Well log values of porous chalk and dense zones.

Chalk type	Gamma-ray (API)	Density (g/cm3)	Calculated porosity 	Comments	
Porous chalk	< 15	< 2	> 25%	Commonly clay-poor chalk belonging to the LC, BHC, HC, DC, PFC and PGC facies (Table 1)	
Flint & silica cemented	< 15	> 2	< 20–25%	High density derived from silica precipitation in pores	
Hardground	> 15	> 2	< 20–25%	High density is due to calcite cementation and high gamma-ray is detected in glauconite and phosphate enriched zones, probably due to elevated concentration of U, Th and K in these minerals	
Clay-rich pelagic	> 15	1.95–2.5	< 20–25%	High gamma-ray and variable density values depend on the relative amount of carbonate vs. clay fraction	
Well log values of porous chalk and dense zones.