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discovery wells . Developmentdrilling has expanded the areas of formal pool
designation and has shown that the four pools are part of the same hydrocarbon trap.
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XI-18
The main.pay..zone in the Los Medanos complex is the D zone.of the lowe­
Brushy Canyon Formation (Fig. 23). The isopach of gross. thick;·cess.of this zone IFig.
28) indicates it is laterally continuous across the study area. ThicKness of the D zone
varies from less than 20 ft to more than 140 ft. Thicker areas define linear trends that
are north-trending, northeast-trending, or northw~st-trending.The D zone consists
primarily of sandstone with lesser amounts of : :.de and only minor amounts of
limestone. Thicker areas are not incised into underlying sediments and do not arpear
to represent channels. Instead, thickness variations are due to paleobathymetric relief
on top of the D zone. Tht: thick areas were. deposited as lobes on the lower part of a
submarine fan; and the intervening thm' areas are interlobe deposits. Lithofacies grade
from dominantly sandstone in the lobes to dominantly shale in t~/ intedobe areas. A
sandstone isolith map of the D zone in the Livingston Ridge an.. ....os Medanos areas
(Fig. 30) shows that trends of net sandstone thickness coincide with trends in gross
thickness of the D zone (Fig. 28).
The crap that for:::s the Los Medanos complex is stratigraphic. Economic
production trom the D zone has been obtained where gross thickness of the D ze" is
more than 90 ft (Fig. 28). In most places, this corresponds to a net sandstone
thickness of more than 70ft (Fig. 30). Thinner areas do not appear to contain sufficient
reservoir-quality sandstone to yield economic levels of production. The trap at
Los Medanos extends northward into the additional study area and uncc' the WIPP
land withdrawal area. Wells in the western part of the Livingston Ridge - Lost T:u1k
pool also produce from the D zone. Several wells in sec. 26 T22S R32E in the
Livingston Ridge pool obtain all of their production from the D zone. Further north in
sees. 2 and 11 of the same township a.~. :l TIIS R3IE wells produce from the D
zone, but most producuon appears to (,';1tained from the the Livingston Ridge main
cay of the upper Brushy Canyon; in the:>e wells, there is insufficient thickness of
'. ~servoir·quality sandstone within the D zone to sustain eeonomic production levels
and the D zone in these wells is a secondary reservoir. The isopach and structure
maps indicate that the D zone will be the probable primary producer in 10740-acre
proration units within the WIPP land·,;thdralllal area and 121 4O-acre proration units
within the additional study area (Fig.
Although Sana Dunes West and Ingle Wells sit astride an east-plunging
structural nose, structure does not appear to exhibit major control on entrapment of
oil and gas. Producing trends continue into off-structure areas: the northern part
Los Medanos, the scl.lthern part of Livingston Ridge, and Livingston Ridge South are
str,;,,",",rally low relative to Sand Dune;: West.
Three casing strings are used during drilling and completion operations in most
wells drilled to de\'~iop the lower Brushy D zone in the Los Medanos complex (FIg.