Reservoir Development in the Shuaiba Formation (Lower Cretaceous) at Al Barakah and Safah Fields, Oman - Similarities

D. R. Prezbindowski and W. C. Benmore

A detailed sedimentological and diagenetic study of the upper Shuaiba in the Al Barakah and Safah Fields indicates that the critically important development of secondary micro-intercrystalline porosity postdates early meteoric water diagenesis. The Shuaiba at Al Barakah and Safah Fields consists of shoaling upward carbonate depositional cycles. The main reservoir is developed in the upper cycle as discrete carbonate accumulations centered around rudist/algal biogenic build-ups with surrounding, deeper water non-reservoir facies. Reservoir porosity is dominated by secondary micro-intercrystalline (chalky) porosity. A moderate sedimentological control on secondary porosity development is evident. The best reservoir quality is developed in the coarse-grained, skeletal-rich p ckstones associated with the carbonate build-ups. Although the presence of a regional unconformity at the top of the Shuaiba has commonly been thought to be responsible for reservoir porosity development, a lack of petrographic and geochemical evidence for early meteoric water diagenesis has made an evaluation of this reservoir development model difficult. Cores taken of the Shuaiba and Nahr Umr contact in the Safah and Al Barakah Fields indicate that meteoric diagenesis did occur, occluding early porosity. Reservoir porosity development significantly postdates early meteoric water diagenesis, equant spar calcite cementation and stylolitization. Porosity was formed by the dissolution of the micritic components in the limestones during burial. Reservoir porosity development in these field is not related to the regional input of meteoric water at the Shuaiba unconformity surface.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California