Source of Hydrocarbons in the Blue Ridge Oil Field, Fort Bend County, Southeast Texas Gulf Coast Basin

The source-formation environment and maturity of hydrocarbons from the Frio formation of the Blue Ridge field of the southeast Texas Gulf Coast Basin were determined by fingerprinting with high-resolution whole-oil gas chromatography (GC). Then, SARA fractionation into saturates, aromatics, resins, and asphaltenes by high-performance liquid chromatography (HPLC) followed by gas chromatography-mass spectrometry (GC-MS) analysis were completed for study by biomarker inversion. PetroMod2012 was used to predict the potential source rock and geologic history of the Blue Ridge field. Blue Ridge oil has an initial heavy-hydrocarbon oil charge that was biodegraded, then followed by influx of a lighter-hydrocarbon oil. GC and biomarker analyses show the heavier-hydrocarbon oil fraction likely formed in a suboxic/oxic, marl-dominated, terrestrial dominant to marine transitional environment with mainly higher-plant input. It was generated in the main oil generation window with %Ro from 0.7 to 0.8% at the expulsion temperature of 122 to 130°C. The oils were likely sourced from the Middle Wilcox or deeper beds, which entered the oil window from 26 to 15 Ma. Comparing biomarker and GC analysis of the Blue Ridge oil with the South Liberty and Brazoria oils, indicates that they share the same genetic family. The minor differences between the three oils are that the South Liberty and Blue Ridge oils contain more higher-plant input, whereas, the Brazoria oil contains more marine input. Comparing the maturity level of the three oils, indicates that the Blue Ridge oil has the same range of maturity as the Brazoria oil, whereas, the South Liberty oil is similar to, but a little more mature than, the Blue Ridge and Brazoria oils. The similar maturation level of the three oils also supports that they share a common maturation history and thus a common source.