AU2017298020A1

AU2017298020A1 - Hybrid system and method for treating produced water and sea water to be re-injected into a subsea oil reservoir

Info

Publication number: AU2017298020A1
Application number: AU2017298020A
Authority: AU
Inventors: Giovani CAVALCANTI NUNES; Joyce MONTEIRO SAMBADE; Crístiano PIACSEK BORGES; Silvio Edegar WESCHENFELDER
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: 2019-03-07
Anticipated expiration: 2037-07-19
Also published as: RU2747649C2; BR102016016758A2; RU2019104644A3; AU2017298020B2; CA3042570A1; CN109963814A; WO2018014096A1; RU2019104644A; CN115925051A

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 SEAWATER TO BE REINJECTED INTO A SUBSEA OIL RESERVOIR

FIELD OF INVENTION [0001] This invention is in regard to water treatment systems at offshore oil-production facilities. More specifically, this invention is in regard to produced water treatment and seawater treatment systems for secondary recovery in oil wells.

FOUNDATIONS OF THE INVENTION [0002] It is known that in offshore oil-production facilities, one of the techniques employed in secondary recovery of oil is the injection of treated seawater. Within this context, it is known that seawater contains significant quantities of sulfate ions (SOz²), around 2800 mg/L. When seawater is injected into fields whose formation water (connate water) contains a sufficient amount of barium (Ba⁺²), strontium (Sr⁺²) or calcium (Ca²⁺) ions in solution, the contact of these two normally causes precipitation of its sulfates: barium sulfate (BaSCU), strontium sulfate (SrSCU), or calcium sulfate (CaSCU). These salts are extremely insoluble and cause damage to the formation by blocking the pores with the precipitated salts. They may also be precipitated in the production lines and equipment at the processing plant.

[0003] Depending on the content of barium and strontium in the formation water, it may be necessary to install a sulfate removal unit (SRU) to treat the seawater to be used for injection into the reservoir, as shown in Figure 1. In the SRU, nanofiltration membranes (which may be made of ceramic or polymers) are used to remove the sulfate ions from the seawater. Since seawater has solid particles, as well as components of marine flora and fauna, it is necessary to install filters upstream of the SRU unit to improve its performance. Initial filtration uses coarse filters, and subsequently cartridge filters whose passage diameter is smaller in size.

[0004] In the SRU, the water permeates through the nanofiltration units, while a fraction

- typically 25% - remains concentrated in sulfate ions; it is separated out, and then subsequently discarded into the ocean. To attain project specifications of sulfate ions in treated water, two sets of membranes are used in parallel, followed by a third set in series, as shown in the drawing in Figure 2.

[0005] Once treated by the SRU, the water reaches the necessary specification and may be injected into the oil reservoir for secondary recovery.

[0006] It is also known that produced water that reaches the treatment unit is treated for removal of oil droplets. The conventional techniques for this type of treatment have - in a general and simplified manner-the configuration shown in Figure 1.

[0007] In particular, the produced water goes through a treatment process to separate the aqueous phase from the oily phase, comprised of gravitational separation, hydrocyclones and floaters, which are then specified to be discarded into the ocean, according to the environmental legislation in force. Water that is not specified to be discarded at some platforms may be sent to a tank called an Off Spec Tank,” where it will have longer to separate from the oily phase, and in some cases it may be reprocessed in the treatment plant.

[0008] This produced water treatment equipment, however, has reduced efficiency in removal of solid particles and oil droplets that are smaller than 5.0 pm. These conditions limit the overall efficiency of treatment, and consequently they limit the ability to obtain an effluent flow that has characteristics that are suitable for reinjection into more restrictive reservoirs in terms of suspended solids content, oils and grease. Therefore, after treatment the produced water is specified for disposal into the ocean, and it is not specified for reinjection due to its content of suspended solids, oils and grease.

[0009] Therefore, the current destination of produced water at offshore oil-production facilities after treatment is only disposal. The low efficiency of produced water treatment plants conventionally used to obtain contents of solids and oil according to the requirements demanded for reinjection into the most restrictive reservoirs, contributes, among other factors, to the impracticality of reinjection. Therefore, in recent projects for secondary recovery, this alternative is still not being considered.

[0010] Note, however, that development of a treatment system that allows reinjection of produced water is a very interesting option for the oil production area, mainly due to the tendency of environmental legislation to become increasingly restrictive, in addition to heading in the direction of increased sustainability of industrial practices in that area of activity.

