WO2016075400A1

WO2016075400A1 - Method and system for treating and separating a non-conventional gas

Info

Publication number: WO2016075400A1
Application number: PCT/FR2015/053028
Authority: WO
Inventors: Maïlys GUERQUIN; Agathe Louise Marie JARRY; Samuel Saysset; Denis FAURE BRAC
Original assignee: Engie
Priority date: 2014-11-14
Filing date: 2015-11-09
Publication date: 2016-05-19
Also published as: FR3028554B1; FR3028554A1

Abstract

The invention relates to a system which includes: an initial hydraulic stimulation unit (3), with a unit (4) for injecting liquid CO2 under pressure into a well (11) producing from an atypical deposit; a unit (10) for recovering, at low temperature after a stimulation operation, a mixture of natural gas and CO2, said recovery unit (10) including in particular a unit (42) for assessing the amount of CO2 in the recovered mixture of natural gas and CO2, and a unit (42) for comparing said amount of CO2 with a threshold (S); a unit for separating at least one portion of the CO2 in liquid, semi-liquid or solid state from the recovered mixture of natural gas and CO2, with at least two different separation units (51, 52, 53) according to whether the amount of CO2 is higher or lower than the threshold (S); at least one unit (81) for provisionally storing the separated CO2 in liquid, semi-liquid or solid state; and at least one land vehicle (501, 502, 503, 504) for moving a provisional storage unit (81) towards another site in order to reuse the CO2 which has been separated and stored in liquid, semi-liquid or solid state, in order to supply a unit (4) for injecting liquid CO2 under pressure into a new stimulation unit (3) on a new adjacent well (11).

Description

Process and system for treating and separating unconventional gas

Field of the invention

The present invention relates to the technical fields of unconventional gas treatment and separation and more particularly relates to a method and an initial hydraulic stimulation system, using carbon dioxide (C0 ₂ ) injection, of any rock of low porosity, for the production of natural gas trapped in this rock.

PRIOR ART Unconventional gases, which are trapped in atypical deposits, include gas trapped in a rock, with in particular shale gas (known as "shale gas"), coal gas (referred to as "coal"). bed methane ") and the compact tank gas (referred to as" tight gas ").

The extraction of these unconventional gases requires the use of specific techniques to release them. In particular, hydraulic rock stimulation techniques are used to increase its permeability.

Hydraulic stimulation is often performed by a technique using the injection of water and a proppant. Water, a proppant and chemical additives are introduced under high pressure into the wellbore to effect stimulation. The proppant, which may be sand or an artificial material, serves to keep open the microcracks created by the hydraulic stimulation.

Hydraulic stimulation using water has drawbacks in a context where one wishes to preserve the environment, partly because there are desert regions rich in shale gas where this water is scarce, whereas it is necessary to have about 10,000 m ³ per well, and secondly because the use of chemical additives, such as gelling agents, disinfectants, gel breakers, friction reducers, acids, corrosion inhibitors or decalcifiers, have potential reactions with the rock that remain unknown. In addition, the treatment of the water after the stimulation operation entails constraints and when the chemicals are injected into the well when it is closed after production, the seismic stability of the production zone is not affected. assured.

This is why alternative techniques of hydraulic stimulation without water have been proposed.

The state of the art is known from the document WO 2014/085057 which describes hydraulic stimulation without water.

Also, it has already been proposed to perform stimulation with fluoro-propane. However, fluoro-propane is expensive and it is necessary to separate the fluoro-propane gas produced, for reasons of safety. For example, in France, it is required that the total quantity of fluorinated compounds introduced when biomethane is injected into a natural gas network is less than 10 mg / m ³ (n), and draft standards even fix this. amount at 3.5 mg / m ³ (n).

Another alternative technique is to inject high pressure liquid CO ₂ instead of water (see in particular documents US 20090260828, CA 1134258, CA 2255413, US 4627495 and US 5883053), which allows in particular to find synergies with industries producing CO ₂ that can then be recycled. These industries may include gas production plants associated with sour natural gas in conventional fields, as well as syngas production plants associated with the production of ammonia, fertilizer and hydrogen or mills. purification associated with biogas or synthetic natural gas. Sources of CO ₂ can also be found in energy production facilities, in cement plants, in the iron and steel industry or in facilities for the capture and geological sequestration of carbon dioxide. Hydraulic stimulation with liquid C0 ₂ has many advantages over hydraulic stimulation using water.

100% liquid C0 ₂ is injected and there is no chemical additive.

The volumes of C0 ₂ liquid injected are lower than the volumes of water required for water stimulation.

The cracks are wider and there is no water condensate in the well, which improves the productivity of the well.

Unlike water stimulation, you do not need to use a valuable natural resource.

Unlike stimulation with LPG (liquefied petroleum gas), stimulation with liquid C0 ₂ does not add additional burdens to the flammability or explosion hazard.

In the case of a stimulation with liquid C0 ₂ , the well can be cleaned quickly after the stimulation, which facilitates the exploitation of the well. The C0 ₂ is returned in gaseous form for a few days, until the return flow comprises only natural gas and the usual proportion of C0 ₂ present in the natural gas, which facilitates the recovery and treatment of the flow in return.

The supply of C0 ₂ is however sometimes difficult.

Also, it has been proposed to recover the C0 _{2 that} has been used for a first stimulation, or at least a large part of it, to store it in a liquid state in a tank placed on a truck and to reuse it on another site requiring a stimulation operation, on a new well next to the same shale gas deposit or in a nearby shale gas deposit.

It should be noted that in this case, in the post-stimulation period, the CO ₂ , and then the shale gas, circulate at a relatively low pressure, which is well below a range of 2 to 10 bar. During the few days following the stimulation, the composition of the recovered stream varies.

