756 



Subsurface Geologic Methods 



(6) Spinner Surveys: The spinner survey is based on the measure- 

 ment of variations in the velocity of fluid being displaced into an exposed 

 formation section. Recordings are controlled by a small propeller-like 

 spinner, which is placed in the fluid column. The spinner increases in r.p.m. 

 when permeable zones are reached as a result of fluid entry into the forma- 

 tion. 



(7) Drill-Time Data: Changes in penetration rates frequently reflect 

 intervals oi permeability. Close attention is given to sections wherein pene- 

 tration rates rapidly increase. The introduction of the mechanically oper- 

 ated Geolograph has permitted better definition of porous phases in both 

 carbonate and shale-sandstone sections. 



(8) Formation Testing: Systematic testing of the penetrated section 

 by standard formation-testing procedure is by far the most conclusive 

 method for evaluating reservoir fluid characteristics. In addition to yield- 



1,1 ,1 ,1 



I. .1 . I. .1 



I. I. I. I. i^7~r 



I .1 .1 .1 .1 .1 .1 I 



r r r I n" 



I I TO Bin 



ACIDIZED j ' I 



' l ' i' ^'l 



I . I TO RF I r~ 

 ACIDIZED I I 



IZI 



T^" 



Figure 404. Acidizing through the jet gun permits more effective treatments because 

 the acid can be directed into all important pays by setting gun opposite these 

 zones (left) . Acidizing below packers is necessary to secure maximum results 

 in treatment of certain types of wells which have been deepened to new pay 

 horizons (right). (From Love, Dowell Incorporated.) 



ing relative permeability data, the method also affords a measure of the 

 saturation values of the formation. 



Acidizing Procedure 



Deeper drilling, selection of thin producing intervals, and increased 

 costs have called for improved efiiciency in acidizing procedure. Greater 

 attention is being given the volume of acid to be introduced into the weU 

 and to whether or not the acid should be added in one stage or in several 

 stages. Study is being given to the length of time of acidization and to the 

 reaction and distribution of the acid in various carbonate rocks. Other 

 problems being considered are the plugging effects of the insolubles in low- 

 pressure formations and the point at which the spent acid should be dis- 

 placed from the hole. 



The general technique and operation of well-acidizing follows: The 

 drilling fluid opposite the exposed section should first be displaced with 

 water. The water is then replaced with oil. It is good practice to evaluate 



