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ABSTRACT: Clay Minerals Diagenesis and Vitrinite Reflectance Analysis in Hamzeh-4 Well, Azraq Basin, Jordan

Faraj S. Basim

One hundred and ten cutting samples and ten core chips were selected for this study. The samples were chosen from the shaley and argillaceous parts of Hamzeh-4 well, Azraq basin, Jordan. This well, compared to other wells in the Hamzeh oil field, is the deepest (3984 m), and contains the most complete stratigraphic section.

Thin section petrography, x-ray diffraction, vitrinite reflectance, scanning electron microscopy, and chemical analyses were used to investigate clay minerals diagenesis and its relationship to kerogen maturation.

The main diagenetic events observed are the illitization of smectites through an intermediate stage with mixed layering of illite/smectite to illite phase. The maturity of organic matter is observed through the vitrinite reflectance. Both events correlate well beyond the onset of oil generation (0.5 %Ro) 33600 m depth. Weaver Index and vitrinite reflectance shows a positive correlation coefficient of 0.5933 at 90% confidence level. Expandability of mixed-layers illite/smectite decrease from approximately 90% at 200 m, to a pure illite phase at peak oil generation of 0.8 %Ro at 3800 m depth.

Vitrinite reflectance revealed the existence of a higher paleogeothermal gradient (5°C/100 m) during the Ordovician to the Jurassic. A lower geothermal gradient did exist from the Early Cretaceous onward (present geothermal gradient is 2.2°C/100 m). The geothermal gradient was calculated by the thermal modeling of the Hamzeh-4 well using the MATOIL computer program. Furthermore, two major unconformities were shown to exist: (1) between the Triassic and Ordovician, with 2000 m of eroded sections and (2) between the Jurassic and Lower Cretaceous, with 650 m of eroded section.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990