In the first period, only C0 ₂ gas is released. Then, gradually with a certain delay due to the inertia of the desorption, the natural gas that was absorbed in the shale is released and flows into fractures and in the well. The recovered stream is then a gaseous mixture of CO2 and mainly methane, the percentage of C0 ₂ decreasing with time until there remains only natural gas in production.

It should be noted that the natural gas produced is generally recovered and stored only after the end of the post-stimulation phase, when there is practically no return of CO ₂ , while during the post-stimulation phase, stimulation the natural gas produced is generally not upgraded and feeds a torch or is simply released into the atmosphere, which in any case contributes to increasing the greenhouse effect and is not conducive to the preservation of the 'environment.

If we want to remedy this inconvenience, it is advisable, in the days immediately following the stimulation:

a) recovering pure C0 ₂ , in liquid form, to allow storage and recycling; and

(b) to recover a stream of natural gas that can be directly transported for commercial sale or use on the field.

However, a whole process of treatment must be used to separate C0 ₂ from natural gas and then liquefy it. Since this treatment is only necessary for the period of a few days corresponding to poststimulation, it is preferable to place the treatment plant on a trailer, in order to allow it to be moved to another site where place a stimulation.

These existing solutions have disadvantages. Thus, in the first phase of the post-stimulation period, the return flux very rich in C0 ₂ can be liquefied, but the C0 ₂ rate varies regularly decreasing from 100% to 5% and the C0 liquefaction systems ₂ are not suitable for treating percentages of CO ₂ ranging in a range as large as 5 to 100%.

On the other hand, in the second phase of post-stimulation, C0 ₂ should be separated from natural gas before liquefaction, but conventional separation techniques are not suitable for this purpose. With chemical absorption using solvents such as amines, C0 ₂ is recovered in the vapor phase at 40 ° C and at a pressure of 1 to 2 bar. Such low pressure makes the reliquefaction step more expensive because lower temperatures and higher volume containers should be used. In addition, the size of such an installation does not make it suitable for installation on the trailer of a semitrailer.

With membranes, again, C0 ₂ is recovered in the vapor phase at 40 ° C and at a pressure of 1 to 2 bar, which makes the reliquefaction more expensive. Although more suitable for installation on a trailer, a membrane installation requires a flexible and expensive compression step, since the inlet pressure must be adapted to correspond to a variable percentage of C0 ₂ .

Economically speaking, with conventional acid gas treatment techniques, there is a tendency to release C0 ₂ and natural gas into the atmosphere in the second phase of the post-stimulation period, which induces an increase in the greenhouse effect, higher C0 ₂ supply costs and natural gas losses.

Definition and purpose of the invention

The present invention aims to overcome the aforementioned drawbacks and in particular to be able to perform a hydraulic stimulation using C0 ₂ which is more environmentally friendly and more effective and which, moreover, advantageously allows:

to limit the quantity of C0 ₂ necessary for stimulation while making it easier to recycle for another stimulation operation, and

- to limit the losses of natural gas and the impact on the greenhouse effect of the flux recovered after a stimulation. These objects are achieved according to the invention by a method of treatment and separation of an unconventional gas comprising a) an initial hydraulic stimulation step, using pressure injection of liquid carbon dioxide in a a well of exploitation of an atypical deposit in which said unconventional gas is trapped in a rock,

characterized in that it further comprises the following steps:

b) recovering at a low temperature after the stimulation operation, a mixture of natural gas and CO ₂ , this low-temperature recovery step comprising in particular a step b1) of evaluation, in the mixture of natural gas and C0 ₂ recovered, the amount of C0 ₂ and a step b2) for comparing this quantity of CO ₂ with respect to a predetermined threshold (S),

c) separating at least a portion of the C0 ₂ in the liquid, semi-liquid or solid state from said mixture of natural gas and recovered C0 ₂ , with a different technique depending on whether the amount of C0 ₂ is greater or less than said predetermined threshold (S),

d) storing temporarily in at least one portable tank on a land vehicle the separated C0 ₂ in liquid, semi-liquid or solid state, and

e) moving the land vehicle with said at least one tank to another site to reuse the separated C0 ₂ and stored in liquid, semi-liquid or solid state in order to perform a new stimulation operation on a new neighboring well, in the same unconventional gas deposit or in a nearby unconventional gas field.

According to one aspect of the process according to the invention, when the amount of CO ₂ recovered is between 100% and said predetermined threshold (S) of the mixture of natural gas and CO ₂ recovered, step c) of separation of CO ₂ in the liquid, semi-liquid or solid state from said mixture comprises a CO ₂ liquefaction step using a cryogenic distillation system.

According to another aspect of the process according to the invention, when the amount of CO ₂ recovered is between said predetermined threshold (S) and 20% of the mixture of natural gas and CO ₂ recovered, step c) of separation of at least a portion of the C0 ₂ in the liquid, semi-liquid or solid from said mixture comprises a rapid cold CO ₂ condensation step passing C0 ₂ from a gaseous phase to a solid phase.

The evaluation step, in the mixture of natural gas and recovered CO ₂ , of the amount of CO ₂ can be carried out using gas analysis by micro-chromatography.

The predetermined threshold is advantageously equal to a value between 55 and 65% and preferably equal to 60%.

After step c) of separating at least a portion of the CO 2 at low temperature after the stimulating operation, the natural gas is recovered in gaseous form for later use.

The mixture of natural gas and C0 ₂ recovered at low temperature after the stimulation operation may further comprise an additional component such as nitrogen N ₂ and, during step c) of separation of at least one part of the C0 ₂ at low temperature after the stimulation operation, the natural gas is recovered with said at least one additional component in gaseous form for later use.

