PROCESS FOR TREATING PRODUCED WATER FROM AN OIL & GAS FIELD

Abstract

A method for treating produced water stream from a production well of an oil and gas field including a first step of ultrafiltration or microfiltration and a second step of removing the alkalinity in produced water.

Claims

1. A method for treating produced water stream from a production well of an oil and gas field, comprising: a first step of obtaining a permeate and a first stream by directing the produced water stream to an ultrafiltration or microfiltration membrane system (30), and a second step of removing the alkalinity as carbon dioxide gas, and volatile organic compounds and H.sub.2S, in the permeate by directing the permeate obtained in the first step to a gas stripping device (40).

2. The method according to claim 1, comprising, before the first step, a third step of decreasing the pH of the produced water stream down to a range of 3 to 6.

3. The method according to claim 1, wherein the second step comprises maintaining the pH of the permeate in a range of 3 to 6 in the gas stripping device.

4. The method according to claim 1, wherein said method comprises, after the second step, a fourth step of directing the permeate obtained in the second step to: an absorbent to remove water soluble oil, and/or a reverse osmosis membrane, a nanofiltration membrane, a forward osmosis membrane, or evaporation/crystallization device (50) to obtain a purified water stream free of most dissolved solids and/or scale forming divalent ions.

5. The method according to claim 1, wherein said method comprises, before the first step, a preliminary step of directing produced water stream from a production well to primary oil-water separation device (20) for a preliminary separation of suspended solids and oil from produced water stream.

6. The method according to claim 5 wherein said method comprises an intermediate step between the first step and the second step, of recirculating the first stream back to the upstream primary oil-water separation device (20).

7. The method according to claim 5, wherein said method comprises a fifth step of treating the first stream by a coalescing contactor (80) to recover: a pure oil stream, and a deoiled concentrate stream and/or a backwash wastewater stream, which is then recirculated back to the upstream primary oil-water separation device (20).

8. The method according to claim 4, wherein the purified water stream recovered from the fourth step is reinjected in a hydrocarbon bearing formation or discharged to a surface water body.

9. The method according to claim 2, wherein the second step comprises maintaining the pH of the permeate in a range of 3 to 6 in the gas stripping device.

10. The method according to claim 2, wherein said method comprises, before the first step, a preliminary step of directing produced water stream from a production well to primary oil-water separation device (20) for a preliminary separation of suspended solids and oil from produced water stream.

11. The method according to claim 3, wherein said method comprises, before the first step, a preliminary step of directing produced water stream from a production well to primary oil-water separation device (20) for a preliminary separation of suspended solids and oil from produced water stream.

12. The method according to claim 4, wherein said method comprises, before the first step, a preliminary step of directing produced water stream from a production well to primary oil-water separation device (20) for a preliminary separation of suspended solids and oil from produced water stream.

13. The method according to claim 10, wherein said method comprises an intermediate step between the first step and the second step, of recirculating the first stream back to the upstream primary oil-water separation device (20).

14. The method according to claim 10, wherein said method comprises a fifth step of treating the first stream by a coalescing contactor (80) to recover: a pure oil stream, and a deoiled concentrate stream and/or a backwash wastewater stream, which is then recirculated back to the upstream primary oil-water separation device (20).

15. The method according to claim 11, wherein said method comprises an intermediate step between the first step and the second step, of recirculating the first stream back to the upstream primary oil-water separation device (20).

16. The method according to claim 11, wherein said method comprises a fifth step of treating the first stream by a coalescing contactor (80) to recover: a pure oil stream, and a deoiled concentrate stream and/or a backwash wastewater stream, which is then recirculated back to the upstream primary oil-water separation device (20).

17. The method according to claim 12, wherein said method comprises an intermediate step between the first step and the second step, of recirculating the first stream back to the upstream primary oil-water separation device (20).

18. The method according to claim 12, wherein said method comprises a fifth step of treating the first stream by a coalescing contactor (80) to recover: a pure oil stream, and a deoiled concentrate stream and/or a backwash wastewater stream, which is then recirculated back to the upstream primary oil-water separation device (20).

19. The method according to claim 5, wherein the purified water stream recovered from the fourth step is reinjected in a hydrocarbon bearing formation or discharged to a surface water body.

20. The method according to claim 6, wherein the purified water stream recovered from the fourth step is reinjected in a hydrocarbon bearing formation or discharged to a surface water body.

Description

[0073] Preferred embodiments of the invention are disclosed in following description and the accompanying drawing which are merely illustrative of such invention.

[0074] FIGS. 1A and 1B are schematic illustration of the process of the present invention including recirculation of the concentrate stream and/or the backwash wastewater stream back to the upstream pretreatment device.

[0075] FIGS. 2A and 2B are schematic illustration of the process of the present invention including recirculation via a coalescing contactor of the concentrate stream and/or the backwash wastewater stream back to the upstream pretreatment device.

[0076] In FIGS. 1A and 1B, the produced water treatment system of the present invention is indicated generally by the numeral 10. The system includes primary oil-water separation device 20, an ultrafiltration or microfiltration membrane 30, a gas stripper 40, a reverse osmosis or nanofiltration or forward osmosis membrane 50, and a pipeline 60 for recycling concentrate stream and/or the backwash wastewater stream obtained in membrane back to the primary oil-water separation device 20.

[0077] According to the preliminary step of the method of invention, produced water stream entering into primary oil-water separation device 20 is generated in oil and gas production well 70.

[0078] According to the first step of the method of invention, produced water stream obtained after oil/water preliminary separation in device 20 is directed to ultrafiltration or microfiltration membrane 30.

[0079] Before being directed to ultrafiltration or microfiltration membrane 30, according to the third step of the method of invention, the pH of the produced water stream is decreased to a range of 3 to 6 by adding strong acid.

[0080] According to the second step of the method of invention, the permeate obtained from ultrafiltration or microfiltration is directed to the gas stripper 40. Volatile organic compounds and CO.sub.2 are escaped from said gas stripper via an outlet for gas. According to an intermediate step, the concentrate and/or backwash wastewater (first stream) obtained in ultrafiltration or microfiltration is recirculated to device 20 via pipeline 60.

[0081] The permeate obtained after gas stripping is directed to a reverse osmosis or nanofiltration or forward osmosis membrane 50. Permeate obtained from a reverse osmosis or nanofiltration or forward osmosis is reinjected in an oil bearing formation (FIG. 1A) or discharged to a surface water body (FIG. 1B). Concentrate obtained is the final by-product to be disposed of.

[0082] In FIGS. 2A and 2B, the produced water treatment system 10 includes an primary oil-water separation device 20, an ultrafiltration or microfiltration membrane 30, a gas stripper 40, a reverse osmosis or nanofiltration or forward osmosis membrane 50, and a coalescing contactor 80.

[0083] According to the preliminary step of the method of invention, produced water stream entering into primary oil-water separation device 20 is generated in oil and gas production well 70.

[0084] According to the first step of the method of invention, produced water stream obtained after primary oil/water separation in device 20 is directed to ultrafiltration or microfiltration membrane 30.

[0085] Before being directed to ultrafiltration or microfiltration membrane 30, according to the third step of the method of invention, the pH of the produced water stream is decreased to a range of 3 to 6 by adding strong acid.

[0086] According to the second step of the method of invention, the permeate obtained from ultrafiltration or microfiltration is directed to the gas stripper 40. Volatile organic compounds and CO.sub.2 are escaped from said gas stripper via an outlet for gas.

[0087] Different from the embodiment disclosed in FIGS. 1A and 1B, according to the fifth step of the method of invention, the concentrate and/or backwash wastewater (first stream) obtained in ultrafiltration or microfiltration is treated by coalescing contactor 80, wherein pure oil is recovered and deoiled concentrate and/or backwash wastewater containing suspended solids is recirculated to primary oil/water separation device 20.

[0088] The permeate obtained after gas stripping is directed to a reverse osmosis or nanofiltration or forward osmosis membrane 50. Permeate obtained from a reverse osmosis or nanofiltration or forward osmosis is reinjected in an oil bearing formation (FIG. 2A) or discharged to a surface water body (FIG. 2B). Concentrate obtained is the final by-product to be disposed of.