WO2016174128A1 - Process for recovering oil - Google Patents
Process for recovering oil Download PDFInfo
- Publication number
- WO2016174128A1 WO2016174128A1 PCT/EP2016/059473 EP2016059473W WO2016174128A1 WO 2016174128 A1 WO2016174128 A1 WO 2016174128A1 EP 2016059473 W EP2016059473 W EP 2016059473W WO 2016174128 A1 WO2016174128 A1 WO 2016174128A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- surfactant
- oil
- formation
- water
- exchange resin
- Prior art date
Links
- 238000000034 method Methods 0.000 title claims abstract description 47
- 239000003921 oil Substances 0.000 claims abstract description 120
- 239000004094 surface-active agent Substances 0.000 claims abstract description 95
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 92
- 239000000203 mixture Substances 0.000 claims abstract description 59
- 230000015572 biosynthetic process Effects 0.000 claims abstract description 54
- 239000012071 phase Substances 0.000 claims abstract description 32
- 239000012266 salt solution Substances 0.000 claims abstract description 19
- 150000003839 salts Chemical class 0.000 claims abstract description 16
- 239000008346 aqueous phase Substances 0.000 claims abstract description 15
- 238000005406 washing Methods 0.000 claims abstract description 9
- -1 sulfonate compound Chemical class 0.000 claims description 20
- 150000001875 compounds Chemical class 0.000 claims description 16
- NWUYHJFMYQTDRP-UHFFFAOYSA-N 1,2-bis(ethenyl)benzene;1-ethenyl-2-ethylbenzene;styrene Chemical compound C=CC1=CC=CC=C1.CCC1=CC=CC=C1C=C.C=CC1=CC=CC=C1C=C NWUYHJFMYQTDRP-UHFFFAOYSA-N 0.000 claims description 12
- 239000000243 solution Substances 0.000 claims description 11
- 230000001172 regenerating effect Effects 0.000 claims description 7
- 239000003945 anionic surfactant Substances 0.000 claims description 6
- 239000003957 anion exchange resin Substances 0.000 claims description 5
- 239000003729 cation exchange resin Substances 0.000 claims description 5
- JRZJOMJEPLMPRA-UHFFFAOYSA-N olefin Natural products CCCCCCCC=C JRZJOMJEPLMPRA-UHFFFAOYSA-N 0.000 claims description 4
- 239000003093 cationic surfactant Substances 0.000 claims description 3
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 claims description 2
- 150000004996 alkyl benzenes Chemical class 0.000 claims description 2
- 150000003868 ammonium compounds Chemical class 0.000 claims description 2
- 125000000129 anionic group Chemical group 0.000 claims description 2
- 229940077388 benzenesulfonate Drugs 0.000 claims description 2
- 238000010612 desalination reaction Methods 0.000 claims description 2
- 239000004711 α-olefin Substances 0.000 claims description 2
- 238000005755 formation reaction Methods 0.000 description 43
- 238000011084 recovery Methods 0.000 description 37
- 229920000642 polymer Polymers 0.000 description 21
- 238000009472 formulation Methods 0.000 description 20
- 239000010779 crude oil Substances 0.000 description 13
- 238000000926 separation method Methods 0.000 description 12
- 239000003456 ion exchange resin Substances 0.000 description 8
- 229920003303 ion-exchange polymer Polymers 0.000 description 8
- 230000008929 regeneration Effects 0.000 description 8
- 238000011069 regeneration method Methods 0.000 description 8
- 239000000839 emulsion Substances 0.000 description 6
- 239000012530 fluid Substances 0.000 description 6
- 239000007864 aqueous solution Substances 0.000 description 5
- 239000000356 contaminant Substances 0.000 description 5
- 150000002500 ions Chemical class 0.000 description 5
- 238000004519 manufacturing process Methods 0.000 description 5
- 239000011347 resin Substances 0.000 description 5
- 229920005989 resin Polymers 0.000 description 5
- 239000000126 substance Substances 0.000 description 5
- SMZOUWXMTYCWNB-UHFFFAOYSA-N 2-(2-methoxy-5-methylphenyl)ethanamine Chemical compound COC1=CC=C(C)C=C1CCN SMZOUWXMTYCWNB-UHFFFAOYSA-N 0.000 description 4
- NIXOWILDQLNWCW-UHFFFAOYSA-N 2-Propenoic acid Natural products OC(=O)C=C NIXOWILDQLNWCW-UHFFFAOYSA-N 0.000 description 4
- HRPVXLWXLXDGHG-UHFFFAOYSA-N Acrylamide Chemical compound NC(=O)C=C HRPVXLWXLXDGHG-UHFFFAOYSA-N 0.000 description 4
- 229920001577 copolymer Polymers 0.000 description 4
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 3
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- YXFVVABEGXRONW-UHFFFAOYSA-N Toluene Chemical compound CC1=CC=CC=C1 YXFVVABEGXRONW-UHFFFAOYSA-N 0.000 description 3
- 239000003513 alkali Substances 0.000 description 3
- 238000002347 injection Methods 0.000 description 3
- 239000007924 injection Substances 0.000 description 3
- 229920002401 polyacrylamide Polymers 0.000 description 3
- 229920005862 polyol Polymers 0.000 description 3
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 2
- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical compound CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 description 2
- 229920002305 Schizophyllan Polymers 0.000 description 2
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 description 2
- 229920001222 biopolymer Polymers 0.000 description 2
- 235000014113 dietary fatty acids Nutrition 0.000 description 2
- 239000000194 fatty acid Substances 0.000 description 2
- 229930195729 fatty acid Natural products 0.000 description 2
- 238000005342 ion exchange Methods 0.000 description 2
- PBOSTUDLECTMNL-UHFFFAOYSA-N lauryl acrylate Chemical compound CCCCCCCCCCCCOC(=O)C=C PBOSTUDLECTMNL-UHFFFAOYSA-N 0.000 description 2
- 239000004530 micro-emulsion Substances 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 125000000740 n-pentyl group Chemical group [H]C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])* 0.000 description 2
- 229920001568 phenolic resin Polymers 0.000 description 2
- 229920000768 polyamine Polymers 0.000 description 2
- 150000003077 polyols Chemical class 0.000 description 2
- 239000011780 sodium chloride Substances 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- WDQLRUYAYXDIFW-RWKIJVEZSA-N (2r,3r,4s,5r,6r)-4-[(2s,3r,4s,5r,6r)-3,5-dihydroxy-4-[(2r,3r,4s,5s,6r)-3,4,5-trihydroxy-6-(hydroxymethyl)oxan-2-yl]oxy-6-[[(2r,3r,4s,5s,6r)-3,4,5-trihydroxy-6-(hydroxymethyl)oxan-2-yl]oxymethyl]oxan-2-yl]oxy-6-(hydroxymethyl)oxane-2,3,5-triol Chemical compound O[C@@H]1[C@@H](CO)O[C@@H](O)[C@H](O)[C@H]1O[C@H]1[C@H](O)[C@@H](O[C@H]2[C@@H]([C@@H](O)[C@H](O)[C@@H](CO)O2)O)[C@H](O)[C@@H](CO[C@H]2[C@@H]([C@@H](O)[C@H](O)[C@@H](CO)O2)O)O1 WDQLRUYAYXDIFW-RWKIJVEZSA-N 0.000 description 1
