CA3042570A1

CA3042570A1 - Hybrid system and method for treating produced water and sea water to be re-injected into a subsea oil reservoir

Info

Publication number: CA3042570A1
Application number: CA3042570A
Authority: CA
Inventors: Giovani CAVALCANTI NUNES; Silvio Edegar WESCHENFELDER; Joyce MONTEIRO SAMBADE; Cristiano Piacsek Borges
Original assignee: Universidade Federal do Rio de Janeiro UFRJ; Petroleo Brasileiro SA Petrobras
Current assignee: Universidade Federal do Rio de Janeiro UFRJ; Petroleo Brasileiro SA Petrobras
Priority date: 2016-07-20
Filing date: 2017-07-19
Publication date: 2018-01-25
Also published as: RU2747649C2; WO2018014096A1; BR102016016758A2; RU2019104644A; AU2017298020A1; CN109963814A; AU2017298020B2; CN115925051A; RU2019104644A3

Abstract

The present invention relates to systems for treating process water and sea water for secondary recovery in oil wells. In this situation, the present invention provides a hybrid system for treating produced water and sea water to be re-injected into a subsea oil reservoir, comprising (i) at least one inlet for the water to be treated, (ii) at least two treatment modules (20), each module comprising (ii-a) at least one set of micro/ultrafiltration membranes (20a, 20b, 20c) suitable for removing oils and solids from the water being treated, or (ii-b) at least one set of nanofiltration membranes (20a, 20b, 20c) suitable for removing sulphate ions from the water being treated, and (iii) at least one outlet for the treated water. The volume of water to be treated is led to a treatment module (20) comprising micro/ultrafiltration membranes or to a water treatment module comprising nanofiltration membranes, depending on the quality of the water, with regard to the oil and solid content or to the sulphate ion content. The present invention further provides a hybrid water treatment method associated with the above-mentioned system. Thus, the present invention provides a system and method for treating sea water and produced water, allowing the produced water to be re-injected without requiring an additional treatment system on the platform. Other advantages of the present invention include reduced oil discharge into the sea and reduced mounting, operation and maintenance costs, in comparison with an additional system on the sea installation.

Description

HYBRID SYSTEM AND METHOD FOR TREATING PRODUCED WATER AND
SEA WATER TO BE RE-INJECTED INTO A SUBSEA OIL RESERVOIR
FIELD OF THE INVENTION
[0001] This invention relates to water treatment systems in offshore oil production installations. More specifically, this invention relates to treatment systems of produced water and sea water for secondary recovery in oil wells.
BACKGROUND OF THE INVENTION

[0002] It is well known that, in offshore oil installations, one of the techniques used in secondary oil recovery is the injection of treated seawater. In this context, it is known that seawater contains significant amounts of sulfate ions (SO4-2), around 2,800 mg/L. When seawater is injected into fields whose formation water (cognate water) contains enough Barium (Ba+2), Strontium (Sr+2) or Calcium (Ca2+) ions in solution, the contact between these two fronts normally causes the precipitation of its sulfates: Barium Sulphate (BaSO4), Strontium Sulfate (SrSO4) or Calcium Sulphate (CaSO4). These salts are extremely insoluble and cause formation damage due to clogging of the pores with the precipitated salts.
They can also precipitate in the production lines and equipment of the process plant.

[0003] Depending on the barium and strontium contents in the formation water, it may be necessary to deploy a sulfate removal unit (URS) for seawater treatment for injection into the reservoir, as shown in Figure 1. In the URS, membranes of nanofiltration (which may be ceramic or polymeric) are used to remove sulfate ions from seawater. Since seawater has solid particles as well as marine flora and fauna components, it is necessary to install filters upstream of the URS unit to improve its performance. The filtration is done initially with coarse filters and later cartridge filters of smaller flow diameter.

[0004] In the URS, water permeates through nanofiltration membranes while a fraction, typically 25%, is concentrated in sulfate ions and separated to be future discarded at sea. To achieve the design specification for sulfate ions in the treated water, two sets of membranes are used in parallel followed by a third set in series, according to the schematic shown in Figure 2.

