Invention

This invention relates to a method for generating steam downhole. The proposed device is an electric steam generator with heating elements installed on the walls of internal communicating tortuous pipes in a cylindrical heating chamber. The heating elements are made of a high electrical resistance alloy to ensure the conversion of water injected from the surface into steam or high temperature superheated steam for injection into the reservoir under pressure.

The power of the heating generated or released per unit volume of the medium during the passage of an electric current, according to the Joule- Lenz law, is proportional to the product of the square of the electric current multiplied by the resistivity of the electrical conductor: w = 6 * E ² where: co is the power of heating generated, E is the electric current, o is the conductivity of the medium.

The alloy in a ratio of 55-78% of nickel and 15-23% of chromium (nichrome or Ni-Cr) with possible additions of silicon, cobalt, iron, aluminum and I or titanium has high oxidation stability, as well as good strength characteristics, retains high strength at high temperatures, up to 1000 degrees Celsius.

Such alloys are optimal materials for the production of heat exchanger tubes for steam generators.

Nichrome is equally successful in resisting the processes of carburization and nitriding. The alloy has a high fatigue strength. This quality is provided by the addition of chromium and cobalt. The melting temperature of the alloy is about 1400 degrees Celsius, the specific heat capacity is 400-450 J / (kg * K), the specific electrical resistance or electrical resistivity is 1.05 - 1.4 1 Q-m. The combination of these properties allows the alloy to be used in heating elements.

The following designs of electric heaters are known today.

Known induction heater (patent RU No. 2010954), having a hollow ferromagnetic housing and a casing between which induction coils are placed. However, the heater is not designed to generate steam and serves to heat the produced viscous and paraffinic oil in the well.

Known downhole electric steam generator (patent Rll No. 2451158) with a central insulated current conductor with phase electrodes installed one above the other in the form of a multi-threaded screw.

Known downhole electric heater (US patent No. 5539853), which uses Inconel wires with high electrical resistivity for heating nitrogen or air injected into the formation.

Known an electric steam generator (patent RU 2324859), which uses a shell and a granular filter around a heater with parallel nichrome wash spirals wound. The disadvantages and limitations in the use of this installation are

(1) the inability to run it into the well to generate steam at the bottomhole and

(2), due to the use of non-flow heating chambers with filters and different filling densities of granular material, periodically filled and emptied using valves, the inability to provide continuous, without stops, pumping and heating large volumes of water, which are required for high pressure injection of overheated steam, if applied in the sub-soil reservoirs.

This invention, which eliminates the above limitations and disadvantages, allows for the generation of superheated steam at the bottom of an injection well for subsequent injection of large volumes of overheated steam at high pressure into the formation. The invention is illustrated by a drawing in Figure 1.

Figure 1 shows the proposed downhole electric steam generator 1 run on tubing 2 to the bottom of the well 3, Figure 1. The downhole steam generator consists of a downhole heater connected by a power cable 4 with an energy source on the surface 5. Water is injected in the well in the umbilical tubing 2 from the surface by pump 6. The electric power cables first connect to the wiring chamber 7, then pass through the low electrical resistance nickel wires through the cooling chamber 8 with heat-resistant insulators and are connected to the wires of the high electrical resistance heaters in the heating chamber 9 located at the bottom of the device. The heating chamber 9 consists of a tortuous passage 10 of a water-vapor mixture between heating elements in the form of rods located on the cylindrical walls of pipes 11. The heating rods are made of an alloy of high electrical resistance nichrome with possible additions of silicon, cobalt, iron, aluminum and I or titanium. The inner housing of the heating chamber of the steam generator device 12 is made of a dielectric material. The tortuous passage of the steam-water mixture through the pipes of the cylindrical heater provides a sufficiently necessary time for the water to warm up to the state of steam and I or superheated steam. The length of the heating chamber can vary depending on the required temperature, productivity and quality of steam produced by the downhole steam generator. The number of heating elements installed on the walls of the pipes of the cylindrical heating chamber depends on the required steam flow rate and its temperature. In the proposed device of the steam generator, the steam heating temperature can be up to 800-900 degrees Celsius. Water, continuously pumped from the surface through the umbilical tubing, enters the downhole heater, passes along a winding path between the heating elements and being heated to the state of steam or superheated steam, is injected under pressure into the reservoir formation through the perforation intervals 13.

The advantages of this invention of a downhole electric steam generator are:

- no heat losses along the wellbore during downhole steam generation and injection, as in the case of using surface steam generators,

- no restrictions on the depth of the well with energy efficient steam generation downhole, at the bottom of the well and its injection into the formation, - the possibility of generating superheated, high temperature steam downhole in the well,

- continuous operation of the steam generator, even with failure of some heating elements of the device,

- the possibility of lifting, repairing and running downhole steam generator equipment into injection wells using tubing pipes.