- PQUXFUBNSYCQAL-UHFFFAOYSA-N 1-(2,3-difluorophenyl)ethanone Chemical compound CC(=O)C1=CC=CC(F)=C1F PQUXFUBNSYCQAL-UHFFFAOYSA-N 0.000 description 1
- FEBUJFMRSBAMES-UHFFFAOYSA-N 2-[(2-{[3,5-dihydroxy-2-(hydroxymethyl)-6-phosphanyloxan-4-yl]oxy}-3,5-dihydroxy-6-({[3,4,5-trihydroxy-6-(hydroxymethyl)oxan-2-yl]oxy}methyl)oxan-4-yl)oxy]-3,5-dihydroxy-6-(hydroxymethyl)oxan-4-yl phosphinite Chemical compound OC1C(O)C(O)C(CO)OC1OCC1C(O)C(OC2C(C(OP)C(O)C(CO)O2)O)C(O)C(OC2C(C(CO)OC(P)C2O)O)O1 FEBUJFMRSBAMES-UHFFFAOYSA-N 0.000 description 1
- BGVCWPVMJIEXBL-UHFFFAOYSA-N 2-ethoxyhexan-1-ol Chemical compound CCCCC(CO)OCC BGVCWPVMJIEXBL-UHFFFAOYSA-N 0.000 description 1
- DQZIMVJHYGEHPY-UHFFFAOYSA-N 2-methyloxirane;sulfuric acid Chemical compound CC1CO1.OS(O)(=O)=O DQZIMVJHYGEHPY-UHFFFAOYSA-N 0.000 description 1
- NIXOWILDQLNWCW-UHFFFAOYSA-M Acrylate Chemical compound [O-]C(=O)C=C NIXOWILDQLNWCW-UHFFFAOYSA-M 0.000 description 1
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 1
- 229920002907 Guar gum Polymers 0.000 description 1
- WHNWPMSKXPGLAX-UHFFFAOYSA-N N-Vinyl-2-pyrrolidone Chemical compound C=CN1CCCC1=O WHNWPMSKXPGLAX-UHFFFAOYSA-N 0.000 description 1
- CTQNGGLPUBDAKN-UHFFFAOYSA-N O-Xylene Chemical compound CC1=CC=CC=C1C CTQNGGLPUBDAKN-UHFFFAOYSA-N 0.000 description 1
- 229910019142 PO4 Inorganic materials 0.000 description 1
- 239000004372 Polyvinyl alcohol Substances 0.000 description 1
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 1
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 description 1
- 229940048053 acrylate Drugs 0.000 description 1
- 229910021529 ammonia Inorganic materials 0.000 description 1
- 125000003118 aryl group Chemical group 0.000 description 1
- 125000000484 butyl group Chemical group [H]C([*])([H])C([H])([H])C([H])([H])C([H])([H])[H] 0.000 description 1
- 125000002091 cationic group Chemical group 0.000 description 1
- 150000001768 cations Chemical class 0.000 description 1
- 238000004581 coalescence Methods 0.000 description 1
- 239000006184 cosolvent Substances 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 150000002148 esters Chemical class 0.000 description 1
- 150000004665 fatty acids Chemical class 0.000 description 1
- 239000013505 freshwater Substances 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 239000000665 guar gum Substances 0.000 description 1
- 235000010417 guar gum Nutrition 0.000 description 1
- 229960002154 guar gum Drugs 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 230000001483 mobilizing effect Effects 0.000 description 1
- 125000001400 nonyl group Chemical group [H]C([*])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])[H] 0.000 description 1
- 238000005191 phase separation Methods 0.000 description 1
- ISWSIDIOOBJBQZ-UHFFFAOYSA-M phenolate Chemical compound [O-]C1=CC=CC=C1 ISWSIDIOOBJBQZ-UHFFFAOYSA-M 0.000 description 1
- 229940031826 phenolate Drugs 0.000 description 1
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 1
- 239000010452 phosphate Substances 0.000 description 1
- 229920001467 poly(styrenesulfonates) Polymers 0.000 description 1
- 229920000058 polyacrylate Polymers 0.000 description 1
- 229920000151 polyglycol Polymers 0.000 description 1
- 239000010695 polyglycol Substances 0.000 description 1
- 229960002796 polystyrene sulfonate Drugs 0.000 description 1
- 239000011970 polystyrene sulfonate Substances 0.000 description 1
- 229920002451 polyvinyl alcohol Polymers 0.000 description 1
- 229920000036 polyvinylpyrrolidone Polymers 0.000 description 1
- 235000013855 polyvinylpyrrolidone Nutrition 0.000 description 1
- 239000001267 polyvinylpyrrolidone Substances 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 150000003856 quaternary ammonium compounds Chemical class 0.000 description 1
- 239000013535 sea water Substances 0.000 description 1
- 229940047670 sodium acrylate Drugs 0.000 description 1
- 235000017550 sodium carbonate Nutrition 0.000 description 1
- 229910000029 sodium carbonate Inorganic materials 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- BDHFUVZGWQCTTF-UHFFFAOYSA-M sulfonate Chemical compound [O-]S(=O)=O BDHFUVZGWQCTTF-UHFFFAOYSA-M 0.000 description 1
- 150000003871 sulfonates Chemical class 0.000 description 1
- 150000003673 urethanes Chemical class 0.000 description 1
- 229920001285 xanthan gum Polymers 0.000 description 1
- 239000000230 xanthan gum Substances 0.000 description 1
- 235000010493 xanthan gum Nutrition 0.000 description 1
- 229940082509 xanthan gum Drugs 0.000 description 1
- 239000008096 xylene Substances 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K8/00—Compositions for drilling of boreholes or wells; Compositions for treating boreholes or wells, e.g. for completion or for remedial operations
- C09K8/58—Compositions for enhanced recovery methods for obtaining hydrocarbons, i.e. for improving the mobility of the oil, e.g. displacing fluids
- C09K8/584—Compositions for enhanced recovery methods for obtaining hydrocarbons, i.e. for improving the mobility of the oil, e.g. displacing fluids characterised by the use of specific surfactants
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/34—Arrangements for separating materials produced by the well
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D17/00—Separation of liquids, not provided for elsewhere, e.g. by thermal diffusion
- B01D17/02—Separation of non-miscible liquids
- B01D17/04—Breaking emulsions
- B01D17/047—Breaking emulsions with separation aids
-
- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
- C10G33/00—Dewatering or demulsification of hydrocarbon oils
- C10G33/04—Dewatering or demulsification of hydrocarbon oils with chemical means
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/25—Methods for stimulating production
Definitions
- the present invention relates to a process for recovering oil from an oil-bearing formation with the help of surfactant .
