EA039982B1 - METHOD AND SYSTEM FOR PRODUCING LOW-MINERALIZED INJECTION WATER - Google Patents

Description

The field of technology to which the invention belongs

The present invention relates to a method for producing low-salinity injection water intended for injection into an oil-bearing formation and having a controlled salinity to prevent deterioration of the reservoir properties of the formation and a sufficiently low concentration of sulfate anions to prevent acidification of this formation, and also relates to a demineralization system for obtaining such injected water .

State of the art

A well-known method for enhancing oil recovery of a productive formation, described in international patent application WO 2008/029124, is based on the injection of brackish water into an oil-bearing formation.

One of the problems associated with brackish water flooding is that water produced by demineralization technologies and destined for injection into an oil-bearing formation may have a less than optimal salinity. Indeed, demineralized water can degrade the reservoir properties of the oil-bearing rock in the formation and slow down the recovery of oil, for example by causing the clays in the formation to swell. Therefore, there is an optimal degree of mineralization of the injected water, which favorably provides increased oil recovery and at the same time reduces the risk of formation damage, and this optimal value may vary from reservoir to reservoir. In general, in an oil containing formation containing a large amount of swellable clays, damage to the formation with continued oil recovery can be avoided if the injected water has a total dissolved solids content (TSDS) in the range of 500 to 5000 parts per million (ppm), preferably - from 500 to 3000 ppm, in particular from 1000 to 2000 ppm.

However, mixing demineralized water having a low content of polyvalent cations and multivalent anions with untreated highly mineralized water, such as sea water, is undesirable due to the high content of sulfate anions and multivalent cations in untreated highly mineralized water and the presence of microelements and nutrients in it. substances. Thus, a high content of sulfate anions in a mixed water stream and the presence of trace elements and nutrients in it can lead to the rapid growth of sulfate-reducing bacteria and, consequently, to acidification of the formation. Further, a high content of multivalent cations in the mixed water stream can lead to the precipitation of insoluble mineral salts (scale formation) in unacceptable amounts when the injected water comes into contact with cations of substances that cause precipitation, such as barium, strontium and calcium cations, usually present in the relict reservoir water. In addition, mixing demineralized water with highly mineralized water, such as sea water, can lead to an increase in the mixed water stream to unacceptable levels of multivalent cations, in particular calcium and magnesium cations. Thus, in order to achieve additional oil recovery by injection of brackish water, the ratio of the concentration of polyvalent cations in the brackish injected water to the concentration of polyvalent cations in the relict water of the productive formation should be less than 1, preferably less than 0.9, more preferably less than 0.8, in particular less than 0 .6, for example less than 0.5.

An international patent application published under the number WO 2011/086346 describes a method related to obtaining a stream suitable for injection into an oil-saturated rock of an oil-bearing formation with a controlled degree of salinity and a controlled concentration of sulfate anions and includes the following steps:

supplying feed water having a total dissolved solids content in the range of 20,000 to 45,000 ppm and a concentration of sulfate anions in the range of 1,000 to 4,000 ppm, preferably 1,500 to 4,000 ppm, to a demineralization plant containing several reverse osmosis (OO) membrane modules and several nanofiltration membrane modules (NF), and the pressure of the source water is increased to a value in the range from 350 to 1250 psi. inch (absolute - abs), and separating the source water to obtain the feed water for the OO membrane modules (also referred to as the incoming OO water stream) and the feed water for the NF membrane modules (also called the incoming NF water stream);

increasing, if necessary, the pressure of the incoming OO-water stream to a value in the range from 900 to 1250 psi. inch (abs.) before supplying the incoming OO-water flow to the membrane OO-modules and the selection of OO-permeate (filtrate) and OO-concentrate from the membrane OO-modules, and the membrane OO-modules operate in a single-pass single-stage or in a single-pass two-stage mode, and the yield of OO-permeate is in the range of 35 to 75% by volume, preferably 35 to 60% by volume, relative to the volume of incoming OO-water supplied to the OO-membrane modules, such that the OO-permeate has a total dissolved solids content of less than 250 ppm and the concentration of sulfate anions is less than 3 ppm;

lowering, if necessary, the pressure of the incoming NF-water stream to a value in the range from 350 to 450 psi. inch (abs.) before supplying the incoming NF water stream to the membrane

- 1 039982

NF-modules and selection of NF-permeate and NF-concentrate from membrane NF-modules, and membrane NF-modules operate in a single-pass single-stage mode, and the output of NF-permeate is in the range from 35 to 60% by volume relative to the volume of the incoming NF-water flow supplied to the NF membrane modules such that the NF permeate has a total dissolved solids content in the range of 15,000 to 40,000 ppm, preferably 15,000 to 35,000 ppm, and a sulfate anion concentration of less than 40 ppm, preferably less than 30 ppm; and mixing at least part of the OO-permeate and at least part of the NF-permeate in a ratio ranging from 2:1 to 40:1, preferably from 4:1 to 27:1, in particular from 10:1 to 25 :1 to produce injection water having a total dissolved solids content in the range of 500 to 5000 ppm, preferably 1000 to 5000 ppm and a sulfate anion concentration of less than 7.5 ppm, preferably less than 5 ppm, more preferably less than 3ppm

However, there is a problem associated with offshore fields, which is the limited space available on the platform or floating system for oil production, storage and offloading - FPSO (from English Floating Production, Storage & Offloading), so it would be desirable to reduce the number NF modules in the NF stage of the membrane demineralization plant, thereby reducing the weight of this plant and the area it occupies.

Disclosure of invention

In a first embodiment, the present invention relates to a demineralization system comprising a feed pump comprising an inlet and outlet;

a first OO stage comprising an inlet, an outlet for an OO permeate, and an outlet for an OO concentrate; a second OO stage comprising an inlet, an outlet for an OO permeate, and an outlet for an OO concentrate; NF-stage containing inlet, outlet for NF-permeate and outlet for NF-concentrate; and a group of pipelines, made with the possibility of connection:

(a) the outlet of the feed pump with the inlet of the first OO-stage;

(b) a first OO-stage concentrate outlet with (I) a second OO-stage inlet and (II) an NF-stage inlet;

(c) a first OO-stage permeate outlet, a second OO-stage permeate outlet, and an NF-stage permeate outlet, directly or indirectly, with a brackish water injection line.

