EP0549440B1 - Method of optimisation of a device for regulating and dampening of a polyphasic flow and device obtained by this method - Google Patents

Description

The subject of the present invention is a method for optimizing the characteristics of a device for regulating and damping the composition fluctuations of a multiphase flow, as well as a device optimized by this method.

The device can in particular be installed between a source of effluents and the inlet of a multiphase type pump making it possible to transfer a fluid composed of at least one liquid phase and at least one gaseous phase.

The invention finds its applications in particular in the field of the production of hydrocarbons comprising a gas-liquid mixture, this production being able to be carried out in an environment of difficult access, for example at the level of a wellhead or a submarine transfer line, or in the virgin forest.

The invention also applies to the chemical and petroleum industry, or generally to all industries employing multiphase fluids.

The invention finds its application in particular to conserve a minimum quantity of liquid to maintain the pumping means in correct operation.

It is known that the routing of fluids or effluents of the multiphase type composed of at least one liquid phase and at least one gaseous phase requires the use of a system to regulate the composition of the fluid placed at the inlet of a pump. and making it possible to deliver to the latter a fluid whose value of the volumetric ratio of gas to liquid, for short, GLR (Gas Liquid Ratio) is compatible with the operating characteristics necessary for the transfer of effluents.

In the present text, in the absence of any contrary specification, the terms upstream and downstream refer to the pump by considering the direction of flow of the effluents.

French Patent No. 2,642,539 describes a device which makes it possible to dampen and regulate the sudden variations of liquid and gas arriving in the device, in particular, during the arrival gas or liquid plugs, that is to say a large amount of fluid composed solely of the gas phase or the liquid phase. This device comprises a reservoir or buffer tank equipped with a sampling tube extending over a certain height of the reservoir, this tube being pierced with orifices or sampling openings. The device placed at the inlet of a pump thus makes it possible to deliver to the pump a multiphase fluid having characteristics, in particular of volumetric ratio gas phase / liquid phase, compatible with the operation of the pump.

The known prior art does not however make it possible to predict the size and structure of a device such on the one hand that there is a quantity of liquid always sufficient to evacuate at any time a pocket of gas or quantity of important gas and that an optimal GLR value is maintained as a function of the characteristics of the multiphase pump located downstream so that it can apply to the effluents to be transferred sufficient compression.

We are thus obliged to change the device as a function of the evolution over time of the composition of the fluid coming from a source of effluents as occurs, for example, during the period of activity of the oil wells, which results in significant operating losses.

The invention remedies these drawbacks in particular by proposing a method making it possible to pre-size a regulation device, comprising a reservoir and a sampling tube, as a function of the composition of the source of effluents to which it is connected and the characteristics of a multiphase pump located after the device, so as to have a fluid whose GLR value allows the pump to ensure sufficient compression to transfer the effluents and that the amount of liquid located in the device allows the evacuation of any amount of foreseeable gas likely to arrive in the tank.

The tube crosses the gas / liquid interface under normal operating conditions. Thus in the case of a straight cylindrical tube it can be vertical or inclined but not horizontal.

Throughout the text, for example, by the word density of the orifices per tube area, the number of orifices uniformly distributed over the same area is defined.

The method according to the invention makes it possible to optimize the characteristics of a device for regulating and damping the fluctuations in composition of a multiphase flow comprising at least one liquid phase and at least one gaseous phase and the volumetric ratio of the gas to the liquid (GLR) is likely to vary within a defined range around an average value, the device being positioned between a source of effluents and a multiphase pump communicating to the effluents a compression value necessary for the transfer of the effluents and consisting of 'a reservoir or buffer tank for receiving said multiphase flow, which is equipped with at least one sampling tube pierced with sampling holes.

