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The generation mechanism of abiogenic alkane gas and whether the gas has industrial values are the focus of international attention. CH4 generated by Fischer–Tropsch synthesis is an important constitutent of abiogenic alkane gas. The study on the components, isotopic compositions, and crust-mantle mixing model indicates that, the alkane gas from the Qingshen gas field in the Songliao Basin is contributed by abiogenic alkane gas from Fischer–Tropsch synthesis, besides the mantle-derived abiogenic alkane gas. The authors have selected the endmembers of typical biogenic and abiogenic gases and conducted mixed source calculation. The abiogenic alkane gas accounts for over 60 × 109 m3 in the proven reserves of the gas field, in which the amount of CH4 generated by Fischer–Tropsch synthesis exceeds 9.6 × 109 m3. The calculation results indicate that, abiogenic alkane gas under organic–inorganic interactions can form commercial accumulations. Since typical biogenic gas is predominant in conventional gas pools, and high- to over-mature coal-derived gas displays a certain similarity with abiogenic alkane gas, the typical characteristics of abiogenic gas is concealed. Therefore, abiogenic alkane gas generated by organic–inorganic interactions may exist widely in petroliferous basins, and its contribution to gas pools may be underestimated previously.

The stability analysis of damaged landslides and unstable debris is important for rescue work and emergency operations. This paper investigates a predisposed geological emergence, inducing the factors and deformation processes of the Zhongbao landslide, which happened on July 25, 2020. The stability of the landslide debris was evaluated by an integrated monitoring system consisting of ground-based radar, unmanned aerial vehicles, airborne Lidar, thermal infrared temperature monitoring, GNSS displacement monitoring, deep displacement monitoring, and rainfall monitoring. The strata and weak layer controlled the landslide failure, and topography defined the boundary of the failed rock mass. A continually intensive rainfall caused the deformation and accelerated failure of the landslide. The shallow and steep deposit (Part I) firstly slid at a high velocity, and then pushed the rear part of the landslide (Part II) to deform, forming numerous cracks, which accelerated the rainfall infiltrating into the rock mass. The moisture content increase could decrease the strength of the shale rock within the bedding planes. Finally, with the rock and soil mass sliding along the weak layer, a barrier dam and a barrier lake were formed. The monitoring and numerical simulation results showed that after the landslide failure, there was still local collapse and deformation occurrences which threatened rescue work and barrier lake excavation, and the stability of the accumulation area gradually decreased as the rainfall increased. Therefore, the barrier dam was not excavated until the accumulation rate gradually stabilized on July 28. Moreover, most of the reactivated deposits still accumulated in the transportation and source areas. Thus, in August, the displacement of the landslide debris gradually accelerated in a stepwise manner, and responded strongly to rainfall, especially in the accumulation area, so that it was inferred that the damaged landslide could slide again and cause a more threatening and severe failure. The analysis results of the study area can provide references for the failure mechanism of a rainfall-induced landslide and the stability evaluation of a damaged landslide.

The sources and origins of polycyclic aromatic hydrocarbons (PAHs) in thirty eight Paleogene organic-rich shales and mudstones from the Shahejie Formation in the Dongying Depression, Bohai Bay Basin have been assessed. Phenanthrene, retene, cadalene, fluoranthene, pyrene, benz[a]anthracene, triphenylene, chrysene, benzofluoranthenes, benzo[e]pyrene, benzo[a]pyrene, indeno[1,2,3-cd]pyrene, benzo[ghi]perylene and coronene were identified in the sediments. The symmetrical 4-ring triphenylene was unequivocally identified by comparison with mass spectra and a synthetic standard. Key PAH ratios including fluoranthene/(fluoranthene + pyrene), benzo[a]anthracene/(benz[a]anthracene + chrysene), indeno[1,2,3-cd]pyrene/(indeno[1,2,3-cd]pyrene + benzo[ghi]perylene) and benzofluoranthene/(benzofluoranthene + benzo[e]pyrene) indicate a mainly diagenetic/catagenetic origin for the PAHs. The relative low abundance of the 6-ring indeno[1,2,3-cd]pyrene and benzo[ghi]perylene and the 7-ring coronene suggest the absence of larger, high temperature wildfires, either due to inadequate seasonality of the humid-arid climate, or limited terrigenous organic matter input. Phenanthrene and alkylphenanthrenes are likely derived from phytoplankton, based on the correlation of the relative abundance of C27 regular steranes and 1-methylphenanthrene and 9-methylphenanthrene. The methylphenanthrenes, triphenylene, alkyltriphenylenes and benzo[e]pyrene may share a common source as their occurrences are closely correlated. Four groups of samples were differentiated on the basis of the relative abundance and distribution patterns of benz[a]anthracene, triphenylene and chrysene, showing that these compounds are useful PAH markers in petroleum geochemistry. Thermal maturation effects are the major control on the relative abundance and distribution of the non-combustion derived PAHs (e.g. biphenyl, fluorene, fluoranthene, pyrene, benz[a]anthracene, triphenylene) in lacustrine sediments. Benz[a]anthracene decreases in relative abundance while triphenylene increases in relative abundance with burial depth. Correlation of the newly defined triphenylene-chrysene ratio (TCR; triphenylene/(triphenylene + chrysene) with burial depth and biomarker maturity parameters was observed, suggesting that it may be a useful maturity indicator for lacustrine oils and sediments in the Dongying Depression.

