Drainage Radius Calculator
Calculate radius of investigation, drainage area, time to reach boundaries, Dietz shape factors, and pseudo-steady-state productivity index.
Reservoir & Fluid Properties
Pseudo-Steady-State Productivity
q = k × h × ΔP / [141.2 × B × μ × (ln(re/rw) - 0.75 + S)]
Radius of Investigation
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Drainage Area
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Drainage Area
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Time to Reach re
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PSS Flow Rate, q
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PSS Productivity Index
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Key Equations
ri = 0.032 × √(k × t / (φ × μ × ct))
A = π × ri² (ft²) | Acres = A / 43,560
tboundary = (φ × μ × ct × re²) / (0.001024 × k) (hr)
Dietz Shape Factors (CA)
Shape factors for common drainage geometries. Used in PSS productivity calculations: ln(CA) replaces the geometric term.
| Shape | Well Position | CA | ln(CA) | Equiv. re (ft) | PSS q (STB/d) |
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Radius of Investigation vs Time
How this was calculated
Radius of Investigation: The distance a pressure disturbance has traveled from the wellbore. Based on diffusivity equation solutions. The constant 0.032 corresponds to the point where pressure change is ~1% of the wellbore pressure change.
Dietz Shape Factors: Account for non-circular drainage shapes and off-center well locations. Published by Dietz (1965) and extended by Earlougher (1977).
PSS Productivity: Applies after the pressure disturbance reaches all boundaries. The reservoir depletes uniformly and the pressure decline rate is constant everywhere.
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Book a free strategy call →Understanding Drainage Radius and Reservoir Limits
The radius of investigation is a fundamental concept in well testing and reservoir engineering. It represents how far a pressure disturbance has propagated from the wellbore at a given time. During the infinite-acting period (before boundary effects), the radius of investigation grows proportionally to the square root of time: ri = 0.032 * sqrt(kt/(phi*mu*ct)).
The time at which the radius of investigation reaches the external boundary (re) marks the transition from infinite-acting (transient) to pseudo-steady-state (PSS) flow. During PSS, the entire drainage area is depleting and the pressure declines at a constant rate everywhere. The PSS productivity equation accounts for the drainage shape through Dietz shape factors (CA).
These calculations are essential for well test design (how long to test), well spacing optimization, and infill drilling decisions. All calculations run in your browser. Built by Groundwork Analytics.