Flow Behavior of Daqing Waxy Crude Oil under Simulated Pipelining Conditions
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- 作者：Jianlin Ding ; Jinjun Zhang ; Hongying Li ; Fan Zhang ; Xiaojing Yang
- 刊名：Energy & Fuels
- 出版年：2006
- 出版时间：November 2006
- 年：2006
- 卷：20
- 期：6
- 页码：2531 - 2536
- 全文大小：95K
- 年卷期：v.20,no.6(November 2006)
- ISSN：1520-5029
文摘
Daqing oilfield is the largest oilfield in China. This crude oil is a typical waxy crude oil, with a wax contentof 26% and a gel point of 32 
C. Flow behaviors of waxy crude oils at temperatures near the gel point/pourpoint are vital for both pipeline hydraulic calculation and evaluation on restartability of a shutdown pipeline.In this study, experimental simulation was conducted by using a stirred vessel with the energy dissipation ofviscous flow as the shear simulation parameter. Crude oil specimens were taken from the stirred vessel atdifferent temperatures during flow simulation, and the DSC (differential scanning calorimetry) curves andrheological properties, such as viscosity, gel point, yield stress, and thixotropy, were measured. The viscosityunder simulated pipelining conditions was found to be much less than that measured under quiescent coolingconditions, and the gel point decreased with decreasing temperature of sampling, i.e., the end temperature ofthe dynamic cooling process. The DSC curves of crude oil specimen captured at different sampling temperaturesand from different positions such as the bulk of crude oil and the wall of the stirred vessel showed no difference,which indicated the depletion of wax due to wax deposition during the shear simulation was not responsiblefor viscosity and gel point reduction in the dynamic cooling measurement. Therefore, this reduction is attributedto shear disturbance on the developing wax crystal structure, called the shear history effect. At samplingtemperatures above 35 C, which is 3 C above the gel point measured under quiescent cooling conditions,both the yield stresses and the thixotropic parameters showed little dependence on the shear history. However,at lower sampling temperatures, remarkable shear history dependence was found. Empirical correlations weredeveloped between the yield stress and the sampling temperature as well as the measurement temperature andbetween the thixotropic parameters and the sampling temperature. These correlations provide not onlyquantitative information on the shear history effect of waxy crude but also accurate rheological properties forassessment of the operation state and restartability of pipelines transporting this crude oil.
C. Flow behaviors of waxy crude oils at temperatures near the gel point/pourpoint are vital for both pipeline hydraulic calculation and evaluation on restartability of a shutdown pipeline.In this study, experimental simulation was conducted by using a stirred vessel with the energy dissipation ofviscous flow as the shear simulation parameter. Crude oil specimens were taken from the stirred vessel atdifferent temperatures during flow simulation, and the DSC (differential scanning calorimetry) curves andrheological properties, such as viscosity, gel point, yield stress, and thixotropy, were measured. The viscosityunder simulated pipelining conditions was found to be much less than that measured under quiescent coolingconditions, and the gel point decreased with decreasing temperature of sampling, i.e., the end temperature ofthe dynamic cooling process. The DSC curves of crude oil specimen captured at different sampling temperaturesand from different positions such as the bulk of crude oil and the wall of the stirred vessel showed no difference,which indicated the depletion of wax due to wax deposition during the shear simulation was not responsiblefor viscosity and gel point reduction in the dynamic cooling measurement. Therefore, this reduction is attributedto shear disturbance on the developing wax crystal structure, called the shear history effect. At samplingtemperatures above 35 C, which is 3 C above the gel point measured under quiescent cooling conditions,both the yield stresses and the thixotropic parameters showed little dependence on the shear history. However,at lower sampling temperatures, remarkable shear history dependence was found. Empirical correlations weredeveloped between the yield stress and the sampling temperature as well as the measurement temperature andbetween the thixotropic parameters and the sampling temperature. These correlations provide not onlyquantitative information on the shear history effect of waxy crude but also accurate rheological properties forassessment of the operation state and restartability of pipelines transporting this crude oil.