FR3088118A1 - SYSTEM AND METHOD FOR TRACKING ION SPECIES BY MULTIPLE ELECTRICAL MEASUREMENTS - Google Patents

Abstract

The present invention relates to a system and a method for measuring at least one flow property of at least one fluid within a porous medium, contained in a cell 4. The system and the method are based on at least three electrical measurements 5, 6, 7, a first measurement 5 in line upstream of the porous medium, a second electrical measurement 7 in derivation of the porous medium and a third electrical measurement 6 downstream of the porous medium. Therefore, the flow properties are determined precisely and reliably, especially when the sample of the porous medium is small.

Description

Description

Title: System and method for tracing ionic species by multiple electrical measurements Technical field

The present invention relates to the field of measurements of flow properties of a fluid in a porous medium, in particular a porous medium originating from an underground formation. The measurements can be used in particular for tracing ionic species, in particular during the exploration and exploitation of hydrocarbon wells, and particularly for the enhanced recovery of hydrocarbons (EOR: from the English Enhanced Oil Recovery) . By tracing of ionic species is meant the displacement of ionic species (ions, charged molecules for example) in the porous medium.

It is estimated today that for all active oil tanks, 60% -65% of the oil in place remains trapped. Different mechanisms are behind this trapping. For example, geological heterogeneity generates an inhomogeneous displacement of the oil across the reservoir. But even on a local scale, the presence of an interfacial tension between water and oil leads to capillary trapping of the oil phase in the center of the pores in the case of rocks wettable with water. This trapping can represent up to 50% of the oil in place. Water-wettable tanks make up roughly half of the world's tanks.

Consequently, mobilizing the residual oil contained in the matrix under conditions of preferable wettability with water is a real challenge. However, the use of surfactants injected in the aqueous phase can allow a very significant reduction in capillary trapping. Surfactants have the property of being able to significantly lower this tension or even almost cancel it. The use of surfactant additives was successfully tested on sandstones in the 1980s and is experiencing a renewed interest. The processes of enhanced recovery of petroleum (hydrocarbons) by injection of surfactant represent a great potential because they make it possible to trap a large quantity of oil blocked in the pores of the rock.

Furthermore, in other technical fields, it may be advantageous to quickly characterize the flow of a fluid within a porous medium, in particular a porous medium formed by a polymer.

Prior art

To characterize capillary trapping, it is necessary to carry out measurements of the relative properties of the flow of fluids in the porous medium.

Measurement systems and methods based on X-ray radiographs to determine the saturation of a fluid have been developed (patent application FR 3 047 315 / WO 17 12 93 12 for example) in order to characterize the trapping. However, these methods are not applicable when the concentration of ionic species or the atomic number of these ionic species does not allow monitoring by X-rays.

The invention relates to a system for measuring at least one flow property of at least one fluid within a porous medium. The measurement system comprises at least one cell containing the porous medium, injection means for injecting the fluid into the cell, electrical measurement means and an analysis means characterizing the flow properties. The measurement system comprises at least three electrical measurement means, at least one first electrical measurement means being positioned between the injection means and the inlet of the cell, at least one second electrical measurement means being positioned as a bypass of the cell, and at least a third electrical measurement means being positioned substantially at the outlet of the cell. The system allows the measurement of flow properties when X-ray measurement is not possible and it improves the accuracy of these properties when they can also be measured by X-rays.

The invention also relates to a measurement method, in which the following steps are carried out using the measurement system according to one of the preceding characteristics:

a) At least one fluid is injected into the porous medium;

b) At least three electrical measurements are carried out simultaneously, at least one first electrical measurement being located upstream of the porous medium, at least one second electrical measurement being located downstream of the porous medium and at least one third electrical measurement was located in derivation of the porous medium;

c) The injection of the fluid into the porous medium is simulated numerically using the input data of the first electrical measurement and the simulations of the second and third electrical measurements are determined;

d) By comparison of the second and third electrical measurements carried out and digital simulations of the second and third electrical measurements and setting of the parameters, flow properties of the fluid in the porous medium are determined.

This method allows the measurement of flow properties when X-ray measurement is not possible and it improves the accuracy of these properties when they can also be measured by X-rays.

Summary of the invention

The invention relates to a system for measuring at least one flowing property of at least one fluid within a porous medium, said measuring system comprising at least one cell containing said porous medium, injection means. of fluid in said cell, electrical measurement means and analysis means characterizing said flow property. The measurement system comprises at least three electrical measurement means, at least one first electrical measurement means being positioned between said injection means and the inlet of said cell, at least one second electrical measurement means being positioned as a bypass of said cell, and at least a third electrical measurement means being positioned substantially at said outlet from said cell.

Preferably, said injection means comprise a plurality of fluids to be injected into said cell, simultaneously or sequentially.

