NO342894B1 - Cementing, aplite-based geopolymer material and method for providing a pumpable, curable slab of a cementing, aplite-based geopolymer material - Google Patents

Abstract

A cementitious aplite-based geopolymer material is disclosed in which a mixture of fine-grained aplite and an alkaline medium concentration including an alkali solution and an alkali silicate solution forms a curable swell. There is also disclosed a method of providing a curable slurry of a cementing, aplite-based geopolymer material, the method comprising the steps of: - providing a fine-grained aplite; - adding a concentration of an alkali solution and an alkali silicate solution to a liquid / solid weight ratio in the range of 0.40-0.50.

Description

CEMENTING APLIT-BASED GEOPOLYMER MATERIAL AND METHOD OF PROVIDING A PUMPABLE, CURING Slurry OF A CEMENTING APLIT-BASED GEOPOLYMER MATERIAL

The invention relates to a cementing, aplite-based geopolymer material and a method for providing a pumpable, hardenable slurry of a cementing, aplite-based geopolymer material.

In general, a distinction can be made between two different types of cement: "hydraulic" cements, such as e.g. portland cements, and "geopolymer" cements.

Since the development of Portland cement, this has become the most common building material. Portland cement is also a widely used material in the petroleum industry for sealing the annular space between feed pipes and for zone insulation. However, there are some disadvantages when it comes to the chemical-physical properties of hardened portland cement and the emission of greenhouse gases in the process of its production.

Production of portland cement contributes between 5 and 7% of the global emission of carbon dioxide (CO2), as approx. 900 kg of CO2 is emitted for the production of one tonne of portland cement. CO2 emissions from the manufacture of portland cement are attributed to:

(i) the formation and release of CO2 due to the breakdown of limestone (a key ingredient); and (ii) high energy consumption when calcining raw materials in an incinerator. Furthermore, chemical shrinkage and autogenous shrinkage, possible gas inflow (permeability), long-term durability, and instability in corrosive environments and at high temperatures are also some disadvantages, which motivate researchers to look for alternatives to Portland cement. Several alternative binders have been identified: calcium aluminate cement, calcium sulphoaluminate cement, supersulphated cement and alkali-activated binders.

Alkali-activated binders are receiving increasing attention as an alternative to Portland cement due to their sufficient strength, durability and low environmental impact. Unlike Portland cement, the source of alkali-activated binders can be waste stream materials used with very limited further processing. Alkali-activated binders are developed by mixing an alkaline activator, which can be an alkaline solution or mixture of an alkaline solution and alkaline silicate solution, with a source of aluminosilicate material, such as fly ash, kaolin, metakaolin, smelter slag, etc. In short, the hydroxyl group (OH-) penetrates the original structure of the aluminosilicate material and depolymerizes the silicates. As a result of alkalization, monomers of silicon tetrahedra and aluminum tetrahedra form covalently bound oligomers. Oligomers are rearrangements of a gel-forming, solidified polycondensation network. Broadly speaking, depolymerisation, transport or orientation and polycondensation are three main mechanisms in the development of alkali-activated binders. The reaction product is an inorganic material, which has been named "geopolymer".

Extensive research has been carried out to investigate the possibility of using artificial pozzolans or industrial waste materials of the aluminosilicate type, such as e.g. fly ash, kaolin, etc. In contrast, little work has been done to investigate the utilization of natural pozzolan or aluminosilicate rock as a source material in geopolymerization. Kawano and Tomita (Kawano M., Tomita K.: "Experimental study on the formation of zeolites from obsidian by interaction with NaOH and KOH solutions at 150 and 200 °C." Journal of Clay and clay minerals 45 (1997) 3, p .365-377) investigated the synthesis of zeolites from obsidian at different concentrations of NaOH and KOH solutions at 150 and 200 °C. Their findings show that smectite, phillipsite, and rhodesite were formed in NaOH solution as pH increased, and smectite, merlinoite, and sanidine resulted in KOH solution as pH increased. The reaction solution's pH value, Si/Al and Na/K ratio are stated to be important factors that determine the character of the products formed from obsidian.

