Ch. 33] PRACTICAL APPLICATIONS 621 



at high velocity. Other fluid held in less porous or less permeable 

 rock has difficulty getting into the "stream." For this reason, much 

 oil still remains locked in voids after the flush production is gone. 



Many of the early Permian fields of west Texas are now producing 

 up to 95 percent water on the pump. Eventually the water percentage 

 will increase until it is no longer economically feasible to operate such 

 wells. The oil now being produced from these fields represents fluid 

 that was "by-passed" during the flush stage of production. Would 

 it not be better conservation and operation to produce the flush oil at 

 a slower rate and in so doing reduce the tremendous amount of water 

 handled in the final "sweeping" process? 



Frequently acid is introduced into limestone and dolomite reservoirs 

 to improve the existing porosity and permeability. The benefits of 

 such treatment are attested by performance data before and after 

 acid treatment. It is not unusual to find a well that does not respond 

 normally to treatment. Repeated applications of thousands of gallons 

 of acid seem to produce few, if any, results. In such instances, con- 

 siderable difficulty is experienced in getting the acid into the formation 

 and in recovering the spent or residue acid. 



Selective acidization has to some extent aided in reducing the fre- 

 quency of "problem wells" and has materially improved the perform- 

 ance of normal treatments. Selective treatment is possible only when 

 something is known about the amount, character, and location of the 

 porosity and permeability in the reservoir to be treated. Each well 

 drilled into a carbonate reservoir exhibits different rock characteristics 

 that call for special consideration. A porosity-permeability log is a 

 part of good operation and should become routine practice. 



The geologist and the engineer can contribute much to a better un- 

 derstanding of carbonate rocks if they will recognize the problem and 

 then do something to improve our knowledge of the subject. This 

 can be done by individual effort or through the work of others. Geolo- 

 gists and engineers working with the carbonate group of rocks should 

 be quite frank regarding our lack of fundamental data and should 

 give wide publicity to the problems confronting the industry. Much 

 good work may be accomplished in universities by graduate students 

 working on the manifold problems as thesis material. Commercial re- 

 search organizations are capable of contributing much worth-while 

 data. Many large oil companies have laboratories completely equipped 

 with the latest type of equipment, and those who are in a position to 

 formulate research projects should attempt to supplement our informa- 

 tion by continuing carbonate research effort. 



