Water treatment method and system

Abstract

Water treatment method and water treatment system. A high-salinity feedwater, such as seawater, is treated to produce a reverse osmosis (RO) concentrate and an RO permeate. Optionally, some or all of the RO concentrate can be filtered to produce a nanofiltration (NF) permeate. Optionally, some of the feedwater can also be filtered to produce NF permeate without first being concentrated by RO treatment. The NF permeate, or a mixture of RO permeate and NF permeate, can be used to produce a product water for injection into an oil-containing reservoir to increase oil recovery. Optionally, the product water can have a higher salinity than the feedwater, or at least 30 g / L. The product water can have a hardness of less than 20 mg / L.

Description

1 / 6 “METHOD AND SYSTEM FOR WATER TREATMENT” Field of the Invention

[001] This invention relates to the treatment of seawater to produce water for injection into a reservoir containing petroleum. Background of the Invention

[002] International publication number WO 2019 / 053092 A1, “Method for Salinity Control of Low-Salinity Injection Water”, describes a method that includes the production of two low-salinity water mixtures for injection into two injection wells in different regions of an oil-bearing reservoir. The mixtures comprise varying amounts of nanofiltration permeate and reverse osmosis permeate, both produced by filtering high-salinity feedwater, such as seawater. Description of the Invention

[003] In one method described herein, a high-salinity feedwater, such as seawater, is treated to produce a reverse osmosis (RO) concentrate and an RO permeate. The RO concentrate (alternatively referred to as reject) is filtered to produce a nanofiltration (NF) permeate. Optionally, some of the feedwater may also be filtered to produce NF permeate without first being concentrated by RO treatment. The NF permeate, or a mixture of RO permeate and NF permeate, may be used to produce a product water for injection into an oil-containing reservoir. The product water may have a salinity of 30 g / l or more, for example, in the range of 30 g / l to 50 g / l. Optionally, the product water may have a higher salinity than the feed water, for example, higher than seawater (typically around 35 g / l Total Dissolved Solids (TDS) or greater than 40 g / l TDS). The product water may have a hardness of less than 20 mg / l.The salinity and hardness of the water. Petition 870240080573, dated 09 / 20 / 2024, page 13 / 32 2 / 6 of the product can be varied, optionally over time, or kept nearly constant despite changes in the feed water, for example, by altering a percentage of the feed water processed by NF treatment, i.e., the RO concentrate, and / or altering a mixing ratio between the RO permeate and the NF permeate in the product water.

[004] A system described herein has a RO system and an NF system. An inlet to the RO system is connected to a feedwater source. An inlet to the NF system is connected to a feedwater source. A concentrate outlet from the RO system is connected to a feedwater inlet of the NF system. A permeate outlet from the NF system is connected to the injection system, for example, through a holding tank. A permeate outlet from the RO system is connected to the injection system, for example, through a holding tank. The injection system is adapted to inject water comprising RO permeate and / or NF permeate, wherein the NF permeate may include treated RO concentrate, at least at some points, into a reservoir containing petroleum.The system has a suitable arrangement of pipes and valves (or other flow control devices) so that various flow ratios in the system can be altered, optionally automatically or by means of a controller, optionally over time. For example, a controller may manipulate the flow control or other devices to vary one or more of (a) the relative amounts of feedwater flowing into the RO unit inlet relative to the NF unit, (b) the amount, if any, of RO concentrate flowing into the NF unit, (c) and the relative amounts of RO permeate and NF permeate in the product water. Brief Description of the Drawing

[005] Figure 1 is a schematic diagram of a system of Petition 870240080573, dated 09 / 20 / 2024, page 14 / 32 3 / 6 water treatment. Description of Embodiments of the Invention

[006] Water is a key constituent in many enhanced oil recovery (EOR) and chemically enhanced oil recovery (CEOR) techniques, which can be employed onshore or offshore. Key parameters such as salinity and hardness are preferably maintained within acceptable ranges to produce a useful fluid for injection. Different oil-bearing reservoirs and different flooding stages within the same reservoir may require injection water of different salinities. Preferably, a water treatment system can provide product waters of different salinities, ideally with minimal or no manual intervention. Feedwater is usually seawater. Seawater typically has a salinity of 35 g / l (measured as total dissolved solids, TDS) or more when collected, but when pretreated to remove suspended solids, its salinity can be 40 mg / l or more.The hardness (total hardness as CaCO3) of seawater can be 6500 mg / l or more, with very little or no removal in pretreatment.

