EP2689245A1

EP2689245A1 - Method and installation for testing a chemical composition including at least brine and a surfactant, in particular an eor composition

Info

Publication number: EP2689245A1
Application number: EP11726488.7A
Authority: EP
Inventors: Patrick Moreau; Mikel Morvan; Bernard Roux; Philippe RIVOAL
Original assignee: Rhodia Operations SAS
Current assignee: Rhodia Operations SAS
Priority date: 2011-03-22
Filing date: 2011-03-22
Publication date: 2014-01-29
Also published as: WO2012127264A1

Abstract

This method of testing a chemical composition including at least brine and a surfactant, in particular an EOR composition, comprises the following steps of: - providing in a vial (V) a mixture (M) having the composition to be tested, - feeding the vial with an inert gas so as to put the mixture in the vial under an essentially anaerobic condition, - keeping the vial at a predetermined temperature for a predetermined time while maintaining the mixture in the vial under the essentially anaerobic condition, and - analyzing at least one visual feature of the mixture in the vial at the end of the step of keeping.

Description

METHOD AND INSTALLATION FOR TESTING A CHEMICAL COMPOSITION INCLUDING AT LEAST BRINE AND A SURFACTANT, IN PARTICULAR AN EOR

COMPOSITION The present invention relates to a method of testing a chemical composition including at least brine and a surfactant, in particular an enhanced oil recovery composition. The invention relates also to an installation for implementing such a method.

After primary production of oil from a petroleum reservoir, more than half of the oil is often left in place in the reservoir. To recover additional oil, it is known to apply enhanced oil recovery (EOR) techniques. Amongst them, the basic technique consists in a water flooding, i.e. an operation in which water is injected into a petroleum reservoir for the purpose of providing a water drive of the oil. Thus, for a majority of oil reservoirs, large amount of oil is still left after extensive water flooding, average worldwide recovery factor being currently about 32%. Chemical EOR technique is the most promising tertiary recovery technique to improve both sweep and displacement efficiency. The well known process to improve reservoir sweep efficiency consists in injecting low concentration of polymer that viscosifies water. This process known as polymer flooding has been used at large scale, for example in China. More complex chemical enhanced oil recovery processes use both surfactant to reduce oil-water interfacial tension and polymer to improve sweep efficiency. Such processes are known as surfactant polymer (SP) flooding. Besides, the addition of alkali to surfactant flooding reduces the amount of surfactant required and form the process known as alkaline surfactant polymer (ASP) flooding.

More precisely, surfactant compositions providing a low interfacial tension with an oil phase are known to effectively displace oil trapped in porous media (see "Mechanisms of oil entrapment and mobilization in porous media" by Stegemeier G. L, Symposium on improved oil recovery by surfactants and polymer, April 1976; see also "Enhanced oil recovery" by Green D. W. and Willhite G. P., SPE Textbook Series, Vol. 6, 1998). In a recent paper, a process based on phase behaviour screening has been described for evaluating potential EOR surfactants ("Identification and evaluation of high performance EOR surfactants" by Levitt D. B. et al, SPE 100089, April 2006). This approach is based on a well established relationship between low interfacial tension and a microemulsion phase behaviour as originally described by Winsor (see "Solvent properties of amphiphilic compounds", Butterworths, London, 1954). According to Winsor, type I (oil in water), type II (water in oil) and type III (bicontinuous oil and water) microemulsions can be found. The type III microemulsion, also referred to as middle phase, exhibits the lowest interfacial tension. The larger is the volume of oil and water per unit volume of surfactant in this middle phase, the lower is the interfacial tension.

