WO2019156547A1

WO2019156547A1 - Pumpable geopolymer cement

Info

Publication number: WO2019156547A1
Application number: PCT/MY2018/050004
Authority: WO
Inventors: Siti Humairah ABD RAHMAN
Original assignee: Petroliam Nasional Berhad
Priority date: 2018-02-07
Filing date: 2018-02-07
Publication date: 2019-08-15
Also published as: MY194344A; US20210087457A1; AU2018407466A1; EP3749732A4; EP3749732A1; US11453815B2

Abstract

This invention relates to an adaptable Geopolymer cement composition for application in oil and gas wells having a wide range of downhole temperatures. The base Geopolymer cement composition has an acceptable rheology of below 200cP and can be tailored by the inclusion of various chemicals to control properties such as thickening time over a wide range of temperatures and densities. The disclosed Geopolymer cement composition is pumpable, mixable and stable. The composition can also be adapted to have expandable and swellable properties.

Description

Pumpable Geopolymer Cement

Field of Invention

The present invention covers the pumpable geopolymer cement composition and its application as a well cement in a wide range of downhole condition and densities.

Background

The listing or discussion of a prior-published document in this specification should not necessarily be taken as an acknowledgement that the document is part of the state of the art or is common general knowledge.

Oil and gas well cements are used to fill and seal the annulus between the casing string and the drilled hole. A casing string is a long section of connected oilfield pipe that is lowered into a wellbore and is then cemented into place by a cement column.

Oil and gas well cement is considerably different to the cement used in construction industry because it has to work in an environment with varied temperatures and pressures. Various types of Ordinary Portland Cement (OPC) are used in the oil industry and these types are classified according to the downhole temperature and pressure that they solidify at. However, OPC has weaknesses associated with strength development under HPHT conditions and this may significantly reduce the strength of the cement, which can lead to failure of the integrity of the cement. In addition, the use of OPC leads to significant amounts of carbon dioxide being released. Thus, there is a need for a more environmentally-friendly material that also overcomes the drawbacks of OPC.

A potential alternative to OPC is to find a suitable geopolymer cement. Geopolymer cements are a low calcium, alkali-activated aluminosilicate cement which is obtained through geopolymerization (i.e. the reaction of aluminosilicates with an aqueous alkaline solution to provide a new class of inorganic binder). Test experiments have indicated that fly ash based geopolymer cement has excellent compressive strength and good acid resistance at atmospheric pressure and temperature. However, the geopolymer cements developed so far do not show a useful rheological properties that would allow it to be pumpable, nor do these materials provide a base formulation that can be readily manipulated to accomodate accommodate various well conditions. Thus, there remains a need for new and improved geopolymenr cements that can solve some or all of these problems.

Summary of Invention

In a first aspect of the invention, there is provided a pumpable geopolymer cement composition comprising:

an aluminosilicate source material;

an alkaline solution comprising a carrier fluid, an alkaline activator material and a silicate material, wherein, the weight:weight ratio of the alkaline solutio aluminosilicate source material is from 0.1 to 2:1 , and the weight:weight ratio of the silicate material: alkaline solution is from 0.15 to 1 :1 (e.g. from 0.25 to 0.4:1).

In embodiments of the first aspect of the invention:

(a) the aluminosilicate source material may be fly ash type F, optionally wherein the fly ash type F has a calcium content of less than 10 wt%;

(b) the alkaline solution may comprise an alkaline activator material at a concentration of from 8 M to 12 M;

(c) the alkaline activator material may be sodium hydroxide and/or potassium hydroxide;

(e) the silicate may be selected from a sodium silicate;

(f) the composition may have a specific gravity of from 1 .40 g/cm³ to 1 .91 g/cm³;

(g) the composition may further comprise a weighting agent selected from one or more of the group consisting of barium sulfate, iron oxide, manganese tetroxide, where the weighting agent is present in an amount of from 30 to 75 wt% (e.g. 55 to 65 wt%) relative to the total weight of aluminosilicate source material in the composition (in certain embodiments, when a weighting agent is used, the composition may have a specific gravity of from 1.92 g/cm³ to 2.99 g/cm³);

