WO2024232759A1

WO2024232759A1 - Separation of oil/water without chemical aids

Info

Publication number: WO2024232759A1
Application number: PCT/NO2024/050110
Authority: WO
Inventors: Svein Viggo Aanesen
Original assignee: Equinor Energy AS
Current assignee: Equinor Energy AS
Priority date: 2023-05-10
Filing date: 2024-05-08
Publication date: 2024-11-14
Anticipated expiration: 2025-11-10
Also published as: GB202306922D0; GB2630027A

Abstract

The invention provides a method for separating particles from a mixture comprising water and particles, comprising: (i) adding a charged gas to said mixture comprising water and particles; (ii) moving said charged gas through said mixture so that said charged gas contacts said particles and associates therewith; and (iii) separating from said mixture said gas and particles.

Description

Separation of oil/water without chemical aids

INTRODUCTION

The present invention relates to a method for separating particles from a mixture comprising water and particles. The present invention also relates to a method for recovering hydrocarbon from a hydrocarbon-containing formation, comprising the method of the present invention for separating particles from a mixture comprising water and particles. The present invention also relates to a system for separating particles from a mixture comprising water and particles. The present invention also relates to the use of the methods and systems of the present invention.

BACKGROUND

A common problem in chemical engineering, especially in the oil and gas industry, is to separate particles from a mixture. For example, a mixture may comprise a continuous water phase and a discontinuous phase of solid or liquid particles dispersed in the water. There frequently exists a need to separate the dispersed particles from the mixture. The two products of such a separation can be considered treated water and separated particles.

In the oil and gas industry, during recovery of hydrocarbons, the mixture which is recovered is often a dispersion comprising hydrocarbon dispersed in water. Particles comprising hydrocarbon, typically in the form of oil droplets, form a discontinuous phase and water forms a continuous phase. In such a circumstance, there is a need to separate hydrocarbon from water in a bulk separation. This yields produced water and hydrocarbon.

The produced water yielded from a bulk separation will still comprise particles of hydrocarbon dispersed in the continuous water phase. In such a case, there will be a need to perform a further separation to separate hydrocarbon particles from the produced water mixture. This is desirable to yield treated water which is of sufficient purity to be reinjected into a formation or to be discharged. A mixture recovered from a hydrocarbon-containing formation, or the mixture yielded in further downstream processes, may also comprise solid particles. In such a circumstance, there may be a need to separate solid particles from a mixture comprising solid particles dispersed in a continuous water phase. For example, there may be a need to separate clays, scale, or other insoluble impurities from water. In the absence of such a separation, the particles may clog or damage pipelines or equipment, reducing the efficiency of hydrocarbon recovery and potentially causes problems during downstream processing.

Gas flotation is a technique commonly used to assist in the separation of particles from a mixture comprising water and particles. Gas is added to, dispersed and moved through the mixture so that gas contacts the particles and associates therewith. The lift from the gas bubbles eventually overcomes the force of gravity and causes the particles to be transported to the surface of the mixture. This better enables the gas and particles to be separated from the mixture.

To improve the efficiency of gas flotation, chemical flocculants are often added to the mixture. A key function of the added flocculants is to improve the coalescence efficiency between the particles and the introduced gas bubbles. In the absence of flocculants, the association between the particles and the gas may be weak. For multiple reasons, the use of such chemical flocculants is often undesirable. Low degradability in the natural environment is one key reason. Several efforts have been made to replace these chemicals with natural components, but the efficiency of these alternatives has not been very successful.

The use of chemical flocculants adds complexity to the separation process and to the logistics in handling this physically rather unstable chemical solution. There is also a risk of overdosing the mixture with chemical flocculants, whereby the efficiency of coalescence and separation is reduced, or the ability of air bubbles to carry the particles to the surface is impaired.

There is therefore a need to develop alternative methods to assist in the separation of particles from a mixture comprising particles and water, for example the separation of hydrocarbon from dispersions comprising hydrocarbon or oil droplets dispersed in a continuous water phase, as encountered in the oil and gas industry. Ideally, the method should be easy to implement and should reduce, minimise, or obviate, the need for chemical flocculants.

US 2013/0118988 A1 relates to a dissolved air floatation unit with an enhanced oil recovery section. The unit makes use of ionised air and a separation apparatus based on lamella plates.

KR 1020210135051 A relates to an apparatus for removing microplastics in water. WO 2011/019373 A1, WO 2005/113446 A2 and US 2004/0099607 A1 relate to wastewater treatment. US 3642618 A relates to the clarification of liquids, in particular sugar solutions.

SUMMARY OF THE INVENTION

Viewed from a first aspect, the present invention provides a method for separating particles from a mixture comprising water and particles, comprising:

(i) adding a charged gas to said mixture comprising water and particles;

(ii) moving said charged gas through said mixture so that said charged gas contacts said particles and associates therewith; and

(iii) separating from said mixture said gas and particles.

In a preferred aspect, the present invention provides a method for separating particles from a mixture comprising water and particles, comprising:

(i) adding a charged gas to said mixture comprising water and particles;

(iii) separating from said mixture said gas and particles, wherein said particles comprise hydrocarbon, preferably oil droplets; and said charged gas is charged N2 gas and/or charged hydrocarbon gas.

In another preferred aspect the present invention provides a method for separating particles from a mixture comprising water and particles, comprising:

(i) adding a charged gas to said mixture comprising water and particles; (ii) moving said charged gas through said mixture so that said charged gas contacts said particles and associates therewith; and

(iii) separating from said mixture said gas and particles, wherein said particles comprise hydrocarbon, preferably oil droplets; and said charged gas is charged IX^ gas and/or charged hydrocarbon gas.

(i) adding a charged gas to said mixture comprising water and particles;

(iii) separating from said mixture said gas and particles, wherein the charged gas is derived from a gas, preferably a hydrocarbon gas, which is a product of hydrocarbon recovery from a hydrocarbon-containing formation.

(i) adding a charged gas to said mixture comprising water and particles;

(iii) separating from said mixture said gas and particles, wherein the charged gas is derived from a gas, preferably a hydrocarbon gas, which is a product of hydrocarbon recovery from a hydrocarbon-containing formation; and said particles comprise hydrocarbon, preferably oil droplets.

