1138 



EXPLORATION GEOPHYSICS 



Equation 14 may be related to the theoretical maximum rate of produc- 

 tion as follows. From Equation 2 



Hence 



V^max — C * pf 



Q_ apr , Pf — Po _ 0.K . hr—hp 



(15) 



Evidently a plot on semilogarithmic paper oi pr — p or hr — h versus time 

 should be a straight line, if the assumptions made in deriving Equation 15 

 are valid. 



The practical use of the above analysis may be summarized as foUovv^s. 

 Determinations are made of the bottom-hole pressure or the fluid level 



Shut-in time.hr. 



Fig. 705. — Average bottom-hole pressure rise for 20 

 wells in the Judkins Field, Ector County, Texas. (Mus- 

 ical, A.I.M.E. Petroleum Technology, 1937.) 



as a function of time. (Compare Figure 705.) An approximate value 

 of the equilibrium bottom-hole pressure pr is read off the curve. A plot 

 is then made on semilogarithmic paper oi pr — p versus time. (Figure 706.) 

 If the estimated or approximate value of pr is inaccurate, the plot (curve 

 II, Figure 706) will deviate from a straight line. The value of pr is then 

 adjusted so as to make the data fall on a straight line. Thus, this method 

 of observing the bottom-hole pressure as a function of time before 

 equilibrium is reached yields an accurate determination of the reservoir 

 pressure. 



Maximum Pumping Efficiencies. — Fluid-level measurements sup- 

 ply information that will allow an operator to ascertain whether a well is 

 pumping-off or is gas-locked. Oftentimes, it is impossible to tell by the 

 pounding on the polished rod which condition exists in a well. Pounding 

 due to the well being pumped-off is caused by a low fluid-level or by the 



