--> Abstract: Faults: Seals or Migration Pathways? Yes, No, Some Are but Some Aren't, and Some Faults Are but only Sometimes!, by A. Aydin, R. Myers, and A. Younes; #90937 (1998).

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Abstract: Faults: Seals or Migration Pathways? Yes, No, Some Are but Some Aren't, and Some Faults Are but only Sometimes!

AYDIN, ATILLA, RODRICK MYERS, and AMGAD YOUNES, Rock Fracture Project, Stanford University, Stanford, California 94305

The purpose of this presentation is to document hydraulic behaviors of faults focusing on the theme of their variation as a function of the physical processes responsible for faulting, the amount of strain, time, and diagenetic history. A cursory survey indicates the existence of the following categories of fault behaviors:

1) Sealing faults,

2) Transmitting faults,

3) Laterally sealing and vertically transmitting faults,

4) Transmitting and sealing faults of low slip (strain) or high slip, respectively,

5) Sealing and transmitting faults of low slip (strain) or high slip, respectively,

6) Faults sealing or transmitting intermittently.

There are excellent examples for sealing faults in the literature. These include faults with shale smear or shale injection as well as faults with gouge material with small pore throat size sufficient to mind fluid pressures accumulated on one side of the fault. Some other faults in low permeability rocks would help the transmmission of fluids if they are not filled by precipitants and fine grained gouge material.

The interplay between structural architecture of fault zones and the nature of fault rock and dilation and contraction associated with fault slip will dictate more complicated behaviors which can't be characterized by a single adjective only. Among these, are faults that are sealing perpendicular to their extend put transmitting along their length and height. Perhaps the most intriguing hydraulic behaviors of faults are those with sharp changes of character as a function of the magnitude and timing of slip and diagenesis, which are represented in the last three categories. Data are presented to demonstrate that faults involving shale smear are better seals for low slip magnitudes whereas faults in low porosity rocks are better lateral seals for high slip magnitudes. Also there are well documented examples showing migration patterns which are consistent with individual slip events.

The field of fault behaviors is indeed complicated. However, this complicated pattern can be understood and may be used as a predictive tool by understanding the physical processes responsible for faulting in various environments.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah