Predictive Model of Restart-Up Pressure Drop after Shutdown for Heavy Oil-Water Ring Transportation Pipeline

Aiming at the problem of restart-up for a heavy oil-water ring transportation pipeline due to instability and damage of the water ring, based on the self-developed design of a small indoor loop simulation experimental device and taking four kinds of ordinary heavy oil in the Lvda oilfield as the research object, the change trend of restart-up pressure drop with time is experimentally studied when the pipeline is restarted-up after shutdown at a constant water flow. On the basis of the regression analysis of the orthogonal restart-up experimental data of four factors (oil holdup, oil viscosity, standstill period, and water cleaning superficial velocity) and mixed levels by the statistical product and service solutions statistical analysis software, a multivariate nonlinear restart-up maximum pressure drop prediction model is established. Through analysis of the characteristics of each stage of the restart-up process, an exponential decay model of restart-up pressure drop with time is created. The research results show that the variations in restart-up pressure drop with time can be divided into two stages: the attenuation stage and the equilibrium stage. The predicted value of restart-up pressure drop with time is in good agreement with the measured one, and the goodness of fit is very close to 1. The maximum restart-up pressure drop rises along with the increase in oil holdup, oil viscosity, standstill period, and water cleaning superficial velocity. The restart-up time prolongs with the increase in oil holdup, oil viscosity, and standstill period but shortens with the increase in water cleaning superficial velocity.