Risking Fault
Seal in the Gulf Coast: A Joint Industry
Study
Grant M. Skerlec
Analysis of more than 200 faults in a joint-industry study of the Gulf Coast
provides a database of actual fault
seal behavior in producing fields. This
empirical database demonstrates that
fault
seal behavior is predictable rather
than random and that faults are more important than is commonly thought in
controlling hydrocarbon accumulations.
Quantitative fault
seal analysis demonstrates that seal behavior is
empirically related to the amount of sand and shale incorporated in the
fault
zone. Faults with sand-rich gouge leak. Faults with shale-rich gouge seal. An
empirically defined threshold allows prediction of
fault
seal behavior with a
high degree of confidence. Fewer than 10% of the faults in the Gulf Coast are
exceptions to the rule. Exceptions are a result of other factors including low
permeability and high displacement pressure sands, and thin-bedded sand/shale
sequences.
Examples from these Gulf Coast fields demonstrate the fundamental importance
of faults in controlling hydrocarbon accumulations. Faults and fault
seal
behavior control the presence or absence of hydrocarbons, percent fill,
hydrocarbon column heights, entrapment of oil versus gas, and high-side and
low-side trap risk. Faults control the lateral distribution of hydrocarbon
within
fault
compartments as well as the vertical distribution of hydrocarbon
among stacked sands. Faults control fluid flow during both field development and
hydrocarbon migration. Bypassed residual accumulations and unnecessary
production wells result from neglecting routine
fault
seal analysis during field
development. Dry holes and mistaken reserves assessments result from neglecting
routine
fault
seal analysis du ing exploration.
AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California