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CCcJ.. From these projections. estimates were made of the potenuaily productive area for
each of the pools. Potentially productive areasiven in terms of the number of potential
drill sites based on proration units consistent :til established spacing in the vicinity of
the WIPP site.
Quantitative resource assessment also utilized historical productio!i data of
producing wells to estimate ultimate recovery and reserves recoverabl'e bY·Primary
production techniques. Monthly production data of oil. gas, and condensate in digital
format were used to produce time-dependent pr"duction plots (see Figs. 4, 5 as examples).
These digital production data were avaij~,le for months up to and including
December 1993. Then a computer program wnnen with Mathematica was used to fit a
custom production decline curve to each well (Figs. 4, 5). The a- under the curve was
then calculated" by mathematical integlition of the formula used t ~fme the curve; this
area is the ultimate primary recovery of oil, gas, or condensate C. _:mate primary recovery
is the total amount of oil and/or gas that a well could economically produce from the date
of first production to the date of eventual abandonment if only primary production
techniques are utilized). The well's reserves are equal to cumulative production subtracted
from ultimate recovery (Fig. 6). Ultimate recovery of associated gas from oil wells was
estimated by a more complex method described below.
Based on analysis of the data. the decline curve fitted to each well was either
exponential or linear (Figs. 4, 5). The following general equations were used for each
type of curve (SustakosId and Morton-Thompson, 1992):
XI-6
q. = ll; e·o. exponential decline
q. = ll;-n(t) linear decline
where:
ll;=iniual production rate (bblslmonth or MCF/month)
q. = production rate at time t
t =time at which production rate is calculated (months)
D = initial decline rate, expressed as a decimal .
n=1inear decline slope (bbls/month 2 )
An exponential decline curve was used to describe production data from most wells.
For ea. well, u1tiiiiate recovel"V was calculated for five lower limits of production
rate (30, 60, 90, 120, and 150 bblsirrnuth for ail wells and 300, 600, 900, 1200, and
1500 MCF/month for nonassociatee gas wells). At current oil and gas prices, the 150
bbl/month and 1500 MCF/month limits are economically appropriate as the minimum
production rates.
Two calculations were performediiforder to test the fit and appropriateness of the
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