Bureau of Economic Geology, The University of Texas at Austin (www.beg.utexas.edu).
SEPM Permian Basin Monthly Luncheon, Midland, Texas, February 17, 2004
Textures, Fabrics, and Petrophysics of the Ghawar Field, Saudi ArabiaThe Largest Oil Field in the WorldAnd It's a Shallow-Water Carbonate
F. Jerry Lucia
It is always instructive to study the great oil fields of the world to see what makes them great and to compare them with Permian Basin oil fields. The Ghawar field in Saudi Arabia is the largest and arguably the most productive oil field in the world. The field produces from limestones and dolostones of the Arab D Formation of Late Jurassic age and covers some 10,000 square kilometers. A complete range of limestone fabrics are present: grainstone, grain-dominated packstone, mud-dominated packstone, wackestone, and mudstone, which are generally arranged in an upward-shallowing succession over a gross interval of about 300 meters. The reservoir is capped by a thick anhydrite unit. Dolostones are typically large crystalline, and the precursor texture cannot be determined. Porosity values range from 1 to 30 percent, and permeability ranges from <0.1 md to more than 1 Darcy. There is little calcite cement, and porosity reduction is mostly due to compaction. Permeability is related to interparticle porosity and rock fabric. Little separate-vug porosity is present, so total porosity can be assumed to be interparticle porosity. The rock fabrics fall into the same petrophysical classes as defined by fabrics from the Permian Basin, with the exception that the porosity and permeability values tend to be higher. Permeability is estimated from wireline logs by substituting rock-fabric information, obtained from saturation-porosity relationships, and porosity, obtained from porosity logs, into the global transform equation. Integrating data from the Ghawar field with data from the Permian Basin confirms and strengthens fundamental relationships between rock fabrics and petrophysics.