In a second embodiment, the present invention relates to a method for treating feed water, comprising the following steps:

directing the feed water flow through the first stage of reverse osmosis (OO) filtration to obtain a first stage OO permeate and a first stage OO concentrate;

directing a first portion of the OO concentrate through a second OO filtration stage to obtain a second stage OO permeate and a second stage OO concentrate;

directing the flow of the second part of the first stage OO concentrate through a nanofiltration (NF) stage to obtain NF permeate and NF concentrate;

combining first stage OO permeate, second stage OO permeate, and NF permeate streams to form a brackish water stream for injection.

The low-mineralized water stream is injected into the oil-bearing formation. At least one injection well and at least one production well are typically drilled into this oil containing formation. The flow of low-salinity water injected into the reservoir through the injection well(s) displaces oil, moving it through the reservoir in the direction of the corresponding production well(s) through which the oil is extracted. In some cases, a portion (slug) of weakly mineralized water is pumped into the injection well(s), having a pore volume in the range from 0.3 to 0.9, preferably from 0.4 to 0.7, referred to the swept (washed out) water) pore volume between the injection well and associated production well(s). After the brackish water slug has been injected, displacement or post-flush water (e.g., seawater, estuary water, highly saline produced water, highly saline aquifer water, or mixtures of the above) may be injected into the injection well to move the brackish water and hence oil into the direction of the production well.

Brief description of the drawings

The drawings show:

fig. 1 is a flow diagram of a first demineralization system according to the invention;

fig. 2 is a flow diagram of a second demineralization system according to the invention.

Terms and Definitions

In the description below, the following terms are used.

Feed water/Inlet water: Water fed to the first OO stage of the demineralization system.

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Produced water: water separated from oil and gas at field equipment.

Unit ppmv: parts per million per volume of water; equivalent to the unit mg/l.

Reverse Osmosis Membrane Element: A filter element containing a reverse osmosis (OO) membrane.

Nanofiltration Membrane Element: A filter element containing a nanofiltration (NF) membrane.

Reverse osmosis (OO) filtration module: comprises a high pressure vessel or housing containing one or more OO membrane elements, preferably 1 to 8, in particular 4 to 8 OO membrane elements.

Nanofiltration (NF) module: contains a pressure vessel containing one or more NF membrane elements, preferably 1 to 8, in particular 4 to 8 NF membrane elements.

Pressure Vessel of an OO or NF Filtration Module: typically a cylindrical shaped vessel containing a cylindrical wall (ie a cylinder) and first and second end caps located at the first and second ends of the cylinder.

Reverse osmosis (OO) stage of the demineralization system: a group of OO filtration modules connected in parallel with each other. Similarly, the nanofiltration (NF) stage of the demineralization system is a group of NF filtration modules connected in parallel with each other.

Membrane block: contains OO- and NF-filtration stages, connected to each other to provide a stepped separation of the concentrate and having, as a rule, a common system of valves and pipelines. One, two or more membrane units can be mounted on a frame base.

Detailed description of embodiments of the invention

Other distinctive features and advantages of the invention will become apparent from the following description of preferred embodiments.

The demineralization system of the present invention comprises at least one membrane unit including an OO-node and an NF-node. The OO assembly includes at least two, preferably two or three OO stages. The NF node includes at least one NF stage, preferably one or two NF stages. The OO-stages are connected to each other, providing a stepped separation of the concentrate in the OO-node. In addition, the first OO-stage is connected to the NF-node, which provides a stepped separation of the concentrate on this OO-stage and NF stage(s) of the NF-node.

Feedwater is pressurized into the first OO stage, which separates it into the first stage OO permeate and the first stage OO concentrate. In some cases, the concentrate may also be referred to as the retentate. Then, the first stage OO concentrate is separated into a first part and a second part, forming, respectively, the incoming OO water stream for the second OO stage and the incoming NF water stream for the NF node. If the NF node includes only one stage, then the incoming NF water flow is divided into NF permeate and NF concentrate. NF-concentrate is removed from the membrane block; for example, in the case of an offshore demineralization system, the NF concentrate is discharged overboard through the discharge line provided for it. If the NF node includes two stages, then the first NF stage separates the incoming NF water flow into the first stage NF permeate and the first stage NF concentrate. The first stage NF concentrate is then used as an input to the second NF stage, which separates it into the second stage NF permeate and the second stage NF concentrate. The NF concentrate of the second stage is removed from the membrane block; for example, in the case of an offshore demineralization system, the NF concentrate is discharged overboard through its intended discharge line. The first stage NF permeate and the second stage NF permeate are then combined to form a combined NF permeate.

The second OO stage separates the first part of the first stage OO concentrate into the second stage OO permeate and the second stage OO concentrate. If two OO stages are provided, the second stage OO concentrate can be withdrawn from the membrane unit; for example, in the case of a marine demineralization system, it can be drained overboard through the provided brine discharge line from the OO plant.

Furthermore, it is envisaged that the second stage OO concentrate can be fed to the third stage OO filtration, where the third stage OO permeate and the third stage OO concentrate are formed. If three OO stages are provided, the third stage OO concentrate can be withdrawn from the membrane unit; for example, in the case of a marine demineralization system, it can be drained overboard through the provided brine discharge line from the OO plant. It is envisaged, however, that the OO concentrate of the second stage may be separated to obtain an incoming OO water stream for the third OO stage and water recycled to the NF node and forming an incoming NF stream containing a mixture of OO concentrate from the first and second stages .

Typically, the first stage OO permeate, the second stage OO permeate, and optionally the third stage OO permeate may be combined to form a combined OO permeate. If two NF stages are provided, the first stage NF permeate and the second stage NF permeate may be combined to form a combined NF permeate. Then NF permeate (obtained from single stage NF unit) or combined NF permeate (obtained from two stage NF unit) and volume

- 3 039982 Dinene OO-permeate can be mixed to form brackish water intended for injection.

However, one skilled in the art will appreciate that the mixing order of the different permeate streams may vary. For example, if two OO stages and two NF stages are provided, the first stage OO permeate can be combined with the first stage NF permeate, the second stage OO permeate can be combined with the second stage NF permeate, and then the two composite streams can be combined to form a brackish water stream for injection.

One skilled in the art will appreciate that:

(1) NF membrane cells typically operate at lower pressures than OO membrane cells;

(2) there are pressure drops at each stage of the membrane unit;

(3) The pressure and flow through the diaphragm assembly can be controlled by one or more pumps and one or more valves (eg, throttle, check, or pressure reducing valves).

One of the advantages of the demineralization system of the invention is that the pressure and flow in the membrane unit can be controlled to adjust the pressure of the first stage OO concentrate to achieve the required inlet pressure for the NF unit. If necessary, the pressure of the first part of the first stage OO concentrate (used as the inlet stream for the second OO stage) is increased, for example, using a booster pump, to a value that is equal to or higher than the minimum supply pressure for the second OO stage.

Alternatively, the pressure and flow in the membrane unit can be controlled to control the pressure of the first stage OO concentrate to achieve the desired inlet pressure for the second OO stage. For example, this can be achieved by applying back pressure to the first stage OO permeate. If necessary, the pressure of the second part of the first stage OO concentrate (used as the inlet stream to the NF node) is reduced to a value that is equal to or lower than the maximum supply pressure for the NF node.

If a part of the second stage OO concentrate is recycled to the NF unit, then it is possible to pressurize this recirculating OO concentrate to a value higher than the minimum supply pressure for the NF unit, if necessary with the help of a booster pump. This need may arise if the initial pressure of the recycle OO concentrate of the second stage is lower than the required supply pressure for the NF node, for example, below the minimum operating pressure for the NF elements of the NF node.

The demineralization system also includes valves and piping providing pathways for the flows described above. Thus, the first OO-stage of the membrane unit additionally contains the main pipeline extending from the outlet for the OO-concentrate of the first stage. This main pipeline splits at a branching point, forming the supply pipeline for the second OO stage and the supply pipeline for the NF node. A flow regulator may be provided in the main pipeline to control the separation of the first stage OO concentrate between the second OO stage and the NF unit. The inlet or supply pressure for NF modules of a single stage NF assembly or for the first stage of a two stage NF assembly is preferably in the range of 350 to 450 psi. inch (abs.), in particular from 380 to 420 psi. inch (abs.), for example, is about 400 psi. inch (abs.). If the pressure of the first stage OO concentrate exceeds the required supply pressure for the NF unit, a relief valve may be provided in the supply line to the NF unit to reduce the pressure to the desired value. Alternatively, a control valve may be provided in the supply line to the NF unit to control the flow of the first stage OO concentrate to the NF unit and also reduce the pressure of this concentrate to the required supply pressure to the NF unit. A booster pump may be provided in the supply line for the second OO stage to increase the supply pressure to a value that is equal to or higher than the minimum supply pressure for the second OO stage. This may become necessary if the pressure of the first stage OO concentrate is below the required supply pressure for the second OO stage, in particular below the minimum operating pressure for the OO elements of the second OO stage.

The NF permeate or combined NF permeate flow line is provided with a check valve located downstream to the point where the NF permeate or combined NF permeate merges with the combined OO permeate. This check valve ensures that the NF permeate or combined NF permeate is sufficiently pressurized over the OO permeate to force the NF permeate or combined NF permeate into the combined OO permeate to form brackish water for injection. The check valve opens when the pressure of the NF permeate or combined NF permeate exceeds a set value, resulting in

- 4 039982 whereby sufficient NF-permeate or combined NF-permeate flows through the valve to maintain the NF-permeate pressure above the set point. The check valve setpoint is typically at least 5 psi above the combined OO-permeate pressure. inch. In general, the pressure of the combined OO-permeate is in the range of 10 to 75 psi. inch (abs.), preferably from 20 to 55 psi. inch (abs.).

The second OO stage of the membrane unit comprises, in one embodiment of the invention, a recirculation conduit configured to recirculate at least a portion of the concentrate from the second OO stage to the NF assembly. The recirculation pipeline can be connected to the supply pipeline for the NF unit. A recirculation pump may be provided in the recirculation line to pressurize the second stage OO concentrate. Depending on the pressure of the second stage OO concentrate, the recirculation line may be connected to the supply line for the NF unit at a point upstream or downstream of the pressure reducing valve.

Another advantage of the demineralization system of the invention is that the first stage OO concentrate (part of which is used as the NF node feed) has a higher total dissolved solids and multivalent cation content than the first stage feed. OO stages, whereby the NF permeate has a higher total dissolved solids and multivalent cation content than when the feed water is split to form an OO inlet stream for the OO node and an NF inlet stream for the NF node. Therefore, to achieve the required ionic composition (total solids dissolved solids, multivalent cations, and multivalent anions) in order to obtain a brackish water stream intended for injection, a lower mixture ratio of NF-permeate to OO-permeate (and therefore , a smaller volume of the obtained NF-permeate).

Due to the increased salinity of the first stage OO concentrate (compared to the mineralization of the feedwater entering the first stage OO), it may be necessary to add a dose of scale inhibitor or mixture of scale inhibitors directly to the concentrate to reduce the risk of plugging the second stage OO elements. OO-stage or NF-elements NF-node by mineral deposits. Similarly, if a third stage OO-concentrate is provided in the membrane unit, then due to the increased degree of mineralization of the second-stage OO-concentrate (compared to the degree of mineralization of the first-stage OO-concentrate), a dose of an inhibitor or a mixture of scale inhibitors with in order to reduce the risk of clogging of the OO-elements of the third OO-stage. Further, if the NF node contains the first and second NF stages, then the NF concentrate of the first stage used as the input stream for the second NF stage, a dose of scale inhibitor can be added, since the NF concentrate of the first stage has a higher degree of mineralization than the incoming stream for an NF node.

The feed water for the first OO stage of the membrane unit can be brackish water such as estuary water, brackish water from an aquifer or brackish bottom water, highly mineralized (salty) water such as sea water (preferred), brackish water from aquifer or highly mineralized wastewater. The feed water for the first OO stage has a total dissolved solids content (TSDS) preferably at least 20,000 ppmv, more preferably in the range of 30,000 to 45,000 ppmv. The feed water for the first OO stage of the membrane unit has a sulfate anion concentration in the range of 1000 to 4000 ppmv, preferably 1500 to 4000 ppmv and a multivalent cation concentration in the range of 700 to 3000 ppmv, preferably 1000 to 3000 ppmv, more preferably from 1500 to 2500 ppmv.

The TWP of the first stage OO permeate is preferably in the range of 50 to 225 ppmv, more preferably 75 to 225 ppmv, most preferably 100 to 200 ppmv, in particular 100 to 150 ppmv.

The sulfate anion concentration of the first stage OO permeate is preferably in the range of 0.5 to 2.5 ppmv, in particular 0.5 to 1.5 ppmv.

The TWP of the second stage OO permeate is preferably in the range of 200 to 350 ppmv, most preferably 200 to 300 ppmv, in particular 225 to 275 ppmv.

The sulfate anion concentration of the second stage OO permeate is preferably in the range of 4 to 7.5 ppmv, most preferably 4.5 to 6.5 ppmv, in particular 4.75 to 5.75 ppmv.

The combined OO-permeate preferably has an RTT of less than 200 ppmv, more preferably less than 150 ppmv.

The RTW of the first stage OO concentrate is higher than the TWT of the first OO stage feed water preferably by 20-35%, more preferably by 27.5-32.5%, in particular by about 30%.

The RTWT of the second stage OO concentrate is typically 20-35% higher than the TWT of the first stage OO concentrate.

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The NF permeate from the single stage NF unit or the mixture of the first stage NF permeate and the second stage NF permeate from the two stage unit (hereinafter referred to as the NF permeate obtained by the NF unit) has a TRTV of 20-35%, preferably 27.5 -32.5%, in particular about 30%, higher than when the water used as input to the first OO stage was also used as input to the NF node. The NF permeate obtained by this unit also typically has a concentration of multivalent cations 20-35%, preferably 27.5-32.5%, in particular about 30% higher than the NF permeate that would be obtained, if the water used as input to the first OO stage was also used as input to the NF node. The higher concentration of polyvalent cations in the NF permeate is an advantage as it can reduce the risk of formation damage due to shale swelling or migration.

Membrane NF elements suitable for use in NF modules must have:

(1) a high sulfate anion retention rate of at least 98%, preferably at least 99.88%, so that the NF permeate obtained by the NF unit has a low sulfate anion concentration of less than 40 ppmv, thereby reducing the risk of reservoir acidification or mineral scale formation, for example, in production wells;

(2) a lower retention rate of divalent cations than that of sulfate anions, ranging from 70 to 80%, in particular from 75 to 77%, thereby ensuring the passage of a part of the divalent cations through the membrane into the NF permeate, which is is an advantage because divalent cations are expected to reduce the risk of formation damage;

(3) high permeability of monovalent ions (monovalent cations such as sodium and potassium cations and monovalent anions such as chloride and bromide anions). The preferred NaCl penetration rate in the NF membrane is at least 43% (NaCl retention rate is less than 57%). This minimizes the required operating pressure of the NF unit and provides a high TWP for the NF permeate to be used as the blend stream.

A suitable NF membrane element is NANO SW™ available from Hydranautics.

If the influent to the first OO stage has a TFR in the range of 30,000 to 45,000 ppmv, then the NF permeate produced by the NF node typically has:

(i) TDS in the range of 25,000 to 30,000;

(ii) a sulfate anion concentration of less than 40 ppmv;

(iii) a concentration of multivalent cations in the range from 550 to 750 ppmv, in particular from 570 to 750 ppmv.

The NF permeate produced by the NF node has a divalent cation concentration in the range of 575 to 725 ppmv, in particular 590 to 725 ppmv.

The second or third stage OO concentrate (especially the second stage OO concentrate) exiting the OO unit is generally under relatively high pressure. Therefore, before leaving the demineralization system, the second or third stage OO concentrate can be passed through a hydraulic energy recovery device (for example, a hydraulic recovery turbine or turbocharger), which can be connected to one or more feed pumps for the first OO stage, an auxiliary booster pump for the first part of the OO concentrate of the first stage used as the input stream for the second OO stage, or an auxiliary recirculation pump for the second part of the OO concentrate of the second stage, recycled to the NF unit. For example, a turbine shaft may drive the shaft of one of the aforementioned pumps. These shafts can be connected through a gearbox. The hydraulic energy recovery device accordingly recovers the energy of the second or third stage OO concentrate and uses this recovered energy to pressurize one or more inlet streams of the membrane OO stages or NF unit, thereby reducing the energy demand of the demineralization system. However, in order to achieve the required supply pressure of the inlet streams, it is usually necessary to supply additional energy to the feed pump/auxiliary booster pump/auxiliary recirculation pump. The pressure of the second or third stage OO concentrate after passing through the hydraulic energy recovery device is typically less than 100 psi. inch (gauge man.), preferably in the range from 10 to 75 psi. inch (man.), in particular from 20 to 55 psi. inch (man.), for example, from 10 to 50 psi. inch (man.).

As a rule, the pressure of the NF concentrate discharged from the NF unit (from a single NF stage or from the second stage of a two-stage NF unit) is too low to provide energy recovery. However, if necessary, energy can be obtained, using a device for recovering hydraulic energy and from the NF concentrate.

The demineralization system must have a capacity sufficient to meet the demand for brackish water intended for injection into the oil-bearing formation. Each unit of a demineralization system is typically capable of producing 20,000 to 200,000 barrels per day,

- 6 039982 eg 40,000 to 60,000 bbl/d of injection water having the desired low salinity, low multivalent cation concentration, and low sulfate anion concentration.

