Miscellaneous Subsurface Methods 



759 



Best shooting results are obtained in sandy limestones, dolomitic lime- 

 stones, anhydritic limestones, and cherty limestones. 



Once a well is shot, there is little opportunity of subsequent remedial 

 work being effective because of the fractured condition of the formation. 



In some wells, production is increased after shooting for a short 

 period — then declines rapidly. 



Several facts should be considered in shooting of carbonate sections: 

 (1) It is not good practice to shoot closer than 20 to 30 feet from the cas- 

 ing shoe; (2) Formations exhibiting less than 10 percent porosity are 



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FicuRE 407. Use of jelly seal to permit blocking off a permeable section for acidizing 

 a tighter zone and to direct acid into more productive section. (From Love, 

 Dowell Incorporated.) 



rarely shot; (3) The average shooting intervals vary between 150 to 225 

 feet; (4) Solidified nitroglycerine is considered safer than the liquid form 

 in shooting procedures; (5) Normal loadings range from 21 to 5 quarts of 

 nitroglycerine per foot of section. Frequently 7 to 10 percent gun cotton 

 is added to increase the shooting power by several percent. 



In the North Cowden Field, Texas, "only 24 wells, or approximately 

 11 percent of the field total, would be commercial producers without the 

 use of nitroglycerine."^^ Most of the clean-up work in this field is accom- 

 plished by the reverse-circulation method in which oil is circulated down 

 the casing and upward and out through the tubing to give a high-carrying 

 velocity. In the Turner Valley field of Alberta, Canada, shooting results 



" Giesey, Sam C, and Fulk, Frank F., North Cowden Field, Ector County, Texas: Am. Assoc. 

 Petroleum Geologists Bull., vol. 25, no. 4, pp. 593-629, 1941. 