In another preferred aspect the present invention provides amethod for separating particles from a mixture comprising water and particles, comprising:

(i) adding a charged gas to said mixture comprising water and particles;

(iii) separating from said mixture said gas and particles in a compact floatation unit, a cyclone separator (e.g. a hydrocyclone) or a vortex separator, preferably wherein said method is conducted offshore and/or subsea. In another preferred aspect the present invention provides a method for separating particles from a mixture comprising water and particles, comprising:

(i) adding a charged gas to said mixture comprising water and particles;

(iii) separating from said mixture said gas and particles in a compact floatation unit, a cyclone separator (e.g. a hydrocyclone) or a vortex separator, wherein the charged gas is derived from a gas, preferably a hydrocarbon gas, which is a product of hydrocarbon recovery from a hydrocarbon-containing formation, preferably wherein said method is conducted offshore and/or subsea.

(i) adding a charged gas to said mixture comprising water and particles;

(iii) separating from said mixture said gas and particles in a compact floatation unit, a cyclone separator (e.g. a hydrocyclone) or a vortex separator; wherein the charged gas is derived from a gas, preferably a hydrocarbon gas, which is a product of hydrocarbon recovery from a hydrocarbon-containing formation; said particles comprise hydrocarbon, preferably oil droplets; and preferably wherein said method is conducted offshore and/or subsea.

In another preferred aspect the present invention provides an offshore and/or subsea method for separating particles from a mixture comprising water and particles, comprising:

(i) adding a charged gas to said mixture comprising water and particles;

(iii) separating from said mixture said gas and particles, preferably wherein: said particles comprise hydrocarbon, preferably oil droplets; and/or said charged gas is charged N2 gas and/or charged hydrocarbon gas.

(i) adding a charged gas to said mixture comprising water and particles;

(iii) separating from said mixture said gas and particles in a compact floatation unit, a cyclone separator (e.g. a hydrocyclone), and/or a vortex separator; wherein: the charged gas is derived from a gas, preferably a hydrocarbon gas, which is a product of hydrocarbon recovery from a hydrocarbon-containing formation; and said particles comprise hydrocarbon, preferably oil droplets.

In another preferred aspect the present invention provides a method for separating hydrocarbon from a mixture comprising water and hydrocarbon, preferably water and oil droplets, comprising:

(i) adding a charged gas to said mixture comprising water and hydrocarbon;

(ii) moving said charged gas through said mixture so that said charged gas contacts said hydrocarbon and associates therewith; and

(iii) separating from said mixture said gas and hydrocarbon, wherein said charged gas is charged IX^ gas and/or charged hydrocarbon gas.

(i) adding a charged gas to said mixture comprising water and particles;

(iii) separating from said mixture said gas and particles wherein said charged gas is in the form of bubbles; and said particles comprise hydrocarbon, preferably oil droplets. In another preferred aspect the present invention provides a method for separating particles from a mixture comprising water and particles, comprising:

(i) adding a charged gas to said mixture comprising water and particles;

(iii) separating from said mixture said gas and particles, wherein the charged gas is derived from a gas which is a product of hydrocarbon recovery from a hydrocarbon-containing formation; and said particles comprise hydrocarbon, preferably oil droplets, recovered from said hydrocarbon-containing formation.

In another preferred aspect the present invention provides a method for separating particles from a mixture comprising water and hydrocarbon, preferably water and oil droplets, comprising:

(i) adding a charged gas to said mixture comprising water and hydrocarbon;

(iii) separating from said mixture said gas and particles, wherein the charged gas is derived from a gas which is a product of hydrocarbon recovery from a hydrocarbon-containing formation; and said hydrocarbon is also recovered from said hydrocarbon-containing formation.

Viewed from another aspect, the present invention provides a method for recovering hydrocarbon from a hydrocarbon-containing formation, comprising:

(i) recovering from said formation a mixture comprising hydrocarbons and water;

(ii) separating the mixture into recovered hydrocarbons and produced water, optionally according to the method of the present invention hereinbefore described for separating particles from a mixture comprising water and particles; and

(iii) optionally, treating said produced water, optionally according to the method of the present invention hereinbefore described for separating particles from a mixture comprising water and particles, wherein at least one of step (ii) and step (iii) is performed according to according to the method of the present invention hereinbefore described for separating particles from a mixture comprising water and particles.

Viewed from another aspect, the present invention provides a system for separating particles from a mixture comprising water and particles, comprising:

(i) a separator, preferably a gravity separator, for separating a mixture comprising water and particles, wherein said separator has an inlet for said mixture;

(ii) a means for adding charged gas into said mixture comprising water and particles; and

(iii) a means for removing gas and particles from the mixture in the separator wherein said means for adding charged gas into said mixture adds said charged gas to said mixture either prior to entry to said separator and/or in said separator.

Viewed from another aspect, the present invention provides uses of the methods and systems of the present invention.

DEFINITIONS

As used herein the term “particles” refers to solids, liquids or gases present in water as a discontinuous phase. The particles may be organic or inorganic. It encompasses hydrocarbons, solids such as inorganic salts, as well as hybrids of organic and inorganic materials.

As used herein, the term “charged gas” refers to a gaseous composition comprising charged gas particles. For example, the term “charged methane gas” refers to a gaseous composition comprising methane ions.

As used herein, the term “methane ion” refers to the ion resulting from the addition or removal, preferably removal, of an electron to/from a methane molecule. Analogous terms are to be interpreted accordingly. As used herein, the term “methane cation” refers to the ion resulting from the removal of an electron from a methane molecule. The methane cation can be depicted according to the following formula: Analogous terms are to be interpreted accordingly.

|CH₄|

As used herein, the term “surface of a mixture” refers to a surface between a mixture and the atmosphere. The atmosphere may be the internal atmosphere of an enclosed container or unit.

As used herein, the term “separated particles” refers to particles separated from a mixture, said mixture comprising water and particles.

