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Oil to Source Rock Correlation of the Lower Cretaceous in the East Texas Basin


Within the Lower Cretaceous section of the East Texas Basin, only the Albian Kiamichi/Goodland fms contain sufficient hydrogen-rich organic carbon to be considered viable source rocks. Where these units occur in salt withdrawl basins, they have a maturity and organic facies which allow for possible unconventional resource targets.

Four major organofacies within a Goodland Fm core from Anderson Co. are recognized (from core extracts) as revealed by changes with depth in key terpane, sterane and carbon isotope ratios. High C26 tricyclic terpane/Ts terpane and corresponding low C24 tetracyclic terpane/C23 tricyclic terpane ratios indicate a large upwelling signal for Facies UW. This appears to represent the maximum flooding surface coinciding with increased primary productivity and the most depleted carbon isotopes. This interval also has the highest sterane/terpane ratio indicating a predominance of algae over bacteria. Facies UW appears to correlate with global OAE 1c occurring ~100mya. In Facies F2, the biomarkers indicate a very different depositional environment of shallow anoxic waters with bacteria predominating and carbon isotopic enrichment. However, a few feet deeper in the section, the depositional environment reverts to more normal conditions (Facies F3). Facies F1 is similar to F2 except for the high proportion of red to green algae. The molecular rearrangement reaction forming diasteranes and diahopanes is catalyzed by silicate minerals. So, assuming a constant maturity, Facies F1 has the lowest dia- to regular ratios and is the most clay-poor (highest carbonate) while Facies F3 has more clay and less carbonate. The C19/C23 tricyclic terpane ratios often specify the relative distance from shore since C19 is a biomarker for terrigenous plants while C23 is more common in microorganisms. Facies UW and F1 have the lowest C19/C23 values (more distal) while Facies F3 and especially F2 are more proximal.

Each organofacies was statistically compared using biomarkers and carbon isotopes to 250 East Texas oils, including an oil produced laterally from the Goodland. Smackover and Eagle Ford-sourced oils in East Texas are well known, but a large group of oils were hypothesized to have originated from LK sources. The four Goodland organofacies explain the compositional variation of these LK oils.