| Description |
Waxy crude oils, which are crude oils containing high paraffin waxes, are becoming increasingly important in worldwide oil production. Wax-related pipeline flow assurance issues are commonly encountered in the petroleum industry. In this work, two major issues regarding waxy suspensions and water-in-oil emulsions were investigated. Waxy crude oils usually exhibit large non-Newtonian shear viscosity values and thixotropic behaviors (time-dependent yield stress) due to the existence of suspended wax crystals during shear flows. Thus, traditional pressure drop prediction models for Newtonian pipe flows are not applicable. The main goal of this work is the development of a computational model for flows of waxy crude oils in pipelines that uses as input experimental results from laboratory rheology measurements. To investigate the pipe flows of model waxy crude oils, a bench-scale flow loop (test section ID =1.02 cm, length = 1.37 m)and a pilot-scale flow loop (test section ID = 2.67 cm, length = 3.81 m) were builtsuitable for studying the steady state and transient flow behaviors. Steady flow pressures and the pressures required for the transient start-up flow were measured after different time periods of waiting. Overshoots in pressure were observed at the beginning of start-up flow. A computational pipeline flow model based upon the isotropic-kinematic hardening (IKH) rheology model was used successfully to explain the flow loop results. The parameters of this model were obtained by laboratory cone and plate rheology measurements. A detailed rheological evaluation of emulsions containing model oils with iv implications on cold-flow restart is the subject of the second part of this dissertation. The applicability of cold-flow restart when varying amounts of emulsified water are present within the oil was examined. Restart studies were conducted in a bench-scale flow loop. The pressure required to restart the gelled pipeline decreased with a decrease in the cold flow shutdown temperature, and with an increase in the water content. Complementary rheological measurements show that the presence of water reduces the yield stress of model waxy crude oil gels. |