(i) the composition may further comprise a lightweight material selected from one or more of the group consisting of silica-alumina microspheres, cenosphere, sodium-calcium- borosilicate in an amount of from 50 to 100 wt% relative to the total weight of aluminosilicate source material in the composition (in certain embodiments, when a lightweight material is used, the composition may have a specific gravity of from 1 .21 g/cm³ to 1 .55 g/cm³);

(j) the composition may further comprise one or more of a defoamer (e.g. a polydimethylsilicone), a fluid loss controller (e.g. hydroxyethylcellulose and/or 2-acrylamido- 2-methylpropane sulfonic acid) and a dispersant (e.g. a polyethylene sulfonate), where each, when present, is provided in a concentration of from 0.001 kg/L to 0.3 kg/L relative to the total volume of the composition;

(k) the composition may further comprise a retarder material at a concentration of from 0.001 kg/L to 0.3 kg/L relative to the total volume of the composition (e.g. the retarder material may be lignosulfonate);

(L) the composition may further comprises a retarder material in an amount of from 5 to 60 wt% relative to the total weight of aluminosilicate source material in the composition (e.g. the retarder material may be a sugar or a sugar-substitute material);

(m) the composition may further comprise a fast set material in an amount of from 25 to 45 wt% relative to the total weight of aluminosilicate source material in the composition, optionally wherein the composition may further comprise ground blast furnace slag;

(n) the composition may further comprise an expanding material in an amount of from 2 to 10 wt% relative to the total weight of aluminosilicate source material in the composition, optionally wherein the expanding material provides the geopolymer cement composition with a linear expansion of from 0.01 % to 2.5% (e.g. the expanding material may be magnesium oxide);

(o) the composition may further comprise a swellable material in an amount of from 10 to 60 wt% relative to the total weight of aluminosilicate source material in the composition, optionally wherein the swellable material provides the geopolymer cement composition with a linear expansion of from 0.1 % to 2% (e.g. the swellable material is butyl polystyrene).

In a second aspect of the invention, there is provided a method of forming a pumpable geopolymer cement formulation comprising the steps of:

(a) mixing a carrier fluid with an alkaline activator material to form a mixture;

(b) adding a silicate material to the mixture of step (a) and mixing to form a mixture;

(c) adding an aluminosilicate material to the mixture of step (b) and mixing; and In embodiments of the second aspect of the invention,

(i) the aluminosilicate source material may be fly ash type F, optionally wherein the fly ash type F has a calcium content of less than 10 wt%;

(ii) the alkaline activator material may be added in amount to the alkaline activator material to provide a concentration of from 8 M to 12 M;

(iii) the alkaline activator material may be sodium hydroxide or potassium hydroxide;

(iv) the silicate may be selected from a sodium silicate; (v) one or more of a defoamer (e.g. polydimethylsilicone), a fluid loss controller (e.g. hydroxyethylcellulose and/or 2-acrylamido-2-methylpropane sulfonic acid) and a dispersant (e.g. polyethylene sulfonate) may be added and mixed into the mixture of step (a) or step (b) and the resulting mixture is then used in the subsequent step, where each of the defoamer, fluid loss controller and dispersant, when present, is provided in a concentration of from 0.001 kg/L to 0.1 kg/L relative to the total volume of the composition; and/or

a retarder material is added and mixed into the mixture of step (a) or step (b) of Claim 23 and the resulting mixture is then used in the subsequent step, where the retarder material is:

(I) provided in a concentration of from 0.001 kg/L to 0.3 kg/L relative to the total volume of the composition, optionally wherein the retarder material is lignosulfonate; or

(II) provided in an amount of from 5 to 60 wt% relative to the total weight of aluminosilicate source material in the composition, optionally wherein the retarder material is a sugar or a sugar-substitute material;

(vi) the mixing may be conducted in line with the API RP10B-2 mixing procedure.

Drawings

Figures 1 to 5 depict the thickening times of samples A1 to A5, respectively as measured using Bearden units.

Figure 6 depicts the linear expansion of samples A9 to A1 1 according to the current invention.