The invention also relates to a system for treating and separating an unconventional gas comprising an initial hydraulic stimulation unit, with a unit for injecting liquid carbon dioxide under pressure into an operating well of an atypical deposit. wherein said unconventional gas is trapped in a rock, characterized in that it further comprises: a low temperature recovery unit after a stimulation operation, a mixture of natural gas and CO2, this recovery unit at low temperature comprising in particular a unit of evaluation, in the mixture of natural gas and of recovered CO2, of the amount of CO2 and a unit for comparing this quantity of C0 ₂ with respect to a predetermined threshold (S),

a unit for separating at least part of the CO2 in the liquid, semi-liquid or solid state from said mixture of natural gas and CO ₂ recovered by said recovery unit, with at least first and second units of different separation according to whether the amount of CO2 is higher or lower than said predetermined threshold (S), at least one temporary storage unit, C0 ₂ separated in the liquid, semi-liquid or solid state, and

at least one land vehicle for moving said at least one temporary storage unit to another site to reuse the separated C0 ₂ and stored in the liquid, semi-liquid or solid state to feed a pressure injection unit of liquid carbon dioxide in a new stimulation unit on a nearby new well, in the same unconventional gas field or a nearby unconventional gas field.

Advantageously, the first separation unit comprises a CO ₂ liquefaction unit using a cryogenic distillation system to ensure the separation of C0 ₂ in the liquid, semi-liquid or solid state from said mixture when the amount of CO ₂ recovered is between 100% and said predetermined threshold (S) of the mixture of natural gas and C0 ₂ recovered.

The second separation unit comprises a fast cooling unit of CO ₂ for passing CO ₂ from a gas phase to a solid or semi-liquid phase when the amount of CO ₂ recovered is between said predetermined threshold. (S) and 20% of the mixture of natural gas and CO ₂ recovered.

The evaluation unit, in the recovered mixture of natural gas and CO ₂ , of the amount of CO ₂ may comprise a gas analyzer by micro-chromatography.

According to a particular characteristic, the first and second different separation units are connected to said recovery unit by a system of valves controlled from the output information of said comparison unit.

According to one possible embodiment, at least one of the first and second different separation units comprises a self-cooling unit in which the mixture of natural gas and recovered CO ₂ is subjected to a heat exchange with a previously separated natural gas stream before reuse.

According to another possible embodiment, at least one of the first and second different separation units comprises a pre-cooling unit in which the mixture of natural gas and recovered CO ₂ is subjected to a heat exchange with the heat. latent of a CO ₂ flow previously separated in the second condensation separation unit and subjected to a passage from the solid state to the liquid state before reuse.

According to another particular embodiment, at least one of the first and second different separation units comprises a complementary cooling unit comprising a Stirling cycle type refrigeration system.

According to another particular embodiment, at least one of the first and second different separation units comprises a distillation column with means for recovering liquid, semi-liquid or solid C0 ₂ at the bottom of the column at the bottom of the column. column and natural gas recovery means at the head of the column.

According to another particular embodiment, at least one of the first and second separation units comprises an expansion unit in a Joule-Thomson valve.

According to yet another particular embodiment, at least one of the first and second separation units comprises a two-phase expansion turbine followed by a centrifugal device for separating the solid CO ₂ .

According to yet another possible embodiment, at least one of the first and second separation units comprises a convergent-divergent nozzle provided in its diverging portion with a liquid or solid C0 ₂ capture slit.

The system may comprise different storage units associated respectively with the first and second separation units.

According to one particular characteristic of the invention, the system may further comprise a CO ₂ gas phase separation unit without a liquefaction device to ensure the separation of the CO ₂ in the gaseous state and the recovery of the natural gas from the mixture of natural gas and recovered CO ₂ , when the amount of CO ₂ is less than 20% in the mixture of natural gas and CO ₂ recovered. Brief description of the drawings Other features and advantages of the invention will emerge from the following description of the particular embodiments given by way of examples, with reference to the appended drawings, in which:

- Figure 1 is a schematic view of a hydraulic stimulation system according to a particular embodiment of the invention;

FIG. 2 is a diagram showing the evolution of the concentration of the stimulation agent at the wellhead as a function of time from the end of the stimulation;

FIG. 3 is a block diagram showing a first example of a low temperature C0 ₂ separation technique using a two-phase turboexpander;

FIGS. 4 and 5 are schematic diagrams showing second and third examples of separation techniques of FIG.

C0 ₂ at low temperature each using a convergent / divergent nozzle; and

Fig. 6 is a block diagram showing a fourth example of a low temperature CO ₂ separation technique using a distillation column.

Detailed description of preferred embodiments

FIG. 1 symbolically shows an example of a hydraulic stimulation system according to a particular embodiment of the invention.

The module 3, which is shown as being mounted on a movable platform 5, such as a trailer or a truck, includes a tank 8 of liquid C0 ₂ and symbolizes hydraulic stimulation equipment using liquid C0 ₂ which, through an injection device comprising at least one valve 4 and a pipe 6 makes it possible to inject liquid C0 ₂ into a main pipe of a well 11 making it possible to carry out an initial hydraulic stimulation stage, with the aid of injection under pressure of liquid carbon dioxide in the well 11 of exploitation of an atypical deposit 7 in which an unconventional gas is trapped in a rock, buried in relation to the ground level 9. The reservoir 8 of liquid C0 ₂ can itself contain liquid C0 ₂ which has been recovered in another exploitation well of the same atypical deposit or of another atypical deposit nearby, according to the process according to the invention, which will be described below.

