Fluid for Stabilising Solids

Abstract

A fluid for stabilising solids formed from particulate material, the fluid comprising glass and a carrier. A method for preparing the fluid comprising melting and fritting a glass, milling the glass to form a powder and adding the milled glass to a carrier. A method of stabilising a solid formed from particulate material, the method comprising the steps of mixing the fluid with a particulate material and setting, and the use of the fluid, in geoengineering, building preservation, construction, tunnelling, landscape restoration, land remediation, and/or flood protection/remediation.

Claims

1. A fluid for stabilising solids formed from particulate material, the fluid comprising: glass and a carrier.

2. The fluid according to claim 1, wherein the fluid comprises a solution of glass or a suspension of glass powder in a liquid carrier.

3. The fluid according to claim 1, wherein the fluid comprises a saturated solution of glass in a liquid carrier.

4. The fluid according to claim 1, wherein the fluid is a product comprising glass and a carrier.

5. The fluid according to claim 1, wherein the particle size distribution of the particulate material is in the range 0.01 μm to 2 mm.

6. The fluid according to claim 1, wherein the mean particle size of the particulate material is in the range 1 μm to 1 mm.

7. The fluid according to claim 1, wherein the particulate material is selected from sedimentary rock, soil, or construction materials formed from particulate matter.

8. The fluid according to claim 7, wherein the sedimentary rock is selected from chalk, shale, halides and sandstone.

9. The fluid according to claim 1, wherein when the glass is a suspension of glass powder in the carrier, the particle size distribution of the glass particles is ±15% of the particle size distribution of the particulate material.

10. The fluid according to claim 9, wherein a particle size distribution of the glass powder is in the range 1 μm to 5 mm.

11. The fluid according to claim 1, wherein the glass is a low melting point glass.

12. The fluid according to claim 1, wherein the glass is selected from a sodium, potassium, lithium, sulfate or phosphate glass.

13. The fluid according to claim 1, wherein the glass comprises an oxide selected from SiO.sub.2, Al.sub.2O.sub.3, Fe.sub.2O.sub.3, SO.sub.3, Li.sub.2O, Na.sub.2O, MgO, ZnO, CaO, PbO, PbO.sub.2, BaO, P.sub.2O.sub.3, P.sub.2O.sub.5 or combinations thereof.

14. The fluid according to claim 13, wherein the glass is a phosphate glass additionally comprising an oxide selected from MgO, CaO, SiO.sub.2, Fe.sub.2O.sub.3, Na.sub.2O, PbO and ZnO.

15. The fluid according to claim 13, wherein the glass is a silicate glass additionally comprising an oxide selected from Na.sub.2O, Li.sub.2O and CaO.

16. The fluid according to claim 1, wherein the carrier is selected from water, brine or an alkaline solution.

17. A method for preparing a fluid for stabilising solids formed from particulate material comprising: melting and fritting a glass; milling the glass to form a powder; and adding the milled glass to a carrier.

18. A method of stabilising a solid formed from particulate material, the method comprising mixing the fluid of claim 1 with a particulate material and setting.

19. The method according to claim 18, wherein stabilisation of the solid comprises sealing pores in the solid such that it is impermeable.

20. The method according to claim 18, wherein stabilisation of the solid comprises strengthening the solid to reduce degradation without loss of permeability.

21. The method according to claim 18 wherein stabilisation-comprises a first step of strengthening the solid to reduce degradation without loss of permeability; and a second step of sealing pores in the solid such that it is impermeable.

22. The method according to claim 18, further comprising a step of adding a setting agent to the solid prior to setting, wherein the setting agent comprises glass of a composition different to the glass in the fluid and/or a non-glass material.

23. Use of a fluid according to claim 1, in geoengineering, building preservation, construction, tunnelling, landscape restoration, land remediation, and/or flood protection/remediation.

Description

[0056] In order that the invention may be more readily understood, it will be described further with reference to the figures and to the specific examples hereinafter.

[0057] FIG. 1 is a table providing composition information for inventive glass compositions;

[0058] FIGS. 2a-c are SEM images at the magnifications 500 μm, 100 μm and 50 μm (a-c respectively) of the surface of a sealed chalk sample as described in Example 1;

[0059] FIG. 3 is an SEM image at 100 μm magnification of an unsealed chalk sample;

[0060] FIG. 4a compares the change in strain experienced by untreated chalk (reference, in both bands the upper line) and chalk treated as in Example 2 (new glass test, in both bands the lower line) for axial (lower band) and tangential (upper band) sections under increased drawdown pressures;

[0061] FIG. 4b compares the change in permeability of untreated chalk (reference, lower plot) and chalk treated as in Example 2 (new glass test, the upper plot) with increased drawdown;

[0062] FIGS. 5a and 5b are CT-scans comparing an untreated chalk sample (a) with a treated chalk sample (b);

