Advanced Formation Evaluation
Read the Well taught you to sign a saturation; this tier is for the wells that fight back. Conductive clays, capillary physics carried from core to field, NMR read as pore size, the borehole wall itself, and the shale plays where the source rock is the reservoir.
You can choose a shaly-sand saturation model and defend the physics behind it, carry one cored well's capillary data across a field with the J-function, split NMR porosity into bound and free fluid and turn the split into permeability, read dip, fractures, and in-situ stress from a borehole image, and land a well in a source-rock play from TOC to brittleness.
Beyond Archie
Clean Archie reads a conductive clay as water and condemns real pay; Simandoux and Indonesia give the shale its own conductance path, and the model you choose changes the saturation you sign.
Waxman-Smits ties the clay correction to measurable chemistry, CEC and brine salinity, and dual-water splits the pore water into bound and free; this is how a zone that reads wet can still produce clean.
Four models on one honest well; where they disagree is exactly where your judgment becomes the deliverable, so prove the call by making it.
Capillarity and height
Drainage set the saturations before any log arrived: entry pressure, the plateau, irreducible water, and a free-water level that is not the contact. Every saturation profile you will ever map is this physics in disguise.
Divide out the square root of k over phi and every rock type's capillary curve collapses onto one J-Sw line; that collapse is what lets one cored well speak for the whole field, and the Ogbon-1 test shows where a blind height model breaks.
The NMR answer
The T2 axis is a pore-size axis, and one cutoff splits the porosity into fluid that is bound and fluid that will flow; set it per lithology or it lies, because surface relaxivity marches the whole spectrum along the axis.
The T1/T2 ratio and the D-T2 map are fluid fingerprints no conventional log carries; gas betrays itself twice, high above the diagonal and pinned against the diffusion ceiling.
One pass of the tool gives porosity, irreducible water, Coates permeability, and a fluid call with no resistivity required; prove you can read all four down a real well.
The borehole image
The image is the borehole wall unrolled, and every plane that cuts it becomes a sine wave; the amplitude is the dip and the trough is the azimuth, geometry you can learn to read by eye.
A tadpole is one dip measurement typeset; the green, red, and blue motifs are the classic structural stories, and removing the structural tilt leaves the paleocurrent behind.
Fractures, breakouts, and induced tensile pairs are the in-situ stress writing on the wall; read them with GR and tadpoles beside them and the structure narrates itself.
The unconventional reservoir
Kerogen is light and resistive, so richness shows as a density deficit and a resistivity excess; Passey's Delta-logR turns that separation into TOC, but only a maturity estimate scales it honestly.
Richness says how much kerogen; maturity says what it became, oil, condensate, or gas by Ro. In a shale the gas ledger has two entries, free in the pores and adsorbed on the kerogen, and Langmuir keeps the second one.
Rich but ductile will not frac; brittle but lean will not pay. The sweet spot is where the two tracks agree, and picking it on the Ogbon shale is the whole unconventional trade in one call.