[0011] Thus separation technologies using micro/ultra-filtration membrane technologies (with ceramic membranes) have been shown to be an interesting option for this challenge, since when it is applied to treatment of produced water, the result is water with low oil and solids content. [0012] In the process of separation using micro/ultra-filtration membranes, as this stateof-the-art is known, the water permeates the membranes while a fraction of the volume provided accumulates the non-permeated oil and is recycled back into the system.

[0013] The document entitled “Ceramic Ultra- and Nanofiltration Membranes for Oilfield

Produced Water Treatment: A Mini Review,’’ written by Ashagi, K. Shams et al., is a study that reviews the use of ceramic micro/ultra-filtration membranes for treating produced water (removal of solids and oil particles). Various techniques using ceramic micro/ultra-filtration membranes are presented in this scientific article, thus its description is incorporated into this document as reference.

[0014] The document entitled “Avaliagao de membranas para o tratamento de agua proveniente do processo de extragao de petroleo” [Evaluation of membranes to treat process water from oil drilling] written by Weschenfelder, Silvio E., et al., one of the inventors of this invention, is a study that evaluates the performance of membranes in treating produced water by means of long-duration tests with real effluent, taking into consideration the evolution of the flow of permeate and the characteristics of the effluent generated. The results indicate that through the use of membranes with holes that are 0.1 mm in size, it is possible to obtain a current of permeate with solids content lower than 1 mg L'¹ and oil and grease content in the range of 1 to 3 mg L’¹. That document also shows that with the chemical regeneration process it is possible to reestablish 95% of the ceramic micro/ultra-filtration membrane’s original permeability. The description of that document is also included in this description as reference.

[0015] In a current approach, if the decision were made to use a micro/ultra-filtration membrane separation process to complement conventional treatment of produced water to make reinjection viable, for example, an additional system would be necessary in the treatment plant, as described in the state-of-the-art documents listed above. This brings significantly higher implementation, operation and maintenance costs and greater operating difficulty, in addition to greater weight and more area occupied on the platform.

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

[0017] As will be better detailed below, this invention seeks to solve the problems in the state-of-the-art described above, in a practical, efficient and low-cost way.

SUMMARY OF THE INVENTION [0018] The main objective of this invention is to provide a system and a hybrid seawater and produced water treatment process that allows produced water to be reinjected without the need for an additional treatment system on the platform.

[0019] In order to attain the objective described above, this invention provides a hybrid produced water and seawater treatment system for reinjection into a subsea oil reservoir, comprising (i) at least one inlet for water to be treated, (ii) at least two water treatment modules, each module comprising (ii-a) at least one set of micro/ultra-filtration membranes adapted to remove oils and solids from the water to be treated, or (ii-b) at least one set of nanofiltration membranes adapted to remove sulfate ions from water to be treated, and (iii) at least one outlet for treated water in which the volume of water to be treated is sent to a water treatment module that contains micro/ultra-filtration membranes, or to a water treatment module that contains nanofiltration membranes, depending on the quality of the water in relation to the content of oils and solids, or the content of sulfate ions.

[0020] This invention also provides a hybrid process for treating produced water and seawater for reinjection into a subsea oil reservoir, basically comprising the stages of (i) sending the water to be treated to a water treatment module that includes at least one set of micro/ultrafiltration membranes adapted to remove oils and solids from the water to be treated, or (ii) sending the water to be treated to a water treatment module comprising at least one set of nanofiltration membranes adapted to remove sulfate ions from water to be treated, in which the volume of water to be treated is sent to the water treatment module, which contains micro/ultra-filtration membranes, or to the water treatment module that contains nanofiltration membranes, depending on the water quality in regard to the content of oils and solids, or the content of sulfate ions.

BRIEF DESCRIPTION OF THE FIGURES [0021] The detailed description presented below references the attached figures and their respective reference numbers.

[0022] Figure 1 contains a schematic diagram of a seawater and produced water treatment system for injection and disposal, respectively, as it is known in the state-of-the-art.

[0023] Figure 2 contains a schematic diagram of an example of seawater treatment for injection into an oil reservoir, through a sulfate removal unit (SRU), as it is known in the state-ofthe-art.

[0024] Figure 3 contains a schematic diagram of a treatment module comprised of nanofiltration or micro/ultra-filtration membranes, according to the final determination of how to build this invention.

[0025] Figure 4 contains a schematic diagram of a of a [sic] hybrid system for treating seawater and produced water for reinjection according to the final determination of how to build this invention.

