Evaluating the total oil yield using a single routine Rock-Eval experiment on as-received shales

Shales in the early maturity and oil window stages contain a considerable amount of heavy hydrocarbons (S-2oil) having strong interactions with kerogen/rock that make the accurate measurement of total oil (total extractable organic matter) more difficult from the routine Rock-Eval experiment. In this study, a fast method for evaluating the total oil yield using a single routine Rock-Eval experiment on as-received shales is proposed. First, the temperature threshold (T-OK) of the S-2oil and cracking hydrocarbons were determined by combining the pyrograms of the as-received shale with a solvent-extracted replicate. Then, the total oil yield was directly derived from the hydrocarbons evaporate at a temperature below than T-OK in a routine Rock-Eval experiment. The results show that the T-OK value is controlled by the sample's maturity and pore structure. The higher the maturity, the larger the specific surface area and the smaller the pore size, the greater the T-OK. A prediction model of T-OK was proposed based on the sample's production index (PI). The total oil yields estimated by the two methods of both the T-OK prediction model and the average T-OK value (465 degrees C) are consistent with those obtained by Jarvie (2012) using the thermal-extraction method with correlation coefficients of 0.983 and 0.9548, respectively. Compared with the previous methods, the single routine Rock-Eval experiment method proposed in this study is convenient and not requires an extraction experiment. In addition, there are archived routine pyrolysis data available that can be used to directly calculate the total oil yield based on the temperature threshold.