Experimental Study On Wax Deposition In Oil Gas Water Three Phase

With the exploration of the subsea oil fields,a new problem-wax deposition in multiphase flow pipelines has to be faced,because of the low environmental temperature in deep sea.In this dissertation,the effect of experimental operation temperature on deposit thickness,component and aging phenomenon of deposit were comprehensively studied,and the experiments of wax deposition for oil gas water three phase and under pressure condition were conducted.Base on the experiments,the prediction model of wax deposition for multiphase flow was established.First,the effect of operation temperature on the deposit thickness was studied by cold finger apparatus and flow loop.The studies validated the effect of wall temperature on deposit thickness in published literatures by other researchers,and also found that the deposit thickness first increased then decreased with the decrease in oil temperature under constant coolant temperature conditions.According to this phenomenon,the corresponding temperature ranges were divided into hot flow area,sensitive precipitation of wax crystal area and cold flow area.The calculation of diffusion mass flow of wax molecular using classical molecular diffusion theory explained the root cause of the impact of temperature on deposit thickness,and the method and steps for judging the impact of temperature on wax deposition were proposed.Second,the aging of deposit was investigated by analyzing the components of wax deposition using the high temperature gas chromatography(HTGC)apparatus.It was found out that the content of wax molecules with high carbon number in deposit layer increase as the time increased,which lead to the hardness of the deposit layer increased.This phenomenon was called deposit aging,which was more apparent for crude oil with higher wax content.It was further proved that the temperature between the oil and pipe wall had a bigger effect on wax content in deposit,and the wall temperature had an bigger effect on carbon number distribution of deposit,while the effect of operation temperature on critical carbon number during the aging of deposit layer could be ignored.Under the oil gas two phase intermittent flow,the wax deposition covered the whole wall of pipe.Whether the top,side or bottom of the pipe wall,it was all found that the deposit layer had the aging phenomenon as the experimental time increased,and the top was most obvious.Third,the wax deposition experiments under oil gas water three phase intermittent flow and under pressurized natural gas condition were conducted for studing the changes of deposit rate with water cut,gas/liquid superficial velocity and pressure.Studies showed that the deposit thickness first decreased then increased with the water cut increased both the mixture oil and the crude oil.The increase in gas or liaquid superficial velocity both had a negative effect on deposit forming.With the increase of pressure with natural gas or nitrogen gas,the wax appearance temperature of oil increased,and the strength of the deposit structure decreased.Due to the combination of these two effect,the deposit mass first increased and then decreased as the pressure increased.At last,based on the molecule diffusion,and considered the shear peel in pipe flow and gelation of water phase,simplified the multiphase flow into single phase flow combining the flow feature under different flow pattern,the predictive model of wax deposition for different flow pattern in oil gas two phase flow and oil gas water three phase flow was established,respectively.Compared with the experimental results,the model could predicted the changes of deposit thickness with gas/liquid superficial velocity and water cut under oil gas two phase stratified flow,intermittent flow,and oil gas water three phase intermittent flow accurately.