3D INTERPRETATION AS A TOOL TO UNRAVEL STRUCTURAL FRAMEWORK

A range of products from exhaustive 2D geological mapping over Earth’s surface is now subject to be dimensionally expanded by advanced tools of 3D interpretation and statistical open source codes to implicitly interpolate data. The products from geological mapping are progressively being required to obey a volumetric QC to be delivered, with subsurface significance of key features.

We have conducted “traditional” volumetric (3D) interpretation over three different regional settings: 1) Sub-Andean fold-thrust belt of Bolivia; 2) Precambrian Ribeira Belt in southeastern Brazil; 3) and Metamorphic Core Complex of southeastern Arizona. By “traditional” we mean hand-made interpretation in regular grids resembling picking over a seismic reflection volume. Models were based and tied to variable amounts and sources of input data, from surface key elements alone to well markers and seismic reflection profiles.

Our interpretation was a good exercise to identify critical steps in drawing a subsurface structural framework. A robust surface mapping and identification of key elements is essential in solving subsurface geology, such as: stratigraphic guide levels, faults, traces and truncations, prevailing fabric orientation, etc. In addition, a good knowledge of regional geology like stratigraphic thicknesses, estimated depth to major decollement and prevailing structural style of deformation (response to mechanical stratigraphy) will allow the interpreters to correctly define relations when no subsurface data is available.

We also found out to be very useful the along-strike interpretation and QC. Because variability is larger along the deformation direction, the strike direction helps to reduce geometrical uncertainties and also check for inconsistencies. For complex structural settings, a best practice is to choose a stratigraphic guide level to adjust by surface relations (e.g., dip measures) and from where to sequentially draw underlying horizons according to stratigraphic thickness.

3D geological mapping is an evolving exercise where products can be progressively improved and shared with the scientific community. Although a limited amount of subsurface data can prevent automatic 3D mapping, geologists are still interpreters to project their knowledge into subsurface. The increasing number of advanced 3D interpretation tools are progressively making it easier for geologists to work and validate their mapping products in a new dimensional perspective.