Currently, between 3 to 10 barrels of formation water are produced to the surface for every produced barrel of oil. There is a need for efficient and versatile oil-water separation systems in order to reduce the costs and environmental impacts associated with managing these large volumes of produced water. Existing separation technologies in the oil production operations utilize hydrodynamic, gravitational or membrane separation techniques to separate oil from water downhole or on the surface. They are either energy-intensive, costly, or suffer from a number of mechanical and operational problems, and are neither adjustable to changes in flow rates or water cuts nor capable of separating solid fines from the water stream. Here, we introduce a new Acoustic Oil-Water-Fines Separation (AOWFS) technique aimed at addressing these challenges and the major global issues associated with the massive volumes of waters produced during oil production operations. AOWFS is a low-energy, three-phase separation technique that can be used downhole or on the surface. It utilizes a sequence of acoustic standing wave patterns along a flow conduit with a decreasing number of loops in the direction of flow. It is capable of simultaneously separating oil droplets and solid fines from water streams in the flow conduit:
oil droplets are directed and coalesced in the bulk of the conduit while solid fines are directed and concentrated near the its walls. The oil/solids-free water can then be reused for waterflood-assisted oil recovery or other high-water-demand operations. AOWFS not only increases the oil-water separation efficiency, but also reduces the risk of pore clogging and formation contamination should water is re-injected back in the formation. Moreover, AOWFS allows for instantaneous tuning via to meet changes in flow rates and water cuts, and can be integrated into existing downhole and surface separation infrastructures.
A set of proof-of-concept experiments using direct microscopic visualization in a microfluidic channel demonstrated the instantaneous separation of micron-sized oil droplets and solid fines from water by exciting the proper acoustic standing wave fields in the flow channel. The oil droplets and solid fines were separated by a distance of λ/4 (λ being the wavelength of the acoustic wave), which is the expected separation between the pressure nodal and antinodal planes of the standing wave. Another set of macroscopic scale experiments was subsequently conducted which employed a 12-ft long conduit with a 4-in x 4-in cross section integrated into a flow-loop system and demonstrated the scalability of the technique. Results of these experiments will be shown and discussed, together with a full description of the technique and the underlying acoustophoretic mechanisms.