• a) en fonction de la composition de l'écoulement, de la pression régnant dans le réservoir ou ballon tampon, de la température de fonctionnement du réservoir, de la valeur maximale du rapport volumétrique et d'un niveau de la phase liquide prédéfini correspondant à cette valeur maximale, on détermine la valeur du rapport des sections de passage respectives offertes au gaz et au liquide, puis on choisit en fonction dudit rapport une répartition des orifices le long du tube de prélèvement ladite répartition se faisant par zones, et
• b) on se fixe une valeur limite maximale pour ledit volume de phase gazeuse susceptible d'arriver dans le réservoir, on détermine alors le niveau de liquide correspondant à cette valeur limite, on vérifie que ce niveau de liquide est sensiblement le même que celui correspondant à la valeur moyenne du rapport volumétrique, et l'on change si nécessaire au moins un des deux paramètres suivants : le volume du réservoir ou la répartition des orifices le long du tube, jusqu'à obtenir une valeur de niveau de liquide correspondant à la valeur moyenne du rapport volumétrique, de façon que le volume de la phase liquide correspondant à ce niveau moyen soit au moins égal au volume de liquide nécessaire à ladite pompe polyphasique pour évacuer du réservoir tout volume de phase prévisible gazeuse issu de la source d'effluents arrivant dans le réservoir.

The method is characterized in that the level of the liquid-gas interface is stabilized substantially at a defined average level by selecting the volume of the reservoir and the distribution of the sampling orifices which are themselves determined for example by a following sequence of steps:

• a) as a function of the composition of the flow, of the pressure prevailing in the tank or buffer tank, of the operating temperature of the tank, of the maximum value of the volumetric ratio and of a level of the predefined liquid phase corresponding to this maximum value, the value of the ratio of the respective passage sections offered to the gas and the liquid is determined, then a distribution of the orifices along the sampling tube is chosen as a function of said ratio, said distribution being done by zones, and
• b) a maximum limit value is set for said volume of gaseous phase capable of arriving in the reservoir, the level of liquid corresponding to this limit value is then determined, it is checked that this level of liquid is substantially the same as that corresponding to the mean value of the volumetric ratio, and at least one of the following two parameters is changed if necessary: the volume of the reservoir or the distribution of the orifices along the tube, until a liquid level value corresponding to the average value of the volumetric ratio, so that the volume of the liquid phase corresponding to this average level is at least equal to the volume of liquid necessary for said multiphase pump to evacuate from the reservoir any volume of predictable gaseous phase originating from the source of effluents arriving in the tank.

The volume of the liquid phase corresponding to the average level can be equal to the volume of liquid necessary for the multiphase pump to evacuate from the reservoir any volume of gaseous phase originating from the source considered likely to arrive in the reservoir or buffer tank while maintaining the ratio volumetric of the effluents admitted into the pump above a threshold determined so as to allow the application to compression of the effluents.

We divide, for example, at least a portion of the length of the tube into several zones each provided with a specific density of orifices and we choose for each zone a density of orifices which can vary between 0 and a defined limit value by the size and shape of the orifices.

The cross-section of the pierced tube is increased by a value equal to a value equal to the increase in surface area of the gas-liquid mixture that is desired, and an undrilled tube is introduced into said pierced tube so as to allow the all of the gas that can pass through the orifices to mix with the oil.

The non-drilled tube is introduced so that the lower end of said non-drilled tube opens below the lower end of the drilled tube.

• qu'il y ait à tout instant dans le réservoir au moins une quantité de liquide suffisante permettant l'évacuation de tout volume de gaz prévisible susceptible d'arriver dans le réservoir en maintenant la valeur du rapport volumétrique de l'écoulement polyphasique inférieure à une valeur limite fixée pour que la pompe lui applique ladite compression
• qu'au moins une partie de la longueur du tube comporte plusieurs zones de hauteurs, percées d'orifices, la densité d'orifices de chaque zone étant choisie pour respecter une fonction de répartition hyperbolique de la forme (ah+b)/(ch+d) où h est la hauteur du tube de prélèvement baignant dans le gaz et Hr la hauteur totale du réservoir, les coefficients a, b, c, d dépendant de la hauteur du tube de prélèvement baignant dans le gaz, de la hauteur totale du réservoir, des hauteurs de chacune des zones et de la densité des orifices de chacune des zones, et le volume du réservoir étant déterminé pour que la quantité de gaz évacuée soit sensiblement égale au plus grand volume de gaz prévisible, en modifiant au moins un es paramètres géométriques dudit réservoir jusqu'à ce que la valeur dudit volume de gaz évacué soit sensiblement égal au volume maximal de gaz prévisible.

