Fault intersecting

The deposits are localized at fault intersections, are associated with breccia zones, and are within clay mineral and silicification/desilicification host-rock... 

The evaluation of fault-seal potential along individual faults can be time consuming if each fault has to be mapped in enough detail to allow accurate definition of reservoir and fault intersections. It is often more efficient to divide the evaluation process into two phases ... 

A continuous supply of clay material from the source bed to the shear zone can be maintained, given the necessary plastic properties of the material, if a driving horizontal stress difference between distant parts of the source bed and the immediate vicinity of the fault can be maintained. This requires some mechanism of horizontal stress relief to operate at the fault intersection of a source bed. Preferably, the same mechanism should be capable of resolving the space problem implied by the emplacement of massive clay smears. 

Fig. 3. Kuparuk River Field fault distribution Note, large older NW-SW trending faults bounding larger grabens, and the more numerous small, later NNE-SSW faults, (a) Kuparuk River Field structural map at the base of the Kuparuk River A Formation showing areas used in text and tables, (b) Two populations of faults intersecting top of the Kuparuk River Formation.

The form of the subsidence profile suggests diffusion of pore pressure drawdown both north and south from the major inflow point at the tunnel. Most certainly there is also diffusion in the East-West direction within the conductive faults intersected by the tunnel. However, there is little data on the pattern of subsidence in these directions. Nonetheless, it seems reasonable to assume that the penetration of drainage along the major fracture zone that produced the largest inflow was extensive. In the 2-D mcxlels, it was assumed that the fracture is sufficiently conductive that is can be taken as constant potential feature at... 

Figure 11. Checkerboard-patterned fault reactivation caused by two groups of faults intersect within the excavation area at a high angle.

Combined Tensile and Shear Faulting Although tensile faults could cause earthquakes that involve volume increases, they caimot explain non-DC earthquakes whose isotropic components indicate volume decreases. Tensile faults can open suddenly for a variety of reasons, but they would be expected to close gradually, and not to radiate elastic waves. If a tensile fault and a shear fault intersect, however, then stick-slip instability could cause sudden episodes of either opening or closing, with volume increases or decreases. The stresses around the... 

Manual Approach for Fault Framework Modelling One approach, a manual technique, is a possibility [64] where the intersections and the fault surfaces are built together, interactively in a 3D visuahsation environment, with visual cues provided by seismic data, interpolated horizons or both. In such an approach lines are digitized onto the observed intersections. Further lines are digitized that manually construct a ruled surface. These smfaces can be interpolated using bilinear patches or sphnes. Thus in this approach the fault-fault intersections are input to the modelhng, provided by the user. A schematic is provided in Figure 9. 

Automatic Approach for Fault Framework Modelling The second approach is to interpolate the fault data for each fault separately and then to compute the fault-fault intersections. This may require some manual assistance to the algorithms to help extend surfaces so that the surfaces do intersect if there is insufficient data. In principle, surface-surface intersections are easy to compute. In practice, however, the intersections may have a very complicated topology largely arising from artefacts of the interpolation. The intersection calculations can be very delicate. At best a great deal of computer time is needed, and in the end a lot of user interaction may be required to clean up the results. Ironically it appears that in practice such an automatic approach is only suited to models with a small number of faults. The most practical... 

Another topological complication occurs when two or more faults intersect. An example of the geological nature of the problem is indicated in Figure 8. 

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