--> Abstract: Integration of Core-Based Chemostratigraphy and Petrography of the Devonian Jauf Sandstones, Uthmaniyah Area, Ghawar Field, Eastern Saudi Arabia, by Ronald A. Sprague, John X. Melvin, Florian Conradi, Tim Pearce, and Michael Dix; #90078 (2008)

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Integration of Core-Based Chemostratigraphy and Petrography of the Devonian Jauf Sandstones, Uthmaniyah Area, Ghawar Field, Eastern Saudi Arabia

Ronald A. Sprague1, John X. Melvin1, Florian Conradi2, Tim Pearce2, and Michael Dix3
1Reservoir Characterization, Saudi Aramco, Dhahran, Saudi Arabia
2Chemostrat, Ltd., Llanfyllin, Wales, United Kingdom
3Halliburton, Inc., Houston, TX

The Devonian Jauf gas reservoirs in the Ghawar Field of Saudi Arabia are composed of estuarine-tidal sandstones interdigitated with barrier bar and foreshore marine sandstones. Tidal bar complexes of 30 - 50 feet thick represent the best reservoir facies in the Uthmaniyah area, but correlation of reservoir sand bodies across the field is complicated by erosional truncation at the top of the Jauf, absence of a high-resolution biostratigraphy, rapid vertical facies changes, intraformational disconformities, and differential clay and quartz diagenesis.

Chemostratigraphy combined with thin section petrography helped to unravel this complexity. Over 390 feet of core from two wells were characterized and closely sampled from all facies (~1 sample per foot) for chemostratigraphic and petrographic analyses. Thin sections prepared from core plug end trims were statistically point-counted, with geochemical samples taken immediately adjacent to them.

Elemental ratios recorded provenance, climatic, diagenetic and facies signals, and revealed a previously-unknown intraformational disconformity within the Lower Jauf. Point count data were used to modify the mineralogical model derived from the elemental data, and provided evidence of a cementation history that alternated between clay-dominated and quartz-dominated diagenetic events, which strongly influenced reservoir quality.

Chemostratigraphic correlation identified 6 geochemical packages and 23 individual units, correlatable to 10-foot intervals between the two wells, which was virtually identical to a previous gamma ray log-only correlation; a geochemical signal for an important intraformational biomarker was also recognized. This chemostratigraphic correlation was used as the basis for a comprehensive layering scheme for 21 wells in an object-based geocellular model.

 

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas