| Description |
As petroleum is becoming increasingly used worldwide, transportation of oil becomes more significant. Finding an effective method to transport petroleum would reduce costs. A pipeline is the most economical and efficient method for the transportation of large quantities of crude oil. However, since many pipelines are usually built under the sea, the ambient temperature is low. Paraffinic crude oils transported in pipelines normally form gels composed of wax crystals during flow shutdowns. These waxy gels may make it difficult to restart flow without breaking the pipe if pipeline flow ceases. A relationship between flow loop experiments and rheology measurements is studied and compared by using similar conditions. Gelled pipeline restart has two main cooling protocols: "slurry flow" and "hot flow." In hot flow, the waxy oil is cooled to the restart temperature under static, no flow conditions. In slurry flow, the oil is cooled during flow to the slurry temperature, and then cooled without flow to the restart temperature. Slurry flow restart became the focus of the author since it is expected to reduce wax deposition in pipelines. For the first and second version of the flow loop, the results showed how the slurry temperature greatly affects restart pressure after when the slurry temperature is below the wax appearance temperature (WAT). This study shows that the gel formed will be weaker when the slurry temperature is lower. This confirms previous research that concluded that varying the upstream pressure used in the range between 1 and 4 psig during the cooling period does not affect the strength of gel clearly. Using a slurry flow method at a restart temperature of 5 °C requires less breaking pressure than hot flow restart. The strength of a gel formed by slurry flow is more than 10 times weaker than its hot flow counterpart. The breaking pressure obtained by converting the static yield stress measured from rheometer measurements under predicted the actual flow loop results. However, both the predicted yield stress and the measured yield stress showed similar trends, but differed by some constant value. |
