WO2007135442A2

WO2007135442A2 - Cement composition containing aplite

Info

Publication number: WO2007135442A2
Application number: PCT/GB2007/001933
Authority: WO
Inventors: Rune GODØY; Hallvar Eide; Arild Saasen
Original assignee: Statoilhydro Asa; Cockbain, Julian
Priority date: 2006-05-24
Filing date: 2007-05-24
Publication date: 2007-11-29
Also published as: WO2007135442A3; GB0610338D0; GB2438398A

Abstract

The invention provides a settable cement or concrete composition comprising: an acid-settable aplite-based cement; at least one of (a) an aqueous acidic solution and (b) an acid in water-soluble form; and optionally an aggregate.

Description

Cement composition

This invention relates to improvements in and relating to cement and concrete, and in particular to cements and concretes which in use may be exposed to an acid environment, e.g. to combustion fumes (for example in tunnels and chimneys), to acid fluids leaching from a material adjacent to or contained by the cement or concrete, or to carbon dioxide being injected underground (for example to enhance hydrocarbon recovery), and to methods of well construction and permanent plugging and abandonment of wells, especially methods of construction and permanent plugging and abandonment of geothermal wells and wells for hydrocarbon extraction.

Cements and concrete are usually set by exposing the cement or concrete mixture to a base (i.e. to a pH above 7). Exposure to an acid environment, before or after setting, can lead to failure to set properly or to cement or concrete corrosion. Thus for example exposure of set Portland cements to carbon dioxide is known to lead to cement corrosion and cement or concrete porosification. The more porous the set cement (or concrete) is, the higher will be the corrosion rate and loss of zonal isolation.

However in many uses cements and concretes are exposed to acid environments, e.g. to oxide gases such as carbon, sulphur and nitrogen oxides or acidic fluids leaching from material adjacent to or contained by the cement or concrete.

While acid-resistant organic polymer based cements are known for small- scale (e.g. dental) use, there is a need for relatively inexpensive inorganic cement or concrete materials which are acid, or at least acid gas, resistant.

We have now surprisingly found that inorganic cements based on aplite and concretes made therewith (i.e. cement and aggregate admixtures) can be set by the use of acids rather than bases and thus offer the prospect of acid resistant cements and concretes.

Viewed from one aspect the invention thus provides a settable cement or concrete composition comprising: an acid-settable aplite-based cement; at least one of (a) an aqueous acidic solution and (b) an acid in water-soluble form; and optionally an aggregate.

Viewed from a further aspect the invention provides a method of producing a set cement or concrete comprising exposing an acid-settable aplite-based cement or an admixture thereof with an aggregate to an acidic aqueous solution whereby to set said cement or admixture.

Viewed from a still further aspect the invention provides an element, e.g. a container or building element, comprising an acid-set aplite-based cement or concrete.

Viewed from a yet still further aspect the invention provides a method of cement coating of a surface comprising applying to said surface a settable cement composition comprising an aplite-based cement and an aqueous acidic solution.

Viewed from a still further aspect the invention provides a method of generating a set cement in a subterranean bore hole, e.g. a water or hydrocarbon well, which method comprises introducing an aqueous, acid-settable aplite-based cement composition into said bore hole and if necessary subsequently introducing an acid in dissolved or water-soluble form.

Viewed from a still further aspect the invention provides an optionally sealed, fluid extraction or introduction well comprising a bore-hole having at at least one depth therein an annular, borehole well-lining comprising a set-cement produced using a pulverulent aplite and optionally carbon fibre containing acid-settable cement composition, e.g. a composition as described herein.

The cement compositions used according to the invention may contain aplite as the sole cement base or alternatively they may additionally contain at least one further cement base, preferably an inorganic cement such as Portland cement. Typically the aplite will constitute at least 82% wt. of the total cement content, preferably at least 84% wt., more preferably at least 85% wt., especially at least 90% wt., e.g. at least 95% wt.

Cement compositions containing aplite at at least 82% wt. relative to total cement composition, e.g. 83 to 99% wt., are also novel and form a further aspect of the present invention as does their use in the various ways described herein.