Referring first to Figure 2 which shows the evolution of the concentration of a fracturing agent, consisting of carbon dioxide, at the head of the well 11, when after the first step of stimulation, it recovers a mixture of gas and fracturing agent.

Initially, there is a proportion of fracking agent that is close to 100% and remains important in the first few moments (of the order of a few hours) of the well 11 operating process.

After a variable time t1, of the order of a few hours or a day, the concentration of fracturing agent falls to a predefined threshold S, which is advantageously defined between 55 and 65%, preferably the order of 60%. The CO ₂ concentration then continues to decrease over time to become, after a few days, equal to the usual C0 ₂ concentration in the natural gas extracted from the deposit to be exploited, that is to say a concentration of the order of 2 or a few percent.

The reference 1 designates the part of the curve of FIG. 2 corresponding to a concentration of C0 ₂ greater than the threshold S and reference 2 designates the part of the curve of FIG. 2 corresponding to a concentration of C0 ₂ below the threshold S.

The method according to the invention takes into account this decreasing evolution of the concentration of fracturing agent to apply different techniques for recovering CO ₂ at low temperature depending on whether the CO ₂ concentration is greater (curve 1) or lower (curve 2 ) at the threshold S.

In the remainder of the description, the case will essentially be described in which two different techniques for recovering CO ₂ at low temperature are used, depending on whether the CO ₂ concentration is greater (curve 1) or lower (curve 2) than the threshold S. , but it is also possible to provide several different thresholds which would be staggered on the curve of Figure 2 and to use a different technique for recovering C0 ₂ at low temperature at each crossing threshold. According to the invention, after the stimulation operation, a mixture of natural gas and CO2 is recovered at the head of well 11, at low temperature.

This low-temperature recovery step comprises in particular a step of evaluating, in the mixture of natural gas and recovered CO2, the amount of CO2 and a step of comparing this quantity of CO2 with respect to at least one predetermined threshold S .

The CO2 in the liquid, semi-liquid or solid state is then separated from the mixture of natural gas and recovered CO2, with a different technique depending on whether the amount of C0 ₂ is greater or less than the predetermined threshold S.

By way of example, if a threshold S of 60% is provided, when the concentration of CO2 is between 100% and 60%, a CO ₂ liquefaction technique can be used, for example by adapting a CO ₂ system. cryogenic distillation of a carbon purification unit used in an oxy-combustion process, whereas, when the CO 2 concentration is between 60% and 20%, it is possible to use a CO ₂ condensation technique to be used. rapid cooling (refrigeration), by direct passage from a gaseous phase to a solid phase.

Then temporarily stored in at least one transportable tank 81 on a land vehicle 504, such as a trailer or a truck, CO2 separated in the liquid state, semi-liquid or solid.

The land vehicle 504 is then moved with the tank 81 to another site to reuse the CO ₂ separated and stored in the liquid, semi-liquid or solid state in order to carry out a new stimulation operation on a new neighboring well, in the same unconventional gas deposit or in a nearby unconventional gas field. The tank 81 will then play the same role as the tank 8 having been used in the stimulation module 3 used for the well 11.

This is done for a succession of stimulation operations in a succession of operating wells with a limited stock of CO2 which is recycled without the need for an expensive liquefaction operation, since the CO ₂ separated from the gas produced is simply subjected to low temperature recovery operations that are relatively inexpensive and easy to implement. We avoid especially to waste and release in the nature of large quantities of fracturing agent as according to the conventional methods.

Naturally, when the amount of CO ₂ recovered is less than about 20% in the mixture of natural gas and CO ₂ recovered, while being greater than the residual rate of about 2% of CO2 present in the natural gas, it is possible to proceed. using conventional techniques for the separation of C0 ₂ in the gas phase without a liquefaction device to ensure the separation of C0 ₂ in the gaseous state and the recovery of natural gas from the mixture of natural gas and recovered C0 ₂ .

The installation shown diagrammatically in FIG. 1 makes it possible to implement the method according to the invention.

The system for treating and separating an unconventional gas according to the invention comprises a hydraulic stimulation unit 3, already mentioned above, mounted on a land vehicle 5 and equipped with a unit 4 for injection under pressure of dioxide. of liquid carbon in a well 11 of exploitation of an atypical deposit 7, in which the unconventional gas is trapped in a rock, buried in relation to the ground level 9. The injection unit 4 connected to the well by a pipe 6 comprises a system of valves for connections and disconnections between the hydraulic stimulation unit 3 and the well 11.

According to an important characteristic, the installation according to the invention comprises a low temperature recovery unit 10 after a stimulation operation, a mixture of natural gas and CO ₂ .

This low temperature recovery unit 10 comprises in particular an analysis module 42 comprising an evaluation unit, in the mixture of natural gas and C0 ₂ recovered at the head of the well 11, the amount of C0 ₂ and a unit comparing this amount of CO ₂ with respect to at least one predetermined threshold S. The evaluation unit, in the mixture of natural gas and CO ₂ recovered, of the amount of CO ₂ may comprise a gas analyzer by micro-chromatography.

The low temperature recovery unit 10 comprises a unit for separating C0 ₂ in the liquid, semi-liquid or solid state. from the mixture of natural gas and CO ₂ recovered by a pipe 13 from the well 11, with at least first and second separation units 51, 52 different depending on whether the amount of CO ₂ is greater or less than the predetermined threshold S The number of these separating units 51, 52 is not limited to two and in FIG. 1 there is shown, in dashed lines, a third separation unit 53 for treating the CO ₂ in a concentration. lower than another threshold itself lower than the threshold S.

