Material Balance Calculator
Estimate original oil in place (OOIP) using the Havlena-Odeh graphical method. Identify drive mechanisms and forecast recovery factors. 100% client-side — your data never leaves your browser.
Reservoir Properties
0 = no gas cap
0 = no water influx
PVT Data
Enter PVT data manually in the production data table below. The Bo, Rs, and Bg columns will become editable.
Production Data
| # | Pressure (psi) | Np (STB) | Gp (Mscf) | Wp (STB) | Bo (bbl/STB) | Rs (scf/STB) | Bg (bbl/scf) |
|---|
Original Oil In Place (N)
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Drive Mechanism
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R² (Regression Quality)
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Higher = better fit
Havlena-Odeh Plot: F vs Eo
Slope of the best-fit line through the origin = OOIP (N). A straight line through the origin confirms solution gas drive with no water influx.
F/Eo vs Cumulative Production
Constant F/Eo = solution gas drive. Increasing = water influx. Decreasing = gas cap expansion.
Pressure vs Cumulative Production
Recovery Factor vs Pressure
Intermediate MBE Calculations
| P (psi) | Np (STB) | Rp (scf/STB) | Bo | Rs | Bg | F (bbl) | Eo (bbl/STB) | Ef (bbl/STB) | F/Eo (STB) | RF (%) |
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Book a free strategy call →Understanding the Material Balance Equation in Reservoir Engineering
The material balance equation (MBE) is the cornerstone of reservoir engineering. First formalized by Schilthuis in 1936 and later refined by Havlena and Odeh in 1963, it applies the principle of conservation of mass to a petroleum reservoir: the volume of fluids produced must equal the expansion of the remaining fluids plus any external influx. This seemingly simple concept enables engineers to estimate the original oil in place (OOIP), identify the dominant drive mechanism, and predict future reservoir performance without requiring expensive full-field simulation.
The general MBE for an undersaturated or saturated oil reservoir is expressed as: F = N [Eo + m Eg + Ef,w] + We, where F represents the total underground withdrawal (oil, free gas, and water produced, each multiplied by its formation volume factor), Eo is the oil and dissolved gas expansion term, Eg is the gas cap expansion term, Ef,w accounts for pore volume compaction and connate water expansion, and We is the cumulative water influx from an aquifer.
The Havlena-Odeh method rearranges the MBE into a straight-line form. For a reservoir with no gas cap (m = 0) and no water influx (We = 0), plotting F versus Eo should yield a straight line through the origin whose slope equals N (OOIP). This graphical approach is powerful because departures from the expected straight line reveal the presence of additional drive mechanisms: an upward-curving trend indicates water influx, while a downward curve suggests gas cap expansion that has not been accounted for.
Drive mechanism identification is one of the most valuable outputs of a material balance study. The ratio F/Eo plotted against cumulative production provides a diagnostic signature: a horizontal trend confirms solution gas drive, a rising trend indicates water drive support, and a falling trend suggests gas cap expansion. Correctly identifying the drive mechanism is essential for forecasting recovery factors and designing optimal depletion strategies. Solution gas drive reservoirs typically recover 15-25% of OOIP, while water drive reservoirs can achieve 30-60% recovery.
This calculator computes PVT properties (Bo, Rs, Bg) automatically using the Standing correlation for solution GOR and oil FVF, and the Hall-Yarborough method for gas Z-factor and gas FVF. You can also enter PVT data manually if laboratory measurements are available. All calculations run entirely in your browser — no data is sent to any server. Built by Groundwork Analytics, an AI and engineering company that builds digital tools and deploys AI agents for the energy industry. We help operators, service companies, and engineering teams automate workflows, optimize operations, and make better decisions with their data. Get in touch or email us at info@petropt.com. Mehrdad Shirangi (Stanford PhD) specializing in reservoir simulation, production optimization, and AI/ML applications for upstream oil and gas.