Classifications

• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
  • E21B43/25—Methods for stimulating production
  • E21B43/26—Methods for stimulating production by forming crevices or fractures
• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B36/00—Heating, cooling or insulating arrangements for boreholes or wells, e.g. for use in permafrost zones
  • E21B36/001—Cooling arrangements
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01T—SPARK GAPS; OVERVOLTAGE ARRESTERS USING SPARK GAPS; SPARKING PLUGS; CORONA DEVICES; GENERATING IONS TO BE INTRODUCED INTO NON-ENCLOSED GASES
  • H01T9/00—Spark gaps specially adapted for generating oscillations
• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B33/00—Sealing or packing boreholes or wells
  • E21B33/10—Sealing or packing boreholes or wells in the borehole
  • E21B33/12—Packers; Plugs
  • E21B33/124—Units with longitudinally-spaced plugs for isolating the intermediate space

Definitions

• the present invention relates to a device and a method for fracturing a hydrocarbon geological reservoir, as well as a method for producing hydrocarbons and a method for calibrating the device.
• the permeability and / or porosity of the material constituting the reservoir has an influence on the production of hydrocarbons, in particular on the speed of production and thus the profitability.
• This is particularly recalled by the article "Porosity and Permeability of Eastern Devonian Shale Gas" by Soeder, D.J., published in SPE Training Evaluation, in 1988, vol. 3, No. 1, pp. 116-124, which presents the study of eight samples of shale gas (i.e. gas schist) from the Devonian, from the Appalachians.
• This article explains in particular that the production of this shale gas presents the difficulty that the permeability of the reservoir (i.e. of the material constituting the reservoir) is low.
• Static fracturing is a targeted dislocation of the reservoir, by means of the injection under very high pressure of a fluid intended to crack the rock.
• the crack is made by a mechanical "stress” resulting from a hydraulic pressure obtained using a fluid injected under high pressure from a well drilled from the surface.
• Hydro fracturing or “hydrosilicous fracturing” (or “frac jobs”, “frac'ing” or more generally “fracking”, or “massive hydraulic fracturing”).
• US 2009/044945 A1 discloses in particular a static fracturing method as described above.
• Static fracturing has the disadvantage that tank fracturing is generally unidirectional. Thus, only the hydrocarbon present in the reservoir portion around a deep but very localized crack is produced more rapidly.
• US 4,074,758 discloses a method of generating an electro-hydraulic shock wave in a liquid in the wellbore to better recover oil.
• US 4,164,978 suggests following the shock wave with an ultrasonic wave.
• Document US 5,106,164 also describes a method for generating a plasma explosion and thus fracturing a rock, but in the case of a shallow hole, for a mining application and not for the production of hydrocarbons.
• US 4,651,311 and US 4,706,228 disclose a device for generating an electrical discharge with electrodes in an electrolyte-containing chamber, wherein the electrodes are not subject to erosion by the plasma of the discharge.
• WO 2009/073475 discloses a method for generating an acoustic wave in a fluid medium present in a well with a device comprising two electrodes between an upper packer and a lower packer defining a confined space. This document describes that the acoustic wave is maintained in a non-"shock wave” state in order to improve the damage, without, however, clarifying the differences between "ordinary” acoustic wave and "shock" wave.
• a fracturing device of a hydrocarbon geological reservoir wherein the device comprises two packings defining between them a confined space in a well drilled in the tank, a temperature control device a fluid in the confined space, a pair of two electrodes arranged in the confined space, and an electrical circuit for generating an electric arc between the two electrodes.
• the circuit comprises at least one voltage source connected to the electrodes and an inductance coil between the voltage source and one of the two electrodes.
• the device may include one or more of the following features:
• the temperature control apparatus regulates the fluid temperature to optimize the energy efficiency of the pre-discharge phase when generating an electric arc
• the temperature control apparatus maintains the temperature of the fluid at a value between 45 and 67 ° C, preferably above 50 ° C and / or below 62 ° C;
• the device further comprises a device for regulating the pressure of the fluid substantially at atmospheric pressure;
• the temperature control apparatus comprises a fluid cooling system;
• the inductance coil is of adjustable inductance, preferably between 1 ⁇ and 100 mH, more preferably between 10 ⁇ and 1 mH;
• the distance between the two electrodes is adjustable, preferably between 0.2 and 5 cm, more preferably between 1 and 3 cm;
• the voltage source comprises a capacitor with a capacity greater than 1 ⁇ , preferably greater than 10 ⁇ ;
• the capacity of the capacitor is adjustable, preferably less than 1000 ⁇ , more preferably less than 200 ⁇ ;
• the circuit further comprises a Marx generator and ferrites forming a saturable inductor in a path leading the capacitor directly to the inductor, the ferrites being saturated once the Marx generator is discharged; the capacitor is separated from the inductor by a spark gap initiated by a pulse generator;
• the electrodes have a radius of between 0.1 mm and 50 mm, preferably between 1 mm and 30 mm;
• the device comprises an unhooking system; and or
• the device comprises several pairs of electrodes.
