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→Mapping to calculate reserves
“Net” pay (see [[Effective pay determination]]) implies that some formation thickness has been excluded from consideration by either (1) occurring below an oil-water contact (or above a gas-water contact), or (2) having porosity and/or [[permeability]] values below a “cutoff” limit for productivity. Not all net pay is necessarily productive at a given well spacing. Discontinuous productive horizons between wells might be described, for example, by the concept of net pay to net connected pay ratio<ref name=pt06r103>Poston, S. W., 1987, Development plan for oil and gas reservoirs, in Bradley, H. B., ed., Petroleum Engineering Handbook: Richardson, TX, Society of Petroleum Engineers, p. 36-1–36-11.</ref>.
“Net” pay (see [[Effective pay determination]]) implies that some formation thickness has been excluded from consideration by either (1) occurring below an oil-water contact (or above a gas-water contact), or (2) having porosity and/or [[permeability]] values below a “cutoff” limit for productivity. Not all net pay is necessarily productive at a given well spacing. Discontinuous productive horizons between wells might be described, for example, by the concept of net pay to net connected pay ratio<ref name=pt06r103>Poston, S. W., 1987, Development plan for oil and gas reservoirs, in Bradley, H. B., ed., Petroleum Engineering Handbook: Richardson, TX, Society of Petroleum Engineers, p. 36-1–36-11.</ref>.
[[file:subsurface-maps_fig5.png|thumb|{{figure number|5}}Porosity-weighted average water saturation map for Layer 2 of a Middle Eastern carbonate reservoir.]]
===[[Porosity]]===
===[[Porosity]]===
===Water saturation===
===Water saturation===
The water saturation (S<sub>w</sub>) within the net pay interval is typically estimated from well logs. Water saturations can also be derived from [[capillary pressure]] testing of cores to determine the relationship of water saturation versus height above the oil-water contact (see [[Capillary pressure]]). Like porosity, the water saturation data in an individual well within the net pay interval can be averaged arithmetically and posted on a map for contouring (Figure 5). The averages should be weighted by porosity.
The water saturation (S<sub>w</sub>) within the net pay interval is typically estimated from well logs. Water saturations can also be derived from [[capillary pressure]] testing of cores to determine the relationship of water saturation versus height above the oil-water contact (see [[Capillary pressure]]). Like porosity, the water saturation data in an individual well within the net pay interval can be averaged arithmetically and posted on a map for contouring ([[:file:subsurface-maps_fig5.png|Figure 5]]). The averages should be weighted by porosity.
[[file:subsurface-maps_fig5.png|thumb|{{figure number|5}}Porosity-weighted average water saturation map for Layer 2 of a Middle Eastern carbonate reservoir.]]
===Oil saturation===
===Oil saturation===