The vertical axis in seismic images is almost never at the same...

The vertical axis in seismic images is almost never at the same scale as the horizontal axis. Indeed, more often than not, the vertical axis represents two-way-time rather than depth (time taken for sound waves to bounce from the seismic vessel guns to the sub-surface reflector and back to the recording device). Note Shine's image is in the Time Domain, whereas OG's is depth converted.

For estimating recoverable resource, the simplest way to describe the calculation is to say it is a multiplication of Gross Rock Volume (GRV) x Net/Gross (i.e. Reservoir %) x Reservoir Porosity (%) x Hydrocarbon Saturation (%) x Oil Formation Factor (oil Shrinkage) (or Gas expansion factor) x Recovery Factor (%) (you can't squeeze every drop out of the field; % value will depend on development plan, permeability, field structure etc... A general guess for RF in an undrilled oil prospect might be around 30%. All these inputs will have wide ranges, particularly in areas of immature exploration, then become fine-tuned once more local-data becomes available.

It gets more complicated than that, and there are other ways, but the above is hopefully an easy to understand explanation for those not involved in the geoscience side of things.