![]() the density and orientation of open fractures.the orientation of the faults can be established and tied to the seismic interpretation.Structural core logging provides a variety of useful information for the reservoir model. Dipmeter data, scribed core, and paleomagnetic data have all been used to work out the spatial orientation of the core. Having established the structures in the core, it is important to know how they were originally oriented within the reservoir. Commercial rigs are also available, which take 360° photographs of the core for the same purpose. The unrolled film shows a 360° depiction of the structure comparable to the display shown by borehole image logs. The whole core is wrapped around with acetate film, and the structures and main bedding planes in the core are traced directly with felt tip marker pens. Structural core logging may be required if there is a high density of such features or where knowledge of the detailed fault or fracture pattern is important for reservoir development.Ĭore goniometry is a method for graphically depicting the structure in the core. Structural features such as fault zones and fractures are commonly seen in cores. Another method is to use semblance data to detect edges in the data (see Lithofacies maps). The interpretation can be cross checked against attribute maps showing changes in seismic dip (magnitude of the time gradient), azimuth (direction of maximum dip), or abrupt changes in amplitude. Various techniques can help in picking faults. The seismic interpreter will look for discontinuities in the seismic reflections likely to represent faulting. These create patterns on a seismic section that give a representation of the geological structure in the subsurface. Continuous reflections stand out as an overlapping array of peaks or troughs. The peaks or the troughs are filled in with black shading or color. These are displays that show a series of vertical seismic traces displayed side by side ( Figure 1). The seismic data set is interpreted primarily using vertical time sections. 7 Fault geometries, linked faults, and relay ramps.This reflects the change in the stress state of the reservoir as a result of pressure depletion. Sometimes sealing faults break down and open up to flow after a field has been producing for a few years. Techniques are available to predict the likelihood of this. Having established a fault framework for a field, it is important to know whether or not fluid flow communication occurs across the faults. The interpretation of faults and structure at the seismic scale is made by the seismic interpreter whereas the production geologist analyzes the structures from core and log data. The reservoir structure can be analyzed at two different scales: the seismic scale and the well scale. This article discusses the data used to establish the presence of faults and how faults are mapped for reservoir models. In structurally complex fields, faults and fractures provide major elements influencing production performance. In structurally simple fields, the main control on production behavior is the distribution of lithofacies.
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