Experimental Study on the Displacement of Completion Fluid with High Viscosity and High Density by Using the Packer Fluid with Low Viscosity and Low Density

The experiment of replacing high viscosity and high density completion fluid with low viscosity and low density packer fluid was conducted in a vertical annular tubing. By collecting the inlet flow rate of the pipeline and the interfacial transport at different locations of the pipe section, the topping off efficiency of low viscosity and low density packer fluid replacing high viscosity and high density completion fluid was analyzed. At the same time, the fluid flow in the pipeline during the whole experiment was filmed with a camera, and the mixing flow characteristics between different fluid interfaces were analyzed. The experimental results show that the higher the flow rate of packer fluid injection, the longer the mixing area between different fluids, and although the topping off time decreases, the amount of required packer fluid increases, the less the completion fluid is completely topped off, and the topping off ratio increases slightly. Under the field sealant injection flow rate standard, the amount of sealant required to completely top off the completion fluid in the wellbore is about twice the volume of completion fluid in the wellbore. At the same time, it was observed that the fluid flow in the wellbore annulus was spiral upward, which was similar to the flow pattern of drilling fluid during the drilling process, so the frictional resistance between different fluids and between fluid and tubing wall had a non-negligible effect on the topping off efficiency. The results show that the topping off of low viscosity and low density packer fluid to high viscosity and high density completion fluid can be achieved with a difference of 10 mPa-s in viscosity and 0.5 g/cm3 in density, but the amount of packer fluid used is closely related to the injection flow rate at the wellhead, and the higher the injection flow rate of packer fluid, the more the amount is used. By revealing the flow change law of the packer fluid-completion fluid interface during the completion fluid topping off process, valuable reference is provided for the injection displacement and dosage of packer fluid in the field completion process.