Estimates of Oil Generation Temperature Based on a Kinetic Recalibration of Heptane Distributions

Requejo, A.G., Geochemical Solutions International, The Woodlands, TX

Thermal maturity estimates of the generation temperature of oils and condensates based on the heptane (C7) ratio 2,4-dimethylpentane/2,3-dimethylpentane (2,4-DMP/2,3-DMP) have become an industry standard. This ratio is thought to be independent of source rock heating rates, age, kerogen type and lithology. However, application to gas condensates or fluids generated at high heating rates often yield anomalously low temperatures, suggesting some dependence on source type as well as rate of heating. A kinetic-based re-calibration of the 2,4-DMP/2,3-DMP ratio is proposed that accounts for variations in heating rates and incorporates source rock type based on fluid chemistry. Its application to thermal classifica­tion of oils and condensates in various offshore hydrocarbon basins is demonstrated, including Trinidad, Nigeria and Brazil.