The method according to the invention can be applied to the manufacture of a device for regulating and damping the composition fluctuations of a multiphase flow optimized by the method, the flow comprising at least one gaseous phase and one liquid phase. , whose volumetric ratio of gas to liquid is likely to vary within a defined range around an average value, said device being positioned between a source of effluents and a multiphase pump communicating to effluents a compression value necessary for the transfer of effluents and comprising a reservoir for receiving said multiphase flow, which is equipped with at least one sampling tube pierced with sampling orifices, device according to which the volume of the reservoir and the distribution of the orifices are chosen for:

• that there is at all times in the reservoir at least a sufficient quantity of liquid allowing the evacuation of any foreseeable volume of gas likely to arrive in the reservoir while maintaining the value of the volumetric ratio of the multiphase flow less than one limit value fixed for the pump to apply said compression to it
• that at least part of the length of the tube has several height zones, pierced with orifices, the density of orifices in each zone being chosen to respect a hyperbolic distribution function of the form (ah + b) / (ch + d) where h is the height of the sampling tube immersed in the gas and Hr the total height of the tank, the coefficients a, b, c, d depending on the height of the sampling tube immersed in the gas, of the total height of the tank, the heights of each of the zones and the density of the orifices in each of the zones, and the volume of the tank being determined so that the quantity of gas evacuated is substantially equal to the largest volume of gas predictable, by modifying at least one of the geometric parameters of said tank until the value of said volume of gas evacuated is substantially equal to the maximum volume of gas predictable.

The device may comprise an unpierced tube placed inside the pierced tube, the lower end of the unpierced tube opening, preferably, below the lower end of the pierced tube.

In a preferred embodiment, the passage section offered to the gas is r times greater than the passage section offered to the liquid, r being a coefficient determined from said fixed limit value.

The tube may include a central zone devoid of orifices around said mean level of the interface.

The density of the holes in the lower zone of the tube is taken equal to 1.

• La figure 1 montre un réservoir équipé d'un tube percé d'orifices;
• La figure 2 montre une courbe qui représente la variation en fonction du temps du niveau de l'interface liquide-gaz dans le réservoir;
• La figure 3 montre une courbe de variation en fonction du temps de la pression Pbt régnant dans le réservoir ou ballon tampon; et
• La figure 4 représente un exemple de distribution des orifices le long du tube.

Other characteristics and advantages of the process and of the reservoirs obtained by the process according to the invention will appear better on reading the description below with reference to the appended figures.

• Figure 1 shows a tank equipped with a tube pierced with orifices;
• FIG. 2 shows a curve which represents the variation as a function of time of the level of the liquid-gas interface in the reservoir;
• FIG. 3 shows a variation curve as a function of time of the pressure Pbt prevailing in the reservoir or buffer tank; and
• FIG. 4 shows an example of the distribution of the orifices along the tube.

The method described below makes it possible to optimize a regulation device, comprising a reservoir or buffer tank and a sampling tube, as a function of fluctuations in composition. of a multiphase fluid, and the characteristics of the pump located downstream.

The optimization carried out by the method will relate to the dimensioning and the arrangement of the elements constituting the reservoir and the definition of a type of drilling, that is to say the distribution of the orifices along the sampling tube. By arrangement of the elements, it is necessary to understand the choice of the various elements constituting the regulation device and their arrangement with respect to each other.

The multiphase fluid is conveyed from the source S, such as an oil well head, for example, by a pipe 1, to the inlet of a device D comprising a reservoir or buffer tank 2 equipped with a tube sampling tube 3. The sampling tube 3 is provided with a plurality of orifices 4 distributed by zones over at least part of its length. The tube can, for example, be subdivided as indicated in FIG. 5 into several zones Z1, Z2 ... Z5 of height H1, H2, ... H5, each zone Zi being provided with a constant density of orifices d1 , ... d5 over its entire length.

The tube 3 is connected to an evacuation tube 5 from the mixture to the pump P. The reference 6 indicates the liquid-gas interface. The tank is equipped with measuring means, such as a temperature sensor 7, a pressure sensor 8 and a level detector 9.

