The Echo Springs (upper Almond) field is an economically successful tight gas reservoir. A study of the upper Almond reservoir petrophysics and performance was undertaken to explain reservoir and production anomalies between the upper Almond “sweetspot” and “non-sweetspot” areas of the field, and to develop a geologic and economic model of the field that could be used to evaluate other areas for tight gas potential. Well performance in the upper Almond is a unique function of depth of burial and reservoir overpressuring, pore size and pore throat radius, and connate water saturation. The sweetspot and non-sweetspot production profiles correspond to two distinct upper Almond rock types. Variations in porosity and permeability between the two rock types appear to be related solely to a unique set of diagenetic conditions. The two rock types can be defined by log analysis, hydrocarbon pore volume calculations, and permeability-thickness data.

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