Reference
Completion Engineering Formulas
The core formulas behind every CasedCalc calculator, in one place — free to use, whether or not you ever open the tool itself.
Area Calculator
Pipe, casing & annular area calculations
Internal area = π/4 × ID². External area = π/4 × OD². Annular area between two concentric strings = π/4 × (ID_outer² − OD_inner²).
Before running a liner or workstring, engineers check whether it will pass through the existing casing with enough annular clearance for cement returns or cuttings circulation — a quick area calculation catches a tight-clearance problem before the string is on location.
View the Area CalculatorString & Casing Volume Calculator
Tubing, casing & annular volume / capacity
Capacity (bbl/ft) = ID² ÷ 1029.4. Annular volume (bbl/ft) = (ID_outer² − OD_inner²) ÷ 1029.4, where diameters are in inches.
Before pumping a cement job or displacing to a completion fluid, engineers calculate exact internal and annular volumes so pump strokes land the fluid interface at the correct depth — a miscalculated volume can leave cement short of the shoe or displace fluid past the intended point.
View the String & Casing Volume CalculatorString Weight Calculator
Air weight & buoyed string weight
Air weight = nominal weight (lb/ft) × string length. Buoyed weight = air weight × buoyancy factor, where BF = 1 − (fluid density ÷ 65.5) for fluid density in ppg.
While picking up a completion string, engineers compare the expected buoyed weight against live weight indicator readings — a reading that doesn't match the calculated figure is often the first sign of a stuck point, an obstruction, or a hanging-up string before it becomes a bigger problem downhole.
View the String Weight CalculatorShear Out Force Calculator
Shear pin & shear screw release force
Shear force = pressure differential × piston area. For a ganged configuration: total rated shear = per-pin rated shear × pin count. Safety margin = rated shear value ÷ applied force.
Before setting a packer or shearing a plug open, engineers confirm the applied setting pressure reliably clears the pins' rated shear value with margin, while staying safely below pressures reached during routine operations like acidizing or pressure testing — so the tool shears when intended and never before.
View the Shear Out Force CalculatorPacker Circulation Calculator
Safe circulating rate & pressure across a packer
Differential pressure across packer = surface pressure + hydrostatic below packer − hydrostatic above packer (U-tube effect). Differential force = differential pressure × packer bore area.
After setting a packer and before starting a kill or fluid-change job, engineers work out the maximum circulating rate that keeps differential pressure across the packer within its rating — circulate too fast or ignore the U-tube effect and you risk unseating the packer or exceeding its rated differential.
View the Packer Circulation CalculatorStretch Calculator
Elastic pipe stretch for spacing & packer setting
Tension stretch (Hooke's Law) = (F × L) ÷ (A × E), where F is applied force, L is string length, A is cross-sectional steel area, and E is Young's modulus for steel.
When landing a tubing string in a hanger or setting a straight-pull permanent packer, engineers calculate expected elastic stretch under a given pickup weight so the string lands at exactly the intended depth — accounting for tension, ballooning, and downhole temperature effects instead of guessing at the overpull.
View the Stretch Calculator