"Mudlogging Gas Content Results Compared to
Production Performance"
by Bill Donovan, P.E.
Presented at the Society of Petroleum
Engineers (SPE) Luncheon Program, Denver,
Colorado, on December 17, 2003.
A method has been developed to calculate gas
content using mudlogging data. The results
of this and previous papers demonstrate that
mudlog gas content can predict production
performance. Previous papers have presented
the theoretical and operational aspects of
the techniques, as well as preliminary
results. This paper presents the mudlogging
gas content results compared to production
history for Fort Union coals wells in
Sheridan County, Wyoming.
A
four-township study area of mature producing
wells showed wide variations in cumulative
and projected Estimated Ultimate Recovery (EUR).
Cumulative gas production for wells with 24
months or more of production indicate this
variation. Fifty percent of the gas
production comes from twenty percent of the
wells and eighty five percent of the
cumulative production comes from fifty
percent of the wells. Also the higher
cumulative gas wells produce less water per
MCF of gas produced. The better wells
typically produce less than two barrels of
water or less per MCF of produced gas.
A smaller
data set of wells in the same area with both
mature production and mudlogs was used in
this study. Mudlog gas content ranged from
27 to 296 SCF/TON. Cumulative gas production
in this smaller data set ranged from 7 to
409 MMCF. A good correlation exists between
cumulative gas production and mudlog gas
content. The data shows a good correlation
without adjusting the data for coal
thickness, drainage area and/or mechanical
well and metering difficulties. A back
calculated volumetric gas content is
determined by using the cumulative gas
production or EUR, the spacing unit, the
coal thickness and the coal density to
determine gas content in SCF/TON. This back
calculated volumetric gas content is
compared to the mudlog log gas content. A
very good correlation exists between the
mudlog gas content and the volumetric gas
content based on production and estimated
EUR.
Some
possible explanations for both the wide
variation in cumulative production and
mudlog gas content are discussed.
Operational aspects of gathering good
mudlogging data are also briefly
discussed.