1132 



EXPLORATION GEOPHYSICS 



obtained by using the relation : 



^_ (Pch+ Pg)2 



(Pch+ Pg)) 



hi — h2 



(7) 



where hi and Hz are the heights of the fluid corresponding to the total gas 

 pressures (pcn + pg)2 and (pch + pg)!- 



It is of interest to point out that Equation 7 tacitly assumes that the 

 total gas pressure versus fluid-level curve is a straight line, that is, the 

 fluid density is constant throughout the well.t (This assumption is usually 

 valid under equilibrium conditions, except near the top of the well.) 



The value of pch may be read directly on a pressure gauge connected to 

 the casing head of the well. The value of pg may be determined by use of 

 charts or by the formula : 



Shf 

 ^°^- ^' ^ 122.82(^ + 460) "^ ^°^^° ^^'^ (^) 



where 6" is the specific gravity of the gas in the well, h is the length of gas 



fOO ISO zoo ZSO 300 



PRESSURE - POUnOS/SQ. IM. 



Fig. 703. — A, determining formation pressure (mean producing pressure) 

 from fluid-level data obtained at a constant rate of production; B, determining 

 formation pressure from measurements wherein the weight of the gas column 

 need be evaluated only once. 



t C. P. Walker, "Method of Determining Fluid Density, Fluid Pressure and Capacity of 

 Oil Wells," U. S. Patent 2,161,733, issued June 6, 1939. 