• the method comprises electrically fracturing the reservoir by generating an electric arc by the above and simultaneously controlling the temperature of a fluid in the confined space of the device.
• the calibration method comprises the steps of providing the device, determining a pre-breakdown voltage above which the electric arc is generated, then measuring a breakdown voltage across the electrodes and a breakdown time as a function of the temperature of the fluid, applying the preclamping voltage and varying the temperature of the fluid, then deduce from the previous step the energy efficiency of the pre-discharge phase as a function of the temperature, and then define a temperature or an interval of target temperatures for the regulating device of the temperature as a function of a maximum of the energy efficiency deduced in the previous step.
• Figures 18 to 20 diagrams showing proposed fracturing methods; and Figures 21 to 23, an example of the electrical fracturing of the fracturing process of any one of Figures 18 to 20.
• a fracturing device for a geological hydrocarbon reservoir comprises two packings defining between them a confined space in a well drilled in the tank (i.e. intended to be confined at least when the device is installed in a well drilled in the tank).
• the device comprises an apparatus for regulating the temperature of a fluid in the confined space.
• the device comprises a pair of two electrodes arranged in the confined space.
• the device also includes an electrical circuit (configured / adapted / provided) for generating an electric arc between the two electrodes.
• the circuit comprises at least one voltage source connected to the electrodes and an inductance coil between the voltage source and one of the two electrodes.
• Such a device makes it possible to fracture a hydrocarbon reservoir in an improved manner.
• such a device makes it possible to generate an electric arc between the two electrodes, and thus to electrically fracture the reservoir when the device is located in a well drilled in the reservoir.
• the inductance coil makes it possible to obtain an electric arc giving rise to a pressure wave which fractures the reservoir in an improved manner.
• the temperature control apparatus makes it possible to regulate the temperature, and thus to have the temperature enabling a pressure wave to be obtained, leading to good fracturing of the tank.
• the term "electric arc” refers to an electric current created in an insulating medium.
• the generation of the electric arc induces a "pressure wave", ie a mechanical wave which in its passage undergoes a pressure in the middle in which the wave passes.
• the generation of the electric arc allows a more diffuse / multidirectional reservoir damage than ⁇ damage resulting from static fracturing.
• the generation of the electric arc thus causes micro-cracks in all directions around the position of the electric arc, and thus increases the permeability of the reservoir, typically a factor 10 to 1000.
• this increase in permeability occurs without using a means to prevent the closure of microfissures, such as propellant injection.
• electric fracturing does not require considerable energy or large amounts of water. There is therefore no need for a particular water recycling system.
• the electric arc is preferably generated in a fluid present in a well drilled in the tank.
• the pressure wave resulting from the electric arc is thus transmitted with fewer attenuations.
• the drilled well contains fluid which is typically water. In other words, when electric fracturing follows a drilling process, the drilled well can be automatically filled with water present in the tank. Potentially, if the drilled well does not fill automatically, it can be filled artificially.
• the device will be described before describing such an electric fracturing method. However, reference will be made to the method when describing the device, and it is understood that the various functionalities of the device (ie the different actions that it makes possible to perform) can be integrated into the process even when they are not repeated in the description of the process.
• the circuit comprises at least one inductance coil between the voltage source and the electrode to which it is connected.
• the inductor is a component that induces a time delay of the current with respect to the voltage.
• the value of an inductance is expressed in Henry.
• the inductance coil may optionally be wound around a ferromagnetic material core, or ferrites.
• the inductance coil is also known as "self”, “solenoid”, or “self-inductance”.
• the inductance attenuates the current front in the circuit. This makes it possible to obtain a rise time of the slower pressure wave, and thus a pressure wave which penetrates better into the tank. Damage to the tank is thus deeper.