[0005] Once the water is treated by URS, it acquires the necessary specification and can already be injected into the oil reservoir for secondary recovery.

[0006] Additionally, it is further known that the produced water arriving at the treatment unit is treated for removal of oil droplets. Conventional techniques for this type of treatment have, in general and simplified form, the configuration shown in Figure 1.

[0007] In particular, the produced water undergoes a treatment process for separating the aqueous phase from the oil phase composed of gravitational separation, hydrocyclones and floats and is then specified for disposal at sea in accordance with current Environmental Legislation. Water that is not specified for disposal in some platforms has the possibility of being directed to a tank called "Off-spec Tank", where it will have a longer time to separate the oil phase, and in some cases may be reprocessed in the treatment plant.

[0008] This produced water treatment equipment, however, has a reduced efficiency in the removal of solids particles and oil droplets of less than 5.0 pm. Such conditions limit the overall efficiency of the treatment and, consequently, the obtaining of an effluent stream with characteristics suitable for more restrictive reservoirs in terms of suspended solids content, oils and greases. Therefore, after treatment, the produced water is specified for disposal at sea, and not specified for reinjection due to its content of suspended solids, oils and greases.

[0009] This way, nowadays the destination of produced water at offshore oil production facilities after treatment is only the disposal. The low efficiency of the conventionally produced water treatment plants employed to obtain solids and oil contents according to the requirements required for the reinjection in the more restrictive reservoirs contributes, among other factors, to the infeasibility of the reinjection. Thus, in recent projects for secondary recovery this alternative is still ignored.

[0010] It is noted, however, that the development of a treatment system that allows the reinjection of the produced water is a very interesting option for the oil production sector mainly due to the tendency of environmental legislation to become increasingly restrictive, in addition to moving towards increasing the sustainability of industrial practices in this action area.

[0011] In this sense, the micro/ultrafiltration membrane splitting technology (with ceramic membranes) have proved to be an interesting option for this challenge, since, when applied to the treatment of produced water, it results in water with low oil and solids contents.

[0012] In the micro/ultrafiltration membrane separation process, as known in the state of the art, water permeates the membranes while a fraction of the fed volume accumulates the non-permeated oil and returns to the system in the recycle form.

[0013] The paper entitled "Ceramic Ultra-and Nanofiltration Membranes for Oilfield Produced Water Treatment: A Mini Review", by Ashaghi, K. Shams et al., discloses a review study regarding the use of micro/ultrafiltration ceramic membranes for treatment of produced water (removal of solids and particles of oil).
Several techniques using micro/ultrafiltration ceramic membranes are presented in this scientific article, so that their description is incorporated herein by reference.

[0014] The paper entitled "Evaluation of membranes for the treatment of water from the oil extraction process", by Weschenfelder, Silvio E. et al., one of the inventors of this invention, discloses a study evaluating the performance of membranes for the treatment of produced water by long-term tests with real effluent, taking into account the evolution of the permeate flow and the characteristics of the generated effluent. The results indicate that by using membranes with pore size equal to 0.1 mm it is possible to obtain a permeate stream with solids contents of less than 1 mg L-1 and contents of oils and greases in the range of 1 to 3 mg L-1.
Further, such document discloses that with the chemical regeneration process 95%
reestablishment of the original permeability of the micro/ultrafiltration ceramic membrane is possible. The disclosure of this document is also incorporated herein by reference.

[0015] In a current approach, if it were decided by the application of the micro/ultrafiltration membrane separation process to complement the conventional treatment of the produced water to enable the reinjection, for example, an additional system would be required in the treatment plant, as described in prior art documents cited above. This brings significantly higher deployment, operation and maintenance costs and greater operational difficulty, as well as greater weight and area occupied on the platform.

[0016] Thus, it is clear that the prior art lacks a produced water treatment system which allows for reinjection without the need for an additional treatment system as known in the prior art.

[0017] As will be better described below, this invention seeks to solve the above-described problems of the prior art in a practical, efficient and cost-effective manner.
SUMMARY OF THE INVENTION

[0018] This invention has the main object of providing a hybrid system and process for the treatment of seawater and production which allow the reinjection of the produced water without the need for an additional treatment system on the platform.

