Properties of deposits in waxy crude oil pipeline

As oil exploitation is moving into deep waters, wax deposition in submarine pipelines has become one critical issue concerned with flow safety in the oil industry. Two sets of tests of wax deposition with different temperatures, flow rates and deposition time were carried out using laboratory loop devices to analyze the variation characteristics of density, wax content, carbon number distribution and yield strength of wax crude oil sediments. Results show that the deposition mass increases over time and its increasing velocity is high at the initial stage and then slows down. The deposition thickness is jointly controlled by the oil wall temperature and the oil flow scouring. Over time, the density, wax content and yield stress of sediments increase, and the content of wax molecules which are heavier (lighter) than the critical carbon number of the sediments increases (decreases). The hotter the oil is, the more the wax molecules with large carbon numbers can diffuse to the pipe wall and deposit on it and the peak value wax molecule moves in the direction of large carbon numbers.