- oil in the formation generally is recovered using primary recovery methods utilizing the natural formation pressure to produce the oil.
- a portion of the oil that cannot be produced from the formation using primary recovery methods may be produced by secondary recovery methods such as water flooding.
- Oil that cannot be produced from the formation using primary recovery methods and optionally secondary methods such as water flooding may be produced by chemical enhanced oil recovery, also referred to as EOR.
- Chemical enhanced oil recovery can utilize
- An aqueous mixture comprising
- surfactant and optionally polymer is injected into an oil- bearing formation to increase recovery of oil from the formation, either after primary recovery or after a secondary recovery water flood.
- Surfactant is thought to enhance recovery of oil by lowering the interfacial tension between oil and water phases in the formation thereby mobilizing the oil for production.
- Polymer is thought to increase the viscosity of the enhanced oil recovery formulation, preferably to the same order of magnitude as the oil in the formation in order to force the mobilized oil through the formation for production by the polymer containing flood.
- the mixture which is produced in an oil recovery process making use of surfactant contains oil, water, surfactant and other compounds which either were present in the fluid which was injected such as polymer or were present in the formation and became incorporated as part of the oil recovery process.
- the amount of water in the mixture recovered can vary widely.
- the oil and water often are present in the recovered fluid as an emulsion of either water in oil or oil in water. Such an emulsion tends to be stabilized by the surfactants which makes that an aqueous phase
- emulsified water from oil can be cumbersome and expensive due to limited differences in specific gravity between the oil and water while their viscosity also can become similar if the aqueous phase contains polymer. Chemical separation can be expensive due to the expense of the chemicals used.
- any surfactant which remains in the crude oil can also cause problems further downstream.
- the surfactants and/or thermally cracked derivatives can end up in refinery products thereby causing these to no longer meet the
- a further complexity is that surfactant which remains in the crude oil cannot again be used in
- a further advantage of the present invention is that cleaner oil can be obtained by washing oil of relatively high surfactant content.
- the present invention relates to a process for recovering oil which process comprises (a) injecting surfactant into the oil-bearing formation and recovering from the formation a mixture containing oil, water and surfactant, (b) treating the mixture recovered in step (a) with salt or an aqueous salt solution and separating the treated mixture into an oil phase containing surfactant and an aqueous phase, and (c) washing the oil phase containing surfactant obtained in step (b) with water and recovering oil having a reduced surfactant content .
- the wash water obtained in step (c) generally will contain a substantial amount of surfactant.
- Oil containing mixtures which have been recovered from a formation with the help of a surfactant flood will contain water besides crude oil and surfactant.
- Water can originate from the aqueous surfactant solution which has been injected and/or from the formation containing water besides oil. The presence of water is undesirable not only because of the water but also because of the salts and other contaminants dissolved in the water.
- the surfactant in the recovered oil can cause relatively stable oil-water micro-emulsions which the current process removes by changing the salinity of the mixture produced by the surfactant flood.
- the increase in salinity is thought to push the surfactant into the oil phase (also referred to as "over-optimum") thus enhancing the separation of the oil phase from the water phase and coalescence of oil droplets in the water.
- this is thought to separate any other solutes such as polymer which may be present in the water phase.
- step (c) washing with low-saline or fresh water in step (c) is thought to bring the surfactant back to the aqueous phase thereby making it possible to remove surfactant from the oil phase and obtain an aqueous surfactant containing mixture which can be injected into the formation.
- the water wash in step (c) may have to be repeated one or more times to remove sufficient surfactant from the oil phase to meet the specifications on the water, salt and/or surfactant content of the oil.
- the process of the present invention employs a surfactant which generally is effective in reducing the interfacial tension between oil and water in the oil- bearing formation. This is thought to mobilize the oil for production from the formation.
- the surfactant may be any enhanced oil recovery surfactant.
- the surfactant is chosen from the group consisting of anionic and cationic surfactants .
- Suitable cationic surfactants may be ammonium compounds, more preferably quaternary ammonium compounds, most preferably benzylic ammonium salts.
- surfactants are especially suitable for use with carbonate formations .
- the anionic surfactant may be a sulfonate-containing compound, a sulfate-containing compound, a carboxylate- containing compound, a phosphate-containing compound, a phenolate-containing compound or a blend thereof.
- the anionic surfactant may be chosen from the group consisting of an alpha olefin sulfonate compound, an internal olefin sulfonate compound, a branched alkyl benzene sulfonate compound, a propylene oxide sulfate compound, an ethylene oxide sulfate compound, a propylene oxide-ethylene oxide sulfate compound, or a blend thereof.
- Anionic surfactants are especially suitable for use with sandstone formations.
- the surfactant preferably contains from 2 to 28 carbons, more specifically of from 2 to 20 carbons, more specifically of from 12 to 20 carbons.
- the surfactant of the oil recovery formulation may comprise an internal olefin sulfonate compound containing from 15 to 18 carbons or a propylene oxide sulfate compound containing from 12 to 15 carbons, or a blend thereof, where the blend contains a volume ratio of the propylene oxide sulfate to the internal olefin sulfonate compound of from 1:1 to 10:1.
- the surfactant generally is present as part of an oil recovery formulation which can contain further compounds.
- the oil recovery formulation may contain an amount of the surfactant effective to reduce the interfacial tension between oil and water in the formation and thereby mobilize the oil for production from the formation.
- the oil recovery formulation may contain from 0.05 % by weight (wt%) to 5 wt% of the surfactant or combination of surfactants, or may contain from 0.1 wt% to 3 wt% of the surfactant or combination of surfactants based on total amount of formulation. This amount can be gradually decreased during operation when the amount of surfactant recovered from the crude oil gradually
- the oil recovery formulation can also contain further compounds such as polymers and/or alkali.
- Polymer can be present to provide the oil recovery formulation with a viscosity of the same order of
- the polymer can be a single compound or can be a mixture of compounds.
- the polymer is selected from the group consisting of polyacrylamide ; partially hydrolyzed polyacrylamide; polyacrylate ; ethylenic co ⁇ polymer; carboxymethylcelloluse ; polyvinyl alcohol;
- polystyrene sulfonate polyvinylpyrrolidone
- biopolymers 2-acrylamide-methyl propane sulfonate (AMPS)
- AMPS 2-acrylamide-methyl propane sulfonate
- styrene- acrylate copolymer co-polymers of acrylamide, acrylic acid and/or acrylate, AMPS and n-vinylpyrrolidone in any ratio; and combinations thereof.
- AMPS 2-acrylamide-methyl propane sulfonate
- styrene- acrylate copolymer co-polymers of acrylamide, acrylic acid and/or acrylate, AMPS and n-vinylpyrrolidone in any ratio; and combinations thereof.
- ethylenic co-polymers examples include co ⁇ polymers of acrylic acid and acrylamide, acrylic acid and lauryl acrylate, and lauryl acrylate and acrylamide .
- biopolymers examples include xanthan gum, guar gum, schizophyllan and scleroglucan .
- the polymer is (hydrolyzed) polyacrylamide .
- the latter includes but is not limited to copolymers of acrylamide and acrylic acid or sodium acrylate such as polymers which are being sold by SNF Floerger under the trade name Flopaam 3630S and Flopaam EM533.
- the concentration of the polymer in the oil recovery formulation to be injected into the formation preferably is sufficient to provide the oil recovery formulation with a dynamic viscosity of at least 0.3 mPa.s (0.3 cP), more specifically at least 1 mPa.s (1 cP), or at least 10 mPa.s (10 cP), or at least 100 mPa.s (100 cP), or at least 1000 mPa.s (1000 cP) at 25°C or at a temperature within a formation temperature range.
- the concentration of polymer in the oil recovery formulation preferably is from 250 ppm to 10,000 ppm, or from 500 ppm to 5,000 ppm, or from 1,000 to 2, 000 ppm.
- the molecular weight number average of the polymer in the oil recovery formulation preferably is at least 10,000 dalton, or at least 50,000 dalton, or at least 100,000 dalton.
- the polymer preferably has a molecular weight number average of from 10,000 to 3,000,0000 dalton, or from 100,000 to 15,000,000 dalton.
- the oil recovery formulation can be prepared with alkali so that the formulation which is injected has a pH of at least 8, more specifically at least 8.5, most specifically at least 9.
- Alkali compounds which are especially suitable are sodium hydroxide, soda ash and ammonia.
- the pH preferably is at most 12, more
- the oil recovery formulation can further contain a low molecular weight alcohol as co-solvent, preferably in an amount of from 100 ppm to 50,000 ppm of the total oil recovery formulation.
- TDS total dissolved solids content
- the TDS of the water to be injected will be of from 1000 to 50,000 ppm, more specifically of from 5,000 to 50,000 ppm.
- the expression "ppm" indicates parts per million by weight on total weight amount present.
- water having a limited amount of divalent ions If such water is not readily available, it can be obtained by so-called softening processes.
- the water has an ionic strength of 0.15 M or less, or from 0.02 M to 0.125 M, or from 0.0 3M to 0.1 M. Ionic strength, as used herein, is defined by the equation
- I is the ionic strength
- c is the molar
- the mixture recovered in step (a) of the process of the present invention contains oil, water and surfactant but can contain other compounds as well depending on the compounds present in the formation and the components present in the original oil recovery formulation.
- Step (b) requires the addition of salt.
- the salt can be in any form such as a solid or as an aqueous solution. Generally, an aqueous solution is preferred as it mixes better with the mixture of oil and water and often is more readily available.
- the salt is thought to cause the surfactant to become part of the oil phase.
- the aqueous salt solution preferably has a TDS of at least 5000 ppm, more specifically at least 10,000 ppm, more specifically at least 20,000 ppm, more specifically at least 40,000 ppm, more specifically at least 50,000 ppm.
- the upper limit generally will be the amount of salt which can be dissolved in the fluid at the operating conditions.
- the aqueous salt solution used in step (b) has a higher molar concentration of salt than the water present in the mixture of surfactant, water and oil obtained in step (a) .
- step (b) an aqueous salt solution which has been used or produced in the recovery process of the present invention.
- a solution which is especially suitable is a reject stream of desalination or a softening process.
- multivalent ions in order to produce water of sufficiently low TDS and/or ionic strength.
- water from another field aquifer water or sea water can be used provided that the aqueous salt solution used in step (b) is more saline than the water present in the mixture of surfactant, water and oil obtained in step (a) .
- phase separation also is referred to as breaking of the emulsion.
- demulsifiers may be selected from the group consisting of amyl resins; butyl resins; nonyl resins; acid- or base-catalyzed phenol-formaldehyde resins; phenol-acrylate anhydride polyglycol resins;
- urethanes polyamines; polyesteramines ; sulfonates; di- epoxides; polyols; esters and polyol esters including triol fatty acid esters, triol adipate esters, and triol fumarate esters; ethoxylated and/or propoxylated compounds of amyl resins, butylresins, nonylresins, acid- or base- catalyzed phenol-formaldehyde resins, fatty acids, polyamines, di-epoxides, and polyols; and combinations thereof which may be dispersed in a carrier solvent selected from the group consisting of xylene, toluene, heavy aromatic naphtha, isopropanol, methanol, 2- ethoxyhexanol, diesel, and combinations thereof.
- a carrier solvent selected from the group consisting of xylene, toluene, heavy aromatic naphtha, isopropano
- step (b) can be enhanced by
- the separation of step (b) is carried out in separation tanks, which may comprise heating elements.
- separation tanks which may comprise heating elements.
- a "continuous feed” operation the mixture and the aqueous salt solution are fed into a separation tank, and substantially dewatered oil and substantially oil-free water phases are removed from the tank, wherein the rate of delivery of crude oil and aqueous salt solution and the rate of removal of the oil and water phases are essentially in equilibrium.
- the oil containing mixture and aqueous salt solution are added to the tank and mixed, optionally heated to accelerate the separation process, and permitted to stand and settle until the separation is sufficiently complete that the aqueous phase and the oil phase can be separately removed.
- the oil phase containing surfactant is washed with water.
- the water can be an aqueous solution or it can be water per se. It depends on the circumstances what aqueous solution or water to use. If an aqueous solution is used, it will generally have a TDS of from 0 to 30,000 ppm, more preferably at most 10,000 ppm, more preferably at most 5,000 ppm, more preferably at most 1,000 ppm and most preferably at most 500 ppm.
- the water can be obtained from any suitable natural source or can have been obtained by treating, purifying, softening or desalinating the source water in order to reduce the contaminants and/or salt content.
- the washing is preferably carried out by thoroughly mixing the oil and water and subsequently allowing the water phase and oil phase to separate as described above.
- the washing can be repeated most preferably of from 1 to 10 times.
- the volume ratio of oil phase to wash water preferably is of from 0.5 to 20.
- wash water which is used in step (c) can be used in various ways .
- a preferred option is to in ect the wash water into the formation and thereby contribute to the surfactant flood for recovering oil.
- Another option is to treat the wash water obtained in step (c) in a further step (d) with an ion exchange resin to obtain wash water having reduced surfactant content. This allows the treated wash water to be used again in step (c) .
- An anion exchange resin is to be used for anionic surfactant, and a cation exchange resin is to be used for cation surfactant.
- An advantageous method is to (e) treat the used ion exchange resin with a salt solution to obtain a regenerated ion exchange resin and a concentrated surfactant-containing regenerating solution, and (f) inject concentrated surfactant- containing regenerating solution obtained in step (e) into the formation.
- the concentrated surfactant-containing regeneration solution obtained in step (e) preferably is combined with injection water before being injected into the formation in step (f) .
- the oil recovered by the process of the present invention will generally contain at most 5 %wt, most preferably of from 0.001 to 3 %wt of surfactant and at most 5 %wt, most preferably of from 0.001 to 3 %wt of water .
- Figure 1 shows a process scheme involving the steps of treating an oil containing mixture with an aqueous salt solution and separating the treated mixture into an oil phase and an aqueous phase followed by 2 subsequent wash steps and injecting the wash water into the formation optionally after further surfactant is added.
- Figure 2 shows a process scheme involving the steps of treating an oil containing mixture with an aqueous salt solution and separating the treated mixture into an oil phase and an aqueous phase followed by a wash step and treating the wash water with an ion exchange resin. Fluid obtained during regeneration can be injected again into the formation optionally after further water is added.
- a mixture of oil, water and surfactant is recovered from reservoir 101 and sent via line 1 to a treating unit 102 for contacting the mixture with an aqueous salt solution added via line 2.
- the mixture is mixed intensely in unit 102 and separated into an aqueous phase which is removed via line 4 and an oil phase which is sent via line 3 to wash unit 103.
- the aqueous phase removed via line 4 is thought to contain a reduced amount of contaminants such as polymers and surfactants.
- wash unit 103 the oil phase is thoroughly contacted with wash water added via line 5.
- the oil phase is separated from the wash water and sent via line 6 to further wash unit 104 where the oil phase is once more thoroughly contacted with wash water added via line 8.
- the crude oil obtained has reduced surfactant content and is removed from the process via line 9.
- the wash water used in unit 103 is combined via line 7 with wash water used in unit 104.
- the combined wash water streams are sent via line 10 back to the formation optionally after further surfactant is added via line 11.
- a mixture of oil, water and surfactant is recovered from reservoir 201 and sent via line 21 to a treating unit 202 for contacting the mixture with an aqueous salt solution added via line 22.
- the mixture is mixed intensely in unit 202 and separated into an aqueous phase which is removed via line 24 and an oil phase which is sent via line 23 to wash unit 203.
- wash unit 203 the oil phase is thoroughly contacted with wash water added via line 25.
- the crude oil obtained has reduced surfactant content and is removed from the process via line 26.
- the wash water used in unit 203 is sent via line 27 to ion exchange unit 204.
- the wash water removed via line 28 is low in contaminants and can be used for many purposes such as fresh wash water for use in wash unit 203.
- the ion exchange resin becomes loaded with surfactant during use and has to be regenerated at certain time intervals.
- several ion exchange units can be operated in parallel. In such operation, one or more units are taken out of operation for regeneration while regenerated units are taken into normal operation again.
- several ion exchange resins are operated in series. This allows regeneration of a particular unit while the remaining units in the series ensure that wash water can continue to be treated.
- the ion exchange resin of unit 204 is contacted with a suitable salt solution added via line 29.
- the used regeneration fluid has a high concentration of surfactant and is especially suitable to be used again in oil recovery. Therefore, it is preferred to send the used regeneration solution via line 30 back to the formation for injection.
- additional injection water is added to the concentrated surfactant fluid in line 30 via line 31.
Abstract
Process for recovering oil which process comprises (a) injecting surfactant into an oil-bearing formation and recovering from the formation a mixture containing oil, water and surfactant, (b) treating the mixture recovered in step (a) with salt or an aqueous salt solution and separating the treated mixture into an oil phase containing surfactant and an aqueous phase, and (c) washing the oil phase containing surfactant obtained in step (b) with water and recovering oil having a reduced surfactant content.
Description
PROCESS FOR RECOVERING OIL
The present invention relates to a process for recovering oil from an oil-bearing formation with the help of surfactant .
In the recovery of oil from a subterranean
formation, only a portion of the oil in the formation generally is recovered using primary recovery methods utilizing the natural formation pressure to produce the oil. A portion of the oil that cannot be produced from the formation using primary recovery methods may be produced by secondary recovery methods such as water flooding. Oil that cannot be produced from the formation using primary recovery methods and optionally secondary methods such as water flooding, may be produced by chemical enhanced oil recovery, also referred to as EOR.
Chemical enhanced oil recovery can utilize
surfactant or a combination of surfactant with other chemicals such as polymer and/or gas to flood an oil- bearing formation to increase the amount of oil recovered from the formation. An aqueous mixture comprising
surfactant and optionally polymer is injected into an oil- bearing formation to increase recovery of oil from the formation, either after primary recovery or after a secondary recovery water flood. Surfactant is thought to enhance recovery of oil by lowering the interfacial tension between oil and water phases in the formation thereby mobilizing the oil for production. Polymer is thought to increase the viscosity of the enhanced oil recovery formulation, preferably to the same order of magnitude as the oil in the formation in order to force the mobilized oil through the formation for production by the polymer containing flood.
The mixture which is produced in an oil recovery
process making use of surfactant contains oil, water, surfactant and other compounds which either were present in the fluid which was injected such as polymer or were present in the formation and became incorporated as part of the oil recovery process.