[0019] In order to achieve the above-described object, this invention provides a hybrid system for the treatment of produced water and seawater for reinjection into an offshore oil reservoir, comprising (i) at least one inlet of water to be treated, (ii) at least two modules of micro/ultrafiltration water treatment, each module comprising (ii-a) at least one set of micro/ultrafiltration membranes adapted for removal of oils and solids from the water to be treated or (ii-b) at least one set of nanofiltration membranes adapted for removal of sulfate ions of the water to be treated, (iii) at least one treated water outlet, wherein the volume of water to be treated is directed to a water treatment module comprising membranes micro/ultrafiltration or to a water treatment module comprising nanofiltration membranes depending on the quality of the water in relation to the oils and solids content or the sulfate ion content.

[0020] This invention further provides a hybrid process for treating produced water and seawater for reinjection into an offshore oil reservoir, comprising basically the steps of (i) directing the water to be treated to a water treatment module comprising at least one set of micro/ultrafiltration membranes adapted for removal of oils and solids from the water to be treated or (ii) directing the water to be treated to a water treatment module comprising at least one set of nanofiltration membranes adapted for removal of sulfate ions of the water to be treated, wherein the volume of water to be treated is directed to the water treatment module comprising micro/ultrafiltration membranes or to the water treatment module comprising nanofiltration membranes depending on the quality of the water with respect to the content of oils and solids or content of sulfate ions.
BRIEF DESCRIPTION OF THE FIGURES

[0021] The detailed description given below refers to the attached figures and their respective reference numerals.

[0022] Figure 1 shows a schematic diagram of a seawater treatment system and produced water for injection and disposal, respectively, as known in the status of technique.

[0023] Figure 2 shows a schematic diagram of an example of seawater treatment for injection into an oil reservoir through a sulfate removal unit (URS), as known in the status of technique.

[0024] Figure 3 shows a schematic diagram of a treatment module comprising nanofiltration or micro/ultrafiltration membranes in accordance with the preferred embodiment of this invention.

[0025] Figure 4 shows a schematic diagram of one of a hybrid treatment system of seawater and produced water for reinjection according to the preferred embodiment of this invention.

[0026] Figure 5 shows a schematic diagram of a complete system for treating seawater and produced water for reinjection comprising the hybrid system of this invention.
DETAILED DESCRIPTION OF THE INVENTION

[0027] In the foregoing, it will be appreciated that the following description will depart from a preferred embodiment of the invention. As will be apparent to one skilled in the subject, however, the invention is not limited to that particular embodiment.

[0028] Figure 4 shows a simplified schematic diagram of one of a hybrid seawater treatment system and produced water for further reinjection according to the preferred embodiment of this invention. Such a figure basically contemplates two intakes of water to be treated, namely one of produced water 2, with high contents of oils and solids, and one of seawater 4, with a high content of sulfate ions.

[0029] The produced water is preferably stored in at least one tank 10 before being directed for disposal or treatment through the hybrid system of this invention.

[0030] Preferably, the seawater collected for treatment and subsequent injection passes through a sequence of filters, being the first one provided with filtering elements with a thicker mesh and the latter having finer mesh filtration elements. Preferably, a first filter 12 retains particles up to 500 pm, a second 14 retains particles up to 25 pm and a third up to 5 pm.

[0031] Preferably, both the produced water and the seawater collected respectively arrive at least one manifold 18 consisting of a plurality of water control valves which will enter each of the treatment modules 20.

[0032] Each treatment module 20 comprises at least one adapted set of micro/ultrafiltration membranes (ceramic membranes) for removal of oils and solids from the produced water or at least one set of adapted nanofiltration membranes (ceramic or polymer membranes) for the removal of sulfate ions from seawater.
Thus, at least one manifold 18, through its control valves, directs the produced water into the modules comprising micro/ultrafiltration membranes and the seawater drawn into the modules comprising nanofiltration membranes. Preferably, the at least one manifold is subdivided into two manifolds, one for controlling the inlet of produced water in the modules comprising micro/ ultrafiltration membranes and another for controlling entry of seawater into the modules comprising nanofiltration membranes.

