Three checks before selecting a drilling fluid for complex formations

Complex-formation fluid design is often reduced to an additive list, but most field problems come from a reversed order of judgement: an additive is chosen first, and lithology is explained afterwards.

The first check is shale reactivity. The degree of swelling and dispersion sets the range for inhibitor selection; polyamines and polyglycols behave differently depending on temperature and salinity.

The second check is the plugging and fluid loss package. Formations with micro-fractures need deformable plugging materials together with fluid loss additives; increasing fluid loss additive dosage alone rarely stops wellbore spalling.

Only the third step is dosage and cost. Dosage should be fixed in a system formulation test and corrected with returned cuttings and friction data, not copied from a neighbouring well.

When we supply products we normally confirm three inputs first: formation lithology and temperature, field mixing water quality, and the main additives already in use. Without any one of them, selection advice stays generic.