What units does the calculator use?

Inputs and primary output use oilfield Darcy units: permeability in millidarcies (md), viscosity in centipoise (cp), pressure in psi, area in ft², length in ft, and flow rate in reservoir barrels per day (RB/D). Enable "Show SI Values" for m², m, Pa, and m³/s equivalents.

What is the linear Darcy flow equation?

For linear flow: q = (1.1271×10⁻³ × k × A × ΔP) / (μ × L), where q is in RB/D, k in md, A in ft², ΔP in psi, μ in cp, and L in ft. The constant converts Darcy units to field units.

What is the radial steady-state flow equation?

For radial flow: q = (7.082×10⁻³ × k × h × ΔP) / (μ × ln(re/rw)), where h is net pay in ft, re is drainage radius, rw is wellbore radius, and all other symbols match the linear equation.

What is a millidarcy?

A millidarcy (md) is one-thousandth of a darcy. One darcy is defined as the permeability that allows 1 cm³/s of a 1-cp fluid to flow through a 1-cm² cross-section under a 1-atm/cm pressure gradient. Most reservoir rocks range from 0.01 md (tight gas) to 5,000 md (unconsolidated sand).

Does the radial equation include skin?

This calculator uses the ideal no-skin form. To account for near-wellbore damage or stimulation, replace ln(re/rw) with (ln(re/rw) + S), where S is the skin factor. Positive S indicates damage; negative S indicates stimulation (fracturing).

What is the difference between reservoir barrels and stock-tank barrels?

Reservoir barrels (RB) are fluid volumes at reservoir temperature and pressure. Stock-tank barrels (STB) are surface volumes after gas breakout and shrinkage. Divide RB/D by the formation volume factor B_o (typically 1.05–1.5 for oil) to get STB/D.

Darcy Flow Reservoir Calculator

Name: Darcy Flow Reservoir Calculator
Availability: InStock
Author: Nham Vu

Calculate reservoir fluid flow rate using Darcy's Law for linear or radial (steady-state) flow in oilfield units (md, cp, psi, RB/D) with optional SI conversion.

Flow Parameters

Flow Regime

Permeability (md)

Viscosity (cp)

Pressure Differential ΔP (psi)

Cross-sectional Area (ft²)

Length (ft)

Show SI equivalent values

Enter parameters and click Calculate

Equations Reference

Linear Flow

q = (1.1271×10−³ × k × A × ΔP) / (μ × L)

Radial Steady-State

q = (7.082×10−³ × k × h × ΔP) / (μ × ln(r_e/r_w))

q in RB/D • k in md • A in ft² • μ in cp • ΔP in psi • L, h, r in ft

Sample Scenarios

Summary