As used herein the term “produced water” refers to water extracted, along with hydrocarbons, from a hydrocarbon-containing formation and thereafter separated from hydrocarbons in a bulk separator. Produced water comprises water and relatively low amounts of hydrocarbon, typically less than 10 %wt hydrocarbons.

As used herein, the term “dispersion” refers to a system where particles of solid, liquid and/or gas are dispersed in a continuous phase of another solid, liquid or gas. As used herein, the term encompasses emulsions and suspensions. For example, the term “suspension” may refer to a system where solid particles are dispersed in a continuous liquid phase, and the term “emulsion” may refer to a system where liquid particles are dispersed in a continuous phase of another liquid. However, it will be understood that both solid particles and liquid particles may be dispersed in a single continuous phase, meaning that the terms emulsion and suspension are not mutually exclusive. As such, in the dispersions of the present invention, more than one type of particle may be dispersed in a single continuous phase.

As used herein, the term “bulk separation” refers to the separation of hydrocarbon from a mixture of water and hydrocarbon recovered from a hydrocarbon-containing formation.

As used herein, the term “flocculant” refers to a chemical added to a mixture comprising water and particles to improve the efficiency of gravity-based separation techniques, such as gas flotation. A key role of flocculants is to improve the association between particles and gas. The term does not include gas used in such techniques. As used herein, the term “hydrocarbon” refers to compounds comprising hydrogen and carbon, including those targeted for recovery in the oil and gas industry. Hydrocarbon particles may be present in the form of oil droplets, especially when dispersed in a continuous water phase.

As used herein, the term “hydrocarbon gas” refers to a gaseous composition which comprises, preferably consists essentially, more preferably consists, of either a mixture of different gaseous hydrocarbons or a single gaseous hydrocarbon. Preferably a hydrocarbon gas which consists essentially of gaseous hydrocarbons contains <5 vol%, more preferably <2 vol%, still more preferably <1.0 vol% and yet more preferably <0.1 vol% non-hydrocarbon gases. A hydrocarbon gas which consists of gaseous hydrocarbons contains <0.05 vol% and more preferably no detectable non-hydrocarbon gases.

As used herein, gases are generally understood to be present in a purity of greater than 80%, preferably greater than 90%, more preferably greater than 95%, still more preferably greater than about 99%, yet more preferably about 100%. For example, air is not considered to be nitrogen gas because it contains <80% nitrogen.

DETAILED DESCRIPTION

The following description is applicable to any of the foregoing clauses.

The present invention provides a method for separating particles from a mixture comprising water and particles, comprising:

(i) adding a charged gas to said mixture comprising water and particles;

(iii) separating from said mixture said gas and particles.

The method comprises a step of moving the charged gas through the mixture. The charged gas may move through the mixture passively, or may be actively moved through the mixture. In practice, the movement of the charged gas through the mixture may have both active and passive contributions.

Preferably, the charged gas moves through the mixture passively, for example by diffusion. Preferably, the charged gas is less dense than water, and preferably therefore the charged gas moves passively through the mixture, preferably to the surface of the mixture. Preferably, the charged gas moves through the mixture, preferably to the surface of the mixture, due to buoyancy.

Preferably, the charged gas is moved, preferably actively moved, through the mixture. For example, preferably the charged gas is added to the mixture as a pressurised stream of gas, which preferably contributes to the movement of the charged gas through the mixture.

In particularly preferred methods of the invention, the charged gas is moved through the mixture so that it disperses throughout the entirety of water as quickly as possible. Rapid dispersion is advantageous because it ensures that charged gas contacts the maximum amount of particles. Preferably, moving the charged gas through the mixture is achieved by a controlled pressure drop. This provides the drive for the charged gas to effectively disperse in the water.

The charged gas may preferably move through the mixture in the form of bubbles. Preferably, the charged gas is added to the mixture as bubbles, more preferably as a stream of bubbles, and still more preferably as a pressurised stream of bubbles.

In the method, the charged gas contacts the particles and associates therewith. Preferably, the charged gas is attracted to the particles, or vice versa. Preferably, there is an attraction between the charged gas and the particles, more preferably an electrostatic attraction, and still more preferably an ionic attraction. Preferably, the association between the particles and charged gas is an electrostatic association. Preferably, the charged gas forms electrostatic bonds, more preferably ionic bonds, with the particles. Preferably, the particles coalesce in the mixture. Preferably, the association of the charged gas with the particles encourages, facilitates, or mediates a coalescence of the particles.

The charged gas preferably moves through the mixture to a surface of the mixture. Preferably, the charged gas transports the particles to the surface of the mixture. Preferably, the charged gas transports the particles to the surface of the mixture, where the particles coalesce.

The method also comprises a step of separating from the mixture the gas and particles.

Preferably, the charged gas and particles are separated from the mixture at a surface of the mixture. Preferably, the separation gives

(a) separated particles and gas; and

(b) treated water, wherein the treated water compromises fewer particles than the original mixture comprising water and particles.

Advantageously, moving charged gas through the mixture comprising particles and water so that the charged gas contacts the particles and associates therewith in step (ii) of the method of the present invention is thought to improve the separation of particles from the mixture in step (iii). This is explained below.

As the charged gas moves through the mixture, it contacts particles and associates therewith. Particles may therefore move with the charged gas through the mixture. In other words, the charged gas may transport the particles through the mixture. Preferably, there is an attraction, e.g. electrostatic or ionic attraction, between the charged gas and the particles, which is preferably responsible for the association between the charged gas and particles, and which better enables the particles to move with the charged gas through the mixture.

Moving charged gas through a mixture comprising particles and water so that the charged gas contacts the particles and associates therewith is thought to improve the coalescence of the particles. This may be rationalised by considering the common movement of charged gas and the particles associated therewith through the mixture. By moving the particles through the mixture, contact between the particles may be increased, increasing the rate of coalescence.

Preferably, the charged gas moves through the mixture to a surface of the mixture. In such a case, the charged gas may transport the particles to a surface of the mixture, where the particles may coalesce.

By improving the coalescence of particles, for example, at the surface of the mixture, separation of particles from the mixture is made more facile.

