Second Oil Zone.—The classification, as arbitrarily assumed for this zone, includes the productive formations from the base of the intermediate edgewater sand to the top of the lower inter mediate water sand.
This oil zone is approximately 1000 ft. thick and the most productive portion is in the lower 500 ft. Production is obtained from grey or brown sandy shale, interstratified with more or less lenticular oil sands, and initial production from this zone has amounted to as much as 15,000 bbl. per day from an individual well.
Lower Intermediate Water.—At the base of the second oil zone, and defining its lower limit in the center of the field, is a second or lower intermediate water formation. This water sand lies at a depth of about 3700 ft. below the surface and from 1450 to 1475 ft. below the indicator (first main oil sand). It has only been encountered in the central dome where the deepest wells (stratigraphically) in the field have been drilled, but may exist throughout the entire field.
Third Oil Zone.—This zone includes all productive formations which have been encountered below the lower intermediate water sand to date and any additional productive formations which may be encountered by deeper drilling, the lower limit to be defined by additional and deeper (stratigraphicalry) water formation, if such a formation is encountered.
Only about 300 ft. of this zone has been penetrated to date, but this much of the zone has produced 1500 bbl. of oil per day, with water from the lower intermediate water sand not excluded. The formation consists principally of hard grey sand.
Basal Conglomerate Zone.—This name is given to designate a certain zone variously logged by rotary drillers as hard sand gravel, conglomerate or shale and boulders, and lying immedi ately above the brown shale which acts as a capping for the first oil zone.
Central Dome.—This phrase has been used to describe that portion of the center of the field constituting the apex of the anticline under which the intermediate edgewater formation carries oil instead of water.
The foregoing subdivision of productive formations embraces the underground structure as it appears at present. The drilling of new wells and the deepening of old wells will probably add much information which is not now available, especially as to location of additional intermediate water sands around the edges of the field and the value of still lower oil horizons not yet penetrated.
with Figs. 36, 37 and 38 in determining in general the depths at which the various oil zones and water sands may be encountered at any particular location in the field. To apply the ideal graphic log, the elevation of the desired location should be secured from Fig. 36, and the depth to first main oil sand from Fig. 37. Then, by adding the intervals as shown on the ideal graphic log, the depth to intermediate edgewater sand, second oil zone, lower intermediate water sand and third oil zone may be figured. These figures will be general, and allowance should be made for increased thickness as the dip increases near the edges of the field.
Figure 41. Ideal cross section along the axis of the Montebello anticline from east to west, showing the position of the various zones in the wells already drilled along such line. The section is reconstructed on the basis of the first main oil sand as an indica tor and with the ideal graphic log as a guide.
Figure 42. Ideal cross section transverse to the axis of the anticline.
Figures 43 and 44. Production charts showing graphically the production of the field from date of discovery to the present time.