Allahverdi et al. (Allahverdi A., Mehrpour K., Najafi Kani E.: "Taftan pozzolan-based geopolymer cement." IUST International Journal of Engineering Science volume 19, no.3, 2008, p.1-5) used a natural pumice-type pozzolan , obtained from Taftan Mountain in southeast Iran, to develop a Taftan-based geopolymer. The natural pumice-type pozzolan has a relatively high silicon content. A mixture of NaOH and Na2OSiO2 was used as an activator in their investigation. Their X-ray diffraction study shows that the Taftan pozzolan had four crystalline mineral phases: quartz, hornblende, anorthite and biotite. Biotite and amorphous part of Taftan pozzolan participated in the reaction, while quartz, hornblende and anorthite were not reactive. Based on their results, the final solidification times were relatively long for all their systems due to the high liquid/solid ratio of 0.44.

From Simonsen, E.: "Strength development of aplite-based geopolymer cements", master's thesis Faculty of Science, University of Stavanger, 2013, aplite-based polymers mixed with 8 M NaOH activation solution and hardening of the mixture are known. High viscosity makes it impossible to pump the aplite-based polymer. Compressive strengths of 5000 psi and more were achieved.

The purpose of the invention is to remedy or reduce at least one of the disadvantages of known technology, or at least to provide a useful alternative to known technology.

The purpose is achieved through features indicated in the description below and in the subsequent patent claims.

Geopolymers are one of those materials whose chemical-physical properties and richness have attracted much attention in recent times. Geopolymer cements are produced by a mineral polycondensation reaction in an alkaline medium. If geopolymers (reactive aluminosilicate materials) are mixed with suitable additives under suitable temperature and pressure, they solidify, and the final product can withstand high pressures, temperatures and corrosive environments for a long time.

Geopolymers are used as an alternative to cement and replacement binder in concrete. The term "geopolymers" was coined by Davidovits to describe inorganic binders having the empirical formula Mn{-(SiO2)z– AlO2}٠ωH2O, where M is a cation (K<+>, Na<+>, Li<+> , or Ca<2+>), n is a degree of polycondensation, and z is the atomic ratio of Si/Al which can be 1, 2, 3 or higher. In other words, geopolymers are aluminum silicate minerals that react in alkaline solution. The reaction shows a complex process, but it could be said that in an alkaline medium the Si-O-Si bonds are broken and Al atoms penetrate into the original Si-O-Si structure; mostly aluminosilicate gels are formed in the process. Cations must be present in the framework cavities to balance the ions' negative charges (J. Davidovits: "Geopolymer chemistry & applications", 3rd edition, July 2011, pp.3-5, 228-230, 365-371, 375-386. F. Skvara: "Alkali activated materials or geopolymers?" Institute of Chemical Technology Prague, May 2007. H. Xu: "Geopolymerisation of alumino-silicate minerals." PhD thesis, University of Melbourne, April 2002). The process is called "geopolymerisation", and the result is a cementing phase with high mechanical strength, high resistance to fire and acid and bacteria. In addition, geopolymers are characterized by a number of physical properties, including thermal stability, high surface smoothness, hard surface, long durability and strong adhesion to natural stone and steel (Davidovits, 2011. Xu, 2002). Geopolymerization development depends on many parameters, including chemical and mineralogical composition, particle size and surface area, curing temperature and pressure, alkali cation type, Si/Al ratio in the substances used, activator/solid ratio, and types of additives (E. I. Diaz, E. N. Allouche, S . Eklund: "Factors affecting the suitability of fly ash as source material for geopolymers" Elsevier, Fuel, year 89, 2010, pp.992-996. D. L. Y. Kong, J. G. Sanjayan, K. Sagoe-Crentsil: "Factors affecting the performance of metakaolin geopolymers exposed to elevated temperatures." Journal of Materials Science, volume 43, 2008, pp.824-831. J. Nemecek, V. Smilauer, L. Kopecky: "Nanoindentation characteristics of alkali-activated aluminosilicate materials." Elsevier, Cement & Concrete Composites, volume 33, 2011, pp.163-170. D. Ravikumar, S. Peethamparan, N. Neithalath: "Structure and strength of NaOH activated concretes containing fly ash or GGBFS as the sole binder." Elsevier , Cement & Concrete Composites, Volume 32, 2010, pp.399-410. J. Stark: "Recent advances in the field of cement hydration and microstructure analysis." Elsevier, Cement & Concrete Research, volume 41, 2011, pp.666-678).

