272 I. C. WHITE PETROLEUM FIELDS OF NORTHEASTERN MEXICO 



limestone above the oil horizon. This method, devised by General Man- 

 ager TYylie after several years of experience with conditions in the Ebano 

 district, which simulate in a miniature way those surrounding the Dos 

 Bocas well (since a surface Laguna also exists during the rainy season 

 between Ebano Hill and La Pez), will, of course, add materially to the 

 cost of drilling ; but the added cost will be much more than offset in the 

 freedom from danger of losing a large well when it becomes necessary 

 to shut it in for want of storage, as was imminent with Casiano Xo. 7 

 until the good judgment of Mr. Wylie intervened and permitted it to 

 flow under only half its normal (585 pounds) pressure, and thus stopped 

 the numerous streams of oil which had begun to issue from every fissure 

 over a considerable area around the well while it remained closed. 



The history of wells Xos. 1 and 6 La Pez, in the Ebano field, throw 

 interesting side-lights upon the water question in the region of lakes or 

 lagunas. After La Pez Xo. 1 had been flowing steadily for nearly five 

 years, La Pez Xo. 6, only a few hundred feet distant from Xo. 1, came 

 in, January 3, 1909, flowing at the rate of 8,000 barrels daily, -10 per 

 rent of which was water. Almost immediately water began to appear 

 in La Pez Xo. 1. although it was producing from a level 300 feet above 

 the bottom of Xo. 6, the water from the latter evidently having found 

 its way across to Xo. 1 through fractures and fissures extending between 

 the two holes. It was Mr. Wylie's experience with these two wells which 

 suggested to his practical mind the policy of preventing any such recur- 

 rence by closing up with cement all such avenues of communication of 

 one well with another. 



This La Pez Xo. 6 is also a good illustration of the fact that a well 

 may produce a large quantity of salt water and yet continue productive 

 for a long time, since it had put into tankage 1,323,837 barrels of oil up 

 to December 1, 1911, and is still flowing at the rate of 700 to 800 barrels 

 daily, in spite of the large quantity of water which comes with the oil ; 

 while La Pez Xo. 1, although producing 10 to 15 per cent of water, 

 apparently as an overflow from Xo. 6, still flows at the rate of 800 

 barrels daily, after having put into the tanks 3.178,983 barrels of oil up 

 to December 1, 1911. This experience with salt water in the Ebano field 

 has a very important bearing on the factors which enter into the esti- 

 mates of oil production in other fields, since the fact is here very forcibly 

 illustrated that the Dos Bocas instance of a large well "going to water 

 suddenly" can not be regarded as an example of what will happen to all 

 other large wells. 



The Potrero del Llano well, which has already put out several million 

 barrels of oil and would probably flow 40,000 to 50,000 barrels daily if 

 fully opened up. is still producing perfectly dry oil under its original 

 rock pressure, which is 850 pounds to the square inch, according to Doctor 



