Origin of condensates and natural gases in the Almond Formation reservoirs in southwestern Wyoming, USA

Condensates and natural gases are significant resources that frequently occur together in many petroleum systems. Unraveling their origins is crucial for effective petroleum exploration and exploitation. This is often a challenge because light crudes are volatile, deficient in biomarkers, and commonly altered. The origin of condensates and natural gases in the Upper-Cretaceous Almond Formation in southwestern Wyoming was unraveled through use of improved analytical and interpretative geochemical approaches constrained by regional geologic perspectives and basin modeling. Here, an improved GC-MS/MS method allowed simultaneous determination of saturate and aromatic biomarkers, diamondoids, and organo-sulfur compounds in the whole crudes. Furthermore, basin-specific calibration of diamondoid-based thermal maturity parameters, through correlation of measured indices for diamondoids in rock extracts versus measured reflectance of vitrinite from the same rocks, allowed reliable interpretation of maturity of the most likely source rocks. Modified interpretation schemes for C7-hydrocarbon distributions, and compositions of C1-C30 alkanes, aromatic and organosulfur compounds, and δ13C1-C5 together indicated that the condensate and natural gas from each well are likely co-generated and thermogenic products from non-marine source rocks, although methane is partially biogenic. The bulk thermogenic petroleum are too mature to have originated in the rocks adjacent to the producing reservoirs. The geochemical, geologic, and modeling interpretations collectively indicate that the condensates and associated natural gases were most likely generated, expelled, and migrated from the downdip, highly mature, near-shore/transitional humic source rocks of the Almond Formation/Mesaverde Group in the Washakie Basin and Great Divide Basin at >1.3% Ro and ∼30 Ma.