首页|On the hydrodynamics of off-bottom plug placement: Effects of geometry in a 2D model
On the hydrodynamics of off-bottom plug placement: Effects of geometry in a 2D model
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NSTL
Elsevier
We investigate the injection of a viscoplastic fluid, through an injector, into a channel filled with a lower density Newtonian fluid. The two-dimensional model problem is informed by plug & abandon practices in Western Canada and is analogous to the early stages of the balanced plug method in placing off-bottom plugs (Trudel et al., 2019). We present a systematic study of the effect of the injector size and position on the flow dynamics and fluid accumulation. When the injector and the channel are centralized, an unstable displacement flow develops below the injector. The instability leads to the formation of a mixing layer below the injector that diverts the injected fluid toward the space between the injector and the channel (the gap). The unsteady development of the mixing layer leads to the episodic mixing of the injected fluid that enters the gap. The frequency and magnitude of these contaminated regions change nonmonotonically with the injector width but decrease with the length of the mixing layer. When the injector is not centralized with the channel, the injected fluid flows toward the wide side of the gap. This leads to the formation of a series of vortices below the injector and a relatively short mixing layer. While the fluid that enters the wide side of the gap remains primarily unmixed with the Newtonian fluid, significant periodic mixing is persistent on the narrow side. On the narrow side of the gap, the average degree of mixing of the fluid entering the gap increases significantly with eccentricity while the velocity of the advancing front of the injected fluid decreases. Our results suggest there may be an optimal range of diameter ratios that minimize the mixing of cement slurry and wellbore fluids. In the absence of a mechanical or non-mechanical barrier, the injected fluid may flow toward the gap and accumulate at the target position irrespective of the relative position of the injector within the wellbore. The quality of the accumulated slurry, however, may vary notably with the size and position of the injector.
Plug and abandonmentOff-bottom plugsInjector sizeEccentricityDisplacement flowsViscoplastic fluidsFLUID DISPLACEMENTINSTABILITY
NSTL
Elsevier