In contrast with standard gas floatation techniques, the method of the present invention uses charged gas. The use of charged gas is thought to enhance the association between the charged gas and the particles, as compared with the association between particles and non-charged gas. For example, the use of charged gas may enhance or introduce an attraction, e.g. electrostatic or ionic attraction, between charged gas and particles, as compared with particles and non-charged gas. Without wishing to be bound by theory, it is thought that the presence of the charged gas interacts with dipoles in the particles, which arise due to the presence of heteroatoms such as O, N and S therein. For example, when the particles comprise hydrocarbon, the heteroatoms present in the hydrocarbon tend to be present at the oikwater interface, and effectively “present” themselves to the charged gas, and are attracted thereto.

Starting mixture

The method of the present invention involves separating particles from a mixture. The mixture comprises water and particles. Preferably, the mixture predominantly comprises water. In other words, preferably, the mixture comprises at least 50 % by weight of water, based on the total weight of the mixture. Preferably, the mixture comprises at least 50 % by volume of water, based on the total volume of the mixture. Preferably, water forms a continuous phase in the mixture and/or preferably the particles form a discontinuous phase in the mixture. In other words, preferably, the mixture is a dispersion comprising particles dispersed in a continuous water phase.

The method of the present invention can be applied to a diverse range of mixtures. For example, the mixture is preferably recovered from a hydrocarbon-containing formation, preferably a subterranean formation. In other words, preferably the mixture of water and particles is a mixture recovered from a hydrocarbon-containing formation, preferably a subterranean formation.

Preferably, the mixture comprises at least 55 % by weight, more preferably at least 70 % by weight, and still more preferably at least 80 % by weight, and yet more preferably at least 90 % by weight of water, based on the total weight of the mixture. Preferably, the mixture comprises less than 45 %, more preferably less than 30 %, and still more preferably less than 20 %, and yet more preferably less than 10 % by weight of particles, based on the total weight of the mixture. These values may be typical of mixtures recovered from a hydrocarbon-containing formation.

Preferably, the method of the present invention is a method for performing a bulk separation, and more preferably a method for performing a bulk separation on a mixture recovered from a hydrocarbon-containing formation.

Alternatively, the mixture is preferably produced water. In other words, preferably, the method is a method for treating produced water. Preferably, the mixture comprises less than 1 %, preferably less than 0.5 %, more preferably less than 0.1 %, and still more preferably less than 0.05 %, and yet more preferably less than 0.01 % by weight of said particles, based on the total weight of the mixture. Preferably, the mixture comprises at least 99 % by weight, more preferably at least 99.5 % by weight, still more preferably at least 99.9 % by weight, and yet more preferably at least 99.95 % by weight, e.g. at least 99.99 % by weight of said water, based on the total weight of the mixture. These values may be typical of produced water.

Particles

The method of the present invention involves separating particles from a mixture comprising water and particles. The method can be applied to a diverse range of particles, and the particles may be selected from any state of matter (solid, liquid, or gas). Preferably, the particles are liquid particles or solid particles. Preferably, the particles form a dispersion when mixed with water. In other words, preferably the particles are insoluble, or only partially soluble, in water. Preferably, the particles are less dense than water. Preferably, the particles are liquid particles. In other words, preferably the mixture comprises liquid particles dispersed in a continuous phase of water.

Preferably, the particles comprise hydrocarbon or consist of hydrocarbon, e.g. the particles may comprise oil droplets. More preferably the particles are oil droplets. In other words, preferably the method of the present invention is a method for separating hydrocarbon from a mixture comprising water and hydrocarbon. More preferably, the method of the present invention is a method for separating hydrocarbon from a mixture comprising water and oil droplets. Preferably, the particles comprise charged, more preferably negatively charged, hydrocarbon or oil droplets.

Alternatively, the particles are derived from a gas condensate.

Alternatively, preferably the particles are solid particles. For example, the particles are preferably particles of clay, alumina silicate, scale or a mixture thereof. Preferably, the particles comprise charged, more preferably negatively charged, solid particles. For example, the particles preferably comprise charged, more preferably negatively charged, particles of clay, alumina silicate, scale or a mixture thereof.

Preferably, the particles comprise hydrocarbon and solids. In other words, preferably the method of the present invention is a method for separating hydrocarbon and solids from a mixture comprising water, hydrocarbon, and solids.

Preferably, the particles comprise or consist of charged particles. Charge may be formal charge or may be partial charge. Charge may be uniform across an individual particle or molecule thereof, or charge may be localised in particular regions or may result from particular charged chemical groups. An individual particle or molecule therefore may be formally charged as a whole, or may be zwitterionic. A sample of particles need not be chemically uniform, meaning that one molecule making up the sample may be chemically different from another. Therefore, it is understood that some individual molecules in the sample may be charged, while others may not.

In other words, the particles preferably comprise charged chemical groups. The charges may be partial charges, such as permanent dipoles or charges resulting from polarised bonds, or may be formal charges, such as formally cationic or anionic groups. Preferably the particles comprise charged chemical groups arising from the presence of polar functional groups. Such polar functional groups typically comprise heteroatoms.

Preferably, the particles have partial charges such as dipoles, more preferably permanent dipoles, or charges resulting from polarised bonds.

Preferably, the particles are charged. Preferably, the particles are cationic or anionic, more preferably anionic.

Preferably, the particles have regions of net charge, more preferably regions of net negative charge. Preferably, the regions of net charge are located at a water-particle interface.

Step (i)

The method of the present invention comprises adding charged gas to a mixture comprising water and particles. Preferably, the charged gas is added to the mixture using an aerator, more preferably a diffusor. Preferably, the charged gas is added to the mixture under pressure. Preferably, the charged gas is added to the mixture as a stream, more preferably as a pressurised stream.

The charged gas is preferably added to the mixture as bubbles, more preferably as a stream of bubbles, and still more preferably as a pressurised stream of bubbles. Preferably, the charged gas is in the form of bubbles, more preferably bubbles with a diameter range of 1-500 .m, preferably 10-200 .m, and more preferably 30-100 .m. Since the diameter of the bubbles may change, e.g. due to coalescence, the values given here refer to the bubble size at the point of formation. In other words, the charged gas is preferably bubbles of charged gas.

