more smaller Vesicles. The Spherulites present in Structured Surfactant systems are typically concentric Multiple Vesicles.
“G” phase refers to a liquid crystal Lamellar Phase, of the type also known in the literature as L&agr;, “neat” phase or “lamellar” phase. The “G” phase for any given surfactant or surfactant mixture normally exists in a narrow range of concentrations. Pure “G” phases can normally be identified by examination of a sample under a polarising microscope, between crossed polarisers. Characteristic textures are observed in accordance with the classic paper by Rosevear, JAOCS Vol. 31 P628 (1954) or in J. Colloid and Interfacial Science, Vol. 20 No. 4, P.500 (1969). “G” phases normally exhibit lamellar symmetry with a repeat spacing of from 4 to 15 nm, in X-ray diffraction or neutron scattering patterns.
“Spherical G Phase” means Multiple Vesicles formed from substantially concentric shells of surfactant Bilayer alternating with aqueous phase with a “G” phase spacing. Typically conventional G phases may contain a minor proportion of Spherical G Phase.
“Spherulitic Composition” means a composition in which a major part of the surfactant is present as spherical G-phase dispersed in an aqueous phase, or which is principally stabilised against sedimentation by a Spherical G-phase.
“Structured Surfactant” as used herein means a pourable fluid composition which has shear dependent viscosity and solid-suspending properties at least partly conferred by the presence of a surfactant mesophase, which may optionally be dispersed in, or interspersed with an aqueous phase. The mesophase may, for example, be a G-phase or may comprise Spherulites, especially Spherical G-phase. Structured surfactants typically maintain solid particles immobile, when at rest, and display no sedimentation over extended periods of weeks or months, but may be readily poured.
“Weighting Agent” means a water insoluble particulate mineral having a specific density greater than 3.5 and preferably greater than 4 e.g. barite or haematite which imparts increased density to the fluid.
“Drilling Mud” is a Drilling Fluid which contains suspended mineral particles, such as rock cuttings and/or Weighting Agents.
“L
2
phase” is a fluid phase comprising surfactant and an organic solvent and/or water wherein the surfactant forms micelles having the hydrophobic portion on the outside of the micelle and any water present in the interior of the micelle. L
2
phases are typically Newtonian and optically isotropic and may be distinguished from aqueous based micellar solutions (“L
2
phase”) by low electrical conductivity, and by a tendency to form G or M phases on dilution with water.
“M” phase is a mesophase in which the surfactant forms cylindrical rods of indefinite length. “M” phases are immobile or viscous, and exhibit characteristic textures under the polarising microscope. They may usually be unambiguously identified by their hexagonal symmetry, which can be detected using small angle x-ray diffraction.
“Shale stabiliser” is a substance which inhibits the disintegration of shale which often occurs in aqueous fluids. This problem can lead to the collapse of the sides of the well when it is drilled through shale.
“Shale inhibitor” is a substance which inhibits the swelling of shale particles in aqueous based mud. This problem can cause the viscosity of the mud to increase. The drilling of oil wells and other boreholes requires the use of drilling fluids which are circulated through the hole to cool and lubricate the drill bit and remove the rock cuttings and transport them to the surface. Conventional drilling muds have been based on oil or on oil/water emulsions. However increasingly strict environmental constraints prevent the release of oil into the sea. Hence offshore installations must either transport oil contaminated rock cuttings ashore for disposal, which would be prohibitively expensive, or develop water based fluids. Two approaches to the latter problem have been suggested. The first involves aqueous solutions of various polymers and the second, the use of structured surfactants. Aqueous polymers capable of providing the required rheological properties generally have poor thermal stability at the temperatures encountered during deep drilling operations and are relatively expensive. Moreover they are generally non-biodegradable and therefore are themselves facing increased environmental constraints. Drilling muds based on structured surfactants have been described in EPO 430 602 and GB2 304 754. They comprise surfactant mesophases generally interspersed with water to give a non-Newtonian system, which exhibits a yield point capable of maintaining even quite large solid particles indefinitely immobilised in suspension, as if in an immobile gel, while the system is at rest, but which breaks under the shear forces associated with pouring or pumping, enabling the system to be handled as a low viscosity liquid.
Structured surfactants have a number of advantages as drilling muds. Their low viscosity under shear enables them to be readily pumped, while their unique ability to suspend solids when at rest prevents sedimentation in the hole if circulation is halted, and facilitates removal of the cuttings. Struc
Albright & Wilson UK Limited
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Tucker Philip
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