Figure 1 also shows at least one temporary storage unit 81 of C0 ₂ in the liquid state, semi-liquid or solid in the separation units 51, 52, 53.

The temporary storage unit 81, but also the separation units 51, 52, 53 are advantageously arranged on land vehicles 501 to 504, such as trailers or trucks, in particular to enable a temporary storage unit 81 to be moved to another site for reusing the C0 ₂ separated and stored in the liquid state, semi-liquid or solid, in order to feed a unit for injection under pressure of liquid carbon dioxide in a stimulation unit on a new well close to the well 11, in the same unconventional gas field or in a nearby unconventional gas field. Naturally vehicles 501 to 504 can be grouped into one or two vehicles for example. The analysis module 42 may itself be mounted on one of the vehicles 501 to 504 provided for the other modular elements of the system.

If we still consider Figure 1, we see that a pipe 13 connected to the wellhead 11 is connected by a valve 21 to a pre-cooling unit 41. This unit 41 may constitute a self-cooling. In this case, the mixture of natural gas and C0 ₂ recovered via the pipe 13 is subjected to heat exchange with a previously separated stream of natural gas circulating in the lines 91, 92, 93 before local reuse or in a natural gas network 94.

A secondary pipe 12 is derived from the main pipe 13 to provide the analysis module 42 with a gas sample to determine the CO ₂ concentration. Similarly, a secondary pipe 14 can be derived from the pipe main 15 receiving the mixture of gas and CO ₂ at the output of the pre-cooling unit 41 to provide the analysis module 42 a gas sample for determining the concentration of C0 ₂ .

A three-way valve 22 makes it possible to connect the pipe 15 either, via a pipe 31, to a first separation unit 51, or, via a pipe 17, to a second three-way valve 23. A secondary pipe 16 is derived from line 17 to provide the analysis module 42 with a gas sample for determining the CO ₂ concentration.

A three-way valve 23 makes it possible to connect the pipe 17 either, via a pipe 32, to a second separation unit 52, or, via a pipe 19, to a third three-way valve 24. A secondary pipe 18 is derived from line 19 to provide the analysis module 42 with a gas sample for determining the C0 ₂ concentration.

The valve 24 allows a connection, via a pipe 33, with a third separation unit 53, which is optional, and optionally a connection to yet another valve associated, if necessary, with yet another separation unit, not shown in FIG. FIG. 1, for example a CO ₂ gas phase separation unit without a liquefaction device for separating the CO ₂ in the gaseous state and recovering the natural gas from the mixture of natural gas and recovered CO _2. when the amount of CO ₂ is less than 20% in the mixture of natural gas and CO ₂ recovered, while remaining greater than the residual amount of CO ₂ in natural gas, which is of the order of 2% or a few percent.

Naturally, if there are for example only the two separation units 51 and 52, the valve 24 does not exist and the valve 23 may be a two-way valve.

Pipes 34, 35, 36 can connect to each other and with a vent 37 the separation units 51 to 53.

At the outlet of each of the separation units 51, 52, 53, a pipe 91, 92, 93 makes it possible to recover the natural gas to send it to a storage zone or a natural gas network 94, which can be a network transport or distribution network. The liquid, solid or semi-liquid C0 ₂ is recovered at the outlet of each of the separation units 51, 52, 53 via the lines 61, 62, 63. The lines 62 and 63 are connected by a three-way valve 72 to a pipe 64 itself connected by a three-way valve 71 to the outlet pipe 61 of the separation unit 51 and to a connecting pipe 65 with a liquid, solid or semi-liquid storage tank C0 ₂ . Of course, again, if the separation unit 53 does not exist, the valve 72 may be a simple two-way valve.

Note that only the pipe 12 or 14 connecting with the analysis module 42 could be used, the pipes 16 and 18 being optional.

Furthermore, it is not shown in Figure 1 the control links of the different valves from the information provided by the analysis module 42 which is in fact a complete control system and control.

During the entire recovery process of the mixture of natural gas and CO2 extracted from the well 11 through the pipe 13, the valve 4 associated with the module 3 remains closed, while the valve 21 is open.

At the beginning of the process of recovery of the mixture of natural gas and CO ₂ extracted from the well 11 via the pipe 13, the analysis carried out within the analysis module 42 from the mixture transmitted via the pipe 12 or 13 normally indicates that the concentration of CO ₂ is greater than the threshold S of for example 60%. As a result, the valve 22 connects the pipe 15 to the inlet pipe 31 to the first separation unit 51, while the following valves 23, 24 are closed.

The analysis module 42 can be installed for example on any of the land vehicles 501, 502, 503. The evaluation unit of the analysis module 42 can determine the concentration of CO ₂ in the return flow of the well 11, either continuously or intermittently, but with a good frequency, for example every thirty minutes.

At the start of the process of recovering the mixture of natural gas and CO2 extracted from well 11 via line 13, or more generally, whenever the CO ₂ concentration is higher at the threshold S of for example 60%, it is the separation unit 51 which is active and the valves 23 and 24 remain closed.

On the other hand, when the C0 ₂ concentration falls below the threshold S of for example 60%, while remaining greater than either a minimum threshold, for example of the order of 20%, or a second intermediate threshold, for example, close to 40%. %, the separation unit 51 is deactivated by the switching of the valve 22 in a position that closes the access to the pipe 31 and communicates the pipe 15 with the pipe 17. The valve 23 is then set manually or automatically in a position which connects the pipe 17 to the inlet pipe 32 of the second separation unit 52, while the next valve 24 remains closed.

