Subsurface Laboratory Methods 317 



lation factor to calculate the maximum recoverable oil from porous lime- 

 stone. 



Gas Reserves 



The dry-gas reserve at reservoir and surface conditions may be cal- 

 culated from core analysis, reservoir temperature, and pressure data. 



Vr = Po{l- 5,„,) X 7,758 X 0.005615 

 Vr = Gas reserve at reservoir conditions, Mcf. per acre-foot. 

 Po — Porosity, expressed as a decimal. 



..-Vr^ (P.+14.7) ^ 520 



Vb— tt ^ TT^ ^ 



Z 14.7 (460+r,) 



V s = Gas reserve at surface conditions, Mcf. per acre-foot at 14.7 



p.s.i. and 60° F. 

 V r — Gas reserve at reservoir conditions. 

 Pr — Reservoir temperature, degrees F. 

 Tr = Reservoir pressure, p.s.i. 

 Z = Compressibility factor, expressed as a decimal. 



Recoverable Gas 



The recoverable gas may be calculated to any required residual pres- 

 sure from the surface gas reserve. 



RG-y y,^lLZlA±Ml 



R.G. = Maximum recoverable gas to required residual pressure, 

 Mcf. per acre-foot. 

 Vs = Gas reserve at surface conditions, Mcf. per acre-foot. 

 P,- = Final residual reservoir pressure, p.s.i. 

 Pf = Final residual reservoir pressure, p.s.i. 



Although this equation is mathematically correct, the calculated re- 

 coverable gas estimate is seldom attained. Conservative estimates of the 

 recoverable gas may be determined by multiplying the value obtained from 

 this equation by 0.60. 



It is apparent from the discussion of hydrocarbon reserves and re- 

 coveries that the calculation of these volumes is not merely the substitution 

 of figures in an equation. 



Graphic Presentation of Core Data 



The core-log (figs. 122, 126, and 130) is a means of presenting the 

 data for visual comparisons. The gas and water-permeability curves, to- 

 gether with the porosity curve, are of value in the selection of completion 

 intervals and may be used to determine the optimum footage available for 

 gas or water injection in pressure-maintenance or secondary-recovery pro- 



