724 



Subsurface Geologic Methods 



It is carried out in three steps: 



1. Fracturing the formation. 



2. Breaking the viscosity of the gel. 



3. Placing the well on production. 



Fracturing is accomplished (fig. 387, step I) by hydraulic pressure 

 transmitted with high-viscosity liquid pumped into the zone to be treated. 

 It is necessary that the viscous medium, referred to as gel, be of such 

 viscosity that entry into the formation at a given rate of flow can pro- 

 duce pressure in excess of that attributable to the overburden in order 



Figure 387. Various steps applied in Hydrafrac treatment. 



to cause the splitting of the formation. The fracturing liquids commonly 

 used include crude oil, kerosene, diesel fuel, and mixtures of these. The 

 fluid is made to gel by the addition of Napalm soap to produce the vis- 

 cosity required. 



After the gelled oily medium is pumped into the formation, it is 

 caused, at a later time, to revert to approximately its original viscosity by 

 following it down the well with oil carrying certain chemicals (fig. 387, 

 step II) , which causes the gel to break down. The gel itself, because it con- 