Preferably, the charged gas is added to the mixture comprising water and particles prior to its introduction into the separator. Optionally, the charged gas may be added to a separator comprising the mixture. Optionally the charged gas may be added to the mixture comprising water and particles prior to its introduction into the separator and into the separator.

The charged gas may be negatively charged or positively charged, preferably positively charged. The charged gas may preferably be anionic or cationic, more preferably cationic. In other words, preferably the charged gas comprises gaseous cations.

Preferably, the charged gas is a non-corrosive gas. Advantageously, this reduces damage to pipelines and equipment which come into contact with the charged gas. Preferably, the charged gas does not comprise oxygen and/or sulfur. Preferably, the charged gas comprises, preferably essentially consists of, more preferable consists of, charged IX^ gas. Still more preferably the charged gas is charged IX^ gas.

Preferably, the charged gas comprises, preferably essentially consists of, more preferable consists of, a charged hydrocarbon gas. More preferably the charged gas is a charged hydrocarbon gas. Preferably, the charged gas comprises charged gaseous hydrocarbon particles. Preferably, the charged gas comprises gaseous hydrocarbon cations. Preferably, the charged gas is a charged Ci-e alkane gas.

Preferably, the charged gas is derived from a gas, preferably a hydrocarbon gas, which is a product of hydrocarbon recovery from a hydrocarbon-containing formation. For example, a gas which is a product of hydrocarbon recovery from a hydrocarbon- containing formation may be ionised to form the charged gas. Advantageously, when the charged gas is derived from a gas which is a product of hydrocarbon recovery, waste from the hydrocarbon recovery process can be minimised by putting the products to useful work. Also advantageously, when the method of the present invention is located at or near to a hydrocarbon recovery facility, the gas may be sourced locally, reducing the challenges, costs, and environmental footprint associated with sourcing charged gas for the method of the present invention.

It is preferred that the charged gas comprises, preferably essentially consists of, more preferable consists of, charged N2 gas and/or charged hydrocarbon gas. The charged hydrocarbon gas is preferably derived from a hydrocarbon gas which is a product of hydrocarbon recovery from a hydrocarbon-containing formation. In another preferred embodiment, the charged gas comprises, preferably essentially consists of, more preferable consists of charged gas which is derived from a gas, preferably a hydrocarbon gas, which is a product of hydrocarbon recovery from a hydrocarbon-containing formation.

In a particularly preferred embodiment: the charged gas comprises, preferably essentially consists of, more preferable consists of charged gas which is derived from a gas, preferably a hydrocarbon gas, which is a product of hydrocarbon recovery from a hydrocarbon-containing formation; and the particles comprise hydrocarbon preferably oil droplets.

In such an embodiment, it is preferred that the charged gas and the particles are derived from the same hydrocarbon recovery process, e.g. from the same hydrocarbon- containing formation. This is advantageous as the method can be self-sustaining at the same hydrocarbon-containing formation. This may be particularly advantageous in preferred offshore and/or subsea methods, where a compact process is particularly desirable and there may be a desire to reduce the need to source and transport materials from offsite.

It is preferred that the charged gas is not derived from air, i.e. it is not charged air or derived from the ionisation of air.

Gases, for example those mentioned above, may be present in a purity of greater than 80%, preferably greater than 90%, more preferably greater than 95%, still more preferably greater than about 99%, yet more preferably about 100%.

Preferably, the charged gas comprises less than 20% O2 (charged or otherwise), more preferably less than 10%, still more preferably less than 5%, yet more preferably less than 2%, still more preferably less than 1 %.

The charged gas preferably comprises, preferably essentially consists of, more preferable consists of, charged methane gas. More preferably the charged gas is charged methane gas. The charged methane gas is preferably derived from methane gas which is a product of hydrocarbon recovery from a hydrocarbon-containing formation, for example as described above. Preferably, the charged gas comprises charged gaseous methane particles. Preferably, the charged gas comprises charged gaseous methane cations. Preferably, the charged gas comprises cations of the following formula:

The method of the present invention preferably comprises a step of ionising gas to produce a charged gas. Preferably, ionising gas comprises removing an electron from said gas. Preferably, ionising gas comprises the application of a high voltage. Preferably, a step of ionising gas to produce a charged gas is performed prior, preferably substantially immediately prior, to the step of adding the charged gas to the mixture comprising water and particles. In other words, once ionised, the gas may be added straight to the mixture comprising water and particles, preferably via a transport line. Advantageously, this reduces the difficulties associated with sourcing and storing charged gas.

Absence of flocculants

Advantageously, the method of the present invention reduces the need for flocculants to be added to the mixture comprising water and particles. Ordinarily, a key role of flocculants is to improve the association between gas and particles in a gas flotation method. In the method of the present invention, the use of a charged gas, rather than a non-charged gas, is thought to improve the association between charged gas and particles, as compared with the association between particles and non-charged gas, thus reducing or eliminating the need for chemical flocculants.

Preferably, in the method of the present invention, flocculants are not added to the mixture comprising water and particles. Preferably, in the method of the present invention, the mixture comprising water and particles comprises flocculants at less than 100 mg/L, more preferably less than 50 mg/L, and still more preferably less than 20 mg/L, based on the total weight of the mixture. Preferably, the mixture does not comprise flocculants.

Example flocculants include hydroloysed polymeric acrylic amides (HPAM). Step (ii)

The method of the present invention comprises a step of moving charged gas through a mixture comprising particles and water, so that the charged gas contacts the particles and associates therewith. As previously discussed, this step is thought to advantageously improve the subsequent separation of particles from the mixture.

Preferably, the charged gas moves through the mixture as bubbles. Preferably, the bubbles coalesce or agglomerate with the particles therein. In other words, preferably the bubbles join together with the particles.

Preferably, the association between particles and charged gas is a coalescence of particles and charged gas. Preferably, the association between particles and charged gas comprises particles adhering to charged gas.

Preferably, there is an attraction between the particles and the charged gas, more preferably an electrostatic attraction, and still more preferably an ionic attraction. Preferably, the particles form electrostatic bonds or interactions with the charged gas, more preferably ionic bonds or interactions.

