Search

Petroleum resource assessment obtained from laboratory tests on old core samples shelved in the open environment tend to underestimate in situ resources. Therefore, hydrocarbon loss and its restoration need to be investigated. The hydrocarbon loss was studied via the difference of programmed pyrolysis parameter (Rock–Eval derived S1) between preserved/fresh cores and their replicas that had been long-term exposed to ambient conditions. However, the in situ hydrocarbon potential is still seemed to be underestimated, because the effect of sample crushing and crucible waiting on pristine S1 detection did not receive enough attention. To solve this issue, 50 preserved shale core samples with R o from 1.00% to 1.51% were collected from the K1qn1 Formation of northern Songliao Basin, Eastern China. All the samples were subjected to four parallel experiments: Dean–Stark extraction and nuclear magnetic resonance (NMR) T1–T2 mapping, using large rock pieces 3–5 cm in size, and thermal desorption gas chromatography (TD–GC) and Rock–Eval analysis, using 60-mesh powdered samples. In addition, a time series of TD–GC and Rock–Eval analyses were conducted on a preserved shale sample to investigate hydrocarbon loss during sample crushing, Rock–Eval crucible waiting process, and elapse-time exposure to the open environment. Rock–Eval pyrolysis was also conducted on one month-exposed shale cores and solvent-extracted samples. The results show that the total hydrocarbon content of large rock pieces is significantly greater than that of powdered samples. Sample crushing or grinding leads C 8− light hydrocarbons to evaporate, and results in a loss of approximately 35% of S1. Rock–Eval crucible waiting process causes C 14− hydrocarbons to evaporate, and results in an additional 25% loss of S1. To compensate for the sample crush induced S1 loss, an exponential distribution model was proposed based on the C 8+ hydrocarbons in the TD–GC S1 fingerprints. Sample maturity, pristine light hydrocarbon (C 14−) proportions, organic matter richness, and oil-bearing pore size primarily control the hydrocarbon loss of old shale samples. The higher the proportion of C 14− and the lower the abundance of organic matter, the higher the amount of hydrocarbon loss. Finally, S1 restoration coefficient charts for large rock pieces and powdered samples with R o ranging from 1.00% to 1.42% are provided. It highlights that previous studies have severely underestimated the in situ S1 when using the Rock–Eval method. This research has great implication for estimating in situ hydrocarbon potential using conventional coring samples. • In situ oil content can be determined by Dean-Stark and NMR T1-T2 mapping using large preserved shale rock pieces. • The C 8- hydrocarbons was restored based on the TD–GC S1 fingerprints using an exponential model. • Factors influencing hydrocarbon loss of old shale samples were discussed. • S1 restoration coefficients charts of large rock pieces and powdered samples were plotted. [ABSTRACT FROM AUTHOR]

The Carnian Pluvial Event (CPE) induced an intense carbon-cycle disturbance and biological crisis at a global scale. The eruption of the Wrangellia Large Igneous Province (W-LIP) is considered a possible triggering mechanism; however, this cannot fully explain the significant differences in environmental perturbations across different regions. In this paper, we present detailed records of petrography, mercury geochemistry, carbon and sulfur isotopes, trace elements, and provenance data for the Triassic lacustrine facies of the Ordos Basin in the North China Plate, which provide insights into the important effects of volcanic activities, other than the W-LIP, on palaeoenvironment during the CPE interval. Massive emissions of SO 2 , CO 2 , and pyroclastic deposits resulting from these volcanic activities triggered four humid episodes, each characterized by lake-level rise, negative δ13C org excursion, a transition from mudstones to organic-rich shales facies, as well as algal bloom within a time span of 180 kyrs. The establishment of an age framework in the Ordos Basin enables comparative analyses of environmental evolution during the Carnian age across the North China Plate, the western Tethys domain, and the South China Plate. During the period of global climate perturbation driven by the W-LIP eruption, we conclude that short-term localized volcanic activities may have further induced high frequentcy environmental perturbations, which influenced biological shifts and increase organic carbon burial. These short-term volcanic activities with different occurrence times and frequencies complicate local-scale palaeoenvironmental evolutions, which may be an important reason contributing to significant differences in environmental perturbations during the CPE interval across different regions of the globe. • Four humid episodes and sedimentary changes occurred within 0.18Ma in the Ordos Basin during Carnian age. • Environmental changes in the Ordos Basin was related to the local volcanisms in its nearby Qinling orogenic belts. • Short-term local volcanisms can complicate the environmental evolutions in different parts of globe during the CPE interval. • Local volcanic processes may cause inconsistent environment perturbation in different parts of globe during the CPE interval. [ABSTRACT FROM AUTHOR]