Experiments on Displacement of Viscoplastic Fluid in an Annulus With Wavy Inner Wall: Applications in Primary Cementing

Abstract This study delves into the dynamics of displacement flow within an annulus characterized by sinusoidally varying gap widths, aiming to replicate the effects of borehole irregularities on flow behavior. The experimental setup mimics a scenario where a spacer fluid displaces the mud initially within the annular region of the well. Our experiments utilize miscible fluids with physical and rheological properties similar to those found in field fluids. Specifically, the displacing fluid, brine, emulates a wash, while the displaced fluid comprises a non-Newtonian Carbopol solution, representing drilling mud properties. The annulus was positioned vertically and the displacing fluid was injected from bottom to top. High-speed cameras were used to capture the instantaneous behavior of the displacement flow. Our investigation reveals that the presence of yield stress in the displaced fluid leads to residual viscoplastic fluid remaining within the wavy annulus, predominantly at locations where the gap width is at its maximum. Continuous injection of the displacing fluid is necessary to eliminate these residual layers effectively. The main purpose of this study is to broaden the industry’s perspective on designing effective cementing jobs, which are vital in the construction of oil and gas wells, by including some assessment of the effects of geometric irregularity in the annular geometry.