--> Abstract: Eocene Rus Anhydrite: Limitations on Exploration, Production, and Seismic Interpretation, by D. Mark Steinhauff, Arthur E. Gregory, and Christian J. Heine; #90077 (2008)

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Eocene Rus Anhydrite: Limitations on Exploration, Production, and Seismic Interpretation

D. Mark Steinhauff*, Arthur E. Gregory, and Christian J. Heine
Saudi Aramco
*[email protected]

The Eocene Rus Anhydrite is an important seismic reflector in the Arabian Peninsula where it is present above the Mesozoic and lower Cenozoic carbonate platforms. It provides reservoir top-seal locally (e.g. Partitioned Neutral Zone, Kuwait and Saudi Arabia). Understanding the deposition and diagenesis of the Rus Formation has broad implications in understanding the limitations on exploration and production, and for better seismic planning, acquisition, processing and interpretation. The Rus Formation typically comprises meter-thick anhydrite parasequences inter-bedded with thinner limestone, dolomite, and marly beds with a gross thickness, in the shallow-basin centers, of more than 700 ft. Sub-meter scale, anhydrite bed sets can be traced on wireline logs for 100s of kilometers. Typically, the Rus has distinctive physical properties, including strong impedance contrasts with over and underlying strata. Less common are seismic zones lacking coherent reflectors and distinctive physical properties. Borehole penetrations show that many incoherent reflectors typically include rubble. These zones present challenges in applying static corrections and interfere in our ability to correlate deeper reflectors. Previous work has shown that the Rus Anhydrite thins or is absent above many structural highs including much of the Qatar Arch, Ghawar field, Dammam Dome and other large anticlines. Features attributed to karst are noted in many areas. The absence of anhydrite can be explained by: (1) non deposition because the structures were moving; (2) deposition followed by erosion; or (3) extensive subsurface dissolution of carbonate and sulfate-evaporites under Mid- Pleistocene wet climatic conditions. Even though the aforementioned structures probably have unique depositional and tectonic histories, some combination of the three proposed processes likely affected them all.

 

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