Earth boring – well treating – and oil field chemistry – Earth boring – Contains organic component
Patent
1995-01-31
1997-05-06
Springer, David B.
Earth boring, well treating, and oil field chemistry
Earth boring
Contains organic component
507203, C09K 702, C09K 706
Patent
active
056271433
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/GB94/01878 filed Aug. 30, 1994.
This invention concerns wellbore fluids suitable for use in the oil and gas exploration and production industries and embraces fluids used for drilling, completion, workover or packing of wellbores. The invention is especially concerned with biodegradable wellbore fluids the liquid phase of which consists of an oil, or of water-in-oil "invert" emulsions, where the oil phase comprises n-alk-1-enes (linear alphaolefins) having from 12 to 20 carbon atoms, or linear polyunsaturated olefins having one of the double bonds in the 1-position and having from 12 to 22 carbon atoms, or mixtures of the two types in any ratio.
A wellbore is drilled by attaching to the bottom of a length of drill pipe a cutting bit which is rotated either by means of a prime mover on the surface which applies rotary motion to the top end of the drill pipe or by means of a turbine motor fixed to the drill pipe near the lower end, the turbine motor being driven by circulating fluid in the wellbore.
In either case a drilling fluid is required to remove cuttings from around the bit and to transport the cuttings to the surface for separation and removal. The drilling fluid also cools the bit and lubricates both bit and drill pipe thus reducing friction.
In many cases it is possible to use as the drilling fluid a simple mixture comprising water and a smectite clay which increases the viscosity of the fluid for the purposes of suspending and transporting the cuttings. However it is often necessary to drill a wellbore through geological formations the constituent materials of which swell or disintegrate on contact with water. In such cases an oil-based drilling fluid is used, that is a fluid in which the liquid phase consists of oil, or of water-in-oil "invert" emulsions.
Such oil based drilling fluids avoid the hydration problems caused by water contacting shale or salt formations. They also possess advantages compared to water based fluids of enhanced lubrication of the drill pipe, inhibition of corrosion of the drill pipe, and high stability at high temperatures.
Originally such oil based drilling fluids utilised diesel fuel or other similar petroleum fractions as the oil phase. However these contain relatively high proportions of aromatic hydrocarbons and other compounds which are toxic to marine life.
More recently, highly refined low aromatic mineral oils have been used. These are of much lower toxicity than diesel fuel. Various environmental authorities therefore permitted the discharge to the sea of cuttings contaminated with "low toxicity" mineral oil based drilling fluids.
However, in many offshore locations, this has caused the smothering of the sea bed with piles of cuttings in which the refined mineral oil has not biodegraded significantly, especially under the anaerobic conditions existing within a pile of cuttings.
This has led to increasingly stringent regulations on the concentration of mineral oils which may be discharged with the cuttings. Also the Paris Convention (Annex A, Part 1) is increasingly restricting the use in drilling fluids of "oils of a petroleum origin" whilst discharging cuttings to the sea.
U.S. Pat. No. 5,068,041 relates to the use of synthetic branched chain polyalphaolefins as a continuous phase for oil based drilling fluids.
GB-A-2258258 describes polyalphaolefins for use in wellbore fluids.
According to the present invention, there is provided a biodegradeable wellbore fluid having a continuous oil phase comprising an n-alk-1-ene having from 12 to 20 carbon atoms or a linear polyunsaturated olefin having one of the double bonds in the 1-position and having from 12 to 22 carbon atoms, or a mixture thereof.
Preferably, the wellbore fluid is substantially free of aromatic hydrocarbons, cycloparaffins, cycloalkenes and iso-alkanes. Thus, the continuous oil phase of the wellbore fluid of the present invention preferably has less than 10%, more preferably less than 5%, by weight of cycloparaffins, iso-paraffins, aromatic compounds and cycloalkene
REFERENCES:
patent: 5096883 (1992-03-01), Mercer et al.
patent: 5432152 (1995-07-01), Dawson et al.
Dowell Schlumberger Incorporated
Springer David B.
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