ITMI20101781A1 - PROCEDURE FOR THE FLUIDIFICATION OF A HIGH VISCOSITY OIL DIRECTLY INSIDE THE FIELD BY MICROWAVES - Google Patents

Description

â € œProcedure for the fluidization of a high viscosity oil directly inside the reservoir using a microwaveâ €

The present invention relates to a process for the fluidization of a high viscosity oil directly inside the reservoir.

More particularly, the present invention relates to a process for the fluidization of a high viscosity oil, for example a bituminous oil, directly inside the reservoir by means of the use of microwaves and / or radio frequencies (RF).

More particularly still, the present invention relates to a process for the fluidization of a high viscosity oil, for example a bituminous oil, directly inside a reservoir, both for on-shore and off-shore production fields, by means of the € ™ use of microwave / RF and a solvent medium.

As is known, oil wells that produce high viscosity oil, for example oil with viscosity higher than 100 cps, generally between 300 and 10 <6> cps, need to fluidize the oil directly in situ to favor its flow towards the well and allow the extraction pumps to push the oil to the surface with a flow rate that makes it convenient to exploit the reservoir. Fields with these characteristics are, for example, â € œheavy oilâ € or bituminous fields.

The fluidization of heavy / viscous crude oils or unconventional oils, such as bitumen, tar sands, oil shale, etc., directly in the reservoir is however a very difficult operation.

For the extraction of viscous oils it is known to use advanced techniques, such as CSS (Cyclic Steam Simulation) or SAGD (Steam-Assisted Gravity Drainage), which are based on injections of hot steam into the reservoir to fluidize the oil and favor its movement towards the well and therefore its outflow to the surface. Techniques of this type are also defined as â € œthermal stimulationâ € of the reservoir. Other alternative and known technologies provide for the injection of hot CO2 or combustion in situ.

However, the implementation of the above techniques requires either large consumptions of water and energy, for the production and injection of steam and / or CO2, or the need to carry out a downhole combustion which involves non-negligible risks. Moreover, their realization can be problematic in the off-shore environment where the availability of space is not excessive.

An alternative to known thermal stimulation systems is represented by the use of microwaves, the use of which is described, for example, in US patent 3.104.711. The use of microwaves generated in situ in the reservoir causes targeted heating of the crude oil which facilitates its handling and, therefore, its extraction.

Applications of this type are also described in US patent 5,082,054 which describes how to apply electromagnetic radiations of a suitable frequency to favor the extraction of high viscosity oils from reservoirs, essentially by means of the selective heating induced by microwaves.

Other literary references that describe the use of microwaves for heating high viscosity oils in situ are the US patent application 2007/131591 and the US patent 4,419,214.

Therefore, the use of microwaves, to thermally stimulate the crude oil directly in the reservoir, is a known procedure but the actual application in a productive well has not proved particularly effective due to the limited range of the heating effect. Furthermore, this problem is typically felt for bituminous oil deposits which have the characteristic of being stationary since, being substantially constituted by high molecular weight hydrocarbons, they are solid at the internal temperature of the well and remain bound to the rock that contains them. , even if they are found in high pressure reservoirs.

The Applicant has now found, as better illustrated in the attached claims, a new method for heating a viscous oil directly in the reservoir by means of the combined use of microwaves, or radio frequencies (RF), and of a liquid solvent compatible with the oil. This method allows the heat produced by microwaves or radiofrequencies to propagate deep into the reservoir allowing a heating effect of the oil, and therefore its fluidification. The oil made more fluid by the heat of the microwaves mixes with the solvent, becoming even more fluid. Thanks to this improved fluidity, the mixture is pushed by the internal pressure of the reservoir towards the well and can be brought to the surface with conventional technology where oil and solvent are separated.

Therefore, the object of the present invention is a process for the fluidization of a high viscosity oil directly inside a reservoir which includes:

to. making a well by drilling an oil field until reaching the oil field;

b. injecting into the reservoir, substantially at the bottom of the well, in a single solution, finely divided particles of ceramic material with high thermal conductivity, dispersed in a fluid with variable viscosity, by means of an induced fracture operation; c. periodically inject a solvent compatible with the viscous oil into the reservoir, substantially at the bottom of the well in correspondence with the injection of the ceramic material, to obtain a wetting / diluting effect of the oil itself;

d. to install, substantially in correspondence with the fractured area of the reservoir, a microwave / RF emission antenna connected, via a waveguide or cable, to a magnetron;

And. fluidize the viscous oil distributed in the reservoir by heating it with the heat produced by the microwaves / RF; And

f. bring to the surface the mixture viscous fluidized oil diluted in the solvent, recover the solvent and inject the solvent again at the bottom of the well.

According to the present invention, the oil production well can be a vertical, horizontal or inclined well, simple or with one or more branches that propagate in the reservoir.

