The Role of Accurate Fluid Characterization in Source Rock Assessment: Insights from Middle-Upper Jurassic Carbonate Source Rocks in Arabia

The distribution of kerogen and its thermal maturity within petroleum source rocks is often associated with uncertainties and subjective interpretations, particularly regarding the impact of source-rock bitumen and free hydrocarbons (oils) on pyrolysis results. Various fluids─such as free hydrocarbons, expelled bitumen, and residual heavy hydrocarbons─can compromise the accuracy of these measurements and the initially measured total organic carbon (TOC). This study aims to examine the effects of free hydrocarbons and bitumen on estimates of source-rock thermal maturity and generative potential. The study presents Rock-Eval pyrolysis results for Jurassic carbonate source-rock samples with and without chemical solvent extraction. Data showed distinct changes in pyrolysis results after the removal of residual hydrocarbons. Postextraction data indicated an overall decline in S1 (from 2.4 to 0.5 mg/g rock), S2 (from 3.3 to 1.9 mg/g rock), and TOC values (from 8.1 to 7.2 wt%), despite a slight increase in T_max values (by approximately 4 °C). This research produced a refined data set that more accurately reflects the subsurface richness and thermal maturity, significantly enhancing the identification of reservoir organic richness and fluid characteristics. Furthermore, by clarifying the nature of hydrocarbons present (oil vs gas), this analysis mitigates uncertainties in resource estimations, thus yielding more tailored volumetric calculations based on the properties and behaviors of the hydrocarbons involved. (Figure presented.)