CHARACTERISTICS OF RESERVOIR GAS 101 



Reservoir gas. — The characteristics of reservoir gas or the gas of porous 

 rocks may be pretty fairly made out by reversing the several statements 

 made for shale gas. 



1. The largest known gas wells — those, for example, whose volumes run up to teus of 



million of cubic feet a day — are all found in sandstones, conglomtraies, and 

 porous dolomites. 



2. In a gas field fed by a porous rock the wells attain the same pressure, approxi- 



mately, irres^DCctive of their widely diflering volumes. The normal pressure 

 can generally be obtained from one well as safely as from another. 



3. In reservoir wells the gas is found at definite horizons. The driller soon learns 



the depth to which a well must be carried. If he does not find his reward 

 at a certain point in the descent, he knows that he is to go unrewarded 

 altogether. 



4. In reservoir wells oil accompanies tlie gas in multitudes of instances. These 



porous rocks are the great repositories of petroleum the world over. With 

 the petroleum, water is invariably associated. The principle that the philos- 

 ophers of the sixteenth century asserted so positively, that "nature abhors 

 a vacuum," applies with special force to porous rocks. They are in the large 

 way filled with water, usually with salt water; but the other substances 

 above named, gas and oil, occupy certain limited portions of these porous 

 beds. 



5. The gas of these porous rocks often, I may say generally, comes to a sudden end. 



Oil comes in and fills the pipes, or salt water shuts off the gas like a light 

 blown out by a gust of wind. Only by constant care and attention in re- 

 moving these substances from the pipes can the life of the well be main- 

 tained, especially in its later stages. 

 (). The structure or arrangevae'nt of ilie strata is found to be the dominant feature in the 

 gas production of porous rocks. Not only is a particular kind of rock de- 

 manded for the accumulation of gas, but the accumulation is strictly limited 

 to certain portions of the stratum 



ANTICLINE AND TERRACE 



Two well known structural features are especially connected with the 

 accumulation of oil and gas, namel}^, the anticline and the terrace. Both 

 of these have passed, in this connection, bej'ond the theoretical stage. 

 Their value in the way of petroliferous accumulation is no longer dis- 

 cussed as a possibility, but has been abundantly demonstrated as amatter 

 of fact. A few geologists and oil producers, having the knowledge by 

 which they can read these structures from the surface, are reaping rich 

 rewards by the application of this knowledge. 



A few years ago, while controversy as to the possible effect of anti- 

 clines was still in progress, some reputable geologists, who happened to 

 be ranged on the wrong side of the question, declared that, instead of gas 

 being confined to anticlines, it was often found in the sjniclines of porous 

 strata, To them it was replied that we occasionally see on the surface 