The amount of water in the mixture recovered can vary widely. The oil and water often are present in the recovered fluid as an emulsion of either water in oil or oil in water. Such an emulsion tends to be stabilized by the surfactants which makes that an aqueous phase
containing a relatively large amount of oil would be obtained and an oil product having a relatively high amount of aqueous phase. The latter can cause the oil product to have a relatively high salt content. Refineries tend to have specifications on both the amount of water and the amount of salt which a crude oil is allowed to contain. Crude oil not meeting these specifications will have to be further treated in order to make the crude oils comply with the refinery specifications. Removing
emulsified water from oil can be cumbersome and expensive due to limited differences in specific gravity between the oil and water while their viscosity also can become similar if the aqueous phase contains polymer. Chemical separation can be expensive due to the expense of the chemicals used.
It is general practice to dehydrate crude oil by allowing the oil to stand. However, this can take a long time and/or require large vessels if a substantial amount of surfactant is present in the oil mixture because surfactants tend to stabilize emulsions. Even worse, enhanced oil recovery surfactants are in principle designed to generate micro-emulsions, which are
thermodynamically stable and hence will not demulsify spontaneously given time. Furthermore, any surfactant
which remains in the crude oil can also cause problems further downstream. The surfactants and/or thermally cracked derivatives can end up in refinery products thereby causing these to no longer meet the
specifications .
A further complexity is that surfactant which remains in the crude oil cannot again be used in
recovering oil from the formation.
We now have found a process for recovering crude oil from a formation with the help of surfactant making efficient use of various process streams already present in the recovery process to recover a crude oil having reduced surfactant content while the surfactant is present in process streams which again can be used in oil
recovery .
A further advantage of the present invention is that cleaner oil can be obtained by washing oil of relatively high surfactant content.
The present invention relates to a process for recovering oil which process comprises (a) injecting surfactant into the oil-bearing formation and recovering from the formation a mixture containing oil, water and surfactant, (b) treating the mixture recovered in step (a) with salt or an aqueous salt solution and separating the treated mixture into an oil phase containing surfactant and an aqueous phase, and (c) washing the oil phase containing surfactant obtained in step (b) with water and recovering oil having a reduced surfactant content .
The wash water obtained in step (c) generally will contain a substantial amount of surfactant.
Oil containing mixtures which have been recovered from a formation with the help of a surfactant flood, will contain water besides crude oil and surfactant. Water can originate from the aqueous surfactant solution which has
been injected and/or from the formation containing water besides oil. The presence of water is undesirable not only because of the water but also because of the salts and other contaminants dissolved in the water.
Without wishing to be bound to any theory, it is thought that the surfactant in the recovered oil can cause relatively stable oil-water micro-emulsions which the current process removes by changing the salinity of the mixture produced by the surfactant flood. The increase in salinity is thought to push the surfactant into the oil phase (also referred to as "over-optimum") thus enhancing the separation of the oil phase from the water phase and coalescence of oil droplets in the water. At the same time, this is thought to separate any other solutes such as polymer which may be present in the water phase.
Furthermore, it is thought that the separation is helped by an increase in the density difference between the oil and water phase due to the high salt content of the aqueous phase besides the viscosity reduction due to the influence of the high salinity on the polymer hydrodynamic radius.
After the oil phase containing surfactant has been separated from the aqueous phase in step (b) , washing with low-saline or fresh water in step (c) is thought to bring the surfactant back to the aqueous phase thereby making it possible to remove surfactant from the oil phase and obtain an aqueous surfactant containing mixture which can be injected into the formation. The water wash in step (c) may have to be repeated one or more times to remove sufficient surfactant from the oil phase to meet the specifications on the water, salt and/or surfactant content of the oil.
The process of the present invention employs a surfactant which generally is effective in reducing the interfacial tension between oil and water in the oil- bearing formation. This is thought to mobilize the oil for
production from the formation.
The surfactant may be any enhanced oil recovery surfactant. Preferably, the surfactant is chosen from the group consisting of anionic and cationic surfactants .
Suitable cationic surfactants may be ammonium compounds, more preferably quaternary ammonium compounds, most preferably benzylic ammonium salts. Cationic
surfactants are especially suitable for use with carbonate formations .
The anionic surfactant may be a sulfonate-containing compound, a sulfate-containing compound, a carboxylate- containing compound, a phosphate-containing compound, a phenolate-containing compound or a blend thereof. The anionic surfactant may be chosen from the group consisting of an alpha olefin sulfonate compound, an internal olefin sulfonate compound, a branched alkyl benzene sulfonate compound, a propylene oxide sulfate compound, an ethylene oxide sulfate compound, a propylene oxide-ethylene oxide sulfate compound, or a blend thereof. Anionic surfactants are especially suitable for use with sandstone formations.
The surfactant preferably contains from 2 to 28 carbons, more specifically of from 2 to 20 carbons, more specifically of from 12 to 20 carbons. The surfactant of the oil recovery formulation may comprise an internal olefin sulfonate compound containing from 15 to 18 carbons or a propylene oxide sulfate compound containing from 12 to 15 carbons, or a blend thereof, where the blend contains a volume ratio of the propylene oxide sulfate to the internal olefin sulfonate compound of from 1:1 to 10:1.
The surfactant generally is present as part of an oil recovery formulation which can contain further compounds. The oil recovery formulation may contain an amount of the surfactant effective to reduce the
interfacial tension between oil and water in the formation and thereby mobilize the oil for production from the formation. The oil recovery formulation may contain from 0.05 % by weight (wt%) to 5 wt% of the surfactant or combination of surfactants, or may contain from 0.1 wt% to 3 wt% of the surfactant or combination of surfactants based on total amount of formulation. This amount can be gradually decreased during operation when the amount of surfactant recovered from the crude oil gradually
increases and wash water and/or regeneration water injected into the formation start to contain a substantial amount surfactant .
The oil recovery formulation can also contain further compounds such as polymers and/or alkali.
Polymer can be present to provide the oil recovery formulation with a viscosity of the same order of
magnitude as the viscosity of oil in the formation under formation temperature conditions so the oil recovery formulation may drive mobilized oil across the formation for production from the formation with a minimum of fingering of the oil through the oil recovery formulation and/or fingering of the oil recovery formulation through the oil. The polymer can be a single compound or can be a mixture of compounds. Preferably, the polymer is selected from the group consisting of polyacrylamide ; partially hydrolyzed polyacrylamide; polyacrylate ; ethylenic co¬ polymer; carboxymethylcelloluse ; polyvinyl alcohol;
polystyrene sulfonate; polyvinylpyrrolidone; biopolymers; 2-acrylamide-methyl propane sulfonate (AMPS) ; styrene- acrylate copolymer; co-polymers of acrylamide, acrylic acid and/or acrylate, AMPS and n-vinylpyrrolidone in any ratio; and combinations thereof.
Examples of ethylenic co-polymers include co¬ polymers of acrylic acid and acrylamide, acrylic acid and
lauryl acrylate, and lauryl acrylate and acrylamide .