There are different types of geopolymers depending on the source used, e.g. kaolinite-based, metakaolin-based, fly ash-based, phosphate-based, etc.

Aplite is an intrusive rock where quartz, alkali feldspar, microcline and albite are the dominant constituents. Oligoclase, muscovite, apatite and zircon are mainly minerals of aplite. Biotite and all ferromagnesium-bearing minerals rarely occur in aplites. Aplitt members are usually rich in Na. Aplites contain SiO2 and Al2O3, making them similar to pozzolans, and they seem to have the potential to be used in the development of an aplite-based geopolymer cement.

The present invention introduces a new geopolymer material which can be called an aplite-based geopolymer and is manufactured for cementing applications in oil fields, such as sealing annulus between casing, sealing an annulus between an extension pipe and a formation, zone isolation, temporary and permanent plugging, and squeeze operations -operations). Aplite is mixed with additives and an alkali activator to produce a geopolymer slurry. The additives are blast furnace slag (BFS = Blast Furnace Slag) and microsilica. The alkali activator is produced by mixing different concentrations of alkali solution and alkali silicate solution. Several tests have been carried out using an aplite to obtain an aplite-based geopolymer binder and an aplite-based geopolymer cement. The aplite-based geopolymer solidifies at 25-200 °C under ambient pressure and high pressure.

The main purpose is to create a cementing material that has high enough compressive strength to withstand some degree of tectonic stress. The product should be impermeable, shrink-proof, withstand corrosive environments and bind to stone and feeding pipes. Several tests were carried out to determine the effect of different additives on the rheological and physical properties of the gruel and the final product after solidification. Uniaxial compressive strength measurements (Uniaxial Compressive Strength (UCS) measurements) have been carried out to determine the development of compressive strength over time. Finally, sets of sensitivity analysis tests have been carried out to find the influence of alkali concentration, liquid/solid ratio, curing temperature and pressure on the chemical-physical property of the developed aplite-based geopolymers.

Little research has been done on the reactivity of natural stone for the production of geopolymer binder and geopolymer cement in an alkaline medium as opposed to an acidic medium. It could be as a result of the lower solubility of natural stones in an alkaline medium than in an acidic medium (J. A. Chermak: "Low temperature experimental investigation of the effect of high pH NaOH solutions on the opalinus shale, Switzerland". Clay and clay minerals, year 40 , no.6, 1992, pp.650-658. Davidovits, 2011). M. Kawano, K. Tomita (see above) reported: smectite, phillipsite, and rhodesite were formed in NaOH solution as pH increased, and smectite, merlinoite, and sanidine were produced in KOH solution as pH increased. They also mentioned that the pH value, Si/Al and Na/K ratio in the reaction solution are important factors that determine the character of the products made from obsidian.

Gougazeh, M., Buhl, J.-C.: "Synthesis and characterization of zeolite A by hydrothermal transformation of natural Jordanian kaolin". Journal of the Association of Arab Universities for Basic and Applied Sciences (2013), http://dx.doi.org/10.1016/j.jaubas.2013.03.007 synthesized zeolite A through treatment of the activated metakaolin from natural kaolin with different concentrations of NaOH at 100 °C. Their obtained results show that zeolite A is the major subphase, and quartz and hydroxysodalite were the minor constituents.

The invention is indicated by the independent patent claims. The independent claims indicate advantageous embodiments of the invention.

