Earth boring – well treating – and oil field chemistry – Earth boring – Contains organic component
Reexamination Certificate
2000-12-20
2003-07-08
Tucker, Philip (Department: 1712)
Earth boring, well treating, and oil field chemistry
Earth boring
Contains organic component
C507S103000
Reexamination Certificate
active
06589917
ABSTRACT:
BACKGROUND OF THE INVENTION
For a number of years, oil based drilling fluids and invert emulsion muds have been utilized in the drilling of subterranean wells. These fluids typically are comprised of a hydrocarbon oil or mixtures of oils as the major component of the liquid phase to which various materials are added to impart the desired drilling fluid properties. These fluids are well adapted for use in underground formations containing water sensitive clays or shales which swell and disintegrate when contacted by water based drilling fluids. True oil-based fluids are substantially free of water, lose mostly oil as the filtrate and cause no swelling or disintegration of water sensitive clays and shales. Water-in-oil emulsions are also used as drilling fluids. These fluids contain oil as the continuous phase and water as the external or discontinuous phase. A water-in-oil emulsion is also known as an invert emulsion. The true oil-based and the invert emulsion muds generally contain one or more weighting agents, surfactants, viscosifiers, fluid loss control agents or bridging agents.
The primary benefits of selecting an oil based drilling fluid include: superior hole stability, especially in shale formations; formation of a thinner filter cake than the filter cake achieved with a water based mud; excellent lubrication of the drilling string and downhole tools; penetration of salt beds without sloughing or enlargement of the hole as well as other benefits that should be known to one of skill in the art.
An especially beneficial property of oil based drilling fluids are their excellent lubrication qualities. These lubrication properties permit the drilling of wells having a significant vertical deviation, as is typical of offshore or deep water drilling operations or when a horizontal well is desired. In such highly deviated holes, the torque and drag on the drill string are significant because the drill pipe lies against the low side of the hole. Under these conditions, the risk of pipe sticking is high when water based muds are used. In contrast oil based muds provide a thin, slick filter cake which helps to prevent pipe sticking. Thus the use of the oil based mud is preferred.
Invert emulsion fluids, i.e. emulsions in which the non-oleaginous fluid is the discontinuous phase and the oleaginous fluid is the continuous phase, are employed in drilling processes for the development of oil or gas sources, as well as, in geothermal drilling, water drilling, geoscientific drilling and mine drilling. Specifically, the invert emulsion fluids are conventionally utilized for such purposes as providing stability to the drilled hole, forming a thin filter cake, lubricating the drilling bore and the downhole area and assembly, and penetrating salt beds without sloughing or enlargement of the drilled hole.
Oil-based drilling fluids are generally used in the form of invert emulsion muds. An invert emulsion mud consists of three-phases: an oleaginous phase, a non-oleaginous phase and a finely divided particle phase. Also typically included are emulsifiers and emulsifier systems, weighting agents, fluid loss additives, viscosity regulators and the like, for stabilizing the system as a whole and for establishing the desired performance properties. Full particulars can be found, for example, in the Article by P. A. Boyd et al entitled “New Base Oil Used in Low-Toxicity Oil Muds” in the Journal of Petroleum Technology, 1985, 137 to 142 and in the Article by R. B. Bennet entitled “New Drilling Fluid Technology-Mineral Oil Mud” in Journal of Petroleum Technology, 1984, 975 to 981 and the literature cited therein.
The components of the invert emulsion fluids include an oleaginous liquid such as hydrocarbon oil which serves as a continuous phase, a non-oleaginous liquid such as water or brine solution which serves as a discontinuous phase, and an emulsifying agent. As used herein, emulsifying agent and surfactant are used interchangeably. The emulsifying agent serves to lower the interfacial tension of the liquids so that the non-oleaginous liquid may form a stable dispersion of fine droplets in the oleaginous liquid. A full description of such invert emulsions may be found in
Composition and Properties of Drilling and Completion Fluids,
5th Edition, H. C. H. Darley, George R. Gray, Gulf Publishing Company, 1988, pp. 328-332, the contents of which are hereby incorporated by reference.
Lime or other alkaline materials are typically added to conventional invert emulsion drilling fluids and muds to maintain a reserve alkalinity. See, for example, API Bulletin RP 13B-2, 1990, p. 22 which describes a standard test for determining excess lime in drilling mud. See also, for example, U.S. Pat. No. 5,254,531 which employs lime along with an ester oil, a fatty acid, and an amine and EP 271943 which employs lime along with oil, water, and an ethoxylated amine. The generally accepted role of the reserve alkalinity is to help maintain the viscosity and stability of the invert emulsion. This is especially important in areas in which acidic gases such as CO
2
or H
2
S are encountered during drilling. Absent an alkaline reserve, acidic gases will weaken stability and viscosity of conventional invert emulsion fluids to the point of failure. That is to say the invert emulsion becomes so unstable that the oil wet solids become water wet and the phases of the invert emulsion “flip” thus rendering the invert emulsion fluid not suitable for use as a drilling fluid. One of skill in the art should understand that due to the high cost of removing and disposing of the flipped mud from a borehole, the formation of flip mud is very undesirable. Further because the beneficial properties of the drilling fluid have been lost, (i.e. viscosity, pumpability and the ability to suspend particles) the likelihood of a blowout is greatly increased. Thus, one of ordinary skill in the art should understand that the maintenance of an alkalinity reserve is critical to the use of conventional invert emulsion drilling fluids and muds.
Environmental regulations have also severely limited the use of oil based and invert emulsion oil muds as drilling fluids. Of particular concern is the disposal of oil coated drilling cuttings especially in offshore or deep water drilling operations. Environmentally sound disposal of oil-coated cuttings is required which in these latter cases, the cuttings must be either processed onboard the drilling rig, or the cuttings must be shipped back to shore for disposal in an environmentally safe manner. In order to address these environmental issues, synthetic based drilling fluids and muds were developed. The oleaginous component of the synthetic based drilling fluid may typically be selected from esters, ethers, internal olefins, polyalpha olefins and other environmentally compatible fluids. However, the formulation and selection of the based fluid had to take into account the compatibility of other components in the drilling fluid.
While synthetic based drilling fluids successfully solve environmental concerns, these fluids often introduce new concerns downhole because the components of the fluid alter the structural compositions and mechanical properties of the elastomers used in oil field equipment. It has been reported in the literature that synthetic fluids, especially those containing esters and ethers exhibit compatibility problems with the elastomers used in a variety of oil field equipment, including blowout preventors, pulsation dampener bladders, drill motors, o-rings, boots and packers. For example see “Drilling Fluid Type Affects Elastomer Selection” by Venu Bodepudi, J. Michael Wilson and Arvind Patel, Oil & Gas Journal, Oct. 26, 1998, pages 75-79. As discussed in this article, the synthetic based drilling fluids can induce hysteresis, swelling, shrinkage, pre-mature degradation, embrittlement, and break-up of the elastomer. Synthetic based drilling fluids may also destroy the bond between the elastomer and the metal portions of the tool. Low molecular weight esters and ethers were found to be partic
Friedheim Jim
Patel Arvind D.
Cagle Stephen H.
Howrey Simon Arnold & White
M-I LLC
Tucker Philip
White Carter J.
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