Structure, as in structural geology, can be considered the response (fold, fracture, fault, and/or compact) of rocks to stress. Since structures can extend over a range of scales, from millimeters to kilometers, then it follows that extent of stresses influence has a similar range of scale. In 1987 (Zoback and Mastin) and again in 1990 (Moos and Zoback), the Stress Polygon method for visualizing the relationship of the magnitudes of overburden stress, maximum horizontal stress, and minimum horizontal stress was introduced and used. When used as a map overlay, as printed on clear plastic, the Stress Polygon provides valuable insight into the stress magnitudes and stress direction that were in place when the larger scale structures, depicted on the map, were created. But perhaps more importantly, integrating the Stress Polygon with smaller scale borehole information, such as breakouts and drilling induced tensile cracks, the Stress Polygon becomes an extent of stress influence scaling tool. This presentation will demonstrate the map overlay technique and how integrating the Stress Polygon with borehole information can be used to evaluate the scale of influence of a particular stress state.

Summary / Discussion
The procedure / concepts just presented focuses on the relative orientation, with respect to north, of the stresses at two locations to infer the extent of stress influence. But what about the stress magnitudes? The evaluation of the Sh magnitude at the active fault region and vertical well location can be independently constrained by careful evaluation of Sv and constructing a Stress Polygon for both locations, assessing the coefficient of friction (u) of the preexisting plane or weakness (fault in this case), evaluating the faulting style, studying drilling / completion history, appraising presence or absence of breakouts and /or tensile cracks, and knowing the strength of the rock and the Pore pressure [see Zoback (2008) for clarification]. If Sh magnitude at both locations appears to be about the same and the stress directions are the same, then there is a chance that the same stress conditions extend from the fault region to the well location. The caveat, of course, would be the possible range in the SH magnitude, but even then SH is somewhat restrained by the Stress Polygon for the faulting style present and the strength of the rocks (end-cap constraints).

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