GIANT RECUMBENT FOLDS AND FRACTURES OCCURENCE IN CARBONATES
Geologic context about this km-scale anticline:
Anticline structures commonly host reservoirs and fractured reservoirs, in particular in carbonates. Assessing and discussing the fracture distribution in such tectonic structure remains challenging, in particular using seismic data in which the accuracy of the resolution does not allow to address this issue with confidence. Storage, injection or production are highly dependent of fracture connectivity, density, and apertures. Fracturing can occur in response to many parameters that need to be understood such as the regional tectonic setting, folding development, faulting development, deconfining phases etc. (Cavailhes et al., 2015). We propose this outcrop picture and related-interpretation to discuss the relations between folding, faulting and fracturing through a fictive well (borehole) crossing a giant recumbent fold.
Scientific questions:
What could be the subsurface seismic expression of such folded structures?
What are the sub-seismic fractures/faults distribution and attributes?
What are the implications for subsurface reservoir compartimentalization?
Outcrop details:
The studied escarpment is 800 meters-high and therefore of seismic-resolution. From the oldest to the youngest, from the lower right corner to the lower left one, the stratigraphy is made of: (j2-4) Bathonian/Oxfordian ‘Terres Noires’ that are black marls deposited in deep marine environments, (J5) Argovian limestones and marls made of alternating dm-thick yellow carbonates and dark marls, (j6-n1a) Lower Oxfordian to lower Beriasian massive carbonates that are 100m-thick and which give the recumbent fold shape. On the left, the escarpment is made of neocomian (lower Cretaceous) brownish marly limestones.
The depth during the compressive deformation phase did not exceed 3-4 km. The exhumation phase has also probably generated fracture sets. The Bathonian/Oxfodian dark marls are organic-rich and could locally have been potential source rocks.
HOW COULD WE USE THIS OUTCROP IN SEISMIC INTERPRETATION?
Seismic-scale:
.. Currently writing the text
Sub-seismic-scale:
Feel free to constructively comment this open discussion. Feel free to provide relevant references where similar structural geometries, sedimentary or diagenetic contexts, have been recognized or forecasted.
Scientific references:
Cavailhes, T.,Funk, E., Monstad, S., Paulissen, W., Marré, J., Riva, A., Looser, M., Chalabi, A., Figa, M., Morset-Klokk, H., Canner, K., Berner Mitchell, K., and N. Bang, 2015, Investigating the hierarchical impact of polygenetic fracture populations in compressive settings: Implications on static fracture modelling: Conference: Banff Alberta, Mountjoy meeting: Advances in characterization and modeling of Complex Carbonate Reservoirs.
Huang, Q., Angelier, J., 2009, Fracture spacing and its relation to bed thickness:Geological Magazine, 126, 4, 355-362, Cambridge University Press.