Investigation of flow modifying tools for the continuous unloading of wet-gas wells

Abstract

Liquid loading in low production gas wells is a common problem faced in many producing regions around the world. Once gas rates fall below the minimum lift velocity, it is essential that some action be taken to maintain continuous operation of the well. Commonly applied solutions include: 1) reduction in wellhead pressure (compression); 2) reduction of tubing diameter (velocity strings); and 3) installation of artificial lift (plunger lift or sucker rod pumping). This thesis examines the use of a patented vortex flow modifier to lift liquids from low rate (stripper) gas wells. Vortex Flow LLC has developed a flow modifying tool using the patented EcoVeyor technology developed by EcoTech. This technology has been used successfully for almost a decade to transport solids in the coal and potash industries and is now being adapted to the oil and gas industries. Recent field tests in horizontal production pipelines have shown the ability to alter basic flow characteristics, significantly decreasing backpressure on wells and increasing production. This thesis evaluates this technology for use in the wellbore, where a tool is introduced at the bottom of the tubing string. Laboratory experiments were conducted using a 125-ft vertical flow loop of 2-in diameter clear PVC. In these experiments, the effects of the vortex device on gas and water flow was examined and compared with the behavior in normal pipe flow. An optimized tool was developed that alters the flow patterns in the pipe resulting in improved liquid unloading accompanied by a decrease in the tubing pressure loss by more than 15 percent. The optimized tool also lowered the minimum lift velocity required for liquid unloading. Visual observations at four locations along the test loop confirmed that the liquid phase is transported in an upward helical manner along the pipe wall, providing an improved flow path for the gas phase. Apart from assisting liquid unloading, the flow modifying tool enhances the operational envelope at low gas rates as well as forming smaller slugs during liquid unloading. Therefore the flow modifier can also reduce gas requirements during artificial gas lift and can also serve as a flow stabilizing device.