Aug 17 Fireside Chat with JRI and Scott Macmillan, page-402

"SM mentioned that the last mud tank they had had an underperforming agitator (since replaced). So they were getting variability in the mix coming out. Significant caking on the side of the bore, fracturing of the formation due to over balance, significant mud loss and clays in the formation breaking down and swelling due to incorrect mud chemistry. Drill string impacting a certain point of the bore due to the deviated well."

Thanks Nergel....I missed most of the above as I came in late in the chat. Thoughts off the top of my head:
- I was aware of the mud cake build up in M-1 main bore.
- Fracturing of formation due to over balance....that would suggest some serious over balance going on. Usually when this goes on you would get things like ballooning going on....the well takes a drink while you're circulating and then gives some of the mud (plus formation gas) back when you stop circulating (ECD drops). The result is connection and pumps off gas and sometimes well flows at connections. If this fracturing was going on in the sidetrack then that would suggest that the well was still significantly over balanced.
- Swelling clays....I'd be curious to know what sort of % KCL they were running in the mud system. Some Cation Exchange Capacity (CEC) studies on SWCs and cuttings might also provide some useful data.
- Drill string impacting on a deviated bore.....possibly. A good reason to run downhole mud motors in all BHAs in M2 so drill string rotary speed can be lowered. BHA design can also help. This sort of hole deterioration happens relatively quickly...ie mainly during drilling...the hole deterioration we saw in M1/S1 appeared to be on a slower scale...ie days. Unfortunately they most likely only have unoriented single arm wireline caliper data from M1 and the side track. Oriented dual axis caliper data and FMI image logs are very useful for nailing down exact nature of well bore deterioration.