[0026] Figure 5 contains a schematic diagram of a complete seawater and produced water treatment system for reinjection, comprising the hybrid system of this invention.

DETAILED DESCRIPTION OF THE INVENTION [0027] First, note that the description that follows will depart from a specific determination of how the invention is to be constructed. As will be evident for any technician in the matter, however, the invention is not limited to that particular configuration.

[0028] Figure 4 contains a simplified schematic diagram of a hybrid seawater treatment and produced water treatment system for subsequent injection, according to the determination of how this invention is to be constructed. This figure basically shows two entries for water to be treated, to wit, one for produced water 2, with high contents of oils and solids, and one for seawater

4, with high content of sulfate ions.

[0029] The produced water is preferably stored in at least one tank 10 before being sent for disposal or treatment using the invention’s hybrid system.

[0030] Preferably, the seawater captured for treatment and subsequent injection passes through a sequence of filters; the first has filtering elements with the largest mesh, and the last has filtering elements with the finest mesh. Preferably, the first filter 12 will catch particles of up to 500 pm, the second 14 catches particles of up to 25 pm, and the third up to 5 pm.

[0031] Preferably, both the produced water as well as the seawater that is captured arrive respectively in at least one manifold 18 that contains numerous valves to control the water that will enter into each of the treatment modules 20.

[0032] Each treatment module 20 contains at least one set of micro/ultra-filtration membranes (ceramic membranes) adapted to remove oils and solids from the produced water, or at least one set of nanofiltration membranes (ceramic or polymer membranes) adapted to remove sulfate ions from seawater. Thus at least one manifold 18, through its control valves, sends the produced water to the modules, which include micro/ultra-filtration membranes and the captured seawater goes to the nanofiltration membranes. Preferably at least one manifold is subdivided into two manifolds, one to control the entry of produced water into the modules that contain micro/ultrafiltration membranes, and another to control the entry of seawater into the modules that contain nanofiltration membranes.

[0033] Preferably at least one manifold 18 is connected fluidly to the two ducts where the seawater to be treated enters, to wit, one for produced water 2 and another for seawater 4. Each of these inlet ducts, separately, is subdivided into several secondary parallel ducts, one secondary duct for each treatment module. The secondary ducts for produced water and for seawater, before the entry into each treatment module 20, drain into a single inlet duct per module, downstream from each control valve.

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

[0035] Preferably there is no mixture between produced water and seawater before entering into 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 contains only one type of membrane, which is the nanofiltration or micro/ultra-filtration membrane. Thus, preferably, if a certain treatment module 20 contains only nanofiltration membranes, only seawater will be sent to it, and the produced water inlet control valve will remain closed. Likewise, the produced water will be sent to a treatment module 20, which comprises only micro/ultra-filtration membranes.

[0037] Each treatment module 20 is designed in such a way as to allow interchangeability between nanofiltration and micro/ultra-filtration membranes. In other words, each module may have its nanofiltration membranes replaced by micro/ultra-filtration membranes (and vice-versa), depending on the demand for treating each type of water.

[0038] By way of example, it is expected that right after implementation of this invention’s hybrid system there will only be demand for treating seawater using nanofiltration membranes, since there will not yet be produced water. Thus nearly all of the treatment modules 20 might be equipped only with nanofiltration units. As produced water is created, the demand to treat seawater will decrease. In this case, the nanofiltration membranes in the treatment modules 20 will be replaced by micro/ultra-filtration membranes.

[0039] The schematic diagram in Figure 3 shows details of a treatment module 20 in accordance with this invention. As mentioned, the treatment module 20 may contain nanofiltration membranes or micro/ultra-filtration membranes, depending on the type of water (produced or seawater), which will pass through that specific module. Each module contains at least one set 20 of micro/ultra-filtration or nanofiltration membranes. Preferably, as with the SRU in the state-ofthe-art, each module contains two sets of membranes in parallel 20a, 20b, followed by a third set of membranes in series 20c.

[0040] Preferably, for the case of a treatment module 20 that contains nanofiltration membranes for 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 will contain low concentrations of sulfate ions, which is then sent to be injected into the reservoir.

[0041] The remaining water that passes through the first sets of membranes, concentrated in sulfate ions, is sent to the third set of membranes 20c, in series with the first two. This third set treats this most concentrated water, and it also creates a larger portion with low concentration of sulfate ions, which will be mixed with the treated water by the first two sets of membranes, and a smaller portion that is extremely concentrated in sulfate ions, which is usually discarded into the sea.