From a practical point of view, this means that rather than performing systematic measurements of interfacial tension, simply observing the microemulsion phase behaviour in transparent vials allows for pre-screening of a large number of compositions. However, as the number of chemical parameters to be screened is very large, the design of a robust surfactant formulation reveals to be time consuming. Besides, apart from low interfacial tension formulations, it is essential to make sure that surfactant formulations are fully soluble in the petroleum reservoirs and in the injection brines at reservoir temperature. In this context, a high throughput workflow has been recently proposed, as described in "A combinatorial approach for identification of performance EOR surfactants" (SPE 1 13705, April 2008). This workflow proposes to automatically prepare and analyze a plurality of surfactant formulations, using a robotic platform. In a first step, one or more surfactants are dissolved in a representative brine and the solubility of the mixture is analyzed. In a second step, the phase behaviour in the presence of oil is investigated. In practice, a robotic platform is used to prepare a large number of different compositions of brine and surfactants by varying brine concentration, surfactant type and concentration, pH, temperature, ... At the end of the process, all the compositions of the tested mixtures and their associated results (solubility and height of the middle phase microemulsion) are stored in a database for further investigations.

Although the method and the installation proposed in the aforesaid paper are significantly efficient, they cannot be used when some formulations should be tested at a quite high temperature, typically greater than 80 : such a value of temperature is reached in a large number of petroleum reservoirs, for example in Mexico, in Venezuela, in Saudi Arabia, ... At such a temperature, the chemical stability of the formulations is very short in aerobic condition, typically encountered at laboratory scale, which makes difficult to investigate these formulations using the known robotic platform. Besides, at such a temperature, the tested formulations tend to evaporate, which modifies the concentrations of the different components in the formulations and which could induce safety issue.

Under these circumstances, an object of the present invention is to enhance the known method and installation, especially in order to use them in case of hot petroleum reservoirs.

To this end, the subject of the invention is a method of testing a chemical composition including at least brine and a surfactant, in particular an EOR composition, as defined in appended claim 1 . Additional advantageous features of this method are specified in dependent claims 2 to 1 1 . The subject of the invention is also an installation for testing a chemical composition including at least brine and a surfactant, in particular an EOR composition, as defined in appended claim 12. Additional advantageous features of this installation are specified in dependent claims 13 and 14.

One of the ideas underlying the invention is to minimize the amount of oxygen in a tested mixture of brine, at least one surfactant and potential additional chemical components, in a workflow where a large number of different mixtures can be prepared and analyzed. According to the invention, an inert gas, such as nitrogen or argon, is used to impose an anaerobic state for the mixture in a vial just after having filled this vial. Different ways to use such an inert gas are proposed, as specified hereafter. In that way, the prepared mixture is chemically stable in time, even when this mixture is at a quite high temperature, corresponding to the effective temperature of a petroleum reservoir for which oil recovery is tried to be improved. In particular, under the essentially anaerobic condition according to the invention, the at least one surfactant and the potential polymers in the prepared mixture are not chemically degraded due to the absence of oxygen. Besides, when the tested mixture includes aerobic bacteria, which could come from the laboratory environment or which are often present when the brine is constituted by natural sea water, bacterial growth and degradation of the mixture are avoided. Besides, as the prepared mixtures are chemically stabilized under the anaerobic condition, the behaviour in time of the mixtures can be investigated, in particular at high temperature, to foresee the use of these mixture in a petroleum reservoir, the flooding of which can take place during several weeks, even several months. More generally, the anaerobic state of the tested mixture is closer to actual conditions encountered in oil reservoirs.

The invention will be better understood from reading the description which will follow, which is given solely by way of example and with reference to the drawings in which:

- figure 1 is a diagram of an installation according to the invention; and

figures 2 to 6 are diagrams showing different operations implemented with a part of the installation of figure 1.

Figures 1 to 6 depict an installation, typically a laboratory installation, which can be used to test an enhanced oil recovery (EOR) chemical composition. This installation comprises a robotic platform including two main robotic tools, i.e. a formulation tool 10 and a gripping tool 20.