• La première étape est une étape de mesure où l'on définit les paramètres caractéristiques du puits à exploiter tels que la valeur du rapport volumétrique moyen GLR de l'effluent, estimé ou mesuré au départ de l'exploitation du puits, les valeurs des masses volumiques pour le liquide ρ 1 et pour le gaz ρg, et les paramètres propres au réservoir tels que sa température T de fonctionnement mesurée en permanence à l'aide du capteur de température 7, la pression Pbt qui règne dans le réservoir à l'aide du capteur de pression 8, sa hauteur Hr et sa longueur L et la valeur Co du coefficient de perçage du tube ou coefficient hydrodynamique. Le coefficient Co est égal au rapport entre la valeur mesurée du rapport des débits de gaz et de liquide à une pression donnée, pour un niveau d'interface, et la valeur du rapport des sections de passage respectivement offertes en gaz et au liquide pour le même niveau d'interface.
• La compression (ΔP) que la pompe doit appliquer aux effluents pour compenser toutes les pertes de charge en aval étant connue, on détermine d'une manière bien connue des spécialistes, la valeur maximale GLRmax du rapport volumétrique à ne pas dépasser pour maintenir au moins cette compression.

The different stages of the process according to the invention are as follows:

• The first step is a measurement step where the characteristic parameters of the well to be exploited are defined such as the value of the average volumetric ratio GLR of the effluent, estimated or measured at the start of the exploitation of the well, the values of the masses volumes for the liquid ρ 1 and for the gas ρg, and the parameters specific to the tank such as its operating temperature T measured continuously using the temperature sensor 7, the pressure Pbt prevailing in the tank at using the pressure sensor 8, its height Hr and its length L and the value Co of the drilling coefficient of the tube or hydrodynamic coefficient. The coefficient Co is equal to the ratio between the measured value of the ratio of gas and liquid flow rates at a given pressure, for an interface level, and the value of the ratio of the flow sections respectively offered in gas and liquid for the same interface level.
• The compression (ΔP) that the pump must apply to the effluents to compensate for all the pressure losses downstream being known, a maximum value GLRmax of the volumetric ratio not to be exceeded in order to maintain at least this compression.

• Ensuite, on détermine pour le GLRmax le rapport qui doit exister entre la surface de passage offerte au gaz Sg et la surface de passage offerte au liquide S1 au moyen de la fonction : $$\text{Sg/S1 = GLRmax*}\sqrt{\frac{\text{K1 Pbt}}{\text{Co}}}\text{,}$$
  
  K1 étant un coefficient tenant compte de la température de fonctionnement du réservoir, des caractéristiques de l'effluent. On définit ainsi pour le tube le rapport des orifices réservés au passage du gaz et au passage du liquide, ce rapport permet à la pompe d'assurer la valeur de la compression (ΔP) requise.
• Le rapport des surfaces des sections de passage offertes respectivement au gaz et au liquide de chaque côté du niveau de départ Nd ayant été déterminé, on définit alors un perçage du tube en imposant, a priori, la répartition des orifices 4 le long du tube 3. Cette répartition se fait, de préférence, en divisant la longueur du tube de prélèvement 3 en zones, la densité des orifices sur chacune d'elles étant constante.

Then, a priori, a starting level Nd is fixed around which the interface of the gas phase and of the liquid phase must be situated in the reservoir, corresponding to a height of the pierced tube hmax immersed in the gas. This level corresponds to the GLRmax value defined previously.

• Then, for the GLRmax, the ratio which must exist between the passage surface offered to the gas Sg and the passage surface offered to the liquid S1 is determined by means of the function: $$\text{Sg / S1 = GLRmax *}\sqrt{\frac{\text{K1 Pbt}}{\text{Co}}}\text{,}$$
  
  K1 being a coefficient taking into account the operating temperature of the tank, the characteristics of the effluent. The ratio of the orifices reserved for the passage of gas and the passage of liquid is thus defined for the tube, this ratio allows the pump to ensure the required value of compression (ΔP).
• The ratio of the surfaces of the passage sections offered respectively to the gas and to the liquid on each side of the starting level Nd having been determined, a drilling of the tube is then defined by imposing, a priori, the distribution of the orifices 4 along the tube 3 This distribution is preferably done by dividing the length of the sampling tube 3 in zones, the density of the orifices on each of them being constant.

