Unconventional Reservoirs · Module U7
Gas in place, free and adsorbed
Gas in a shale sits in two places: compressed in the pores and adsorbed on kerogen surfaces. The module builds adsorbed gas content from a Langmuir isotherm scaled by TOC and corrected for temperature, ash and moisture, takes pressure from a gradient or measured points, removes the sorbed phase from the free-gas pore volume, gates each zone on its fluid type, net pay and TOC cut-off, and carries the result into Volumetrics and its Monte Carlo without counting any term twice.
- Level
- Advanced
- Position
- Module 7 of 8
- Video
- About 21 minutes, narrated
- Format
- Narrated video lesson with captions and slide reading view; with the certified option, a quiz whose pass unlocks the next module.
What the module covers
- The Langmuir isotherm and its reference TOC
- Temperature, ash and moisture corrections
- Pressure and the gas formation volume factor
- Free gas net of the sorbed phase
- Which zones book gas, and why
- The bridge to Volumetrics and the Monte Carlo
Learning outcomes
After the module you should be able to:
- Book free plus adsorbed gas in place per zone and carry it to Volumetrics with each term counted once.
- Compute adsorbed gas content from an isotherm at reservoir pressure
- Explain how a gas-in-place total avoids booking any term twice
A short preview
A Langmuir isotherm gives adsorbed gas content as VL times P divided by PL plus P. With a Langmuir volume of 90 scf/ton and a Langmuir pressure of 650 psia, a reservoir at 4,000 psia holds about 77 scf/ton. The curve is already flattening there, so doubling the pressure would add only six more. Scale for TOC as well, since the isotherm was measured on a sample of known richness: rock with half that sample's TOC holds about half the gas. Multiplied by bulk density and rock volume, adsorbed gas is booked on the rock, not in the pores.
Who it is for
Petrophysicists, geoscientists and reservoir engineers who evaluate organic shales and source rocks from logs and core, and carry TOC, net pay and gas in place into appraisal and development decisions.
Prerequisites: The Intermediate track, or working experience with shale volume, porosity and water saturation; the Geomechanics course is recommended before U8. The hands-on steps use the Organic Matter workspace in Formation Evaluation, and the brittleness steps in U8 use the Geomechanics workspace, available from the Professional plan.
Take the module in the Learning Hub
Unconventional Reservoirs: Specialty course, sold separately: eight modules that evaluate an organic shale from logs and core, from TOC methods fused and calibrated to core, through kerogen-corrected porosity and net pay, to free and adsorbed gas in place and brittleness. The lesson opens in the Learning Hub once the track is purchased; graded quizzes and the certificate come with the certified option.