Using The Other End of the Capillary Pressure Curve - Discriminating Permeability Based Rock Types With Well Logs When the Permeability Mechanism is Related to Displacement Pressure and not Porosity

By

 Yousef Al Shobaili¹, Edward A. Clerke¹

(1) Saudi Aramco, Dhahran, Saudi Arabia

 A large Lower Cretaceous age carbonate reservoir in Saudi Arabia contains reservoir rocks with permeabilities that vary from 0.2 to 2000 md. Characterization efforts to model the reservoir proceed from the very important highest permeability rock types that dominate well and inflow behavior to the lower quality storage and dispersed delivery rock types.

Investigations of capillary pressure data suggested three petrophysical rock types (PRT’s), one petrophysical rock type with permeability related to porosity and two PRT’s with permeability unrelated to porosity but strongly related to the systematic decrease of the entry or displacement pressure, Pd, or the increase in the largest pore throats.

Well logs that are sensitive to porosity are well known and recognized. Our reservoir, however, needed to use well log responses related to the Pd (displacement pressure) end of the capillary pressure curve. This rock property is usually assessed with invasion related well log responses. A range of potential well log candidates were investigated, robust discrimination of order of magnitude changes in permeability caused by increases in large pore throat sizes were successfully discriminated by the judicious use of the combination of porosity, SP and sonic well logs.