As mentioned above, one preferred use of the invention is in methods of well construction and permanent plugging and abandonment of wells, especially methods of construction and permanent plugging and abandonment of geothermal wells and wells for hydrocarbon extraction. When a well is constructed, after drilling has taken place, a cylindrical metal tube, the casing or liner, is placed in the borehole and the space between the outer wall of the tube and the inner wall of the borehole is filled with cement. In this way different zones are isolated and escape of fluid, e.g. water, gas or oil, along the well bore is prevented. Cement is also used for permanent plugging and abandonment of wells. Down hole cementing is described for example in "Well Cementing" edited by E.B. Nelson, Schlumberger Educational Services, Sugar Land, Texas, USA, 1990.

Carbon fibre may be added to the cement or concrete of the invention so as to affect several important properties thereof. The most essential of these properties are those related to the set cement, but also in the fluid state, carbon fibres in the cement may increase the ability of the cement to reduce fluid losses. Fluid loss is often a problem during well cementing operations, since the cement often has a higher density than the drilling fluid it displaces. The carbon fibres might in some cases bridge the small fractures causing the losses, and thus lessen the losses during the pumping operation.

More important are the properties of the set cement, since the carbon fibres will effect properties such as compressive strength, tensile strength and bond to casing/ formation. Compressive strength is important, but even more important is the increased tensile strength the carbon fibres will give the set cement. Temperature- and pressure-cycling in a well is especially critical, for the set cement, since it causes the casing/tube to expand/contract. This movement of the casing is known to cause the set cement to fail, causing poor zonal isolation along the wellbore. By using carbon fibres together with aplite in a well cement, the most critical mechanical properties can be controlled for optimum zonal isolation.

Suitable carbon fibres for use in the invention include those from Devoid AMT AS, N-6030 Langevag, Norway. Preferably the carbon fibres are between 0.1 cm and 10.0 cm in length, more preferably between 0.3 cm and 2.5 cm especially preferably between 0.5 cm and 1.0 cm. Preferred fibres have a diameter of between 1 μm and 15 μm, preferably between 3 μm and 10 μm, more especially between 6 μm and 8 μm, particularly 7 μm. The amount of fibre added per m³ of cement mix is preferably 0.1 kg to 10 kg, more preferably 0.3 kg to 7 kg, especially preferably 0.5 kg/m³ to 5 kg/m³.

The term well or bore hole as used herein means a well for extraction of fluids from below the earth's surface or for the subsurface injection of fluids. Typically such wells will be for water or hydrocarbon (e.g. gas or oil) extraction or for injection of water, carbon dioxide or hydrocarbon gas, especially for introduction of carbon dioxide.

^"By settable as used herein it is meant that the composition is capable of setting (e.g. setting down-hole following its application) either with or without intervention. Intervention in this regard might typically involve addition of an acid, an acid generating catalyst, or a pH modifier following placement of the cement composition. Where the intervention required involves addition of a further material, e.g. an acid or a pH modifier, the compositions are referred to herein as "non-self-settable".

Aplite is a granitoid mineral found for example in Montpelier, Virginia, USA, Owens Valley, California, USA and in Finnvolldalen in Norway as well as in Japan, Russia and Tuscany, Italy. Aplite is currently used almost exclusively as a flux in single-fired ceramic tile production. Aplite may be obtained commercially, e.g. from Maffei Natural Resources, Italy and the US Silica Company, West Virginia, USA. Typically aplite contains silicon, magnesium, iron, sodium, aluminium, potassium, titanium and calcium with the major components (expressed as oxide content) being silicon and aluminium, these generally being present at 60- 85% wt. and 10 to 25% wt. respectively.

The aplite used according to the present invention is preferably a high silicon content aplite, e.g. with a silicon content (expressed as oxide content) of at least 68% wt., more preferably at least 70% wt., especially at least 75% wt. The aplite from Finnvolldalen in Norway which has a silicon content (expressed as oxide content) of about 80% wt. is especially preferred.

The silicon content is expressed as an oxide content as it is standard geological practice to express elemental contents in this fashion. Thus for example the US Silica Company provides a typical chemical analysis for its aplite (from Montpelier) Of SiO₂ 62.0%, Fe₂O₃ 0.18%, Al₂O₃ 21.7%, TiO₂ 0.30%, CaO 5.6%, MgO 0.034%, Na₂O 5.5%, K₂O 2.9%, P₂O₅ 0.22% and LOI (loss on ignition) 0.1%.

