--> --> 4-D Fault Seal Analysis by Fault Displacement Backstripping
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AAPG Annual Convention and Exhibition

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4-D Previous HitFaultNext Hit Seal Analysis by Previous HitFaultNext Hit Displacement Backstripping

Abstract

The methodology for 3D Previous HitfaultNext Hit seal analysis in siliciclastic sequences is now well established. Using a structurally robust framework model, Previous HitfaultNext Hit-rock phyllosilicate content can be estimated from a combination of Previous HitfaultNext Hit displacement and stratigraphic architecture, and can then be used in combination with faulting/burial history to predict present-day seal parameters such as threshold capillary pressure and permeability. Sensitivities can be investigated, for example varying the Previous HitfaultNext Hit displacement to model uncertainty in seismic mapping or sub-resolution structure (e.g. normal drag). Extending this methodology to previous geological time steps requires careful restoration of the displacement pattern on the Previous HitfaultNext Hit, a technique usually referred to as Previous HitfaultNext Hit displacement backstripping. Different approaches are required depending upon the Previous HitfaultNext Hit style. ‘Growth faults’, i.e. those where sediment thickening across the Previous HitfaultNext Hit at the free surface dominates the Previous HitfaultNext Hit displacement gradient, are backstripped by removing horizon offset down-dip on the Previous HitfaultNext Hit surface. By contrast, for post-depositional faults it may be more appropriate to remove uniform increments of displacement to restore the horizon offsets to previous time-steps in the Previous HitfaultNext Hit propagation history. For faults that have been inverted, it is possible to restore them to their pre-inversion displacement pattern for input to Previous HitfaultNext Hit seal analysis. Applying Previous HitfaultNext Hit displacement backstripping to a number of examples, we make the general observation that on any given Previous HitfaultNext Hit, Previous HitfaultNext Hit seal properties were likely to have been more heterogeneous in the geological past, with greater distinction between sealing and non-sealing parts of the Previous HitfaultNext Hit surface. Considerable complexity is added to this process when faults are linked together at branch lines. Firstly, Previous HitfaultNext Hit displacements on each of the linked faults are likely to have been locally subparallel to the branch line rather than being dip-slip. Secondly, the relative timing of activity on the different Previous HitfaultNext Hit surfaces can lead to various ways of partitioning the Previous HitfaultNext Hit displacements through time. In turn this leads to significant differences in the restored offsets. Failure to consider them correctly (geologically and analytically) yields incorrect predictions of reservoir connectivity and Previous HitfaultTop seal at earlier geological times.