Examples of biopolymers include xanthan gum, guar gum, schizophyllan and scleroglucan .
Most preferably, the polymer is (hydrolyzed) polyacrylamide . The latter includes but is not limited to copolymers of acrylamide and acrylic acid or sodium acrylate such as polymers which are being sold by SNF Floerger under the trade name Flopaam 3630S and Flopaam EM533.
The concentration of the polymer in the oil recovery formulation to be injected into the formation preferably is sufficient to provide the oil recovery formulation with a dynamic viscosity of at least 0.3 mPa.s (0.3 cP), more specifically at least 1 mPa.s (1 cP), or at least 10 mPa.s (10 cP), or at least 100 mPa.s (100 cP), or at least 1000 mPa.s (1000 cP) at 25°C or at a temperature within a formation temperature range. The concentration of polymer in the oil recovery formulation preferably is from 250 ppm to 10,000 ppm, or from 500 ppm to 5,000 ppm, or from 1,000 to 2, 000 ppm.
The molecular weight number average of the polymer in the oil recovery formulation preferably is at least 10,000 dalton, or at least 50,000 dalton, or at least 100,000 dalton. The polymer preferably has a molecular weight number average of from 10,000 to 3,000,0000 dalton, or from 100,000 to 15,000,000 dalton.
Furthermore, the oil recovery formulation can be prepared with alkali so that the formulation which is injected has a pH of at least 8, more specifically at least 8.5, most specifically at least 9. Alkali compounds which are especially suitable are sodium hydroxide, soda ash and ammonia. In order to prevent damage to the formation, the pH preferably is at most 12, more
specifically at most 11, most specifically at most 10.5.
The oil recovery formulation can further contain a low molecular weight alcohol as co-solvent, preferably in an amount of from 100 ppm to 50,000 ppm of the total oil recovery formulation.
The total dissolved solids content (TDS, measured according to ASTM D5907) of water which can be injected together with the surfactant can vary widely and depends on the availability of the various water sources.
Generally, the TDS of the water to be injected will be of from 1000 to 50,000 ppm, more specifically of from 5,000 to 50,000 ppm. The expression "ppm" indicates parts per million by weight on total weight amount present. In order to prevent scaling, it is generally preferred to use water having a limited amount of divalent ions. If such water is not readily available, it can be obtained by so-called softening processes. Most preferably, the water has an ionic strength of 0.15 M or less, or from 0.02 M to 0.125 M, or from 0.0 3M to 0.1 M. Ionic strength, as used herein, is defined by the equation
I=½*∑1=i n C i Z i where I is the ionic strength, c is the molar
concentration of ion i, z is the valency of ion i, and n is the number of ions in the measured solution. Such water including its preparation is described in WO-A- 2014/0041856.
The mixture recovered in step (a) of the process of the present invention contains oil, water and surfactant but can contain other compounds as well depending on the compounds present in the formation and the components present in the original oil recovery formulation.
Step (b) requires the addition of salt. The salt can be in any form such as a solid or as an aqueous solution.
Generally, an aqueous solution is preferred as it mixes better with the mixture of oil and water and often is more readily available. The salt is thought to cause the surfactant to become part of the oil phase. The aqueous salt solution preferably has a TDS of at least 5000 ppm, more specifically at least 10,000 ppm, more specifically at least 20,000 ppm, more specifically at least 40,000 ppm, more specifically at least 50,000 ppm. The upper limit generally will be the amount of salt which can be dissolved in the fluid at the operating conditions. The aqueous salt solution used in step (b) has a higher molar concentration of salt than the water present in the mixture of surfactant, water and oil obtained in step (a) .
From an efficiency point of view, it is preferred to use in step (b) an aqueous salt solution which has been used or produced in the recovery process of the present invention. A solution which is especially suitable is a reject stream of desalination or a softening process.
These streams can be produced in removing salt or
multivalent ions in order to produce water of sufficiently low TDS and/or ionic strength. Alternatively, water from another field, aquifer water or sea water can be used provided that the aqueous salt solution used in step (b) is more saline than the water present in the mixture of surfactant, water and oil obtained in step (a) .
If the mixture is an emulsion, phase separation also is referred to as breaking of the emulsion. In specific circumstances, it can be preferred to add demulsifiers to the separation step (b) to further aid in breaking the emulsion. Suitable demulsifiers may be selected from the group consisting of amyl resins; butyl resins; nonyl resins; acid- or base-catalyzed phenol-formaldehyde resins; phenol-acrylate anhydride polyglycol resins;
urethanes; polyamines; polyesteramines ; sulfonates; di-
epoxides; polyols; esters and polyol esters including triol fatty acid esters, triol adipate esters, and triol fumarate esters; ethoxylated and/or propoxylated compounds of amyl resins, butylresins, nonylresins, acid- or base- catalyzed phenol-formaldehyde resins, fatty acids, polyamines, di-epoxides, and polyols; and combinations thereof which may be dispersed in a carrier solvent selected from the group consisting of xylene, toluene, heavy aromatic naphtha, isopropanol, methanol, 2- ethoxyhexanol, diesel, and combinations thereof.
The separation of step (b) can be enhanced by
electrostatic methods. Preferably, the separation of step (b) is carried out in separation tanks, which may comprise heating elements. In a "continuous feed" operation, the mixture and the aqueous salt solution are fed into a separation tank, and substantially dewatered oil and substantially oil-free water phases are removed from the tank, wherein the rate of delivery of crude oil and aqueous salt solution and the rate of removal of the oil and water phases are essentially in equilibrium. In the traditional "batch" gravity-style separation process, the oil containing mixture and aqueous salt solution are added to the tank and mixed, optionally heated to accelerate the separation process, and permitted to stand and settle until the separation is sufficiently complete that the aqueous phase and the oil phase can be separately removed.
Other methods are sometimes used in conjunction with the above separation processes such as large-scale centrifuge separators .
In step (c) , the oil phase containing surfactant is washed with water. The water can be an aqueous solution or it can be water per se. It depends on the circumstances what aqueous solution or water to use. If an aqueous solution is used, it will generally have a TDS of from 0
to 30,000 ppm, more preferably at most 10,000 ppm, more preferably at most 5,000 ppm, more preferably at most 1,000 ppm and most preferably at most 500 ppm. The water can be obtained from any suitable natural source or can have been obtained by treating, purifying, softening or desalinating the source water in order to reduce the contaminants and/or salt content.
The washing is preferably carried out by thoroughly mixing the oil and water and subsequently allowing the water phase and oil phase to separate as described above.
