In bohai offshore oilfield, about 98% oil wells produce with electric submersible pump (ESP). For the common ESP system, workover is needed to replace the failed pump about every 4 years, resulting in significant operation cost and production lost. To solve this problem, a new type of rigless fully retrievable electric submersible pump (RFR-ESP) is developed and applied in bohai oilfield.
This paper mainly introduces the technical details of the used RFR-ESP system, and the real application effects in typical wells. This new system consists of downhole permanent part and retrievable part, with the power cable clamed externally along with the tubing. The core of the system is a specially designed wet connector system. Through this connector, any ESP manufacture's equipment can be used. For this technology, the retrieval of ESP can be finished by standard oilfield wireline operation, and no rig workover is required any more. Till now, two different systems suitable for 7″ tubing and 5-1/2″ tubing have been developed in order to meet the yield of different wells.
Bohai oilfield installed the first RFR-ESP in 2013. Up to now, 6 wells have applied this technology, including one water source well and five oil wells. The longest running time of the ESP is about 2000 days, and it is still in service now. The maximum liquid production is about 2800m3/d. For this new system, the workover time of ESP replacement reduces from 10 days to about 2 days comparing to the traditional rig workover process, and the number of the workover operators reduces from 30 to about 10. All of these are helpful to reduce the workover cost and the production lost. Besides, several problems encountered in the wells, such as power cable failure provides valuable field experience for the promoted application in bohai offshore oilfield.
The successful application of this technology indicates that it has the potential to lower ESP operating costs, and even improve the artificial lift status of offshore oilfield. What's more, this new system is expected to be used in unmanned platform, thus no workover boat is needed any more, which will drastically cut down the development cost.
