Abstract
Waxy crude oil emulsion has thixotropic properties at the temperature near gel point, which is a macro-mechanical characterization of the structure failure and recovery of waxy crude oil emulsion. In this paper, the thixotropic behaviors of waxy crude oil emulsion near gel point were studied using hysteresis loop formed by stress linear increase and decrease, as well as the structural recovery characteristics. The influence of the loading conditions and water content on the thixotropy of waxy crude oil emulsion were analyzed with hysteresis loop area. The concept of “structural recovery” was introduced to study the degree of structural recovery after different stewing, and influencing factors were taken into account. Results have shown that for waxy crude oil emulsion, the failure to fully restore of the structure after lysis is the cause of the formation of hysteresis loop, and the loading conditions will not affect the strength of thixotropy and the degree of structural recovery. Additionally, the dispersed phase droplets weaken the thixotropy and structure recovery characteristics of waxy crude oil emulsion, and the greater the water content, the weaker the thixotropy. The findings can help to better understand the safe and economic operation of waxy crude oil-water pipeline transportation.
1. Introduction
With the development of global oil and gas exploitation to the deep sea, the ocean has become the main battlefield of oil and gas exploitation. In the production of offshore oilfield, waxy crude oil and water flow together in the pipeline. Due to the low-speed shear of the wellbore and pipeline and the high-speed shear of the pump and throttle valve, it is easy to form a water-in-oil (W/O) emulsion (Umar et al., 2016). Meanwhile, the resin and asphaltenes in crude oil are natural surfactants, which promote the formation of crude oil emulsion with good stability (Mirshekar et al., 2020).
4. Summary and conclusions
In this paper, the thixotropic characteristics near the gel point of W/O waxy crude oil emulsion gel system are studied by using the loading mode that shear stress increases linearly and decreases linearly to form hysteresis loop. Taking the area of hysteresis loop as the characterization quantity, the thixotropic characteristics and the influencing factors of structural recovery characteristics of W/O waxy crude oil emulsion gel system were analyzed.
- Because the structure of gelled system has a certain strength near the gel point, the oil sample is in a creep process at the initial stage of loading, and then shows an upward process of increasing shear rate. After that, the oil sample undergoes a downward process of shear rate reduction caused by shear stress reduction. The upward curve and downward curve form a hysteresis loop under stress loading.
