The hollow rod electric heating (HREH) technology can greatly increase the temperature of the fluid in wellbore and improve its fluidity, which is widely used in rod pump wells. Bohai offshore oilfields also have urgent application requirements for HREH technology due to the wide distribution of heavy oil and high waxy crude oil. However, more than 90% of the oil wells there are produced by electric submersible pumps (ESPs). None of these christmas trees in use are suitable for ESP wells using HREH technology.
Based on the conventional christmas tree with only one main channel, a new type of eccentric christmas tree, with separated main channel and cable channel, is designed. As with the conventional ones, the main channel works as the flow passage of wellbore fluids. And the cable channel is used to run and pull out the heating cable. The eccentric design of the main channel provides the space for the cable channel. The separate cable channel avoids the cable crossing the main channel, so that the master valve of the christmas tree can be opened and closed normally, which contributes to ensuring safe production. In the meanwhile, the christmas tree can also seal the heating cable owing to some special design.
This new device has been successfully tested on 6 ESP wells in Bohai Bay. After the installation of the christmas tree, the cable was smoothly run down to the predetermined depth. The construction operation was simple and convenient. There was no oil or gas leakage at wellhead after it was put into use. The wellhead temperature of all these wells reached above 50°C and no wax deposited in tubing any more, verifying its safety and reliability.
This new type of safe and reliable christmas tree lays a solid foundation for the popularization and application of HREH technology, especially in those waxy oil wells and heavy oil wells with ESPs.
