Sequence Stratigraphy and Facies Analysis of Arab-C and Sub Arab-C Reservoirs: A Case Study from Eastern Saudi Arabia

Busbait, Emad A.
Saudi Aramco, Dhahran, Saudi Arabia.

This study focuses on reservoir quality, facies analysis, development of a depositional model, and building of a high-resolution sequence stratigraphic framework of the Upper Jurassic Arab-C and sub Arab-C Members. The study area covers oil fields in the eastern province of Saudi Arabia. The fields are located several hundred kilometers to the west of Late Jurassic margin with the Tethys on a nearly flat-topped carbonate platform within intershelf basins.

From landward to seaward, the facies and interpreted environments include: anhydrite (sabkha and salina), mud-rich and grain-rich stromatolites (tidal flats), thrombolites (inner lagoon), fine peloidal grainstone (outer lagoon), ooid grainstone (shoal), and ooid-intraclast-mollusk rudstone (foreshoal). The Arab-C and sub Arab-C are composed of two composite sequences that form six high frequency sequences (HFS). The composite sequence boundary lies within the upper part of the evaporite units and the maximum flooding surfaces has been picked in the middle of the coarsest most open marine facies within the Arab-C carbonate. The sequences coarsen upward in the lower transgressive system tract (TST) as higher-energy shoal facies - backstep over lagoonal, tidal flat, and sabkha facies - and are coarsest in the maximum flooding interval. The sequences subsequently change to fining upward as shoal facies, and are capped by finer and/or muddier lagoonal, tidal flat and/or sabkha facies in the HST.

The sub Arab-C reservoir is made up of two high frequency sequences composed of multiple fining-upward cycles; while the Arab-C composite sequence is made up of four HFSs. Cycle boundaries are picked at the base of the coarsest facies and top of the finer facies. The highest porosity-permeability ooid grainstone facies are thickest in the northern part of the study area, and the peloid grainstone and anhydrite are thickest in the southern part.

This study improves greatly the understanding of the Arab-C and sub-C reservoir stratigraphic framework by giving further information on suitable data to be used in a geocellular model for optimization of field development plans and wells placement.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012