Following the same field method for permeability determination, aAP, 

 across one logarithmic cycle is determined. The final flowing pressure, P f , is 

 obtained directly from the chart. Figure 12-5 illustrates the procedure used. 



As a specific example: DST: Open 45 minutes. Shut-in 15 minutes. Re- 

 covery: 100 ft. mud with show of oil. 



ISIP = 2780 psi FSIP = 2720 psi FFP = 50 psi. 

 Pio = 2680 psi. Ps - P 10 = 100 psi. 



.183(2780-50) 



D.R. 



= 5. 



(2780 - 2680) 



The above calculation indicates that approximately five times as much 

 fluid would have been recovered had no damage occurred, or if the tool had 

 remained open a sufficient length of time to sample the formation more effective- 

 ly. Had no damage occurred or had the tool been left open longer, the next 

 influx of formation fluid into the testing tool would presumably have been oil. 

 The operator, at this point, may desire to retest the formation to prevent the 

 possibility of passing up a potentially productive zone. By determining the 

 formation damage immediately after the test, the operator's evaluation of the 

 productivity of the tested interval may be considerably different from that based 

 on recovery alone and may warrant retesting the zone, a change in the drilling 

 schedule, or a change in completion interval. 



L±J 



rr 



z> 

 co 



CO 

 LlI 



rr 

 o_ 



Figure 37-5. Technique for field interpretation of damage ratio. 



750 



