Nozzle design and experimental evaluation to mitigate liquid loading in gas wells

Abstract

This study consists of an experimental investigation of nozzle geometry effect on critical/subcritical flow transitions with applications on liquid loading mitigation in gas wells. Experiments were conducted in a facility with 1.5 in. ID PVC pipelines and a 30 ft long vertical section, which mimics two-phase flow (air and water) in gas wells. In total, 27 different nozzle geometries were tested, which were divided into two groups – conical and parabolic nozzles. The nozzle geometries tested were 3D printed and had a throat size of 0.25 in. The experimental investigation was divided into three phases. The first phase consisted of a series of tests using 27 nozzle geometries in a single-phase (air) horizontal flow facility, with the purpose of determining the most optimum nozzle geometries groups based on measured key performance indicators. Phase two involved testing these top performing nozzle geometries in a two-phase horizontal flow loop. Phase three consisted of testing the same geometries as for phase two in a two-phase vertical flow loop, determining nozzle performance in vertical flow, comparing with horizontal flow observations and determining the most optimum nozzle geometry. A nozzle geometry was considered optimum if it exhibited the highest critical pressure ratio and at the same time minimized pressure drop across the nozzle. Experimental results from phase 1 showed that nozzle geometry does have a significant impact on nozzle performance. Nozzles from ASTAR, Deich, LJ and Moby Dick nozzle groups showed improved performance compared to other nozzle groups. An empirical model was created based on phase 1 data in order to determine the effect of surface area of convergent and divergent section of nozzle on nozzle performance. The map created can be used to predict critical pressure ratio of a nozzle geometry by matching the nozzle design to the ones that have been tested. It was also determined that a smaller diverging angle resulted in a higher critical pressure ratio. A nozzle with an elongated throat had a higher critical pressure ratio, but at the same time it had a higher pressure drop across the nozzle, hence was not optimum. Length of a nozzle did not have as much of an impact on nozzle performance as the throat diameter and shape of nozzle converging and diverging sections immediately before and after the throat. Phase 2 experimental results showed that critical pressure ratio decreases when two phases are flowed through the nozzle. The length of the annular churn flow pattern observed at the exit of the nozzle may have a correlation to the nozzle performance. Based on data analysis, ASTAR nozzle geometry was the most optimum nozzle. Phase 3 data was analyzed and the most optimum nozzle geometry was determined to be ASTAR nozzle 2. Comparison with phase 2 data indicated a further drop in critical pressure ratio and an increase in pressure drop due to the effect of gravitation of the fluid flow.