ABSTRACT: Diagenetic Stratification in the Talisman Field, North West Shelf, Australia
ELLIS, GRANT K., Marathon, Perth, Western Australia, Australia, and SALLY E. PHILLIPS, Amdel Core Services, Frewville, South Australia, Australia
Oil is currently being produced from two clastic sequences in the Talisman field of the Dampier subbasin. The Late Jurassic to Early Cretaceous Angel Formation quartzarenites are characteristic of mass-flow deposits and the glauconitic nature of overlying Early Cretaceous Talisman Sandstone, reflects deposition on a continental shelf. These reservoirs have excellent porosity and permeability except in zones of authigenic siderite, ankerite, dolomite, and pyrite cementation which locally reduce reservoir quality. The Talisman structure, which is a tilted fault block, developed as a result of wrenching in the Early Cretaceous.
To ascertain the mineralogy and paragenetic sequence in the reservoir, cuttings and sidewall cores for seven wells were analyzed using x-ray diffraction, stable isotopes, electron microprobe and petrological techniques. The distribution of authigenic cements and their influence on reservoir properties were determined from wireline logs.
Micritic, low-magnesium siderite probably formed soon after deposition in association with glauconitic. This siderite is pervasive in the Talisman Sandstone but absent from the Angel Formation. Euhedral ankerite spar has partially replaced siderite in the Talisman Sandstone but in the Angel Formation ankerite precipitated below the oil-water contact. The source of iron for ankerite, high-magnesium siderite and pyrite may have been related to glauconite dissolution and/or aluminum substitution for iron in glauconite. These phases of cementation compartmentalized the reservoir, thus fluids below this interval were relatively iron deficient and as a consequence dolomite precipitated. Dolomite appears to be the final carbonate cement in the Angel Formation, concentrating at similar struct ral depths across the field.
AAPG Search and Discovery Article #91015©1992 AAPG International Conference, Sydney, N.S.W., Australia, August 2-5, 1992 (2009)