Study on the first pigging of crude oil pipeline with high thickness of waxy deposits in winter

In the frigid winter, the transportation of waxy crude oil through pipelines encounters numerous thorny problems. The viscosity of the crude oil increases remarkably, and the thickness of the wax layer rises sharply. This undoubtedly leads to a significant increase in the power consumption required for pipeline operation, posing a severe challenge to the efficient and stable transportation of crude oil. Mechanical pigging has always been a powerful measure to deal with the problem of wax deposition in crude oil pipelines. However, due to the lack of relevant theoretical guidance, the planning of the initial pigging plan in winter often has to rely on traditional experience, and the foam pig has become a relatively common choice. To effectively overcome the difficulty of pigging in pipelines with a thick wax layer in winter, a series of deposition and pigging experiments have been carried out, including pigging experiments and blending experiments of deposits in front of the pigs. During this process, the wax layer removal characteristics of disk pigs, cup pigs, and fully coated foam pigs have been deeply explored, and the different impacts of the front products generated by cup pigs and foam pigs on pipeline operation have been carefully compared. The experimental results clearly showed that although the disk pig performs outstandingly in terms of wax removal efficiency, it is not an ideal choice for the first pigging operation of pipelines with a thick wax layer in winter. The wax removal efficiencies of the cup pig and the fully coated foam pig are quite similar. However, thanks to the scouring effect generated by the discharge hole structure, it is not easy for the cup pig to form a wax plug at the front end, and the changes in physical properties such as the pour point and viscosity of the oil-wax slurry in front of it can meet the operation specifications, and the resistance encountered during the migration process is also smaller. Therefore, the cup pig has more advantages in the first pigging operation of pipelines with a thick wax layer in winter. For the KS crude oil pipeline with a thick wax layer, the bypass cup pig was selected for its first winter pigging operation and achieved satisfactory pigging results. This undoubtedly provides a valuable reference example for the planning of pigging schemes for pipelines with a thick wax layer in winter, and provides reliable practical basis and idea references for the subsequent related operations.