EP0917905B1 - Process and device for diphasic compression for the treatment of oil products - Google Patents

Description

The present invention relates to a method for treating a petroleum effluent and a compression device biphasic for the implementation of the process.

The invention finds in particular its application for fluids which are present under an essentially gaseous form and which are miscible or soluble in a fluid essentially liquid.

The present invention allows in particular, through the same machine, both the compression of an acid gas and formation water from an oil deposit, and mixing them in an essentially liquid form, the acid gases being particularly soluble in formation water. The liquid mixture obtained can be sent to an area storage or reinjected into a production well or aquifer.

The invention applies in particular to the treatment of a natural gas containing gases acids, carbon dioxide and / or hydrogen sulfide which are generally at least in part separated from natural gas. When present in small quantities, these acid gases separated can be released directly or after incineration in the atmosphere. However, the standards to fight against pollution being more and more restrictive, these discharges in the atmosphere are less and less tolerated, and it becomes necessary to find other solutions easy to implement, respecting these new standards, and this with minimum investment.

The prior art describes various solutions for eliminating acid gases as in FR 2424472. One solution is to inject the acid gases individually into a deposit in using centrifugal or reciprocating compressors.

Another way is to inject the acid gases with another fluid, for example formation water available at the level of the deposit. This solution presents in particular as an advantage of simultaneously eliminating the acid gases and the formation water considered to be two pollutants.

The process of reinjection of formation water and acid gases from the company Pan Canadian Limited, the essential steps of which are summarized below and described in Figure 1, is based on this principle.

The fluid from the production wells is separated into an oil phase which is recovered, an aqueous phase and a gaseous phase circulating respectively in conduits 1 and 2. The aqueous phase is stored in atmospheric tanks 3, while the phase gas containing the acid gases is treated in a unit 4 with amines so as to obtain a gas, without acid components, and a gas with a high content of acid components to a pressure close to atmospheric pressure. The gas fraction rich in acid gases is sent to a compressor 5, and the formation water is sent to a pump monophasic 6. The formation gas and water having separately acquired a level of given pressure, are then mixed in a mixer 7. The mixing is carried out at a high pressure to facilitate the dissolution of gases in water, the amount of acid gases dissolved increasing with the pressure level. This mixture is in a form liquid, is then reinjected for example into an underground tank using a pump monophasic 8 adapted to pump liquid monophasic fluids. Upstream of the high pressure pump the gas must not only be completely dissolved in the liquid, but the NPSHA (Available height in relation to the vapor pressure of the gas) must be greater than NPSHR (Height required at the inlet of the pump in relation to the voltage steam).

In the case of applications with high reinjection pressure and for production with a high gas content, the mixing of water and gas is carried out in stages successive and separate pumping, compression and mixing.

This process requires equipment which has the disadvantage of being heavy and expensive, using both single-phase compressors and pumps, as well as many heat exchangers. In addition, the dissolution of acid gases in water is not instant, it is necessary to use static or dynamic mixers in order to to obtain perfect dissolution of the gas in the liquid upstream of the pumps monophasics further increasing the complexity of equipment, cost and size of such a system.

The present invention proposes to remedy the drawbacks of the prior art, by adopting a new approach which in particular makes it possible to minimize the number commonly used equipment.

According to the invention, a two-phase compression device capable of communicate energy to several fluids, at least one of the fluids being soluble in at at least one other fluid, and also to simultaneously mix the fluids, so as to obtain at the outlet a fluid which is essentially or completely in the form liquid.

The present invention relates to a two-phase compression device as described in claim 5.

According to one embodiment, the two-phase compression device may include at least one input stage and / or at least one output stage, each of said stages comprising hydraulics suitable for pumping an essentially liquid fluid.

The compression device can be formed of at least two sections, the first section for obtaining a mixture Mi having a pressure level Pi and the second section allowing to obtain from the mixture Mi a mixture Ms having a level of pressure Ps, a conduit for discharging the mixture Mi and a conduit for introducing the fluid Mi in the second section, said two sections being separated by a sealing device and the hydraulics of the two sections being mounted "back to back" so as to minimize axial thrust efforts.

The two-phase compression device may include a device arranged between two compression stages and suitable for at least mixing the fluid essentially liquid and essentially gaseous fluid, for example in the case where these two fluids are introduced on stages of different ranks.

The compression device can also include a processing unit and / or mixing of fluids, said treatment and / or mixing unit being connected to the compression by fluid inlet and outlet pipes, before treatment and after treatment.

In certain embodiments, the processing unit includes a means of refrigeration inserted in the processing unit.