[007] In some examples, a system described herein can be used to produce treated water of varying salinity. The system can be used to treat feedwater of varying salinity levels, for example, 35 g / l 50 g / l or 40 g / l 50 g / l TDS and create product fluids that can have less than 20 mg / l of hardness (total hardness as CaCO3). Optionally, the system can maintain a generally constant effluent salinity over a period of time during which the feedwater salinity varies. The salinity of the product water can be between 30 g / l TDS and 50 g / l TDS, which is desirable for use in at least some of the world's oil-bearing reservoirs. In some examples, the system has the capability to produce product water with different salinity in Petition 870240080573, dated 09 / 20 / 2024, page 15 / 32 4 / 6 different moments. Optionally, the system can be modular so that it can be more easily moved from location to location or scaled in size. The system may include an OR system and an NC system with suitable auxiliary equipment, such as pipes, pumps, tanks, valves and other control devices, sensors and one or more controllers.

[008] In a process described herein, water is treated with RO and / or NF membranes to produce different output streams. The different output streams can be mixed in different proportions to create product water with selected characteristics. The feed water can be pre-treated, for example, with one or more solid-liquid separation units, to protect the membranes.

[009] Product water can be treated with polymers. Product water can be produced according to the requirements for specific reservoirs containing petroleum and polymer mixtures. The system optionally includes digital controls to track fluid properties or modulate the combination of different streams.

[010] The system and method feed a selected quantity of RO concentrate into an NF system. This, along with the optional variable combination of RO permeate with NF permeate, helps to enable modification of the product TDS. By using RO concentrate, we concentrate the hardness and also the TDS. However, the NF units (which can be multi-pass, i.e., 3-pass) remove the hardness (and typically other potential fouling ions, such as sulfate) while retaining most of the desirable monovalent salinity (i.e., NaCl).

[011] Product water may have (a) one or more of the following: total hardness such as CaCO3 below 20 mg / l or below 10 mg / l and sulfate less than 10 mg / l, with (b) TDS greater than 30,000 mg / l or greater than 35,000 mg / l. The system produces high TDS product water with low hardness without the need for Petition 870240080573, dated 09 / 20 / 2024, page 16 / 32 5 / 6 Adding salt to the product water.

[012] Figure 1 shows an example of a water treatment system. In the top line, a portion of the feed water flows in line (3) to a seawater RO unit (SWRO). The feed water in this example is filtered and seawater, but other feed water sources and other pre-treatments can be used. The permeate from the seawater RO unit (SWRO permeate) is subsequently treated in a brackish water RO unit (BWRO). This produces brackish water RO permeate (BWRO). The use of the BWRO unit is optional and can be omitted. Alternatively, a bypass line around the BWRO unit can be provided, optionally with one or more controllable valves, so that a selected portion of the SWRO permeate bypasses the BWRO unit. In general, a SWRO unit can produce permeate with a TDS or salinity of around 1000 mg / L and very low hardness.A BWRO unit can produce permeate with almost no salinity and almost no hardness (i.e., the permeate can be potable). The presence or absence of a BWRO unit, or the extent to which it is bypassed, can be used to alter the qualities of the RO permeate. Optionally, the SWRO unit and / or the BWRO unit can have one or more stages.

[013] Part of the feedwater optionally flows in line (5) to one or more NF units. The division of feedwater between lines (3) and (5) is preferably controllable and variable, for example, through a range between 0-100% in line (3) or line (5). In some examples, there may be no flow through line (3), or no flow through line (5), at some or all times. In some examples, there is always at least some flow through line (3). The NF units may also selectively receive SWRO reject from line (21). In another option, not shown, the NF units may also selectively receive BWRO concentrate. As Petition 870240080573, dated 09 / 20 / 2024, page 17 / 32 6 / 6 quantities of OR concentrate sent to the NF units, if any, may vary. In some instances, at least some OR concentrate, for example, SWRO concentrate, is sent to the NF units at some or all times.

