| Crude oil contains a wide range of hydrocarbon components with extremely differing physical properties. The major constituent of these hydrocarbon streams is generally described as paraffin wax. Most of oilfields in our country yield high waxy crude oil, in which paraffin content is about 20%, even reaches to 40%. Waxy-paraffinic-crude oils exhibit a high pour point and possess non-Newtonian flow characteristics at temperatures equal to or lower than the pour point due to wax crystallization and gel formation of their heterogeneous matrix. It may crystallize during production, transportation and storage of the oil, resulting in an increase in viscosity by several orders of magnitude and oil gelation. This may cause major difficulties in pipeline transportation.Pretreatment of the crude oil is necessary for transportation of these waxy crudes through the pipeline. Pretreatment of the crude oil with flow improver is one method by which the rheological character of the gelled waxy crude is changed for easier transportation. The main attraction of this method is its relative cheapness and variability of dosage. Thus, chemical products known as flow improvers, crystal modifiers and pour point reducers need to be used to reduce the apparent viscosity, the flow limit and the pour point.In this paper, the components of crude oil and their interactions were studied at first. Chromatogram separation, differential scanning calorimetry(DSC) and optical microscope methods were used to study the components and the effect on the wax precipitation process of three kinds of crude oils from Yanchang oilfield. The result indicates:(1) The components of the crude oils are quite different.(2) The groups, which can inhibit precipitation of wax crystal effectively, are contained in the crude oil.(3) The addition of high polar components to saturated hydrocarbons could increase the number of wax crystal particles and decrease the dimensions of the wax particles during the cooling crystallization process, which prevented the particles from contacting and crosslinking each other and forming bulk wax crystal aggregation.Then, polyamine amide and polyhydroxy amide were prepared from fatty acid and polyamine as row materials. The effect as flow improvers on the pour point and viscosity of Yanchang crude oils was evaluated. The result indicates:(1) For Chang-2 crude oil, polyamine amide(PAA-7) and polyhydroxy amide(HAA-5 & HAA-9), with 500mg/kg, shows that viscosity reduction and the highest reduction rate reach to 74% in 15℃ and 93% in 20℃, respectively.(2) For Chang-6 crude oil, PAA-24 and HAA-1, with 500mg/kg, shows that viscosity reduction and the highest reduction rate reach to 74% in 5℃ and 61% in 20℃.(3) For Yanchang pipeline crude oil, PAA-20 and HAA-7, with 500mg/kg, shows that viscosity reduction and the highest reduction rate reach to 77% in 15℃ and 79% in 20℃.(4) With 500mg/kg, PAA-20 and HAA-7, can depress the pour point of Chang-2 crude oil, among which the highest pour point depression is 6.3℃ and 7.4℃. PAA-18 and HAA-8 can depress the pour point of Chang-6 crude oil, among which the highest pour point depression is 4.4℃ and 6.5℃. PAA-7 and HAA-9 can depress the pour point of Yanchang pipeline crude oil, among which the highest pour point depression is 9.3℃ and 5.4℃, respectively.At last, the effect as flow improvers on crude oil was also analysized by DSC, and evaluated in the crude oils from different oilfield. The result shows that the addition of polyamine amine can decrease the wax appearance and the peak temperature of wax precipitation, and polyhydroxy amine can also bring down the pour point and viscosity of crude oils from different oilfield. |
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