Similarly, if there is an additional separation unit 53 to which is associated a valve 24, and which is provided to ensure a separation of C0 ₂ when the CO ₂ concentration is between the intermediate threshold and the minimum threshold, when the analysis module 42 has defined that the concentration of CO ₂ is in this range, the separation unit 51 is deactivated by the switching of the valve 22 in a position which closes the access to the pipe 31 and sets communication the line 15 with the pipe 17, the separation unit 52 is also deactivated by the switching of the valve 23 in a position that closes the access to the pipe 32 and communicates the pipe 17 with the pipe 19. valve 24 is then placed manually or automatically in a position that connects the pipe 19 to the inlet pipe 33 of the third separation unit 53, while any valves following antes remain closed.

The control of such subsequent valves associated with any additional separation units to be implemented in other ranges of CO ₂ concentration value is similar.

The control of the various valves 22, 23, 24 is preferably reversible, that is to say that in the case where the CO ₂ concentration would rise to go from a value below the threshold S to a value located at above the threshold S, the separation unit 52 would be deactivated and the separation unit 51 would be reactivated. As indicated above, at the outlet of the separation units 51, 52, 53, the natural gas is evacuated via lines 91, 92, 93 to a network 94 of natural gas or to a storage zone, while the liquid CO2, solid or semi-liquid is transferred through lines 61 to 65 and valves 71, 72 to the tank 81 mounted on a land vehicle 504.

The pre-cooling unit 41 may be associated with one or the other of the separation units 51 to 53.

More particularly, in the pre-cooling unit 41, the mixture from the well 11 or tubing 13 associated with the well 11 is subjected to cooling by heat exchange with:

or the flow of cold natural gas separated in the separation units 51 to 53, which can then be recycled in one or more of these separation units 51 to 53 for further purification, prior to be sent to a distribution network, a storage area or used locally;

or the flow of liquid, solid or semi-liquid C0 ₂ before it is introduced into the tank 81.

In the case where the second separation unit 52 is used with a rapid cold CO ₂ condensation unit for passing CO 2 from a gas phase to a solid or semi-liquid phase when the amount of CO ₂ recovered is between the predetermined threshold S and about 20% natural gas mixture of C0 ₂ recovered can be recovered latent heat C0 ₂ semisolid or liquid before the C0 ₂ is transferred in liquid form in the tank 81.

The pre-cooling unit 41 may comprise a complementary cooling unit comprising a refrigeration system which may be an optimized refrigeration cycle system or a Stirling cycle system (which is suitable for medium-sized mobile applications, for example in submarines).

The first separation unit 51 may comprise a CO ₂ liquefaction unit using a cryogenic distillation system, such as for example those used in carbon purification units, to ensure the separation of the CO ₂ in the liquid state. , semi-liquid or solid from the mixture from the unit of pre-cooling 41 and makes it possible to separate the greater part of the CO ₂ present in the mixture, when the proportion of CO ₂ in the mixture is between 100% and the predetermined threshold S of, for example, between 55% and 65%.

It is also possible to use a cryogenic distillation system with a fast cooling unit of CO ₂ for passing CO ₂ from a gaseous phase to a solid or semi-liquid phase, in the separation unit. 52, when the amount of CO ₂ recovered is between the predetermined threshold S and a lower threshold for example between 20% and 40% of the mixture of natural gas and CO ₂ recovered.

FIG. 6 shows an example of a cryogenic distillation system 400 that can be implemented in the separation unit 52 and that can use a CFZ type of technique (for the English expression "Controlled Freeze Zone" designating a zone of controlled freezing).

In this case, a distillation column 400 comprises a lower stage 401, which is a conventional lower distillation stage, an intermediate stage 402, which constitutes the controlled freezing zone and an upper stage 403, which is a conventional upper distillation stage. . A mixture containing CO ₂ is introduced via a line 404 in the intermediate stage 402. The liquid or semi-liquid CO ₂ is collected at the base of the lower stage 401 and is heated in a heater 405. The shale gas is taken from the top of the upper stage 403, is partially condensed in a condenser 406 and is separated in the separator 407 into a gaseous phase which is discharged and into a liquid phase which is recycled in the upper stage 403. The liquid produced in the upper stage 403 is collected and stored in a tank 408, where it can be pumped to be sprayed in the intermediate stage 402. Installations such as those of Figure 6 are described for example in US 4533372 , US 8312738 and US 2009/0266107.

As can be seen in FIG. 1 with the connecting pipe 37, it is possible to implement successively the separation units 51 and 52 which then operate in cascade, a first CO ₂ separation being carried out within the separation unit 51 with a first separation process and the residual mixture with a reduced proportion of C0 ₂ being introduced into the separation unit 52 with a second separation process more suitable for a mixture containing a lower concentration of C0 ₂ .

Similarly, with the connecting pipe 35 between the separation unit 52 and the separation unit 53, it can be seen that it is possible to continue the gas purification process within one or more additional units, such as unit 53, which provide cooling and liquefaction of CO ₂ or rapid cooling to pass CO ₂ from a gaseous phase to a solid or semi-liquid phase.

In this case, it is possible to use, for example, an expansion unit in a Joule-Thomson valve, as described for example in documents US Pat. No. 7,325,415, WO 2010/141996, WO 2011/026170 and WO 2010/141995.

It is also possible to use a two-phase expansion turbine, as described, for example, in documents US 2011/226010, WO 2010/105820 and WO 2012/068588, which supplies energy for example for re-compressing natural gas or to ensure additional refrigeration. A non-stick coating prevents the CO _{2 from} settling on the blades of the turbine and the solid CO ₂ can be recovered in a centrifugal device after the turbine.

