and, since 



0'4) 



v 2 + d 



-> e as 8 -> cc . 



then the error will vanish at infinite shut-in time. 



In terms of percentage, the error in using the average production rate, q a , 

 in Equation 2 instead of Equation 7, which corrects for varying production rate, 

 may be expressed as follows: 



100 X 



[q n ~ qi) I (l/ 2 + 8) In ( 1 + — L_) - 1 j 



X 100 



7a In ( 



1 + 



•) 



(10) 



Figure 37-8 illustrates how much difference the error will make. As long 

 as the difference in initial and final production rate is not extreme, use of the 

 average production rate will be a good approximation for the latter part of the 

 plot. Empirically this fact was borne out in the electric analyzer studies of the 



100 80 50 40 30 20 



10 8 6 5 4 3 



Figure 37-8. Influence of production rate of pressure build-up. 



757 



