Explain what gamma ray, resistivity, density, neutron and sonic tools physically measure downhole.
Oil, Gas & Energy
Open-Hole Log Interpretation for Porosity, Water Saturation and Net Pay
Teaches petrophysicists, geologists and reservoir engineers to derive lithology, porosity, water saturation and net pay from open-hole logs, with core calibration and uncertainty checks at every step.
🗓️Duration5 training days
📚Content4 modules · 8 sessions
🎓On completionAccredited attendance certificate
About the programme
Course Overview
A porosity value that is half a percentage point too high, or a water saturation cut-off set in the wrong place, can move a net pay estimate enough to change a development decision. This course works through open-hole log interpretation in the order a petrophysicist actually applies it: understanding what gamma ray, resistivity, density, neutron and sonic tools physically measure, correcting readings for borehole size and invasion, computing shale volume and lithology, deriving porosity from density-neutron and sonic combinations, and estimating water saturation with Archie's equation and shaly-sand models such as Waxman-Smits and Simandoux. Participants work through real log suites and core reports, pick formation water resistivity from spontaneous potential and water catalogues, set porosity, shale volume and saturation cut-offs to define net pay and net-to-gross, and reconcile log-derived porosity and saturation against core measurements. The course closes with uncertainty: how sensitive a net pay estimate is to each input, and how to present a saturation-height model that a reservoir engineer can carry into volumetrics with confidence.
Expected Learning Outcomes
Correct open-hole log readings for borehole size, mud filtrate invasion and bed thickness effects.
Calculate shale volume from gamma ray and neutron-density separation and select the most reliable method.
Derive total and effective porosity from density, neutron and sonic log combinations.
Apply Archie's equation and shaly-sand models to estimate water saturation in clean and shaly reservoirs.
Set porosity, shale volume and saturation cut-offs to define net pay and net-to-gross.
Calibrate log-derived porosity and saturation against core data and quantify the remaining uncertainty.
Who Should Attend
Petrophysicists building formation evaluation models from open-hole log data.
Development and exploration geologists who interpret logs alongside seismic and core data.
Reservoir engineers who need porosity and saturation inputs for volumetrics and simulation.
Wellsite and operations geologists responsible for real-time formation evaluation decisions.
Petroleum engineering graduates moving into a petrophysics or subsurface role.
Data managers and technicians who process and quality-check open-hole log data.
Course Modules
Select any module to see its sessions and points.
01Logging Tool Physics and Environmental Corrections
2 sessions · 8 points
Session 1How Open-Hole Logging Tools Respond to the Formation
- Explain the physical principle behind gamma ray, spontaneous potential and caliper measurements.
- Describe how laterolog and induction resistivity tools respond differently in resistive and conductive muds.
- Relate density, neutron and sonic raw signals to the formation properties they are used to estimate.
- Identify the depth of investigation and vertical resolution of each open-hole logging tool.
Session 2Correcting Logs for Borehole and Invasion Effects
- Apply borehole size and mud weight corrections to raw density and neutron log readings.
- Distinguish flushed zone, invaded zone and virgin formation resistivity on a resistivity log suite.
- Use a resistivity ratio method to estimate invasion diameter and support saturation interpretation.
- Recognise bed boundary and thin-bed effects that distort log readings near formation contacts.
02Lithology and Porosity Determination
2 sessions · 8 points
Session 1Shale Volume and Lithology Identification
- Calculate shale volume from the gamma ray index using linear and non-linear response equations.
- Build a neutron-density crossplot to identify lithology and estimate shale volume independently.
- Compare shale volume estimates from gamma ray, neutron-density and spontaneous potential methods.
- Select the most reliable shale volume method for a given lithology and mineralogy.
Session 2Deriving Total and Effective Porosity
- Calculate density porosity from bulk density and matrix and fluid density assumptions.
- Combine neutron and density porosity on a crossplot to correct for gas effect and lithology.
- Derive sonic porosity using Wyllie's time-average equation and a compaction correction.
- Convert total porosity to effective porosity using the shale volume and shale porosity endpoint.
03Water Saturation Modelling
2 sessions · 8 points
Session 1Archie's Equation and Formation Water Resistivity
- Apply Archie's equation to estimate water saturation in clean, water-wet sandstone reservoirs.
- Determine formation water resistivity from a clean water sand using the spontaneous potential method.
- Cross-check formation water resistivity against regional water catalogues and produced-water analyses.
- Select cementation and saturation exponents appropriate to the reservoir rock fabric.
Session 2Shaly-Sand Saturation Models
- Explain why Archie's equation overestimates water saturation in shaly sandstone reservoirs.
- Apply the Waxman-Smits model to account for clay-bound cation exchange capacity in saturation.
- Apply the Simandoux and Indonesia equations as practical shaly-sand alternatives.
- Compare shaly-sand saturation results against core-derived saturation to test model choice.
04Net Pay Definition and Core Calibration
2 sessions · 8 points
Session 1Setting Cut-Offs and Calculating Net Pay
- Set porosity, shale volume and water saturation cut-offs based on core and production data.
- Calculate net pay and net-to-gross from a cut-off log and reconcile it against geological zonation.
- Test the sensitivity of net pay to reasonable changes in each cut-off value.
- Present net pay results in a format a volumetrics or simulation team can use directly.
Session 2Core-Log Calibration and Uncertainty
- Compare core porosity and permeability against log-derived porosity at matched depths.
- Build a saturation-height function from core capillary pressure data and tie it to log saturation.
- Adjust log interpretation parameters where core data reveals a systematic bias.
- Quantify the uncertainty range on net pay arising from tool, model and cut-off choices.
What the participant receives
4 course modules
A structured syllabus
8 training sessions
across 5 days
32 detailed points
Applied, detailed content
Accredited attendance certificate
On completing the programme
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