Total, Mobile, and Non-producible Oil: A Game-Changing Geochemical Method for Optimum Perforation Interval Selection and Eor Strategies

ABSTRACT In the oil industry, high-saturation zones often yield little to no oil flow despite promising petrophysical measurements. The original oil in place (OOIP) is estimated using core analysis and geochemical tests, but these estimates often change over time. Lewan and Sonnenfeld (2017) introduced low-temperature hydrous pyrolysis (LTHP) to improve reserve estimates by better quantifying mobile oil saturation. LTHP heats crushed mature source-rock core at 300°C for 12 to 24 hours, releasing retained oil similar to produced oil without generating new oil from bitumen or kerogen. This method also works for non-source rock tight-oil reservoirs, providing sufficient quantities of released oil to assess mobile oil, API gravity, and other properties. The examined well shows evidence of significant hydrocarbon saturations in primarily carbonate lithology reservoir sections, as identified by log evaluations. Core analyses indicate hydrocarbon saturations that resemble tar/bitumen with a potentially mobile oil component, supported by elevated S1 yields from programmed pyrolysis results. However, subsequent stimulation of these reservoir intervals resulted in low oil recovery despite the indications of good hydrocarbon saturation. The LTHP workflow was applied to core samples to measure: (1) vaporizable oil, (2) mobile/immobile oil, (3) total oil, and (4) EOR oil. The HRGC fingerprints of these oils were analyzed for geochemical parameters to identify the characteristics of the mobile oil and detect any secondary alterations like water washing or biodegradation. The results indicate that mobile oil is only a minor fraction (28% in high saturation zones) of the total in-situ oil. Vaporizable oil overestimates mobile oil likely due to the vaporization of immobile oil bound to tar/bitumen. Elevated total and mobile oil zones are free of dolomite. HRGC shows mobile oil has lost volatile compounds but retains n-alkane envelopes and molecular ratios indicating late oil window maturity from marine carbonate or shale sources. LTHP supplements conventional core analyses and pyrolysis, providing a true and collectable petroleum phase.