The pressure vessels of the filtration modules of each stage of the demineralization system are cylindrical and have a length in the range of approximately 80 to 475 inches (2.0 to 12.1 m), preferably 80 to 400 inches (2.0 to 10.2 m ). Cylindrical pressure vessels have an internal diameter ranging from 4 to 20 inches (0.10 to 0.51 m), such as an internal diameter of 4, 6, 8, 9, or 16 inches (0.10; 0.15; 0. 20; 0.23 and 0.41 m).

The OO membrane elements placed in the pressure vessels of the OO stages and the NF membrane elements placed in the pressure vessels of the NF stage(s) are usually spiral wound (preferred) or tubular hollow fiber elements. Typically, each membrane element placed in a pressure vessel is cylindrical in shape, ranging in length from 20 to 40 inches (0.51 to 1.02 m) and an outside diameter slightly smaller than the inside diameter of the cylindrical pressure vessel. so that the membrane element is located in the pressure vessel with a tight fit.

The first and second end caps of the pressure vessels are preferably removable to allow maintenance and replacement of the OO or NF elements. A single set of successive membrane elements may be placed in the pressure vessel, in which case the feedwater inlet is at or near the end of the pressure vessel. Feed water passes through all elements of the set in sequence and exits as a concentrate through an outlet located at or near the opposite end of the pressure vessel. The permeate may exit the pressure vessel through an outlet located at one end of the pressure vessel or through the first and second outlets located respectively at the first and second ends of the pressure vessel. The outlet(s) port(s) is(are) usually provided in one or both end caps of the pressure vessel.

Alternatively, the pressure vessel may comprise a central opening with two sets of membrane elements located on either side of the central opening, each set of membrane elements including a drive element positioned in the end position of the pressure vessel. Each set of membrane elements preferably comprises two to four, in particular two to three, successive membrane elements. Feed water enters the pressure vessel containing the central opening through the first and second inlets located respectively at or near the first and second ends of the pressure vessel and sequentially passes through each set of membrane elements. The concentrate can be removed from the pressure vessel through the central opening, and the permeate through the first and second end openings located respectively at or near the first and second ends of the pressure vessel. The first and second permeate ports are preferably provided in the end caps of the pressure vessel. Favorable results in the operation of OO-modules are provided by the passage of a turbulent water flow through the entire sequence of membrane elements, since this minimizes the risk of concentration polarization (excessive salt concentration on the membrane surface). A particular advantage of an OO vessel with a center hole is that a lower pressure drop occurs across each set of OO membrane elements compared to a design without a center hole that includes a single set of OO elements (assuming both types of OO vessels accommodate the same number of OO elements with the same size). This means that the feed rate to the driver of each set of OO vessel elements with a central hole may be lower than the feed rate to the driver of a single set of vessel elements without a center hole. For example, if a vessel with a central opening holds two sets of three OO-membrane elements, then flow turbulence can persist in the last (third) element of each set of elements even at a low feed rate to the leading element of each set of 7 to 9 m/h . In contrast, to maintain flow turbulence in the last of six to seven OO membrane elements (same size as those used in a vessel with a center hole) arranged in series in a vessel without a center hole, supply pressure to the drive element may be required, close to the maximum allowable, at which the feed rate to the leading element is from 14 to 17 m/h. Therefore, the supply pressure in the case of a vessel with a center hole is less related to the restrictions imposed by the maximum allowable feed rate into the leading OO element than in the case of a vessel without a center hole containing the same number of OO elements.

Membrane NF modules of the NF node can also contain vessels with a central hole containing a set of membrane NF elements located on both sides of this central hole. However, a beneficial effect can also be achieved by using a traditional (not containing a central hole) pressure vessel in the NF modules and

- 7 039982 sequential placement inside this vessel of 6 or more, for example from 6 to 12, preferably from 8 to 12 membrane NF elements, which can result in both the advantage of a pressure drop across successive NF membranes and the possibility of increasing the level concentration polarization, when the NF water flow passes through a sequence of membrane elements, in particular in membrane elements located in the set at positions from fifth to twelfth. Concentration polarization would lead to a deterioration in the quality (higher TRTW and higher concentration of multivalent cations) of the permeate compared to using an NF vessel containing a central hole and containing the same number of NF membrane elements of the same size. This would make it possible to reduce the ratio of NF- and OO-permeate in the mixture during the formation of low-mineralized water intended for injection, and, therefore, would create prerequisites for reducing the volume of NF-permeate production.

Each OO- and NF-stage contains several parallel pressure vessels. The first OO stage is preferably larger (ie contains more OO elements of the same size in the OO modules, or in other words has a larger OO surface area) than the second OO stage. The preferred ratio of the number of OO elements in the first OO stage and the number of OO elements in the second OO stage, as well as the ratio of the surface area of the OO elements in the first OO stage and the surface area of the OO elements in the second stage, is in the range of 2 :1 to 5:3 (with the same size of OO-elements in each stage).

The first OO stage is usually larger than the NF node. For example, the surface area of the OO elements in the first OO stage may be greater than the surface area of the NF elements in the NF node, or more OO elements may be provided in the first OO stage than there are NF elements in the NF node when OO- and NF elements have the same size. The quantitative ratio of OO elements in the first OO stage and NF elements in the NF node is preferably in the range from 10:1 to 15:1 (with the same size of OO and NF elements).

If the NF node is two-stage, then the first NF stage is larger than the second NF stage. The quantitative ratio of NF elements in the first NF stage and NF elements in the second NF stage is preferably in the range of 10:1 to 15:1 (with the same size of NF elements).

By the same element size is meant that these elements have the same membrane surface area.

The OO and NF modules are preferably arranged horizontally, in rows and one above the other (i.e., the longitudinal axes of the cylindrical pressure vessels are aligned horizontally), thereby reducing the area occupied by the membrane unit. The NF modules are preferably arranged together, for example in a single row. When placing OO and NF modules horizontally on top of each other, vertical arrangement of the feed header, OO-permeate header (for a combined OO-permeate flow), OO-concentrate header, NF-permeate header (for a single or combined NF-permeate flow) is preferable. ) and an NF-concentrate collector.