Figure 3 shows an example of a bi-phasic expansion turbine system 100. The gaseous mixture to be treated is introduced through an inlet 111 into a heat exchanger 101 providing condensation. The flow at the outlet of the heat exchanger-condenser 101 is applied to a compressor 102 whose output stream is applied to a heat exchanger 103. The output of the heat exchanger 103 is applied to a small refrigeration loop 104. additional which itself feeds an exchanger-freezer 105 which produces on the line 114 a solid CO ₂ stream and also feeds an expansion stage 106, followed by a solid-gas separation unit 107, with an output line 113 providing a solid CO ₂ stream and an outlet line 112 providing a depleted CO ₂ stream which is reapplied to the exchanger 103. The lines 113, 114 in which a solid CO ₂ stream flows are applied to a compressor 108 of solid. In At the outlet of the exchanger 103, a line 116 feeds a liquid pump 109 to provide a pressurized liquid C0 ₂ stream, a line 117 provides a de-cooled C0 ₂ stream, and a line 118 provides SO _x and other freezable components. .

At least one of the first and second separation units

51, 52, 53 may comprise a convergent-divergent nozzle provided in its diverging portion with a liquid or solid C0 ₂ capture slit.

FIG. 4 shows an example of a "twister", that is to say, swirling, convergent-divergent nozzle separation system 200, which is described, for example, in US 8475572 B2. A saturated gas flow 211 is introduced into a body 201 defining a chamber 202 generating a vortex and equipped with static guide vanes 203. The chamber 202 is followed by a Laval nozzle 204 with a converging tapered inner body 205 followed by a neck and a diverging portion. The supersonic velocities reached at the level of the neck correspond to a transformation of the energy in speed and provoke relaxation and cooling. By cyclone effect of the vortex flow, a separation of C0 ₂ 206 droplets or flakes occurs, which are projected outwardly of the nozzle and can be captured by a side slot 209, while a central diverging diffuser 207 provides at exit 208 a dry gas.

The embodiment of FIG. 5 shows a separation system 300 similar to a convergent-divergent nozzle, which is described in particular in document US Pat. No. 7985278. The inlet 301 of the convergent portion 302 of the nozzle receives from a compressor a flow gaseous subsonic regime. At the neck 303 of the nozzle equipped with valves 304 creating a vortex effect, we obtain a transient regime creating shock waves with a Mach number equal to 1. In the divergent portion 305, we obtain supersonic speeds with a number Mach typically typically between 3 and 5 and there is rapid isentropic relaxation. Freezing of CO ₂ begins and solid particles 306 created in the outer zone can be evacuated and captured by a lateral opening 307. The technologies described with reference to Figures 3 to 6 are only examples and can be adapted for example to be as compact as possible. For example, the distillation column of FIG. 6 may be equipped with gaskets or the various heat exchangers may comprise different types of fins.

Each separation unit 51, 52, 53 can itself be divided into several units operating in parallel and can be installed on different land vehicles.

Each separation unit 51, 52, 53 can itself also be divided into several units operating in series, each performing part of the process and can be installed on different land vehicles.

As mentioned above, the C0 ₂ recovered in liquid form or in the form of semi-liquid slurry is stored in one or more tanks 81 placed on one or more trailers or the like for reuse. Each reservoir 81 may be associated with a separation unit 51, 52, 53, but a reservoir 81 may also be used with several or all of the separation units 51 to 53, in particular as shown in the example of FIG.

The natural gas recovered during the separation phase with CO ₂ immediately following the CO ₂ stimulation step, that is to say before the normal production of well 11, can be evacuated by a pipe. line to a storage or consumption area or can be consumed on the spot, for example to supply motors, such as engines of electrical energy production plants used for example for the drive of C0 ₂ injection pumps _/ or for the operation of low temperature separation systems.

Claims

A method of treating and separating an unconventional gas comprising a) an initial hydraulic stimulation step, using pressure injection of liquid carbon dioxide into a well (11) for operating a atypical deposit in which said unconventional gas is trapped in a rock,

the method comprising in particular the step:

b) recovering at low temperature after the stimulation operation, a mixture of natural gas and CO ₂ ,

the method being characterized in that this low temperature recovery step comprises in particular a step b1) of evaluation, in the mixture of natural gas and recovered CO ₂ , of the amount of CO ₂ and a step b 2) of comparison of this amount of CO ₂ with respect to a predetermined threshold (S), and the method further comprising the following steps:

c) separating at least a portion of the CO ₂ in the liquid, semi-liquid or solid state from said mixture of natural gas and recovered CO ₂ , with a different separation technique depending on whether the amount of CO ₂ is greater or less than said predetermined threshold (S),

d) storing temporarily in at least one portable tank (81) on a land vehicle (504) the CO ₂ separated in the liquid, semi-liquid or solid state, and

e) moving the land vehicle (504) with said at least one tank (81) to another site to reuse the separated CO ₂ and stored in the liquid, semi-liquid or solid state in order to perform a new stimulation operation on a new neighboring well, in the same unconventional gas field or a nearby unconventional gas field.

2. Method according to claim 1, characterized in that when the amount of CO ₂ recovered is between 100% and said predetermined threshold (S) of the mixture of natural gas and recovered CO ₂ , the step c) of separation of CO ₂ in the liquid, semi-liquid or solid state from said mixture comprises a CO ₂ liquefaction step using a cryogenic distillation system.

3. Method according to claim 1, characterized in that when the amount of CO ₂ recovered is between said predetermined threshold (S) and 20% of the mixture of natural gas and recovered CO2, step c) of separation of at least a portion of the C0 ₂ in the liquid, semi-liquid or solid state from said mixture comprises a rapid cold CO ₂ condensation step passing CO ₂ from a gaseous phase to a solid phase.

