There is abundant heavy oil resource in Bohai Oilfield and thermal recovery is an effective method to realize the high-efficient development. Till now, several field pilots have been conducted. However, for the offshore thermal recovery well, the onshore common used rod pump artificial lift technology is not applicable. The ordinary electric submersible pump (ESP) system cannot be directly used either, because it cannot stand the high-temperature steam. Therefore, artificial lift technologies suitable for offshore thermal recovery well is developed in recent years.
For the ESP system, a high-temperature safety control system was developed, consisting of downhole safety valve, cable packer, and vent valve. The overall temperature and pressure resistance value could reach as high as 350°C and 21MPa, respectively. And the high temperature electric submersible pump could stand 250°C cyclic steam. This ESP system has been used in about 30 thermal recovery wells in Bohai Oilfild, satisfying the artificial lift requirements for the moment. With this ESP system, the overall process of each huff-and-puff cycle includes: lowering steam injection tubing, steam injecting, soaking, replacing production tubing, producing. That means two workover operations for tubing changes are required in each huff-and-puff cycle, which adds more cost to the oil production and has bad effect on the thermal recovery.
Considering the drawbacks of the current ESP system, a new concentric-tubing jet pump system suitable for offshore oilfield with function of both steam injection and oil production is developed. Besides, the matched surface equipment, such as oil-water-sand separator and power fluid pump, are designed. The temperature resistance of the designed jet pump system reaches 400°C. With this system, no workover for tubing replacement is needed any more during one huff-and-puff cycle. Till now, this new jet pump system has been put into field pilot in one thermal recovery well. Both the steam injection and oil production process completed successfully, indicating its applicability for the offshore thermal recovery wells. In this paper, the tubing string structure details of the jet pump system and the specific field operation process is introduced. This new artificial lift technology will be gradually applied in other wells to improve the thermal recovery effect because of its advantages comparing with ESP system.
Great progress and breakthrough of the artificial lift technologies suitable for offshore thermal recovery have been achieved in recent years in Bohai Oilfield, which will provide powerful technical support for the high efficiency development of the heavy oil resource in Bohai Bay.