Good hole cleaning ensures that cuttings are completely removed and therefore maximises the chance of an easy exit and re-entry (e.g. with liner). Bypassing the BHA will improve hole cleaning, especially when pressure hungry devices such as motors or turbines are being used.
Rotating the pipe also improves hole cleaning by providing additional agitation to prevent 'static zones' and cuttings beds. Cuttings removal improves exponentially with improved circulation and so a circulating valve can be vital for marginal or sub-optimal hydraulic situations.
Rotating whilst bypassing - Overheating problems
A common problem when rotating and bypassing simultaneously is that the
fluid below the valve will be static if the valve does not split flow
to send some down to the bit. Just a small amount of circulation reduces
friction heat build up by supplying cooler mud to remove some heat to
surface.
The absence of cooling flow can, in the worse case lead to pipe failure or if less severe cause expensive damage to temperature sensitive jewellery in the BHA. Therefore if the program requires that hole cleaning be assisted with rotation a split flow circ sub such as the DAV mx should be used.
In split flow configuration the
DAV mx has ideal characteristics
for providing maximum hole cleaning by enabling safe circulation with
rotation
