Projecting Cores Into the Time Dimension
Cores allow us to measure physical properties (such as porosity and permeability), and to associate such measurements to observed textures and contextual (facies) frameworks. It is widely understood how to project that core information into the spatial domain, via geomodelling that creates 3D distributions of geobodies and their properties. After we have determined the paragenetic sequence (i.e. diagenetic evolution) of the cores, we can project core-derived properties into the dimension of time, as described below. If the current spatial arrangement is also projected into a time sequence (restoring the shape changes, for example), then the approach described here provides the property information that adds value to those geometric restorations. This time-projection of core observations is possible because: (1) rock textures record the geohistory processes (e.g. diagenetic changes and past mechanical responses) that have operated on that rock; and (2) the textures, and their associated 3D pore-space architecture, determine the properties. Using concepts about how these processes alter textures, core observations and measured properties can be extended into the time domain, in both backward and forward directions. The backward direction is addressed by sequential removal of diagenetic features (i.e. diagenetic back-stripping sensu van der Land et al. 2013), or deformation effects. These textural “restorations” can be accomplished in 2D (observed in thin section, or via SEM & auto-determination minerals/orientations), followed by creating digital rock models, which allow property calculations for each of the past states. The methods can also operate directly on 3D digital rock models. (The digital rock methodology has been documented elsewhere, but key aspects will be reviewed in this paper.) The main challenge for this approach is how to take account of the textural consequences of compaction/consolidation, which results in grain rearrangement and thus alterations of the pore space. Forward projection can be literal or figurative. If literal, this might address texture and property changes resulting from reservoir operations (e.g. scale deposition, consolidation from pressure depletion, or even activities such as fracturing). Figurative forward models can estimate how the equivalent rock would have changed in, say, a deeper and un-sampled location, or in a location where deformation occurred (but was not sampled), such as in a fault zone.
AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015