Origin and Migration of Hydrocarbons in the Paleozoic System of Saudi Arabia

FRANZ, ULRICH A., Mobil Exploration and Producing Services, Dallas, TX

This paper is a progress report on geochemical studies of the sub-Khuff Paleozoic rocks in Saudi Arabia, summarizing current laboratory results from both Saudi Aramco and American companies and their preliminary interpretations. From oil/oil and oil/rock correlations as well as maturity modeling, it may be concluded that "sweet" sub-Khuff oils, condensates, and gases are closely related to each other, and are derived from a common source: the "hot" shales of the basal Qusaiba Formation (Lower Silurian). The hydrocarbons that have been discovered in the Hawtah trend must have migrated updip from the presently overmature Rub-Al-Khali depocenter, where oil generation was initiated as early as 160 Ma. The oil window in the Rub-Al-Khali embayment, where active oil and condensate generation is taking place at present, is at depths between approximately 10,000 and 14,000 ft. Oil accumulation housed at depths more than approximately 14,000 +/- 500 ft are being cracked into gas and condensate depending on variations in the generally low geothermal gradients of 1.5 +/- 0.1 degree F/100 ft. The residue of this "natural refinery" process is pyrobitumen, or "deal oil," that is a pore plugging agent in many reservoirs at these depths. All products have very low sulfur and the gases are H2S-free because they are all derived from low-sulfur kerogen. The economic impact of these findings is very significant.

AAPG Search and Discovery Article #91007© 1991 AAPG International Conference, London, England, September 29-October 2, 1991 (2009)