Detecting bed boundary locations based on measurements from multiple tool depths in a wellbore

A non-transitory computer-readable medium encoded with instructions that, when executed by data processing apparatus, perform operations comprising:

• determining boundary locations for a subsurface layer in a subterranean region based on:
• a first measurement associated with a first tool depth in a wellbore defined in the subterranean region, the first measurement generated based on operating a transmitter and a receiver of a resistivity logging tool at the first tool depth;
• and
• a gradient associated with the first tool depth, the gradient being calculated from the first measurement and a second measurement, the second measurement generated based on operating the transmitter and the receiver of the resistivity logging tool at a second, different tool depth in the wellbore.

A resistivity logging system comprising:

• a computing system operable to:
• receive information generated by a resistivity logging tool disposed in a wellbore defined in a subterranean region;
• and
• determine boundary locations for a subsurface layer in the subterranean region based on:
• a first measurement generated based on operating a transmitter and a receiver of the resistivity logging tool at a first tool depth in the wellbore;
• and
• a gradient calculated from the first measurement and a second measurement, the second measurement generated based on operating the transmitter and the receiver of the resistivity logging tool at a second, different tool depth in the wellbore.