• the inductance may be greater than 1 ⁇ or 10 ⁇ , and / or less than 100 mH or 1 mH.
• the seals may be provided to conform to the well wall, generally cylindrical, thereby defining a confined space therebetween.
• the device may comprise a membrane that delimits the confined space.
• the membrane can be hermetic (or waterproof) and rigid. This makes it possible to dissociate the pressure prevailing in the confined space from the surrounding pressure, for example the hydrostatic pressure of the well if the latter is flooded (eg following hydraulic fracturing).
• the membrane is then preferentially in a material adapted to a good conduction of pressure waves, which optimizes electrical fracturing.
• the fluid may be a fluid (eg water) present in the drilled well, or already included in the device, even before use.
• the device may provide an opening for renewing the water.
• “Confined” means that the confined space is provided so that the prevailing temperature can be modified by means of the temperature control device, and optionally so that the pressure therein may also be modified by means of a possible apparatus for regulating the fluid pressure in the confined space (eg the pressure regulating apparatus comprises a pump, eg a pump for increasing the pressure of the fluid).
• the pressure regulating apparatus comprises a pump, eg a pump for increasing the pressure of the fluid.
• This (these) regulation (s) optimize the fluid present in the confined space to promote the appearance of an electric arc between the two electrodes and / or for the electric arc obtained gives rise to a good wave pressure, depending on the conditions of the reservoir or the nature of the fluid.
• “containment” may but does not necessarily mean complete closure, and similarly, the seal may but is not necessarily total.
• the temperature control apparatus is a device that maintains (at least approximately) the temperature of the fluid equal to a target value or within a target range.
• the temperature control apparatus may include a thermostat.
• the target may be predetermined or calculated, possibly as a function of input values, for example values derived from measurements, e.g., fluid pressure.
• the target may be adapted to the conditions of the reservoir and / or the fluid in the confined space and / or the characteristics of the fracturing device and / or the fluid, so as to have the "best" temperature or the "best” temperature range according to these conditions and / or characteristics.
• the temperature control apparatus may therefore comprise a temperature sensor and / or a control unit with a processor coupled to a memory recording the target or a program for calculating the target. Additionally, the temperature control apparatus may include a fluid heating system and / or a fluid cooling system for effecting control. These different components are known to those skilled in the art.
• better temperature or “better” temperature range is meant the temperature (s) which, given the characteristics of the device and the fluid, and the pressure of the fluid, allows (tent) to obtain a pressure wave (following the generation of the electric arc) resulting in a deeper and / or more diffuse damage. Indeed, following tests, especially those that will be presented later, it was surprisingly found that such a temperature optimum existed, while one could think that the fluid approached its temperature boiling, remaining however below, better would be ⁇ damage.
• the temperature control apparatus thus makes it possible to regulate the temperature for example around a target well below the boiling temperature of the fluid, and to obtain, surprisingly, better damage.
• the temperature control apparatus can (be provided to) regulate the temperature of the fluid to optimize the energy efficiency of the pre-discharge phase during the generation of an electric arc.
• the energy efficiency of the pre-discharge phase is the ratio (or a measure proportional to this ratio) between the electrical energy necessary to initiate the pressure wave induced by the electric arc and the electrical energy supplied by the experimental device (which electrical energy is determined by the dimensioning of the device).
• the higher the energy efficiency of the pre-discharge phase the more the energy available for the discharge phase itself remains after the pre-discharge phase, which results in a higher performance pressure.
• the target is chosen to optimize (at least approximately) this measurement.
• this can be accomplished by a calibration method (ie, a pre-use configuration) of the apparatus temperature control apparatus.
• the device can first be provided, eg under real conditions in the well, or by reproducing in the laboratory the pressure of the fluid for which it is intended to use the device (in other words, the fluid is also provided) . It is also possible to determine a pre-breakdown voltage of the device (ie the voltage threshold applied between the electrodes beyond which the electric arc is generated). This can be done in different ways, one of which is explained later during the presentation of the tests, in particular with reference to FIGS. 11 to 17.
• the breakdown voltage across the terminals of the electrodes ie the voltage at the terminals of the electrodes necessary for the initiation of the electric arc
• the breakdown time ie the duration of application of the voltage necessary for the initiation of the electric arc
• the pre-breakdown voltage previously determined
• the temperature of the fluid is varied.
