--> Abstract: Using High-Resolution Sequence Stratigraphy for Characterizing the Khuff C Reservoirs in Hawiyah, Ghawar Field, Saudi Arabia, by Ghazi A. Al Eid, Aus A. Al Tawil, and Ahmad M. Al Moosa; #90077 (2008)

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Using High-Resolution Sequence Stratigraphy for Characterizing the Khuff C Reservoirs in Hawiyah, Ghawar Field, Saudi Arabia

Ghazi A. Al Eid*, Aus A. Al Tawil, and Ahmad M. Al Moosa
Saudi Aramco
*[email protected]

The Permian-Triassic Khuff carbonates were deposited during a major marine transgression on the Arabian Plate. The Khuff Formation is made up of four subsurface members: strati-graphically D, C, B and A. In Ghawar field, the Late Permian 270-foot-thick Khuff C car-bonates contain three reservoir-bearing high-resolution sequences: Khuff C1 to Khuff C3 (KC1 to KC3). The reservoir facies indicate heterogeneity in rock fabric and reservoir qual-ity. Lithological and porosity-based stratigraphy does not necessarily honor the time-equivalent relationships of different rock and reservoir facies. Taking a sequence strati-graphic approach to defining reservoir architecture, however, presents a temporal frame-work within which porosity can be tied to depositional and diagenetic facies. Hence, predic-tive mapping of porosity within layers of time-equivalent heterogeneous facies is possible. It also provides a stratigraphic architecture that is much better suited to the analysis of diagenesis and related geological events that altered sediments and impacted both primary and secondary porosity development. The Late Permian Khuff C sequences are defined by their bounding, Ghawar-wide, disconformities/sequence boundaries. The transgressive and highstand systems tracts (TST and HST) and component cycle sets for each sequence are mappable along the length of Ghawar field. Exposure surfaces in core are defined by pe-dogenic features, which can be identified on gamma-ray logs. This identification allowed mapping of the high-resolution sequences and cycle boundaries of the TST and HST in cored and uncored wells. Reservoir developed in both the TST and HST, with inter-crystalline porosity in the HST of KC2 and KC3, whereas moldic porosity developed in the late TST of KC3.

Taking a closer look at these reservoirs using the current sequence stratigraphic framework derived from extensive core and log correlation has enabled better numeric modeling of the distribution of porosity in the reservoir. This core-and-log based sequence stratigraphic framework is a genetic-based layering scheme that has become a predictive foundation for numeric modeling of such layers. Numerical modeling of facies distributions within the framework is also possible, but more challenging, especially when grainstone facies are fully cemented by anhydrite and are indistinguishable as such on wireline logs. If it be-comes possible to define controls on anhydrite cementation, more refined predictive models can be put forth. Iterative studies between conceptual and numerical models, which account for diagenesis, can provide the best refined predictive models.

 

AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain