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Field Trip 3

Topic: Fractured Carbonate Reservoirs in the Northern Calcareous Alps

Date: Friday 3 June 2016

Field trip leaders: Dr Kurt Decker & Dr Philipp Strauss

Itinerary: Grossau quarry - Hohe Wand view-point - Gaaden quarry - smaller outcrops (to be determined)

Field trip description

The excursion addresses the characterization of the physical structures, which contribute to the properties of fractured carbonate reservoir rocks. In such rocks most of the effective porosity and permeability is carried by tectonically formed fractures and faults of various type, origin and scale. Reservoir characterization therefore requires quantitative data on structures ranging from centimetre-scale fractures to faults with kilometres length.

Fracture scales ranging over several orders of magnitude pose a serious challenge to quantitative structural analyses and reservoir characterization. The main objective of the field excursion is therefore to discuss structural geology techniques which allow for the characterization of rock volumes with dimensions which are comparable to hydrocarbon reservoirs, and the translation of structural models into reservoir models. Both objectives require the analysis of outcrops with up to several hundreds of metres size. The analysis therefore has to find a trade-off between the detailedness of structural mapping and the objective to characterize large rock volumes.

The visited reservoirs the trade-off resulted in the distinction between the so-called ‘fractured matrix’, which is assessed by a semi-quantitative classification scheme rather than exact measurements of small-scale fractures, and ‘faults’, which are analysed with highest possible accuracy. The ‘fractured matrix’ contains small-scale (centimetre to metre-sized) fractures and joints of various types, but it is otherwise undeformed. Fractures of the ‘fractured matrix’ show no offset at the outcrop observation scale. ‘Faults’, in contrast, are planar structures offsetting the rock. An important feature that distinguishes ‘faults’ from fractures in the matrix is the formation of fault rock (e.g., cataclasite) with a porosity/permeability that differs from the fractured matrix, and the existence of damage zones at the transition to the undeformed rock which show higher porosity/permeability than both, fault rocks and fractured matrix.

The excursion will provide ample possibilities to put hands on all types of structures and rocks, which characterize a fractured and faulted carbonate reservoir, and discuss appropriate structural modelling techniques that lead to a better understanding of reservoir properties.

 

Stops  
Stop 1 Kaltenleutgeben Quarry – Tectonics and Stratigraphy, analogue of Dolostone drilled below the Miocene fill of the Vienna Basin, introduction to Petroleum System and producing reservoirs
Lunch Gaaden
Stop 2 Gaaden Quarry – Poro/Perm properties of fractured Dolostone, Faults and Fault Rocks
Stop 3 Grossau Quarry – Fractured and faulted Dolostone reservoir, large-scale patterns of faults and fracture corridors