Advantageously, the fluids of said plurality of fluids have different electrical conductivities.

Advantageously, the fluids of said plurality of fluids have concentrations of different ionic species.

According to one embodiment of the invention, said measurement system includes means for controlling said injection means.

According to a variant of the invention, said cell has a substantially cylindrical shape.

Preferably, the diameter of said cell is substantially between 2 mm and 20 mm, preferably between 5 mm and 10 mm.

Advantageously, the height of said cell is substantially between 2 mm and 5 cm, preferably between 5 mm and 2 cm.

According to a variant of the invention, said fluid is chosen from an aqueous phase and an oil phase.

According to one embodiment, at least one aqueous phase comprises at least one additive, preferably a surfactant.

Preferably, said electrical measurements are acquired simultaneously and collected in acquisition software.

According to one embodiment, the measurement system comprises at least one X-ray radiography means comprising a source and a detector, said porous medium being positioned between said source and said detector, said source, said porous medium and said detector being substantially aligned, said analysis means characterizing said flow property of said fluid within the porous medium by radiographs obtained by said X-ray radiography means.

The invention also relates to a method for measuring at least one flow property of at least one fluid within a porous medium, in which the following steps are carried out using the measuring system according to one of the previous characteristics:

a) said at least one fluid is injected into said porous medium;

b) At least three electrical measurements are carried out simultaneously, at least one first electrical measurement being located upstream of said porous medium, at least one second electrical measurement being located downstream of said porous medium and at least one third electrical measurement was located in derivation of the porous medium;

c) The injection of said at least one fluid into said porous medium is simulated numerically using the input data of said first electrical measurement and the simulations of said at least second and third electrical measurements are determined;

d) By comparison of said second and third electrical measurements carried out and of said digital simulations of said second and third electrical measurements and setting of the parameters, flow properties of said at least one fluid are determined in said porous medium.

According to a variant, beforehand, a calibration step is carried out, said calibration step comprising the steps of the method according to the preceding characteristic where said porous medium is replaced by a connecting tube.

Advantageously, the properties determined in the calibration step are the dead volumes, located upstream and downstream of the connecting tube.

Preferably, said flow properties are chosen from the volumes and dispersivities of the different zones, upstream of said porous medium, downstream of said porous medium and within the porous medium.

Advantageously, the injection of the fluid into the porous medium is controlled in real time during the measurements.

According to an embodiment of the invention, an x-ray radiography of the porous medium is carried out simultaneously with the electrical measurements.

Preferably, said flow properties are determined by comparison of the changes in profile and / or time shift of the electrical signal obtained by said electrical measurements, during the transient regime linked to the injection of said fluid into the porous medium.

List of figures [Fig 1]

FIG. 1 represents an embodiment of a system for measuring a flow property of at least one fluid within a porous medium according to the invention.

[Fig 2]

FIG. 2 represents the temporal evolution of the electrical measurements of the system during the transient phase of injection of the fluid according to the invention.

[Fig 3a]

FIG. 3a represents the comparison between the measurement carried out and the digital simulation at the level of the electrical measurement situated in bypass of the porous medium, during the calibration step according to the invention.

[Fig 3b]

FIG. 3b represents the comparison between the measurement carried out and the digital simulation at the level of the electrical measurement located downstream of the porous medium during the calibration step according to the invention.

[Fig 4]

FIG. 4 represents the temporal correction of the signal of the electrical measurement downstream of the porous medium, according to the invention.

[Fig 5a]

FIG. 5a represents the comparison between the measurement carried out and the digital simulation at the level of the electrical measurement situated downstream of the porous medium, in the case where only the electrical measurement situated downstream is available (prior art), with the volume data porous medium and dispersivity obtained by the method according to the invention.

[Fig 5b]

FIG. 5b represents the comparison between the measurement carried out and the numerical simulation at the level of the electrical measurement situated downstream of the porous medium, in the case where only the electrical measurement situated downstream is available (prior art), with a calibration of volume porous medium and dispersivity suitable for this case.

[Fig 6a]

FIG. 6a represents the comparison between the measurement carried out and the numerical simulation at the level of the electrical measurement situated in diversion from the porous medium, for the determination of the characteristics of the porous medium, according to the invention.

[Fig 6b]

FIG. 6b represents the comparison between the measurement carried out and the digital simulation at the level of the electrical measurement located downstream of the porous medium for the determination of the characteristics of the porous medium, according to the invention.

Description of the embodiments

The invention relates to a system for measuring at least one flow property of at least one fluid within a porous medium. By flow property is meant, for example, a saturation of the porous medium with a fluid, saturation which may be global in the porous medium or, on the contrary, localized at a particular location in the porous medium.

The porous medium can be, for example, an element of rocky medium resulting from an underground formation (rock sample from an oil reservoir for example), or a porous polymer type material, or any similar material.

