vugular and cavernous, page-24

Yes..get the mud back out and we will see a difference.
Remove the standing hydrostatic head caused by the mud in the tubing and you create an area of low pressure for the reservoir fluids to move into. Initially more mud, followed by hydro carbons. The lower gravity/density fluids will then flow more easily through the formation and into the well tubing. Calculating the flow of fluids through a vugular formation is quite difficult (I believe) with variation for single phase and 2 phase flow.
In laymens terms, imagine 2 bottles full of pressurised liquid,connected by a straw through corks in the necks. Then punch a hole in 1 bottle. The liquid comes out fast until the pressure is depleted. It relies on the 2nd bottle to fill it up again via the straw, which has a much smaller diameter than the hole. It cant do it unless you plug the hole, and then it takes time. Of course the formation has a lot of 'bottles' interconnected, but the nearest ones to the bottom of the well are full of mud.
Hope I'm not being too simplistic for the oil techs.