(72g) Investigation on the Effect of Wax on Hydrate Formation Characteristics and Flow Properties in a High Pressure Flowloop

With the development of oil and gas industry toward the deep water, flow assurance problems represented by wax deposition and hydrate plugging arose. Due to the transportation of production liquids from wellheads, wax crystals and hydrate might coexist under certain conditions in transmission lines, which would lead to a higher pipeline blockage tendency and risk. In this work, a diesel oil + natural gas + 20% (volume fraction) deionized water + 1% (volume fraction of water) AA + 0.75% (mass fraction of oil) wax experimental system under different controlled water bathes temperatures (set as -1°C, 1°C, 3 °C and 5°C, respectively) and velocities (0.72m/s, 0.91m/s and 1.07m/s) was used to study the effect of wax on hydrate formation induction time and hydrate formation rate in a water-in-oil system, and flow properties before and after hydrate formation. Pressure drop and flow rate were used to manifest flow properties and to judge the tendency of blockage. Results show that hydrate formation characteristics and flow properties are quite different under different controlled temperature and velocities. For all experimental conditions, induction times for hydrates formation were prolonged in varying degrees compared to that under the non-wax situation. Meanwhile, the hydrate formation rates were significantly lower than the non-wax situation. As for flow properties, three changings were observed: (a) pressure drop increased sharply with flow rate decreasing sharply, (b) pressure drop increased gradually with flow rate decreasing gradually and (c) pressure drop decreased gradually with flow rate decreasing gradually. For (a) resulted in a rapid hydrate plugging, while for (c) resulted in a gradual hydrate plugging. These phenomena were entirely different from the flow systems without wax under same experimental conditions. With the assistant of FBRM (focus beam reflectance measurement) probe, PVM (particle video microscope) probe and high pressure visual window, the interaction relationships between wax crystals, water droplets and hydrate particles, the formation of wax-hydrate-agglomerates and the coupling deposition process were assumed to be the mechanism for these phenomena. It could be concluded that although the presence of wax inhibited the nucleation and growth process of hydrate formation, once hydrate began to form, there were a catastrophic decrease of the transportation ability for the pipeline, which meant an extremely high plugging tendency.