The processing unit may include a cooling circuit of at least one part of the two-phase mixture taken from the two-phase compression device and / or part of the liquid phase from the two-phase compression device.

The compression device includes, for example, means for determining parameters related to the fluid and / or its operation, means of calculation and data processing capable of modifying the speed of rotation of the two-phase compression and / or act on the efficiency of the refrigeration means and / or on the flow rate of the recycled fluid in the cooling circuit.

The invention also relates to a method for treating a petroleum effluent as described in claim 1.

• si la valeur de cette différence est inférieure à une valeur fixée, on envoie les deux fluides à un même étage de compression diphasique du dispositif de compression,
• si la valeur de cette différence est supérieure à une valeur fixée, on envoie le fluide de plus basse pression à un étage du dispositif de compression de rang i et le fluide de plus haute pression à un étage de rang supérieur i+n, le nombre n étant déterminé en fonction de la différence de pression,

The pressure difference between the fluids to be mixed is determined for example before their introduction into the two-phase compression device, and

• if the value of this difference is less than a fixed value, the two fluids are sent to the same two-phase compression stage of the compression device,
• if the value of this difference is greater than a fixed value, the lower pressure fluid is sent to a stage of the compression device of rank i and the higher pressure fluid to a stage of higher rank i + n, the number n being determined as a function of the pressure difference,

The method may include a step of removing at least part of the mixing of fluids after passage through a number of stages m of the two-phase compression, a step of processing the removed part and a step of return after treatment to a stage of the compression device of rank higher than the row of the sampling stage.

It is also possible to refrigerate the fluid and / or a fluid such as part of the mixture. two-phase sample taken or at least part of the liquid phase extracted from the mixture two-phase sample taken or at least part of the liquid from the compression device two-phase, the refrigerated fluid possibly being able to be recycled.

It is also possible to regulate the speed of rotation of the compression device and / or to control the efficiency of the refrigeration step and / or to control the flow of fluid recycled.

The invention is particularly applicable for the simultaneous transfer of acid gases and formation water to an underground reservoir.

Thus the present invention offers compared to the prior art as an advantage of simplify the devices necessary to achieve compression and mixing of several fluids, for example at least one essentially gaseous fluid and at least one fluid essentially liquid miscible with each other.

The method according to the invention can be applied in all fields where it is sought to communicate energy simultaneously to a gas phase and a liquid phase, the gas phase being soluble in the liquid phase, the pressure values of the phases may be different.

• la figure 1 schématise le procédé de la société Pan Canadian selon l'art antérieur,
• la figure 2 montre un dispositif de compression diphasique adapté pour mettre en oeuvre le procédé selon l'invention,
• la figure 3 schématise un exemple d'agencement d'étages de compression diphasique,
• les figures 4A et 4B représentent deux variantes de réalisation pour les étages d'entrée et de sortie du dispositif de pompage monophasique et de compression diphasique combinés,
• la figure 5 montre une autre variante pour le système de la figure 3,
• les figures 6, 7 et 8 schématisent une variante du procédé adaptée à des fluides de différentes pressions et leur mode d'introduction dans le dispositif de compression diphasique,
• la figure 9 schématise une variante de réalisation où il est possible d'effectuer un traitement du mélange des deux fluides au cours de l'opération de compression,
• les figures 10A et 10B représentent deux dispositifs de recyclage du liquide au travers de l'unité de réfrigération,
• la figure 11 représente une généralisation du principe selon l'invention appliqué pour plusieurs fluides liquides et gazeux présentant des valeurs de pression différentes avant l'entrée du dispositif, et
• la figure 12 représente un schéma possible de régulation du dispositif de compression.

Other advantages and characteristics of the invention will appear better on reading the description given below by way of exemplary embodiments, in the context of non-limiting applications, for the transfer of acid gases and formation water. , to an underground reservoir or aquifer, referring to the attached drawings where:

• FIG. 1 schematizes the process of the company Pan Canadian according to the prior art,
• FIG. 2 shows a two-phase compression device suitable for implementing the method according to the invention,
• FIG. 3 shows diagrammatically an example of arrangement of two-phase compression stages,
• FIGS. 4A and 4B represent two alternative embodiments for the input and output stages of the combined single-phase pumping and two-phase compression device,
• FIG. 5 shows another variant for the system of FIG. 3,
• FIGS. 6, 7 and 8 show diagrammatically a variant of the process suitable for fluids of different pressures and their mode of introduction into the two-phase compression device,
• FIG. 9 shows schematically an alternative embodiment where it is possible to carry out a treatment of the mixture of the two fluids during the compression operation,
• FIGS. 10A and 10B represent two devices for recycling the liquid through the refrigeration unit,
• FIG. 11 represents a generalization of the principle according to the invention applied for several liquid and gaseous fluids having different pressure values before the entry of the device, and
• FIG. 12 represents a possible diagram of regulation of the compression device.

In order to better understand the device according to the invention, the example given below by way of illustration and in no way limitative relates to the transport of acid gases and water formation, the acid gases being soluble in the formation water.

The mixing and dissolution of the acid gases in the formation water is based on physical phenomena which will be recalled below.

Under equilibrium conditions, the dissolution of an acid gas in water, by example of formation water, varies with pressure and temperature. The rate of dissolution expressed in volume units of gas per volume unit of liquid in the normal pressure and temperature conditions increase respectively when the pressure increases and when the temperature decreases.

The dissolution will be carried out gradually taking into account the time of diffusion between phases, and the approach to an equilibrium condition can, therefore, be activated by an increase in the contact surfaces between the acid gases and the water training.

In the case of two-phase compression using a type pump rotodynamics, reaching equilibrium conditions will be facilitated by the formation of bubbles having small dimensions. These bubbles appear at the junction between the fixed parts and the rotating parts of the pump, a place where great shear forces are exerted.

This approach towards equilibrium is however slowed down by the coalescence of bubbles may appear at the level of the impellers and / or rectifiers of the two-phase compression. For substantially equal performance, (height gauge and axial length), it will be advantageous to increase the number of cells of compression (impellers and / or rectifiers) and to reduce their axial length, so as to increase the number of times the size of the bubbles can be reduced.

Figure 2 shows schematically an example of implementation of the adapted method when the formation water and the acid gases have a pressure level close to the inlet of the device two-phase compression, the difference between the pressure levels being sufficient low to allow their introduction into the same floor.

The pumping device 10 is connected by the conduit 11 to the device 12 which receives the acid gases from a source referenced 13 through line 14, and through line 16 water from training stored in a tank referenced 15.

The acid gases can come from a treatment unit such as that described in the applicant's patents FR 2,605,241 and FR 2,616,087. At the output of these units of treatment, the acid gases have a pressure which can vary between 0.5 and 1.5 MPa and a temperature between -30 ° C and -10 ° C. In the case of amine processing units, the pressure value is of the order of 0.1 MPa and the temperature between 10 and 40 ° C.

The device 12 is chosen to favor the at least partial dispersion of the gases acids in the form of bubbles in the liquid or at least partial of the liquid in the form droplets in the gas.

The two-phase pumping or compression device 10 is provided with at least an evacuation duct 17 for the essentially liquid mixture. The pressure level of this mixing at the outlet of the compression device is sufficient to ensure its transfer to an aquifer or an underground reservoir referenced 18.

The initial pressure value of the acid gases and the formation water, can be measured by pressure sensors 19a, 19b disposed respectively at the outlet the processing unit 13 and the storage tank 15.

The two-phase compression device 10 comprises at least one stage of pumping comprising an impeller and a rectifier referenced li and Ri in the figures following. The impeller and rectifier hydraulics have specific characteristics, adapted to communicate energy to a two-phase fluid comprising at least one gaseous phase and at least one liquid phase, the ratio of volume flow rates of these two phases can vary from 0 to infinity, such as impellers heli-axial. The layout and characteristics of these hydraulics are similar to those described in one of the applicant's patents FR 2,333,139, FR 2,471,501, EP 0781929 and FR 2,665,224. Such a device also makes it possible to dissolve and mix the acid gases in the formation water to obtain an essentially liquid mixture or liquid.

The number of compression stages used will depend on the pressure level required output.

Preferably, the two-phase compression device will be designed using impellers of an axial length less than that of the impellers usually used in the aforementioned applicant's devices as well as a greater number impellers so as to maintain the same overall performance (same pressure output for the same total axial length). As explained above, we will increase the number of times the gas pockets and macro bubbles that have formed inside an impeller can be reduced at the interface between organs rotating and static (impeller-rectifier and rectifier-impeller), in the form of micro-bubbles, with a diameter varying between a micron and a millimeter.

Without departing from the scope of the invention, it is possible for technological reasons to realize the compression device in several compression machine bodies or pumping, each of these bodies consisting of one or more sections and each sections comprising one or more compression or pumping stages. A example of such a device in several bodies is given in FIG. 11.

FIG. 3 shows diagrammatically an example of a compression device 10 which comprises, in the present case, 4 compression stages E ₁ to E ₄ mounted in line.

