Page 240 - Geology of Carbonate Reservoirs

DEPOSITIONAL RESERVOIRS 221

US Hwy 287 to
Quanah, Texas

SHELL SHELL MELEAR 1
CONLEY 5
SHELL
-6300
CONLEY 7
-6400
-6500
SHELL & PAN AMERICAN
CASCADE 1
-6600

0 1000 2000 3000
Feet
0 500 1000
Meters N
Contour Interval 25 Feet
Chappel Production
No Chappel Production
Figure 8.7 Present - structure map on the top of the Chappel (Mississippian) Formation res-
ervoir horizon at Conley Field. Note the position of the present structural highs indicated by
the negative numbers along contour lines and compare with the position of an underlying
fault block (Figure 8.8 ) by noting the names and locations of wells.

reef (mudstone or cementstone buildup). After examining borehole cores from
several fi eld wells, it became clear that the buildup is composed of bioclastic grain-
stones instead of a reef or a mudstone – cementstone buildup of the type commonly
found on platforms of Mississippian age.

Depositional Succession After learning that the Chappel buildup at Conley Field

is a skeletal grainstone accumulation — not a reef — our next step was to identify
which of the seven depositional successions is present. Fragmented and moderately
well - sorted skeletal grains along with poorly preserved, low - angle inclined bedding
suggested that these bioclastic grain - supported rocks represent a reworked death
assemblage composed mainly of crinoids and fenestrate bryozoans. Broken and
abraded skeletal remains indicate that the skeletons were vigorously moved by wave
and current activity typical of a high - energy shoreline or slope - break environment.
Some fragmentation may have been the result of predation, but evidence of chewing
or grinding was not readily visible in thin sections, the degree of grain sorting is
inconsistent with haphazard predation, and the inclined bedding suggests that the