The measurement system comprises at least one cell containing the porous medium, means for injecting fluid into the cell, electrical measurement means and an analysis means characterizing the flow property. In fact, the cell is used to integrate the porous medium into the measurement device. The means for injecting fluid into the cell allow the injection of fluid into the cell and therefore into the porous medium. The electrical measurement means allow electrical measurements at different measurement points of the system. These electrical measurements are then used by the analysis means which processes the electrical measurements to characterize the flow property of the fluid within the porous medium.

In addition, the measurement system comprises at least three electrical measurement means, at least one first measurement means being positioned between the injection means and the inlet of the cell, at least one second electrical measurement means being positioned in bypass of the cell and at least a third electrical measurement means being positioned substantially at the outlet of the cell.

The first and third electrical measurement means are so-called "online" measurement means, that is to say which are integrated directly into the experimental device where the fluids circulate. They measure an electrical voltage between two close measurement points on this line, allowing to have a local measurement. The second measurement means is a so-called “bypass” measurement means for which a voltage is measured across the terminals of the cell, which makes it possible to evaluate a larger volume, in this case, that of the cell and of the medium. porous it contains.

By these three electrical measurements, we can characterize the evolution of the system signal:

- between the point of injection of fluids (at the level of the means of injecting fluids) and the entry of the cell,

- between the terminals of the cell (that is to say between the input and the output of the cell),

- between the cell output and the electrical output measurement.

The system is thus particularly advantageous for following in real time and in a precise manner the displacement of ionic species in the porous medium, and in particular when the concentration or the atomic number of the charged ions or molecules does not make it possible to have a contrast of sufficient X-ray attenuation (several gray levels) to perform precise X-ray tracking.

Indeed, the electrical measurement, after calibration, makes it possible to calculate the concentration of ionic species. By ionic species is meant ions or charged molecules for example. The study of the transport of an ionic species is therefore made by injecting into the porous medium fluids having different electrical conductivities, for example water having a different salinity than that initially present in the porous medium. The injection of a different fluid therefore makes it possible to impose a variation in the electrical conductivity at the inlet of the porous medium. The transport of chemical species being strongly impacted by the geometry of the porous medium, the signal imposed on the input will be distorted during its circulation in the system and in particular within the porous medium. The signal imposed on the input can be for example a Dirac, a ramp or any other profile. The monitoring of the signal at different measurement points of the assembly therefore makes it possible to characterize different properties of the porous medium affecting the transport of ionic species, such as the volume of the porous space crossed, its dispersivity (characterizing the diffusion of chemical species) or else the retention capacity (adsorption, trapping ...) of ionic species.

The study of the evolution of the signal, in particular by the analysis of the delay of the signal on the one hand and by the distortion of the signal on the other hand, makes it possible to characterize the dead volumes and the dispersivities or the capacities of retention of the porous medium such as adsorption or trapping, for example. This characterization can be made for different zones of the system, namely the zones being a first zone situated between the injection means and the inlet of the cell, a second zone constituted by the porous medium within the cell and a third zone located between the cell outlet and the measurement point of the third electrical measurement. Each of these zones is assigned a volume and a dispersivity (and possibly a retention capacity), the dispersivity being the capacity of the fluid (and of the ionic species which it contains) to move in the zone considered. More specifically, the signal delay reflects a volume, the signal distortion reflects a dispersivity and the relative delay between two ionic species (one of which is said to be passive or with very low retention) reflects a retention capacity.

For example, Figure 1 shows an embodiment of the system according to the invention. Cell 4 contains a porous medium such as a rock sample from an oil reservoir. The system includes two electrical measurements in lines 5 and 6 and an electrical measurement in bypass 7. The system allows the injection of several fluids A, B, C, D, E by injection means (not shown). The fluids are then mixed through the mixing means 15 in order to have a stable and known composition in order to effect the introduction of the mixture of fluid into the cell 4. In the example of FIG. 1, the injection of fluid is done, at the level of the mixing means 15 by a Dirac type signal, and the evolution of this signal is observed at the various electrical measurement points corresponding to the electrical measurement means 5, 6 and 7. On the one hand, we observe , that the delay of the signal increases when one moves away from the mixing means 15 and on the other hand, that the distortion of the signal, compared to the initial Dirac signal, also increases when one moves away from the mixing means 15. In this case, the distortion of the signal is reflected in particular by the evolution of the slope (the Dirac has a vertical slope and the angle of the slope with respect to the vertical tends to increase when one moves away from the means of mixed). The example in FIG. 1 relates to an input signal of the Dirac type but other signals could be envisaged whose deformation evolutions could be different and to be interpreted as a function of the input signal.

The identification of the volumes and dispersivities of the different zones, by the three electrical measurements 5, 6 and 7 mentioned makes it possible to take into account the impact of the fluid flow zones located upstream and downstream of the cell 4 and thus to gain precision on the characteristics of the porous medium.

