Prediction Of Hydrate Formation Conditions And Pipeline Transportation Risk Assessment For The Fireflood Exhaust

Fireflood exhaust is a by-product of fire drive oil recovery technology.Its composition is singular,which makes the applicability of the commonly used equations of state implicit now.In addition to CO2,H2 S and a small amount of alkanes,the exhaust also contains a large amount of saturated water vapor,which makes the risk of freezing and blocking in winter gathering and transportation high,and seriously threatens the safe operation of pipelines.Therefore,it is necessary to focus on the risk of freezing and blockage of the exhaust gathering and transportation pipelines,to carry out research on the evaluation of exhaust physical properties prediction models,and to identify the risk of icing/hydrate formation in various production conditions of exhaust pipelines,which will help establish a sound the flow safety evaluation system of the exhaust gathering and transportation system,guiding the production operation of the pipeline system,and ensuring the safe operation of the exhaust production system.In response to the above problems,this paper conducted a research on the risk assessment of ice/hydrate formation in the process of exhaust gathering and transportation,and compiled a prediction program for the generation conditions of exhaust hydrate.First,based on the experimental data of exhaust,the SRK,PR,LKP,GERG-2008 and BWRS equations were screened and evaluated.The results show that the SRK equation has the highest prediction accuracy for gas density,compression factor,and volume factor.The overall MAPE is 3.84%,5.17%,and 5.53%,respectively.And on this basis,combined with the development status and application level of the hydrate model,the Chen-Guo hydrate model is selected to predict the formation conditions of exhaust hydrate.A program for predicting hydrate formation conditions was compiled based on the C++ language,and compared with the literature data,it was shown that the relative error of the program was 9.34%,and the relative error of HYSYS was 10.52%.The results can lay the foundation for the risk assessment of exhaust transportation.Secondly,because the operating parameters and environmental parameters of the pipeline system fluctuate,the formation of hydrates has significant uncertainties in time and space.Therefore,based on the reliability theory,this paper establishes the hydrate formation limit state equation,and proposes a hydrate formation risk assessment method based on Sequential Probability Ratio Test,and an alarm mechanism has been established with reference to industry norms.The example simulation test shows that the response mechanism of the method is good,and the evaluation results conform to the objective law.Thirdly,for the typical and atypical components of the exhaust,a shutdown and restart model for branch lines and different ambient temperatures(buried,bare)is established.The simulation results show that for the wellhead exhaust gas at 0.5MPa and 50℃,no matter how long the pipeline is shut down,there is no risk of hydrate formation.However,the hydrate formation temperature under the shut-down pressure of the bare pipeline is lower than the freezing point,and there is a maximum shutdown time for the pipeline not to enter the freezing point.Finally,for the existing exhaust pipelines,the controlled variable method is used to quantify the risk of icing and hydrate formation caused by the wellhead exhaust pressure,temperature,and flow rate changes to the exhaust pipeline,clarify the principles of icing/hydrate prevention,and determine the use of electric heating antifreeze technology.The example compares and analyzes the control effects of different heating temperatures(65°C,85°C and 105°C)and different heating lengths(10m,15 m,20m,25 m and 30m),which can provide a reference for the later reconstruction of the built exhaust pipeline.