As schematically shown in figure 1 , the formulation tool 10 comprises a robotic arm 1 1 provided with at least one movable transfer tube 12, such as a pipette. As well known in laboratory technique, the arm 1 1 is motorized so as to be able to move the transfer tube in space, both in a vertical direction and in a horizontal plane. In the area which can be reached by the transfer tube 12, the installation is provided with both containers 30A, 30B, ..., 30N, into which the lower end of the transfer tube can dip, as indicated by dotted lines for the container 30A in figure 1 , and a filling station 40 where a vial V can be dip so as to receive the lower end of the transfer tube 12, as also indicated by dotted lines in figure 1. Each of the aforesaid containers 30A, 30B, ..., 30N is filled with a stock solution of a known chemical component: in particular, in the embodiment considered in figure 1 , the container 30A is filled with brine and the container 30B is filled with a surfactant stock solution.

As shown by figures 2 to 4, the transfer tube 12 is intended to be controlled by the robotic arm 1 1 in order to transfer a volume of each of the stock solutions of the containers into the vial V. More precisely, if we consider for example the brine of the container 30A, the robotic arm 1 1 controls the transfer tube in a first configuration shown in figure 2, in which, after having dipped the lower end of the transfer tube in the brine, a volume of brine is sucked up within the tube, typically by vacuum succion indicated by an arrow S in figure 2. Then the robotic arm 1 1 controls the transfer tube 12 from this first configuration to a second configuration shown in figure 4, the tube being successively movable upwards, as indicated by an arrow A1 in figure 2, laterally in a horizontal direction as indicated by an arrow A2 in figure 3, and downwardly as indicated by an arrow A3 in figure 4. In the configuration of figure 4, the lower end of the transfer tube 12 opens into the vial V so that a volume of brine stored within the tube can be released into the vial, typically by a gas pressure applied to the upper end of the tube, as indicated by an arrow P in figure 4. Advantageously, the exact quantity of brine which is delivered into the vial V is checked or controlled by a balance integrated in the base 41 of the filling station 40, on which is carried the vial.

Of course, the above description of the use of the transfer tube 12 to deliver a volume of the brine of container 30A into the vial V can be implemented for each of the other containers 30B, ..., 30N. In that way, it will be understood that the robotic arm 1 1 controls the formulation of a mixture in the vial V, with a predetermined chemical composition resulting from the different volumes of the stock solutions that are thus mixed in the vial.

In practice, according to the type of the components of the stock solutions, the same transfer tube 12 can be used with all the containers, if necessary with providing some intermediate rinsings, or, on the contrary, several transfer tubes, similar to the transfer tube 12, are respectively provided for some of the containers. Furthermore, this or these transfer tube(s) correspond to either reusable standard needles or disposable tips.

For reasons which will be specified later, the containers 30A, 30B, ..., 30N are advantageously arranged in a heating tank 31 : in that way, the stock solutions of these containers can be maintained at a predetermined temperature. Besides, the containers 30A, 30B, ..., 30N are arranged on a magnetic stirrer 32 adapted to set in motion bar magnets 33 which are respectively provided in the bottom of the containers: by that way, these bar magnets 33 can stir permanently or regularly the stock solutions of the containers.

As schematically represented in figure 1 , the gripping tool 20 comprises a robotic arm 21 which ends with a movable gripper 22 adapted to grasp and move in space a vial similar to the aforesaid vial V. As well known in the laboratory technique, the gripping tool 20 is thus able to move a vial between different stations which can be reached by the arm 21 , including the filling station 40. The other stations provided in the installation will be described hereafter, taking in consideration a detailed example of the use of the installation.

In a first step, it is considered that the vial V is at the filling station 40, on the base 41 , as represented in figure 1 . In practice, this vial comes from a not shown stock of vials which can be reached by the gripper 22 after an appropriate movement of the robotic arm 21. Initially, this vial V is empty, then the formulation tool 10 is activated to provide in this vial a mixture having a predetermined composition. To do this, the transfer tube 12 is moved and controlled by the robotic arm 1 1 , as explained here-above in view of figures 2 to 4. At this stage of the present explanation, it can be considered that, for example, a volume of the brine of the container 30A and a volume of the surfactant stock solution of the container 30B are thus successively delivered into the vial V to provide a mixture M in the vial, as shown in figure 1.

