--> ABSTRACT: Reviving a Classic Exploration Play in Kuwait: The Lower Cretaceous Ratawi Formation, by Al-Tendail, Sara B.; Taal, Aavo ; Al-Adwani, Talal; Abu-Ghneej, Ali; Barr, Duncan ; Clews, Patrick J.; #90142 (2012)

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Reviving a Classic Exploration Play in Kuwait: The Lower Cretaceous Ratawi Formation

Al-Tendail, Sara B.*1; Taal, Aavo 1; Al-Adwani, Talal 1; Abu-Ghneej, Ali 1; Barr, Duncan 2; Clews, Patrick J.2
(1) Exploration Group, Kuwait Oil Company, Ahmadi, Kuwait.
(2) Landmark, Halliburton Company, Dubai, United Arab Emirates.

The Ratawi Fm constitutes a significant hydrocarbon reservoir in many parts of the Middle East. North of Kuwait, the Ratawi is productive in several fields. It is also productive in northern Saudi Arabia and the Neutral Zone. In Kuwait, the Ratawi Fm has tested oil and gas in many wells, but is classed a minor reservoir. So why is the Ratawi not a significant producing horizon in Kuwait?

To answer this question, in 2007 KOC undertook a geological study of approximately 1310-ft of Ratawi core from 18 wells across Kuwait. Detailed core descriptions were supported by thin section, SEM, XRD and conventional core data. The Ratawi Fm has traditionally been divided into an upper Ratawi Shale Mbr and a lower Ratawi Limestone Mbr, with the latter being the main exploration target. Major discoveries were made in the lower part of the Limestone Mbr (then termed the Ratawi Oolite) at Wafra Field in 1953 and Umm Gudair Field in 1964. In Kuwait, the Ratawi Oolite interval was renamed the Minagish Oolite, or more formally, the Middle Minagish Member (Oolite) of the Minagish Formation.

The 2007 study identified several factors which negatively affected the hydrocarbon potential of the Ratawi Limestone Mbr. Its diagenetic history records up to 11 periods of porosity reduction by calcite and other cements. Where oil is present in cores, it appears to have migrated into the reservoir during late diagenesis, following precipitation of these cements. The study also identified several positive factors. There are packstone and grainstone facies present in the Limestone Mbr with porosities up to 25% in southern and offshore Kuwait. Oil quality is good (28-46° API). Reservoir potential may also be enhanced by late fracturing.

KOC has now shifted its exploration efforts to the Ratawi Shale Mbr. In northern Kuwait, this shallow marine interval of limestones (30-50%), sandstones (10-15%) and shales (35-60%) has already tested oil in Abdali, Raudhatain and Sabriya fields. Both structural and stratigraphic plays are being pursued. Seismic mapping has identified several structural traps at the Ratawi Shale level. Additional cores acquired in the Ratawi Shale in 2010-11 are now being evaluated. A review of existing exploration wells identified a number of intervals with possible bypassed oil pay in the Ratawi Shale Mbr; these zones will be tested in 2012-13. Outside the established fields, Kuwait still has areas of low well density with plenty of room for new discoveries to be made.

 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California