Structural Evolution of the Hawasina Window (Oman Mts) and Its Relation to Hydrocarbon Generation

László Csontos¹*, Ágoston Sasvári², Tamás Pocsai², Gizella B. Árgyelán², István Dunkl², and László Fodor^3
1MOL
²University of Göttingen
³Hungarian Geological Institute
*[email protected]

Extensive field studies in the Hawasina Window region of the Oman Mountains led to the recognition of four major structural processes, linked with: (1) intra-oceanic obduction; (2) emplacement of ophiolites onto the Arabian continental margin; (3) unroofing of the subthrust margin; and (4) Tertiary folding and extension. The first Cenomanian process is not relevant to the formation of hydrocarbons in the Arabian margin. The second Turonian process led to the formation of out-of-sequence nappes and ductile extension. It provided tectonic burial of the margin. An omnipresent NE-vergent syn-cleavage folding is also associated to emplacement. The shortly following tectonic unroofing rafted ophiolite blocks away from the window areas. Break-up of the nappes is suggested along a pre-existing strike-slip fault system. Isostatic compensation led to uplift and folding of the nappe succession. Finally the Tertiary Period was characterised by across-strike normal faulting and numerous steps of folding, ramp-thrusting and transpression. This process uplifted potential reservoir sections in Late Tertiary times. The play concept proposes classical Natih source rocks and reservoirs in the autochtchon. Since original porosity is reduced due to tectonic loading, fracture porosities in the limestones and Upper Permian-Triassic dolomites are considered viable in the reservoir rocks. Seals are formed by shaly sections of the autochtchon (Salil, Nahr Umr and Muti formations) and of a regional evaporitic detachment at the base of the Hawasina Nappes. The major upwarp of autochtchon and three local antiforms in the Hawasina Window form the potential trap(s). Vitrinite reflectance and clay mineralogy both reflect anchimetamorphic conditions for the Hawasina Nappes. Thermal conditions probably did not exceed late-stage, gas maturity levels. The main burial is estimated to have lasted for 10 million years. Therefore the Hawasina Window area is considered gas-prone. Both MOL Hungarian Oil & Gas Plc and Hawasina LLC Oman Branch wish to thank the Exploration Directorate of Ministry of Oil & Gas of the Sultanate of Oman for the continuous support to the work.

AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain