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Abstract: Permeability Porosity Relationships (K, Phi, Cut-Off)

Farid Djettou, Hannoun Reda

Several reservoirs of Lower Devonian in Ghadames basin present porosities greater than 10 pu, but during the test they are rather impermeable. It seems that this phenomena extends to Berkine and Rhourd Messaoud areas.

This can seriously affect the estimation of recovery reserves. The best we can do is to study and try to understand reservoir problems.

The method we choose is based on statistical analysis of test results and their comparison with core and log measurements. It concerns mainly cumulative curves of productive non-productive tests (dry test). This involves about 20 wells where are can define:

- Siegenian with:

Fine grained in BBK and ROM
Coarse grained toward BRN.

- Emsian is rather homogeneous in the region.

The sand cut-off porosity is greater than 11 Pu. However the reservoir can't produce itself then we can not take account in reserve estimation.

In conclusion, a sandy reservoir of Lower Devonian in Ghadames basin may be very porous (11-12%) and impermeable while in the other cases reservoirs can produce with porosity of 7 or 8 Pu.

However an HC definition based on cut-off porosity in Ghadames basin should be done before net pay an recovery reserves estimation.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France