• a temperature or a target temperature range for the temperature control apparatus may be set based on (ie in agreement with) a maximum of the energy efficiency deduced in the previous step.
• the temperature control apparatus can maintain the temperature of the fluid at a value between 45 and 67 ° C, preferably above 50 ° C and / or below 62 ° C. These values of the temperature of the fluid in the confined space make it possible to obtain an energy efficiency of the pre-discharge phase greater than 80% at atmospheric pressure.
• the device suitably comprises a fluid pressure regulating apparatus adapted to regulate the pressure of the fluid substantially at atmospheric pressure.
• the temperature control apparatus may comprise a fluid cooling system. This allows a better use of the device, including staying at the optimum temperature. Indeed, each generated electric arc raising the temperature beyond the target by release of heat, it is appropriate to cool the water from the generation of a certain number of generations of such an electric arc to remain at home. optimum temperature.
• the device can be movable along the well and set before the generation of an electric arc.
• the device may include moving means, e.g., by remote control.
• the device can then be powered by a high voltage power supply located on the surface and connected to the device by electrical cables following the well.
• the device can then also include a stall system. This allows the device to remain in the well when it is blocked. We can then recover the well and / or the stem train.
• the device may be of generally elongated shape, which allows it to be moved more easily in the well.
• the device may also include several pairs of electrodes, over a length.
• the electrodes can be powered by several storage capacities. This makes it possible to perform the fracturing more quickly. Indeed, several arcs can then be generated at the same time between each pair of electrodes, and achieve several damages at the same time.
• the device may include a chemical additive injection system that includes a storage tank for storing the additive and a pump for injecting the additive into the confined volume during use of the device.
• the heater may include a source of hot fluid and a delivery conduit, the conduit having an opening near the electrodes such that, during operation of the device, hot fluid can be routed from the source to the electrodes.
• the conduit can pass through one or both electrodes.
• FIGS. 1 to 4 show a device 100 constituting an example of the fracturing device of a hydrocarbon geological reservoir presented here. -above.
• the device 100 of FIG. 1 comprises the two packings 102 and 103 defining between them the confined space 104.
• the confined space 104 is here delimited by the membrane 108.
• the device 100 also comprises the two electrodes 106. arranged in the confined space 104.
• the two electrodes 106 are in the example respectively connected to the voltage source by an input 109 and a ground 103 (here merged with the seal 103) of the circuit, which allows the formation of the electric arc between the two electrodes 106.
• the electrodes may have a radius of between 0.1 mm and 50 mm, preferably between 1 mm and 30 mm.
• the inlet 109 may consist of an insulated cable.
• FIG. 1 also schematically shows the apparatus for regulating the temperature 105 of the fluid in the confined space and the pressure regulating apparatus 107.
• the electrical circuit for generating an electric arc between the two electrodes 106, its voltage source and the inductance are not shown, but may be in accordance with Figures 2 to 4 which show schematically examples of the device 100.
• the device 100 of FIG. 2 comprises the inductor 110.
• the voltage source comprises the capacitor 112.
• the capacitor 112 may have a capacity greater than 1 ⁇ , preferably greater than 10 ⁇ . Such a capacity makes it possible to reach an energy causing the appearance of a subsonic arc.
• the electric discharge is called “subsonic” or “supersonic” depending on its formation rate.
• a “subsonic” discharge is typically associated with thermal processes: the arc propagates through gas bubbles created by warming water. We speak of “slow” propagation of the electric discharge, typically of the order of 10 m / s. The main characteristics of a subsonic discharge are related to high energies involved (typically beyond several hundred Joules), thermal processes associated with a long time of application of the voltage and at low levels of energy. voltage (low electric field). In this discharge regime, the pressure wave propagates in a large volume of gas before spreading in the fluid.
• a “supersonic” discharge is typically associated with electronic processes. The discharge spreads in water without thermal process with a filamentary appearance.
• the capacitor 112 may have a capacity less than 1000 ⁇ , preferably less than 200 ⁇ .
• the capacitor 112 is separated from the inductor by the spark gap 114 which can be initiated by the pulse generator 116. This makes it possible to control the discharges of the capacitor 112 and thus the pressure waves generated by the electric arc.
• the pulse generator 116 may be configured for wave repetition, as described later.
