Viscosities are important parameters for design and operation of crude pipelines. The heating temperature is the major factor affecting viscosities of waxy crude below the wax appearance temperature. Below the abnormal point, waxy crude exhibits non-Newtonian flow behavior with the viscosity dependent on the shear rate. Both of these make determination of the non-Newtonian viscosities of waxy crude a very time-consuming job. On the basis of the model for predicting non-Newtonian viscosity of waxy crudes as a function of temperature and precipitated wax, an approach to predict non-Newtonian viscosity of waxy crude heated to various temperatures has been developed only based on a few measurements. The accuracy of prediction by this approach has been verified by 468 viscosity data from the Daqing crude heated at various temperatures. The totally average relative deviation between the measured and predicted viscosity is 9.42%.
The susceptibility of 316L stainless steel to crevice corrosion was investigated by using immersion test and electrochemical test. Three kinds of crevices including 316L-to-polytetrafluoroethylene (PTFE) crevice, 316L-to-fluoroelastomeric (FKM) crevice and 316L-to-316L crevice were tested in artificial seawater at 508C. The results indicate that 316L stainless steel specimen is the most susceptible to crevice corrosion when it is coupled to 316L stainless steel crevice former, while it is the least susceptible when it is coupled to FKM crevice former. It suggests that during submersible solenoid valve design, the crevice of metalto-metal should be moderately large so that crevice corrosion can not initiate and propagate, and FKM O-ring rather than PTFE O-ring should be selected as obturating ring. The corroded surface morphology was investigated using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Three regions including passive region, active region and variable region can be observed on crevice corrosion sites.
Critical flow rate models are widely used for liquid loading prediction in gas wells, take Turner's model as representative, but these models only analyze critical flow rate under wellhead or bottom hole condition, and take surface tension as constant, which results in a relatively large deviation between prediction result and actual liquid loading condition in condensate gas wells. In order to increase precision of liquid loading prediction, critical flow rate models are improved, aiming at solving above-mentioned problems. Different distribution of critical flow rate and surface tension along wellbore are considered, and the largest value of critical flow rate is taken as criterion of liquid loading condition, surface tensions under different temperature and pressure conditions are also calculated. Besides, on the basis of analyzing temperature and pressure distribution in dry gas wellbore by using temperature and pressure coupling method, a reasonable temperature and pressure coupling calculation model for condensate gas well is established, which considers the actual situation that both condensate and formation water exist in wellbore and revises relative density and flow rate of gas accordingly. Through verification by field case, it can be seen that precision of liquid loading prediction of improved critical flow rates models increases compared to that of original models, amongst which the precision of and the increased range of precision of liquid loading prediction of improved Li Min's model is highest. Therefore, the improved Li Min's model is the most suitable model for liquid loading prediction in condensate gas well.
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