In a first aspect, the invention specifically relates to a cementing, aplite-based geopolymer material comprising a mixture of fine-grained aplite with a particle size of up to 75 μm and an alkaline medium concentration including an alkali solution comprising NaOH in the range 6M-10M and/or KOH in the range 4M-8M, characterized in that the mixture further comprises an alkali silicate solution comprising Na2SiO3 or K2SiO3; and the mixture's liquid/solid weight ratio is in the range 0.42-0.47; thereby forming a pumpable and hardenable gruel.

The alkali solution may comprise NaOH in the range 7M-9M.

The alkali solution may comprise KOH in the range 5M-7M.

In a second aspect, the invention specifically relates to a method for providing a pumpable, hardenable slurry of a cementing, aplite-based geopolymer material, characterized in that the method comprises the steps:

- to provide a fine-grained aplite with a particle size of up to 75 μm;

- to add a concentration of an alkali solution comprising NaOH in the range 6M-10M and/or KOH in the range 4M-8M, and an alkali silicate solution to a liquid/solid weight ratio in the range 0.42-0.47, the alkali silicate solution comprising Na2SiO3 or K2SiO3, thereby forming the pumpable and hardenable gruel.

The invention offers several advantages over prior art:

● High pressure / high temperature conditions (up to 8000 psi (approx.55 MPa) and 700 °C) ● Low mass shrinkage factor (less than 4%)

● Withstand corrosive environments

● Low permeability and better suited for gas reservoirs (less than 20 micron Darcy) ● There are retarders, accelerators and viscosity regulating additives

● The same equipment as that used in cementing operations, for placing the slurry at the desired depth.

Experimental part

Materials

Table 1 shows in tabular form the chemical composition of crushed aplite which was supplied by HELI Utvikling AS, Namsskogan. Fig.1 shows the particle size distribution analysis for the aplite used. Elkem microsilica quality 955 was supplied by Elkem AS, Oslo. Blast furnace slag (BFS) was manufactured in Sweden and supplied by SSAB Merox AB, Oxelösund, Sweden, under the trademark Merit 5000. Sodium hydroxide (NaOH) and potassium hydroxide (KOH) came as pellets with 99% purity supplied by Merck KGaA, Darmstadt, Germany. Sodium silicate solution (Na2SiO3) was supplied by Merck. The chemical composition of Na2SiO3 was: 28.5% SiO2, 8.5% Na2O and 63% H2O. The calcium silicate solution (K2SiO3) used was supplied by Univar AS, Oslo. Potassium silicate solution was stated to have 38% K2SiO3 and 62% H2O. Distilled water was used throughout the experiments.

Table 1

The chemical composition of the original aplite

Preparation of samples

Sodium hydroxide solutions were prepared in three different concentrations of 6, 8 and 10 M NaOH. Potassium hydroxide solutions were prepared in concentrations of 4 and 6 M. Activators were prepared with different proportions as Table 2 summarizes the alkali solution/alkali silicate ratio. It is recommended to prepare the activator one day before to get the ingredients evenly mixed. Liquid-solid mixture should be observed to obtain the most effective product. First, microsilica should be added to the activator and mixed for 2 minutes. Aplit was then added and mixed for 2 minutes. Later BFS was added and mixed. Liquid and solid phases were mixed using a Hamilton-Beach mixer. Porridges were cast in cylindrical plastic molds with dimensions of 5.2 cm in diameter and 10 cm in length. Table 3 shows the various prescriptions that have shown the excellent results. Samples were cured at ambient pressure and temperature for 7 and 28 days in a plastic box filled with tap water. Please note that samples will be able to harden outside the plastic box.

Table 2

Table 3

Analytical methods

In order to investigate the mechanical properties of the developed aplite-based geopolymer cement, the compressive strength development of geopolymers has been calculated. The compressive strengths of the samples were measured using a Toni Technik-H mechanical tester. The device uses a test software TestXpert v7.11 to assess the uniaxial compressive strength.

A Zeiss Supra 35VP scanning electron microscope analyzer was used to reveal the microstructure of the aplite-based geopolymers.