• the voltage source (i.e. the capacitor 112) is charged by a high voltage charger 120 provided in an auxiliary circuit 122 at a voltage U of between 1 and 500 kV, preferably between 50 and 200 kV.
• the auxiliary circuit is preferably located on the surface, and is then separable from the device.
• the device 100 of FIG. 3 is different from the example of FIG. 2 in that a Marx generator 118 replaces the capacitor 112 and the assembly (spark gap 114 + pulse generator 116).
• the generator Marx 118 allows during its discharge the creation of a supersonic electronic arc, imposing a higher voltage than the capacitor 112.
• the voltage source comprises the capacitor 112 of FIG. 2 and the Marx generator 118 of FIG. 3.
• the pulse generator 116 primes the first spark gap 117 of the Marx generator 118.
• Device 100 further comprises ferrites 119 forming a saturable inductance in a path leading the capacitor directly to the inductor.
• the ferrites 119 are configured to be saturated once the Marx generator 118 is discharged. Once the ferrites 119 are saturated, only the capacitor 112 discharges. This allows a temporary isolation of the capacitor 112 and thus the passage (ie switching) of a supersonic arc to a subsonic arc. The device thus ensures a coupling between a supersonic and subsonic discharge.
• the subsonic discharge produced by the capacitor 112 occurs after a delay corresponding to the breakdown time of the generator Marx 118.
• the switching can be done in a time less than 1 s.
• the duration of the discharge produced by the Marx generator 118 is very short, lasting less than 1 microsecond, and amplitude greater than 100 kV.
• the various components of the device 100 have adjustable characteristics, ie their characteristics can be modified before use as a function of the reservoir, or during use as a function of the response or advancement of fracturing.
• the coil 110 may be of adjustable inductance.
• the characteristics of the Marx generator 118 (capacity of each capacitor in parallel, number of capacitors operating) can be adjustable.
• the distance between the electrodes 106 preferably between 0.2 and 5 cm, more preferably between 1 and 3 cm, can also be adjustable.
• the capacitance of the capacitor 112 can also be adjustable. This makes it possible to have a device 100 adapted to the fracturing of any type of tank. Indeed, it is not necessary to replace the device 100 when changing the reservoir to be fractured (and that the material is different) because it is sufficient to modify one or more of the adjustable parameters. This also makes it possible to optimize ⁇ damage by modifying, possibly remotely, the parameters in use.
• the generation of the pressure wave can be broken down into two phases: a pre-discharge phase S 100 and a post-discharge phase. discharge SI 10, separated by the appearance S 105 of the arc.
• the voltage drops. This fall corresponds to the discharge of the equivalent capacity of the energy bank or the Marx generator into the equivalent resistance of the device 100.
• the greater the equivalent resistance the best is the conservation of energy in the pre-breakdown phase.
• the configuration of electrodes can therefore, in each case (subsonic or supersonic) allow to obtain the least possible loss of energy. This corresponds to the optimization of the water heating in one case and the electric field in the other.
• the electrical circuit can be modeled by an RLC circuit in oscillating mode.
• This current i ⁇ t) is a function of the breakdown voltage U B (dielectric breakdown of the medium) of the capacitor, the inductance and the resistance of the circuit.
• FIGS. 6 and 7 represent the peak pressure measurements as a function of the maximum current during the discharge phase S11 and the linear regression of the measurements, respectively in subsonic and supersonic mode. It can be seen that the pressure at a similar peak current is greater for a "supersonic" discharge. This can be explained in part by the processes generating the electric arc in the water and the volume of gas between the electric arc and the liquid in the inter-electrode space present.
• a pressure sensor has been used to visualize the waveforms of the pressures generated as a function of the frequency spectrum.
• This frequency spectrum can indeed be modified by the dielectric breakdown mode, by the parameters of the electric circuit, by the volume of gas, as well as by the nature of the liquid used.
• Two examples of frequency spectrum associated with a subsonic and supersonic discharge were tested. It appeared that the lower frequencies the spectrum has, the less diffuse the damage.
• the result of various experiments carried out shows a linear relation of the dPmax / dtp as a function of the current front ⁇ max max , shown in FIG. 10.
• the current front has an influence on the pressure front. The slower the current front, the lower the pressure.
• the peak current i max is controlled by the energy available at the time of the arc noted Eb and the inductance of the circuit L, these are the two parameters on which the user must act.
• the resistance R is considered very weak and the capacitance C is a function of the energy Eb.