As it is known, the walls of the well, while proceeding towards the reservoir, are reinforced with a cylindrical steel structure, called â € œcasingâ €, which adheres and is bound to the walls with cement / mortar or concrete, generally consisting of from a mixture of Portland cement and inert aggregates such as silica sand and possibly gravel. When the drilling phase of the well is finished, with the possible formation of one or more branches, the operational phases begin to complete the safety phase of the well and start the production of oil.

When the well goes into production, the oil is recovered through a dedicated pipeline, known as a production tubing, or â € œtubingâ €. It is a steel pipe that is inserted into the well, even in each branch, until it reaches the level of the reservoir. At the bottom of the well (also at each branch), the tubing is fixed by means of a combined hydraulic and mechanical sealing system, called â € œpackerâ €, which forces the oil to rise to the surface from the inside of the tubing without touching the walls of the casing.

According to the present invention, the terminal part of the casing, downstream of the packer, is made with a cylindrical structure in plastic material, being the organic polymeric materials used as plastic material, much more transparent to microwaves / RF than steel. The size of the plastic casing section or segment is substantially dictated by the size of the reservoir and the size of the well. In general, the segment (with a substantially circular section) has a length of between 2 and 20 meters and a wall thickness that varies from 1 to 5 cm.

The plastic material can be a thermoplastic polymer or a thermosetting resin. In the first case, a polymer such as polypropylene, polyvinyl chloride, polyesters (for example PET, PBT), thermotropic polyesters, â € œengineering polymersâ €, polyamides, etc. can be used, and in the second case, polyester resins can be used. thermosets or epoxy resins. In both cases, the materials can be reinforced with mineral fillers, such as talc or calcium carbonate, and / or with fibrous material such as glass fibers, carbon fibers, aramid fibers, continuous or short, etc.

To promote transparency to microwaves, the terminal section of the plastic casing is fixed to the walls of the well with mortar in which the part of inert materials is essentially made up of alumina (Al2O3), which was found to be more transparent to microwaves / RF silica-based sand.

The part of the casing above the section of plastic material is a steel casing. In turn, the part of the steel casing directly above the plastic casing and below the packer includes the production section, which can be associated with a mesh structure (screen) to allow the oil to flow from the reservoir into the well without producing any sandy materials, and then rising to the surface through tubing.

The second stage (b) of the process object of the present invention provides for the injection into the reservoir, substantially at the bottom of the well, of finely divided particles of ceramic material with high thermal conductivity, dispersed in a fluid, by means of an induced fracture operation. The induced fracture operation, as a general principle, is an operation that is applied in the oil industry, to allow the oil to flow more easily towards the well. According to the process object of the present invention, however, the induced fracture operation will allow the heat generated by the microwave / RF emission to be transferred deep into the reservoir, through the fractures that also propagate in all directions, and to involve , in the heating and fluidization phase, volumes of high viscosity oil greater than those treated with the methods of the known art.

Induced fracture is a known technique which involves subjecting a variable viscosity fluid to the bottom of the well under high pressure so that it penetrates the reservoir by fracturing the geological formation in which the reservoir is located. The fluid, which under shear stress has a viscous rheological behavior, drags a finely divided solid material known as â € œproppantâ € which is a fracture maintenance agent. At the end of the fracturing phase, the suspension (viscous fluid proppant) present in the fractures passes from the agitated state, associated with the cutting action of the system to create the fractures, to a state of rest during which the viscous fluid tends to assume a rheological behavior of Newtonian fluid. By becoming less viscous, the fluid is slowly absorbed by the reservoir and flows from the fractures diluting in the formation. The proppant, on the other hand, remains in the fractures and consolidates them.

Information and details on induced fracture techniques, variable viscosity fluids and proppants are available in the scientific literature, for example in J.M. McGowen et al. â € œFluid Selection for Fracturing High-Permeability Formationsâ €, SPE 26559, 1993, 451-466 or in M.B. Smith et al. â € œHigh-Permeability Fracturing: The Evolution of a Technologyâ €, JPT, July 1996, 628-633.

According to the present invention, the variable viscosity fluid generally consists of a base chosen from water, oil, alcohols, etc. in which a substance capable of giving the desired rheological behavior of fluid capable of producing a fracture is dispersed / dissolved. induced at the bottom of the well. Examples of these substances are guar gum or materials such as CMHPG (Carboxy Methyl Hydroxy Propyl Guar) or CMHEC (Carboxy Methyl Hydroxy Ethyl Cellulose).