[014] The NF system may have one or more stages. In the example shown, a triple-pass RO system may be used. Part or all of the NF permeate (in line (9)) may be mixed with part or all of the RO permeate (in line (16) or (25) or a mixture thereof) to create the final product water. The final product water may be injected into a formation containing oil, optionally after being mixed with one or more chemicals, to improve oil recovery.

[015] In general, the optional and / or controllable elements of the system in Figure 1 can be used to produce one or more qualities in the final product water. It is generally desirable that the final product water have low hardness, for example, less than 20 mg / l of hardness as CaCO3. However, the salinity (or TDS) requirement of the final product water may vary in time or location and may be more or less than the salinity of the feed water. The system shown in Figure 1 is normally capable of producing final product water with hardness less than 20 mg / l when fed with normally pre-treated seawater (i.e., seawater that has been treated by one or more of a clarifier, dissolved air filtration unit, filter media and microfiltration or ultrafiltration membrane or similar treatment units).The system shown in Figure 1 is also capable of receiving feed water with salinity up to 50 g / l and producing final product water with more, less, or the same salinity as the feed water. Petition 870240080573, dated 09 / 20 / 2024, page 18 / 32

Claims

1 / 3 Claims 1. WATER TREATMENT METHOD, characterized by comprising: - treating a portion of feed water by means of reverse osmosis to produce a reverse osmosis permeate and a reverse osmosis concentrate; - treating a portion of the reverse osmosis concentrate by means of nanofiltration to produce nanofiltration permeate; - optionally, treating a portion of the feed water by means of nanofiltration to produce additional nanofiltration permeate; - using the nanofiltration permeate or a mixture of the nanofiltration permeate and the reverse osmosis permeate as product water to be injected into an oil-containing formation, the product water having a higher salinity than the salinity of the feed water.

2. METHOD, according to claim 1, characterized in that the feed water has a salinity of 35 g / l of Total Dissolved Solids or more, or the feed water comprises seawater.

3. METHOD, according to any one of claims 1 to 2, characterized in that the product water has a salinity of 40 g / l of Total Dissolved Solids or more.

4. METHOD, according to any one of claims 1 to 3, characterized in that the feed water comprises seawater and the product water has less than 20 mg / l of hardness as CaCO3.

5. WATER TREATMENT SYSTEM, comprising: - a reverse osmosis system; - a nanofiltration system, wherein an inlet to the reverse osmosis system is connected to a feed water source and a concentrate outlet from the reverse osmosis system is connected to a feed inlet of the nanofiltration system, and characterized in that the reverse osmosis system and the nanofiltration system are configured to produce a product water having a salinity higher than the salinity of the feed water.

6. SYSTEM, according to claim 5, characterized by an inlet for the nanofiltration system being connected to the feed water source.

7. SYSTEM, according to any one of claims 5 to 6, characterized in that a permeate outlet from the nanofiltration system is connected to an injection system and a permeate outlet from the reverse osmosis system is connected to the injection system.

8. SYSTEM, according to any one of claims 5 to 7, characterized in that the injection system is adapted to inject product water comprising reverse osmosis permeate and / or nanofiltration permeate, wherein the nanofiltration permeate may include treated reverse osmosis concentrate, at least at some points, into a reservoir containing petroleum.

9. SYSTEM, according to any one of claims 5 to 8, characterized by having a suitable arrangement of pipes and valves or other flow control devices, such that various flow rates in the system can be changed, optionally automatically or by means of a controller, optionally over time.

10. SYSTEM, according to any one of claims 5 to 9, characterized in that a controller can manipulate the flow control or other devices to vary one or more of (a) the relative amounts of feed water flowing into the inlet of the reverse osmosis unit relative to the nanofiltration unit, (b) the amount, if any, of reverse osmosis concentrate flowing into the nanofiltration unit, (c) and the relative amounts of reverse osmosis permeate and nanofiltration permeate in the product water.

Images