Controlled Salinity Injection Water via RO-NF Membrane Blending
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Solution Overview
Problem
Low salinity injection water for oil reservoirs often results in formation damage and reservoir souring due to inappropriate salinity and sulfate anion concentrations, which can inhibit oil recovery and cause scaling issues.
Innovation Solution
A process involving a desalination system with reverse osmosis and nanofiltration membrane units to produce injection water with controlled salinity, sulfate anion concentration, and multivalent cation levels, ensuring the water has a total dissolved solids content of 500 to 5,000 ppm and sulfate anion concentration below 7.5 ppm, achieved by blending RO and NF permeates in specific ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If desalination techniques are used to produce low salinity injection water, then the salinity is reduced to enhance oil recovery, but the water becomes damaging to the oil-bearing rock formation by causing swelling of clays
Solution Approach 1:
The patent applies parameter changes by precisely controlling the salinity concentration of injection water within the optimal range of 500-5000 ppm TDS, and multivalent cation concentration ratio less than 1.0, to simultaneously achieve enhanced oil recovery while preventing formation damage from clay swelling
Solution Approach 2:
The patent applies local quality by selectively removing sulfate anions to achieve specific concentration ratios (sulfate in permeate less than 10% of feed) while maintaining appropriate levels of other ions, creating water with a specific ionic composition tailored to prevent formation damage
2Quantity of substance
If desalinated water is mixed with high salinity water to increase salinity, then the optimal salinity for enhanced oil recovery is achieved, but the sulfate anion content and multivalent cation content become unacceptably high causing reservoir souring and scale formation
Solution Approach 1:
The patent applies taking out by selectively extracting and removing sulfate anions from the water stream through membrane filtration, achieving sulfate concentration less than 10% of feed levels while maintaining appropriate salinity, thereby preventing reservoir souring and scale formation
Solution Approach 2:
The patent applies parameter changes by controlling the concentration ratio of multivalent cations in injection water to be less than 1.0 relative to connate water, and sulfate anion concentration to be less than 10% of feed, to prevent harmful effects while maintaining enhanced oil recovery benefits
3Productivity
If high pressure is applied to source water for reverse osmosis desalination, then the salinity reduction efficiency is improved, but the energy consumption and operational complexity increase
Solution Approach 1:
The patent applies segmentation by dividing the desalination process into two distinct stages: reverse osmosis for bulk salt removal followed by nanofiltration for sulfate anion selective removal, with each stage operating at optimized pressure levels to balance efficiency and complexity
Solution Approach 2:
The patent applies intermediary by using nanofiltration membranes as a intermediate step between reverse osmosis and final injection, selectively removing sulfate anions while maintaining appropriate salinity levels, thereby simplifying overall system design compared to single-stage high-pressure systems
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The process effectively mitigates formation damage and reservoir souring while maintaining sufficient salinity for oil recovery, reducing the risk of mineral scale precipitation and hydrogen sulfide production, thereby enhancing incremental oil recovery.
Implementation Method 1
a first reverse osmosis (RO) train comprising a plurality of RO membrane units (2)
Implementation Method 2
a second nanofiltration (NF) train comprising a plurality of NF membrane units (3)
Data Source
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AI summary
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, preferably, 1,500 ppm 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, 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) if necessary, increasing the pressure of the RO feed water to a value in the range of 900 to 1250 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, preferably, 35 to 60% 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) if necessary, reducing the pressure of the NF feed water to a value in the range of 350 to 450 psi absolute 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, preferably, 15,000 to 35,000 ppm, and a sulfate anion concentration of less than 40 ppm, preferably less than 30 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, preferably, 4: 1 to 27:1, in particular, 10: 1 to 25: 1 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, preferably, less than (5) ppm, more preferably less than 3 ppm.