It is necessary to also take into account the signal actually imposed and not the theoretical signal which can represent a significant source of error.

In addition, another approximation relates to the form of the disturbance imposed by the means for mixing fluids. The values of imposed flows (often by numerical controls) are really reached with a certain inertia, so that it is impossible to pass from a value A to B instantaneously, without passing by intermediate values. This means that a signal, for example from Dirac requested by the user, is really not a perfect Dirac but a Dirac slightly distorted by the inertia of the control means. If the disturbance is imposed by varying a ratio between two injected fluids, the mixing point between these two fluids can result in a heterogeneous mixture and therefore lead to a poor interpretation of the results. The first electrical measurement notably allows to know the real profile of the input signal which differs slightly from the theoretical Dirac.

The means of analysis allows the determination of the properties of the system (volumes, dispersivities, adsorption for example) by comparison of the electrical measurements carried out compared to the electrical measurement signals obtained with digital simulations of the transport of fluids in the system. Indeed, by calibrating the digital model used for digital simulations, it is possible by comparison of digital and measured signals to determine the properties of the system and thus to characterize the flow properties of the fluid within the porous medium.

The numerical model consists of simulating the transport of ionic species from the first means of electrical measurement to the last. Thus, the measurement given by the first measuring means makes it possible to characterize precisely the form of the disturbance which will be observed with the second and third measuring means. The measurement given by the first measurement means is the signal input data for the digital simulation. All the other measurement points are used to individually characterize as many different elements of the assembly. For example, for a system with two other measurement points, one of which is bypassed on the injection cell and the other at the output of the system, the measurements from the second and third measurement means are used for setting the parameters of the model and deduce the flow properties of the fluid in the porous medium.

Preferably, the injection means can comprise a plurality of fluids to be injected into the cell, simultaneously or sequentially. Therefore, the characteristics of the porous medium can be known more precisely. In addition, the injection flow properties of several fluids simultaneously within the porous medium can also be determined. In the event of sequential injection of fluid, one can evaluate the flow properties of a fluid, after the injection of another fluid, which is often necessary to determine the curves of saturation of fluid at the injection of another fluid in a porous medium. Sequential injection also allows automatic injection sequences which accelerate the test phases and thus obtain results more quickly.

Preferably, the system can comprise a means for mixing fluid to allow the simultaneous injection of several fluids, after a preliminary mixing allowing a stable composition of the mixture of these fluids, for a more in-depth study of the behavior of the porous medium.

Advantageously, the fluids of the plurality of fluids can have different electrical conductivities. Thus, the monitoring of each of the fluids in the porous medium is facilitated and the distinction of the electrical conductivities between the different fluids makes it possible to improve the accuracy of the characteristics expected of the porous medium.

According to an implementation of the system according to the invention, the fluids of the plurality of fluids can have concentrations of different ionic species. Thus, the electrical conductivity of each of the fluids is different. Thus, the monitoring of each of the fluids in the porous medium is facilitated and the distinction of the concentrations of ionic species between the different fluids makes it possible to improve the accuracy of the characteristics expected of the porous medium.

According to one embodiment of the invention, the measurement system may include means for controlling the injection means. Thus, the fluid injection profile can be controlled and its monitoring can therefore be more easily established. This makes it possible to establish injection profiles which facilitate the monitoring and interpretation of the evolution of the curves.

Advantageously, the cell can have a substantially cylindrical shape. Therefore, the flow of fluid in the cell, and therefore in the porous medium, is not disturbed by variations in shape. This allows a homogeneous distribution of the fluid over the section of passage of the fluid in the cell and in the porous medium.

Advantageously, the diameter of the cell can be substantially between 2 and 20mm, preferably between 5mm and 10mm. Indeed, the miniaturization of the cell is made possible by the characterization of the saturation in fluid by means of at least three electrical measurements. Furthermore, the use of a small cell and therefore of a small porous medium sample makes it possible to speed up the time for testing and analysis. Thus, we can obtain results more quickly and / or test more configurations. In addition, the use of the system comprising at least three electrical measurements with a miniaturized porous medium is particularly relevant. Indeed, by using a small porous medium, the influence of dead volumes upstream and downstream of the cell, that is to say respectively the volume located between the first electrical measuring means and the input of the cell and the volume located between the cell outlet and the third measurement means can be significant and significantly disturb the analysis of the results. In the case of miniaturization, it is important to precisely determine these volumes, which the system allows thanks to at least three electrical measurements, a first electrical measurement being located between the mixing means and the inlet of the cell, a second measurement electric being located in derivation of the cell and a third measurement being located downstream of the cell output. Thus, the system according to the invention allows good accuracy when using small samples.

