3.16. Content and Features of Offshore Workover Operations

3.16.1. Reasons for Oil Well Failure

1. The well itself fails
    Failure of the well itself includes downhole sand plugging of the well, severe wax and salt precipitation in the wellbore, oil layer blockage, permeability reduction, oil-gas and water layer collusion, production oil layer exhaustion, etc. For instance, the crude oil in the China Bohai oilfield have generally high wax content, often up to 13 to 18 percent, and the freezing point is between 22 degrees and 35 degrees, so it has the characteristics of hypercoagulability and high wax content. In addition, the wellhead pressure and temperature are both very low, with the wellhead temperature of most oil wells between 20 degrees ...

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