The demineralization system is typically operated at a pressure drop across the OO-stages and NF-stage(s) of the membrane unit, providing a permeate yield by volume of 40 to 60%, preferably 45 to 55%, in particular about 50% (based on volumetric water flow rate (feed water flow) included in the first OO-stage, and the total volumetric flow rate of OO-permeate and NF-permeate obtained through this membrane unit). Operating the demineralization system at this rate of permeate recovery increases the flow of water through the system and into the second OO stage and NF stage(s). However, if the capacity of the demineralization system has been limited by the feedwater space velocity, then it may be beneficial to operate the system at a higher recovery rate by increasing the feedwater pressure.

The NF assembly of at least one membrane unit of the demineralization system can be disconnected in the event of a decrease in the need for NF permeate, for example, in the late stage of a low-salinity water flood, when the amount of high-salinity produced water increases, which can be mixed with the permeate streams obtained by the membrane unit.

Alternatively, the NF membrane elements of some or all of the NF modules of at least one membrane unit can be replaced with OO membrane elements if there is a greater need for OO-permeate and less for NF-permeate due to the presence of highly saline bottom water for mixing with permeate streams. In this scenario, the NF pressure vessels must be sized for the operating pressure of the OO membrane elements, which is typically higher than the operating pressure of the NF elements.

The first stage OO permeate is of higher quality (lower TWP) than the OO permeate taken from the second OO stage. Similarly, in cases where a third OO stage is provided, the second stage OO permeate is of higher quality (lower TWP) than the OO permeate taken from the third OO stage. Therefore, it is preferable for an OO node to work with

- 8 039982 higher permeate yield from the first OO-stage than from the second OO-stage. If a third OO stage is provided, it is preferable to operate an OO unit with a higher permeate yield from the first OO stage than from the second OO stage and a higher permeate yield from the second OO stage than from the third OO stage. .

The first OO stage of the membrane unit can provide an OO permeate yield of 30 to 35% based on the volumetric flow rate of the water flowing into the first OO stage. The second OO stage may provide an OO permeate yield of 20 to 27.5% based on the volumetric flow rate of the water (the first part of the first stage OO concentrate) entering the second OO stage. Optionally, a third OO stage can provide an OO permeate yield of 10 to 20% based on the volumetric flow rate (second stage OO concentrate) entering the third OO stage. The yield of the combined OO-permeate may be from 45 to about 52%, preferably from about 47.5 to about 50% (based on the volumetric flow rate entering the first OO-stage).

If the NF unit contains a single NF stage, then the NF permeate yield is typically in the range of 30 to 60%, preferably 35 to 55%, based on the volumetric flow rate (the second part of the first stage OO concentrate) entering the NF -step. If an NF assembly contains a first and a second NF stage, then the first NF stage typically provides an NF permeate yield of 45 to 55% based on the volumetric flow rate of the first NF stage, while the second NF stage typically provides a yield of 20 to 55% based on the volumetric flow rate (first stage NF concentrate) entering the second NF stage. The yield of the combined NF permeate from the first and second NF stages may range from 65 to 75%, preferably from 70 to 75%, based on the volumetric flow rate (the second part of the first stage OO concentrate) entering the first NF stage . The percentage yield of NF permeate in the NF node is typically in the range of 3 to 5%, preferably 3.25 to 3.75%, in particular about 3.5%, based on the space velocity of the water flow entering the first OO- step.

Mixing ratio of OO-permeate (1st stage OO-permeate, 2nd-stage OO-permeate and, if available, 3rd-stage OO-permeate) and NF-permeate (NF-permeate from a single-stage NF-assembly or combined NF-permeate from a two-stage NF-node) is chosen in order to obtain low-mineralized water intended for injection and having a degree of mineralization that is within the range optimal for a given oil-bearing formation, and providing an increase in oil recovery while reducing the risk of damage to the formation. One skilled in the art will appreciate that the optimal range of salinity can be determined from experiments involving core flooding and permeability measurements performed using wall samples taken from the formation and various brackish injection water compositions.

The ratio in the mixture depends on:

(i) the ratio of the volumetric flow rate of the first part of the first stage RO concentrate entering the second RO stage and the second part of the first stage RO concentrate entering the NF unit;

(ii) the amount of second stage RO concentrate (if any) recycled to the NF unit;

(iii) percentage of RO permeate yield from each RO stage;

(iv) the percentage of NF permeate from a single NF stage or from each stage of a two-stage NF unit;

(v) discharging (if any) a portion of the pooled OO-permeate or pooled NF-permeate (performed up to the point of confluence to form brackish water to be injected) into the water body.

A typical ratio of the volumetric flow rate of the first part of the first stage OO concentrate (used as the input to the second OO stage) to the volumetric flow rate of the second part of the first stage OO concentrate (used as the input to the NF node) is preferably in the range from 5:1 to 15:1, more preferably from 7.5:1 to 12.5:1, in particular from 8:1 to 10:1.

If the first part of the second stage OO concentrate is used as the input stream for the third stage OO concentrate, and the second part of the second stage OO concentrate is recycled to the NF unit, then the volumetric flow rates of the first and second parts of the second stage OO concentrate are approximately equal to each other , and their ratio is, for example, in the range from 0.75:1 to 1.25:1, in particular about 1:1.

If a three-stage OO-node is provided and the second-stage OO-concentrate is used as the input stream for the third OO-stage and for the NF-node, then the volumetric flow rate of the second-stage OO-concentrate entering the third OO-stage and the NF-node, may be limited by the operating pressure of the 3rd OO stage and NF unit and the requirements to control scaling (formation of mineral deposits) in the 3rd OO stage and NF unit.

A typical volume ratio in which OO-permeate is mixed with NF-permeate to form

- 9 039982 the value of the flow of low-mineralized water intended for injection is in the range from 2:1 to 40:1, preferably from 4:1 to 27:1, in particular from 10:1 to 25:1, while the resulting water has a total dissolved solids content in the range of 500 to 5000 ppm, preferably 1000 to 5000 ppm, and a sulfate anion concentration of less than 10 ppm, preferably less than 5 ppm.

In some cases, bottom water may be mixed into the OO-permeate and NF-permeate to produce low-salinity water for injection, and here it may be necessary to reduce the volume of NF-permeate in the combined stream.

