THE IMPORTANCE OF DRAINAGE AREA IN ESTI- 
MATING THE POSSIBILITIES OF PETROLEUM 
PRODUCTION FROM AN ANTICLINAL 
STRUCTURE 
KIRTLEY F. MATHER and MAURICE G. MEHL 
So fully is the general dependence of commercial accumula- 
tions of petroleum on rock structure accepted among the oil 
fraternity that the average report setting forth the possibilities 
of oil and gas production properly centers about the structure 
of the region concerned. Experience has indicated that accumu- 
lations of petroleum usually coincide with certain variations in 
the attitude of the reservoir rocks; mobility of liquid and gaseous 
hydrocarbons in tilted porous beds has been recognized to the 
extent that these structures are looked upon as entrapping 
basins’’ or checks to the upward movement of hydrocarbons 
along the inclined strata. Attention, however, is usually focused 
on the nature of the accumulating structure or trap rather than 
on the nature of .the area from which petroleum or gas could have 
been gathered. In the more common descriptions of a favorable 
structure, concise statements are made concerning its effective- 
ness as a trap as indicated by the amount of closure and the 
size of the area beneath which accumulations of oil or gas should 
occur; too often nothing is stated concerning the possible feeding 
ground which may have served as the source from which the oil 
or gas must come. Account is seldom taken of the fact that a 
large and effective accumulating structure may be so situated 
that it could have drawn an accumulation of petroleum from 
only a very small area; or, as we are here using the term, that 
the “drainage area” may be of such slight extent as to be in- 
sufficient to supply all the oil or gas which could be retained in 
the structural trap. 
A map showing geologic structure by means of contour lines 
should therefore convey two items of valuable information to the 
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