According to a variant, the height of the cell can be substantially between 2 mm and 5 cm, preferably between 5 mm and 2 cm. Indeed, the miniaturization of the cell is made possible by the characterization of the saturation in fluid by means of at least three electrical measurements. In addition, the use of a cell and therefore of a sample of small porous medium makes it possible to speed up the time for testing and analysis. Thus, we can obtain results more quickly and / or test more configurations. In addition, the use of the system comprising at least three electrical measurements with a miniaturized porous medium is particularly relevant. Indeed, using a small porous medium, the influence of the dead volumes upstream and downstream of the cell, that is to say respectively the volume located between the first electrical measuring means and the input of the cell and the volume located between the cell outlet and the third measurement means can be significant and significantly disturb the analysis of the results. In the case of miniaturization, it is important to precisely determine these volumes, which the system allows thanks to at least three electrical measurements, a first electrical measurement being located between the mixing means and the inlet of the cell, a second measurement electric being located in derivation of the cell and a third measurement being located downstream of the cell output. Thus, the system according to the invention allows good accuracy when using a small sample.

According to one embodiment of the invention, the fluid can be chosen from an aqueous phase and an oil phase. Thus, it is particularly suitable for EOR applications.

According to an implementation of the invention, at least one aqueous phase can comprise at least one additive, preferably a surfactant. Indeed, the surfactant is particularly interesting for increasing the yields of oils produced in petroleum tanks.

Preferably, the electrical measurements can be continuously acquired simultaneously and collected in an acquisition means (computer memory for example). Thus, the simultaneous acquisition allows a direct and precise comparison of the curves obtained on the different measurement points, and allows a precise definition of the delay. In addition, the electrical measurements are collected in an acquisition means which makes it possible to recover them if necessary at a later time. The acquisition means is also useful for transmitting information to the digital model, either as input data, via the first electrical measurement, or as comparison of output data, with regard to the second and third electrical measurements.

According to a variant of the system according to the invention, the measurement system can comprise at least one X-ray radiography means, the X-ray radiography means comprising a source and a detector. The porous medium can be positioned between the source and the detector so that the source, the porous medium and the detector are substantially aligned. The analysis means characterizes the property of flow of the fluid within the porous medium by radiographs obtained by means of X-ray radiographs. Thus, the combination of electrical measurements and radiographs makes it possible to increase the accuracy of the results. and / or to correlate measurements on fluids by X-ray radiography when the conditions of concentration in ionic species or atomic number ie allow (sufficient contrast of attenuation of X-rays), to measurements on fluids where only measurements electrical are possible (concentration in ionic species or atomic number does not allow a sufficient contrast of attenuation of X-rays).

The invention also relates to a method for measuring at least one flow property of at least one fluid within a porous medium in which the following steps are carried out using the measuring system according to one previous characteristics:

a) At least one fluid is injected into the porous medium;

b) At least three electrical measurements are carried out simultaneously, at least one first electrical measurement (M1) being located upstream of said porous medium, at least one second electrical measurement (M2) being located downstream of said porous medium and at least one third measurement electric (M3) was located bypassing the porous medium;

c) The injection of the fluid into the porous medium is simulated numerically using the input data of the first electrical measurement (M1). The first electrical measurement in fact serves as boundary conditions for digital simulation. The digital simulations of the second and third electrical measurements (S2, S3) are then determined by setting parameters (which can be the volume located between the first electrical measurement and the cell input, the volume of the porous medium or the volume located between the output of the cell and the third electrical measurement, the dispersivity and / or adsorption of the zones of each of these volumes);

d) By comparing the second and third electrical measurements carried out (M2, M3) and digital simulations of said second and third electrical measurements (S2, S3) and setting parameters determined in c), flow properties of said at least are determined a fluid in said porous medium. The flow properties can in particular be the dispersivity of the fluid in the porous medium, the adsorption of the fluid in the porous medium or even the volume of the porous medium.

The method according to the invention allows the determination of the flow properties in a precise manner and in particular for fluids whose concentration in ionic species or atomic number does not allow the use of X-ray radiographs. The method allows the monitoring of the ionic species in real time in the porous medium. The use of at least three electrical measurements allows good precision of the values and the comparison of the shapes of the signals and their time offset. The use of digital simulation, by testing different parameters such as volumes, dispersivity and / or adsorption for example, and the comparison of the results from digital simulations (called digital calibration) to the measurements carried out makes it possible to determine the parameters and thus the flow properties of the fluid in the porous medium. The method is particularly interesting for monitoring ionic species during the transient phases of fluid injection into the porous medium. By a transient phase is meant a phase over which the electrical measurement varies significantly over a short period.

