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How Porosity is Developed or Preserved in Unconventional Hemipelagic Carbonate Reservoir? Case Study in SE France (Provence, Durance Area)

Pierre-Olivier Bruna¹^,², Yves Guglielmi¹^,², Juliette Lamarche¹^,², Marc Floquet¹^,², François Fournier¹^,², Jean-Pierre Sizun³, Arnaud Gallois¹^,², Lionel Marie¹^,², Catherine Bertrand³, and Fabrice Hollender^4,5
¹Aix-Marseille Université, Marseilles, France
²CEREGE UMR 7330, Marseille Cedex, France
³Laboratoire de Chrono-environnement, Université de Franche-Comté, Besançon Cedex, France
⁴CEA de Cadarache, Saint-Paul-lès-Durance Cedex, France
⁵ISTerre, BP, Grenoble, France

Understanding unconventional reservoirs with low porosity and permeability of the host rock is a major scientific and economic challenge with applications for oil and gas industry, underground water management and industrial risk assessments. Hydrogeologists consider that tight rocks have high fracture permeability and negligible storage capacity, although deep unconventional tight reservoirs can produce significant quantities of oil and gas.

The key question addressed in this poster is how fluid flow through the tight host rocks? This question is of prime importance for better understanding fluid flow both in the near surface aquifers and in the deep buried sedimentary reservoirs.

We investigated the lower Cretaceous carbonates of the Durance area. From Berriasian to Valanginian the area of interest is positioned in the steeply slope-to-basin transition open towards the Vocontian basin. In such context, deposits are represented by a mix of micritic and fine grained sediments. This association is representative of hemipelagic environment.

Present day observations of hemipelagic carbonate matrix allow comparing these rocks as analogues for unconventional reservoir with a host rock average permeability of 10-16 m2 and porosity of 0-to-4 %. Permeability in fracture zone, composed by a large variability of fracture type and fracture size, reaches high values of 10-8 m2 and allows the shallow aquifer drainage through a dozen of perennial springs with a significant annual flow of 1000 m3/h. The question of the diffusivity in these rocks at depth is addressed through a pluri-disciplinary approach including: i) a sedimentological analysis of upper Berriasian to lower Valanginian rocks based on outcrop observations and thin sections description; ii) micro-structural and geodynamic (burial history) analyses; and iii) petrophysical measurements, including helium, water and mercury porosimetry and p-wave measurements, on deep borehole core and on outcrops.

AAPG Search and Discovery Article #120034©2012 AAPG Hedberg Conference Fundamental Controls on Flow in Carbonates, Saint-Cyr Sur Mer, Provence, France, July 8-13, 2012