100 E. ORTOX — GEOLOGICAL STRUCTURE OF lOLA GAS FIELD 



Pennsylvania, Ohio, WrA \'iri;inia. Kcntncky, Indiana, Illinois, aiul 

 Kansas. 



AnuNDAN(;K AND (;i'X)LO(;i(: Rklations ok Gas Rock 



As to its productive horizons, there is liardly a stratum in the Paleo- 

 zoic column of the countr}^ that is not somewhere, in some of its phases 

 or conditions, a gas rock. 



Discussion of Occurrence in General 



GAS-BEAjRI^'G ROCKS 



M'hile it occurs in shales, sandstones, conglomerates, limestones, and 

 dolomites, it still remains true that it has its preferences and that its 

 great accumulations are to be found onl}' in certain kinds of strata. 



MODES OF OCCURRENCE 



The classes. — Two distinct modes of its occurrence are to hd recognized : 

 That which prevails in shales and in certain limestones, and that which 

 is found in sandstones, conglomerates, and in a certain class of dolomitic 

 limestones. The rocks of the first group are generally counted impervi- 

 ous, while the porosity of the second group is universally recognized. 



The gas found in the first group may be provisionalh" termed shale 

 gas; that of the second group may be provisionall}' styled reservoir </as. 

 These terms are obviousl}^ open to criticism and objection, but no other 

 simple terms have been suggested that will avoid the apparent contra- 

 dictions or erroneous assumptions of those here proposed. 



Shale gas. — Gas wells in the two classes of strata named above are 

 sharply distinguished from each other. 



1. Shale gas wells are generally of comparalirely small volume. 



2. They lack tunformHy of rock pressiire. Wells drilled in close proximity and to 



the same depth may show very different figures on the pressure gauge. 



3. Tliere is no definile horizon from irJdcJi tlielr gas sxippUj is derived. The stratum 



that yields it may be several hundred feet thick, and gas is likely to be 

 found at any point in the descent. Shale gas wells, though in the same field, 

 may be expected to show a considerable range in depth. 



4. Shale gas wells often occur independently of oil prodnvtioit. Gas may be abundant, 



while jjetroleum is altogether wanting. No large oil fields are known in 

 connection with shale gas. 



5. Shale gas has good staying properties. Weak flows are maintained for long 



periods. Most of the gas springs that have been flowing fiom immemorial 

 time are to be referred to this division. 

 0. Shale gas is not dependent on the structural arrangement of the rocks which contain 

 it. Not being associated with oil or water, it cannot be displaced or crowded 

 out l)y them. 



