What is the effect of pulling through tight spots with the pump off during drilling?

Pulling through tight spots with the pump off can lead to a phenomenon known as swabbing. Swabbing occurs when the removal of a string of drilling pipe from the wellbore creates a vacuum effect, which can draw the wellbore fluids up into the annulus. This happens because the hydraulic pressure that would normally counteract this effect is eliminated when the pumps are not circulating the drilling fluid.

When a drill string is pulled through a tight spot, the change in fluid volume within the wellbore does not allow for instantaneous equalization of pressure, leading to a drop in pressure in the wellbore. If the pumps are off, there is no additional hydrostatic pressure provided by the mud, which makes swabbing more pronounced. This can result in well control issues as formation fluids might be drawn into the wellbore, potentially leading to wellbore instability or a kick.

Understanding the implications of swabbing is crucial in well control, as it affects the management of pressure in the wellbore and the overall integrity of the drilling operation.