Miscellaneous Subsurface Methods 731 



mediately after treatment the well produced 48 BOPD and gradually de- 

 creased to 35 BOPD at the end of one month. This level was maintained 

 for two more months, after which the production gradually decreased to 

 where, at the end of one year, it was producing 18 BOPD. Average in- 

 crease during the last eight months was 12 BOPD. 



A survey of one twelve-month period showed 330 Hydrafrac treat- 

 ments were performed on 285 wells in the United States with a production 

 increase obtained in 70 percent of the wells treated. Approximately 40 

 percent of these wells were in Oklahoma and were producing from 28 diff- 

 erent formations. Another 25 percent of this number were located in the 

 north central Texas area. The remainder were in various sections extend- 

 ing from the Rocky Mountain region to the Louisiana Gulf coast. 



The extremely dense sands of Colorado and Wyoming have made 

 treatments effective in that region. Long sections of producing formations 

 in firm open holes have allowed the use of special packers permitting 

 several treatments per well. Certain sands and dolomite formations in 

 Kansas, where acid has not been effective, have responded and resulted in 

 good production increases. Low-pressure formations in the region in- 

 cluding Illinois, Indiana, and Kentucky have caused limitations; however, 

 successful treatments have been accomplished in that area. The long sec- 

 tions of slotted liners in California has made the factor of zone isolation 

 most diflBcult, but successful treatments have been performed there on wells 

 completed with Hydrafrac in mind. 



Generally speaking, the sands of east Texas and the Texas and 

 Louisiana Gulf coast are highly permeable, a fact which limits the need 

 for a treatment of this nature. In the lower coastal region they are even 

 unconsolidated. There are some sections throughout this region in which 

 favorable results have been obtained, but not to the extent found in the 

 mid-continent and northern areas. 



FORMATION TESTING 

 W. A. WALLACE 

 Formation testing, sometimes designated as drill stem testing is 

 designed to produce economically samples in sufficient quantities, of fluids 

 at the surface from subsurface formations, the samples being accompanied 

 by recorded subsurface formation pressures to determine a satisfactory 

 well-completion program. This method of testing presents more direct 

 evidence of formation-fluid content in both quantity and in quality than 

 any method other than actual production of a completed well. The present 

 technique of this type of testing, developed from the original unique 

 ideas, now is accepted as conforming to conventional practices of oil-well 

 drilling. Originally the procedures were simple, but increased demands 

 for more information has resulted in an assembly of highly specialized 

 equipment qualified to produce desired specimens from shallow to ex- 

 treme-depth wells. These tools and techniques have made possible the 



