Integration of Middle Eastern Source-Rock Kinetics into a Regional Thermal-Maturity Model

Abstract

Abstract A regional thermal-maturity model of the Arabian Plate petroleum source rocks was constructed using ExxonMobil's Stellar ™ basin-modeling software. The model integrates plate-wide structural maps at 19 unconformities spanning the Phanerozoic era, with estimates of the amount of missing section at ten major unconformities (Figure 1) and is calibrated to regional temperature and maturity data. Timing of generation and volume of hydrocarbon yields are constrained by sourcerock kinetics. Kinetic parameters from the analysis of individual source rocks were used in conjunction with maps of sourcerock distribution to predict thermal maturity, volume and extent of oil and gas generation (Figure 2a; 2b; 2c). Volume and timing of generated hydrocarbon predicted from source-rock kinetic analyses have implications for regional hydrocarbon system evaluations. Several Middle Eastern organic-rich rocks were subjected to open-system programmed pyrolysis to determine the activation-energy distributions for petroleum generation. A burial rate of 1°C/m.y. was assumed. The resultant kinetic parameters were incorporated into the basin model and yield volumes were calculated. The source rocks were deposited in marine to restricted-marine environments and contain Type I or II Organic Matter. Oil generation curves for each source rock were compared to curves from "standard" Type I, II, IIS and III source rocks (Sweeney et al., 1987; Lewan, 1985; Lewan and Buchardt, 1989; Issler and Snowdon, 1990). The integration of Rock-Eval pyrolysis geochemical data with custom kinetics in numerical modeling indicates that source rocks of the Silurian Qusaiba Formation will generate light hydrocarbons at a lower maturity and over a wider range of maturity than other Middle Eastern marine source rocks, such as the Upper Jurassic Naokelekan Formation (Type I) and Cretaceous Shilaif Formation (Type I/II). The Silurian Qusaiba organic-rich rock is considered a Type-II source deposited in a marine environment (Luning et al., 2000; Grabowski, 2006). Qusaiba samples from Jordan were analyzed for organic-matter composition and petroleumgeneration kinetics. Total Organic Carbon (TOC) of our samples ranges from 2% to 11% and Hydrogen Indices (HI) range from 366 to 498 mg HC/g organic carbon. While the Qusaiba is a Type-II source rock, pyrolysates have relatively low concentration of higher molecular weight aliphatic groups compared to other Type-II marine sources. Based on these distributions, the Qusaiba will generate significantly higher proportions of condensate-range components compared to those generated from the other marine source rocks studied, regardless of level of thermal maturity or phase behavior. Kinetics analyses indicate a range of activation energies with 90% total generation occurring between Level of Organic Metamorphism (LOM) 9 (0.65% Ro equivalent) and LOM 11.25 (1.15% Ro equivalent). When transformation ratios calculated from custom kinetics are plotted against maturity, the resultant curve is similar to one for a "standard" Type-II source rock (Figure 3a). While there is generally agreement between the custom and "standard" oil generation curves for the Qusaiba, we know that the hydrocarbons it generates will not be the same as a typical Type-II source rock. The difference is a function of the unique composition of organic matter in the Qusaiba.