The pulverulent aplite used according to the invention preferably has a particle size of less than 250 μm, more preferably less than 200 μm, e.g. 1 to 180 μm, more typically 10 to 150 μm, e.g. 50 to 100 μm, especially less than 75 μm- Particle size in this regard may be measured by screening or using particle size measuring apparatus. Where it is stated that the particle size is less than a certain value, then normally at least 50% volume will be that size or smaller, preferably at least 80% volume. Alternatively particle size may be taken to be mode particle size as measured by a particle size analyser, e.g. a Coulter particle size analyser. Coarse aplite may be transformed into finer grained aplite by conventional rock pulverizing techniques, optionally followed by screening to separate out oversized and/or undersized grains.

While aplite is a well understood geological term, it should be emphasized herein that other granitoid rocks having the same or similar acid-settable effect, may be used according to the invention in place of materials formally recognised as aplites and that such usage is considered to be according to the invention, although less preferred than the use of materials recognised as aplites.

In addition to aplite, other pulverulent silicates, e.g. silica, in particular silica flour, may also be used in the cement and concrete compositions according to the invention. Typically the weight ratio of non-aplite silicate to aplite will be in the range of 0:100 to 90:10, more particularly 2:98 to 70:30, especially 10:90 to 30:70.

In a preferred embodiment of the invention, the compositions herein described comprise an amount of pulverulent material (e.g. pulverulent aplite) having a particle size of less than 15 μm, preferably less than 10 μm. Typically, the production of such fine material is achieved by grinding coarser particles, preferably by grinding coarse aplite.

A further advantage of the cements of the present invention is the very low porosity and/or very low permeability of the resulting set cement compositions. Reduced permeability will reduce the invasion of any fluid or gas and will thus reduce the corrosion of the cement and the transfer of gas or fluid across the cement plug or wall. The water permeability of set Portland cement with slurry density of 1.90 SG is around 0.0010 mD (millidarcies), and increases as density is reduced. If reduced to 1.44 SG the water permeability increases to approximately 0.1380 mD. API Spec.10, section 11.4 describes how these permeability tests are performed and will be familiar to one of skill in the art.

The aplite-containing cements of the present invention have reduced permeability in comparison with non-aplite containing equivalents. For example, aplite in a Portland cement reduces the permeability over a Portland cement composition of equivalent density. This decreased permeability thereby reduces the invasion of any fluid or gas which will cause cement corrosion and/ or loss of zonal isolation.

Aplite content in the cement compositions of the invention is defined as a percentage by dry weight relative to the total cement composition, i.e. excluding other additives such as colorants, antimicrobials, organic polymers, fibres, (e.g. carbon fibres or inorganic fibres such as glass or "rock wool" fibres), etc. Such other additives, with the exception of additives significantly contributing to the structural (e.g. load-bearing) properties of the set cement, such as silica, will generally contribute no more than 10% wt. dsb to the total cement composition, typically less than 5% wt. Besides such additives, the cement composition may, as discussed above, comprise a further cement base, i.e. a material capable of setting to form a cement, more particularly an inorganic cement base. Cement bases, such as Portland cement, are well known and require no further description here. Cements are discussed for example in Lea, "The Chemistry of Cement and Concrete", 3rd Edition, Edward Arnold, Old Woking, UK, 1970, and Taylor, "Cement Chemistry", Academic Press, London, UK, 1990.

In a particular embodiment of the invention, blast furnace slag (BFS) may be used as part of the nόn-aplite cement base. The use of BFS in down-hole cementing applications is discussed for example by Saasen et al in SPE28821, a paper presented at' the European Petroleum Conference, London, UK, 25-27 October 1994.

The cement compositions of the invention may also be used for other cementing applications where acid resistant cement is desired, e.g. for plugging or filling crevices in rock or for the lining of other subterranean volumes such as storage volumes, pipes or tunnels. Such applications are also deemed to form part of the present invention. They may also be used for tunnel or chimney lining or construction or for the manufacture of containers, e.g. waste (in particular radioactive waste) containers, or building elements, e.g. bricks, blocks, tiles, slabs, conduits, channels, etc.

The cement and concrete compositions of the invention may be applied by procedures and equipment conventional in the art for settable cement and concrete compositions.

Where a concrete, rather than a cement is to be produced, an aggregate, e.g. sand, pebbles or rocks, may be incorporated, for example in conventional quantities. The use of aplite as the aggregate is especially preferred.