According to a variant of the method according to the invention, it is possible, beforehand, to carry out a calibration step, the calibration step comprising the steps of the method defined above where the porous medium is replaced by a connecting tube. By replacing the porous medium with a connecting tube, this calibration step makes it possible to define beforehand the volumes located upstream and downstream of the connecting tube (a fortiori of the cell if necessary) and their dispersivity / adsorption. This step can be carried out only once at the time of commissioning, or at each test launch (to check the absence of significant variation in these parameters), or even regularly, for example, a step of calibration for ten tests with cell, so as to check the absence of significant variation of the parameters without significantly impacting the cost and / or the duration of the tests with cell.

Advantageously, the properties determined in the calibration step can be the dead volumes located upstream and downstream of the connecting tube. These dead volumes are positioned respectively between the first electrical measurement and the inlet of the connecting tube and between the outlet of the connecting tube and the third electrical measurement, the inlet of the connecting tube corresponding to the inlet of the cell and the exit of the connecting tube to that of the cell when the cell replaces the connecting tube. This calibration step is particularly relevant because it allows these volumes to be obtained in a reliable and precise manner. Thus, the results obtained with the cell can be obtained with greater precision thanks to this calibration step.

Advantageously, the flow properties can be chosen from the volumes and dispersivities of the different zones, upstream, downstream of the porous medium and within the porous medium. Indeed, the determination of the volumes and dispersivities of the zones located first between the first electrical measurement and the entry of the cell (therefore of the porous medium), second within the cell itself (therefore of the porous medium) and thirdly between the exit of the cell and the third electrical measurement, makes it possible to precisely define the specific characteristics of the porous medium, without the error which could be inherent in the integration of upstream and downstream zones in the calculation of the properties of the porous medium, error which would exist if at least three electrical measurements were not available.

According to a variant of the method according to the invention, an x-ray radiography of the porous medium can be carried out simultaneously with the electrical measurements. When the concentration of ionic species or the atomic number makes it possible to obtain a sufficient contrast of attenuation of the X-rays, an X-ray radiography can be carried out. Thus, the reliability of the results and their precision are greater. The simultaneous nature of the measurements also allows greater precision in the results.

According to a preferred embodiment of the method according to the invention, the flow properties can be determined by comparison of the changes in profile and / or time shift of the electrical signal obtained by the electrical measurements, during the transient regime linked to the injection of the fluid into the porous medium. Indeed, during the transient phase of the injection of the fluid in the porous medium, the signal of the transient phase of the electrical measurement is shifted in time, as a function of the advancement of the fluid. The delay thus observed on the second and third electrical measurements compared to the first electrical measurement gives indications on the volumes of the different zones, also dependent on the injection rate.

Furthermore, the signal of the electrical measurement deforms as the fluid advances from its injection to its exit. The distortion of this signal gives information on the dispersivity and / or the adsorption of the different zones. For example, for a controlled input signal such as a Dirac, the deformation of the signal can be for example, the evolution of the slope: vertical slope for the perfect Dirac and slope having a non-zero angle with the vertical for ie distorted signal, the angle increasing as we move away from the injection point.

The comparison of the second and third electrical measurements to the digital simulations obtained with the first electrical measurement as input, makes it possible to define the dispersivities / adsorptions, with good precision and good reliability, by comparing the shapes of the signals obtained by simulation and by measure.

Examples

The determination of the volume of the porous medium and of its dispersivity is shown in the following example according to the invention. This determination is carried out in two stages:

- first step: calibration of the assembly

- second step: determination of the properties of a porous medium

First step: calibration of the assembly

In this step, the porous medium is replaced by a connecting tube allowing direct connection of the upstream and downstream areas of the system of [Fig 1j. The purpose of this step is to determine the properties (volumes and dispersivities) of the two dead volumes located upstream and downstream of the connecting tube (and therefore of the cell when the latter replaces the connecting tube), the two dead volumes being on the one hand the volume located between the first electrical measurement means 5 and the inlet of the cell 4 (inlet corresponding to the inlet of the connecting tube which replaces it), which is called V1 and on the other hand the volume located between the output of cell 4 (corresponding to the output of the connecting tube which replaces it) and the third electrical measurement means 6, which is called V3.

The study of the transport of ionic species in this assembly therefore makes it possible to characterize their respective volumes V1 and V3, as well as their respective dispersivities, which are called D1 and D3.