[0033] Preferably, at least one manifold 18 is fluidly connected to the two water inlet ducts to be treated, namely one for produced water 2 and one for seawater 4. Each of these inlet ducts, separately, is subdivided into a plurality of secondary ducts in parallel, a secondary duct for each treatment module. The secondary ducts of produced water and seawater, prior to entering each treatment module 20, flow into a single inlet duct per module, downstream of each of the control valves.

[0034] The control valves are positioned upstream of each treatment module 20, so that each of the valves controls the entry of one type of water to be treated, namely produced water or seawater from each of secondary ducts.

[0035] Preferably, there is no mixing between produced water and sea water prior to entering the treatment modules 20. That is, if the produced water inlet control valve is open, the seawater inlet control valve should preferably be closed.

[0036] Preferably, each treatment module 20 comprises only one type of membrane, namely nanofiltration or micro/ultrafiltration. Thus, preferably, if a particular treatment module 20 comprises only nanofiltration membranes, only seawater will be directed thereto, the produced water inlet control valve being closed. Likewise, the produced water will be directed to a treatment module 20 comprising only micro/ultrafiltration membranes.

[0037] Each treatment module 20 is designed to allow interchangeability between nanofiltration membranes and micro/ultrafiltration membranes. In other words, each module may have its nanofiltration membranes replaced with micro/ultrafiltration (and vice versa) depending on the demand for treatment of each of the waters.

[0038] By way of example, it is to be expected that soon after the implementation of the hybrid system of this invention there will be only demand for treatment of seawater through nanofiltration membranes, since there will still be no produced water. Thus, practically all the treatment modules 20 may be equipped with only nanofiltration membranes. As the produced water is generated, the demand for treatment of seawater decreases. In that case, the nanofiltration membranes of the treatment modules 20 are being replaced by micro/ultrafiltration membranes.

[0039] Figure 3 shows in a schematic diagram details of a treatment module 20 according to this invention. As mentioned, the treatment module 20 may comprise nanofiltration membranes or micro/ultrafiltration membranes depending on the type of water (produced or sea) that will pass through that particular module.
Each module comprises at least one set 20 of micro/ultrafiltration or nanofiltration membranes. Preferably, like the URS of the status of technique, each module comprises two sets of parallel membranes 20a, 20b followed by a third set of series membranes 20c.

[0040] Preferably, in the case of a treatment module 20 provided with nanofiltration membranes, for the removal of sulfate ions from seawater, the water to be treated passes through the first two sets of nanofiltration membranes in parallel, so that the largest fraction of the volume of treated water becomes low sulfate ions concentration and are sent to the injection in the reservoir.

[0041] The remainder of the water passing through the first sets of membranes, concentrated in sulfate ions, is directed to the third set of membranes 20c in series with the first two. This third set treats this more concentrated water and also generates a larger portion with a low concentration of sulfate ions, which will be mixed with the water treated by the first two sets of membranes, and a smaller portion extremely concentrated in sulfate ions that is normally discarded in the sea.

[0042] The water with low sulfate ions concentration from the treatment of the nanofiltration membranes sets is used for injection into the reservoir, but may undergo further treatment steps.

[0043] In the case of a treatment module 20 provided with micro/ultrafiltration membranes, for removal of oils and solids from the produced water, the procedure is quite similar to the above. Preferably, the water to be treated passes through the first two sets of membranes 20a, 20b in parallel, so that the largest fraction of the volume of treated water is comprised of low concentration of oils and solids and is directed for reinjection into the reservoir.

[0044] The remainder of the water passing through the first sets of membranes, concentrated in oils and solids, is directed to the third set of membranes 20c in series with the first two. This third set treats this more concentrated water and also generates a larger portion with a low concentration of oils and solids, which will be mixed with the water treated by the first two sets of membranes. The water with low concentration in oils and solids coming from the treatment of all three sets of micro/ultrafiltration membranes is used for reinjection into the reservoir.

[0045] Depending on the quality of the water to be treated, each treatment module 20 may comprise more or fewer serial and/or parallel membranes sets.
Thus, it is pointed out that this invention is not limited to the configuration of membranes sets shown in Figure 3.

