# Reservoir Engineering Formula Guide

> A reservoir engineering formula guide for Darcy flow, straight-line productivity index, Vogel IPR, material balance, and original oil in place checks.

## Key Takeaways
- Straight-line productivity index is a convenient drawdown model but can miss nonlinear two-phase behavior.
- Vogel IPR was developed for solution-gas-drive oil wells and should not be treated as a universal deliverability equation.
- Material balance relates in-place volumes to pressure, produced and injected fluids, aquifer influx, and fluid-rock properties.

## Workflow
1. Use Darcy or radial-flow equations when the flow geometry, fluid properties, and pressure boundary assumptions match the case.
2. Use productivity index for quick linear inflow checks where rate is proportional to drawdown.
3. Use Vogel IPR for oil-well two-phase inflow screening when the solution-gas-drive assumptions are reasonable.
4. Use material-balance calculators as consistency checks against production, pressure, PVT, and aquifer assumptions.

## Calculators
- [Vogel IPR calculator](/calculators/vogel-inflow-performance-relationship)
- [Productivity index calculator](/calculators/productivity-index-and-straight-line-ipr)
- [Radial liquid flow calculator](/calculators/steady-state-radial-liquid-flow-rate)
- [Oil material balance calculator](/calculators/original-oil-in-place-from-general-oil-material-balance)

## Formula References
- [Darcy's Law for Linear Single-Phase Flow calculator](/calculators/darcy-s-law-for-linear-single-phase-flow)
- [Darcy's Law for Linear Single-Phase Flow formula and calculator](/calculators/darcy-s-law-for-linear-single-phase-flow#formula-reference)
- [Steady-State Radial Liquid Flow Rate calculator](/calculators/steady-state-radial-liquid-flow-rate)
- [Steady-State Radial Liquid Flow Rate formula and calculator](/calculators/steady-state-radial-liquid-flow-rate#formula-reference)
- [Productivity Index and Straight-Line IPR calculator](/calculators/productivity-index-and-straight-line-ipr)
- [Productivity Index and Straight-Line IPR formula and calculator](/calculators/productivity-index-and-straight-line-ipr#formula-reference)
- [Vogel Inflow Performance Relationship calculator](/calculators/vogel-inflow-performance-relationship)
- [Vogel Inflow Performance Relationship formula and calculator](/calculators/vogel-inflow-performance-relationship#formula-reference)
- [Original Oil in Place from General Oil Material Balance calculator](/calculators/original-oil-in-place-from-general-oil-material-balance)
- [Original Oil in Place from General Oil Material Balance formula and calculator](/calculators/original-oil-in-place-from-general-oil-material-balance#formula-reference)

## Verified Sources
- [Inflow Performance Relationships for Solution-Gas Drive Wells](https://blasingame.engr.tamu.edu/z_zCourse_Archive/P613_02A/Gas_IPR/00001476.pdf) - Jo V. Vogel / SPE paper archive
- [Material Balance Concepts](https://blasingame.engr.tamu.edu/z_zCourse_Archive/P620_09C/P620_09C_Lectures/P620_09C_Lec_15_Mod3_FunFld_03_MatBal.pdf) - Texas A&M University

Important use note: calculator outputs support engineering checks, study, and review. They do not replace professional engineering judgment, company procedures, regulatory requirements, or source standards.