Buoyant Miscible Jets in a Viscoplastic Medium With Applications in Plug and Abandonment of Oil and Gas Wells

Abstract

Abstract Plug and abandonment (P&A) is the final stage in the lifetime of oil and gas wells, during which the well is properly sealed to prevent fluid movements between different layers. The main steps of P&A include accessing the annulus section, cleaning the target area, and installing the cement plug barrier. Jet cleaning is an efficient technique for the second step of P&A, in which a heavy fluid is injected to displace lighter undesirable fluids. It is crucial to understand the effects of fluid properties on the jet cleaning process to achieve efficient cleaning. This study focuses on the jet flow dynamics in a miscible buoyant jet, where a Newtonian fluid is discharged through a circular nozzle into a viscoplastic ambient fluid. The effects of different parameters on the jet flow behaviour are analyzed, including the injection velocity and the yield stress of the ambient fluid. The buoyant jet flow behaviour is characterized using various jet features, including the laminar length and the penetration length. Our results show that the yield stress of the ambient fluid resists the jet evolution, decreases the jet penetration length, and changes the laminar length variation.