Online Journal for E&P Geoscientists

Hakimi, Mohammed H.^*1; Abdullah, Wan H.¹; Shalaby, Mohamed R.¹
(1) Geology, University of Malaya, Kuala Lumpur, Malaysia.

The Masila Basin is one of the most productive basins in the Republic of Yemen and located in the Hadramaut region in East Central Yemen. It has long been the site of hydrocarbon exploration but the origin of its hydrocarbons is not fully understood. In the Masila Basin, one petroleum system was identified in this study. The Madbi Formation, deposited during Upper Jurassic time, constitutes the main source rock of the one oil family. Marine organic matter is the main source input for the Upper Jurassic Madbi Formation. This has been identified based on organic petrological studies and from the n-alkane distributions. Organic-rich shales with excellent potential to generate mainly oil are present in the upper part of the Madbi Formation. An oil-source rock correlation is established between produced oil and the Upper Jurassic Madbi source rock strata. A close similarity between the crude oil sample and the shale interval of the Madbi Formation is evident from the thermal maturity and biomarker distributions. The similarities in biomarker characteristics of crude oils and source rock extracts in addition to the geologic occurrences are related to the stratigraphic as well as structural entrapment elements that play an important role during the hydrocarbon accumulations in Masila Basin. The Lower Cretaceous Biyad and Saar Formations are known reservoir rocks but in this study the Upper Biyad Sandstones were recognised to have good reservoir quality and represent the main producing reservoir rocks. Good reservoir quality occurs in braided fluvial and tidal channel sandstones of the Upper Biyad Clastic (S3 and S2 reservoir units). Seal rocks are the Lower Cretaceous carbonate and shales of the Qishn Formation. Overburden includes Cretaceous and the Tertiary rocks. Structural traps were created during the Late Jurassic to Early Cretaceous rift. Based on basin modeling analysis, the Madbi source rock reached maturity and started hydrocarbon generation during Late Cretaceous time and maximum expulsion reached during Early Tertiary time. A huge amount of oil migrated from the source rock via vertical migration pathways through faults as a result of Tertiary rifting during Miocene-Oligocene time.