Knowing the distribution of the orifices in each zone along the tube, we can deduce the function f (h, H) characteristic of the bore of the tube and representative of the ratio of the passage section offered to gas and the passage section offered to liquid depending on the height of the pierced tube immersed in the gas. This function can be of the form: (ah + b) / (ch + d) where h is the height of the tube immersed in the gas. In each zone the coefficients a, b, c and d are determined according to the height of the tube immersed in the gas, the total height of the pierced tube H, the height of the zones of the tube and the constant density chosen for each zoned.
- The objective of the next step is to permanently keep in the tank a sufficient quantity of liquid so that the pump can evacuate with the compression value (ΔP) necessary for the transfer of the effluents, the largest quantity of predictable gas from from the source likely to accumulate there. The maximum foreseeable volume of this accumulation of gas is therefore evaluated or estimated beforehand taking into account the source which produces it and the configuration of the pipe 1 between the source S and the reservoir or buffer tank 2.

Likewise, the value of the height of the tube h1 immersed in the gas corresponding to a level N1 is estimated at the start of the evacuation of the largest foreseeable volume of gas. The height of the pierced tube immersed in the gas at the end of the evacuation of the largest foreseeable volume of gas is taken equal to the value hmax defined previously and corresponding to a level Nd. The heights of the part of the tube immersed in the gas are measured or estimated, in our example, from the top of the tank.

The level of liquid corresponding to the volume necessary for the evacuation of the largest foreseeable volume of gas is then determined as follows:

The shape, the size of the reservoir and the function f (h, H) of distribution of the orifices along the drilled tube are taken into account. We deduce, for an increment dh of the height of the tube immersed in the oil, the quantity of evacuated gas, knowing that at any moment the quantity of evacuated gas dVg is equal to the product of an elementary quantity of liquid dV1 by the value the GLR volumetric ratio, which varies with the height h of the tube immersed in the gas, the coefficient C0, the dimensions of the reservoir, the characteristics of the effluent, the pressure and the temperature prevailing in the reservoir. It is quite clear that the elementary quantity of liquid dV1 is, here, the product of the surface of the tank taken at height h by the increment of height dh.

Thus in the case of a cylindrical tank or balloon whose axis is horizontal, we have: $$\begin{gathered} \text{dVg = GLR (h) .d1} \\ \text{= 2.GLR (h) .L.}\sqrt{{\text{<figure-callout id="2" label="H r hh" filenames="imgf0001.png,imgf0002.png" state="{{state}}">H </figure-callout>}}_{\text{r}}{\text{hh}}^{}{}^{\text{2}}}\text{.dh} \end{gathered}$$

By integrating this product between the values h1 and hmax, the quantity of gas Vg evacuated is obtained. We check that the value obtained Vg corresponds to the value of the largest foreseeable volume of gas estimated at the start Vgm and we change, if necessary, at least one of the parameters defining the size of the tank until we obtain a volume of evacuated gas Vg substantially equal to Vgm. The last value obtained for h1 corresponds to the height that one must have at the start of the evacuation of the largest foreseeable volume of gas. This value h1 defines the average level of liquid N1 above which the liquid phase must be located in order to evacuate any foreseeable quantity of gas likely to arrive in the tank.

It is then checked, using the orifice distribution function along the drilled tube that the level N1 previously determined corresponds to the average value of the GLR fixed during the first step.

In the case where the value N1 is different, at least one of the following parameters is modified: the volume of the reservoir, by touching either its height H _r , its length L or both, or the distribution of the sampling orifices along the tube until a value is obtained for the level N1 corresponding to the average value of the GLR fixed during the first step.

The volume of the reservoir and the distribution of the orifices along the sampling tube are thus determined by zone of constant orifice density so that the liquid-gas interface is stabilized in normal operation substantially at the average level corresponding to the average value of the average volume ratio GLR. This ensures a sufficient reserve in the tank to evacuate any significant amount of foreseeable gas likely to arrive in the tank.

This procedure also makes it possible to have a GLRmax value so that the pump applies to the effluents a compression (ΔP) necessary for the transfer of the effluents.

The method for predimensioning a tank and its associated sampling tube, described above, is well suited when the maximum foreseeable quantity of gas estimated at the start Vgm is small. In the case where the foreseeable volume of gas to be transferred is large, experience has shown that the quantity of gas mixing with the oil in the drilled tube is less than the quantity which should theoretically mix, this quantity being a function of the number of holes drilled in the gas tube. To overcome this drawback, it has been observed that by dividing the flow of gas entering the tube so that the gas-liquid mixture is carried out at different places in the tube, the quantity of gas mixing with the oil is increased.

