An 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 has demonstrated that the behavior of seals is empirically related to the amount of sand and shale incorporated in the fault zone. Faults with sand-rich gouge leak, and 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 hydrocarbons within fault compartments, as well as the vertical distribution of hydrocarbons 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 assessments of reserves result from neglecting routine fault seal analysis during exploration.

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