The finely divided ceramic solid, which is dispersed in the variable viscosity fluid, like a traditional proppant, is preferably constituted by silicon carbide, SiC, with a particle size ranging from 1 to 500 µm, preferably from 1 to 50 µm, more preferably from 1 to 10 µm. This material is preferred because it allows optimal diffusion of the heat generated by the microwave / RF. The concentration of finely divided ceramic material, for example SiC, in the suspension varies from 20 to 60% by weight (calculated on the total fluid ceramic material), preferably from 30 to 50%. If required, conventional suspending agents can be used, for example to favor the redispersion of the solid, and to avoid its packing, in case of sedimentation of the suspension following prolonged storage.

The choice of silicon carbide is substantially dictated by the fact that it is a material with very good mechanical properties, including a high hardness and a high elastic modulus, has low density, a low coefficient of thermal expansion, excellent resistance to thermal shock and is substantially inert to the chemical products generally present in the reservoir, for example H2S, mercaptans, nitrogen compounds, CO2, etc. In particular, however, the preferred characteristics of silicon carbide are the good absorbing power of the microwaves / RF and a high thermal conductivity, which allows the heat generated by the microwaves / RF to be transferred deep into the reservoir.

According to a preferred embodiment of the present invention, the ceramic material, i.e. silicon carbide, is mixed with stainless steel microbeads, in a quantity between 2 and 10% by weight, (calculated on the total of steel microbeads ceramic material ). The latter, not being transparent to microwaves, reflect them in all directions, making it possible to improve the diffusion of heat in the fractures and from these towards the reservoir, thus favoring the fluidization of the oil contained therein.

Thanks to the viscosity of the fluid injected at the bottom of the well, it is possible to obtain fractures that are distributed in depth in the geological formation in which the reservoir is present. The fractures can be distributed and developed at 360 °, in all directions and in three dimensions, with lengths that can be greater than 20 meters, generally between 20 and 50 meters, preferably between 25 and 30 meters.

The part of the well involved in the induced fracturing operation is preferably the terminal part of the casing, the one made of plastic material. In order to allow the fluid generating the induced fracture to penetrate and fracture the formation, the plastic casing is previously drilled so that the viscous suspension can flow through the corresponding holes. At the end of the fracturing phase, in order to prevent the crude fluidized by the heat generated by the microwaves / RF from entering through these holes at production rate, the plastic casing is coated internally, for example by means of a continuous elastic sheet, also in thermoplastic material, which blocks the holes while pushing elastically against the internal cylindrical walls. However, nothing prevents the part of the well involved in the induced fracturing operation from being that corresponding to the production area immediately above the plastic casing. If the formation of the deposit is not consolidated, `` screens '' (steel casings with a mesh structure), can be added around the production area to prevent the entrainment of sand, or other material of the formation, which could clog the well. .

At the end of the induced fracturing phase, after allowing the variable viscosity fluid to be absorbed into the reservoir, the solvent is injected into the reservoir itself, also exploiting the induced fractures filled by the proppant. The solvent of the viscous oil is preferably virgin naphtha or diesel fuel or kerosene. The solvent can be injected deep into the reservoir, in order to wet it substantially completely, or it can be injected not deeply in order to wet it only partially, for example limited to the area where the proppant is distributed.

Once the induced fracturing and solvent injection phase is over, the well can go into production. To facilitate the flow from the reservoir to the well, the viscous oil is heated with microwaves / RF. In particular, a microwave / RF antenna capable of radiating radio frequencies between 0.1 and 1 GHz or microwaves with frequencies between 1 GHz and 300 GHz and global wavelength between 0.001 and 3 meters. The antenna is connected, via cable or waveguide, to a magnetron with power between 50 and 500 kw, placed on the surface or inside the well in a dedicated position.

In the operational phase, the antenna continuously emits microwave / RF beams that spread throughout the formation and the reservoir even at 360 ° in all directions and in three dimensions. In this phase of global diffusion, the microwaves encounter both the reservoir and the fractures filled with ceramic material, in particular silicon carbide (SiC) and possibly stainless steel microbeads. The electromagnetic waves are either absorbed by the SiC or homogeneously reflected by the stainless steel beads in all directions and transformed into heat which diffuses further into the reservoir. In this way, the fractures become additional sources of heat that penetrate the reservoir, allowing greater volumes of viscous oil to be fluidized than those fluidized with the methods of the known art. The thermally fluidized oil mixes with the solvent becoming even more fluid, enters the well and is brought to the surface by the extraction pumps. Here the mixture is treated to recover the solvent which is periodically injected back into the reservoir.

The process for the fluidization of a high viscosity oil directly inside a reservoir object of the present invention can be better understood with reference to the diagram of the attached figure which represents an illustrative and non-limiting embodiment.

In the Figure, the numerical reference 1 indicates the reservoir in which a â € œheavy oilâ € type crude oil is contained. Reference 2 indicates the steel casing whose end part, reference 3, indicates the â € œscreenâ € or â € œsection or production rangeâ €.