The gas flow is divided by introducing inside the pierced tube 3 an additional tube 10 (Fig. 2) of diameter smaller than the pierced tube and the length of which is such that the end bottom of this tube arrives in the sampling line so that the mixture of gas escaping through the lower end of the additional tube with the fluid in this part of the sampling tube takes place at a place for which the pressure is lower than the pressure in the part of the drilled tube containing only gas. In this way, the gas mixes both in the annular between the pierced tube and the non-pierced tube and at a location located near the bottom of the non-pierced tube. The surface area of the gas-liquid mixture has thus been increased and, in fact, a possible phenomenon of "saturation" has been prevented, that is to say any phenomenon which prevents all of the gas from mixing with the liquid in the drilled tube.

• on élargit la section du tube percé précédemment défini d'une valeur égale à l'augmentation de surface d'échange entre le gaz et le liquide que l'on veut obtenir,
• on introduit un tube, de préférence non percé à l'intérieur du tube percé, la section dudit tube étant égale à l'augmentation nécessaire pour la surface d'échange, ce qui permet de diviser le flux de gaz.

The method described above includes the following additional steps:

• the section of the previously defined pierced tube is enlarged by a value equal to the increase in the exchange surface between the gas and the liquid which it is desired to obtain,
• a tube, preferably not drilled, is introduced inside the drilled tube, the section of said tube being equal to the increase necessary for the exchange surface, which makes it possible to divide the gas flow.

The value of the increase in exchange surface is defined as a function of the maximum foreseeable quantity of gas. Tests carried out beforehand make it possible to trace an abacus which gives, as a function of the maximum foreseeable quantity of gas, the section of the non-pierced tube which must be inserted into the pierced tube so that the mixture of gas in the liquid do it optimally.

Figures 3 and 4 show curves recorded during on-site tests using a multiphase type pump such as that described in patent application FR.90 / 09.607, associated with an optimized reservoir and sampling tube. The curve I1 (Fig. 3) represents, the variation of the level of the interface N as a function of time, the value of the height hg1 corresponds to the height of the tube immersed in the gas at the start of the evacuation of a quantity of gas and the value hg2 represents the height of the pierced tube immersed in the gas at the end of the evacuation of the quantity of gas.

The curve I2 (Fig. 4) represents the variation as a function of time of the value of the pressure Pbt prevailing in the tank 2.

The tube shown in FIG. 5, by way of example, comprises five zones Z1-Z5 having densities of orifices respectively d1 = 7, d2 = 6, d3 = 0, d4 = 2 and d5 = 1.

These values correspond to an optimized tube installed on site during tests carried out with a pump such as that described in the aforementioned application FR 90 / 09.607.

The area around the average value does not have any openings so as not to reflect variations in GLR until the level of the liquid-gas interface has shifted by a certain value until it reaches an adjacent zone Z2 or Z4.

This exemplary embodiment is in no way limiting, the sampling orifices being able to have a shape other than the circular shape. One can thus envisage any other form such as for example the forms described in the French patent FR 2,642,539 cited above.

Of course, various modifications and / or additions can be made to the process, the description of which has just been given by way of illustration and in no way limitative, without departing from the scope of the invention, as defined in the claims below.

Claims (10)

1. Method for optimising the characteristics of a device for regulating and damping fluctuations in the composition of a multi-phase flow consisting of at least one liquid phase and at least one gaseous phase and whose gas/liquid ratio (GLR) is likely to vary around an average value within a defined range, the said device being positioned between an effluent source (S) and a multi-phase pump (P) transmitting to the effluent a compression value (ΔP) needed to convey the effluent and consisting of a tank or buffer tank (2) to receive the said multi-phase flow, which is fitted with at least one drawing-off tube (3) pierced with drawing-off orifices (4), the said method being characterised in that the level of the liquid-gas interface (6) is stabilised essentially at an average level defined by selecting the volume of the tank and the distribution of the drawing-off orifices which are themselves determined by a succession of steps as follows:

   a) the value of the ratio of the respective passage sections to be provided for the gas and liquid are determined on the basis of the composition of the flow, the pressure prevailing in the tank or buffer tank, the operating temperature of the tank, the value of the maximum volumetric ratio (GLRmax) and a pre-defined level of the liquid phase (Nd) corresponding to this maximum value (GLRmax), after which an orifice distribution along the length of the drawing-off tube is chosen, the said distribution being arranged by zones, and

