GB2153411A

GB2153411A - Aqueous drilling fluid

Info

Publication number: GB2153411A
Application number: GB08501466A
Authority: GB
Inventors: Giuseppe Radenti; Sergio Palumbo; Giovanni Zucca
Original assignee: Agip SpA
Current assignee: Agip SpA
Priority date: 1984-01-25
Filing date: 1985-01-21
Publication date: 1985-08-21
Also published as: GB8501466D0; NO850277L; EG19739A; NO161625B; NO161625C; GB2153411B; IT8419307A0; IT1173505B

Abstract

An aqueous drilling fluid consists of an aqueous slurry of clays, thickeners and filtrate reducing agents, optionally fluidizers, optionally weight-increasing agents, optionally clogging agents, and possibly surfactants, together with potassium carbonate in an amount of from 1% to 10% by weight.

Description

SPECIFICATION Aqueous Drilling Fluid The present invention relates to an aqueous drilling fluid. More particularly, the present invention relates to a drilling fluid having anti-swelling properties for clays.

Drilling fluids containing K+ ions are known, which ions are necessary, according to the known art, for the purpose of inhibiting the swelling of plastic clays. In such slurries, the K+ ions are essentially derived from KCI, whilst small amounts of potassium ions can be supplied also by potassium lignites, potassium surfactants and KOH.

The quantity of KCI used (on average from 4 to 5%), is on the one hand such as to allow a good action of clay containment, but is on the other hand, due to the presence of CI anions, such as to increase the extent of corrosion by the fluid, due to the oxygen dissolved in the fluid. The chloride ions are indeed present in the drilling fluid at a concentration corresponding to the highest corrosion rates (35 g/litre as NaCI).

Well-completion fluids are also known, containing potassium carbonate. These fluids have a relative density not lower than 1.190.

It has been surprisingly found that potassium carbonate can be used in a fluid for drilling purposes. The drilling fluid according to the present invention comprises the following components in the following percentages: (a) Clays, from 2% to 8% by weight; (b) Thickeners and filtrate reducing agents, from 0.1% to 3% by weight; (c) Optionally fluidizers, from 0.05% to 2% by weight; (d) Optionally weight-increasing agents, in the required amount; (e) Optionally clogging agents for circulation losses, from 5 to 30% by weight; (f) Optionally surfactants, from 0.5% to 2% by weight; (g) Water; (h) Potassium carbonate, from 1% to 10% by weight.

The percentages are all relative to pure water.

The clogging agents, the fluidizers, the weight-increasing agents and the surfactants are used on the basis of drilling requirements; however, not in amounts outside ihe ranges mentioned above.

The clays, used as single products or as mixtures thereof, are preferably selected from bentonite attapulgite and sepiolite.

The thickeners and filtrate reducing agents which may be used in the fluid according to the invention are preferably organic polymers having a molecular weight of from 2,000 to 3,000,000, and in particular synthetic polymers (preferably selected from copolymers of vinyl acetate and maleic anhydride, polyacrylates, polyacrylamides and polyacrylonitriles), natural polymers (preferably selected from starch, carboxymethylcellulose, carboxymethyi-hydroxyethyl-cellulose and guar gum), and biopolymers (in particular xanthan gum). It is possible to use mixtures of polymers.

The fluidizers are preferably selected from tannines, alkali metal and alkaline earth metal polyphosphates, treated lignins, lignosulphonates, in particular of iron or chromium. It is possible to use mixtures of fluidizers.

The weight-increasing agents are preferably selected from baryte (BaSO4) limestone (CaCO3), haematite (Fe2O3), magnetite (Fe304) and siderite (FeCO3). These minerals can be pure or of technical grade.

It is possible to use mixtures of weight-increasing agents.

The clogging agents for circulation losses may be lamellar (such as cellophane, micra and vermiculite), granular (such as limestone, gilsonite, and almond shells), or fibrous (such as asbestos, straw and vegetable fiber), on the basis of requirements. It is possible to use mixtures of clogging agents.

The surfactants may be, according to requirements, anionic, cationic or non-ionic.

Tests carried out with the drilling fluid according to the invention show that it has the following advantages: (1) In Relation to Drilling: (a) the fluids, containing K2CO3 efficiently inhibit the swelling of plastic clays; (b) the greater content of potassium atoms per molecule allows a saving, relative to KCI of 7% by weight; (c) the hydrolysis pH (11 1) is such as to eliminate the need to use strong alkalies such as NaOH and KOH, necessary for the purpose of maintaining the alkalinity of the fluid containing KCI; (d) the presence of K2CO3 does not compromise the use of chemical fluid-correctives; (e) the drilling wastes require chemical and physical treatments to a reduced extent.

