Yemen Red Sea Subsalt Tectonics/Petroleum System Analysis from Seismic Stratigrahy-Basin Modeling

Omer Aksu, John D. Pigott, and Ahmed Alahdal
University of Oklahoma, Norman, OK

Subsalt geological interpretations are commonly complicated by poor seismic imaging and without borehole geovalidation, yield interpretations which are often problematic. However, for the Yemen Red Sea, basin analysis-seismic stratigraphy of industry seismic reflection profiles integrated with seismic refraction and kinetic thermal modeling using “lithologic replacement” allows a constrained non-borehole approach to its subsalt petroleum system analysis.
Four discrete rifting episodes (E) and respective betas determined by 1D subsidence analyses are; E1: pre18 Ma beta of 1.22, E2: 18-14 Ma beta of 1.195, E3: 11-5 Ma beta of 1.21, and E4: post 5 Ma beta of 1.24. Associated lithologies vary greatly and are; E1: crystalline basement, E2: subsalt mixed clastics, E2-E3: salt, E3: salt with interbedded shale capped with anhydrite, and E4: clastics and carbonates. These episodic changes in rifting, associated lithologies, and concomitant changes in thermal conductivities greatly affected maturities of ~14 Ma subsalt potential source rocks.
“Lithologic replacement” kinetic thermal modeling reveals 3km subsalt temperatures owing to thermal refraction of the overlying salt to be 30-40 ^oC cooler than if these salts were replaced with sand lithologies. Importantly, for subsalt source rocks, the respective kinetic maturity change reflects a decrease from 2.5 to 1.8 in modeled %Ro. Such findings are strongly encouraging for exploraing for subsalt oil in this frontier Yemen basin and argue against the generally held “overcooked” myth for Red Sea exploration.

AAPG Search and Discovery Article #90072 © 2007 AAPG and AAPG European Region Conference, Athens, Greece