Description

It has been surprisingly found that a specific combination of an aluminosilicate material and an alkaline solution in controlled ratios can provide a suitable geopolymer cement base solution that is easily modified to suit a broad range of down-well conditions, while remaining pumpable. Thus, there is provided a pumpable geopolymer cement composition comprising:

an aluminosilicate source material;

an alkaline solution comprising a carrier fluid, an alkaline activator material and a silicate material, wherein, the weighbweight ratio of the alkaline solutio aluminosilicate source material is from 0.1 to 2:1 , and the weighbweight ratio of the silicate material: alkaline solution is from 0.15 to 1 :1 (e.g. 0.25 to 0.4:1). In embodiments herein, the word“comprising” may be interpreted as requiring the features mentioned, but not limiting the presence of other features. Alternatively, the word “comprising” may also relate to the situation where only the components/features listed are intended to be present (e.g. the word“comprising” may be replaced by the phrases“consists of or“consists essentially of). It is explicitly contemplated that both the broader and narrower interpretations can be applied to all aspects and embodiments of the present invention. In other words, the word“comprising” and synonyms thereof may be replaced by the phrase“consisting of” or the phrase“consists essentially of or synonyms thereof and vice versa.

When used herein“pumpable” as it applies to the geopolymer cement composition means that the composition once formed has a viscosity less than or equal to 300 centipoise (cP) (e.g. less than or equal to 250 cP, such as less than or equal to 200 cP) until it reaches the targeted top of the cement column in the annulus within the desired pumping time.

The aluminosilicate source may be selected from ASTM Class F Fly Ash with a calcium component of less than 10% by weight. When used herein, the term“carrier fluid” means fresh water, a brine solution or a combination of both.

The alkaline activator material may be sodium hydroxide, potassium hydroxide or a combination of both, with the molarity being from 8 molar to 12 molar to ensure the pumpability of geopolymer cement. The optimum molarity for better mixability of the geopolymer cement composition is 8 molar. This is because the viscosity of the resulting geopolymer cement composition increases when the molarity of the alkaline material is increased, which may affect the mixability and stability of the pumpable geopolymer cement composition.

The other essential component of the geopolymer cement composition is a silicate. A suitable class of silicate that may be mentioned herein are the sodium silicates, which are compounds with the formula (Na₂Si0₂)_n0. A well-known member of this series is sodium metasilicate, Na₂Si0₃. It is noted that the weighfweight ratio of the silicate material: alkaline solution is from 0.15 to 1 :1 (e.g. from 0.25 to 0.4:1 or any combination of said numbers, such as from 0.15 to 0.25:1 , from 0.25 to 1 :1 , from 0.15 to 0.4:1 , or from 0.4. to 1 :1). It is noted that a lower ratio of silicate results in too low a compressive strength, while a higher ratio does not further improve the compressive strength of the geopolymer cement. The base geopolymer composition comprising the aluminosilicate and alkaline solution (which in turn comprises a carrier fluid, an alkaline activator material and a silicate material) may be provided as a slurry having a specific gravity of suspension of from between 1 .40 g/cm³ (12.5 Ib/gal) to 1 .91 g/cm³ (15.9 Ib/gal). This specific gravity may be increased or decreased by the addition of specific additives.

To increase the specific gravity of the slurry suspension, a heavy weight material (e.g. a weighting agent, such as barium sulfate, iron oxide, manganese tetraoxide or combinations thereof) may be blended with the aluminosilicate source material at a concentration of from 55% to 65%, relative to the total weight of aluminosilicate source material in the composition. The use of such a concentration of these materials may result in a more dense composition, having a specific gravity of suspension of from 1 .92 g/cm3 (16 Ib/gal) to 2.99 g/cm3 (25 Ib/gal).

To decrease the specific gravity of the slurry suspension a light weight material (e.g. silica- alumina microspheres, cenosphere, sodium-calcium-borosilicate and the like) may be blended with the aluminosilicate source material at a ratio (lightweight material: aluminosilicate source material) of from 0.5:1 to 1 :1 . The use of such an amount of these materials may result in a less dense composition, having a specific gravity of suspension of from 1 .21 g/cm3 (10 Ib/gal) to 1 .55 g/cm3 (12.9 Ib/gal).

One of the most important properties of a well cement is the ability for it to remain pumpable at any selected wellbore circulating temperature. One of the ways to accomplish this is to add a retarding agent, or retarding material, to the composition, which acts to control the hardening time or the setting/thickening time of the composition. The retarding material may be added in any suitable amount to the composition described above. For example, the retarding material be added to the composition at a concentration of from 0.001 kg/L to 0.3 kg/L relative to the total volume of the composition, or it may be added in an amount of from 5 to 60 wt% relative to the total weight of aluminosilicate source material in the composition.

