Acoustic Downhole Three-Phase Separation Method in Oil Field Applications

Abstract

Abstract The need for downhole oil-water separation systems increases with the rising water cuts in producing wells worldwide. This need is driven by the urge to reduce costs and environmental risks associated with managing and treating the expected large volumes of produced water. Available technologies utilize hydrodynamic, gravitational, or membrane separation techniques to separate oil from water downhole. They suffer from a number of systemic problems, including flow intervention and possible subsequent pressure drop in the well and failure of mechanical parts. They require a specific range of flow rates and water cut percentages in order to function properly. If well conditions deviate from these operational ranges, partial or complete failure of function is the result, unless some system parts are replaced, which in turn may require costly workover and temporary shutdown. Existing technologies are also incapable of separating fine solids from the fluid stream downhole, and thus run the risk of clogging the formation zones in which the water is reinjected. Acoustic separation techniques provide a viable solution to these limitations and add a number of advantageous functions. In this article, a concept for an Acoustic Downhole Oil Water Separation (ADOWS) tool and its field implementation is introduced. ADOWS is a three-phase separation concept in which both oil droplets and solid fine particles are separated downhole simultaneously from water. Oil is directed to the surface and water is allowed to enter a cavity equipped with a membrane to remove the already-separated particles before reinjecting the water back into the formation. ADOWS thus has the potential of not only increasing oil-to-water ratio and reducing produced water pumped to the surface, but also removing fine particles from the water so it can be reinjected into the formation without the risk of pore clogging. ADOWS is versatile, does not intervene the flow, and does not require narrow ranges of flow rates or water cuts to function properly. The underlying acoustic separation forces can be tuned instantaneously via surface controls to accommodate changes in flow rates and water cuts. Direct microscopic visualization experiments in a microfluidic channel demonstrate the key phenomena underlying ADOWS. The experiments show simultaneous separation of micron-sized oil droplets and solid particles from water by exciting the proper acoustic standing wave patterns in the flow channel.