The particles and the charged gas are preferably oppositely charged. Preferably, the particles have regions of charge which are opposite in charge to the charged gas. Advantageously, opposite charges on the particles and charged gas enhances the electrostatic interactions between the two, further enhancing separation.

Preferably, the particles comprise charged groups which are opposite in charge to the charged gas. In other words, the particles preferably comprise charged chemical groups which are opposite in charge to the charged gas. Preferably, the particles comprise positively charged groups and the charged gas is negatively charged. More preferably, the particles comprise negatively charged groups and the charged gas is positively charged.

Preferably, the particles have dipoles, more preferably permanent dipoles. Preferably, the charged gas interacts, preferably is attracted to, regions of opposite charge on said permanent dipoles. Preferably, the particles are charged. Preferably, the particles are of opposite charge to the charged gas. Preferably, the particles are cationic and the charged gas is anionic. More preferably, the particles are anionic and the charged gas is cationic.

Preferably, the particles have regions of net charge. Preferably, these regions are of opposite charge to the charged gas. Preferably, the particles have regions of net positive charge and the charged gas is negatively charged. Preferably, the particles have regions of net negative charge and the charged gas is positively charged. Preferably, the regions of net charge are located at a water-particle interface.

Step (Hi)

The method of the present invention comprises a step of separating gas and particles from the mixture. Preferably, the separation of step (iii) is carried out in a separator, more preferably a gravity separator. Preferred examples of separators include a compact floatation unit, a cyclone separator (e.g. a hydrocyclone), and a vortex separator. Such separator means are particularly suited to offshore and/or subsea methods, where there is a need for highly efficient and compact equipment. The methods of the present invention further improve the efficiency of separation, providing a synergistic effect.

Alternatively, preferably, the separation of step (iii) is carried out in a degasser unit. Preferably, the separation of step (iii) is carried out in a gravity separator and a degasser in series.

The products of the separation of step (iii) are preferably: a) separated particles and gas; and b) treated water; or a) separated particles; b) gas; and c) treated water.

The treated water is preferably characterised in that it comprises fewer particles than the original mixture comprising water and particles. The weight % of particles in the treated water is preferably minimised. Preferably, the particles are solid particles and the treated water comprises less than 5 % by weight of said solid particles, more preferably less than 3 % by weight, and still more preferably less than 2 % by weight, based on the total weight of the treated water.

Preferably, the particles are hydrocarbon particles and the treated water comprises less than 1 % by weight of hydrocarbon particles, more preferably less than 0.5 % by weight, and still more preferably less than 0.2 % by weight, based on the total weight of the treated water. These values may be typical of a bulk separation. Preferably, the particles are hydrocarbon particles and the treated water comprises less than 0.1 % by weight of hydrocarbon particles, more preferably less than 0.05 % by weight, and still more preferably less than 0.01 % by weight, based on the total weight of the treated water. These values may be typical of produced water treatment.

The separated particles are preferably coalesced particles. Preferably, the particles separated from the mixture are at least partially coalesced. Preferably, the separated particles form a continuous phase. Preferably, the separated particles form a continuous phase which comprises less than 50 % by weight of water, more preferably less than 10 % by weight, and still more preferably less than 0.5 % by weight, based on the total weight of the separated particles.

Preferably, the separated particles are hydrocarbon particles. Preferably, the separated particles are coalesced hydrocarbon particles. Preferably, the separated particles form a continuous phase of hydrocarbon. Preferably, the separated particles form a continuous phase of hydrocarbon which comprises less than 50 % by weight of water, more preferably less than 10% by weight, and still more preferably less than 0.5 % by weight, based on the total weight of the separated particles.

The gas and particles separated from the mixture are preferably in the form of bubbles. Preferably, the gas and particles separated from the mixture are in the form of a froth. Preferably, the froth comprises gas and particles.

The method may preferably further comprise a step of removing gas, where the gas may comprise charged gas, from the separated particles and charged gas. Preferably, the method further comprises a step of removing charged gas from the separated particles. Process features

As previously described, the particles in the method of the present invention preferably comprise hydrocarbon, and more preferably the particles comprise oil droplets or are oil droplets. In other words, preferably the method of the present invention is a method for separating hydrocarbon from a mixture comprising water and hydrocarbon, preferably oil droplets. In such a case, it is preferred that the charged gas is derived from a gas, preferably a hydrocarbon gas, which is a product of hydrocarbon recovery from a hydrocarbon-containing formation. It is preferred that the particles, preferably the mixture as a whole, and the gas are derived from the same hydrocarbon recovery process and/or from the same hydrocarbon-containing formation. This is advantageous as the method can be self-sustaining at the same hydrocarbon-containing formation, such as a reservoir or well, without the need to transport gas from offsite.

Accordingly, preferably the method is a method for separating particles from a mixture comprising water and particles, comprising:

(i) adding a charged gas to said mixture comprising water and particles;

In other words, preferably the method is a method for separating particles from a mixture comprising water and hydrocarbon, preferably water and oil droplets, comprising:

(i) adding a charged gas to said mixture comprising water and hydrocarbon;

(iii) separating from said mixture said gas and hydrocarbon, wherein the charged gas is derived from a gas which is a product of hydrocarbon recovery from a hydrocarbon-containing formation; and said hydrocarbon is also recovered from said hydrocarbon-containing formation.

In such a method, the charged gas is preferably a charged hydrocarbon gas, more preferably charged methane gas.

The methods of the present invention are preferably conducted offshore. In such a case, only some steps need be conducted offshore, though it is preferred that all steps are conducted offshore. In offshore processes, there is a particular need for separation methods to be as efficient as possible, owing to the recued amount of space for equipment. The improved efficiency offered by the present method therefore has particular advantages for offshore processes, for example offshore hydrocarbon recovery.

The methods of the present invention are preferably conducted subsea, by which it is meant that the steps are conducted underwater, for example at the sea bed. In such a case, only some steps need be conducted subsea, though it is preferred that all steps are conducted subsea. In subsea processes, the use of traditional chemical flocculants has particular difficulties. The pressures, temperatures and long residence times associated with the subsea environment have a negative impact on the stability of such flocculants, impairing their normal function. The methods of the present invention are not subject to such limitations, and may therefore have particular advantages for subsea processes.

