In Changqing oilfield,the pipelines between Jingsi and Jingsan consociation station is vital for the waxy crude oil pipelining.The wax deposition,however,triggers huge economic,safe and efficient problems to the pipeline operation.A series of polyacrylate paraffin inhibitor (WI) with various side chain carbon number distributions were first synthesized by free radical polymerization,and the structural properties and crystallization properties were characterized by using the FTIR and DSC method.Then,the effects of the WIs on the rheological properties of the Changqing waxy crude oil were studied.The results show that after adding 400 mg/kg WI⁃2,the pour point of Changqing crude oil can be reduced by 10 ℃,the anomalous point can be decreased by 8 ℃,and the viscosity of non⁃Newtonian fluid region can be greatly reduced.After that,based on the indoor wax deposition experiment,the influences of the WI on the Changqing crude oil wax deposit properties were studied by settling various conditions and the wax deposition models of Changqing crude oil undoped /doped with WIs were developed.Using the wax deposition models to predict the wax deposit under the field operation condition,it is found that without adding WIs,the prediction error of the wax deposit thickness at different time is less than 5%,and the wax inhibition efficiency can reach 88%~95% after adding 400 mg/kg WI⁃2.

Via heating pipelining method, Changqing waxy crude oils with few resins and asphaltenes are transported in Jiangsan-Jinger pipelines, which makes great demands on the safe, economic and efficient pipelining technology. Based on crude oil rheology, physical chemistry and gel chemistry theory, the control stress rheometer was first used to test the complex rheological behaviors of the crude oil, such as viscosity-temperature, yielding, viscoelastic and thixotropic properties. The rheological equation and thixotropic model were then created to fit the Changqing waxy crude oil. Finally, based on the rheological properties, pipeline flow and heat transfer properties, thermal and hydraulic coupling characteristics of the Jingsan-Jinger pipelines, the restart characteristics were forecasted. Results showed that the shear dilution properties became more obvious with the decreasing temperatures below abnormal point; above the pour point, the gelled crude oil showed ductility properties, while below the pour point, it showed a strong brittleness nature, and with the decrease of temperature, yielding stress value increased exponentially; under the constant shear rate, the destruction and reformation of the gel structure occurred in the early 10 min. The prediction of the pipeline restart properties showed that after being shut down for 32 h, pipeline crude oil temperature at the end would drop to the abnormal point; after being shut down for 48 h, pipeline crude oil temperature at the end would drop to the pour point. Considering the safety of pipeline operation, the maximal shutdown time was 32 h, corresponding to the restart pressure of 1.51 MPa.