An Unconventional Shale on Ogbon
Learning objectives
- Read a shale as a TOC track, a brittleness track, and a sweet-spot flag
- See two equally rich zones split by their brittleness
- Flag the sweet spot only where richness and brittleness both pass
- Summarize net sweet-spot thickness, average TOC, and gas-in-place
The Whole Chapter on One Shale
The unconventional workflow lands on a single organic-shale interval, the Ogbon Shale, in three tracks. The first is the TOC from the Passey separation, the second the brittleness index from the mineralogy, and the third a flag that turns on only where both pass their cutoffs.
Two Rich Zones, One Target
The shale has two organic-rich zones, and on the TOC track alone they look the same. The brittleness track splits them. The upper zone is quartz-rich and brittle, so the flag turns green: a true sweet spot. The lower zone is just as rich but clay-rich and ductile, so it will not hold a fracture, and the flag stays off. Same richness, opposite verdicts.
Where the Course Has Brought You
Out of the three tracks come the numbers a development needs: net sweet-spot thickness, average TOC, and a gas-in-place estimate from the Langmuir capacity. This is the whole of petrophysics in miniature, logs read for richness, fluid, storage, and rock strength, and turned into the one decision that matters, where to land the well. From the first porosity in Chapter 1 to this, the job has been the same: turn a measurement into a number you can drill on.
References
- Jarvie, D. M. et al. (2007). Unconventional shale-gas systems. AAPG Bulletin, 91(4).
- Passey, Q. R. et al. (2010). From oil-prone source rock to gas-producing shale reservoir. SPE 131350.