726 Subsurface Geologic Methods 



be used and the rate of input necessary to secure high pressures. 



4. Prior workovers. The effects of all prior workovers should be 

 carefully considered, especially jobs that may have resulted in 

 some fracturing of the formation, as, for example, shooting. If 

 these fractures have occurred opposite gas or water zones, then it 

 may be necessary to seal or pack them off; for extending them 

 would simply produce more gas or water where oil was desired. 

 Furthermore, prior workovers such as acidizing or shooting may 

 have altered the nature of the bore in open hole in the well and 

 made it impossible to use segregation packers for the isolation of 

 sections within the zone which is to be treated. 



5. Isolation of formation. The ability to isolate the zone to be 

 treated, whether it be behind casing and contacted by means of 

 perforations, or in open hole, is a most important factor to be 

 considered. Obviously packing off in open hole is more difficult 

 than in casing, especially when enlarged sections of open hole 

 occur in the zone to be treated. In open hole it is desirable to 

 have a caliper log of the section to be treated before attempting 

 to determine whether or not packers, if necessary, can be used. 

 In wells produced through perforations, the original cementing job 

 behind the casing should be studied to determine if it is satis- 

 factory to hold pressures at the points desired and not allow the 

 fluids to migrate into other zones along and behind the casing. 



6. Condition of well equipment. It is necessary to check the condi- 

 tion of casing and tubing in place in the well since high pressures 

 will be encountered. Pressures to be applied will seldom exceed 

 one pound per foot of depth as the total sub-surface pressure at 

 the face of the formation. In a few cases the theoretical max- 

 imum of one pound per foot of depth has been exceeded; how- 

 ever, these are rare and are usually attributable to zones of local 

 high rigidity. 



7. Production of a well to be treated. A thorough study of the pro- 

 duction history of the well to be treated is highly desirable since 

 much information from such study can be had for comparison of 

 results after the treatment. Such items as size of the pump in- 

 stalled in the well, length of the stroke, condition of all the 

 equipment and their effects on the production of the well will in- 

 fluence the comparison of the old and new results of a Hydrafrac 

 treatment. 



Hydrafrac is no cure-all and will not produce oil where there is no 

 producible oil present, yet it has resulted in vast improvement in a large 

 number of wells where proper planning was undertaken and the well con- 

 ditions were evaluated as being good for the application of the procedure. 

 It is believed that where Hydrafrac improves production of any given 



