Five Reasons for Carbonate Oil Production at High Archie Calculated SW
Water free oil production from carbonates at high Archie calculated SW may occur when: (1) The calculated SW is not correct. (2) The calculated SW is correct but the water is immobile. (3) A combination of the previous two. High SW is generally considered above 50%. Five reason for water free oil production at high Archie SW are: (1) Layer formation – Stacked layers of small pore size rock (micritic Wackestone) with coarse pore system rock (Grainstone) below the resolution of the resistivity tool. (2) Dual porosity system – Large pores surrounded by micritized grains. The large pores flow oil while the capillary bound water in the micrite grains is immobile. (3) Fractures – Fine grained matrix with capillary bound water combined with fractures flowing oil and a lowering of Archie’s cementation exponent. (4) RT lowered due to deep conductive mud filtrate invasion. (5) Conductive minerals such as pyrite. Whether a porous rock at a given saturation produces water free oil depends on the assemblage of pore and pore throat sizes and the rock wettability.
AAPG Datapages/Search and Discovery Article #90356 ©2019 AAPG Middle East Region Geoscience Technology Workshop, Low Resistivity Pay, Muscat, Oman, October 7-9, 2019