[0042] Water with low concentrations of sulfate ions that comes from treatment from the sets of nanofiltration membranes is used for injection into the reservoir, and may first pass through additional treatment stages.

[0043] For a treatment module 20 that has micro/ultra-filtration membranes to remove oils and solids from produced water, the procedure is very similar to the previous one. Preferably, the water to be treated will pass through the first two sets of membranes 20a, 20b in parallel so that the larger fraction of the volume of treated water will contain a low concentration of oils and solids. It is then sent to be reinjected into the reservoir.

[0044] The rest of the water that passes through the first sets of membranes, concentrated in oils and solids, is sent to the third set of membranes 20c in series with the first two. This third set treats this most highly concentrated water, and it also creates a larger portion with low concentration of oils and solids, which will be mixed with water that has been treated by the first two sets of membranes. The water with low concentrations of oils and solids comes from treating all three sets of micro/ultra-filtration membranes, and it 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 sets of membranes in series and/or in parallel. Thus note that this invention is not limited to the configuration of sets of membranes illustrated in Figure 3.

[0046] Also in the case of a treatment module 20 that contains micro/ultra-filtration membranes, the smaller portion that comes from the third set of membranes 20c, concentrated in oils and solids, may be sent 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 facility), the water that is highly concentrated in oils and solids (oily recycling) may be sent to the water treatment system for separation from the oily phase. Preferably the water that is highly concentrated in oils and solids may be sent to a treatment tank, shown schematically in Figure 5 (treatment tank 24). This tank may be, for example, an off spec tank that is normally used in produced water treatment stations. Alternatively, an additional tank may be provided for this stage, 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 to remove water with low oil concentration, since the oil, which is less dense than the water, after a certain period of time will be concentrated in the upper portion. The water removed through the water outlet in the lower portion of the treatment tank 24, which has relatively low or medium concentration of oils, may be discarded, if there is a specification to do so, or it may be sent to the hybrid treatment system in accordance with this invention, where it will be sent to treatment modules 20 that comprise micro/ultra-filtration membranes to pass through a new treatment to remove oils and solids. The oily concentrate remaining in the treatment tank 24, after removal of part of the water, is preferably sent to the separation system 23 for oil and water, so that the oil can be used in production. This contributes to minimizing the disposal of oil into the sea, and makes better use of the oil that is present in the produced water in total production of the well.

[0049] This invention also foresees the possibility of using a back-flush procedure for the membranes used in the treatment modules, especially the micro/ultra-filtration membranes. That procedure may be done, for example, using pumps (not shown) or by manipulating timed valves on the treated water line and on the feed line of each set. This procedure allows 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 the treatment modules 20 for deaeration of seawater, if necessary, before reinjection into the reservoir.

[0051 ] This invention also provides a hybrid process for treatment of produced water and seawater for reinjection into the subsea reservoir, comprising basically the following stages:

a) Sending the water to be treated to a water treatment module comprising at least one set of micro/ultra-filtration membranes adapted to remove oils and solids from water to be treated; or

b) Sending the water to be treated to a water treatment module comprising at least one set of nanofiltration membranes that have been adapted to remove sulfate ions from the water to be treated, in which the volume of water to be treated is sent to the water treatment module comprised of micro/ultra-filtration membranes, or to the water treatment module comprised of nanofiltration membranes, depending on the quality of the water in regard to the content of oils and solids, or the content of sulfate ions.

[0051] Also note that all stages of treatment described in this detailed description apply both to the system as well as to the process of this invention.

[0052] Therefore, based on the description above, this invention provides a system and process for treating seawater and produced water, which allows the produced water to be reinjected without the need for an additional treatment system on the platform. This invention also provides other advantages, such as reducing the amount of oil discarded into the sea, due to the fact that the produced water is treated more efficiently, and the costs of installation, operation and maintenance associated with an additional system on the offshore facility are reduced.

[0053] Countless variations in the scope of protection of this application are allowed.

This reinforces the fact that this invention is not limited to the configurations/particular manifestations described above.

