Well-developed sands of Cretaceous age have been found to be able to produce dry oil at rates in excess of 5000 b/ d. Log-derived average water saturations in these sands range from 10 to 60% with resistivity indices from 100 to as low as 2.5. Water-producing zones, which frequently contain "residual" oil, have been encountered with resistivity ratios ranging from 1.O to 2.0. A reliable assessment of pay zones on the basis of logs is therefore not possible and production testing is frequently required. Detailed mineralogical and petrophysical analysis of cores indicated the presence of two rock types in thin laminae in the oil-bearing sands with high water saturations. One type, which contains kaolinite in moderate quantities, has permeabilities in the Darcy range. The other type displays massive pore fill by kaolinite with low permeabilities. This results in a dual porosity system with fully water-bearing micropores associated with the kaolinite and largely oil-saturated macropores in the cleaner layers. Dry oil can be produced from the macropores without mobilking the capillary-bound water in the micropores. Since the log response of an oil-filled laminated sand, capable of dry oil production, and a moderately kaolinitic water sand can be very similar, recognition of laminated sections from cores or logs is essential in reliably identifying pay zones.

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