The study of the transport of ionic species is carried out by successively injecting two brines having different salinities, for example 40g / L and 20g / L of NaCl, at 0.1 cm ³ / min (or 1.67 10 ⁹ m ³ / s). The difference in salinity causes a variation in the electrical conductivity. This variation is transported in the different volumes of the assembly from the means 15 for mixing the fluids, and measured by the three electrical measurement means 5, 6 and 7. The figure [Fig 2] illustrates the three electrical measurements carried out during the calibration step, during the transitional brine injection phase. The measurements M1, M2 and M3 are the electrical measurements ME, measured over time T (in minutes), respectively at the level of the first electrical measurement means (reference 5 of [Fig 1]), of the second electrical measurement means ( reference 7 of [Fig 1]) and the third electrical measurement means (reference 6 of [Fig 1]). The first electrical measurement from the first electrical measurement means (reference 5 of [Fig 1]) is used as the initial condition (that is to say as input data) of the digital simulation. Thus, it is exactly this form of variation of the electrical conductivity whose transport is simulated in the numerical simulation. The second electrical measurement, from the second electrical measurement means (reference 7 in [Fig 1]) is used to calibrate the properties V1 and D1 of the volume located upstream of the connecting tube, while the third electrical measurement from the third measurement means electric (reference 6 of [Fig 1]) is used to calibrate the properties V3 and D3 of the volume downstream of the connecting tube.

For this calibration step, the calibration results of this example, by comparison between digital simulation and electrical measurements, are shown in [Fig 3a] and [Fig 3b], [Fig 3a] comparing the second electrical measurement M2 and the second simulation electrical measurement S2, at the level of the measurement means located in derivation of the connecting tube, [Fig 3b] comparing the third electrical measurement M3 and the third simulation of electrical measurement S3, at the level of the measurement means located downstream of the link, [Fig 3a] and [Fig 3b] showing the evolution of the electrical measurement ME over time T in minutes. At the end of the calibration step on which there are good correlations between measurements and simulations in the figures [Fig 3a] and [Fig 3b], we find V1 = 0.085cm ³ , V3 = 0.137cm ³ and D1 = D3 = 9 * 10 ^A -5m ² / s.

The precise and reliable characterization (in volume and dispersivity) of these two elements is permitted thanks to the invention which is the subject of this patent application. Without this invention, it would not have been possible to differentiate the two volumes.

Second step: determination of the properties of the porous medium

In this step, we remove the connecting tube that was used in the previous step and replace it with the cell, in which we mount the porous medium whose volume properties we want to measure, called V2, and dispersivity, which is called D2.

In this example, the porous medium is a sample of Fontainebleau sandstone of cylindrical shape with diameter D = 0.999 cm and height L = 2.104 cm. The porosity of the porous medium, which is unknown, is the parameter affecting the volume of the porous medium.

The study of the transport of ionic species is carried out by successively injecting two brines having different salinities, for example 40g / L and 20g / L of NaCl, at 0.1 cm ³ / min. The difference in salinity causes a variation in the electrical conductivity. And we measure this variation by the three means of electrical measurements. The electrical measurement originating from the first electrical measurement means is always used as the initial condition (that is to say as input data) of the digital simulation. Thus, it is exactly this form of variation of the electrical conductivity whose transport is simulated the other volumes of the system. The second and third electrical measurements respectively from the second and third electrical measurement means 3 both serve to calibrate the volume V2 and dispersivity D2 properties of the porous medium. The calibration result for this example is shown [Fig 6a] and [Fig 6b]. These two figures show the changes in electrical measurements ME over time T in minutes, the [Fig 6aj comparing the second electrical measurement M22 obtained with the porous medium and the second simulation of electrical measurement S22 by simulating the porous medium, the [Fig 6b] comparing the third electrical measurement M32 obtained with the porous medium and the third simulation of electrical measurement S32 by simulating the porous medium. These two figures show a good correlation between measurement and simulation and allows validation of the setting of the parameters. Thus, the calibration is obtained by taking V2 = 0.219 cm ³ and D2 - 1 * 10 ^Λ -7 m ² / s.

In the case where only the electrical measurement downstream of the cell is possible (prior art), that is to say where only the electrical measurement means 6 of [Fig 1] is available, the first calibration step allows then obtain as a single measurement said third measurement from the third electrical measurement means (then being the only electrical measurement means). This measurement calculates the dead volumes of the assembly. This dead volume is interpreted as a signal delay. For this example, the measured delay is 4.4min. The second step with the injection of the fluids into the porous medium makes it possible to acquire the third electrical measurement M3 of [Fig 4], curve M3 representing the third electrical measurement of evolution of the electrical measurement ME over time T in minute. This measurement is corrected for the delay calculated previously. The curve thus corrected is the M3cor curve of [Fig 4].

[Fig 5a] shows a comparison of the simulation obtained with the volumes and dispersivities of the porous medium, obtained according to the system and the method according to the invention (V2 = 0.219cm ³ and D2 = 1 * 10 ^A -7m ² / s ) when only the downstream electrical measurement is available, i.e. without taking into account the actual profile of the input electrical measurement. In this case, the entry profile is a theoretical Dirac profile. There is a bad correlation of the two curves M3c measured and S3c simulated: this indicates that the only correction of the delay is not sufficient to obtain a good correlation and / or that the information of V2 and D2 could seem erroneous if one did not use than the electrical measurement downstream of the cell.

