Bohai J Oilfield has typical characteristics of high wax content and wax precipitation point (WPT). Wax deposition in the tubing had been an ongoing problem after this Oilfield came on stream, which caused significant productivity losses. Various methods of wax control and removal, such as injection of wax inhibitor, wireline dewaxing, hot-water treatment and continuous tubing had been tried to guarantee the normal production of the wells. However, none of these methods was long-time effective. Considering that vacuum-insulated tubing (VIT) plays an important role in thermal insulation, 4 wells of J Oilfield are equipped with different length of VIT for wax control by increasing the flowing wellhead temperature (FWHT).

This paper presents the methodology for design of VIT as well as the application evaluation in the 4 wells. The apparent heat transfer coefficient of VIT is determined after analyzing the influence of coupling on VIT heat transfer properties. The distribution of wellbore temperature profile is calculated based on conservation of energy. Existing FWHT data is collected to verify the accuracy of the temperature profile calculation model. As a result, the length of VIT installed for each well is optimized through sensitivity analysis. After VIT is installed, the production performance of the 4 target wells is monitored.

After installing VIT, FWHT of the 4 wells obviously increased, and no wax deposition occurred any more when the production was stable. The actual FWHT agrees well with the prediction result, indicating the accuracy of numerical calculation.

The successful application of VIT for wax control for the first time in Bohai Oilfield indicates its effectiveness for Chinese offshore wells. This will also be one promising wax control method for other similar wells.

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