Each stage Ei of the system comprises an impeller li, followed by a rectifier Ri, the impeller li being integral with the rotation shaft 30, the index i designating the rank of the stage of two-phase compression, the stages being arranged in a casing 31.

The two-phase compression device 10 has an opening 33 communicating with the fluid introduction conduit 11 and an inlet part 34 disposed upstream of the first impeller I1.

At its output, the two-phase compression device may include a adapter, such as a volute 35, for transforming kinetic energy into potential energy to minimize energy losses at the outlet, connected to the conduit discharge 17 of the essentially liquid mixture.

Acid gases and formation water introduced at a pressure P0 and a temperature T0 through opening 33, then entry piece 34, are compressed in the first stage (I1, R1). At the end of this stage, part of the acid gases are dissolved in the water of training in a proportion close to that fixed by the equilibrium conditions of dissolution at the exit of stage E1, at a pressure P1 and a temperature T1. The mixture thus produced M1 passes in the compression stages of higher rank in order to increase the pressure and intensify the mixture of acid gases in the formation water until reaching the total dissolution of acid gases. At the output of the two-phase compression device, the Ms mixture formed by the acid gases dissolved in the formation water is evacuated by a conduit 17 in an essentially liquid or liquid form at a pressure Ps and a temperature Ts.

Advantageously, the last pumping stage or stages of the compression can include hydraulics suitable for single-phase fluids, such as radial impellers well known to those skilled in the art. Examples adaptations of the output and input stages of the compression device are shown by way of illustration and in no way limitative in FIGS. 4A and 4B.

FIGS. 4A and 4B schematize variants of the compression device where the characteristics of the input and / or output pumping stages are optimized and chosen according to the nature of the fluids.

In the case where the acid gases have a pressure significantly higher than water formation, the acid gases are introduced through a conduit 43 at a pressure level compression intermediate in the two-phase compression device 10, the device 12 no longer used. It then becomes advantageous to use, for the first stages of compression 40, adapted hydraulics (impellers, referenced 41 and rectifiers 42) when pumping liquid, for example, radial wheels, as shown schematically in Figure 4A.

In the case where the acid gases are completely dissolved in the formation water in upstream of the output of the two-phase compression device 10, it is advantageous to use for the last compression stages, hydraulics (impellers, referenced 45 and rectifiers) suitable for pumping a liquid, for example radial wheels, such as shown schematically in Figure 4B.

In both cases, the outside diameter of the radial impellers, Dr, can be greater than the outside diameter of the helical-axial impellers, Dm, in order to reduce the minimum number of single-phase stages.

Mechanical-hydraulic adaptation between a pumping stage of the type multiphase and a single-phase pumping stage (liquid or gas phase) will be performed as shown in FIG. 7 in the case of a helical-axial impeller in downstream of a radial impeller.

Figure 5 shows schematically a variant of the two-phase compression device composed of two sections 50, 51 where the compression stages are mounted "back to back", the two sections being separated by a sealing device 52, for example, a sealing at labyrinths. The mixture flows in section 30 in a direction opposite to that from section 31.

According to this alternative embodiment, the section 50 comprises several stages of compression Ei (li, Ri) followed by a volute 54. The mixture composed of acid gases and the formation water is sent to the first section 50 where it acquires a level of intermediate pressure Pi and where the at least partial dissolution of the acid gases is carried out. The partial mixture Mi is discharged through a conduit 55 located downstream of a volute 54.

This Mi mixture from the first section 50 is then sent to the second section 51 of the compression device into which it is introduced by a conduit 56. The mixture compressed through the compression stages of the second section 51 is evacuated by a volute 57 then a conduit 58 corresponding to the high pressure outlet of the compression device. Going into the second section of the device compression, the pressure of the mixture Mi rises to a level Ps sufficient to achieve almost complete dissolution of the acid gases in the formation water until a essentially liquid form Mj.

Such an arrangement has in particular the advantage of minimizing the efforts axial thrust acting on the shaft, in the case of high pressure applications.

When the acid gases and the formation water have as input the two-phase compression of fairly distant pressure levels, it is preferable to introduce on separate stages of the compression device, so as to avoid losses in energy. Figures 6, 7 and 8 show different embodiments.

FIG. 6 represents an arrangement adapted to the case where the formation water is at a pressure level Pe, lower than the pressure level Pg of the acid gases. Water training is introduced by a low pressure input 60 into the first pumping stage while the acid gases are sent through a conduit 62 connected to a corresponding input 61 to a compression stage located downstream from the inlet stage. The gases are introduced from preferably at the level of the rectifier Ri of the pumping stage of rank i at the outlet of which the formation water has a pressure level Pe 'close to the inlet pressure level acid gases Pg.

