Study On Fouling Mechanism And Prediction Method Of Produced Water Conveying Pipeline In Western Yunnan Gas Field

The well sites in the Qiongxi gas field is in the development of middle and later stage.The gas field produced water containing high concentrations of scale-forming ions.When the gas field produced water flowing along the transmission pipelines,the parameters such as temperature,pressure,flow rate and flow environmentals are changed.These variation would destruction of chemical reaction balance between scale ions,so that react to form scale particles.Scale particles crystallization and crystal attaches itself to the wall,lead to pipe scaling,or even blocking tube and valve.These seriously affected the safe and efficient operation of the produced water transmission pipelines.For scaling problems of the produced water transmission pipelines in the Qiongxi gas field,this paper has carried out the following research:(1)Investigated the produced water transmission pipelines arrangement and field operation parameters of the Qiongxi gas field,and collected the water samples and scale samples of the produced water transmission pipelines.Using liquid ion chromatography to analyzed the water samples,which contained high levels of HCO3-.SO42-,Ca2+,Mg2+,Ba2+,Sr2+ and other scale ions.Used those methods to analyze the microstructure and the composition of scaling samples which are scanning electron microscope(SEM),weight loss in high temperature and X-ray energy dispersive spectroscopy(EDS).The results show that the main component of the scale samples is calcium carbonate.Further carried out the indoor static experimental analysis about the scale formation,come to conclusions that the scale quantity and change law under temperature,pressure.These provide the basis for the establishment of chemical model.(2)On the basis of experimental data,combined with the chemical reaction mechanism and kinetics of crystallization theory and fluid dynamics theory,studied the scaling mechanism of the produced water transmission pipelines in the Qiongxi gas field.And further analyzed the main scaling factors of the produced water transmission pipelines in the Qiongxi gas field.Specific to the situation of scaling in the Qiongxi gas field,so analyzed the scale trend prediction model of calcium carbonate scale.Finally chose the Oddo-Tomson saturation index method for scaling trend forecast analysis of well 6,12 and 14 of Qiongxi gas field.According to this method without considering the effect of flow rate and flow environments on scaling,prediction results are accurate enough.So used the BP neural network and Radial Basis Function neural network scale trend prediction analysis,prediction results show that the artificial neural network can predict the scale trend of the produced water transmission pipelines.This method overcomes the limitations of the saturation index method and provides the possibility analysis of pipe scaling theory basis.(3)Researched and analyzed the scale formation process and the force about scale particles in the produced water transmission pipelines,which provide the theory basis for scaling rate prediction model.Established the scaling rate numerical simulation model of the produced water transmission pipelines which included the chemical reaction,and chose the chemical reaction model.On the basis of the scale of the experimental data,calculated specific reaction in chemical reaction rate constant(k),the positive rate of reaction of index factor(A)and temperature index(β).(4)Based on the above research results,used the established scaling rate prediction model of the produced water transmission pipelines of Qiongxi gas field,adopt Qiongxi 12 Well data to simulate the migration settlement law of CaCO3 particles and its amount of deposition in different environments such as straight pipe,horizontal bend pipe,vertical bend pipe and ball valve.And analyzed the major influence factors and the influence law of precipitation amount in these environments.The reliability of the model was verified through the analog scale conversion for actual scaling layer thickness and the comparison of the actual data.The adaptability of the model was also verified through the predicte and comparative analysis about the amount of scale in the Qiongxi 12 well and Qiongxi 14 well external pipelines.And provided a new theoretical basis for the produced water transmission pipelines pigging plan formulation of Qiongxi gas field.