Claims

Claims

1. Hybrid system to treat produced water and seawater for reinjection into a subsea oil reservoir, characterized by comprising:

At least one inlet for water to be treated;

At least two treatment modules (20), each module comprising:

At least one set of micro/ultra-filtration membranes (20a, 20b, 20c) adapted to remove oils and solids from the water to be treated; or

At least one set of nanofiltration membranes (20a, 20b, 20c) adapted to remove sulfate ions from the water to be treated; and

At least one outlet for treated water in which the volume of water to be treated is sent to a treatment module (20) comprising micro/ultra-filtration membranes, or to a water treatment module comprising nanofiltration membranes, depending on the quality of the water in regard to the content of oils and solids, or the content of sulfate ions.
2. A system, in accordance with claim 1, characterized by each of the treatment modules (20) comprising at least two sets of membranes (20a, 20b) in parallel.
3. A system, in accordance with claim 1 or 2, characterized by each treatment module (20) comprising at least one set of membranes (20c) in series with the other sets of membranes (20a, 20b).
4. A system, in accordance with any of claims 1 to 3, characterized by at least one inlet for water to be treated to be two entries for water, to wit, one for produced water (2) and one inlet for seawater (4).
5. A system, in accordance with claim 4, characterized by additionally comprising at least one manifold (18) that contains several valves, adapted to control the type of water that will enter into each water treatment module (20), to wit, produced water or seawater.
6. A system, in accordance with claim 5, characterized by each inlet duct (2, 4) separately being subdivided into numerous secondary ducts in parallel, one secondary duct for each treatment module (20).
7. A system, in accordance with any of claims 1 to 6, characterized by each treatment module (20) comprising just one type of membrane, namely nanofiltration and/or micro/ultrafiltration.
8. A system, in accordance with any of claims 1 to 7, characterized by the membranes of each treatment module (20) being interchangeable for another type of membrane.
9. A system, in accordance with any of claims 1 to 7, characterized by additionally comprising at least one water treatment tank (24) adapted for separation of the aqueous phase from the oily phase due to a difference in density.
10. A system, in accordance with claim 9, characterized by the water treatment tank (24) being in fluid communication with at least two treatment modules (20), downstream and upstream of those modules, closing a cycle.
11. A system, in accordance with claim 9 or 10, characterized by the water treatment tank (24) also being in fluid communication with at least one outlet tank for disposal into the sea, and the inlet duct for produced water for separation of water and oil.
12. A hybrid process to treat produced water and seawater for reinjection into a subsea oil reservoir, characterized by comprising the stage of:

Sending the water to be treated to at least one water treatment module (20) comprising at least one set of micro/ultra-filtration membranes adapted to remove oils and solids from the water to be treated; or

Sending the water to be treated to at least one treatment module (20) comprising at least one set of nanofiltration membranes adapted to remove sulfate ions from the water to be treated,

In which the volume of water to be treated is sent to at least one treatment module (20) comprising micro/ultra-filtration 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. A process, in accordance with claim 12, characterized by the stage of sending the water to be treated to a treatment module (20) that also includes treating water through at least two sets of membranes (20a, 20b) in parallel.
14. A process, in accordance with claim 12 or 13, characterized by the stage of sending water to be treated to a treatment module (20), which also includes treating water through at least one set of membranes (20c) in series with the other sets of membranes (20a, 20b).
15. A process, in accordance with any of claims 12 to 14, characterized by the water to be treated being produced water, concentrated in oils and solids, and seawater concentrated in sulfate ions.
16. A process, in accordance with claim 15, characterized by also comprising the stage of controlling the type of water that will enter into each treatment module (20), namely produced water or seawater, through at least one manifold (18) that has several valves.
17. A process, in accordance with any of claims 12 to 16, characterized by also comprising the stage of sending a fraction of water concentrated in oils and solids from at least one treatment module (20) comprising at least one set of micro/ultra-filtration membranes to at least one treatment tank (24).
18. A process, in accordance with claim 17, characterized by also comprising the stage of separating the less-dense oily phase from the denser aqueous phase on the inside of the treatment tank (24), using the difference in density for a certain period.
19. A process, in accordance with claim 18, characterized by also comprising a stage to remove the separated aqueous phase by at least one water outlet, located on the lower portion of the treatment tank (24).
20. A process, in accordance with claim 19, characterized by also comprising a stage to send the removed aqueous phase for disposal into the sea, or to at least one treatment module (20).
21. A process, in accordance with any one of claims 18 to 20, characterized by also comprising a stage to send the remaining oily concentrate in the treatment tank (24), after the stage of removal of the aqueous phase, to the water and oil separation system (23).
22. A process, in accordance with any one of claims 14 to 24, characterized by also comprising at least one stage of deaeration of treated water through at least one deaeration unit (28).
23. A process, in accordance with any one of claims 12 to 22, characterized by also comprising at least one back-washing stage of the membranes in at least one treatment module (20) through inversion of the flow of water through it.