• the peak pressure generated is thus controlled by the current i max (parameters Eb and L) and by the coefficient (function of inter-electrode distance and dielectric breakdown mode of water). We can therefore act on Eb, L and to obtain the desired pressure.
• the coefficient & 2 corresponds to the electro-acoustic physical coupling.
• the front of the pressure wave is controlled by the coefficients and & 2 and by the values of L and C (electrical circuit parameters).
• the maximum of the pressure wave, resulting from the dielectric breakdown of water depends mainly on the value of the maximum current, called i max .
• This value of the peak current is a function of the breakdown voltage and the impedances of the electrical circuit.
• a means of optimizing the current is to increase the breakdown voltage of the gap. This amounts to maximizing the switched electrical energy in the medium.
• the amplitude of the pressure wave is optimized by reducing the impedance of the circuit.
• the current injection form, the dielectric breakdown mode and the nature of the liquid have an influence on the dynamics of the pressure wave.
• This dynamic and the acoustic performance of the device can also be modified by the injection of artificial bubbles and by the "double pulse” method (subsonic and supersonic).
• the value of the pressure peak is greater in supersonic mode than in subsonic mode.
• the value of the pressure peak is greater the greater the inter-electrode distance.
• the geometry of the electrodes, with constant injected current, has no influence on the peak pressure generated, but may play a role in reducing the electrical losses in the pre-discharge phase.
• the above studies confirm the utility of introducing an inductance between the voltage source and one of the two electrodes to act on the pressure wave generated in the end.
• the studies also confirm the interest of having adjustable parameters, e.g. the inductance, the capacity of the capacitor, the characteristics of the generator of Marx. Indeed, the pressure wave depends on these parameters, the ability to adjust them to control the pressure wave.
• the electrode configuration consists of two spike electrodes (2.5 mm radius of curvature) and an inter-electrode distance of 3 mm.
• the insulating material used for the High Voltage bushing is PEEK 450G.
• the dielectric strength of the water is characterized by determining the preclamping voltage t / 50, which is a voltage value which causes 50% hold and 50% of strokes.
• the method used to determine this voltage U50 is called "up and down”. Voltage levels are pre-selected and a series of tests is carried out at these different levels, the result of each test determining the next level: next higher level when held, next lower level when primed. It then takes about fifty attempts to acquire the U50 value. In the set of curves presented, the value noted U50 represents the average of a series of 50 shocks.
• Equivalent water resistance was determined using an experimental method and simulation using the COMSOL software.
• R water is determined by measuring the exponential decay of the voltage wave, as shown in Figure 11.
• the value of the discharge constant is the time required for a 37% fall. the initial voltage value of the capacitor.
• the evolution of the conductivity of water as a function of temperature is not the same depending on the type of water used (pure, demineralised, tap or seawater for example). Indeed, the initial conductivity determines the influence of the temperature with respect to the posterior evolution of the conductivity. In our case we used demineralized water and the initial parameters were determined by experimentation.
• the resistance could be determined from Ohm's law.
• the objective of this part of the simulation tests was to characterize the HP enclosure in terms of voltage withstand and equivalent impedance (capacitance and resistance).
• Electrothermal losses related to heating are thus defined by:
• the efficiency of the pre-discharge phase is expressed by:
• FIG. 14 shows the evolution of the breakdown voltage U b and the corresponding time T b as a function of the water temperature, as well as the standard deviations.
• the interpretation of the variation of the parameter U b is more delicate. It takes into account the small variation of / / 50 over the range 25 ° C - 60 ° C coupled with a significant decrease in the duration of application of the voltage wave.
• the voltage U b therefore increases over this temperature range. Beyond this temperature range, the breakdown voltage decreases significantly as the temperature increases from 60 ° C to 90 ° C. The duration of application of the voltage being further reduced, the breakdown voltage U b can only decrease.
• FIGS. 11 to 17 therefore shows the advantage of regulating the temperature of the fluid in the confined space in order to improve the energy efficiency and to induce a pressure wave, the dimensions of the device being fixed, allowing better damage.
• the fracturing device can be used in a method of fracturing a hydrocarbon geological reservoir.
• the method includes electrical fracturing of the reservoir by the generation of an electric arc by the device, which induces a pressure wave leading to the fracturing.
• the process can understand the regulation of the temperature of a fluid in the confined space of the device, thanks to the temperature control device.