Recovery method

The present invention also relates to a method for recovering hydrocarbon from a hydrocarbon-containing formation, comprising:

(i) recovering from said formation a mixture comprising hydrocarbons and water;

(ii) separating the mixture into recovered hydrocarbons and produced water, optionally according to the method of the present invention hereinbefore described for separating particles from a mixture comprising water and particles; and (iii) optionally, treating said produced water, optionally according to the method of the present invention hereinbefore described for separating particles from a mixture comprising water and particles, wherein at least one of step (ii) and step (iii) is performed according to the method of the present invention hereinbefore described for separating particles from a mixture comprising water and particles.

In the manner described above, the charged gas is preferably derived from a gas which is a product of the recovery of step (i). In such a case, the charged gas is preferably a charged hydrocarbon gas, more preferably charged methane gas. Accordingly, the method may comprise a preliminary step of separating gas from the mixture recovered in step (i). The method may also comprise a further step of ionising that gas.

A preferred method is therefore a method for recovering hydrocarbon from a hydrocarbon-containing formation, comprising:

(i) recovering from said formation; a mixture comprising hydrocarbons and water; and a gas, preferably a hydrocarbon gas;

(iii) optionally, treating said produced water, optionally according to the method of the present invention hereinbefore described for separating particles from a mixture comprising water and particles, wherein at least one of step (ii) and step (iii) is performed according to the method of the present invention hereinbefore described for separating particles from a mixture comprising water and particles; and said gas is optionally ionised for use in the method of the present invention hereinbefore described for separating particles from a mixture comprising water and particles. As described above, preferred methods are offshore and/or subsea methods.

As noted above, step (iii) is optional. Preferably, the method comprises steps (i) and (ii). Alternatively, preferably the method comprises steps (i) to (iii).

At least one of step (ii) and step (iii) is performed according to the method of the present invention hereinbefore described for separating particles from a mixture comprising water and particles. Preferably, step (ii) is performed according to the method of the present invention hereinbefore described for separating particles from a mixture comprising water and particles. In this case, the particles are understood to be hydrocarbon and the mixture is understood to be the mixture recovered in step (i).

Preferably, step (ii) is performed according to the method of the present invention hereinbefore described for separating particles from a mixture comprising water and particles. In this case, the particles are understood to be hydrocarbon and the mixture is understood to be the produced water yielded in step (ii).

Preferably, both steps (ii) and (iii) are operated according to the method of the present invention.

Some preferred methods are as follows:

A method for recovering hydrocarbon from a hydrocarbon-containing formation, comprising:

(i) recovering from said formation a mixture comprising hydrocarbons and water;

(ii) separating the mixture into recovered hydrocarbons and produced water, according to the method of the present invention hereinbefore described for separating particles from a mixture comprising water and particles; and

(iii) optionally, treating said produced water, optionally according to the method of the present invention hereinbefore described for separating particles from a mixture comprising water and particles. A method for recovering hydrocarbon from a hydrocarbon-containing formation, comprising:

(i) recovering from said formation a mixture comprising hydrocarbons and water;

(iii) treating said produced water, according to the method of the present invention hereinbefore described for separating particles from a mixture comprising water and particles.

(i) recovering from said formation a mixture comprising hydrocarbons and water;

(iii) treating said produced water, according to the method of the present invention hereinbefore described for separating particles from a mixture comprising water and particles, wherein at least one of step (ii) and step (iii) is performed according to the method of the present invention hereinbefore described for separating particles from a mixture comprising water and particles.

A system

The present invention also relates to a system for separating particles from a mixture comprising water and particles, comprising:

(ii) a means for adding charged gas into said mixture comprising water and particles; and (iii) a means for removing gas and particles from the mixture in the separator wherein said means for adding charged gas into said mixture adds said charged gas to said mixture either prior to entry to said separator and/or in said separator. Preferably the means for adding charged gas into said mixture adds said charged gas to said mixture prior to entry to said separator.

Preferably, the system is a system for performing a method as hereinbefore described. The system is preferably for use in a method as hereinbefore described.

The means for removing gas typically removes a mixture of non-charged gas and any remaining charged molecules.

Preferably the system further comprises a means for ionising a gas to form a charged gas. Preferably said means for ionising a gas to form a charged gas is fluidly connected to said means for adding a charged gas into said mixture.

Preferably, the system further comprises a continuous gas supply. This may, for example, be a tank for storing gas. Preferably, the tank is fluidly connected to said means for ionising a gas.

The separator may be selected from separators known in the art. Preferably, the separator is a gravity separator, more preferably a gravity separator selected from a compact floatation unit, a cyclone separator (e.g. a hydrocyclone) or a vortex separator. Such separator means are particularly suited to offshore and/or subsea methods, where there is a need for highly efficient and compact equipment. The methods of the present invention further improve the efficiency of separation, providing a synergistic effect. Alternatively, preferably the separation is carried out in a degasser unit.

The system comprises a means for adding charged gas into the mixture. Preferably, this means is an aerator, preferably a diffuser. Preferably, the means for adding charged gas into the mixture is configured to add the charged gas into the mixture as bubbles. Preferably, the means for adding charged gas into the mixture is configured to bubble charged gas through the mixture. Preferably, the means for adding charged gas into the mixture is configured to add charged gas into the mixture as a pressurised stream of gas, preferably a pressurised stream of bubbles. Optionally the separator has an inlet for charged gas. This is necessary when the means for adding charged gas into the mixture includes adding the charged gas in the separator.

The system comprises a means for ionising a gas, which preferably comprises a means for applying a high voltage.

The system also comprises a means for removing gas and particles. Preferably, this means is selected from conventional units, e.g. a weir, a skimmer, an outlet. Advantageously, this allows the system of the invention to be readily retrofitted into existing installations. Preferably, the means for removing gas and particles is located at the surface of the mixture in the separator.

Preferred systems are offshore and/or subsea systems, the advantages of which are discussed above. The system may preferably be a modular system, which can provide ease of assembly, particularly at challenging offshore and/or subsea environments.

