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Line 83:
Line 83: − [[file:subsurface-maps_fig5.png|thumb|left|{{figure number|5}}Porosity-weighted average water saturation map for Layer 2 of a Middle Eastern carbonate reservoir.]]+ − ===Porosity===+
→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 [[Fluid contacts|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, [https://www.onepetro.org/book/peh/spe-1987-36-peh 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 [[Fluid contacts|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, [https://www.onepetro.org/book/peh/spe-1987-36-peh 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>
===Porosity===
[[file:subsurface-maps_fig5.png|thumb|300px|{{figure number|5}}Porosity-weighted average water saturation map for Layer 2 of a Middle Eastern carbonate reservoir.]]
The [[porosity]] (ϕ) in a reservoir zone can be determined from log and/or core data. The data in an individual well within the net pay interval can be averaged arithmetically and posted on a map for contouring. The averages should be weighted by thickness.
The [[porosity]] (ϕ) in a reservoir zone can be determined from log and/or core data. The data in an individual well within the net pay interval can be averaged arithmetically and posted on a map for contouring. The averages should be weighted by thickness.