A Study on Creep Behavior of Gelled Daqing Crude Oil

Gelled waxy crude oils have complex rheological properties. Experimental research and mechanical analogy were performed for the creep behavior of Daqing crude oil. The experienced stages in creep process were partitioned based on the changes of strain and strain rate with the increasing loading time. When the loading stress was lower than the yield stress, there existed three stages; namely, instant elastic deformation, decelerated creep, and constant rate creep. When the applied stress was higher than the yield stress, accelerated creep occurred after the above three stages. By applying mechanical analogy, the elastic element, viscous element, plastic element, and accelerated creep element were employed to reflect the interior strain mechanism of crude oil under creep condition. A creep equation was proposed by incorporation with the analysis on the creep experiment. Based on the creep equation, nonlinear regression was conducted by using the creep experiment data of Daqing crude oil at different temperatures of 28 degrees C, 29 degrees C, 30 degrees C, and 31 degrees C, respectively. The average correlation coefficient was 0.9907. Substituting the calculated equation parameters into the creep equation, the creep behavior under other shear stresses can be predicted at the same temperatures. The average relative deviation is 8.29%. The change of strain of crude oil before yielding can be accurately described by the creep equation