Earth boring – well treating – and oil field chemistry – Earth boring – Contains inorganic component other than water or clay
Patent
1994-09-14
1997-07-01
Gibson, Sharon
Earth boring, well treating, and oil field chemistry
Earth boring
Contains inorganic component other than water or clay
507145, 507272, 507277, 507269, 420415, 420513, C09K 700
Patent
active
056438583
DESCRIPTION:
BRIEF SUMMARY
This application is filed under rule 371 of PCT/GB93/00323 filed Feb. 15, 1993.
The present invention relates to aqueous compositions containing calcium chloride intended for use particularly (but not exclusively) in the drilling of wells in subterranean formations, e.g. for oil or gas exploration/recovery.
BACKGROUND OF THE INVENTION
It is known to use a solution of calcium chloride (a so-called calcium chloride brine) as a fluid for use in the course of oil-well drilling, both as a drilling fluid and as a workover fluid/completion fluid after an oil-well is in production. However, solutions containing calcium chloride as the only dissolved salt have a maximum practical density of about 1.35 g/cm.sup.-3 which may not be sufficiently high for drilling at great depths or into high pressure formations. To increase the density of calcium chloride solutions, it is known to include calcium bromide and/or zinc bromide but the zinc bromide component has acute environmental and economic disadvantages.
A further problem is that the low ambient temperatures encountered in oil/gas/hydrocarbon exploration in some areas of the world (e.g. the North Sea) can result in crystallisation of the calcium chloride from solutions containing more than 35% calcium chloride so that the fluid cannot be used.
U.S. Pat. No. 4,609,476 states that high density brine fluids for drilling operations may be solutions containing 10-60% by weight of salts such as CaCl.sub.2, NaBr, NaCl, KSCN, Ca(NO.sub.3).sub.2, ZnCl.sub.2, ZnBr.sub.2, CaBr.sub.2, KI, LiCl. CaI.sub.2, Ca(SCN).sub.2 and their mixtures having densities up to about 2.4 g/cc. Although one possible mixture which is covered by this statement would comprise calcium chloride and calcium nitrate, there is no specific disclosure of such a formulation in the patent and therefore no suggestion as to the relative proportions in which these two components would be used.
BRIEF SUMMARY OF THE INVENTION
According to a first aspect of the present invention there is provided an aqueous composition comprising water in which are dissolved calcium chloride and calcium nitrate wherein the composition has a density of at least 1.35 g cm.sup.-3, and the weight ratio of calcium chloride to calcium nitrate is in the range 5:95 to 95:5 e.g. 5:95 to 85:15.
Although the compositions of the invention are defined as comprising dissolved calcium chloride and calcium nitrate, it should be appreciated that (at least in certain cases) it may be possible to formulate the compositions by dissolving other compounds which together provide the necessary calcium, chloride and nitrate ions. Therefore the terms dissolved calcium chloride and calcium nitrate are not to be construed as implying that calcium chloride per se and calcium nitrate per se have been used in preparation of the composition but rather that ions equivalent to those obtained by dissolution of calcium chloride and calcium nitrate are present in the solution. Thus, for example, in some cases compositions may be formulated by dissolution of sodium chloride and calcium nitrate.
The present invention has been based on our investigations of aqueous compositions comprising calcium chloride and calcium nitrate, and more particularly investigations to determine how the crystallisation temperature of such compositions varies with the formulation thereof. As a result of these investigations, we have established that it is possible to produce relatively high density formulations which have a predetermined crystallisation temperature provided that the relative amounts of calcium chloride and calcium nitrate are adjusted accordingly.
DETAILED DESCRIPTION OF THE INVENTIONS
The compositions may be formulated so that there is no substantial crystallisation above -10.degree. C. Alternatively compositions may be formulated so as to crystallise only below -20.degree. C., below -30.degree. C., below -40.degree. C., or below -50.degree. C. as desired. Such formulations are therefore useful in those areas of the world where oil/gas/hydrocarbon exploration (or ex
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Links, William F., Ph.D., Solubilities inorganic and metal -organic compounds A -Ir, A compliation of Solubility Data from the Periodical Literature, vol. 1, 4th ed., D. Van Nostrand Company, Inc., 1958, pp. 527-573.
McGlasson, R.L., Greathouse, W.D. and Hudgins, C.M., Stress Corrosion Cracking of Carbon Steels in Concentrated Sodium Nitrate Solutions, Corrosion --National Association of Corrosion Engineers vol. 16, Nov. 1960, pp. 557-561.
Hudgins, C.M., Landers, J.E., and Greathouse, W.D., Corrosion Problems in the Use of Dense Salt Solutions as Packer Fluids, Corrosion--National Association of Corrosion Engineers vol. 16, Nov. 1960, pp. 535-538.
Browning Clifford W.
Brunner Mond & Company Limited
Fee Valerie
Gibson Sharon
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