--> Abstract: Depositional Environments and Reservoir Characterization, Upper Saar, Masila Block 14, Republic of Yemen, by D. Dearborn, M. Kerman-Milne, and Dale A. Leckie; #90039 (2005)

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Depositional Environments and Reservoir Characterization, Upper Saar, Masila Block 14, Republic of Yemen

D. Dearborn, M. Kerman-Milne, and Dale A. Leckie
Nexen Inc, Calgary, AB

In the Nexen-operated Masila Block 14, of southern Yemen, the Hauterivian to lower Barremian Upper Saar Formation unconformably overlies carbonates of the Saar Formation and is unconformably overlain by the clastics of the Qishn Formation. The Upper Saar comprises of four alternating clastic and carbonate cycles in descending order designated as A, B, C and D members. The Upper Saar is approximately 60 to 80 ft thick, with the uneroded individual cycles approximately 12 to 20 ft thick.

The Upper Saar is bounded by low-topographic relief sequence boundaries and within the formation there are exposure and flooding surfaces attributed to relative sea-level changes. The reservoir quality of the Upper Saar is strongly controlled by the primary depositional environments and the subsequent diagenetic history, particularly that affected by subaerial exposure of the B and D carbonate members.

Detailed petrophysical and depositional studies indicate that primary depositional grain size and the presence or absence of diagenetic cement controls reservoir quality. Porosity distribution and porosity types are related to rock texture and fabric. The Upper Saar A and C members are quartzarenite to subarkose, whereas the B and D members are mudstone to wackestone-packstone.

The lowermost D member overlies and onlaps the irregular topography of the Saar Carbonate. The dolomitic limestone D member is interpreted to have been deposited in a shallow muddy shelf. Reservoir is encountered in a shoaling facies which has secondary porosity due to leaching and karsting due to exposure.

The overlying C member has a sharp basal contact with a coarse lag. The sandstone is very fine to fine grained and is interbedded with siltstone and shale. Double mud drapes, Zoophycos and Arenicolites indicate a shallow marine environment near to coast with evidence of tides. Reservoir quality is controlled primarily by grain size.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005