Earth boring – well treating – and oil field chemistry – Earth boring – Contains organic component
Patent
1995-03-13
1997-07-08
Tucker, Philip
Earth boring, well treating, and oil field chemistry
Earth boring
Contains organic component
507108, 507119, 507120, 507901, C09K 702
Patent
active
056460929
DESCRIPTION:
BRIEF SUMMARY
This application is a 35 USC 371 of PCT/EP93/02586 filed Sep. 23, 1993.
The present invention relates to pre-treated clays, their preparation, and their use in formulating drilling muds which are not aggressive to layer clays.
In oil well drilling, very often water-based fluids are used which contain clays, in particular bentonite and various kinds of additives, among which are the necessary dispersants in order to obtain the desired rheological properties. As compared to oil-based muds, these water-based muds display the advantage of a lower cost and lower polluting capability; unfortunately, they display the drawback of being aggressive to the clay layers met during the borehole drilling and to the clay scraps generated during the course of the same drilling.
The dispersion of this clay into the fluid leads to the drilling fluid rheological properties becoming worse, and borehole sidewalls undergoing a partial or, in the worst case, a total failure, with the borehole becoming consequently occluded.
The aggressivity is partially due to the dispersants, generally of polymeric type, added to the mud in order to favour the dispersion of bentonitic clay and endow the mud with suitable fluidity. Because the polymeric dispersant is only partially adsorbed on bentonite, that portion of dispersant which remains free in solution can thus act also on layer clay and on the clay contained in the drilling scrap material, increasing the above problems.
In order to solve, or, at least, reduce these drawbacks, the prior art describes the use of further additives (which anyway cause an increase in total mud cost. For example, U.S. Pat. No. 4,664,818 claims an additive for borehole drilling fluids which is constituted by a partially hydrolyzed copoly(acrylate-acrylamide), a carboxy methyl cellulose and KCl at a level higher than 50%.
GB-A-2,216,574 teaches the addition of a polyglycerol to the drilling mud, as a solution to the problem.
EP-A-333,458 discloses mixtures of water-soluble, high-molecular-weight additives capable of forming strong enough nucleophilic sites when treated with bases and one or more potassium salts having a high enough alkalinity to increase the pH value of the drilling mud up to a higher value than 9.
U.S. Pat. No. 3,953,336 claims the use of water based muds containing a cellulose derivative.
The present Applicants have found now a process for preparing drilling muds which are less aggressive to layer clays, which overcomes the drawbacks which affect the prior art, by not containing more than minimal amounts of free dispersant dissolved in the solution.
In accordance therewith, the present invention relates to a process for preparing aqueous clay-based drilling muds which are not aggressive to layer clays, which process comprises: dispersant amount for fluidifying the mud; dispersant; mud.
According to the preferred embodiment, the clay used in order to prepare the mud is bentonite.
The most commonly used dispersants in order to fluidify bentonite-based muds are lignosulfonates, lignites, polyacrylates and partially hydrolyzed polyacrylamides.
According to the preferred embodiment of the present invention, the dispersants are polyacrylates or their copolymers, still more preferably polyacrylates.
The necessary dispersant amount in order to fluidify said muds depends on the chemical nature of the same dispersant, and on the type of bentonite.
When ligninic dispersant are used, such an amount is generally comprised within the range of from 0.5 to 3% by weight based on the mud, whilst when polymeric dispersants are used, such an amount is comprised within the range of from 0.03 to 0.5% by weight.
The clay may be suspended in water and the dispersant added, or, indifferently, the aqueous solution of dispersant may be added to pristine clay.
The aqueous dispersion of bentonite and the dispersant are mixed for a time period which is at least long enough in order to obtain the adsorption of the dispersant; said time period generally is of the order of approximately 30 minutes.
During this step, a portio
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Burrafato Giovanni
Carminati Stefano
Agip S.p.A.
Eniricerche S.p.A.
Tucker Philip
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