We can use various data sources to sedimentological interpretations of siliciclastics and carbonates, such as borehole images in combination with wireline logs, seismic cross-sections, correlation charts, cores, CT-scans or outcrops.
The combination of borehole images and cores is probably the most powerful tool for interpreting high-resolution sedimentology, and can also significantly influence seismic-scale reservoir models.
Information from borehole images ranges in scale between seismic-scale and core-derived data. Depending on the quality of the image and its type, images offer resolutions down to millimeter-scale, suitable for detailed facies interpretation (e.g. showing rootlets or bioturbation). We can get more reliable results if we are able to calibrate the borehole images to cores, although this is not absolutely necessary for the interpretation.
Based on typical and systematic dip patterns as well as resistivity variations within borehole images, the logged interval can be subdivided into individual facies types. Correlated to wireline logs, these facies types can be calibrated to cores (see below) and attributed to specific depositional systems. In this way, we extend facies characterisation to uncored intervals, showing a continuous record of facies evolution in time.
As all measured planes are oriented in space, we use directional results from borehole images to show the evolution of palaeo-current directions (e.g. from cross bedded sandstones), slope orientation derived from slump axes, angularity of unconformities as well as spatial geometry and architecture of sedimentary bodies formed by their genetically related depositional agents.
By recognizing sequence boundaries and flooding surfaces, sedimentary packages can be subdivided into, for example TR cycles (transgressive-regressive), which are indispensable for sequence stratigraphic correlations along specific transects. The sedimentary packages can be split into chronostratigraphic time-slices, which enable us to create palaeo-geographic reconstructions for each time step. This lets us show the history of a depositional area in a series of palaeo-geographic maps, for example, showing the migration of facies belts or changes in palaeo-current directions. These tectono-stratigraphic models are an important source of data for regional, seismic-scale studies and are used as input for geocellular reservoir models.
Resistivity variations in borehole images have a characteristic response to individual facies types as well as their pore fluids. We can exploit this to obtain high resolution thin-bed or vuggy porosity results and hence detailed N/G estimations.