Modeling Crossing Conjugate Faults in Structural Frameworks

Karen S. Hoffman, John W. Neave, and Erik H. Nilsen
Roxar, Inc., Houston, TX

Crossing conjugate faults can often be difficult to incorporate into an earth model due to complex fault interactions and the limitations of fault modeling methods to handle these fault relationships. These limitations are not usually solely the result of the number of faults involved, although that can be a consideration; rather, it is the nature of the truncations that pose a problem. Y or λ faults often require special handling, not only in the fault modeling stage but also when creating the horizon model and the reservoir grid. Some methods of gridding do not allow stair-stepped faults to truncate on or be truncated by pillar faults in the grid, and using both faults as pillar in Y or λ situations results in collapsed or twisted cells. Correctly modeling half-Y or half-λ faults - created by overlapping convergent or divergent conjugate faults - is even more problematic. These faults have the truncation characteristics of Y or λ faults along part of their length, but are not truncated in other sections. Previous methods of fault modeling, based on pillars or on binary trees, do not provide the flexibility necessary for modeling the complex truncations present in these situations. Our method not only provides a simple solution to modeling Y and λ faults, but also to the more complex problem of the half-Y or half- λ, including fault modeling, horizon modeling, and reservoir gridding. The inclusion of these faults in the framework not only results in a more accurate representation of the structure, but also improves the subsequent workflow. Volume calculations, well planning, reservoir gridding, and property modeling all benefit from the improved structural framework.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas