A Mechanistic Model To Predict Natural Gas Separation Efficiency in Inclined Pumping Wells

摘要

A new mechanistic model to predict the natural separationefficiency in deviated pumped wells has been developed basedupon the combined phase momentum equations and a generalslip closure relationship. The model incorporates twoimportant parameters that are both functions of flow pattern;the local void fraction in front of the pump intake ports and thedrag coefficient. The void fraction is, in turn, a function of thebubble rise velocity. The model uses existing void fractionand bubble rise velocity correlations developed by Hasan andKabir1 for both bubbly and slug flow. The transition betweenbubbly and slug flow is determined by using the Hasan2 andHasan and Kabir3 criteria. The Barnea et al.4 critical anglecriterion below which bubbly flow cannot exist is also used bythe model. A general drag coefficient correlation for slug flowhas been developed based on data gathered by Serrano5 on awater-air system for inclination angles of 30 and 60 degrees.Comparisons between the model's predictions and theexperimental data of Serrano5 show excellent agreement.Sensitivity studies developed using the model indicates that thenatural separation efficiency decreases as the liquid rate,inclination angle and gas-liquid ratio increase and as theannulus area decreases. For the wellbore configuration andoperating conditions under investigation, the model predictsthe existence of a minimum liquid rate below which the systemreaches 100 percent gas separation efficiency.