"I am struggling to get my head around why he would say that then basically drill at the same pressure as main well given the issues encountered there. Surely if a mud pump can pump at 2000 psi it can pump at 200 psi? I would have thought that pumping at lower pressures that the mud mixture would be easier to get more consistent??"
The inconsistencies that SM refers to is the ability to maintain mud properties at surface in the mud processing system...ie it'a nothing to do with the ability of the rig pumps to move the mud down the drillstring.
Maintenance of mud properties involves not just the agitation system in the tanks but also the solids control equipment (shakers, desander and centrifuge if fitted). Difficulties moving mud between tanks can also affect your ability to maintain mud properties.
When SM talks about drilling at the "same pressure" he would be referring to what is known as Equivalent Circulating Density (ECD). ECD is the density of the mud as it comes out of the bit...while you're pumping ECD is higher than your static mud density (what is measured at surface from a mud sample). ECD is controlled by static mud density, depth and the pressure drop in the annulus between the outside of the drill string and the borehole. Hole cleaning efficiency can also affect ECD.....if you aren't efficiently lifting cuttings out of the annulus then this can lead to an increase in ECD.
IVZ Price at posting:
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