[0046] Still in the case of a treatment module 20 provided with micro/ultrafiltration membranes, the minor portion from the third set of membranes 20c, concentrated in oils and solids, may be directed to the inlet of the treatment module 20 as shown in Figure 3.

[0047] Alternatively, as shown in Figure 5 (complete diagram of the offshore installation), the water concentrated in oils and solids (oily recycle) may be routed to the water treatment system for separation of the oily phase.
Preferably, the water concentrated in oils and solids may be routed to some treatment tank, schematically shown in Figure 5 (treatment tank 24). This tank can be, for example an off-spec tank that is normally already used in produced water treatment plants.
Alternatively, an additional tank may be provided for carrying out this step, in addition to the off-spec tank.

[0048] Optionally, at least one water outlet is provided in the lower portion of the treatment tank 24 for withdrawing water with low concentration in oil, since the oil, less dense than water, after a certain period will be concentrated on top. The water withdrawn through the outlet of water in the lower portion of the treatment tank 24, which has relatively low or medium concentration in oils, may be discarded, if specified, or be directed to the hybrid treatment system according to this invention where it will be routed to treatment modules 20 comprising micro/ultrafiltration membranes to undergo a new treatment for removal of oils and solids. The oily concentrate remaining in the treatment tank 24, after removal of some of the water, is preferably directed to the oil and water separation system 23 for utilization of the oil in the production. This contributes to minimizing the discharge of oil into the sea and to a better utilization of the oil present in the produced water in the total production of the well.

[0049] This invention further provides for the possibility of performing a backwashing procedure of the membranes used in the treatment modules, especially the micro/ultrafiltration membranes. Such a procedure can be performed, for example, by pumps (not shown) or manipulation of timed valves in the treated water line and in the feed line of each set. This procedure allows the periodic inversion of the flow in the membrane, cleaning it and maintaining its performance.

[0050] Optionally, at least a first deaerator unit 28 is provided upstream or downstream of treatment modules 20 for deaeration of seawater, if necessary, prior to reinjection into the reservoir.

[0051] This invention further provides a hybrid process for treating produced water and seawater for reinjection into the offshore reservoir, comprising basically the steps of:
a) directing the water to be treated to a water treatment module comprising at least one set of micro/ultrafiltration membranes adapted for removal of oils and solids from the water to be treated; or b) directing the water to be treated to a water treatment module comprising at least one set of nanofiltration membranes adapted for removal of sulfate ions from the water to be treated, wherein the volume of water to be treated is directed to the treatment module of water comprising microfiltration/ultrafiltration membranes or the water treatment module comprising nanofiltration membranes depending on the quality of the water relative to the oils and solids content or the sulfate ion content.

[0052] It is further emphasized that all the treatment steps described herein detailed description apply to both the system and the process of this.

[0053] Thus, based on the above description, this invention provides a system and process for treating seawater and production which allow the reinjection of produced water without the need for an additional treatment system on the platform. Further advantages are still achieved by this invention, such as the reduction of offshore oil disposal by the more efficient treatment of the produced water and the reduction of installation, operation and maintenance costs associated with an additional system at the offshore installation.

[0054] Numerous variations relating to the scope of protection of the present application are permitted. Accordingly, the fact that this invention is not limited to the particular sets/embodiments described above is reinforced.

Claims

1. A hybrid system for the treatment of produced water and seawater for reinjection in an offshore oil reservoir, characterized in comprising:
at least one water inlet to be treated;
at least two treatment modules (20), each module comprising:
at least one set of micro/ultrafiltration membranes (20a, 20b, 20c) adapted for removal of oils and solids from the water to be treated; or at least one set of nanofiltration membranes (20a, 20b, 20c) adapted for removal of sulfate ions from the water to be treated; and at least one treated water outlet, wherein the volume of water to be treated is directed to a treatment module (20) comprising micro/ultrafiltration membranes or to a water treatment module comprising nanofiltration membranes depending on the quality of the water content in relation to oils and solids content or sulfate ion content.

2. System according to claim 1, characterized in that each of the treatment modules (20) comprises at least two sets of membranes (20a, 20b) in parallel.

