SILICA REDUCER COMPOSITIONS AND METHODS FOR TREATMENT OF PRODUCED WATER FROM THERMAL IN SITU BITUMEN OR HEAVY HYDROCARBON RECOVERY OPERATIONS

Abstract

The present disclosure relates to the treatment of produced water from SAGD operations or other thermal in situ hydrocarbon recovery operations. The innovative products and techniques have been developed by Baymag Inc, a subsidiary of Refratechnik Holding GmbH. For example, the disclosure relates to a silica reducer composition for use in warm or hot lime softeners or evaporators for treating produced water generated from in situ hydrocarbon recovery operations. The silica reducer composition has an enhanced combination of particle sizing and surface area for facilitating silica reduction while minimizing hydration. The silica reducer composition can be manufactured by calcining followed by milling and other optional process steps.

Claims

1. A silica reducer composition for use in a produced water treatment vessel, comprising magnesium oxide in a concentration between 90 wt % and 99 wt % on a loss free basis, wherein the magnesium oxide is in the form of particles having a specific surface area between 20 m.sup.2/g and 65 m.sup.2/g and a median particle sizing of between 3 and 20 microns.

2. The silica reducer composition of claim 1, further comprising calcium oxide in a concentration below 4.0 wt % on a loss free basis.

3. The silica reducer composition of claim 1, further comprising calcium oxide in a concentration below 2.5 wt % on a loss free basis.

4. The silica reducer composition of claim 1, further comprising ferric oxide in a concentration below 3.0 wt % on a loss free basis.

5. The silica reducer composition of claim 1, further comprising aluminum oxide in a concentration below 1.5 wt % on a loss free basis.

6. The silica reducer composition of claim 1, further comprising aluminum oxide in a concentration below 1.0 wt % on a loss free basis.

7. The silica reducer composition of claim 1, further comprising silicon oxide in a concentration below 1.5 wt % on a loss free basis.

8. The silica reducer composition of claim 1, further comprising silicon oxide in a concentration below 1.0 wt % on a loss free basis.

9. The silica reducer composition of claim 1, wherein the concentration of the magnesium oxide is at least 95 wt % on a loss free basis.

10. The silica reducer composition of claim 1, wherein the concentration of the magnesium oxide is between 95.5 wt % and 98 wt % on a loss free basis.

11. The silica reducer composition of claim 1, wherein the median particle sizing is below 15 microns.

12. The silica reducer composition of claim 1, wherein the median particle sizing is below 10 microns.

13. The silica reducer composition of claim 1, wherein the median particle sizing is below 5 microns.

14. The silica reducer composition of claim 1, wherein the specific surface area of the particles of the magnesium oxide is between 20 m.sup.2/g and 40 m.sup.2/g.

15. The silica reducer composition of claim 1, wherein the specific surface area of the particles of the magnesium oxide is between 28 m.sup.2/g and 32 m.sup.2/g.

16. The silica reducer composition of claim 1, wherein the specific surface area of the particles of the magnesium oxide is provided to inhibit hydration of the magnesium oxide above 10% for a residence time between addition into the produced water until entering the produced water treatment vessel at an operating temperature.

17. The silica reducer composition of claim 16, wherein the operating temperature is between 20° C. and 50° C. and the residence time is between 1 and 45 minutes.

18. The silica reducer composition of claim 1, wherein the composition has a loose bulk density of 0.30 to 0.75 kg/L and a packed bulk density of 0.80 to 1.2 kg/L.

19. A method of manufacturing a silica reducer composition, comprising: calcining a magnesium containing material to form a calcined material comprising calcined magnesium oxide; and milling the calcined material to form the silica reducer composition having a magnesium oxide concentration between 90 wt % and 99 wt % on a loss free basis, a specific surface area between 20 m.sup.2/g and 65 m.sup.2/g, and a median particle sizing of between 3 and 20 microns.

20. A process for treating produced water generated in a thermal in situ bitumen or heavy hydrocarbon recovery operation, the process comprising: adding a silica reducer composition to the produced water; feeding the produced water into a produced water treatment vessel comprising a warm lime softener, a hot lime softener, an evaporator, or a combination thereof, wherein the silica reducer composition comprises magnesium oxide in a concentration between 90 wt % and 99 wt % on a loss free basis and in the form of particles having a specific surface area between 20 m.sup.2/g and 65 m.sup.2/g and a median particle sizing of between 3 and 20 microns; and withdrawing a treated water stream from the produced water treatment vessel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 is flow diagram of a method of manufacturing a silica reducer composition.

[0023] FIG. 2 is a flow diagram of a process for treating produced water where a lime softener is implemented.

[0024] FIG. 3 is a flow diagram of a process for treating produced water where an evaporator is implemented.

