Toward a quantitative definition of mechanical units: New techniques and results from an outcropping deep-water turbidite succession (Tanqua-Karoo Basin, South Africa)

The physical properties of reservoirs are strongly influenced by distributed fracture fields. Outcrop studies are commonly used to determine them but have provided unsatisfactory results because the definition of mechanical units, i.e., (groups of) layers displaying homogeneous fracture patterns, is difficult and typically conducted in a qualitative manner. We have developed a systematic methodology to acquire and process fracture patterns in outcrops and to define their relation with stratigraphy. We dedicate particular attention to the vertical distribution of fractures in a sedimentary succession, commonly composed of layers of different thicknesses and compositions. The method makes full use of geographic information system technologies and allows for direct digital acquisition in the field leading to time-efficient acquisition. Data are processed with a newly developed routine that permits an objective description of the changes of fracture characteristics along the stratigraphy of the outcrop. The operator is then able to define the most suitable fracture stratigraphy. The integration of results from different outcrops is thought to provide a tool for predicting fracture distributions in subsurface target areas.