3. System according to claim 1 or 2, characterized in that each of the treatment modules (20) comprises at least one set of membranes (20c) in series with the other sets of membranes (20a, 20b).

4. System according to any one of claims 1 to 3, characterized in that the at least one water inlet to be treated and two water inlets, namely one of produced water (2) and one inlet of sea water (4).

5. System according to claim 4, characterized in that it further comprises at least one manifold (18), provided with a plurality of valves, adapted to control the type of water that will enter each of the water treatment modules (20), namely, produced water or seawater.

6. System according to claim 5, characterized in that each of the inlet ducts (2, 4) is separately subdivided into a plurality of secondary ducts in parallel, a secondary duct for each treatment module (20).

7. System according to any one of claims 1 to 6, characterized in that each treatment module (20) comprises only one type of membrane, namely nanofiltration or micro/ultrafiltration.

8. System according to any one of claims 1 to 7, characterized in that the membranes of each treatment module (20) are interchangeable with another type of membrane.

9. System according to any one of claims 1 to 7, characterized in that it additionally comprises at least one water treatment tank (24) adapted to separate the aqueous phase from the oily phase by density difference.

10. System according to claim 9, characterized in that the water treatment tank (24) is in fluid communication with at least two treatment modules (20), downstream and upstream thereof, terminating a cycle.

11. System according to claim 9 or 10, characterized in that the water treatment tank (24) is furthermore in fluid communication with at least one outlet for disposal at sea and a water inlet duct produced for the separation of water and oil.

12. A hybrid process for the treatment of produced water and seawater for reinjection in an offshore oil reservoir, characterized in that it comprises the step of:
directing the water to be treated to at least one water treatment module (20) comprising at least one set of micro/ultrafiltration membranes adapted for removal of oils and solids from the water to be treated; or directing the water to be treated to at least one treatment module (20) comprising at least one set of nanofiltration membranes adapted for removal of sulfate ions from the water to be treated, wherein the volume of water to be treated is directed to at least one treatment module (20) comprising micro/ultrafiltration membranes or to at least one water treatment module comprising nanofiltration membranes depending on the type of water to be treated, namely produced water or seawater.

13. Process according to claim 12, characterized in that step of directing the water to be treated to a treatment module (20) further comprises treating the water through at least two sets of membranes (20a, 20b) in parallel

14 Process according to claim 12 or 13, characterized in that step of directing the water to be treated to a treatment module (20) further comprises treating the water through the at least one membrane set (20c) in series with the further sets of membranes (20a, 20b).

15 Process according to any one of claims 12 to 14, characterized in that water to be treated is produced water, concentrated in oils and solids, and seawater concentrated in sulfate ions.

16. Process according to claim 15, characterized in that it additionally comprises the step of controlling the type of water which will enter each of the treatment modules (20), namely produced water or seawater, through at least one manifold (18) provided with a plurality of valves.

17 Process according to any one of claims 12 to 16, characterized in that it further comprises the step of directing a concentrated water fraction in oils and solids from the at least one treatment module (20) comprising at least one set of micro membranes/ultrafiltration to at least one treatment tank (24).

18. Process according to claim 17, characterized in that it further comprising the step of separating, by density difference over a given period, the less dense oil phase of the denser aqueous phase within the treatment tank (24)

19. Process of claim 18, characterized in that it further comprising a step of withdrawing the separated aqueous phase through at least one water outlet provided in the lower portion of the treatment tank (24).

20. Process according to claim 19, characterized in that it further comprises a step of directing the aqueous phase withdrawn for disposal at sea or to at least one treatment module (20).

21. Process according to any one of claims 18 to 20, characterized in that it further comprises a step of directing the remaining oily concentrate into the treatment tank (24), after the aqueous phase withdrawal step, to the water and oil separation system (23).

22. Process according to any one of claims 14 to 24, characterized in that it further comprises at least one step of deaeration of the treated water through at least one deaerator unit (28).

23 Process according to any one of claims 12 to 22, characterized in that it further comprises at least one step of backwashing the membranes of at least one treatment module (20) by reversing the flow of water therein