Sequence Stratigraphy Framework of late Early to Middle Cenomanian Rumaila and Late Cenomanian to earliest Turonian Mishrif Formations, Onshore Kuwait

Abstract

Abstract A high resolution biostratigraphic and paleoenvironmental investigations were integrated with sedimentology and wireline-log-data to establish a sequence stratigraphic framework of Rumaila/Mishrif section, Kuwait. The biostratigraphic analysis of over 500 core/chips from 9 wells recognized six 4th order sequences over the study section. All the identified sequences correlated regionally. Three 4th order sequences were identified within the Rumaila Formation: RU100, RU200, and RU300. The RU100-SB lies on the boundary between the non-calcareous restricted shale of the upper Ahmadi Formation and the highly fossiliferous, calcareous marine shale at base of Rumaila Formation. The RU100 and RU200 sequences are represented by marine calcareous shale or marl containing common nannofossils and marine microfossils at their MFSs. The RU300-SB lies on top of the shallower facies, poorly fossiliferous highstand of the under-laying sequence. The RU300-MFS is indicated by abundant micro/nannofossils. This marine event is equated with the regionally known K130. The Rumaila/Mishrif contact is placed at the shift in facies from the deeper water facies of Rumaila to a shallower facies of Mishrif. The shallower facies of Mishrif is bioclastic wack/packstone enriched upward in rudistid and coralline fragments forming a fair/good quality reservoir. Three 4th order sequences were identified within the Mishrif Formation: MISH100, MISH200 and MISH300. The MISH100-SB lies on top of recrystallized wack/mudstone and packstone ending up with a dolomitic wackstone. The MISH100-MFS is indicated by planktonic foraminifers. MISH200-SB lies on top of Praealveolinid wack/packstone of the previous sequence. MISH200-MFS is indicated by planktonic and benthonic foraminifers. The MISH300-SB lies on top of the Praealveolinid wack/packstone ending up with lagoonal non-calcareous shale. The MISH300-MFS is indicated by planktonic and benthonic foraminifers. This marine event could be equated with the regionally known K140. The Rumaila is considered as a good seal all over Kuwait while the Mishrif is considered as a fair/good quality reservoir towards the south. Micritic matrix, moldic, vuggy and fracture porosity reservoir is represented in parts of MISH100, MISH200 and MISH300, while the rudist, coralline floatstone reservoir is existing within MISH300-HST of some areas. Geologic model is presented to show; depositional setting, paleoenvironments, basin configuration and geographic extension of different sequences. INTRODUCTION The focus of this study is on the Rumaila and Mishrif section which occupies the upper part of Middle Cretaceous Wasia Group, which is composed of Burgan, Mauddud, Wara, Ahmadi, Rumaila and Mishrif formations. The group was formed during the latest Aptian, Albian, Cenomanian to earliest Turonian (111 Ma - 92 Ma), and was deposited in about 19 m.y.