Gas Well Deliverability Calculator
Calculate Absolute Open Flow (AOF) and gas IPR using Rawlins-Schellhardt back-pressure and Laminar-Inertial-Turbulent (LIT) methods from multi-rate test data.
Reservoir & Well Data
Multi-Rate Test Points (2-4 points)
AOF (Rawlins-Schellhardt)
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AOF (LIT)
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C (flow coeff.)
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n (flow exponent)
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LIT Coeff. a (laminar)
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LIT Coeff. b (turbulent)
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Gas IPR Curve (Pwf vs q)
Back-Pressure Plot: log(Pr²-Pwf²) vs log(q)
Slope = 1/n for Rawlins-Schellhardt
How this was calculated
Rawlins-Schellhardt: q = C × (Pr² - Pwf²)^n. The exponent n (0.5-1.0) and coefficient C are determined from a log-log plot. n=1.0 is fully laminar (Darcy), n=0.5 is fully turbulent.
LIT Method: (Pr² - Pwf²) = a×q + b×q². Coefficients a (laminar) and b (turbulent) determined by linear regression of (Pr²-Pwf²)/q vs q.
AOF: Absolute open flow potential, the theoretical rate at Pwf = atmospheric (14.7 psi).
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Gas well deliverability testing determines a well's production capacity as a function of bottomhole flowing pressure. The Absolute Open Flow (AOF) potential is the maximum theoretical rate a well could produce if the sandface pressure were reduced to atmospheric. While never achievable in practice, AOF serves as a standard benchmark for well comparison and regulatory reporting.
The Rawlins-Schellhardt (empirical back-pressure) equation q = C(Pr2 - Pwf2)^n is the most widely used deliverability relationship. The flow exponent n characterizes the degree of turbulence: n = 1 for purely laminar flow and n = 0.5 for purely turbulent flow. Most gas wells exhibit n between 0.5 and 1.0. The back-pressure coefficient C and exponent n are determined from a log-log plot of (Pr2 - Pwf2) versus q.
The LIT (Laminar-Inertial-Turbulent) method provides a more rigorous, theoretically grounded approach by separating laminar and turbulent pressure drops explicitly. This makes it more reliable for extrapolation beyond the tested rate range and is recommended by regulatory bodies for gas well deliverability analysis.
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