It will be appreciated that specific retarding materials may be more suited to certain downhole temperatures. For example, the retarding material lignosulfonate may be particularly suited to use (e.g. at a concentration of from 0.001 kg/L to 0.3 kg/L relative to the total volume of the composition) at a downhole temperature of from 30 to 85°C. When the downhole temperature is from 85 to 250°C, the retarding material may be selected from a sugar or a sugar-substitute material (e.g. in an amount of from 5 to 60 wt% relative to the total weight of aluminosilicate source material in the composition). A sugar or sugar substitute retarder is able to increase the hardening time of the geopolymer cement for more than 17 hours at 150°C.

Suitable sugar materials that may be mentioned herein include monosaccharides (e.g. glucose, dextrose, fructose, and galactose), disaccharides (e.g. sucrose, fructose, maltose, and lactose) and oligosaccharides. Suitable sugar-substitute materials include natural sugar substitute materials (e.g. sugar alcohols, stevia and mogrosides) as well as artificial sweeteners. Suitable sugar alcohols include arabitol, erythritol, glycerol, hydrogenated starch hydrolysates, isomalt, lactitol, maltitol, mannitol, sorbitol and xylitol. Suitable artificial sweeteners include acesulfame potassium, advantame, alitame, salts of aspartame, salts of aspartame-acesulfame, sodium cyclamate, dulcin, glucin, neohesperidin dihydrochalcone, neotame, P-4000, saccharin and sucralose.

The thickening time test was performed as per ISO 10426-2/ API RP-10B2 Recommended practice for testing well cement using High Pressure High Temperature (HPHT) Consistometer. The hardening time of cement was measured by the unit of Berden consistency (Be), where cement is considered hardened or un-pumpable at 100 Be. The material is considered to be unpumpable and to have thickened at 70 Be.

In the event of lower temperature below than 40°C, a fast set material (e.g. ground blast furnace slag (GBFS)) may be added as a blend together with the aluminosilicate material (e.g. fly ash) at a concentration of from 25% to 45% by weight of the aluminosilicate material to control the setting time and improve strength. It was found that the higher the amount of GBFS added, the shorter the hardening time of Geopolymer cement. Thus, the lower the downhole temperature, the higher the amount of GBFS needed to achieve setting.

To control the viscosity of the geopolymer cement compositon, a dispersant from the polyethylene sulphonate group may be added at concentration of from 0.001 kg/L to 0.15 kg/L relative to the total volume of the composition. When used in this concentration, this material may provide a viscosity of from 5cP to 200cP in the geopolymer cement composition used here.

A defoamer (e.g. polydimethylsilicone) may be added to control the presence of foam during the mixing/preparation of the geopolymer cement composition. When a defoamer is used, it may be added at a concentration of from 0.001 kg/L to 0.15 kg/L relative to the total volume of the composition.

To control the amount of fluid that escapes from the prepared cement slurries, a fluid loss controller may be added at a concentration of from 0.001 kg/L to 0.3 kg/L relative to the total volume of the composition. A suitable fluid loss controller may be hydroxyethylcellulose and/or 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS). When a fluid loss controller is used, the API fluid loss amount may be controlled to from 20ml to 300ml in a 30 min test time.

The geopolymer cement compositions described herein may be further combined with an expandable material (e.g. selected from the magnesium oxide group) at a concentration more than 1 % (e.g. from 2 to 10 wt%) relative to the total weight of aluminosilicate source material in the composition to produce cement linear expansion more than 0.1 %. The expansion of geopolymer cement is tested as per API RP 10B-5 - Recommended Practice on Determination of Shrinkage and Expansion of Well Cement at Atmospheric Pressure using the expansion ring.

Additionally or alternatively, a swellable effect may be provided to the geopolymer cement by the addition of a suitable swellable material (e.g. butyl polystyrene), which may be added in an amount of from 10 to 60 wt% relative to the total weight of aluminosilicate source material in the composition. The swellable material may provide the geopolymer cement composition with a linear expansion of from 0.1 % to 2% as measured using API RP 10-B5 using an expansion cell inside water and a hydrocarbon fluid.

