90 E. ORTON — ROCK PRESSURE OF NATURAL '.As. 



To accept it brings us no advantage whatever beyond the satisfaction that 

 we may feel in having an answer at hand that can be promptly given to a 

 troublesome inquiry. 



in v own part. I have fell certain for more than two years that the 

 lock pressure of gas in the Trenton limestone of Ohio and Indiana is hydro- 

 static in origin, and I have published a number of facts that seem to me to 

 give Bupport to this view. 1 find that some sagacious operators in the new 

 and oil fields are coming to the same ground. They have become 

 thoroughly satisfied by their own experiences that the root of rock pressure 

 i- to be found in the water column that stands connected with the porous 

 rock in which the gas and oil are contained. In the present paper, I desire 

 to present to the < reological Society a few facts and conclusions hearing upon 

 the subject. 



Thk Data fob the Hydrostatic Theory. 



The first question is, What are the fact- as to the rock pressures of the gas 

 rock in question, and what relations do they hear to the depth of wells and 

 other condition- in the Trenton limestone? The answer is not as full and 

 definite as may be expected, certainly not as may be desired. There is but 

 one date in the development of a gas field in which the normal gas pressure 

 can he ascertained, and that is when the first well reaches the reservoir and 

 releases the long-imprisoned and greatly compressed gas. But often this 

 favorable opportunity is lost, and gauges are not applied to wells until the 

 energy of the first flow is somewhat abated. Again, different wells in the 

 -ame field, as Findlay for example, give different results. The wells vary 

 with the depth at which the gas rock is found. This factor is found to be 

 an essential one, as will presently be Bhown, in connection with rock pressure. 

 Moreover, gauges are sometimes inaccurate, and their errors come in to con- 

 fuse the Study of the subject. Furthermore, the exact depth of the wells 

 and the exact altitude of the surface where they are' located cannot be as- 

 certained in all cases. Small errors of this sort must be provided for. and 



there also enters into the discussion a question as to the specific gravity of 



the water which i.- to be made the moving force of gas ami oil. The water 

 found in association with these substances is never fresh. It is always saline, 

 and often highly mineralized. The weight of fresh water to the square inch 

 is 0.43285 pound lor one foot in heighl <I use Professor Lesley's tables). 

 The average weight "i sea water is 0.445 pound to the Bquare inch for one 



foot ; but the mineral waters with which we find the Trenton limestone sat- 

 urated often reach a much higher figure. An examination of several speci- 

 men- -how- that a column one foot high would weigh to the square inch 



0.476 pon ml. I n fact, some of these watu rs are more like bitterns, and their 



column- would equal or 0.5 pound per foot. 



