We're currently using invert diesel emulsion mud (70/30) for deep gas wells and see significant increase in gas production rates vs previously used biopolymer clayless mud.
Despite sufficient increase in production we're concerned with a probability of formation damage due to addition of third phase to the system (gas-water) and reducing gas flow?
What would be your experience, and what type of mud would you recommend for gas condensate fields (average water rate 2-4m3/day) with carbonate and sandstone reservoirs (lower carboniferous - visean).
Any help would be greatly appreciated!
What do you mean by addition of a third phase (gas-water) to the system?
What actually is happening.
For a diesel OBM in HTHP wells (never advised for your rig crew breathing, skin problems or cancer risk) I would do the basic conventional formation damage tests .You will need an approved laboratory to evaluate a diesel mud system.
As Scott said do the testing!
If you have a core samples look at the barytes particle size distribution possibly with addition of calcium carbonate. Also look at the base OBM system ensure you have no spurt loss, reduce fluid loss to as low as possible with additives. Evaluate whether the diesel, the whole mud, the water phase, plus all individual mud additives include any fluid loss control additives are non damaging and compatible with the formation and formation fluid. Formation damage prevention is not often so simple !
Best of luck Ian
Dave - it might be that an OBM using diesel is so rare these days that nobody has the experience to reply?
I know they are still regularly used Offshore Mexico, so maybe someone in that neck of the woods could help?
If the OBM is getting better production, then all other things being equal it would appear that the use of a WBM is causing formation damage (higher skin factor).
As Ian Petitt said in another post, using a WBM in an HPHT well is problematical and if the spurt loss is not being controlled, then this could be causing the higher skin factor - at least in the sandstone.
But really it needs the Operator &Fluids Company to do a proper investigation of formation / drilling fluid compatibility, preferably using core plugs rather than just cuttings samples returned from the well.
All the best
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