To manufacture the base geopolymer cement formulation used herein, the following steps are conducted in sequence:

(b) adding a silicate material to the mixture of step (a) and mixing to form a mixture; and

(c) adding an aluminosilicate material to the mixture of step (b) and mixing.

Conveniently, the above process may be conducted according to the API RP10B-2 mixing procedure. It is important that step (c) is conducted last so as to prevent the premature aging (i.e. reduced thickening time) of the composition. Such an effect would potentially make it harder to achieve the desired column height of cement in the bore. If the base geopolymer cement formulation needs to be adjusted to suit the particular downhole conditions of the bore, then all additional water-soluble solid components or liquids may be added as described hereinbefore in any technically sensible combination. Such additional components will be added to the mixture before any non-water-soluble solids are added (e.g. the aluminosilicate material, GBFS etc). For example, they may be added to the mixture of step (a) before step (b) is conducted or to the mixture of step (b) before step (c) is conducted. Alternatively, the additional components may be added as part of steps (a) and (b).

It will be appreciated that the geopolymer cement formulations discussed herein may be used in a method of fixing a casing into a wellbore, whereby there is an annulus between the casing and a wall of the wellbore, which method comprises pumping a geopolymer cement formulation through the casing and into the annulus up to a desired column height and allowing the cement to set, thereby fixing the casing into the wellbore. Reference to a wellbore in the context of the current invention may relate to an oil wellbore or a gas wellbore.

The invention will now be further illustrated with the following examples.

Examples

Example 1 : 1 .8 g/cm³ (15 Ib/gal) Geopolymer cement tested at different downhole circulating temperatures

Geopolymer cement slurries A1 , A2, A3, A4 and A5 were prepared and tested in accordance with API/ISO 10426-2.

• Slurry A1 : 600g of type F fly ash, 240g of sodium hydroxide solution at 8 molarity, 60g of Sodium silicate, 100g of fresh water, 3g of polyethylene sulphonate dispersant, 3g of lignosulphonate retarder and 20g of hydroxylethylcelulose fluid loss controller.

• Slurry A2: 600g of type F fly ash, 240g of sodium hydroxide solution at 8 molarity, 60g of sodium silicate, 100g of fresh water, 3g of polyethylene sulphonate dispersant, 50g of lignosulphonate retarder and 35g of hydroxylethylcelulose fluid loss controller.

• Slurry A3: 600g of type F fly ash, 240g of sodium hydroxide solution at 8 molarity, 60g of sodium silicate, 100g of sea water, 3g of polyethylene sulphonate dispersant, 100g of monosaccaride retarder corresponded to 17% by weight of Fly Ash (BWOFA) and 35g of hydroxylethylcelulose fluid loss controller.

• Slurry A4: 600g of type F fly ash, 240g of sodium hydroxide solution at 8 molarity, 60g of sodium silicate, 100g of sea water, 3g of polyethylene sulphonate dispersant, 200g of monosaccaride retarder corresponded to 33% by weight of Fly Ash

(BWOFA) and 90g of hydroxylethylcelulose fluid loss controller.

• Slurry A5: 600g of type F fly ash, 240g of sodium hydroxide solution at 8 molarity, 60g of sodium silicate, 100g of sea water, 3g of polyethylene sulphonate dispersant, 260g of monosaccaride retarder corresponded to 43% by weight of Fly Ash (BWOFA) and 1 10g of hydroxylethylcelulose fluid loss controller. Table 1 shows the properties of Geopolymer cement when tested at three different Bottom Hole Circulating Temperature (BHCT).

The slurries above were manufactured by mixing NaOH and water together, then the other materials, excluding the fly ash were added and mixed together, then fly ash was added.

Table 1 shows the properties of these Geopolymer cement slurries when tested at four different Bottom Hole Circulating Temperatures (BHCT; 60 °C, 93 °C, 1 10 °C and 150 °C), as well as the effect of a retarder on thickening time. Figures 1 to 5 depict the thickening time of formulations A1 to A5 over a period of time at the selected BHTCs, using Bearden units of consistency.

Table 1

The plastic viscosity of the Geopolymer cement formulations after mixing was between 29 to 96 cP, which shows good fluidity for all of cement slurries and was similar to the plastic viscosities obtained after conditioning, which were between 37-87cP. The free fluid for all of the Geopolymer cement formulations was zero ml_, which is suitable for application across the horizontal section in gas wells.