[Fig 5b] shows the parameters V2 'for the volume of the porous medium and K2' for the dispersivity of the porous medium that should have been taken to calibrate a model with only electrical measurement data downstream of the cell. Although it is mathematically possible to find a pair of values V2 ’and K2’ that allow the model to be calibrated, the values taken (especially for K2 ’) are not realistic. Indeed, the example shows that the method of the prior art, based on a single electrical measurement downstream of the cell, would have resulted in an overestimation of 10% of the volume of the porous medium, and of 350% on the dispersivity of the medium porous. The error on the dispersivity is such that a person skilled in the art could not have considered this data as realistic.

This example illustrates well the approximation which is made on the form of the input signal when the assembly is equipped with only one measurement means at the output of the injection cell, the approximation causing erroneous results. On the contrary, the system and the method according to the invention allow more reliable and precise results, in particular for estimating the volume of the porous medium and its dispersivity.

Claims (18)

Claims I. System for measuring at least one property of flow of at least one fluid within a porous medium, said measurement system comprising at least one cell (4) containing said porous medium, injection means (1) of fluid in said cell (4), electrical measurement means (5, 6, 7) and an analysis means characterizing said flow property, characterized in that the measurement system comprises at least three means of electrical measurement (5, 6, 7), at least one first electrical measurement means (5) being positioned between said injection means and the inlet of said cell, at least one second electrical measurement means (7) being positioned as a bypass of said cell, and at least one third electrical measurement means (6) being positioned substantially at said exit from said cell. 2. Measuring system according to claim 1, for which said injection means (1) comprise a plurality of fluids to be injected into said cell (4), simultaneously or sequentially. 3. Measuring system according to claim 2, for which the fluids of said plurality of fluids have different electrical conductivities. 4. Measuring system according to claim 3, in which the fluids of said plurality of fluids have concentrations of different ionic species. 5. Measuring system according to one of the preceding claims, wherein said measuring system includes means for controlling said injection means (1). 6. Measuring system according to one of the preceding claims, wherein said cell (4) has a substantially cylindrical shape. 7. Measuring system according to claim 6, in which the diameter of said cell (4) is substantially between 2 mm and 20 mm, preferably between 5 mm and 10 mm. 8. Measuring system according to claim 6 or 7, wherein the height of said cell (4) is substantially between 2 mm and 5 cm, preferably between 5 mm and 2 cm. 9. Measuring system according to one of the preceding claims, in which said fluid is chosen from an aqueous phase and an oil phase. 10. Measuring system according to claim 10, in which at least one aqueous phase comprises at least one additive, preferably a surfactant. II. Measurement system according to one of the preceding claims, for which said electrical measurements are acquired simultaneously and collected in acquisition software. 12. Measuring system according to one of the preceding claims comprising at least one X-ray radiography means comprising a source and a detector, said porous medium being positioned between said source and said detector, said source, said porous medium and said detector being substantially aligned, said analysis means characterizing said flow property of said fluid within the porous medium by radiographs obtained by said X-ray radiography means; 13. Method for measuring at least one flow property of at least one fluid within a porous medium, in which the following steps are carried out using the measurement system according to one of the preceding claims : a) said at least one fluid is injected into said porous medium; b) At least three electrical measurements are carried out simultaneously, at least one first electrical measurement (M1) being located upstream of said porous medium, at least one second electrical measurement (M2) being located downstream of said porous medium and at least one third measurement electric (M3) was located bypassing the porous medium; c) The injection of said at least one fluid into said porous medium is simulated numerically using the input data of said first electrical measurement (M1) and the simulations of said at least second and third electrical measurements are determined (S2, S3). ; d) By comparison of said second and third electrical measurements carried out (M1, M2, M3) and of said digital simulations of said second and third electrical measurements (S2, S3) and setting of the parameters, flow properties of said at least one fluid are determined in said porous medium. 14. The method of claim 13, for which, beforehand, a calibration step is carried out, said calibration step comprising the steps of the method according to claim 13 wherein said porous medium is replaced by a connecting tube. 15. The method of claim 14, for which the properties determined in the calibration step are the dead volumes, located upstream and downstream of the connecting tube. 16. Method according to one of claims 13 to 15, wherein said flow properties are chosen from the volumes and dispersivities of the different zones, upstream of said porous medium, downstream of said porous medium and within the porous medium. 17. The method of claim 16, for which the injection of the fluid into the porous medium is controlled, in real time, during the measurements. 18. Method according to one of claims 13 to 17, for which an x-ray radiography of the porous medium is carried out simultaneously with the electrical measurements. 19. Method according to one of claims 13 to 18, for which said flow properties are determined by comparison of the changes in profile and / or time offset of the electrical signal obtained by said electrical measurements, during the transient regime linked to the injection of said fluid into the porous medium.