[0025] FIG. 4 is a graph of hydration percentage versus slaking time at different temperatures.

[0026] FIG. 5 is a graph of silica content versus dosage of magnesium oxide for two products added to produced water and each having different particle sizes.

DETAILED DESCRIPTION

[0027] The present disclosure relates to silica reducer compositions for use in lime softeners or evaporators that treat produced water generated from thermal in situ bitumen or heavy hydrocarbon recovery operations. The disclosure particularly relates to the application of compositions that include magnesium oxide (MgO) for silica reduction from produced water in Warm Lime Softener (WLS), Hot Lime Softener (HLS), or evaporators for in situ heavy oil operations, such that those typically used in Alberta, Canada.

[0028] In some implementations, the silica reducer composition is a free-flowing magnesium oxide based product that can be produced by calcining high purity natural magnesite developed specifically for this application. Without being limited by theory, silica reduction from produced water can be facilitated by the adsorption and/or co-precipitation with MgO and/or magnesium hydroxide (Mg(OH).sub.2). MgO hydration, which is also known as slaking, occurs when MgO and water are mixed to form Mg(OH).sub.2 slurry via the following reactions:

Dissociation: MgO+H.sub.2O.Math.Mg.sup.2++2OH.sup.−

Precipitation: Mg.sup.2++2OH.sup.−.Math.H Mg(OH).sub.2

[0029] Silica removal efficiency is notably decreased if the MgO in the slurry hydrates to Mg(OH).sub.2 before entering the produced water treatment vessel (e.g., WLS, HLS or evaporator). As illustrated in FIG. 4, the magnesium oxide feed system can be advantageously designed with low retention times and low water temperature. The silica reducer composition can include magnesium oxide having a relatively reduced particle size for enhanced silica reduction while maintaining a specific surface area that promotes resistance to the premature formation of magnesium hydroxide.

[0030] In a typical steam-assisted in situ heavy hydrocarbon recovery operation, much of the steam injected into the reservoir is recovered as produced water at the surface. The produced water must be treated and recycled for further steam production. The water treatment can include WLS or HLS precipitation softening processes for hardness and silica removal, followed by filtration for suspended solids removal, and a weak acid cation (WAC) exchange to remove remaining dissolved hardness. The resulting treated water can be suitable for use as boiler feed water and is fed to a steam generator, such as a drum boiler or an OTSG.

[0031] Warm or hot lime softening is a process which combines lime and magnesium oxide slurries with warm or hot produced water to remove silica and hardness. In some implementations, hydrated lime is added to the produced water and reacts with the bicarbonates in the water to form CaCO.sub.3. Magnesium oxide can be added as a slurry into the rapid mix zone of WLS or HLS units where it reacts with water to form Mg(OH).sub.2. The conversion of MgO to Mg(OH).sub.2 preferably occurs within the water treatment vessel (e.g., WLS, HLS, or evaporator) to ensure maximum surface interaction for silica adsorption and subsequent removal. The resulting CaCO.sub.3 and Mg(OH).sub.2 solids are removed from the water treatment vessel as part of the sludge.

[0032] In some implementations, the silica reducer composition has reduced particle size characteristics to leverage size effects for silica removal via adsorption mechanisms. The smaller particle size provides an increase in adsorption sites for reaction per unit volume of the composition. The silica reducer composition can have a particle sizing where a minimum of 96.5 wt % of the particles pass through a 200-mesh screen. The particle sizing can also be provided such that the silica reducer composition has a median particle size less than 20 microns. In addition, the specific surface area of the silica reducer composition can be provided between 20 m.sup.2/g and 65 m.sup.2/g or between 25 m.sup.2/g and 35 m.sup.2/g or between 28 m.sup.2/g and 32 m.sup.2/g, for example.

[0033] In some implementations, the silica reducer composition has one or more additional compositional and physical properties. For example, the reducer composition can have a loose bulk density of 0.30 to 0.75 kg/L, and a packed bulk density of 0.80 to 1.2 kg/L. While the composition is magnesium oxide based with for example between 90 wt % and 99 wt % MgO on a loss free basis, the composition can also include other components, such as various oxides depending on the source of the magnesite ore. For instance, the silica reducer composition can include CaO up to 4% or up to 2.5%, Fe.sub.2O.sub.3 up to 3% or up to 1.5%, Al.sub.2O.sub.3 up to 1.5% or up to 1%, and SiO.sub.2 up to 1.5% or up to 1%, all being on a loss free basis. The silica reducer composition can also have a loss on ignition of between about 1 and 3.5 wt %.

