Source: Meunier, J., 1996, Red Fork Sandstone, Benson #35-5 Ferguson, Pawnee County, Oklahoma, Pawnee Lake Field: Hydrocarbon Production from Low Contrast, Low Resistivity Reservoirs: Rocky Mountain and MidContinent regions: Log Examples of Subtle Pays, Rocky Mountain Association of Geologists.
This sandstone reservoir averages 0.8 ohm-m over an 84-foot pay section. The well has produced 103,000 barrels of oil. The initial production was 93 BOPD and 4300 BW. The serrated gamma ray curve on the well log and the moderate gamma ray values hint at a sandstone containing laminated shale/clay layers. The sandstone is described as a very fine to fine grained, well sorted, friable sandstone with interstitial clay. Little or no cementation is noted. More than 15 wells were drilled in the field before the sandstone reservoir was discovered.
PfEFFER analysis consisted of Pickett cross plots with points
annotated with depth and gamma ray. The cross plot reveals a
cluster of points where BVW ranges between 0.015 to 020, Sw of
65 to 80%, and porosity of 24%. These values are indicative of
a fine grained reservoir as verified by samples. The lower portion
of the sandstone retains elevated porosity and resistivity with
depth while BVW is remains low. This is not indicative of a transition
zone. Rather, the trend suggests larger pores and lesser amounts
of clay at greater depths. The lowest points for a cluster around
a BVW of 0.09 and 15% porosity before abruptly falling to the
water line. The falling trend is associated with increased gamma
ray, probably reflecting a transition from sandstone to shale.
The patterns suggest that the porosity cut off for this sandstone
is around 15%.