How do you calculate annular capacity in bbl per foot?

Subtract the squared pipe outside diameter from the squared hole or casing inside diameter, then convert the resulting annular area to barrels per foot.

Should I enter casing OD or ID?

Enter the inside diameter of the outer casing or the open-hole diameter. Enter the outside diameter of the tubing, drill pipe, or inner casing.

Can the calculator add stepped well intervals?

Yes. The multi-interval editor adds up to three sections with different outer IDs, inner ODs, and lengths.

Annular Space & Capacity Calculator

Calculate annular space capacity and volume, solve target fill length, total stepped intervals, and estimate bottoms-up strokes and circulation time.

Annular capacity between casing and pipe

Use casing ID or hole diameter—not casing OD—plus tubing or drill-pipe OD. See capacity per foot, total barrels, gallons, liters, fluid weight, and stepped intervals.

bbl/ft · gal/ft · ft/bbl

Edit the annulus

Hole or casing ID, inEnter the inner diameter of the outer boundary.Pipe or tubing OD, inEnter the outside diameter of the inner body.Annular length, ftFluid fill, %Fluid density, ppg8.33 ppg is approximately fresh water.

How much annular length will a target volume fill?

Use the current hole or casing ID and pipe OD. Enter available fluid, cement or spacer volume to solve the inverse annular-space problem.

Target volumeVolume unit

Calculated fill length2,178.65 ft664.05 m · based on 0.04590 bbl/ft

100.00 bbl ÷ 0.04590 bbl/ft = 2,178.65 ft

Stepped or multi-interval well

Add sections with different casing IDs, pipe ODs, or lengths.

Bottoms-up and annular circulation plan

Convert the calculated annular volume into pump strokes and estimated bit-to-surface travel time.

Volume → strokes → time

Annular volume sourcePump output, bbl/strokeUse calibrated output at operating efficiency.Pump rate, strokes/minUse the planned stable SPM.

Annular volume45.90 bbl

Bottoms-up strokes459 strokes

Estimated time11 min 29 sec

Average pump rate4.00 bbl/min · 168 gpm

Operational estimate only. Confirm the well programme, actual geometry, pump calibration, efficiency, washout, returns and surface line volume. This is not a well-control procedure.

How annular capacity is calculated

The outer value is the hole diameter or casing inside diameter. The inner value is the outside diameter of drill pipe, tubing, or inner casing. The calculator subtracts the inner circular area from the outer circular area and multiplies by interval length.

In US oilfield units, the exact geometric conversion uses 9,702 cubic inches per 42-US-gallon barrel. The familiar rounded field form is approximately (outer ID² − inner OD²) ÷ 1,029.4 for bbl/ft.

Need volume inside the tubing rather than around it? Use the Tubing Capacity Calculator. Need to compare closed-end and open-end pipe body volume? Use the Pipe Displacement Calculator.

Planning estimate only. The model assumes concentric, constant-diameter cylinders. Verify actual casing ID, drift and open-hole caliper, and account for washout, eccentricity, tool joints, couplings, cable, packers, scale, and other displaced equipment before field operations.

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