Earth boring – well treating – and oil field chemistry – Earth boring – Contains inorganic component other than water or clay
Patent
1996-07-29
1999-10-05
Tucker, Philip
Earth boring, well treating, and oil field chemistry
Earth boring
Contains inorganic component other than water or clay
507269, 507922, 507925, 507928, C09K 702, C09K 706
Patent
active
059623756
DESCRIPTION:
BRIEF SUMMARY
This invention relates to wellbore fluids suitable for use in the oil and gas exploration and production industries and embraces fluids used for drilling, completion, cementing, workover or packing of wellbores, and includes so called "spacer fluids" and "spotting fluids" whose functions are, respectively, to separate dissimilar fluids during pumping operations, and to spot or treat certain intervals of the wellbore. The term "wellbore fluid" also embraces so-called "fracturing fluids" which are pumped at a pressure sufficient to fracture the rock forming the producing reservoir.
During well construction, there are many occasions when it is necessary to pump wellbore fluids which are viscosified in order to, for example, remove debris such as cuttings from a well, or which are gelled sufficiently to suspend quantities of powdered dense minerals such as barytes.
It is also frequently important that the slurries forming the wellbore fluids do not leak-off or filter into permeable formations at a high rate. For instance during drilling, high filtration rate fluids may produce a thick filter cake leading to sticking of the drill string. Equally the invasion of large quantities of filtrate may damage the permeability of reservoir rocks causing reduced hydrocarbon production. If cement slurries filter too readily, premature solidification of the cement may occur during the pumping operation. Fracturing operations are less efficient if the fracturing fluid "leaks-off" into porous rock, losing the pressure required to fracture further.
Whilst many soluble polymers have been developed to provide viscosity and filtration control, it is frequently desirable to combine these with, or use alone, finely divided minerals to enhance or achieve the above properties.
According to a first aspect of the invention, there is provided a wellbore fluid comprising a liquid dispersion of a particulate mixed divalent metal carbonate which has a generally platy crystal form.
Where the wellbore fluid is two phase, for example an emulsion wellbore fluid having oily and a water phases, the particulate carbonate may be dispersed or mixed in either or both of the phases.
Preferred mixed divalent metal carbonates are the mixed alkaline earth metal carbonates, and presently the most preferred of these is huntite.
Huntite is a carbonate of calcium and magnesium of the general formula CaMg.sub.3 (CO.sub.3).sub.4. It occurs in nature in the USA and Greece as compact masses of very small crystals of the order of 1 micron and the crystals are generally platy in nature. The chalk-like material as mined is readily milled, and the mineral easily disperses to discrete crystals on shearing in water.
The particulate mixed metal carbonate, such as huntite, should preferably have an aspect ratio of at least 5 and will typically have a particle size distribution such that a high proportion, such as 90% or more, of the particles have an equivalent spherical diameter (esd) in the range of from 0.1-5 microns.
The invention is not restricted to mixed metal carbonates, such as huntite, obtained from natural deposits. Synthetic huntite or other synthetic mixed metal carbonates obtained by precipitation from aqueous solutions may be a potential alternative source.
In the wellbore fluid of the invention, the mineral particles may be dispersed or mixed in any liquid phase, suitable for a wellbore fluids such as, for example, fresh water, sea water, brines of water soluble salts, oily liquids such as petroleum oils and derivatives, esters, ethers, mono alphaolefins, polyalphaolefins, acetals, and emulsions.
It has surprisingly been found that mixed metal carbonates having a generally platy crystal character, such as huntite (natural or synthetic) will confer the advantageous properties of increased viscosity and gelation, and of reduced filtration rate, when mixed into the liquid phase.
Unlike bentonite which will only develop viscosity and filtration control in relatively fresh water, platy mixed metal carbonates such as huntite are effective by direct mixing int
REFERENCES:
patent: 4422948 (1983-12-01), Corley et al.
patent: 4426296 (1984-01-01), Crowe
Rutherford, Spec. Publ.--R. Soc. Chem., vol. 76, pp. 266-276, (1990).
Mehta Shreekant Babulal
Sawdon Christopher Alan
Dowell, a division of Schlumberger Technology Corporation
Tucker Philip
Vick, Jr. John E.
Y'Barbo Douglas
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