Petrophysics

Reservoir Engineering
By OgbonLab

Read the rock from logs: the full formation-evaluation workflow, hands on.

Read the rock from well logs: from gamma ray and porosity to saturation, permeability, and net pay, from first principles to confident formation evaluation.

17 parts 101 sections Free, browser-native
Start reading → First up: What Petrophysics Asks

Table of contents

Every section is a working session: text, math, code, interactive widgets. Click any title to jump in.

Part 1: Chapter 1: Rocks, Pores, and Fluids

  1. What Petrophysics Asks
  2. Porosity: The Space in the Rock
  3. Saturation: Filling the Pores
  4. Permeability: Can It Flow
  5. The Fluids and Their Contacts
  6. Reading a Well: The Log Display

Part 2: Chapter 2: The Logging Environment and Invasion

  1. The Borehole and Drilling Mud
  2. Formation Water and Mud Filtrate
  3. Invasion: Flushed and Virgin Zones
  4. Depth of Investigation
  5. Borehole and Environmental Effects
  6. How Logs Measure

Part 3: Chapter 3: Gamma Ray and Spontaneous Potential

  1. The Gamma Ray Log
  2. Shale Volume from the Gamma Ray
  3. Spectral Gamma Ray
  4. The Spontaneous Potential Log
  5. Reading Rw from the SP
  6. Reading Gamma Ray and SP Together

Part 4: Chapter 4: Density and Neutron Porosity

  1. The Density Log
  2. Porosity from Density
  3. The Neutron Log
  4. The Neutron-Density Crossplot
  5. Gas Effect and Crossover
  6. Shale and Effective Porosity

Part 5: Chapter 5: Sonic and Acoustic Logs

  1. The Sonic Log
  2. Porosity from the Sonic
  3. The Compaction Correction
  4. Wyllie versus Raymer-Hunt-Gardner
  5. Secondary Porosity
  6. Velocity and the Seismic Tie

Part 6: Chapter 6: Resistivity Logs and Invasion Profiles

  1. Why Resistivity Matters
  2. The Formation Factor
  3. Laterolog and Induction
  4. The Resistivity Profile
  5. Reading True Rt
  6. Resistivity on the Ogbon-1 Well

Part 7: Chapter 7: Archie's Equation and Water Saturation

  1. Archie's Equation
  2. The Pickett Plot
  3. Bulk-Volume Water
  4. The Saturation Exponents
  5. The Rw Problem
  6. Water Saturation on the Ogbon-1 Well

Part 8: Chapter 8: Shaly-Sand Saturation Models

  1. Why Clean Archie Fails
  2. The Simandoux Equation
  3. The Indonesia Equation
  4. Waxman-Smits
  5. The Dual-Water Model
  6. Shaly-Sand Models on the Ogbon-1 Well

Part 9: Chapter 9: Permeability Estimation

  1. Why Permeability Is Hard
  2. The Timur and Tixier Estimators
  3. The Poro-Perm Crossplot
  4. Flow Units: RQI and FZI
  5. Permeability from NMR
  6. Permeability on the Ogbon-1 Well

Part 10: Chapter 10: NMR Logging

  1. What NMR Measures
  2. The T2 Distribution
  3. The T2 Cutoff: BVI and FFI
  4. T1, T2, and Fluid Typing
  5. Diffusion and Gas
  6. NMR on the Ogbon-1 Well

Part 11: Chapter 11: Capillary Pressure and Saturation-Height

  1. Capillary Pressure: The Physics
  2. Drainage and Imbibition
  3. The Free-Water Level and the Transition Zone
  4. The Leverett J-Function
  5. The Saturation-Height Model
  6. Saturation-Height on the Ogbon-1 Well

Part 12: Chapter 12: Lithology and Mineralogy

  1. The Photoelectric Factor
  2. The M-N Plot
  3. The MID Plot
  4. The Matrix-Density / U Plot
  5. The Multimineral Solver
  6. Lithology on the Ogbon-1 Well

Part 13: Chapter 13: Net Pay, Cutoffs, and Volumetrics

  1. Cutoffs: Net Reservoir and Net Pay
  2. Net-to-Gross
  3. The Volumetric Equation
  4. Cutoff Sensitivity
  5. Volumetric Uncertainty
  6. Net Pay and Volume on the Ogbon-1 Well

Part 14: Chapter 14: Borehole Image Logs

  1. The Borehole Image
  2. Reading Dip from a Sinusoid
  3. The Tadpole Plot
  4. Structural vs Stratigraphic Dip
  5. Fractures on Images
  6. Image Logs on the Ogbon-1 Well

Part 15: Chapter 15: Formation Pressures and Fluid Contacts

  1. Formation Pressure: The Pretest
  2. Pressure Gradients and Fluid Density
  3. Fluid Contacts from Pressure
  4. The Free-Water Level
  5. Compartmentalization
  6. Pressures on the Ogbon-1 Well

Part 16: Chapter 16: Unconventional and Source-Rock Petrophysics

  1. Source Rocks and Organic Carbon
  2. The Passey Delta-logR Method
  3. Maturity and the Hydrocarbon Windows
  4. Adsorbed and Free Gas
  5. Brittleness and the Sweet Spot
  6. An Unconventional Shale on Ogbon

Part 17: Chapter 17: Capstone, Evaluate the Ogbon-1 Well

  1. Evaluate Ogbon-1, End to End
  2. Volumes: From Pay to Barrels
  3. The Uncertainty in the Answer
  4. The Petrophysics Workflow
  5. Final Examination

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