Mixing OO-permeate and NF-permeate in a separate membrane unit is preferable, as this reduces the hydraulic delay when the ratio of NF- and OO-permeate in the mixture changes (for example, in the case of an increase in the amount of produced water available for mixing, or a change in quality the latter, which consists in changing the TSPTS or the concentration of individual ions contained in it). Hydraulic delay occurs due to the presence of some volume of liquid in the pipelines (for example, NF-permeate supply lines and headers, OO-permeate supply lines and headers) up to the point where the OO-permeate, NF-permeate, and produced water flows meet.

The feed water for the first OO stage may be treated using at least one of the following processes:

i) filtration to remove suspended solids;

ii) removal of free chlorine;

iii) adding a biocide;

iv) deaeration;

v) adding a scale inhibitor.

As an alternative to deaeration of feed water before it enters the demineralization system, a deaerator may be placed at the outlet of the system to control corrosion in injection lines, pumps, and wells. The advantage of placing a deaerator at the outlet is that the volume of deaerated water in this case is significantly less than in the case of placing a deaerator in the direction of flow to the demineralization system. On the other hand, placing a deaerator upstream of the demineralization system reduces the risk of corrosion within this system and therefore allows the use of cheaper steel grades.

The performance of the demineralization system must be sufficient to meet the demand for low-salinity water injected into a given oil-bearing formation. Typically, each unit of the demineralization system is capable of producing 20,000 to 200,000 barrels, such as 40,000 to 60,000 barrels per day of water having the desired low salinity and the desired low sulfate anion concentration.

An exemplary embodiment of the invention is described below with reference to the attached drawings.

In FIG. 1 shows a membrane unit 1 of a demineralization system for treating feed water 2. The membrane unit 1 includes a feed pump 3 on the feed line, a first OO stage 4, a second OO stage 5 and a single NF stage 6. Each OO stage contains several OO modules. The NF stage contains several NF modules. The second OO rung usually contains fewer OO modules than the first OO rung.

Membrane block 1 contains valves V1-V3 and various pipelines, made with the possibility of implementing the flow paths described below. Valves V1-V3 can move between fully open and fully closed positions. However, in one embodiment of the invention, valves V2 and V3 are throttle valves that can be set to various intermediate positions, and valve V1 is a step down valve. Flows and pressures in the membrane block can be controlled using the supply pump 3, valves V1, V2 or V3, or any combination of the above.

In the scheme shown in Fig. 1, the feed pump 3 pumps feed water 2 into the first OO stage 4, where this water stream is separated into the first stage OO permeate 9 and the first stage OO concentrate 10. At the bifurcation point, the first stage OO concentrate 10 separates to form an inlet 11 for the second OO stage 5 and an inlet 12 for the NF stage 6. The flows and pressure in the membrane unit can be adjusted so that the pressure of the inlet stream 11 corresponds to the working pressure of the second OO - steps. The pressure of the inlet stream 12 for the NF stage can be adjusted using the reduction valve V1, bringing it into line with the operating pressure of the NF stage. If necessary, the pressure of the inlet stream 11 for the second OO stage 5 can be increased by means of a booster pump (not shown) to a value higher than the minimum operating pressure of the second OO stage 5. Alternatively, a check valve (not shown) can be provided in the line for OO-permeate 9 of the first stage in order to increase the pressure of the OO-concentrate 10 of the first stage to a value exceeding the minimum operating pressure of the second OO-stage 5.

The second OO-stage 5 separates the incoming stream 11 into the OO-permeate 13 of the second stage and the OO-concentrate 7 of the second stage, which is removed from the membrane unit. In order to drain the OO concentrate 7, the valve V2 is at least partially open. Then

- 10 039982

The second stage OO permeate 13 is combined with the first stage OO permeate 9 to form a combined OO permeate stream 14. The NF stage separates the inlet stream 12 into NF permeate 15 and NF concentrate 8, which is discharged from the membrane unit. To ensure that the NF concentrate 8 is drained, the valve V3 is at least partially in the open position. The NF permeate 15 is then mixed with the combined OO permeate 14 to form a brackish water stream 16 for injection.

In FIG. 2 shows a modified membrane block of the demineralization system shown in FIG. 1, including a first NF stage 6 and a second NF stage 17. In addition, the second stage OO concentrate 7 separates at the branch point to form an OO concentrate recycle stream 19 and an OO concentrate drain stream 21. Valve V2 is at least partially in the open position so that the drained stream 21 of the OO concentrate is discharged from the membrane unit 1. The recycle stream 19 of the OO concentrate is then mixed with the inlet stream 12, forming a combined inlet stream for the first NF stage 6 If the second stage OO concentrate 7 has a pressure below the minimum operating pressure of the first NF stage, then the pressure of the OO concentrate recycle stream 19 is increased by means of a booster pump 22 until it combines with the inlet stream 12.

The second NF stage 17 separates the NF concentrate 8 from the first NF stage 6 into the second stage NF permeate 18 and the second stage NF concentrate 19, which is discharged from the membrane unit. When this valve V4 is at least partially open, allowing the NF concentrate 19 to drain. The second stage NF permeate 18 then combines with the first stage NF permeate 15 to form a combined NF permeate 20. The combined NF The permeate 20 mixes with the combined OO-permeate 14 to form a brackish water stream 16 for injection.

One skilled in the art will appreciate that the demineralization systems shown in FIG. 1 and 2 may be modified by including a third OO stage receiving as input an OO concentrate from the second stage. The third OO stage would separate the second stage OO concentrate to form a third stage OO permeate mixed with the first and second stage OO permeates and an OO concentrate (OO brine) discharged from the system.

From the above description of embodiments of the invention illustrated with FIG. 1 and 2, it can be concluded that feedwater from a single source can be treated with multiple OO stages and one or more NF stages, with the concentrate (e.g., retentate) from the first OO stage being used as the input stream for one or more more additional OO stages and one or more NF stages. The resulting permeate streams can be combined to form a single brackish water stream for injection into an injection well.

