382 F. H. OLIPHANT 



sure has been proven to be quite near the actual results ob- 

 tained. 



The rock pressure and the output of gas wells are usually- 

 measured when the well is new and they are at their maximum. 

 Even the longest life of a gas well is short, and the rock pressure 

 decreases with every foot of natural gas taken out. It is not 

 usual for wells having the greatest rock pressure to produce the 

 greatest volume of natural gas, as an open pebble sand gives up 

 its stored products more rapidly than a sand of closer texture; 

 therefore the more open the texture of the strata, the shorter 

 but more vigorous will probably be the life of the pool. Many 

 pools that were most vigorous are almost entirely destitute of 

 natural gas to-day. The gas in some of them has been so far 

 removed by gas pumps that when they are opened the air flows 

 into the vacuum in the porous strata once packed with high 

 pressure gas. In many virgin fields, especially in the beds of 

 streams, innumerable small vents and bleeders are often found, 

 from which there is an escape of more or less natural gas in the 

 form of bubbles. Against the hydrostatic pressure the bubbles 

 find vent, and escape into the air. As the pressure decreases, 

 the water usually climbs up toward the more elevated portion 

 of the reservoir. These innumerable vents, during the ages 

 that have passed, have acted as safety valves, and have al- 

 lowed the escape of many milhons of cubic feet of gas into the 

 atmosphere. The contents of the known reservoirs are prob- 

 ably but a small fraction of the gas that has been dissipated 

 in the air. 



The search for and the production of petroleum, moreover, 

 has caused a great loss of natural gas, since frequently the gas 

 is found in the higher portion of the sand containing the petro- 

 leum, and is tapped before the petroleum is reached. In 

 many cases the natural gas has been allowed to flow into the 

 atmosphere and be wasted imtil the pressure was sufficiently 

 exhausted to permit drilling to proceed. 



In the most important fields of Pennsylvania, the original 

 rock pressure varied from 375 to 1,000 pounds to the square 

 inch, the average being 700 pounds. The output of some of 

 the largest wells in the state ranged from 7,500,000 to 25,000,- 