Particle size distributions (PSD) for aplite were calculated with a Sympatec HELOS laser diffraction particle size analyzer, and the experiment was carried out at the Tel-Tek National Research Institute in Norway. Sauter mean diameter (SMD) and volume mean diameter (VMD) were reported as 3.20 and 19.68 μm, respectively. Aplite's density was calculated to be 1.18 (g/cm<3>).

Results and discussion

Effect of curing time

Different samples were prepared and cured for 7, 28 and 56 days. Measured compressive strength of the samples showed strength development with time after 56 days.

X-ray diffraction (XRD) analysis

X-ray powder diffraction (XRD) analysis of the aplite and the prepared geopolymers was performed using 0.6888Å wavelength synchrotron radiation. The XRD measurements were performed with a PILA-TUS2M-based diffractometer at the European Synchrotron Radiation Facility (ESRF). The angular range was 0-46, 2theta.

The obtained result shows that the aplite and the aplite-based geopolymers are crystalline.

Permeability measurement

A QX series of Quizix pump manufactured by AMETEK Chandler Engineering was used for permeability measurement.

Injection pressure of 210 bar (3045 psi) was chosen based on permeability measurement experience. Cover pressure chosen to be 240 bar (3480 psi) and pump pressure limit set at 210 bar (3045 psi). Distilled water used for injection. Outlet pressure was chosen to be ambient pressure. The experiment was carried out at ambient pressure. Measured permeability after 30 days of testing is k = 0.07 x 10<-7>mD, which can be considered to be 0 compared to portland cement permeability.

Conclusion

Some samples were cured at 87 °C for 28 days and calculated compressive strength was 517 bar (7500 psi) and in some cases 597 bar (8660 psi).

Aplite-based geopolymers were cured at 500 °C for 12 h and no change in their mechanical properties was observed.

Due to the low CaO content (20%), the aplite-based geopolymers can resist carbon dioxide attack.

Mass shrinkage has been measured and a value of less than 4% was measured, and in some cases it was 0.0%.

During manufacture, the aplite-based geopolymer does not emit greenhouse gases; it can be called an environmentally friendly cementing material.

Sodium hydroxide concentration can vary between 6 and 10 M and even higher.

Potassium hydroxide concentration can vary between 4 and 8 M.

The ratio alkali solution/alkaline silicate solution can vary between 0.3 and 1.

List of illustrations:

Fig.1 Particle size distribution (PSD) analysis of the aplite used;

Fig.2a Calculated compressive strength for the aplite-based geopolymer with an alkali solution comprising NaOH after 7 and 28 days;

Fig.2b Calculated compressive strength for the aplite-based geopolymer with an alkali solution comprising KOH after 7 and 28 days.

Claims (4)

Patent claims 1. Cementitious, aplite-based geopolymer material comprising a mixture of fine-grained aplite with a particle size of up to 75 μm and an alkaline medium concentration including an alkali solution comprising NaOH in the range 6M-10M and/or KOH in the range 4M-8M, characterized in that the mixture further comprises: an alkali silicate solution comprising Na 2 SiO 3 or K 2 SiO 3 ; and the mixture's liquid/solid weight ratio is in the range 0.42-0.47; thereby forming a pumpable and hardenable gruel. 2. Cementing, aplite-based geopolymer material according to claim 1, where the alkali solution comprises NaOH in the range 7M-9M. 3. Cementing, aplite-based geopolymer material according to claim 1, where the alkali solution comprises KOH in the range 5M-7M. 4. Method for providing a pumpable, hardenable slurry of a cementing, aplite-based geopolymer material, characterized in that the method comprises the steps: - to provide a fine-grained aplite with a particle size of up to 75 μm; - to add a concentration of an alkali solution comprising NaOH in the range 6M-10M and/or KOH in the range 4M-8M, and an alkali silicate solution to a liquid/solid weight ratio in the range 0.42-0.47, the alkali silicate solution comprising Na2SiO3 or K2SiO3 , thereby forming the pumpable and hardenable gruel.