Dynamics of Surface Hydrocarbon Gas Patterns During Oil Production
Gary K. Rice, John Q. Belt Jr.
Improved soil gas sampling methods, developed during the last ten years, have
significantly increased measurement reproducibility. Case studies show results
can be duplicated after years between surveys, even in difficult sampling areas.
This ability to make precise measurements has 1) increased our understanding of
vertical gas migration
processes, 2) improved reliability in current
applications, and 3) created new applications for near-surface geochemistry.
It is now possible to measure temporal variations in vertical migration
of
hydrocarbon gases. Repeated measurements over producing oil fields show that
background concentrations remain reasonably constant. High concentrations may
vary in magnitude, but remain near the original locations. Intermediate
concentrations are more difficult to reproduce. A five-year monitoring study in
one oil field shows variations in annual measurements throughout that period.
Reliable measurements make possible more precise determination of vertical
migration
rates. Cases show that vertical
migration
may occur at rates on the
order of several meters per day. Relatively rapid vertical
migration
suggests
the use of soil gas geochemistry for finding unproduced compartments in
partially depleted fields. Actually monitoring reservoir changes during
petroleum production is possible where gas
migration
to the surface is
sufficiently rapid. These potential new applications are illustrated by
examples.
AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995