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Abstract: The Effects of Residual Oil Saturations on the Interpretation of Water Productive Vs. Oil Productive Delaware Sandstones

Markus D. Thomerson, George B. Asquith

Delaware sandstones in west Texas and southeast New Mexico that have excellent hydrocarbon shows and calculated water saturations of 60% or less sometimes produce only water. The problem with these silt- to very fine-grained reservoirs is whether the hydrocarbons in these reservoirs are moveable. Using net pay cutoffs of Vcl<15%, effective porosity >15% and Archie water saturation <60%, Bell Canyon and Brushy Canyon example zones contained 18 ft and 22 ft of net pay, respectively. However, when these two zones were tested, the Bell Canyon zone produced only water and the Brushy Canyon zone produced 125 bbl of oil/day and some water.

A series of cross plots that include (l) shallow resistivity porosity vs. deep resistivity porosity, (2) Archie water saturation vs. ratio water saturation, and (3) Rxo/Rmf vs. Rt/Rw (Dew Plot) were used to differentiate moveable and residual oil. On all three cross plots, the Bell Canyon example exhibited almost no moveable oil. In contrast, the Brushy Canyon example exhibited a higher proportion of moveable oil. Thus, with the use of these cross plots, the oil productive vs. water productive Delaware oil-bearing sandstones were differentiated by determining what proportion of the oil was moveable.

AAPG Search and Discovery Article #90980©1994 AAPG Southwest Section Meeting, Ruidoso, New Mexico, April 24-26, 1994