High Frequency Sequence Stratigraphic Surfaces and Associated Reservoir Facies in Lower Cretaceous Ratawi Shale Formation in Kuwait
Tanoli, Saifullah K.
The Lower Cretaceous Ratawi Shale Formation in Kuwait is a predominantly siliciclastic unit overlying a thick succession of platform carbonates. Lithofacies within it are variable both spatially and temporally. It dominantly consists of shale with sandstone, siltstone and limestone interbeds. Appreciable amount of sandstone facies are developed within the 3rd order lowstand systems tract in the middle of the formation. Sandstone development is more prominent in western part of Kuwait. Overall, both the lower and upper parts of the formation were deposited under transgressive conditions. The formation displays one complete 3rd order sequence and another incomplete 3rd order sequence with recognizable transgressive systems tract and locally possibly part of highstand systems tract as well. It is possibly locally eroded by the overlying late Valanginian unconformity.
High frequency sequences and important related surfaces were identified and described from the cores study. The regressive surface of marine erosion (RSME) is usually sharp and wavy separating the underlying offshore muddier facies from the overlying shoreface sandier facies. The sequence boundary is marked by exposed surface locally represented by rooted interfluves, by the weathered horizons and still in others by incised fluvial surface. The transgressive surfaces and or major flooding surfaces usually make thin burrowed horizon with the fining and deepening upward trend. The reservoir facies are variably associated with the falling stage systems tract (e.g. shoreface sandstone above the RSME), and with the lowstand systems tract (e.g. delta plain sediments). An insight into the sequence stratigraphic set up along with the paleoenvironmental regime, as obtained from the study of core and log data, is crucial for identification and distribution of reservoir facies. Such study may lead in deciphering the potentially prospective areas for hydrocarbon exploration.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013