The implication of resolution of oil maturity parameters to the petroleum systems analysis
Oil maturity represents the extent of thermal stress which converts organic matter into petroleum in the source rocks, and the degree of oil cracking in the reservoirs. Petroleum systems are open or semi‐open in most basins, therefore the integration of spatial oil maturity fluid data for top down analysis can constrain the properties and size of source kitchen and scenarios of petroleum migration. This paper aims to discuss the resolution and precision of oil maturity parameters based on case studies from the Junggar Basin, which include 765 oil samples with systematic data for bulk properties, biomarkers, light hydrocarbons and aromatic hydrocarbons, and 158 oil samples with the absolute concentration and ratios of diamondoids. These oil maturity parameters were compiled into a refined geological framework and petroleum system model according to the spatial locations via Trinity 3D with Hotspot technology, and the most reasonable migration scenarios were selected to fit the fluid and source rock data spatially. Whole oil bulk properties (API gravity, GOR, saturation pressure, AARN fraction and whole oil GC fingerprint) were presented as a regular spatial change pattern along migration pathways, which are high resolution parameters and correspond easily to the expelled hydrocarbon from various organiofacies (C,D/E, and F) in the source kitchen during various maturation stages. Maturity data from steranes isomerization and aromatization, and methylphenanthrene index only exhibit the trend along migration pathways with poor resolution, The concentration of diamondoids and related ratios show the expected regular change only in the condensate stage, which makes them not suitable for assessing the oil window, Molecular level maturity parameters cannot provide higher resolution data than bulk fluid properties to calibrate petroleum maturity. Changes in bulk properties (API and GOR) directly reflect organofacies, maturation and phase fractionation, and the magnitude of the data varies greatly, while most molecular level maturity parameters vary less during hydrocarbon generation. Petroleum systems analysis emphasizes organic matter type or organofacies of source rocks, and provides the two component (gas and oil) or n‐component hydrocarbon generation volumes, which are related to the spatial trend of bulk properties (API, GOR etc. ) and PVT data of oil accumulation. Therefore bulk fluid properties, molecular level parameters and bottom up petroleum systems modeling should be synthesized and point in the same direction to establish the spatial and quantitative genetic relationship between petroleum accumulations and generated hydrocarbon from source kitchens.
AAPG Datapages/Search and Discovery Article #90349 © 2019 AAPG Hedberg Conference, The Evolution of Petroleum Systems Analysis: Changing of the Guard from Late Mature Experts to Peak Generating Staff, Houston, Texas, March 4-6, 2019