   b) a maximum limit value is set for the said volume of gaseous phase likely to flow into the tank, after which the level of liquid (Nl) corresponding to this limit value is determined and a check carried out to ensure that this level of liquid is essentially the same as that corresponding to the average value of the volumetric ratio (GLR) and, if necessary, at least one of the following two parameters is changed : the volume of the tank or the distribution of orifices along the tube, until a value corresponding to the average value of the volumetric ratio has been obtained for the level of liquid (N1) so that the volume of liquid phase corresponding to this average level is at least equal to the volume of liquid required by the said multi-phase pump to empty entirely from the tank the foreseeable volume of gaseous phase flowing into the tank from the effluent source.
2. Method as claimed in claim 1, characterised in that the volume of the liquid phase corresponding to the average level is equal to the volume of liquid needed by the said multi-phase pump to empty from the tank entirely the volume of gaseous phase likely to flow from the source in question into the tank or buffer tank whilst keeping the volumetric ratio of the effluent admitted into the pump below a determined threshold (GLRmax) so that the said compression (ΔP) can be applied to the effluent.
3. Method as claimed in claim 1, characterised in that at least a portion of the tube is divided into several zones (Z1-Z5), each of which is given a specific orifice density (d1-d5), and an orifice density that may vary between 0 and a limit value defined by the size and shape of the orifices is selected for each zone.
4. Method as claimed in one of claims 1 or 3, characterised in that the section of the pierced tube is increased by a value equal to a value equating to the desired increase in the surface of the gas-liquid mixture and an unpierced tube (10) is inserted inside the said pierced tube so as to allow all of the gas that might pass through the orifices to mix with the oil.
5. Method as claimed in claim 4, characterised in that the unpierced tube (10) is inserted in such a way that the lower end of the unpierced tube opens below the lower end of the pierced tube.
6. Device for regulating and damping fluctuations in the composition of a multi-phase flow optimised by the method defined in one of the preceding claims, the said flow consisting of at least one gaseous phase and one liquid phase whose volumetric ratio of gas to liquid is likely to vary around an average value within a defined range, the said device being positioned between an effluent source (5) and a multi-phase pump (P) transmitting to the effluent a compression value (ΔP) required to convey the effluent and comprising a tank (2) to receive the said multi-phase flow fitted with at least one drawing-off tube (3) pierced with drawing-off orifices (4), in which the volume of the tank and the distribution of orifices of the device are chosen so that :

   - there is at least a sufficient quantity of liquid in the tank at any instant to enable the foreseeable volume of gas (Vg) likely to flow into the tank to be emptied whilst keeping the value of the volumetric ratio of the multi-phase flow below a fixed limit value (GLRmax) so that the pump applies thereto the said compression (ΔP)

   - at least a portion of the length of the tube has several zones (Z) of heights (Hi) pierced with orifices, the orifice density (di) of each zone being selected so as to comply with a hyperbolic distribution function in the form (ah+b)/(ch+d) where h is the height of the drawing-off tube submersed in the gas and Hr is the overall height of the tank, the coefficients a, b, c, d being dependent on the height of the drawing-off tube submersed in the gas (h), the overall height of the tank (H_r), the heights (Hi) of each of the zones (Zi) and the orifice density (di) of each of the zones, and

   the volume of the tank is determined so that the quantity of gas emptied is essentially equal to the largest foreseeable volume of gas Vgm by modifying at least one of the geometric parameters of the said tank until the value of the said volume of gas discharged Vg is essentially equal to the maximum foreseeable volume of gas Vgm.
7. Device as claimed in claim 6, characterised in that it has an unpierced tube (10) inserted inside the pierced tube (3), the lower end of the unpierced tube opening by preference below the lower end of the pierced tube.
8. Device as claimed in claim 6, characterised in that the passage section provided for the gas is r times greater than the passage section provided for the liquid, r being a coefficient determined on the basis of the said fixed limit value (GLRmax).
9. Device as claimed in claim 6, characterised in that the tube has a central zone with no orifices around the said average level of the interface (6).
10. Device as claimed in claim 6, characterised in that the orifice density of the lower zone of the tube is taken as being equal to 1.

Images