Summary

We demonstrate below that Tengiz Field was not uplifted and eroded by 4 km, as was previously proposed by one of us and other colleagues (Baskin et al., 1997; Hallager et al., 1997). Instead, maturity data are consistent with a more moderate 500m of erosion and uplift prior to the Artinskian. We interpret that the hydrocarbon charge is predominantly post-Kungurian (post-Permian), originating from postulated Devonian, Lower Carboniferous and Permian source rocks. This is significantly later than the initial Carboniferous hydrocarbon charge implied by earlier studies.

Both high and low bitumen and vitrinite reflectance populations exist in the pre-Artinskian section. The high reflectances appear to be restricted to the Bashkirian through Upper Visean, with low reflectance values present both above and below this interval. We suggest that the low reflectance population represents the burial trend, whereas the high reflectance population is due to some other geological process, such as localized heating by hydrothermal fluids or some as yet poorly understood low-temperature process involving organic-sulfur reactions.

Tests of various proposed heat flow histories against the existing temperature and maturity data show that there were no regional rift-type heating events in the Cenozoic and the Mid-to-Late Mesozoic. While rifting is possible in the Carboniferous, rifting in the Devonian would have had no impact on the maturation history at Tengiz.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah