Characteristic of Spiral Displacement Process in Primary Cementing of Vertical Well Washout

Abstract

Summary Cementation is an essential process in well drilling, which provides security and isolation for following operations and for wells’ long-life production. Irregularity of the wellbore makes cementing more complex, with displaced fluid becoming easily trapped and leading to poor isolation. Here, we investigated spiral displacement of washout, which is one kind of irregularity, where the spiral flow is induced by a cyclone centralizer. The features of spiral flow with sudden hole enlargement, differences between spiral and nonspiral displacement processes, and influence of some parameters were investigated with a simulation method. First, the induced radial flow is around zero (10−1) of the main flow, which is enough for displacing radially, and this radial flow results in radial migration and dispersion of flow field. Cooperating with reversing flow after hitting the outer wall, radial migration leads to flow field mixing and spiral velocity dissipating quickly along the axial direction. Moreover, spiral flow is beneficial for cementing of washout, and the displacing pattern with spiral flow is different compared with axis flow. In spiral displacement, cement slurry accumulates at the bottom and outer side of the washout, while accumulation happens at the top and inner side of the washout for nonspiral flow. The accumulation pattern in spiral displacement prompts movement of residual fluid, but topside accumulation hinders removal of that. Of these parameters, density difference can depress the elongation of the interface and has a positive effect on displacement. An increase in washout length and diameter has a favorable influence, as such enlargement allows for further development of displacing flow and delays the breakthrough. An increase in displacing velocity and rotation angle has a nonmonotonic effect in that with the displacing velocity increasing, the displacement first worsens, then improves, but increasing the rotation angle has the opposite effect.