Title: Fracture controlled fluid flow in Cretaceous carbonates of the Natih Formation (Jabal Qusaybah, North Oman)
Authors: Mozafari, Mahtab
Swennen, Rudy
Balsamo, Fabrizio
Clemenzi, Luca
Storti, Fabrizio
El Desouky, Hamdy
Tueckmantel, Christian
Solum, John
Taberner, Conxita
Issue Date: 28-May-2014
Conference: Reservoir Quality of Clastic and Carbonate Rocks: Analysis, Modelling and Prediction location:Geological Society of London date:28-30 May 2014
Abstract: Among all the factors contributing to the rock properties of carbonate reservoirs, faults and associated fracture networks play a critical role in low-permeability rocks. They contribute to the secondary porosity and enhanced permeability allowing rapid vertical and lateral fluid migration. Moreover, they facilitate fluid redistribution between different reservoirs (Roure et al., 2005; Cox, 2007). The carbonates of the Natih Formation (Late Albian - Early Turonian) have been studied in the Jabal Qusaybah to reconstruct the circulation of paleo-fluids in fault damage zones formed during the development of the North Oman fold and thrust belt. Applying an integrated diagenetic-structural approach, we have been able to link the fluid circulation, geochemical and thermal evolution to the structural history. This has enabled us to understand when and to what extent the fractures were open and acted as conduits to fluids. In addition, it provides new insights about the tectonic influence on regional fluid circulation including hydrocarbons.

Jabal Qusaybah is an E-W trending anticline affected by widespread fold-related NE-SW and NW-SE strike slip, N-S normal, and inverted E-W extensional fault zones. Migration of fluids during major deformational events associated with progressive faulting, folding and exhumation have been recorded by several stages of calcite and localized minor dolomitization and dolomite cements. Based on petrography, geochemical and structural characteristics, the calcite cemented fracture-fills and veins can be related to early deformational (pre-fold), syn-deformational and late deformational episodes. The early deformational calcite veins are characterized by rock-buffered fluids, displaying stable isotopic values of +1.2‰ < δ13C V-PDB < +3.5 ‰ and -10.3‰< δ18O V-PDB <-6 ‰. The calcite vein generations linked to faulting and folding events (syn-deformational) are mainly controlled by strike slip faults and associated transtensional horsetail structures. They demonstrate clustered δ13C signatures and a wide range of δ18O values (+1.0‰ < δ13C V-PDB < +3 ‰ and -11.2‰ < δ18O V-PDB < +0.3 ‰). The late deformation (late folding) calcite veins are mostly cemented along the N-S extensional faults related to a final stage of folding and exhumation. They are typified by enriched δ13C values and less depleted δ18O values (+3.5‰ < δ13C V-PDB < +8 ‰ and -3.5‰< δ18O V-PDB < +1.5 ‰). Based on microthermometry and structural evidences, we suggest that the deep-seated strike slip faults were responsible for precipitation of the veins with the most depleted δ18O values. The mineralization along these faults most likely occurred from low salinity (Ave=2 eq. wt. % NaCl) fluids originating from topography driven heated meteoric waters. However, after mixing with formation fluids at depth (75 < TAVE < 115°C), the average salinity reached up to 10 eq. wt. % NaCl, while the calcites along the N-S extensional faults precipitated from moderately saline fluids (8.5 to 14 wt. % NaCl) with average temperatures between 65 and less than 50°C. Furthermore, the gradual increase of salinity is simultaneous with the change from NaCl-H2O to NaCl-CaCl2-H2O fluid composition. The 87Sr/86Sr isotope values of early deformational veins are in good agreement with Sr isotopes of Cretaceous marine carbonates, however, 87Sr/86Sr ratios in syn- and late tectonic calcite generations show values up to 0.70845. Finally, the coeval increase of the 87Sr/86Sr ratios with δ18O signature suggests the interaction with siliciclastics and / or with Pre-cambrian/Cambrian evaporites.


Cox, S. F. (2007). Structural and isotopic constraints on fluid flow regimes and fluid pathways during upper crustal deformation: An example from the Taemas area of the Lachlan Orogen, SE Australia. Journal of Geophysical Research: Solid Earth (1978–2012), 112(B8).
Roure, F., Swennen, R., Schneider, F., Faure, J. L., Ferket, H., Guilhaumou, N., Osadetz, K., Robion, P., Vandeginste, V. (2005). Incidence and importance of tectonics and natural fluid migration on reservoir evolution in foreland fold-and-thrust belts. Oil & gas science and technology, 60(1), 67-106.
Publication status: published
KU Leuven publication type: IMa-p
Appears in Collections:Division of Geology

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