In a second step, the formulation tool 10 is used to put the mixture M in the vial V under an essentially anaerobic condition. More precisely, as shown in figures 5 and 6, the transfer tube 12 or a similar tube is used to inject an inert gas, such as argon or nitrogen, within the vial V. To do this, an inert gas source is connected to the tube 12, typically at the upper end thereof, and the robotic arm 1 1 controls the injection of the gas towards the lower end of the tube, which is positioned within the vial. Two configurations are possible for the lower end of the tube, as respectively shown in figures 5 and 6. According to a first solution, the lower end of the tube is dipped in the mixture M in the vial V, as shown in figure 5, which implies that the inert gas injected in the tube, as indicated by an arrow IG, makes bubbles in the mixture in the vial. This bubbling is intended to degas the mixture M from oxygen. In practice, this bubbling is maintained for several seconds, which is sufficient to remove almost all of the oxygen initially present in the mixture, due to the small amount of liquid in the vial V, which is typically lesser than 10 ml. As shown in figure 6, the second solution consists in positioning the lower end of the tube 12 within the vial V, just above the liquid surface of the mixture M. In that case, the injection of the inert gas IG flushes the air initially present in the upper part of the vial V and replaces it by a layer of inert gas to prevent outside oxygen of being in contact with the liquid surface of the mixture M.

One and the other of these two solutions make the mixture M in the vial V in an essentially anaerobic state, in the sense that, after the injection of the inert gas IG, very little oxygen remains within or in contact the mixture M in the vial V. Of course, according to a preferred embodiment, the first and the second solutions are successively implemented to enhance the anaerobic state of the mixture in the vial.

Based on the foregoing explanations, it will be understood that an advantageous option is to provide each of the containers 30A, 30B, ..., 30N with a bubbling tube 34, as shown in figure 1 . Each of these bubbling tubes 34 is fed by an inert gas and bubbles in the stock solution of the corresponding container. In that way, after having maintained a bubbling for a sufficient time, very little oxygen remains in the stock solutions which are then used to provide the mixture M. The anaerobic state of this mixture is even better. In practice, the aforesaid bubbling tubes 34 are advantageously supported by the robotic arm 1 1 and connected to the same inert gas source as the one feeding the transfer tube 12 in figures 5 and 6.

In a third step, the robotic arm 21 is activated: the gripper 22 is moved closer to the vial V and grasps this vial. Then, the gripper 22 moves the vial V from the filling station 40 to a capping station 50, as indicated by an arrow 23 on figure 1 . At this capping station, the robotic arm 21 is used to put a cap C at the top of the vial V in order to seal the vial. For example, the cap C is screwed around the upper end of the vial, being driven by the gripper 22. In that way, the cap C maintains the anaerobic condition of the mixture M in the vial V, forming a mechanical barrier for the outside oxygen, in addition to the gaseous barrier provided by the inert gas injected in the top of the vial on figure 6.

In a fourth step, the robotic arm 21 is again activated to move the vial V closed by the cap C from the capping station 50 to a stirring station 60 where the vial V is engaged in a vortex shaker 61 , as indicated by an arrow 24 on figure 1. In use, this vortex shaker 61 stirs the vial to homogenize the mixture M.

In a fifth step, the robotic arm 21 is again activated to move the vial V closed by the cap C from the stirring station 60 to a storage station 70 where the vial is kept at a predetermined temperature for a predetermined time, as indicated by an arrow 25. For this purpose, the storage station 70 comprises a heating tank 71 adapted to receive the vial V and to maintain it at the aforesaid predetermined temperature. This temperature can be quite high, especially greater than 80 , even g reater than 120 , without the risk of chemical degradation of the mixture M because the anaerobic state of this mixture is maintained. Conversely, it can be noted that, at such a high temperature, an aerobic mixture would tend to be quickly altered because of some spontaneous reactions between oxygen and the surfactant of the mixture.

It will be understood that the high temperature which is chosen at the storage station 70 corresponds to the effective temperature of a petroleum reservoir for which the composition of the mixture M is tested in view of potentially using this composition as an EOR formulation. That is also the reason why the stock solutions of the containers 30A, 30B, ..., 30N are heated in the tank 31 while being degassed from oxygen.

In the same way, the time of storage of the vial V at the station 70 is chosen to correspond to a relevant time for testing an EOR composition, as explained in the introductive part of the present document. That is the reason why the aforesaid time of storage is typically greater than one hour, even greater than twenty-four hours and can even reach several weeks.

In a sixth step, at the end of the aforesaid time of storage, the robotic arm 21 is activated again to move the vial V from the storage station 70 to an analyzing station 80 as indicated by an arrow 26 on figure 1 . At the analyzing station 80, the vial V is positioned in the field of view of a camera 81 which is linked to a computer 82 to be controlled and to store the photographs taken by the camera. In the present document, the implementation of this analyzing step will not be more specified because the reader can easily refer both to the paper "A combinatorial approach ..." mentioned in the introductive part of the present document and to 'An integrated workflow for chemical EOR formulation design" (Chemical Industry Digest, August 2009, pp 56-68). Briefly, it can be reminded that, based on the data provided by the camera 81 , the computer 82 is used to analyze at least one visual feature, for example the colour or the transparency, of the mixture M in the vial V. Of course, the vial itself is transparent, for example being made of glass.

By implementing the six steps disclosed here-above, the installation of figure 1 can test the composition of the mixture M, typically the turbidity of this mixture. Then, a second composition can be tested, by these six process steps implemented for another mixture. And so on for a great number of compositions. In that way, a screening of the solubility of the surfactant in the brine can be provided, especially in view of eliminating the compositions for which the solubility of the mixture is not sufficient at the aforesaid predetermined temperature, after the aforesaid predetermined time of storage. Of course, the interest of the installation is to provide other screenings by varying all the parameters having a potential impact on the turbidity of the tested mixtures. In particular, it can be interesting to vary salinity of the brine, temperature, pH and the presence of other active chemical agents. Thus, in the installation considered in figure 1 , the containers provided in addition to the containers 30A and 30B can be respectively filled with one or more other surfactants than the surfactant of container 30B, a polymer, an alkaline agent, an antioxidant agent, a biocide agent, a sequestering agent, an alcohol and an organic solvent.

In the same way, an oil, especially an oil corresponding to the petroleum present in a given reservoir, can be added to the mixture in the vial before feeding the vial with the inert gas. To do this, an additional container, which is similar to the containers 30A, 30B, ..., 30N, is provided in the installation, especially inside the heating tank 31 , being filled with oil, in particular model oil, for example polar oil or alkane, or crude oil. And a transfer tube, similar to the transfer tube 12, is controlled by the robotic arm 1 1 to deliver a volume of this oil in the vial. In that case, the visual feature which is analyzed at the analyzing station 80 is relative to the phase behaviour of the mixture, as explained in detail in the aforesaid papers "A combinatorial approach ..." and "An integrated workflow ..." As oxygen content is usually quite low in oil, oil can be added to the mixture in the vial after having put the mixture under the anaerobic condition.

As a great number of compositions have to be tested to provide a relevant screening, the fact that the installation comprises the two tools 10 and 20 can be advantageously used to speed up implementation of the testing process. More precisely, while the formulation tool 10 is acting on a first vial, the gripping tool 80 can be used to act on a second vial. In other words, after having provided a first mixture in a first vial, this first vial can be sealed at the capping station 50 and stirred at the stirring station 60 while a second mixture is delivered in a second vial at the filling station 40.

Other embodiments of the invention are possible, including by recombining the various elements disclosed herein in different or alternative combinations. Although the above description contains many specifics, this should not be considered as limiting the scope of the invention as defined by the appended claims, but as merely providing illustrations of some of the embodiments of this invention.

Thus, according to an implementing variant, the vial V containing the mixture M can be directly moved from the filling station 40 to the storage station 70, without capping and stirring the vial. In that case, the anaerobic state of the mixture M in the vial V, which is provided after feeding the vial with the inert gas, is essentially maintained only by the barrier which is formed by the inert gas at the liquid surface of the mixture. Of course, this gas barrier can be maintained only if the vial V is moved softly by the robotic arm 21. According to another variant, rather than implementing each step of the testing process vial per vial, some of these steps can be implemented with a group of several vials, typically arranged in a common rack. For example, such a rack with several vials can be used at the storage station 70 and at the analyzing station 80.