Lacustrine organic-rich source rocks (shales and mudstones) were examined to assess the depositional environment and organic input sources of the third and fourth members of the Eocene Shahejie Formation, Bohai Bay Basin, China. Major organic contributions to the Shahejie Formation from dinoflagellates, diatoms, Botryococcus and marine pelagophyte/chrysophyte algae were determined using n-alkane distributions, gammacerane index and diagnostic steranes. Traces of higher plant biomarkers suggest that terrigenous organic inputs were limited. The pervasive presence of β-carotane, aryl isoprenoids, paleorenieratane, renieratane, isorenieratane, 2α-methylhopanes and crocetane indicate significant organic contributions from bacterial communities including cyanobacteria, purple sulfur bacteria (Chromatiaceae), green sulfur bacteria (Chlorobiaceae), and sulfate-reducing bacteria. The extent of H2S content, bacterial sulfate reduction, and photic zone euxinia (PZE) were evaluated by determining the aryl isoprenoids ratio (AIR: 0.7–9.0), the presence of isorenieratene derivatives, and the fate of sulfur in the water column. There was a decrease of PZE extent and duration from the northeast to the southwest of the palaeo-lake, and there was a decrease of water body salinity and bottom water anoxia from the fourth to the third member of the Shahejie Formation. Abrupt environmental perturbations in the third member of the Shahejie Formation are indicated not only by significant changes in parameters such as the pristane/phytane and β-carotane/n-C20 alkane ratios, the gammacerane index, the isorenieratane/C18 aryl isoprenoid, and the AIR, but also by the time lag in the expansion of cyanobacterial lineages after the expansion of purple/green sulfur bacteria, as well as seawater incursions. The unexpected occurrence of intact C30 4-desmethylsteranes (24-n-propylcholestanes) in the Shahejie Formation is first reported here, after very careful checking, and provides unambiguous biological evidence for at least two marine transgression events reaching the Eocene Dongying palaeo-lake. The organic enrichment of the petroleum source rocks in the Shahejie Formation is a consequence of combined indigenous lacustrine algal production, the constrained and favourable preservation conditions, and significant bacterial contributions and marine organic matter inputs to the lake.

The Northeastern Laizhouwan Sag (NLS) is a marginal sag in the Bohai Bay Basin, China. Paleogene source rocks from 3 wells (K-a, K-b and K-c) in this region, i.e., the third to the first member of the Shahejie Formation (Es3, Es2, and Es1), and the third member of the Dongying Formation (Ed3) were investigated for their petroleum potentials and depositional environments using geochemical and palynological methods. Among these members, the Es3 and Es1 members hold considerable hydrocarbon potential, while the rest are relatively fair. Although there are variations between the wells, the organic matter (OM) in the Es3 member is primarily composed of low mature or mature type I-II1 kerogen, which were primarily contributed by lower aquatic organisms and prokaryotes. During the Es3 stage, saline, stratified, and anoxic bottom water prevailed in the K-a well, while freshwater and weak reducing conditions dominated the K-b well. The OM in the Es1 member was contributed more by lower aquatic organisms than that in the Es2 member, but both are primarily composed of types II1-II2 kerogen; further, OM in the Es2 member is low mature, while that for the Es1 member ranges from immature to low mature, and higher maturity is expected in deeper buried places for the two members. Saline and anoxic bottom water prevailed during the both Es2 and Es1 members. Compared with other members, noticeable terrigenous OM was deposited during the Ed3 stage, which is dominated by immature type II2 kerogen. Lower salinity and weak reducing depositional conditions occurred in the Ed3 member. OM enrichment in the Es3 member was mainly determined by primary productivity, while that of the K-a well was also enhanced by the anoxic bottom water condition. The accumulations of OM in other members are speculated to have been controlled by the deposition rate.

Micro-variations of lipid hydrocarbons and biomarkers in well-laminated shales have not been extensively documented, especially within different rock textures, fabrics and mineralogies. Comparison of a pyrite cemented zone and its surrounding sediment may offer a new perspective on mineral control on preservation of hydrocarbons and organic carbon. A black well-laminated shale comprising two adjacent and contrasting calcareous (light) and pyrite (dark) laminae at the millimetre scale was selected from the Eocene Shahejie Formation, Dongying Depression, Bohai Bay Basin. It was horizontally sliced to separate a pyrite cemented concretion from the unaltered laminated shale, and investigated using geochemical techniques to assess the heterogeneity of elements, minerals, microfossils and hydrocarbons within the two slices. Micro-scale changes in source inputs were noted. For instance, the 4α-methylsteranes, dinosteranes and the triaromatic dinosteranes show varying distributions between the two slices, attributed to slight differences in dinoflagellate contributions. Similarly, variation in the amount of bacterial sulfate reduction is indicated by variations in the aryl isoprenoid ratio, relative amount of isorenieratane, long-chain n-alkane carbon isotopic composition and other molecular indicators including the relative amounts of dibenzothiophene, dibenzofuran, methyldibenzothiophene and methyltrimethyltridecylchromans. The primary control on these variations appears to be different euxinic water conditions, but diagenesis has also influenced the distributions. Differential anaerobic bacterial reworking of organic matter and pyrite concretion protection are responsible for organic geochemical variations on a millimetre-scale in the shale. The pyrite concretion has an altered record of its thermal history, but has a more accurate record of the organic geochemistry of microfossils and water column conditions. This study shows the potential for future investigations of closely-spaced vertical variation in organic geochemical parameters that may shed light on rapid temporal variation in organic matter input and depositional environment.