A New Exploration Play for Saudi Arabia, the Lower Qusaiba Sandstone

Hayton, Shaun ¹; Heine, Chris ¹; Shenggen, Zhang ²; Sherba, Eugene ¹; Gratto, Brian ¹; Shicheng, Wang ^2
1 Upstream Ventures, Saudi Aramco, Dhahran, Saudi Arabia.
² Sino Saudi Gas Ltd, Al Khobah, Saudi Arabia.

Exploration activity always has its surprises.

For Sino-Saudi Gas (SSG) a joint venture between Sinopec and Saudi Aramco, exploration in the Southern-RAK has resulted in a number of unexpected geological findings.

One of these has been the identification and confirmation of an entirely new exploration play within the well known Silurian (Ruddanian-Aeronian) aged Qusaiba Formation. This formation, and in particular the basal hot shale and cooler, but still carbonaceous shales above, is the primary source rock for the vast hydrocarbon resources of Saudi Arabia. While predominantly a shale, previous work (Miller and Melvin, 2005) has identified and defined a regionally correlatable sandstone near the top of the Qusaiba, the Aeronian-aged mid Qusaiba Sandstone. This sandstone is well known and a proven reservoir within Saudi Arabia.

Recent exploration activity by SSG in the Southern-RAK has resulted in the identification of a Ruddanian-aged sandstone (the Lower Qusaiba Sandstone) directly above the Base Qusaiba Hot Shale and interbedded with the cooler shales. While not as extensive and prominent as the mid-Qusaiba Sandstone, this lower sandstone has great potential as a hydrocarbon reservoir given its location directly above and interbedded within Saudi Arabia's premier source rock.

A sudden increase in mud gas and sandstone cuttings while drilling the Qusaiba shale in an SSG exploration well, lead SSG to cut a 30' conventional core. The core contained interbedded sandstone and shale. FMI logs also clearly showed interbedded sandstone and shales, which allowed the very precise location (to within less than 3") of rotary SWC's to complement the conventional core.

While routine porosity and permeability analysis of the conventional core plugs and rotary SWC's indicates that this is a very low permeability reservoir at this location, it did flow hydrocarbons on cased hole test.

Detailed analysis of the conventional cores indicates that the sandstones were deposited by mass-flow mechanisms including turbidity flows. The depositional system is interpreted as the lateral edges of a slope or basin floor fan. If the primary channel or fan complex with its coarser-grained lithofacies can be located, we feel that the Lower Qusaiba Sandstones has significant potential as an exploration target within Saudi Arabia.

This poster presents some of the early work on this new play.

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009