Comparison of the diagenetic and reservoir quality evolution between the anticline crest and flank of an Upper Jurassic carbonate gas reservoir, Abu Dhabi, United Arab Emirates

Daniel Morad (1) , Fadi Henri Nader (2) , Marta Gasparrini (2) , Sadoon Morad (3) , Carlos Rossi (4) , Elisabetta Marchionda (5) , Fatima Al Darmaki (6) , Marco Martines (6) , Helge Hellevang (1)

1 Department of Geosciences [Oslo]
2 IFPEN - IFP Energies nouvelles
3 Khalifa University for Science Technology [Abou Dabi]
4 UCM - Universidad Complutense de Madrid = Complutense University of Madrid [Madrid]
5 UNIPV - Università degli Studi di Pavia = University of Pavia
6 ADNOC - Abu Dhabi National Oil Company

This petrographic, stable isotopic and fluid inclusion microthermometric study of the Upper Jurassic limestones of an onshore field, Abu Dhabi, United Arab Emirates (UAE) compares diagenesis in flanks and crest of the anticline. The results revealed that the diagenetic and related reservoir quality evolution occurred during three phases, including: (i) eogenesis to mesogenesis 1, during which reservoir quality across the field was either deteriorated or preserved by calcite cementation presumably derived from marine or evolved marine pore waters. Improvement of reservoir quality was due to the formation of micropores by micritization of allochems and creation of moldic/intragranular pores by dissolution of peloids and skeletal fragments. (ii) Obduction of Oman ophiolites and formation of the anticline of the studied field was accompanied by cementation by saddle dolomite and blocky calcite. High homogenization temperatures (125–175 °C) and high salinity (19–26 wt% NaCl eq) of the fluid inclusions, negative δ18OVPDB values (−7.7 to −2.9‰), saddle shape of dolomite, and the presence of exotic cements (i.e. fluorite and sphalerite) suggest that these carbonates were formed by flux of hot basinal brines, probably related to this tectonic compression event. (iii) Mesogenesis 2 during subsidence subsequent to the obduction event, which resulted in extensive stylolitization and cementation by calcite. This calcite cement occluded most of the remaining moldic and inter−/intragranular pores of the flank limestones (water zone) whereas porosity was preserved in the crest. This study contributes to: (1) our understanding of differences in the impact of diagenesis on reservoir quality evolution in flanks and crests of anticlines, i.e. impact of hydrocarbon emplacement on diagenesis, and (2) relating various diagenetic processes to burial history and tectonic events of foreland basins in the Arabian Gulf area and elsewhere.

Mots clés: Diagenesis; Carbonate; Reservoir quality; Fluid evolution; Foreland basins

Domaines: Sciences de la Terre

Daniel Morad, Fadi Henri Nader, Marta Gasparrini, Sadoon Morad, Carlos Rossi, et al.. Comparison of the diagenetic and reservoir quality evolution between the anticline crest and flank of an Upper Jurassic carbonate gas reservoir, Abu Dhabi, United Arab Emirates. Sedimentary Geology, 2018, 367, pp.96 - 113. ⟨10.1016/j.sedgeo.2018.02.008⟩. ⟨hal-01877229⟩