The acid used in setting the cements and concretes of the invention may be any strong or weak acid, e.g. a mineral acid such as hydrochloric acid or an organic acid such as a carboxylic acid, e.g. citric, malic, acetic, etc. acids.

In one preferred embodiment of the invention, the cement (or concrete) is formulated as a solid mix using a solid or encapsulated water-soluble acid, e.g. an acid encapsulated in a soluble polymer, for example a biopolymer such as gelatin. Alternatively an acid may be applied in fluid form, e.g. as a pure liquid acid or an aqueous solution. The acid may even be applied in gaseous form, e.g. by bubbling it through the cement or concrete composition.

Generally the acid will be used at a concentration or in an amount such that the pH of the aqueous phase of the cement or concrete composition is in the range 2 to 6.9, preferably 3 to 6, more preferably 4 to 5.

In certain instances, a neutral pH may be used to set high aplite-content cements and concretes and such use is also deemed to fall within the scope of the invention.

One particular advantage of the high aplite content elements of the invention is that by selection of the aplite particle size and the aplite content, the temperature reached within the cement during setting may be regulated, e.g. to keep it below 60°C in temperature sensitive environments or end-uses.

The products and processes of the invention will now be illustrated further with reference to the following non-limiting Examples. Example 1

Aplite-containiήg cement composition

A dry cement composition is prepared by mixing 23.5 parts by weight Class G

Portland cement (from Norcem) with 127.5 parts by weight pulverulent aplite

(drilling dusts of particle size 50 - 150 μm) from Finnvolldalen, Norway (content

SiO₂ 79.20%; MgO 0.11%; Fe₂O₃ 0.20%; Na₂O 3.0%; Al₂O₃ 11.10%; K₂O

3.90%; TiO₂ 0.02%; CaO 1.29%; P₂O₅ 0.1%).

To this is added 62.01 L/100kg fresh water, and optionally hydrochloric acid to bring the aqueous phase pH to below 6.

The mixture is cured under ambient conditions for 2 to 3 hours and then at 40°C for 8 hours.

Example 2

Aplite-only cement composition

A cement composition was prepared according to Example 1 by adding fresh water to Class G aplite of particle size 10-75μm (achieved by crushing and sieving). pH was adjusted to 4-5 using hydrochloric acid and the composition was allowed to set for 24 hours at 15O⁰C.

Compressive strength, measured in an ultrasonic cement analyser, at 3000 psi and 15O⁰C (according to the API Recommended Practice for Testing Well Cements, 22nd Edition, 1997) was as set out in Table 1 below:

Table 1

Claims

Claims:

1. A settable cement or concrete composition comprising: an acid-settable aplite-based cement; at least one of (a) an aqueous acidic solution and (b) an acid in water-soluble form; and optionally an aggregate.

2. A composition as claimed in claim 1 wherein said aplite-based cement contains aplite as at least 80% wt of the total amount.

3. A composition as claimed in claim 2 1 wherein said aplite-based cement contains aplite as at least 90% wt of the total cement.

4. A composition as claimed in any one of claims 1 to 3 wherein the aplite has a particle size of less than 250 μm.

5. A composition as claimed in any one of claims 1 to 4 further containing carbon-fibre.

6. A method of producing a set cement or concrete comprising exposing an acid-settable aplite-based cement or an admixture thereof with an aggregate to an acidic aqueous solution whereby to set said cement or admixture.

7. A method as claimed in claim 6 wherein said cement or admixture comprises aplite as defined in any one of claims 2 to 4.

8. An element comprising an acid-set aplite-based cement or concrete.

9. A method of cement coating of a surface comprising applying to said surface a settable cement composition comprising an aplite-based cement and an aqueous acidic solution.

10. A method of generating a set cement in a subterranean bore hole, which method comprises introducing an aqueous, acid-settable aplite-based cement composition into said bore hole and if necessary subsequently introducing an acid in dissolved or water-soluble form.

11. An optionally sealed, fluid extraction or introduction well comprising a borehole having at at least one depth therein an annular, borehole well-lining comprising a set-cement produced using a pulverulent aplite and optionally carbon fibre containing acid-settable cement composition.

12. A cement composition containing at least 82% wt. aplite relative to total cement forming components.