Post-Hydrocarbon Migration Deep Burial Diagenesis of Smackover Formation, Black Creek Field, Wiggins Arch, Mississippi Salt Basin

Ezat Heydari, Clyde H. Moore

The Smackover Formation is buried to over 6 km in Black Creek field and exhibits diagenetic phases unique to deep burial. These include replacement of sulfates by calcite, pore-fill calcite cement, silicification, and elemental sulfur as cement. The above diagenetic products are the result of thermal reduction of sulfates and thermal degradation of hydrocarbons and have formed at temperatures greater than 140°C.

Calcite replaces anhydride in two textural forms, one of which is pseudomorphic. Pore-fill calcite cement contains inclusions of pyrobitumen and heals cracks formed in the pyrobitumen due to high thermal maturity. This indicates that calcite cement postdates bitumen formation. Silicification is a major deep burial event. Micron to millimeter-size crystals of quartz replace the host carbonate rock as well as other deep burial diagenetic phases. Elemental sulfur occurs as inclusions in incompletely destroyed sulfates and as pore-fill cement. In both cases it exhibits extensive bubble-shaped cavities similar to "pumiceous texture" found in volcanic rocks. This indicates that elemental sulfur was possibly crystallized rapidly from a liquid sulfur while the cores were being taken.

Similar diagenetic products are formed by low-temperature (< 80°C) bacterial reduction of sulfates and bacterial degradation of hydrocarbons. However, carbon isotopic composition of calcite, sulfur isotopic composition of elemental sulfur, and textural characteristics of elemental sulfur produced by the two diagenetic processes are significantly different.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.