(2) In Relation to the Corrosion of Metallic Materials: (a) the corrosive effect of the fluids containing K203 is clearly lower not only than that of the KCI containing fluids as such, but also than that of the KCI containing systems treated with oxygen sequestering agents and corrosion inhibitors; (b) the high alkalinity of the fluids according to the invention is such as to control the possible entry of CO2 and of H2S.

(3) In Relation to Considerations of a Financial Character Market researches have shown that potassium carbonate costs about 60% more than KCI (710 to 750 Italian Lire/kg directly from the producer). However, looking on them as a whole, the fluids containing potassium carbonate appear to be cheaper, essentially because: (a) the high purity level of the industrial product (9100%) allows its consumption to be reduced; (b) NaOH and KOH need not be used; (c) expensive corrosion inhibitors need not be used; - (d) the drilling wastes can be submitted to chemical and physical treatments to a reduced extent (because they are free from chlorides).

The results shown hereunder for non-limitative purposes are rheological tests comparing a fluid according to the invention (K203 fluid) and a fluid containing KCI-fluid), and having the compositions given in the following Table 1 (wherein all percentages are based upon 100 g of H2O): TABLE 1

KCI-Fluid K2CO3-Fluid Bentonite 4% Bentonite 4% HV CMC 0.7% HV CMC 0.7% LVCMC 0.7% LVCMC 0.7% KOH 0.25% KOH Nil KCI 4% K2CO3 4% CMC=Carboxymethylcellulose LV= Low viscosity HV=High viscosity The following Table 2 gives an indication of the type of tests carried out, and a comment on the results obtained.

TABLE 2

Rheologioal Tests Comment At room temperature No substantial differences After ageing for 24 hours at 100 C No substantial differences After ageing for 24 hours at 1200C No substantial differences After ageing for 24 hours at 1500C No substantial differences After ageing for 24 hours at 170 C KCI-Fluids appear not to be any longer governable.

The behaviour of K2CO3 Fluids is good.

After contamination by i Slightly higher viscosities gypsum (2%) for K2CO3 Fluids. Higher gels for KCI-Fluids After contamination by KCI-Fluids appear to notably cement (0.5%) suffer from this type of contamination (higher viscosity, yield and gel).

K2CO3-Fluid after fluidization No substantial differences with and without NaOH j The system is fluidized as well in the absence of NaOH.

y increasing by means KCl-Fluids appear to suffer to of baryte: rheological tests a greater extent from the at room temperature solids content

Claims

CLAIMS 1.An aqueous drilling fluid comprising: (a) a clay in an amount of from 2 to 8% by weight; (b) a thickener or filtrate reducing agent in an amount of from 0.1 to 3% by weight; (c) optionally a fluidizer in an amount of from 0.05 to 2% by weight; (d) optionally a weight-increasing agent; (e) optionally a clogging agent in an amount of from 5 to 30% by weight; (f) optionally a surfactant in an amount of from 0.5 to 2% by weight; (g) water; and (h) potassium carbonate in an amount of from 1 to 10% by weight.
2. A fluid as claimed in Claim 1 wherein the clay is bentonite, attapulgite or sepiolite, or a mixture thereof.
3.Afluid as claimed in Claim 1 or 2,wherein the thickener is an organic polymer having a molecular weight of from 2,000 to 3,000,000.
4. A fluid as claimed in Claim 3, wherein the polymer is a synthetic polymer.
5. A fluid as claimed in Claim 4, wherein the synthetic polymer is a copolymer of vinyl acetate and maleic anhydride, a polyacrylate, a polyacrylamide, or a polyacrylonitrile, or a mixture thereof.
6. Afluid as claimed in Claim 3, wherein the polymer is a natural polymer.
7. A fluid as claimed in Claim 6, wherein the natural polymer is starch, carboxymethylcellulose, carboxymethyl-hydroxyethylcellulose or guar gum.
8. A fluid as claimed in Claim 3, wherein the polymer is a biopolymer.
9. A fluid as claimed in Claim 8, wherein the biopolymer is xanthan gum.
10. A fluid as claimed in any of Claims 1 to 9, wherein thefluidizer is a tannin, a polyphosphate of an alkaline metal, a treated lignin, or a lignosulphonate, in particular of iron or chromium.
11. A fluid as claimed in any of Claims 1 to 10, wherein the weight-increasing agent is baryte, limestone, haematite, magnetite or siderite.
12. Afluid as claimed in any of Claims 1 to 11, wherein the clogging agent for circulation loss is of lamellar character, and is cellophane, mica or vermiculite.
13. Afluid as claimed in any of Claims 1 to 11, wherein the clogging agent for circulation loss is of granular character, and is limestone, gilsonite or almond shells.
14. A fluid as claimed in any of Claims 1 to 11, wherein the clogging agent for circulation loss is of fibrous character, and is asbestos, straw or vegetable fiber.
15. A fluid as claimed in Claim 1, substantially as hereinbefore described.