Process for producing an injection water for an oil reservoir by pressurizing water having a total dissolved solids content of 20,000 to 45,000 ppm and a sulfate concentration of 1,000 to 4,000 ppm to 350 to 1250 psi absolute; and dividing the water into first and second feeds for reverse osmosis (R
Process for producing an injection water for an oil reservoir by pressurizing water having a total dissolved solids content of 20,000 to 45,000 ppm and a sulfate concentration of 1,000 to 4,000 ppm to 350 to 1250 psi absolute; and dividing the water into first and second feeds for reverse osmosis (RO) and nanofiltration (NF) units respectively. The units are operated in single-pass, single-stage mode or single-pass, two-stage mode, the NF permeate has a pressure at least 5 psi higher than the RO permeate, and the recoveries of the RO and NF permeates are 35 to 75% and 35 to 60% by volume respectively. RO permeate and NF permeate are mixed in a ratio of 2:1 to 40:1 to provide injection water having a TDS content of 500 to 5,000 ppm, and a sulfate concentration of less than 7.5 ppm.
대표청구항▼
1. A process of producing an injection water stream of controlled salinity and controlled sulfate anion content that is suitable for injection into an oil bearing formation of an oil reservoir, the process comprising the steps of: (a) feeding a source water having a total dissolved solids content in
1. A process of producing an injection water stream of controlled salinity and controlled sulfate anion content that is suitable for injection into an oil bearing formation of an oil reservoir, the process comprising the steps of: (a) feeding a source water having a total dissolved solids content in the range of 20,000 to 45,000 ppm and a sulfate anion concentration in the range of 1,000 to 4,000 ppm to a desalination plant that comprises a plurality of reverse osmosis (RO) membrane units and a plurality of nanofiltration (NF) membrane units wherein the source water is pressurised to a pressure in the range of 350 to 1250 psi absolute by a pumping system common to said plurality of RO membrane units and said plurality of NF membrane units, and dividing the source water to provide a feed water for the RO membrane units (hereinafter “RO feed water”) and a feed water for the NF membrane units (hereinafter “NF feed water”);(b) increasing the pressure of the RO feed water to a value in the range of 900 to 1250 psi absolute if the RO feed water divided from the source water has a pressure lower than 900 psi absolute before introducing the RO feed water to the RO membrane units and withdrawing an RO permeate and an RO retentate from the RO membrane units wherein the RO membrane units are operated in either a single-pass, single-stage mode or in a single-pass, two-stage mode and wherein the recovery of RO permeate is in the range of 35 to 75% by volume based on the volume of the RO feed water that is fed to the RO membrane units such that the RO permeate has a total dissolved solids contents of less than 250 ppm, and a sulfate anion concentration of less than 3 ppm;(c) reducing the pressure of the NF feed water to a value in the range of 350 to 450 psi absolute if the NF feed water divided from the source water has a pressure higher than 450 psi absolute by means of a pressure let down valve or a control valve before introducing the NF feed water to the NF membrane units and withdrawing an NF permeate and an NF retentate from the NF membrane units wherein the NF membrane units are operated in a single-pass, single-stage mode and wherein the NF membrane units are operated with a recovery of NF permeate in the range of 35 to 60% by volume based on the volume of the NF feed water that is fed to the NF membrane units such that the NF permeate has a total dissolved solids content in the range of 15,000 to 40,000 ppm and a sulfate anion concentration of less than 40 ppm; and(d) mixing at least a portion of the RO permeate and at least a portion of the NF permeate in a ratio in the range of 2:1 to 40:1 at a mixing point, to provide an injection water having a total dissolved solids content in the range of 500 to 5,000 ppm and a sulfate anion concentration of less than 7.5 ppm; andwherein the pressure of the NF permeate is maintained at least 5 psi higher than the pressure of the RO permeate by means of a back pressure valve that is provided upstream of the mixing point for the NF permeate and RO permeate and wherein the NF permeate is injected into the RO permeate at the mixing point to form the injection water. 2. A process as claimed in claim 1 wherein the source water has a multivalent cation concentration in the range of 700 to 3,000 ppm, the RO permeate has a multivalent cation content of up to 10 ppm, the NF permeate has a multivalent cation content of up to 200 ppm; and the injection water has a multivalent cation content of up to 50 ppm. 3. A process as claimed in claim 1 wherein energy is recovered from the RO retentate using a hydraulic recovery unit and wherein the pressure of the RO feed water is increased in step (b) using a booster pump that is coupled to the hydraulic recovery unit. 4. A process as claimed in claim 1 wherein the pressure of the NF feed water is reduced in pressure in step (c) to a pressure in the range of 350 to 450 psi absolute by means of a pressure let down valve. 5. A process as claimed in claim 1 wherein the source water is selected from seawater, estuarine water, a produced water, an aquifer water, and a waste water. 6. A process as claimed in claim 1 wherein the total dissolved solids content of the RO permeate is in the range of 50 to 225 ppm and the sulfate anion content of the RO permeate is at least 0.5. 7. A process as claimed in claim 1 wherein the total dissolved solids content of the NF permeate is not more than 15,000 ppm less than the total dissolved solids content of the source water and wherein the NF permeate has a sulfate anion concentration of at least 10 ppm. 8. A process as claimed in claim 2 wherein the concentration of multivalent cations in the RO permeate is in the range of 1 to 10 ppm and the concentration of multivalent cations in the NF permeate is in the range of 50 to 200 ppm. 9. A process as claimed in claim 1 wherein one or more of the flow rate of the source water, the mixing ratio of the RO permeate and NF permeate, and the flow rate of the injection water is determined in accordance with a measured variable that is selected from one or more of the conductivity of the injection water, the total concentration of divalent anions in the injection water or in the NF permeate, and the concentration of sulfate anions in the injection water or in the NF permeate. 10. A process as claimed in claim 4 wherein the pressure of the NF feed water is reduced in pressure in step (c) to a pressure in the range of 380 to 420 psi absolute, by means of a pressure let down valve.
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이 특허에 인용된 특허 (3)
King Duane E. (Wake Forest NC) O\Brien John R. (Creve Coeur MO), Gas permeation apparatus having permeate rate controlled valving.
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