Work out cementing volume instantly with clear inputs, formula shown and shareable results.
Annular capacity in barrels per foot is (hole diameter squared minus casing OD squared) divided by 1029.4, with diameters in inches. Multiplying by the cemented length gives the theoretical volume, to which an excess of 20-50% is added for hole washout measured by caliper log where available.
Annular capacity
Capacity (bbl/ft) = (D_hole^2 - D_casing^2) / 1029.4
Cement volume
Volume = capacity x cemented length x (1 + excess %)
Cement volume and top-of-cement requirements are usually set by regulation for well integrity and aquifer protection. Verify against the applicable well construction rules.
The drilled hole is rarely to gauge — washouts in soft formations can enlarge it substantially. A caliper log lets excess be reduced to 10-20%; without one, 30-50% is prudent in open hole.
The top of cement falls below the design point, leaving the annulus uncemented. That risks loss of zonal isolation, sustained casing pressure and a costly remedial squeeze.