Advantageously, the system of the present invention can be obtained by modifying a preexisting gas flotation system and/or gas flotation separator. Such a modification requires the provision of a means for ionising a gas to form a charged gas. The present invention therefore also relates to method of modifying a gas flotation system, comprising providing a means for ionising a gas to form a charged gas, wherein said means for ionising a gas to form a charged gas is fluidly connected to a means for adding the charged gas into a separator.

The system of the present invention is preferably a system for performing the method of the present invention hereinbefore described for separating particles from a mixture comprising water and particles.

Uses

The present invention also relates to uses of the methods and systems of the present invention. For example, the present invention relates to the use of a method or a system of the present invention to treat produced water. The present invention also relates to the use of a method or a system of the present invention to perform a bulk separation. The present invention also relates to the use of a method or a system of the present invention in hydrocarbon or oil recovery.

FIGURES

The invention will now be described with reference to the following non-limiting figure:

Figure 1 is a schematic representation of a preferred system of the present invention.

The system comprises a separator (1) configured for separating particles from a mixture comprising water and particles. Preferably, the separator is a gravity separator. The separator optionally has an inlet (2) to receive the mixture comprising water and particles.

The system preferably comprises a means for ionising a gas (3), which is preferably a means for applying a high voltage to a gas. The system optionally comprises a gas store (4), which is configured to store gas. The gas store (4) is fluidly connected to the means for ionising a gas, such that the stored gas can be ionised. Gas enters the means for ionising a gas (3), where it is ionised. The gas which exits the means for ionising a gas (3) is therefore charged gas.

The means for ionising a gas is fluidly connected to a means for adding charged gas into the mixture comprising water and particles (5a/5b). Preferably the means for adding charged gas into the mixture may be fluidly connected to a line supplying the mixture to the separator (in the case of 5b) or may be fluidly connected to the separator (in the case of 5a).

Preferably, the means for adding charged gas into the mixture (5a/5b) is configured to add the charged gas into the mixture as bubbles. Preferably, the means for adding charged gas into the mixture (5a/5b) is configured to bubble charged gas through the mixture. Charged gas passes from the means for ionising a gas (3), via the means for adding charged gas into the mixture (5a/5b), into the separator (1). The charged gas may be added to the mixture prior to (in the case of 5b) or (in the case of 5a) in the separator (1). Once in the separator (1), the charged gas moves through the mixture so that the charged gas contacts the particles and associates therewith. Preferably, this movement is a passive movement, for example due to buoyancy of the gas bubbles. Preferably, this movement is facilitated by the means for adding charged gas to the mixture, for example by adding the charged gas to the mixture as bubbles. Preferably, the charged gas is attracted to the particles and preferably electrostatically associates therewith. Preferably, the charged gas transports the particles to the surface of the mixture.

The separator (1) also comprises means for removing gas and particles from the mixture in the separator (6). Preferably, the means for removing gas and particles from the mixture in the separator (6) is configured to remove gas and particles from the surface of the mixture in the separator, via an outlet.

Claims

CLAIMS:

1 . A method for separating particles from a mixture comprising water and particles, comprising:

(i) adding a charged gas to said mixture comprising water and particles;

2. A method according to claim 1 , wherein said charged gas is a charged hydrocarbon gas and is derived from a gas which is a product of hydrocarbon recovery from a hydrocarbon-containing formation.

3. A method according to claim 1 or 2, wherein said method is conducted offshore.

4. A method according to any preceding claim, wherein said method is conducted subsea.

5. A method according to any preceding claim, wherein said charged gas moves through said mixture in the form of bubbles, and wherein said bubbles coalesce in said mixture.

6. A method according to any preceding claim, wherein said charged gas is attracted to said particles, preferably by ionic or electrostatic interactions.

7. A method according to any preceding claim, wherein said charged gas transports said particles to the surface of the mixture, and wherein preferably said charged gas and particles are separated from said mixture at a surface of the mixture.

8. A method according to any preceding claim, wherein said mixture comprising water and particles is produced water or water from a bulk separation.

9. A method according to any preceding claim, wherein said particles are charged, preferably anionic.

10. A method according to any preceding claim, wherein said particles comprise oil droplets.

11. A method according to any preceding claim, wherein said particles are derived from a gas condensate.

12. A method according to any preceding claim, wherein said particles are solid particles.

13. A method according to any preceding claim, wherein said charged gas is cationic.

14. A method according to any preceding claim, wherein said charged gas is a hydrocarbon gas, preferably a Ci-e alkane gas.

15 A method according to any preceding claim, further comprising a step of ionising gas to produce a charged gas, wherein preferably ionising said gas comprises the application of a high voltage.

16. A method according to any preceding claim, wherein said charged gas comprises or consists of gaseous methane cations.

17. A method according to any preceding claim, wherein flocculants are not added to said mixture comprising water and particles.

18. A method according to any preceding claim, wherein, in step (i), said charged gas is introduced using an aerator, preferably a diffuser.

19. A method according to any preceding claim, wherein, in step (ii), said charged gas is attracted to said particles and forms ionic bonds therewith.

20. A method according to any preceding claim, wherein, in step (iii), separation is carried out in a gravity separator, preferably a gravity separator selected from a compact floatation unit, a cyclone separator (e.g. a hydrocyclone) or a vortex separator.

21. A method of recovering hydrocarbon from a hydrocarbon-containing formation, comprising:

(i) recovering from said formation a mixture comprising hydrocarbons and water;

(ii) separating the mixture into recovered hydrocarbons and produced water, optionally according to the method of any one of claims 1-20; and

(iii) optionally, treating said produced water, optionally according to the method of any one of claims 1-20, wherein at least one of step (ii) and step (iii) is performed according to the method of any one of claims 1-20.

22. A system for separating particles from a mixture comprising water and particles, comprising:

23. A system according to claim 22, further comprising a means for ionising a gas to form charged gas.

24. Use of a method according to any one of claims 1-20 or a system according to claim 22 to treat produced water or to perform a bulk separation.

25. Use of a method according to any one of claims 1-20 or a system according to claim 22 in hydrocarbon or oil recovery.