Claims (15)

CLAIM 1. A demineralization system for producing low-mineralized water having the required ionic composition for injection into an oil-bearing formation containing relict water, including a feed line for feed water; a first reverse osmosis (OO) stage having a first OO stage inlet in communication with a feed line, a first OO stage permeate outlet for the first OO stage permeate, and a first OO stage concentrate outlet for the first OO stage concentrate; a second OO stage having a second OO stage inlet in communication with a first OO stage concentrate outlet, a second OO stage permeate outlet for the second OO stage permeate, and a second OO stage concentrate outlet for the second OO stage concentrate; a nanofiltration (NF) stage having an NF stage inlet in communication with a concentrate outlet of the first OO stage, an NF permeate outlet for the NF permeate, and an NF concentrate outlet for the NF concentrate; and a group of pipelines that provides the ability to: (a) connecting the feed line to the inlet of the first OO stage; (b) connecting the outlet for the concentrate of the first OO stage to (i) the inlet of the second OO stage and (ii) the inlet of the NF stage, so that the first part of the concentrate of the OO stage is introduced as an inlet to the second OO stage through the inlet the second OO stage and the second part of the concentrate of the first OO stage as an inlet to the NF stage through the inlet of the NF stage; (c) connecting (i) a first OO-stage permeate outlet, (ii) a second OO-stage permeate outlet, and (iii) an NF-stage permeate outlet to provide a mixture with a certain ratio of components to form a low-salinity water stream intended for injection and having the required ionic composition, and the specified mixture ratio is the ratio of the flow rate of the permeate of the first OO-stage and the permeate of the second OO-stage to the permeate of the NF-stage; and (d) the direct or indirect supply of brackish water intended for - 11 039982 for injection, into the brackish water injection line, and the specified required ionic composition includes a total content of dissolved solids (TSDS) in the range from 500 to 5000 ppm, a concentration of sulfate ions less than 7.5 ppm and a concentration of multivalent cations less than the concentration of multivalent cations in relict water. 2. The system of claim 1, wherein the conduit group includes a concentrate conduit connecting the concentrate outlet of the second OO stage to the inlet of the NF stage, and wherein a recirculation pump is located on the concentrate conduit. 3. The system of claim 1, comprising a third OO-stage having an inlet, an outlet for an OO-permeate and an outlet for an OO-concentrate, and the piping group is also configured to (i) connect the second OO-stage concentrate outlet to the third inlet OO-stage and (ii) direct or indirect connection of the third OO-stage permeate outlet to the brackish water injection line. 4. The system according to one of the previous paragraphs, including the first NF stage and the second NF stage, where the first NF stage has an inlet of the first NF stage, an outlet for the permeate of the first NF stage and an outlet for the concentrate of the first NF stage, and the second The NF stage has a second NF stage inlet, a second NF stage permeate outlet, and a second NF stage concentrate outlet, the piping group also being configured to (i) connect the first NF stage concentrate outlet to the second NF stage inlet, and (ii) direct or indirect connection of the permeate outlet of the second NF stage to the brackish water injection line. 5. The system according to one of the preceding claims, wherein the first OO stage contains more OO elements than the second OO stage, or wherein the first OO stage has a larger OO surface area than the surface area of the second OO stage. 6. The system of claim 5, wherein the ratio of the number of OO elements in the first OO stage to the number of OO elements in the second OO stage is between 2:1 and 5:3. 7. A system according to one of the preceding claims, wherein the ratio of the number of OO elements in the first OO stage to the number of elements in the NF stage(s) is in the range of 10:1 to 15:1. 8. A method of treating feed water using a device according to claim 1 for obtaining brackish water having the required ionic composition and intended for injection into an oil-bearing formation, including directing the flow of feed water through the first stage of reverse osmosis (OO) filtration to obtain OO-permeate of the first stage and OO-concentrate of the first stage; directing the flow of the first portion of the OO concentrate through the second stage OO filtration to obtain a second stage OO permeate and a second stage OO concentrate; directing a second portion of the first stage OO concentrate to flow through the first nanofiltration (NF) stage as feed to the first NF stage to obtain a first stage NF permeate and a first stage NF concentrate; combining first stage OO permeate, second stage OO permeate, and first stage NF permeate streams to form a brackish water stream for injection. 9. The method according to claim 8, including the discharge of the second stage OO concentrate and the first stage NF concentrate into the reservoir. 10. The method according to claim 8, including directing the flow of the first stage NF concentrate through the second stage of nanofiltration to obtain the second stage NF permeate and the second stage NF concentrate; combining the first stage NF permeate and second stage NF permeate streams with the first stage OO permeate and second stage OO permeate streams to form a brackish water stream intended for injection. 11. The method according to claim 10, including discharging the second stage OO concentrate and the second stage NF concentrate into the reservoir. 12. The method according to claim 8 or 10, including the flow of the first part of the OO-concentrate of the second stage through the third stage of OO-filtration to obtain OO-permeate of the third stage and OO-concentrate of the third stage; combining the second part of the second stage OO concentrate with the second part of the first stage OO concentrate to form a combined OO concentrate; directing the combined OO concentrate flow through the first NF stage and/or the second NF stage; discharge of the OO-concentrate of the third stage into the reservoir. 13. The method according to one of claims 8 to 12, wherein the conversion ratio of feed water to brackish water to be injected is 60% or more based on the volume flow rate of feed water supplied to the first OO stage. 14. The method according to one of claims 8 to 13, in which the ratio of the volumetric flow rate of the first part of the concentrate of the first OO-stage to the volume - 12 039982 flow rate of the second part of the concentrate of the first OO-stage is in the range from 5:1 to 15:1; the percentage yield of the NF permeate, including the NF permeate of the first stage and the NF permeate of the second stage, is in the range from 3 to 5% and/or the volume ratio of the mixture of the OO permeate, including the OO permeate of the first stage and the OO permeate of the second stage , with NF-permeate, including NF-permeate of the first stage and NF-permeate of the second stage, in the low-salinity water flow intended for injection, is in the range from 2:1 to 40:1. 15. System according to one of pi. 1-7, which provides a mixture ratio in the range from 2:1 to 40:1.