According to a not shown embodiment, the installation comprises a containment of gas, in which the robotic tools 10 and 20 and the stations 40, 50, 60, 70 and 80 are arranged and within which an inert gas is introduced to lower the internal oxygen content and thus make easier processing of the vials to put them in the essentially anaerobic condition.

Claims

1.- A method of testing a chemical composition including at least brine and a surfactant, in particular an EOR composition, said method comprising the following steps of:

- providing in a vial (V) a mixture (M) having the composition to be tested,

- feeding the vial with an inert gas so as to put the mixture in the vial under an essentially anaerobic condition,

- keeping the vial at a predetermined temperature for a predetermined time while maintaining the mixture in the vial under the essentially anaerobic condition, and

- analyzing at least one visual feature of the mixture in the vial at the end of the step of keeping.

2. - A method according to claim 1 , wherein the composition to be tested further includes one or more other surfactants, a polymer, an alkaline agent, an antioxidant agent, a biocide agent, a sequestering agent, an alcohol and/or an organic solvent.

3. - A method according to claim 1 or claim 2, wherein the method further comprises a step of adding an oil to the mixture in the vial before or after feeding the vial with an inert gas.

4. - A method according to any one of the preceding claims, wherein said predetermined temperature is greater than 80 , pre ferably greater than 120 .

5.- A method according to any one the preceding claims, wherein said predetermined time is greater than one hour, preferably greater than twenty-four hours, even greater than one week.

6. - A method according to any of the preceding claims, wherein, in the step of feeding, the inert gas is introduced in the vial (V) within the mixture (M) so as to degas the mixture from oxygen.

7. - A method according to any one of the preceding claims, wherein the inert gas is introduced in the vial (V) above the mixture (M) to flush the air from the vial and forms a gas barrier.

8. - A method according to any one of the preceding claims, wherein, in the step of providing, each of the components of the mixture (M) is delivered into the vial (V) from a stock solution within which an inert gas is introduced to degas the stock solution from oxygen.

9. - A method according to claim 8, wherein each stock solution is kept at said predetermined temperature and is stirred permanently or regularly.

10. - A method according to any one of the preceding claims, wherein the method further comprises:

- a step of sealing the vial (V) with a cap (C) after having put the mixture in the vial under the essentially anaerobic condition, and

- a step of stirring the vial (V).

1 1 .- A method according to claim 10,

wherein at least two mixtures are provided in respective vials,

and wherein the step of providing one of these mixtures in one of the vials is at least partly implemented while implementing the steps of sealing and stirring for the other vial.

12. - An installation for testing a chemical composition including at least brine and a surfactant, in particular an EOR composition, said installation comprising:

- a first robotic tool (10) adapted both to provide in a vial (V) a mixture (M) having the composition to be tested and to feed the vial with an inert gas so as to put the mixture in the vial under an essentially anaerobic condition, and

- a second robotic tool (20) adapted to grip and move a vial (V) between at least a filling station (40), in which the first robotic tool (10) acts on the vial, and a storage station (70), in which heating means (71 ) of the installation keep the vial at a predetermined temperature.

13. - An installation according to claim 12, wherein the first robotic tool (10) comprises at least one transfer member (12) adapted both to pick a volume of a component of the mixture (M) from a stock solution, to be moved from the stock solution to the vial (V) by a motorized arm (1 1 ) of the first robotic tool, and to deliver said volume into the vial, said transfer member being further used to feed the vial with the inert gas.

14.- An installation according to claim 12 or claim 13, wherein the installation further comprises a capping station (50) adapted to seal the vial (V) with an added cap (C) and a stirring station (60) adapted to stir the vial, and wherein the second robotic tool (20) is adapted to move the vial (V) from the filling station (40) successively to the capping station (50), to the stirring station (60) and to the storage station (70).