4. Method according to claim 1, characterized in that the evaluation step, in the mixture of natural gas and CO ₂ recovered, of the amount of CO ₂ is carried out using gas analysis. by micro-chromatography.

5. Method according to any one of claims 1 to 4, characterized in that said predetermined threshold is equal to a value between 55 and 65% and preferably equal to 60%.

6. Method according to any one of claims 1 to 5, characterized in that, after step c) of separation of at least a portion of C0 ₂ at low temperature after the stimulation operation, the natural gas is recovered in gaseous form for later use.

7. Method according to any one of claims 1 to 6, characterized in that the mixture of natural gas and CO ₂ recovered at low temperature after the stimulation operation further comprises at least one additional component such as the nitrogen N ₂ and in that during step c) of separation of at least a portion of the CO ₂ at low temperature after the stimulation operation, the natural gas is recovered with the at least one additional component in gaseous form for later use.

8. An unconventional gas treatment and separation system comprising an initial hydraulic stimulation unit (3), with a unit (4) for injecting liquid carbon dioxide under pressure in a well (11) for operating an atypical deposit in which said unconventional gas is trapped in a rock,

the system comprising a low temperature recovery unit (10) after a stimulation operation, a mixture of natural gas and CO ₂ ,

the system being characterized in that the low temperature recovery unit (10) comprises in particular an evaluation unit (42), in the mixture of natural gas and recovered CO ₂ , the amount of CO ₂ and a unit ( 42) for comparing this amount of C0 ₂ with respect to a predetermined threshold (S), and the system further comprises: a unit for separating at least a portion of the C0 ₂ in the liquid, semi-liquid or solid from said mixture of natural gas and C0 ₂ recovered by said recovery unit, with at least first and second separation units (51, 52, 53) different depending on whether the amount of C0 ₂ is above or below said threshold predetermined (S),

at least one unit (81) for temporary storage of C0 ₂ separated in the liquid, semi-liquid or solid state, and

at least one land vehicle (501, 502, 503, 504) for moving said at least one temporary storage unit (81) to another site to reuse the separated CO ₂ and stored in the liquid, semi-liquid or solid state , in order to supply a unit (4) for injecting liquid carbon dioxide under pressure into a new stimulation unit (3) on a new neighboring well (11), in the same unconventional gas deposit or in a deposit unconventional gas neighbor.

9. System according to claim 8, characterized in that the first separation unit (51) comprises a CO ₂ liquefaction unit using a cryogenic distillation system to ensure the separation of C0 ₂ in the liquid state, semi liquid or solid from said mixture when the amount of CO ₂ recovered is between 100% and said predetermined threshold (S) of the mixture of natural gas and CO ₂ recovered.

10. System according to claim 8, characterized in that the second separation unit (52) comprises a condensation unit of C0 ₂ to rapid cooling to pass CO ₂ from a gas phase to a solid or semi-liquid phase when the amount of CO ₂ recovered is between said predetermined threshold (S) and 20% of the mixture of natural gas and CO ₂ recovered.

11. System according to any one of claims 8 to 10, characterized in that the unit (42) of evaluation, in the mixture of natural gas and CO ₂ recovered, the amount of CO ₂ , comprises an analyzer. of gas by micro-chromatography.

12. System according to any one of claims 9 to 11, characterized in that the first and second different separation units (51, 52, 53) are connected to said recovery unit (81) by a system of valves (22). , 23, 24, 71, 72) controlled from the output information of said comparison unit (42).

13. System according to any one of claims 9 to 12, characterized in that at least one of the first and second different separation units (51, 52, 53) comprises a unit (41) of self pre- cooling in which the mixture of natural gas and recovered CO ₂ is subjected to heat exchange with a separate natural gas stream before reuse.

14. System according to any one of claims 9 to 13, characterized in that at least one of the first and second different separation units (51, 52, 53) comprises a pre-cooling unit in which the gas mixture. and recovered CO ₂ is subjected to heat exchange with the latent heat of a CO ₂ stream previously separated in the second condensing separation unit (52) and subjected to a passage from the solid state to the liquid state before reuse.

15. System according to any one of claims 9 to 14, characterized in that at least one of the first and second different separation units (51, 52, 53) comprises a unit of further cooling comprising a Stirling cycle type refrigeration system.

16. System according to any one of claims 9 to 15, characterized in that at least one of the first and second different separation units (51, 52, 53) comprises a distillation column (400) with means recovering liquid, semi-liquid or solid C0 ₂ at the bottom of the column and means for recovering the natural gas at the top of the column.

17. System according to any one of claims 9 to 16, characterized in that at least one of the first and second separation units (51, 52, 53) comprises an expansion unit in a Joule-Thomson valve.

18. System according to any one of claims 9 to 16, characterized in that at least one of the first and second separation units (51, 52, 53) comprises a two-phase expansion turbine followed by a centrifugal device. to separate the solid C0 ₂ .

19. System according to any one of claims 9 to 16, characterized in that at least one of the first and second separation units (51, 52, 53) comprises a convergent-divergent nozzle (200; 300) provided with in its diverging portion of a slot (209; 307) for capturing liquid or solid C0 ₂ .

20. System according to any one of claims 9 to 19, characterized in that it comprises different storage units associated respectively with the first and second separation units (51, 52, 53).

21. System according to any one of claims 9 to 20, characterized in that it further comprises a CO ₂ gas phase separation unit without liquefaction device to ensure the separation of C0 ₂ in the gaseous state and recovery of natural gas from said recovered natural gas and CO ₂ mixture, when the amount of CO2 is less than 20% in the mixture of natural gas and recovered CO2.