• the device can also be used in a hydrocarbon production process comprising the fracturing of a geological reservoir of hydrocarbons according to the preceding method.
• FIG. 18 there is also provided a method of fracturing a hydrocarbon geological reservoir.
• the process of Figure 18 comprises static fracturing (S20) of the tank by hydraulic pressure.
• the method of FIG. 18 also comprises, before, during or after the static fracturing (S20) (these three possibilities being represented by the dotted lines in FIG. 18), the electrical fracturing (S 10) of the reservoir by generating a electric arc in a well drilled in the tank, as described above.
• the process of Figure 18 improves the fracturing of the reservoir.
• Static fracturing can be any type of static fracturing known from the prior art.
• the static fracturing (S20) may comprise, after the eventual drilling of a well in the reservoir, the injection of a fluid under high pressure into the well.
• Static fracturing (S20) thus creates one or more unidirectional cracks, typically deeper than those created by electrical fracturing (S 10).
• the fluid can be water, a mud or a technical fluid with controlled viscosity enriched with hard agents (grains of sieved sand, or ceramic microbeads) which prevent the fracture network from closing on itself at the time of the pressure drop.
• hard agents grains of sieved sand, or ceramic microbeads
• Static fracturing may comprise a first injection phase in a well drilled with a fracturing fluid that contains thickeners, and a second phase that involves the periodic introduction of propant (ie a proppant) into the fracturing fluid to feed the fracture created by propelling.
• propant ie a proppant
• the second phase or its sub-phases involves the additional introduction of a reinforcement and / or consolidation material, thereby increasing the strength of the propant clusters formed in the fracturing fluid.
• Such static fracturing (S20) makes it possible to obtain fractures typically between 100 and 5000 meters.
• Static fracturing (S20) can precede electrical fracturing (S 10).
• the pressure wave generated by the electrical fracturing (S 10) can follow the course of the fluid introduced into the cracks created by the static fracturing (S20) and thus improve the damage.
• static fracturing (S20) may precede electrical fracturing (S10) by less than a week.
• FIG. 19 there is also provided a method of fracturing a geological reservoir of hydrocarbons previously statically fractured by hydraulic pressure.
• the process of FIG. 19 then comprises the single electrical fracturing (S 10) of the reservoir, carried out in a reservoir where a well has already been drilled and has already been statically fractured.
• the process of FIG. 19 allows the damage of tanks already exploited after static fracturing.
• the process of FIG. 19 allows the exploitation of an abandoned reservoir because already exploited, potentially by reusing a well already drilled.
• the method of FIG. 19 corresponds to the method of FIG. 18 (where static fracturing (S20) corresponds to this prior static fracturing).
• the preliminary static fracturing may have been carried out according to the method of FIG. 18.
• FIG. 20 there is provided a method of fracturing a hydrocarbon geological reservoir comprising a particular electrical fracturing (S 10).
• the electrical fracturing (S 10) proposed in the process of FIG. 20 can of course be used in the process of FIG. 18 and / or in the process of FIG. 19.
• the process of FIG. 20 mainly comprises electrical fracturing (FIG. S 10) of the reservoir by the generation of an electric arc in a fluid present in a well drilled in the reservoir (thus combined or not with static fracturing, for example the static fracturing (S20) of the process of FIG. 1).
• the electric arc induces a pressure wave whose rise time is greater than 0.1 ⁇ , preferably greater than 10 ⁇ .
• the process of Figure 20 improves the fracturing of the reservoir.
• the rise time of the pressure wave is the time required for the pressure wave to reach the pressure peak, i.e. the maximum value of the wave (also called “peak pressure").
• a rise time greater than 0.1 ⁇ , preferably greater than 10 ⁇ corresponds to a pressure wave which penetrates better into the reservoir.
• Such a pressure wave is particularly effective (ie the wave penetrates deeper) in the case of ductile materials, such as those composing shale gas reservoirs.
• the rise time is less than 1 ms, advantageously less than
• the pressure wave may have a maximum pressure of up to 10 kbar, preferably greater than 100 bar and / or less than 1000 bar. This may correspond to an energy stored between 10 J and 2 MJ, preferably between 10 kJ and 500 kJ.
• 10 J and 2 MJ preferably between 10 kJ and 500 kJ.
• the well can be horizontal.
