Source: Meunier, J., 1996, Muddy Sandstone, Pan American #A-2 Norfolk, Collums Field, Campbell County, Wyoming: Hydrocarbon Production from Low Contrast, Low Resistivity Reservoirs: Rocky Mountain and MidContinent regions: Log Examples of Subtle Pays, Rocky Mountain Association of Geologists.
The well was cored and perforated for production. Coring encountered two possible pays. An upper zone is a very fine grained, partially quartz-cemented sandstone. Core analysis of this upper zone indicated an average porosity of 12.6%, permeability of 1.18 md, and oil saturation of 12.5%. This quartzitic sandstone was perforated from 7117 to 7180 feet and produced little oil.
A lower zone consists of very fine to fine grained sandstone containing abundant clay surrounding sand grains and also filling some of the pore space. The average core porosity is 24.6%, permeability of 13.4 md, oil saturation of 10.3%, and water saturation of 37.9%. The interval was perforated from 7182 to 7199 feet and initial production was 1400 BOPD. The low resistivity that typifies this reservoir is attributed to diagenetic clay minerals containing a large amount of bound water.
PfEFFER analysis was done including generation of Pickett cross plots with points annotated with depth and gamma ray. The upper zone has less porosity, but low bound water. The shoulder in the curve at the lowest BVW between 7175 to 7178 feet suggest that this interval might be productive. BVW varies from .03 to .04 and Sw lies between 22 and 30%. The lower zone has high porosity and high BVW (0.1 to 0.12) attributed to high clay content. The cluster pattern located the pay having an Sw of 40 to 50%. Furthermore, the pay is probably at irreducible BVW.