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XI-35
ECONOMICS AJ.'IID DRll..LING FOR PENNSYLVANIAe~ GAS
Although significant Pennsylvanian probable resources are almost certainly present
under the WIPP land withdrawal area, their recovery is critically dependent on several
economic factors. The most important and variable of these include, but are not limited
to, drilling and completion costs, wellbore deviation costs, and product price. Since
controls on prices of oil and gas are independent of geological and engineering parameters,
they will not be included in this discussion (see chapter by Anselmo, this report, for
a discussion of oil and gas prices).
Most wells which have been drilled in the vicinity of WIPP below the Pertnian
section, which were not specifically se.~. up as Devonian or deeper tests, have penetrated
well into the Morrow clastic interval, -most often reaching a total depth approximately
100 to 150 ft into the Barnett Shale (Figs. 50, 56). The Morrow is most often the target
of deeper PennsylVanian tests in this area, even when the primary objective may be
uphole in the Strawn or Atoka Groups. This is due to the relatively minor incremental
cost of the additional drilling as opposed to the significantly increased odds of fmding
economical reserves from the numerous Morrow pay zones which might be penetrated.
Currently, the cost for a typical vertical Morrow well in this area ranges from roughly
$900,000 dry hole cost and $1,225,000 for a completed well of 13,700 ft, to well in
excess of $1,500,000 dry hole cost and $2,000,000 completed cost for a well exceeding
15,000 ft in depth (Table 9b). If there is specific need to deviate a wellbore of this
depth, well costs increase dramatically. It is estimated that for an 1100 ft deviation at this
depth range, completed well costs would increase by approximately 45 to 50+%, which
speaks nothing of the added risk involved in drilling, maintaining, and producing a
deviated wellbore. It is obvious that vertical Pennsylvanian wells are quite expensive in
this area due to their extreme depth and strict drilling parameters. With the additional
cost which any deviation would add, the economic justification for drilling based on
expected reserves would be significantly decreased.
PRE-PENNSYLVANIAN SECTION
A significant amount of sedimentary rock, approximately 5700 ft, is present below
the Permian section in the vicinity of the WIPP site. These strata range from Pennsylvanian
to Cambrian in age (Fig. 8), and are at depths ranging from approximately 12,000 ft
to over 18,000 it within the WIPP land withdrawal area.
To date, numerous oil and gas reservoirs have been discovered and developed
within the Pennsylvanian section in this area. The most significant of these are found in
the Strawn, Atoka, and Morrow Groups. Deeper zones of interest, found primarily in the
Siluro-Devonian and Ordovician intervals, have been tested in several wells around the
WIPP site, with no success to date (Fig. 60). These deeper reservoirs are generally
composed primarily of porous carbonate shelf facies; the most common hydrocarbon traps
are closed structures exhibiting significant amounts of relief (Speer, 1993a). It is probable
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