The bottomhole zone warming up
The issue of bottomhole zone warming up is important and actual as the oil with the high content of heavy hydrocarbons and wax are characterized by the low crystallization temperatures and high viscosity. High power consumption for the hydrocarbons elevation from the well and pipeline networks transportation is required. The borehole submersible equipment is exposed to the increased wear due to the strengthened operating mode and it leads to its premature failure.
The lowest oil recovery coefficients forcing oil companies to use the expensive submersible equipment for production of the product limited quantity are the other problem of high-viscosity oil production.
Numerous researches of high-viscosity oil production showed that one of the most effective ways of its viscosity decrease is the thermal method with special submersible borehole heaters use.
Original scientific and technological decisions are taken as a basis of the bottomhole zone warming up solution:
The bottomhole zone warming up device includes one or several borehole electric resistive adjustable heaters (Electrical Near-Wellbore Heater) connected among themselves mounted on the liner pipe attached to the lower part of the submersible borehole equipment. Depending on a well operation method (screw-pump, ESP, flowing or gas-lift) the Electrical Near-Wellbore Heater (ENWH) can have an appearance of the extended cylinder or a thick-walled pipe that provides heating of borehole liquid, both with external, and with internal heater surfaces. Depending on a well operation method liner pipe can have the slot-hole openings providing the free passing of heated-up borehole liquid both in tubing inside and in annular space.
Electrical Near-Wellbore Heater (ENWH) design
1. Filler neck
2. Upper flange (thread 73mm)
3. Upper head body
4. Compensating expansion chamber
5. Current feedthrough
6. Heat-transfer liquid level neck
7. Heater body
8. Heater internal thermal gage
9. Heat elements
10 Heat-transfer liquid
11. Drain port
Well Heating Unit downhole diagram
1. Electrical Near-Wellbore Heater
2. Upper flange (thread 73mm)
3. Perforated 73 mm tubing
5. Crossover shoe 73/60mm
6. 60mm liner
7. Liner to submersible electrical motor flange
8. Submersible electrical motor
10. ESP flange
12. WHU power cable
13. Current lead shoe
14. Submersible electrical motor power cable
17. Perforation interval
Control of the heater operation and control of heating is exercised automatic Control Station of management which allows to maintain heater temperature in the set mode depending on a well operating mode. The power cable providing giving of electric power on the heater has a measuring strand for the heater temperature control and also can have the built-in temperature sensor with necessary number of additional measuring strands for control of the liquid temperature outflowing from the heater.
Placement of the heater directly in the perforation allows warming up not only the borehole liquid coming to intra borehole space, but also near-bottomhole formation zone and perforation channels. Such heating helps to clear the perforation channels from the heavy fractions and, therefore, to increase the formation liquid flow.
Oil fluid passing along the heater body heated ranging from 50 ° and to 200 °C allows increasing temperature of the intra borehole liquid up to 50 °C from the initial.
Provided that oil fluid viscosity decreases approximately twice when heating by 10 °C, the load of a submersible pump respectively decreases also.
The submersible equipment load reduction also leads to significant between-repairs period increase.
Depending on a wells temperature profile, technical characteristics, formation fluid physical properties one or several ENWHs can be used.
The borehole liquid temperature increase helps not only to reduce its viscosity and pumping equipment load, but also allows to prevent crystallization of wax and tar and, respectively, to increase the capacity of pump and pipes and well production.
Besides, change to the best of the oil physical properties received at a capture of daily borehole liquid samples was also noted.
Use of the standardized electric sockets, couplings, current leads and power cables used in submersible pumps installations, and also the Control Stations, programmatically and functionally compatible to ESP and WEUH Control Stations, allows expanding considerably possibilities of Electrical Near-Wellbore Heaters installations service on fields.