[0063] FIG. 6 compares the strength of chalk after injection with glass composition P in conjunction with sodium bromide brine at different injection pressures relative to a comparative glass composition in tap water by function of core length (5% glass solution in water, specific gravity 1.3, 90° C.). The inventive examples were injected under the following conditions (25-30 bar with up to 10 pore volumes (pv) of glass solution passing through the core; 26-7.5 bar, 7 pv; 27-14 bar, 9 pv; 29-30 bar, 10 pv, 30-25 bar, 10 pv);

[0064] FIGS. 7a and 7b are photographs of treated (a) and untreated (b) sandstone cores;

[0065] FIG. 8 is a schematic representation of a core forming apparatus used in Example 3;

[0066] FIG. 9 is a photograph of crushed brick dust treated with glass to form a solid block as in Example 4; and

[0067] FIG. 10 is a photograph of a core of crumbled brick treated with a glass solution followed by a calcium carbonate solution to bind the brick particles together and form a seal as in Example 5.

EXAMPLES

[0068] The Compositions tested are shown in FIG. 1, unless otherwise stated in the specific examples below, these were tested in water as the carrier. The glass samples were prepared by melt combination and ball milling and all were found to be effective for the purposed identified in the “utility” column, with at least the primary solid, often with both chalk and sandstone.

Example 1: Stabilisation of Chalk (Sealing)

[0069] Chalk Core Preparation: Blocks of chalk were sourced from a disused chalk pit in the Thames Valley. These chalks were found to be 98% CaCO.sub.3; cores were taken from the raw blocks with a 39 mm core drill, and the surfaces then ground flat. Both drilling and grinding were carried out using water as a lubricant. Core dimensions were then measured from which their volumes were calculated. The cores were then soaked in the appropriate glass solution until no further weight gain was measured, at which point they were assumed to be saturated. Based on a preliminary set of incremental measurements a time of 1 hour was chosen for soaking subsequent samples process. They were then air dried prior to testing.

[0070] Porosity Measurement: Samples were soaked in deionised water for 1 hour then weighed to determine the saturated weight. The samples were then dried in an oven to constant weight at 120° C. and the dry weight recorded. This was used to calculate the volume of water absorbed by the chalk and allow the percentage porosity to be calculated.

[0071] Chalk has porosity between 40 and 50%. By soaking the chalk with glass composition G, for two hours, a reduction in porosity of 50% can be observed. Glass composition G is a glass solution consisting of Na.sub.2O, SiO.sub.2 and CaO ball milled to <45 μm in water.

[0072] By reducing the percentage of CaO to in the range 2-4 wt % as in glass compositions H-J, it is possible to prevent the flow of fluid through the rock completely creating an effective seal from the rock, as is shown in FIGS. 2a-c and 3 which provide a comparison between chalk treated with composition H (FIGS. 2a-c) and untreated (FIG. 3) chalk. As can be seen, in particular from a comparison of FIG. 2a and FIG. 3 (both at 100 μm magnification), there is an almost complete sealing of the surface of the treated sample, with the characteristic granular chalk surface (evident in FIG. 3), being replaced by a smooth sealed surface in FIG. 2b. The cracks evident in these images are as a result of surface drying in the laboratory, which would not occur in applications such as oil well sealing due to the presence of ambient moisture. However, even in laboratory tests, permeability tests show that internal sealing is intact, no fluid flows through the cracks, these in themselves being sealed.

Example 2: Stabilisation of Chalk (Strength without Loss of Permeability)

[0073] Under fluid flow conditions chalk has a tendency to form a paste and block pipework used for pumping fluids. Glass composition D, a glass consisting of ZnO, MgO and P.sub.2O.sub.5 finely milled to <10 μm (ball milling) was used to produce a suspension in brine. This suspension was pumped into the chalk and allowed to set for a period of >10 hours at a temperature of 90-100° C. (ambient for underground chalk formations).

[0074] After this time water or brine can be pumped through the rock at a rate of 20 ml/min for more than 7 days without the rock losing its integrity and collapsing. Untreated chalk disintegrates under these conditions in just one hour. Porosity tests on chalk treated in this manner retain at least 80% of their initial permeability.

[0075] Similar results were observed with glass composition F.

[0076] Crushing Strength Measurement: The cold crushing strength of each core was tested using a Houndsfield Compression Tester H25KS. Each core was compressed under increasing load until failure or the instrument threshold of 25,000 N was reached. Two cores from each treatment were crushed the third core was retained for reference. Crushing was carried out using a flat piston of 75 mm diameter until the block failed or the instruments limit of 25,000 N was reached.

[0077] Porosity was measured as described in Example 1 above.

[0078] Unconfined crush tests on the treated chalk show that it maintains the strength of the original rock despite having fluid passing through it where an untreated sample fails as soon as load is applied. Specifically, FIG. 4a compares the strain to failure at various fluid drawdown pressures for an untreated chalk and a chalk treated with glass composition F. FIG. 4b compares the permeability for the same two samples. It can be seen that there is a significantly greater change in strain exhibited by the reference sample as it deforms and collapses under increased pressure compared to the treated sample which maintains its shape as pressure increases and therefore shows only a very small change in strain with increased drawdown. This change is most clearly shown in the axial tests. In addition, the loss of permeability is around 0.3 mD, showing a good retention of permeability with increasing drawdown pressure, this shows that following an initial increase in permeability in the treated sample it retains over 80% of the initial permeability over time despite treatment with the glass solution. The reference sample maintains permeability as would be expected.

[0079] FIGS. 5a and 5b show that there are fewer fractures in chalk cores which have been treated (FIG. 5b) and which have not (FIG. 5a).

[0080] It was further noted that, as shown in FIG. 6 for composition P, consistent strength increases were observed relative to the comparative examples (exp 5, 1 and 2) by combining the glass solution with a salt brine solution of for example (exp 3, 6 and 7); sodium or potassium bromide or chloride injection depth and therefore overall core strength improvement was observed, even where residence times were short. Without being bound by theory it is believed that the increased acidic nature of composition D in combination with CI and Br ions slows the formation of precipitate whilst allowing the chalk to dissolve forming “wormholes” into which calcium-phosphate precipitates and reacts improving the tensile strength of the chalk by up to 5-times the natural strength of the chalk substrate without loss of permeability. Further, on the scale tested there was no drop off in strength along the core, the strength increase being as large proximal to the point of injection as distal to this at the point of the core farthest from the injection point.

Example 3: Stabilisation of Sandstone (Strength without Loss of Permeability)

[0081] By adding a solution of glass E in water to a beaker of sandstone that has been crushed in a pestle mortar into a powder (particles size <5 mm) it is possible to replicate natural sandstone, producing a solid mass of material capable of supporting a weight of 2.5 kg without disintegration.

[0082] After treatment with the glass E, strength increased over time. The consolidated material can be left soaking in water for 4 weeks and remains intact. Untreated sandstone disintegrated in a few hours under these conditions. A comparison is shown in FIGS. 7a and 7b.

[0083] In order to test a larger sandstone sample under flow at simulated oil well temperatures a crushed sandstone sample (particle size <6 mm) was prepared in a Hoek pressure cell and treated with glass composition D at 10% by weight suspension of glass in brine. The setup of the cell is shown in FIG. 8. FIG. 8, shows cell 10, with acrylic spacer ring 15, perforated acrylic disks 20, and a crushed sandstone core 25 within a rubber sleeve 30.

[0084] The sample was flooded with 90 ml of composition D. A control with no glass addition was also tested. The cell was heated in a laboratory oven at 90° C. overnight for a minimum of 20 hours then allowed to cool for 3-4 hours. This produced simulated sandstone rock. Confining pressure was applied to the outside of the sample and then water pumped through at 1 bar. The time taken for failure to occur was measured, as failure did not occur water pressure was increased to ˜75 bar by means of a pressure washer pump to induce failure. The level of sand generation was observed by collecting outflow water in a bucket.

[0085] The control sample crumbled immediately at pressures of 1 bar.

[0086] By changing the composition of the glass similar results have been obtained in limestone and other rock types.

Example 4: Stabilisation of Clay Brick (Strength without Loss of Permeability)

[0087] Treatment of an aged house brick that has begun to crumble using glass composition O containing P.sub.2O.sub.5, CaO, PbO, Na.sub.2O and K.sub.2O in water produces a crust on the surface of the brick when left for several weeks in ambient conditions (see FIG. 9). This crust prevents further deterioration in the surface of the brick material compared to an untreated sample which continues to crumble to a powder that can be brushed away.

Example 5: Stabilisation of Clay Brick (Two-Step—Sealing)

[0088] Glass composition E, was added in water to an aged house brick that has started to crumble and left for 4 hours. A suspension of calcium carbonate in water was then added to the brick sample. The addition of calcium carbonate stimulates a sealing reaction which blocks the pores in the rock, making it impermeable to fluids and creating a waterproof material (FIG. 10). The seal was observed to improve over time.

Example 6: Stabilisation of the Bored Surface of a Tunnel (Strength and Sealing)

[0089] A fluid produced from a calcium, phosphate, silicate containing glass such as glass composition L, in a carrier such as water, can be used to seal a porous or fractured rock substrate (for instance sandstone) in the ceiling of a tunnel during the tunnel boring process, or later where fluid ingress is problematic. The fluid would react with the sandstone resulting in mineralisation which consolidates the rock, sealing pores and small fractures in the rock stabilising the tunnel surface and preventing water seepage.

[0090] It is possible to stabilise the floor of the tunnel to improve strength without loss of porosity by applying a glass composition such as composition P. In this way, any water that does seep into the tunnel would drain away through the floor of the tunnel.

[0091] It would be appreciated that the fluids, methods and uses of the invention are capable of being implemented in a variety of ways, only a few of which have been illustrated and described above.