FIG. 7 details an example of a device 70 for introducing acid gases arranged downstream of the inlet 61 having both the functions of facilitating the mixing of the gas and the liquid and channel the mixture towards the inlet of an impeller adapted to the compression of the two-phase mixture.

The device 70 is arranged between the impeller li of the pumping stage of row i consisting for example of a radial wheel and the two-phase compression stage E2 consisting a helical-axial wheel.

The device 70, similar to a stator stage separating two radial wheels and known to those skilled in the art, essentially comprises a diffuser 71 for the transformation of kinetic energy into potential energy and a return channel 72.

It also includes a part 73 comprising a passage 74 communicating with the conduit 62 for the introduction of acid gases and several channels 75, of very small diameter, drilled in the part 73. These channels open into the return channel 72 and can be regularly arranged in the radial plane.

In the case of a body with a horizontal joint, the part 73 is supported directly by the housing 31.

In the case of a body with vertical joint, the part 31 as well as all the internal parts of the device 70 constitute a cartridge mounted inside a cylindrical casing, not shown in the figure. Such a construction method is known to those skilled in the art.

Acid gases are introduced into the two-phase compression device successively at the level of the external conduit 62, in the internal conduit 74 and finally in the return channel 72 through the channels 75.

The device allows an intimate mixture of gas and liquid, increasing efficiency with the number of channels.

In certain application cases it may be advantageous to introduce a fluid (gas or liquid) at any level of two-phase compression.

FIG. 8 shows in detail an example of arrangement of the casing 31 of the compression 10 communicating with an auxiliary introduction conduit 80 for a fluid monophasic.

An opening 81 is made for example at the level of the rectifier Rj of the stage of row j of the compression device. Downstream of the opening 81, a device 82 pierced with channels 83 of very small diameter makes it possible to introduce the monophasic fluid and to diffuse it in the two-phase mixture from the impeller Ij. The new mixture formed from the mixture two-phase and the single-phase external fluid from the rectifier Rj is directed to the impeller Ij + 1 of the row compression stage (j + 1). The impeller diameters of rows Ij and Ij + 1 are adapted to the change in volume flow rate due to the introduction of the fluid additional through conduit 80.

It is also possible to use this arrangement to introduce additives used in the petroleum field such as anti-corrosion additives, anti-hydrates or surfactants.

During two-phase compression, it may be advantageous to perform a treatment of the acid gas-formation water mixture to activate the dissolution.

The treatment will consist, for example, of stabilizing the dissolution or of cooling the acid-water gas mixture whose temperature rose during the compression of the even the compression of the mixture, but also the exothermic nature of the dissolution reaction. Other treatments and their associated devices may be imagined without departing from the scope of the invention.

Figure 9 shows schematically an exemplary embodiment where the compression device 10 of Figure 5 is associated with a processing unit 90 arranged in series.

The mixture Mi from the medium pressure outlet 55 is sent through a pipe 91 to the processing unit 90. Downstream of the processing unit 90, the mixture Mi is then sent via a conduit 92 to the medium pressure inlet 56 of the second part of the compression device.

By the simple fact of the flow of the two-phase mixture and the residence time in conduits 55, 91, 92 and 56 as well as in the treatment unit, it is possible to approach the dissolution conditions defined in equilibrium condition. Consequently, the diameters and lengths of the pipes located on either side of the treatment unit 90 could be calculated in order to adjust this residence time.

The residence times to be observed will possibly be defined from tests preliminary performed under real operating conditions. This will make it possible to predict the dissolution differences between the transient and equilibrium conditions, these differences can be expressed in time or in gas flow.

• elle augmentera la capacité du liquide à dissoudre le gaz dans les conditions d'équilibre,
• elle permettra de s'approcher des conditions d'équilibre, compte tenu du temps de résidence dans le système de réfrigération,
• elle permettra une augmentation de la densité du mélange, paramètre favorable à la compression d'un mélange diphasique,
• elle permettra une réduction du rapport des débits volumiques de gaz et de liquide, paramètre également favorable à la compression d'un mélange diphasique.

The processing unit may include a refrigeration system. Refrigeration of the mixture will have many advantages:

• it will increase the capacity of the liquid to dissolve the gas under equilibrium conditions,
• it will make it possible to approach equilibrium conditions, taking into account the residence time in the refrigeration system,
• it will allow an increase in the density of the mixture, a parameter favorable to the compression of a two-phase mixture,
• it will allow a reduction in the ratio of the volume flow rates of gas and liquid, a parameter also favorable to the compression of a two-phase mixture.

The treatment / cooling unit may be designed so as to cool the two-phase mixture and / or part of the liquid phase taken from this mixture or still the liquid from the two-phase compression device or part of this liquid. FIGS. 10A and 10B schematize two exemplary embodiments of the processing device comprising means for withdrawing and recycling the liquid.

In FIG. 10A, the processing unit 90 comprises a static type mixer or dynamic 93 arranged on the duct 91, a pressure drop adjustment valve 94, a means 95 for extracting at least part of the liquid phase contained in the mixture biphasic circulating in the conduit 91, a conduit 96 and a pump 97 making it possible to send the liquid fraction extracted to be cooled, to a cooling device such as an exchanger 98 at the outlet of which the cooled liquid fraction is recycled via a line 99 to the mixer static 93 to be mixed with the fluid circulating in the conduit 91.

When the fluid is in the form of a stratified flow in the duct 91, the extraction means 95 are chosen to carry out the removal of at least one part of the liquid phase at a low point in the pipe.

For fluids in annular flow the extraction means 95 will allow to extract a fraction of the liquid phase at the periphery of the pipe 91.

The pump 97 can be a single-phase pump of low head.

FIG. 10B shows schematically another alternative embodiment where the removal of the liquid phase to be cooled is produced at high pressure on the liquid fluid coming from the compression.

The processing unit comprises the static or dynamic mixer 93 placed on the conduit 91, means 100 for extracting a fraction of liquid from the device compression and which are connected to the heat exchanger 98 by a conduit 101, a valve 102 allowing the adjustment of the flow rate of liquid cooled in the heat exchanger 98, the cooled liquid being sent through a pipe 103 to the static mixer 93.

The part of the liquid phase not withdrawn and corresponding substantially to the flow rate of the liquid circulating in the conduit 11 is discharged through a conduit 104.

Recirculation of the cooled liquid to the pipe 91 is allowed during operation normal without the help of an additional pump due to the positive pressure difference between conduit 58 and conduit 55.

• une plus grande efficacité et une réduction en volume de l'échangeur opérant à une pression élevée ou moyennement élevée,
• un accroissement du débit de liquide dans la zone de recyclage favorable à la dissolution du gaz dans le liquide.

Such arrangements (Figures 10A and 10B) will in particular allow:

• greater efficiency and reduction in volume of the exchanger operating at high or medium-high pressure,
• an increase in the liquid flow rate in the recycling zone favorable to the dissolution of the gas in the liquid.

The processing unit 90 can be fitted with other conduits 91b allowing the addition a fluid with the mixture Mi, for example additives mentioned above.

FIG. 11 schematizes an example of generalization of the use of a two-phase compression device comprising two machine bodies CM ₁ and CM ₂ , forming the two-phase compression device and which are connected together by a conduit 123, suitable for example when there are several sources of fluids at different pressure levels.

In this example, the second body CM ₂ is associated with a processing device 116 according to an arrangement similar to that of FIG. 9.

At the outlet of the body CM _1, the fluid is for example in a multiphase form.

In FIG. 11, the compression device is supplied by three sources of acid gases referenced respectively 110, 111 and 112 at pressures PG ₃ , PG ₂ and PG ₁ , temperatures TG ₃ , TG ₂ and TG ₁ and with for example PG ₁ <PG ₂ <PG ₃ .

The acid gases G ₁ (112) and G ₂ (111) are introduced into the first body CM ₁ by conduits 113, 114 corresponding to different compression stages of the body, the ranks of which are determined according to the values of the pressures PG ₁ and PG ₂ .

The acid gases G ₃ (110) are sent via a pipe 115 to the treatment device 116.

Two sources of liquid L ₁ and L ₂ at pressures respectively PL ₁ and PL ₂ and temperatures TL ₁ and TL ₂ are also shown in this figure.

The liquid L _1, (117), is sent via a conduit 120 into the first body of CM ₁ . Assuming that PL ₁ <PG ₁ the conduit 120 is directly connected to the first stage of the body CM ₁ while the acid gases G ₁ and G ₂ are sent to pumping stages of higher rank according to a diagram similar to that of Figure 6.

The liquid contained in the source L ₂ (118) is sent directly to the second body CM ₂ by a conduit 121, for example at its inlet stage.

Following the distribution of fluids given above, the mixture of fluids and their pressure gain is effected, for example, as follows:

The pressure level PL ₁ of the liquid L ₁ increases until it reaches a pressure level substantially identical to that of the gas G ₁ , PG ₁ . Inside the first part of the body CM ₁ , the acid gases G, are dissolved in the liquid L ₁ at least partially, the mixture M obtained being at a pressure level P. The acid gases G ₂ having a pressure PG ₂ are introduced into the stage at the outlet from which the mixture M has a substantially identical pressure level. These three fluids are mixed by passing through the different compression stages of the body CM ₁ , the resulting multiphase mixture M 'being evacuated through a conduit 122 at a pressure level P'.

