viii, a, 5 Pratt and Smith: Petroleum Resources 367 



The foregoing brief statement includes practically all that is 

 known concerning petroleum fields in the vicinity of the Philip- 

 pine Archipelago. 



AREAS TO BE PROSPECTED 



Drilling on Bondoc Peninsula should be directed so as to 

 answer three questions. It should determine (1) whether a 

 sufficient quantity of oil is accumulated in the Bacau stage of 

 the Vigo shale to afford a commercial production, (2) whether 

 any members of the Vigo shale concealed by the overlap of the 

 Canguinsa sandstone may be made to yield petroleum, and (3) 

 whether there is petroleum in the unexposed base of the Vigo 

 shale. 



The same work should serve to determine points (1) and 

 (2), since if wells are drilled through the Canguinsa sandstone 

 to the Bacau stage of the Vigo shale on the limbs of the anticlines 

 at varying distances from the axes, as is recommended later in 

 this discussion, they will necessarily pass through any higher 

 beds in the Vigo shale which may be covered unconformably 

 by the Canguinsa sandstone. 



If the Vigo shale is constant in the thickness which it displays 

 in the Matataha River sections, it would not be feasible to 

 explore both the Bacau stage and the basal portion of the Vigo 

 shale with a single well, since the depth involved — even if the 

 strata were horizontal — would approach 2,000 meters. It is 

 possible that the Vigo shale is not of uniform thickness and 

 that in some parts of the field a deep well might penetrate the 

 entire series. Even so, however, wells from 400 to 600 meters 

 in depth, located so as to pierce different horizons in the shale, 

 would probably be less expensive and more suitable for initial 

 exploration than a smaller number of very deep wells. 



Without more data the anticlines in Bondoc Peninsula must 

 be considered as the most favorable zones for exploration. The 

 oil seeps are near the crests of anticlines generally and possibly 

 in all cases. Experience in other oil fields has proved the theory 

 of the accumulation of petroleum in anticlinal zones 25 to be of 

 wide application. In the South Sumatra field and the Echigo 

 field in Japan,- which have been cited in comparison with the 

 Bondoc field, production is reported to have come largely from 

 the anticlines. In the former field only wells on the immediate 

 crests of anticlines have been productive. 



"For a discussion of this theory consult Bull. U. S. Geol. Surv. (1907), 

 322, 71 et seq. 