Slurry A3 shows that the retardation effect of a monosaccharide is higher than that displayed by the use of a lignosulphonate retarder in slurry A2 at 93°C. Indeed, the use of a sufficient quantity of a monosaccaride retarder was able to retard the setting of Geopolymer cement formulation A5 150° C for more than 1020min.

Example 2: Geopolymer cement tested at 30 °C incorporating ground blast furnace slag (GBFS)

Geopolymer cement slurries A6, A7 and A8 were prepared and tested in accordance with API /ISO 10426-2. Table 2 lists the formulations of the slurries.

Table 2

For each of the formulations, the fly ash was blended in the solid state with GBFS (and with the barium sulfate or silica-alumina when used) before addition of this blended material to a solution containing sodium hydroxide and sodium silicate.

Table 3 details the effect of GBFS on thickening time and compressive strength of the geopolymer cement at 30 °C and 1000 psi.

Table 3

The addition of GBFS into the aluminosilicate blend can help to accelerate the setting time of the Geopolymer cement formulation as shown by slurry A8 in comparison to slurries A6 and A7. In other words, as the amount of GBFS added increases, the shorter the thickening time. In addition, increasing presence of GBFS also contributes to increased compressive strength after 24 hours following exposure to bottom hole conditions of 30°C and 1000psi.

Example 3: Geopolymer expansion

Geopolymer cement slurries name as A9, A10 and A1 1 were prepared and tested in accordance with API/ISO 10426-5 at 60 °C. Slurry A9 comprises: 400g of type F fly ash blended with 20g of magnesium oxide that was then added into a solution formed from mixing 444g of an 8 M aqueous sodium hydroxide solution with 156g of sodium silicate in 100g of fresh water. Slurry A10 comprises: 600g of type F fly ash blended with 30g of magnesium oxide that was then added into a solution formed from mixing 240g of an 8 M aqueous sodium hydroxide solution with 60g of sodium silicate in 100g of fresh water. Slurry A1 1 comprises: 600g of type F fly ash blended with 150g of a swellable material that comprises butyl polystyrene, the blended mixture was added into a solution formed from mixing 240g of 8 M aqueous sodium hydroxide solution with a solution of 60g of sodium silicate in 100g of fresh water. Table 4 provides details of the linear expansion of the geopolymer cements tested at 60 °C.

Table 4

The percentage of linear expansion of A9 was 0.38% after 19 days curing at 60°C, while A10 only showed 0.18% over the same time period. The addition of a swellable material increased linear expansion to 0.99% in A1 1 after 40 days of curing. Addition of expandable material at higher concentration is required to increase the amount of expansion in Geopolymer cement.

Claims

1. A pumpable geopolymer cement composition comprising:

an aluminosilicate source material;

an alkaline solution comprising a carrier fluid, an alkaline activator material and a silicate material, wherein, the weight:weight ratio of the alkaline solutio aluminosilicate source material is from 0.1 to 2:1 , and the weight:weight ratio of the silicate material: alkaline solution is from 0.15 to 1 :1.

2. The composition of Claim 1 , wherein the aluminosilicate source material is fly ash type F, optionally wherein the fly ash type F has a calcium content of less than 10 wt%.

3. The composition of Claim 1 or Claim 2, wherein the alkaline solution comprises an alkaline activator material at a concentration of from 8 M to 12 M.

4. The composition of any one of the preceding claims, wherein the alkaline activator material is sodium hydroxide and/or potassium hydroxide.

5. The composition of any one of the preceding claims, wherein the silicate is selected from a sodium silicate.

6. The composition of any one of the preceding claims, wherein the composition has a specific gravity of from 1.40 g/cm³ to 1.91 g/cm³.

7. The composition of any one of Claims 1 to 5, wherein the composition further comprises a weighting agent selected from one or more of the group consisting of barium sulfate, iron oxide, manganese tetroxide, where the weighting agent is present in an amount of from 30 to 75 wt% relative to the total weight of aluminosilicate source material in the composition.