Depending on the amount of contaminants present in the oil phase and the purity required, the washing can be repeated most preferably of from 1 to 10 times. The volume ratio of oil phase to wash water preferably is of from 0.5 to 20.
The wash water which is used in step (c) can be used in various ways . A preferred option is to in ect the wash water into the formation and thereby contribute to the surfactant flood for recovering oil.
Another option is to treat the wash water obtained in step (c) in a further step (d) with an ion exchange resin to obtain wash water having reduced surfactant content. This allows the treated wash water to be used again in step (c) . An anion exchange resin is to be used for anionic surfactant, and a cation exchange resin is to be used for cation surfactant.
It can be desirable to regenerate the ion exchange resin used for removing the surfactant. An advantageous method is to (e) treat the used ion exchange resin with a salt solution to obtain a regenerated ion exchange resin and a concentrated surfactant-containing regenerating solution, and (f) inject concentrated surfactant- containing regenerating solution obtained in step (e) into the formation. The concentrated surfactant-containing
regeneration solution obtained in step (e) preferably is combined with injection water before being injected into the formation in step (f) .
The oil recovered by the process of the present invention will generally contain at most 5 %wt, most preferably of from 0.001 to 3 %wt of surfactant and at most 5 %wt, most preferably of from 0.001 to 3 %wt of water .
Embodiments of the process as described herein are shown in Figure 1 and Figure 2.
Figure 1 shows a process scheme involving the steps of treating an oil containing mixture with an aqueous salt solution and separating the treated mixture into an oil phase and an aqueous phase followed by 2 subsequent wash steps and injecting the wash water into the formation optionally after further surfactant is added.
Figure 2 shows a process scheme involving the steps of treating an oil containing mixture with an aqueous salt solution and separating the treated mixture into an oil phase and an aqueous phase followed by a wash step and treating the wash water with an ion exchange resin. Fluid obtained during regeneration can be injected again into the formation optionally after further water is added.
Specific embodiments of the invention are shown herein by way of example only. The invention is susceptible to various modifications. It should be understood that the process schemes shown are not intended to limit the invention to the particular process disclosed but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the scope of the invention as defined by the appended claims.
In the process scheme of Figure 1, a mixture of oil, water and surfactant is recovered from reservoir 101 and sent via line 1 to a treating unit 102 for contacting the
mixture with an aqueous salt solution added via line 2. The mixture is mixed intensely in unit 102 and separated into an aqueous phase which is removed via line 4 and an oil phase which is sent via line 3 to wash unit 103. The aqueous phase removed via line 4 is thought to contain a reduced amount of contaminants such as polymers and surfactants. In wash unit 103, the oil phase is thoroughly contacted with wash water added via line 5. The oil phase is separated from the wash water and sent via line 6 to further wash unit 104 where the oil phase is once more thoroughly contacted with wash water added via line 8. The crude oil obtained has reduced surfactant content and is removed from the process via line 9. The wash water used in unit 103 is combined via line 7 with wash water used in unit 104. The combined wash water streams are sent via line 10 back to the formation optionally after further surfactant is added via line 11.
In the process scheme of Figure 2, a mixture of oil, water and surfactant is recovered from reservoir 201 and sent via line 21 to a treating unit 202 for contacting the mixture with an aqueous salt solution added via line 22. The mixture is mixed intensely in unit 202 and separated into an aqueous phase which is removed via line 24 and an oil phase which is sent via line 23 to wash unit 203. In wash unit 203, the oil phase is thoroughly contacted with wash water added via line 25. The crude oil obtained has reduced surfactant content and is removed from the process via line 26. The wash water used in unit 203 is sent via line 27 to ion exchange unit 204. The wash water removed via line 28 is low in contaminants and can be used for many purposes such as fresh wash water for use in wash unit 203. The ion exchange resin becomes loaded with surfactant during use and has to be regenerated at certain time intervals. In order to ensure continuous operation,
several ion exchange units can be operated in parallel. In such operation, one or more units are taken out of operation for regeneration while regenerated units are taken into normal operation again. Alternatively, several ion exchange resins are operated in series. This allows regeneration of a particular unit while the remaining units in the series ensure that wash water can continue to be treated. During regeneration, the ion exchange resin of unit 204 is contacted with a suitable salt solution added via line 29. The used regeneration fluid has a high concentration of surfactant and is especially suitable to be used again in oil recovery. Therefore, it is preferred to send the used regeneration solution via line 30 back to the formation for injection. Preferably, additional injection water is added to the concentrated surfactant fluid in line 30 via line 31.
Claims
1. A process for recovering oil which process comprises (a) injecting surfactant into an oil-bearing formation and recovering from the formation a mixture containing oil, water and surfactant,
(b) treating the mixture recovered in step (a) with salt or an aqueous salt solution and separating the treated mixture into an oil phase containing surfactant and an aqueous phase, and
(c) washing the oil phase containing surfactant obtained in step (b) with water and to recover oil having a reduced surfactant content.
2. A process according to claim 1 in which the salt or aqueous salt solution in step (b) is the reject stream of desalination or a softening process.
3. A process according to claim 1 or 2, which process further comprises injecting surfactant containing wash water obtained in step (c) into the formation.
4. A process according to any one of claims 1-3, in which the formation is a sandstone formation and the surfactant is an anionic surfactant selected from the group
consisting of an alpha olefin sulfonate compound, an internal olefin sulfonate compound, a branched alkyl benzene sulfonate compound, a propylene oxide sulfate compound, an ethylene oxide sulfate compound, a propylene oxide-ethylene oxide sulfate compound, or a blend thereof anionic and the process further comprises
(d) treating surfactant containing wash water obtained in step (c) with an anion exchange resin to obtain wash water having a reduced surfactant content.
5. A process according to claim 4, which process further comprises
(e) regenerating the anion exchange resin used in step
(d) by treating the used anion exchange resin with a salt solution to obtain a regenerated anion exchange resin and a concentrated surfactant-containing regenerating
solution, and
(f) injecting surfactant containing regenerating solution obtained in step (e) into the formation.
6. A process according to any one of claims 1-3, in which the formation is a carbonate formation and the surfactant is a cationic surfactant, preferably an ammonium compound, and the process further comprises
(d) treating surfactant containing wash water obtained in step (c) with a cation exchange resin to obtain wash water having a reduced surfactant content.
7. A process according to claim 6, which process further comprises
(e) regenerating the cation exchange resin used in step (d) by treating the used cation exchange resin with a salt solution to obtain a regenerated cation exchange resin and a concentrated surfactant-containing solution, and
(f) injecting concentrated surfactant-containing
concentrated regenerating solution obtained in step (e) into the formation.
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