• the well may be horizontal and have a length preferably between 500 and 5000 m, preferably between 800 and 1200 m, for example at a depth between 1000 and 10000 m, for example between 3000 and 5000 m.
• Electric fracturing (S10) can be repeated in different treatment zones along the well. Indeed, with electric fracturing (S 10), a pressure wave usually penetrates less deeply than static fracturing. Thus, with electrical fracturing (S 10), cracks of length less than 100 m, typically less than 50 m, and typically greater than 20 m, are typically obtained. For a well several hundred meters long, the repetition of electrical fracturing (S 10) along the well allows damage along the well and therefore a better possible exploitation of the reservoir.
• each treatment zone or in the single treatment zone if it is unique, several arcs can be generated afterwards.
• the generation of an electric arc is repeated in a substantially fixed position. This improves the damage by repeating the pressure wave.
• the generated arcs can be the same or different.
• the arcs generated subsequently induce a pressure wave whose rise time is decreasing.
• the arches in succession can present an increasingly steep front, thus inducing a pressure wave having a rise time faster and faster.
• the first impulses have slower fronts to penetrate deeply, whereas the pulses to the stiffer fronts fracture closer to the well and more densely. This optimizes ⁇ damage.
• the first arcs can for example induce a pressure wave whose rise time is greater than 10 ⁇ , preferably 100 ⁇ .
• the last arcs can then induce a pressure wave whose rise time is less than the rise time of the first arcs, for example less than 10 or 100 ⁇ .
• the first arcs comprise at least one arc, preferably a number less than 10,000 or even 1000, and the last arcs comprise at least one arc, preferably a number less than 10,000 or even 1000.
• the arcs can be generated at a frequency less than 100 Hz, preferably less than 10 Hz, and / or greater than 0.001 Hz, preferably greater than 0.01 Hz.
• the frequency of the arcs can be (substantially) equal to the resonant frequency of the material to be fractured in the tank. This ensures more effective damage.
• the reservoir may have a permeability less than 10 microdarcy. This may include a shale gas tank. In this type of reservoir, the gas is typically adsorbed (up to 85% on Lewis Shale) and poorly trapped in pores.
• Electric fracturing may comprise the prior injection into the fluid of an agent improving the plasticity of the material constituting the reservoir.
• the agent may comprise a chemical additive.
• the chemical additive may be an agent inducing the rock fracture.
• the additive may include steam. This helps to further improve the fracturing.
• electrical fracturing is carried out (S 10).
• Electrical fracturing (S 10) is here combined with static fracturing, not specifically illustrated and possibly prior, which has induced major fractures 41 in the reservoir.
• the fracturing process makes it possible here to produce hydrocarbon by means of a production pipe situated at the surface, at the wellhead 45.
• the electric arc is generated at the level of a fracturing device 47, which may be in accordance with FIG. to the fracturing device 100 of FIG.
• electrical fracturing induces secondary fractures 42 at the point where the arc is generated.
• the secondary fractures 42 are shorter but more diffuse than the main fractures 41.
• the electrical fracturing (S 10) is repeated in different treatment zones along the well.
• Figure 21 shows indeed an initial phase of the electric fracturing (S 10) downhole.
• Figure 22 shows an intermediate phase in the middle of the well.
• Figure 23 shows a final phase at the beginning of the well.
• the secondary fractures 42 are dispersed all around the well 43. It is then possible to recover the hydrocarbon surrounding these secondary fractures 42, a hydrocarbon potentially distant from the main fractures 41 and thus difficult to recover by a single static fracturing.
• the mobility of the fracturing device 47 which may be the particular device, makes it possible to fracture the reservoir all along the well.
• the device 47 is supplied in this example with a high voltage power supply 44 located at the surface and connected to the device 47 by the cables 46.
• the present invention is not limited to the examples described and shown, but it is capable of numerous variants accessible to those skilled in the art.
• the principles outlined above can be applied to the production of seismic data.
• the generation of the electric arc could alternatively induce a pressure wave having characteristics lower than those required for the fracturing of the reservoir. This can be done, for example, by adapting the charging voltage of the fracturing device and the charging voltage, and by varying the inductance.
• Such a seismic data production method can then comprise the reception of a reflection of the pressure wave, the reflected wave then being typically modulated by its passage through the material constituting the reservoir.
• the seismic data generating method can then also include analyzing the reflected wave to determine reservoir characteristics. We can then build a seismic survey based on the reception.

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