Wax deposition prediction and pigging simulation in waxy crude oil tieback deepwater pipelines

Key words:  deepwater oilfield  waxy crude oil  tieback pipeline  wax deposition  pigging period  OLGA software

Abstract:

Wax deposition in waxy crude oil pipelines can cause the flow safety problems of the tieback pipes, therefore it is necessary to make a full study on the deposition and control laws for these pipes. In this study, based on certain waxy crude oil tieback flowlines for South China Sea deepwater oil development, the OLGA software is used to simulate transient flow characteristics in waxy crude oil tieback pipelines, such as wax precipitation rate, thickness of the wax layer deposited on the wall, pigging frequency and so on. The results show that, the pigging period is 35 days during the first 2 year after put into production. The pigging periods is 60 days from the third year with the increase of water content. The maximum liquid flow rate for a 233 mm pipeline is 7 000 m³/d. It is suggested that one single pipeline is used to transport while the flow rate is lower than 7 000 m³/d, and two pipelines are used while the flow rate is more than 7 000 m³/d. The maximum pump pressure at FPSO is kept at 6 000 kPa, and the required maximum liquid flow rate at FPSO is 4 200 m³/d(175 m³/h).