Well-Production Data and Gas-Reservoir Heterogeneity -- Reserve Growth Applications

Oil and gas well production parameters, including peakmonthly
production (PMP), peak-consecutive-twelve month
production (PYP), and cumulative production (CP), are tested
as tools to quantify and understand the heterogeneity of reservoirs
in fields where current monthly production is 10 percent
or less of PMP. Variation coefficients, defined as VC=
(F5-F95)/F50, where F5, F95, and F50 are the 5th, 95th, and
50th (median) fractiles of a probability distribution, are calculated
for peak and cumulative production and examined with
respect to internal consistency, type of production parameter,
conventional versus unconventional accumulations, and reservoir
depth.
Well-production data for this study were compiled for
69 oil and gas fields in the Lower Pennsylvanian Morrow
Formation of the Anadarko Basin, Oklahoma. Of these, 47
fields represent production from marine clastic facies. The
Morrow data were supplemented by data from the Upper
Cambrian and Lower Ordovician Arbuckle Group, Middle
Ordovician Simpson Group, Middle Pennsylvanian Atoka
Formation, and Silurian and Lower Devonian Hunton Group
of the Anadarko Basin, one large gas field in Upper Cretaceous
reservoirs of north-central Montana (Bowdoin field),
and three areas of the Upper Devonian and Lower Mississippian
Bakken Formation continuous-type (unconventional)
oil accumulation in the Williston Basin, North Dakota and
Montana.
Production parameters (PMP, PYP, and CP) measure the
net result of complex geologic, engineering, and economic
processes. Our fundamental hypothesis is that well-production
data provide information about subsurface heterogeneity
in older fields that would be impossible to obtain using
geologic techniques with smaller measurement scales such
as petrographic, core, and well-log analysis. Results such as
these indicate that quantitative measures of production rates
and production volumes of wells, expressed as dimensionless
variation coefficients, are potentially valuable tools for
documenting reservoir heterogeneity in older fields for field
redevelopment and risk analysis.