LAUSR

Abstract Twelve third order depositional sequences (SQ1 to SQ12) are defined of the Upper Jurassic-Lower Cretaceous succession in the Masilah oilfields, Sayun-Masilah Basin, Yemen based on analysis of well logs and integrated datasets (biostratigraphic, petrographic and seismic data). These sequences which are bracketed by thirteen sequence boundaries (SB1 to SB13) represent several stages of transgression and regression that caused changes in facies types. The base of the sequences in this study unconformably overlies the basement complex at the start of the regional transgression represented by Shuqra Formation (TST1), whereas the top is bounded by normal regression represented by Qishn Carbonate Member (HST12). The producing horizons in this succession are located in highstand and transgressive systems tracts of the Lower and Upper Qishn clastic in the depositional sequences (SQ8 to SQ11). The main producing sandstone reservoir of Lower and Upper Qishn clastic that is recorded in four progradational highstand systems tracts (HST8-HST11) is about 224.5 m. It occurs as transgressive systems tract (TST11) of the Upper Qishn clastic representing of about 67 m.