--> ABSTRACT: Dynamics of Surface Hydrocarbon Gas Patterns During Oil Production, by Gary K. Rice, John Q. Belt Jr.; #91020 (1995).

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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