We interpret a discrete, stratigraphic fault-deformed interval in the Paleocene-Eocene of the Magallanes foreland basin as a widespread polygonal fault system (PFS). Based on the integration of 3D-seismic attribute analysis, drill core evaluation and fracking-microseismic data, the purpose of the present work is twofold:
to describe the widespread and well-developed PFS, and
to highlight its potential effects on the Paleogene petroleum system of the basin.
The deformed interval is bounded by relatively undisturbed and continuous reflections, more likely coinciding with important stratigraphic surfaces or horizons. It has a wedge shape and is characterized by normal faults with small throws (<40 m) that form polygonal patterns in map view. The polygons are largely rectangular to pentagonal in shape and may range from 0.5 up to 3 km across; the largest polygons tend to occur toward the foredeep domain. Faults are normal and have no preferred directions, which together with their strata-bounded nature and geometry relationships of the faults, suggest an early diagenetic rather than a tectonic origin for the system. In drill cores, single or conjugate sets of faults occur and the fault surfaces display striations with no filling material in between. Polygonal faults locally crosscut amplitude anomalies associated with post-depositional sand remobilization and injection.
Because the Paleogene PFS extend for more than 20000 km2 and their formation is dependent, among other factors, on grain-size and lithology, they are useful as a basin-wide correlation tool. The PFS apparently exert no control over the size and orientation of induced hydraulic fractures in the study area, but they are potential elements affecting the geometry and extension of reservoirs. In addition, the combination of polygonal and tectonic faults in the basin might control sealing capacity of caprock and hence fluid flow patterns on a regional scale. Thus, an understanding of the timing and distribution of the PFS in the Magallanes basin may provide important clues about petroleum migration, compartmentalization history and future well and reservoir management for unconventional resource plays.
