PRODUCTION PROBLEMS 1133 



column between top of fluid and casing head, / is the deviation factor from 

 Boyle's Law, and t is average temperature in degrees Fahrenheit. 



Hence, an average value of the fluid density may be obtained by keeping 

 the rate of production constant and determining two vakies of h correspond- 

 ing to two vakies of (pcn + Pp)- 



Determination of Formation Pressure 



The original bottom-hole pressure and its rate of decline as the well 

 produces are of considerable importance. These data may be obtained by 

 direct measurement with a subsurface pressure gauge or they may be cal- 

 culated from the known relations between fluid level, casing-head pressure, 

 and rate of production. 



A plot of fluid-level data with h as ordinate and total gas pressure on 

 the fluid as abscissa is a straight line, provided the production rate is held 

 constant and the density does not vary with depth. Hence, the pressure at 

 the reservoir depth, pr, may be approximated by extrapolation. Curve A 

 of Figure 703 shows a typical fluid-level versus gas-pressure curve. The 

 data plotted in this curve are given in Table 28. The density of the fluid 

 may be determined by applying Equation 7 to a small portion of the curve. 



TABLE 28 

 TYPICAL WELL AND FLUID-LEVEL DATA 



Calculations 



Pressure at Pump 258 lbs. per sq. in. 



Mean Producing Pressure 296 lbs. per sq. in. 



Fluid Gradient in Casing 0.241 lbs. per sq. in. per ft. 



* Includes casing-head pressure plus weight of gas column from fluid surface to the 

 casing-head gauge. Weight of gas is calculated by formula 



^°^" ^' = 122.82 + 460) + '°^^" ^'^ 