The mixture M ′ coming from the body CM ₁ is introduced with the liquid L ₂ having a pressure P _L2 , through a conduit 123 in the second body CM ₂ .

At the outlet of the first part of the second body, the mixture Mi which is at an intermediate pressure level Pi is sent via a conduit 124 to the treatment device 116 in which it is mixed at least in part with the gas G ₃ .

The mixture M'i from the treatment device is then sent through a conduit 125 in the second part of the body CM ₂ , passes through the various compression stages. At the outlet from the body CM _2, an essentially liquid fluid Ms is discharged at a pressure level Ps via the outlet 126, for example in an aquifer.

According to another way of operating, it will be possible to make up for differences in operating parameters of the two-phase compression device from different measurements on the two-phase compression device.

In FIG. 12, a manometric height diagram has been schematized (in ordered) - output volume (on the abscissa) - parameterized in speed (N), performance of the two-phase compression device. On this diagram have been represented a desired operating point C, as well as two points, A and B, representing two cases of dysfunction.

• de mesurer différents paramètres :
  • les valeurs de débit de la phase gazeuse et de la phase liquide avant leur entrée dans le dispositif de compression diphasique Qg et QI, pour chacun de mesurer les valeurs de la température et de pression associées Tg et Tl, Pg et Pl,
  • en sortie du dispositif de compression des valeurs liées au liquide telles que sa pression Pm, sa température Tm, son débit Qm et sa densité pm,
• de mémoriser les paramètres caractéristiques des fluides gazeux et liquides en entrée du dispositif de compression par exemple la densité pour le fluide liquide, ρl, et la masse molaire Mg et le facteur isentropique yg pour le fluide gazeux,
• à partir de ces différentes mesures, des données précédemment mentionnées et d'un traitement des données approprié, de déterminer le point de fonctionnement du dispositif de compression et la courbe de vitesse correspondante, et
• en comparaison avec une valeur déterminée de vérifier que ce point de fonctionnement appartient à un domaine permis de fonctionnement ou un domaine optimal de fonctionnement.

By equipping the two-phase compression device with an appropriate measurement system such as pressure, temperature, flow, density (or vacuum rate) sensors, and a control and calculation device such as a micro- controller connected to all these elements, it is possible:

• to measure different parameters:
  • the flow values of the gas phase and of the liquid phase before they enter the two-phase compression device Qg and QI, for each to measure the values of the associated temperature and pressure Tg and Tl, Pg and Pl,
  • at the output of the compression device, values linked to the liquid such as its pressure Pm, its temperature Tm, its flow rate Qm and its density pm,
• memorize the characteristic parameters of gaseous and liquid fluids at the input of the compression device, for example the density for the liquid fluid, ρl, and the molar mass Mg and the isentropic factor yg for the gaseous fluid,
• from these various measurements, from the previously mentioned data and from appropriate data processing, to determine the operating point of the compression device and the corresponding speed curve, and
• in comparison with a determined value to verify that this operating point belongs to a permitted operating domain or an optimal operating domain.

If the operating point is outside the range of desired operation, it will be possible to act on the speed of rotation if the device has a variable speed drive, and possibly on the efficiency of the refrigeration or on the flow of recycled liquid depending on the design of the compression.

For example, if point A indicates too rapid dissolution with a downstream flow too low and too great downstream pressure, to remedy this problem it will be possible to act by reducing the speed of rotation of the two-phase compression device to bring the operating point A to the desired operating point C.

The operating point B diagrams the opposite case.

The compression device will preferably be equipped with a speed drive variable. The speed regulation can be done automatically or manually.

Comparative example

• une plus grande sécurité en présence de gaz nocifs tels l'hydrogène sulfuré H₂S,
• une réduction des coûts dans un environnement corrosif et / ou soumis à une forte pression.

The two-phase compression and mixing device has many advantages compared to a single-phase compression and mixing system, including a significant reduction in the number of devices, resulting in:

• greater safety in the presence of harmful gases such as hydrogen sulfide H ₂ S,
• lower costs in a corrosive and / or high pressure environment.

The reduction in the number of equipment depends strongly on the application cases, mainly, the volumetric ratio of gas and liquid (GLR) and the pressure at the inlet of the compression device. Pressure inlet is approximately equal to the pressure downstream of the deacidification unit.

