A model used to describe the structural breakdown behavior of waxy crude oil emulsion gel

Under atmospheric temperature or deep sea low temperature, W/O emulsion composed of waxy crude oil and water tends to gelatinize, threatening the restart safety of pipelines. Based on the complex rheological properties of waxy crude oil emulsion gel, two kinds of thixotropic models proposed for waxy crude oil (i.e., the viscoplastic thixotropy model and the viscoelastic thixotropy model) were investigated in terms of their applicability to the emulsion gels. The rheological model that could accurately describe the whole rheological response process after the adding of emulsion gel was selected by comparing four viscoplasticity models which are commonly used for waxy crude oil and the viscoelasticity models which are developed recently. The experimental data fitting results show that the viscoelasticity model developed by Teng Houxing provides the most accurate description on the whole rheological response, including the creep before the yielding and the breakdown after the yielding. Among all viscoplastic thixotropy models, the one developed by Teng Houxing is the least deviated in the description of breakdown process after the yielding point, while the traditional Houska model can not describe the breakdown process of emulsion gel properly mainly because its rate equation can not reflect the actual breakdown process accurately. To sum up, the viscoplastic thixotropy models can not describe the viscoelastic response before the yielding point, so it is recommended to adopt the viscoelastic thixotropy model developed by Teng to perform pipeline restart calculation.