8. The composition of Claim 7, wherein the composition has a specific gravity of from 1.92 g/cm³ to 2.99 g/cm³.

9. The composition of any one of Claims 1 to 5, wherein the composition further comprises a lightweight material selected from one or more of the group consisting of silica- alumina microspheres, cenosphere, sodium-calcium-borosilicate in an amount of from 50 to 100 wt% relative to the total weight of aluminosilicate source material in the composition.

10. The composition of Claim 9, wherein the composition has a specific gravity of from 1 .21 g/cm³ to 1 .55 g/cm³.

1 1 . The composition of any one of the preceding claims, wherein the composition further comprises one or more of a defoamer, a fluid loss controller and a dispersant, where each, when present, is provided in a concentration of from 0.001 kg/L to 0.3 kg/L relative to the total volume of the composition.

12. The composition of Claim 1 1 , wherein, when present:

(a) the defoamer is a polydimethylsilicone;

(b) the fluid loss controller is a hydroxyethylcellulose and/or 2-acrylamido-2- methylpropane sulfonic acid;

(c) the dispersant is a polyethylene sulfonate.

13. The composition of any one of the preceding claims, wherein the composition further comprises a retarder material at a concentration of from 0.001 kg/L to 0.3 kg/L relative to the total volume of the composition.

14. The composition of Claim 13, wherein the retarder material is lignosulfonate.

15. The composition of any one of Claims 1 to 12, wherein the composition further comprises a retarder material in an amount of from 5 to 60 wt% relative to the total weight of aluminosilicate source material in the composition.

16. The composition of Claim 15, wherein the retarder is a sugar or a sugar-substitute material.

17. The composition of any one of Claims 1 to 12, wherein the composition further comprises a fast set material in an amount of from 25 to 45 wt% relative to the total weight of aluminosilicate source material in the composition.

18. The composition of Claim 17, wherein the fast set material is ground blast furnace slag.

19. The composition of any one of Claims 1 to 1 1 , 17 and 18, wherein the composition further comprises an expanding material in an amount of from 2 to 10 wt% relative to the total weight of aluminosilicate source material in the composition, optionally wherein the expanding material provides the geopolymer cement composition with a linear expansion of from 0.01 % to 2.5%.

20. The composition of Claim 19, wherein the expanding material is magnesium oxide.

21 . The composition of any one of Claims 1 to 1 1 , 17 and 18, wherein the composition further comprises a swellable material in an amount of from 10 to 60 wt% relative to the total weight of aluminosilicate source material in the composition, optionally wherein the swellable material provides the geopolymer cement composition with a linear expansion of from 0.1 % to 2%.

22. The composition of Claim 21 , wherein the swellable material is butyl polystyrene.

23. A method of forming a pumpable geopolymer cement formulation comprising the steps of:

(c) adding an aluminosilicate material to the mixture of step (b) and mixing.

24. The method of Claim 23, wherein the aluminosilicate source material is fly ash type F, optionally wherein the fly ash type F has a calcium content of less than 10 wt%.

25. The method of Claim 23 or Claim 24, wherein the alkaline activator material is added in amount to the alkaline activator material to provide a concentration of from 8 M to 12 M.

26. The method of any one of Claims 23 to 25, wherein the alkaline activator material is sodium hydroxide or potassium hydroxide.

27. The method of any one of Claims 23 to 26, wherein the silicate is selected from a sodium silicate.

28. The method of any one of Claims 23 to 27, wherein: (i) one or more of a defoamer, a fluid loss controller and a dispersant are added and mixed into the mixture of step (a) or step (b) of Claim 23 and the resulting mixture is then used in the subsequent step, where each of the defoamer, fluid loss controller and dispersant, when present, is provided in a concentration of from 0.001 kg/L to 0.1 kg/L relative to the total volume of the composition; and/or

(ii) a retarder material is added and mixed into the mixture of step (a) or step (b) of Claim 23 and the resulting mixture is then used in the subsequent step, where the retarder material is:

(II) provided in an amount of from 5 to 60 wt% relative to the total weight of aluminosilicate source material in the composition, optionally wherein the retarder material is a sugar or a sugar-substitute material.

29. The method of Claim 28, wherein, when present:

(a) the defoamer is a polydimethylsilicone;

(c) the dispersant is a polyethylene sulfonate.

30. The method of any one of Claims 19 to 29, wherein the mixing is conducted in line with the API RP10B-2 mixing procedure.