• une pompe diphasique comportant 13 étages de compression. La pression de refoulement est déterminée par le dispositif de compression diphasique. Les mêmes conditions de pression sont utilisées pour les deux types de compression,
• deux valeurs de hauteur manométrique monophasique de 150 m et 300 m par étage de compression diphasique. La hauteur manométrique de compression diphasique est obtenue par le produit de la hauteur monophasique et de l'efficacité diphasique, cette dernière étant une fonction du GLR et du rapport des densités des phases,
• un débit liquide de 200 m³/Heure et un débit de gaz qui varie entre des valeurs correspondant à un GLR de 1 et un GLR de 15,
• une pression de 1 MPa abs en sortie d'un procédé de traitement par solvant physique et de 0,1 MPa abs en sortie d'un procédé de traitement par solvant chimique.

A comparative study between two-phase and single-phase compression systems (compressor and pump) was carried out on the following bases:

• a two-phase pump comprising 13 compression stages. The discharge pressure is determined by the two-phase compression device. The same pressure conditions are used for both types of compression,
• two values of single-phase head of 150 m and 300 m per two-phase compression stage. The two-phase compression head is obtained by the product of the single-phase height and the two-phase efficiency, the latter being a function of the GLR and the ratio of the phase densities,
• a liquid flow of 200 m ³ / hour and a gas flow which varies between values corresponding to a GLR of 1 and a GLR of 15,
• a pressure of 1 MPa abs at the outlet of a physical solvent treatment process and of 0.1 MPa abs at the outlet of a chemical solvent treatment process.

The table below represents in the conditions of the study, the number of compression sections and therefore the number of cooling units (also the number of balloons upstream of the compression sections) required by a single-phase compression when a maximum cooling unit is required by two-phase compression. GLR of the fluid at the inlet
of the two-phase compression device: 1 4 9 15 CASE I
Physical solvent treatment
Manometric height by two-phase impeller: 150 m 2 2 1 1 CASE II
Physical solvent treatment
Manometric height by two-phase impeller: 300 m 3 3 2 2 CASE III
Chemical solvent treatment
Manometric height by two-phase impeller: 150 m 5 5 5 4

Claims (7)

1. A method of treating a petroleum effluent wherein the following stages are carried out :

   a) a petroleum effluent from an oilwell is separated into an oil phase, an aqueous phase and a gas phase,

   b) the gas phase is treated so as to produce acid gases and a gas free of acid compounds,
   characterized in that :

   c) the aqueous phase from stage a) and the acid gases produced in stage b) are combined so as to obtain a two-phase fluid,

   d) the two-phase fluid obtained in stage c) is compressed with a two-phase compression device (10) comprising at least one two-phase compression stage including an impeller and a diffuser so as to dissolve said acid gases in said aqueous phase and to transmit energy to the two-phase fluid and thus to obtain an essentially liquid fluid.
2. A method as claimed in claim 1, wherein the following stage is carried out :

   e) the essentially liquid fluid obtained in stage d) is fed into an underground reservoir.
3. A method as claimed in any one of claims 1 and 2, characterized in that, in stage d), the following stages are carried out :

   f) two-phase fluid is withdrawn from two-phase compression device (10),

   g) part of the two-phase fluid withdrawn is cooled,

   h) said part of the cooled two-phase fluid is fed into the two-phase compression device.
4. A method as claimed in any one of claims 1 to 3, characterized in that the rotating speed of said compression device is regulated and/or the cooling efficiency in stage g) is controlled and/or the flow rate of the fluid cooled in stage g) is controlled.
5. A two-phase compression device for implementing the method as claimed in any one of claims 1 to 4, comprising at least one two-phase compression stage including an impeller and a diffuser, characterized in that the device comprises a second diffuser (70, 80, 81, 82, 83) arranged upstream from said two-phase compression stage and provided with an element (73, 82) pierced with several channels (75, 83) for delivering and diffusing a fluid such as acid gases in two-phase compression device (10), said two-phase compression stage allowing stage d) to be carried out.
6. A two-phase compression device as claimed in claim 5, characterized in that two-phase compression device (10) comprises a pumping stage arranged upstream from said second diffuser, said pumping stage allowing to pump said aqueous phase from stage a) and said element allowing to feed said acid gases produced in stage b) into two-phase compression device (10).
7. A two-phase compression device as claimed in claim 5, characterized in that two-phase compression device (10) comprises a second two-phase compression stage arranged upstream from the second diffuser, said second two-phase compression stage allowing stage d) to be carried out, said element allowing to feed a liquid or gaseous fluid into the two-phase compression device.

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