Under the production section, there is the perforated plastic casing, reference (4), through which the induced fracture operation takes place. Reference (5) indicates fractures filled with the thermally conductive ceramic material, for example with SiC, while references (6) and (7) indicate respectively the microwave / RF antenna and the cable or guide rail wave connecting the antenna to the magnetron, not shown in the figure.

The thick dashed arrows and compact arrows indicate respectively the microwaves / RF emitted by the antenna, reference (8), and the flow of heated and fluidized oil, reference (9), which moves from the reservoir towards the range of production (3). Finally, the reference (10) indicates a part of the reservoir impregnated with the solvent, for example â € œdiesel fuelâ €.

The operation of the process object of the present invention is evident from the previous description and from the diagram of the attached figure. After having carried out a first fracturing action at the bottom of the well with the suspension containing the ceramic material (SiC) and after having carried out a second action of injection of solvent â € œdiesel fuelâ € in the reservoir, the antenna is lowered to the bottom of the well to microwaves or radio frequencies (6).

When fully operational, the antenna (6) transmits microwave or radio frequency beams (8) which spread both in the reservoir (1) and in the part of the reservoir (10) impregnated with the solvent, causing it to heat up. Furthermore, during this irradiation phase, the waves also encounter and heat the SiC contained in the fractures (5). Thanks to its thermal properties, including thermal conductivity, SiC heats up easily and allows the heat to be transferred deep inside the reservoir.

The heated oil, both by direct action of the microwaves / RF and by the transfer of heat from the SiC contained in the fractures, becomes more fluid, moves, dilutes with the solvent, becoming even more fluid and is easily transferred ( 9) towards the production interval (3) to go up in the casing (2) towards the pumping system (not shown in the Figure) which will bring it to the surface through the tubing.

On the surface, the viscous oil / solvent mixture is separated for the recovery of the solvent. When substantially all the injected solvent is brought back to the surface, the operation of the microwave / RF antenna stops and can be recovered. The solvent is then injected back into the reservoir and the heating process proceeds.

Claims (12)

CLAIMS 1. Process for the fluidization of a high viscosity oil directly inside a reservoir which includes: to. making a well by drilling an oil field until reaching the oil field; b. injecting into the reservoir, substantially at the bottom of the well, in a single solution, finely divided particles of ceramic material with high thermal conductivity, dispersed in a fluid with variable viscosity, by means of an induced fracture operation; c. periodically inject a solvent compatible with the viscous oil into the reservoir, substantially at the bottom of the well in correspondence with the injection of the ceramic material, to obtain a wetting / diluting effect of the oil itself; d. to install, substantially in correspondence with the fractured area of the reservoir, a microwave / RF emission antenna connected, via a waveguide or cable, to a magnetron; And. fluidize the viscous oil distributed in the reservoir by heating it with the heat produced by the microwaves / RF; and f. bring to the surface the mixture viscous fluidized oil diluted in the solvent, recover the solvent and inject the solvent again at the bottom of the well. 2. Process according to claim 1, in which the walls of the well are reinforced with a cylindrical steel structure, defined â € œcasingâ €, whose end part is made with a cylindrical structure in plastic material transparent to microwaves / RF housing the € ™ emission antenna of the latter. 3. Process according to claim 2, wherein the plastic material is selected from the thermoplastic polymers and the thermosetting resins. 4. Process according to any one of the preceding claims, in which the terminal portion of the casing made of plastic material is bonded to the walls of the well by means of mortar comprising alumina (Al2O3). 5. Process according to any one of the preceding claims, in which the variable viscosity fluid generally consists of a base chosen from water, oil, alcohols in which a substance capable of giving the desired rheological behavior of fluid is dispersed / dissolved capable of producing an induced fracture at the bottom of the well. 6. Process according to any one of the preceding claims, in which the induced fractures are distributed and developed at 360 °, in all directions and in the three dimensions, with lengths that are greater than 20 meters. 7. Process according to any one of the preceding claims, in which the finely divided ceramic solid is constituted by silicon carbide, SiC, with a particle size ranging from 1 to 20 µm. 8. Process according to any one of the preceding claims, in which the concentration of finely divided ceramic material in the suspension varies from 20 to 60% by weight, calculated on the total fluid ceramic material. 9. Process according to any one of the preceding claims, in which the ceramic material is mixed with stainless steel microbeads, in a quantity comprised between 2 and 10% by weight. Method according to any one of the preceding claims, wherein the microwave / RF antenna radiates radio frequencies between 0.1 and 1 GHz or microwaves with frequencies between 1 GHz and 300 GHz. 11. Process according to any one of the preceding claims, wherein the solvent for the viscous oil is virgin naphtha, diesel fuel or kerosene. 12. Process according to any one of the preceding claims, wherein the high viscosity oil is bituminous oil.