Work out casing depth instantly with clear inputs, formula shown and shareable results.
Casing depth is chosen so the shoe can withstand the mud weight needed to reach the next target plus a kick margin. Working from the bottom up, the shoe must sit deep enough in competent rock that its fracture gradient exceeds the required mud weight by the safety margin.
Casing shoe depth
Shoe depth = required mud weight x target depth / (fracture gradient at shoe - kick margin)
Mud weight
Required mud weight = pore pressure gradient + trip margin
Casing design is a safety-critical engineering activity governed by regulation. It must be carried out by qualified well engineers using verified geopressure data.
Because the deepest objective sets the mud weight, which sets the strength needed at the shoe above it, which in turn sets the next casing point. Designing top-down usually produces an infeasible string.
Isolating loss zones, unstable shales, shallow gas and freshwater aquifers, plus regulatory requirements for surface casing depth and cement coverage.