[0034] The silica reducer composition can be formulated and manufactured in various ways to provide a product having target compositional, particle size and specific surface area properties. By providing the specific surface area below 65 m.sup.2/g, below 55 m.sup.2/g, below 45 m.sup.2/g, below 35 m.sup.2/g, or preferably between 25 m.sup.2/g and 35 m.sup.2/g, the composition can have reduced hydration in produced water treatment applications, such that the magnesium oxide does not substantially convert to magnesium hydroxide before it reaches the produced water treatment vessel. For a given material, lower surface areas facilitate lower hydration rates of the magnesium oxide. For instance, a preferred surface area in the range of 25 m.sup.2/g and 35 m.sup.2/g can facilitate reduced hydration rates for enhanced application of the silica reducer to produced water streams.

[0035] The silica reducer composition can be manufactured using various processes and starting materials. In one implementation, as shown in FIG. 1, magnesium containing ore 10 is obtained by mining and then supplied to a crushing stage 12 to produce crushed ore 14. The crushed ore 14 is then supplied to a calcining stage 16 that is operated as residence times and temperatures to produce a calcined material 18 having certain desired properties, such as surface area, and comprising magnesium oxide. The calcined material 18 is then supplied to a milling stage 20 to reduce the particle size of the material to produce the silica reducer composition 22. The milling stage increases the surface area only slightly while notably reducing the particle size. The silica reducer composition 22 can have a magnesium oxide concentration between 90 wt % and 99 wt % on a loss free basis, a specific surface area between 20 m.sup.2/g and 65 m.sup.2/g, and a median particle sizing of between 3 and 20 microns. The silica reducer composition 22 can then subjected to packaging and shipping 24 and the packaged product 26 can be used for addition to produced water that is treated in a water treatment unit for silica reduction.

[0036] Turning now to FIG. 2, in the produce water treatment facility, the produced water 28 is supplied to a water treatment unit, such as a WLS 30, for silica removal and removal of other compounds in the produced water. The WLS 30 produces sludge 32 and treated water 34. A similar setup could be implemented with an HLS instead of a WLS.

[0037] FIG. 3 shows an alternative water treatment unit, i.e., an evaporator 34, which receives the produced water and produces blowdown 36 and condensate 38. The condensate 38 can be considered a treated water stream. The treated water from the WLS or evaporator can also be further treated prior to being used as boiler feed water in an OTSG or another type of steam generator to produce steam for injection into the subterranean reservoir as part of the thermal in situ bitumen or heavy hydrocarbon recovery operation.

EXPERIMENTATION & DATA

[0038] It has been found experimentally that magnesium oxide particle sizing has an impact on silica reduction from produced water. Experiments were conducted to assess two products A and B, each at two different particle sizes “fine” and “coarse”, to assess effects of particle size on silica reduction. For each experimental run, a sample of the produced water was mixed with a dose of the magnesium oxide based product and then allowed to settle. The mixture was then filtered for Inductively Coupled Plasma Mass Spectrometry (ICP-MS) analysis. Results are illustrated in FIG. 5, showing that the “fine” samples of both magnesium oxide based products A and B enabled greater silica reduction compared to the respective “coarse” products. More particularly, for each product A and B, the fine product gave better maximum silica reduction as well as better silica reduction per magnesium oxide dosage compared to the coarse product. The “fine” product A was 98.9% at 200 mesh (median particle sizing below 20 microns) in terms of particle size with a surface area between 25 m.sup.2/g and 35 m.sup.2/g, while the “fine” product B was 96.6% 325 mesh (median particle sizing below 20 microns) in terms of particle size with a surface area between 45 m.sup.2/g and 60 m.sup.2/g. The coarse products had a median particle sizing above 20 microns in both cases. It is noteworthy that for the lower surface area product, i.e., product A, the impact of reducing particle size is quite pronounced. The fine product A can facilitate the multiple effects of enhancing silica reduction along with reduced hydration rates and incorporation into existing facilities based on existing operating conditions.

[0039] Referring to FIG. 4, the effect of residence time and temperature on hydration is shown. These results illustrate that higher residence times of the magnesium oxide in the produce water and higher temperatures result in great hydration of the magnesium oxide. To reduce hydration, the magnesium oxide based product can be added at a certain location in the process to minimize temperature and the time to reach the water treatment unit. In some scenarios where the product is added into a relatively hot produced water and/or upstream of the treatment unit such that notable slaking time exists prior to the treatment unit, the product can be dosed higher to account for the hydration that occurs before the product reaches the treatment unit. It is also possible to add certain products directly to the treatment unit to minimize slaking.

[0040] It is also noted that the particle size reduction to below a median of 20, 15, 10, or 5 microns can be performed while keeping the surface area within a low enough range such that the finer particles do not experience a notable increase in hydration. Since hydration is strongly linked to surface area and not particle size, the particle size can be advantageously reduced to enhance silica reduction while keeping the surface area within an acceptably low range to mitigate against hydration issues.