Stratigraphic Tests 



The first stratigraphic test, Amprex No. 1-A, located just west of the town 

 of Arido, surprised even the most optimistic when it drilled through 1810 feet 

 of alluvium into a carbonate section of young Permian sediments and was in 

 marine Silurian elastics at 10,880 feet, its total depth. Paleontologists studied 

 the samples and determined that an almost complete marine Paleozoic section 

 had been encountered. Permeable sands and porous dolomites in the Pennsyl- 

 vanian section and fractured dolomites and cherts of the Devonian were potential 

 reservoir rocks. Dark brown, gray, and black sands, silts, shales, and dark 

 limestones distributed throughout the Paleozoic column were potential source 

 rocks. Faint, although positive, oil staining was noted in cores from several of 

 the formations, and gas shows were recorded by the mud-logging unit while 

 drilling through a clastic section of the Pennsylvanian. Formation fluids from 

 all of the porous zones carried high salinities, indicating that, at least in this 

 basin position, the reservoirs had not been flushed by meteoric waters. Minute 

 quantities of hydrocarbon gases associated with several of the formation waters 

 were indicated by geochemical analyses. These facts were very encouraging. 



Moving approximately 30 miles to the northwest to a location 10 miles 

 east of the eastern scarp of the Sangre de Diablo Mountains, the Amprex No. 

 1-B was drilled as the second stratigraphic test. The Paleozoic section penetrated 

 was lithologically similar to the outcrop section but nearly twice as thick as that 

 in the mountains to the west. The Paleozoic facies encountered in Amprex's 

 No. 1-B were quite different from the basin facies of dark limestones and fine 

 elastics encountered in Amprex's No. 1-A; the sediments of the No. 1-B were 

 mainly light-colored carbonates and coarser elastics suggestive of a shelf or 

 platform environment. Well-developed zones of porosity in dolomites and 

 highly permeable sand sections characterized the Permian, Pennsylvanian, and 

 pre-Pennsylvanian sediments. The subsurface waters recovered from formation 

 tests were not as saline as waters from equivalent formations of the No. 1-A. 

 Formation waters from the shallow Permian section were brackish to fresh, 

 suggesting that meteoric waters had, at least partially, flushed subsurface areas 

 of these rocks at this basin position. This would not necessarily preclude the 

 possibility of encountering closed traps where oil and/or gas had been trapped 

 prior to this flushing action. No shows of oil or gas were noted in the cuttings 

 or cores from the No. 1-B test or by the mud-logging unit. A granitic basement 

 was encountered at 6600 feet. 



Amprex drilled its third stratigraphic test, the No. 1-C, about 35 miles 

 north at a location at the foot of the Plateau de Caballos, where granitic base- 

 ment rocks were encountered at 6809 feet. Its regional structural position was 

 approximately the same as that of Amprex's No. 1-B. The thickness and facies 

 of each of the formations were very similar to those of the No. 1-B and those 



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