Yan-Rong Zou

Overpressure retardation of organic-matter maturation: a kinetic model and its application

Abstract A kinetic model, T–P–Ro, has been developed to address the issue that overpressure increases the activation energies during organic-matter maturation and that the retardation of organic-matter maturation by overpressure is due to the fact that organic-matter is hindered from progressive molecular ordering. Under overpressured conditions, the mean effective stress (i.e. mean stress minus pore pressure) is much lower and the pore pressure is usually higher than under hydrostatic pressure conditions. As a result, the progressive molecular ordering of the vitrinite, such as the aromatization, is retarded, and the vitrinite reflectance can hardly be increased. The reflectance values predicted by T–P–Ro model as it has been applied to the Well LD3011 at Yinggehai Basin in South China Sea, are similar to the measured ones. The kinetic model predicts that overpressure can cause the oil window floor and the peak oil generation to shift to greater burial depth. In the case of Yinggehai Basin, the local geological conditions are prone to generate light hydrocarbons and natural gas (instead of oil), hence they constitute the predominant products in this high temperature (heating rate) basin.

EasyDelta: A spreadsheet for kinetic modeling of the stable carbon isotope composition of natural gases

A new kinetic model and an Excel^(C) spreadsheet program for modeling the stable carbon isotope composition of natural gases is provided in this paper. The model and spreadsheet could be used to describe and predict the variances in stable carbon isotope of natural gases under both experimental and geological conditions with heating temperature or geological time. It is a user-friendly convenient tool for the modeling of isotope variation with time under experimental and geological conditions. The spreadsheet, based on experimental data, requires the input of the kinetic parameters of gaseous hydrocarbons generation. Some assumptions are made in this model: (1)the conventional (non-isotope species) kinetic parameters represent the light isotope species; (2)the initial isotopic value is the same for all parallel chemical reaction of gaseous hydrocarbons generation for simplicity, (3)the re-exponential factor ratio, ^1^3A/^1^2A, is a constant, and (4)both heavy and light isotope species have similar activation energy distribution. These assumptions are common in modeling of isotope ratios. The spreadsheet is used for searching the best kinetic parameters of the heavy isotope species to reach the minimum errors compared with experimental data, and then extrapolating isotopic changes to the thermal history of sedimentary basins. A short calculation example on the variation in @d^1^3C values of methane is provided in this paper to show application to geological conditions. ple on the variation in @d^1^3C values of methane is provided in this paper to show application to geological conditions.

Kinetic modeling the effects of primary migration, diffusion and waterwashing on Upper Paleozoic coal-derived gas at the center of Ordos Basin

Gold reactor pyrolysis system is used to model the gas formation from the Upper Paleozoic coal measures and the results show coal-derived gas characterized with δ13C1 of −33.46‰, δ13C2 of −23.1‰, dryness (C1/C1–4) 85.6%. And then, effects of the post-genetic processes on coalderived gas are analyzed in turn: (i) About 27% coal-derived gases constituted with more methane are calculated to be lost during diffusion. The residual in reservoir are characterized with almost the same compositions as the original, which suggests faint influence by diffusion (the residual, δ13C1 of −32.78‰, δ13C2 of −23.1‰, C1/C1-4 83%); (ii) Water washing made about 8% coal-formed gases lost and their components and stable carbon isotopes are stable; (iii) In the final, it is speculated that primary migration makes much more wet gas (C2–4) leave in coal measures. The variance of gas dryness induced by this factor is estimated to be about 10%.

Composition of Closed-System Fischer-Tropsch Synthesis Gases and the Constraint Factors

Biogenic gases were reported to exhibit a ‘‘normal’’ carbon isotope order, whereas abiogenic gaseous hydrocarbons in igneous rocks and meteorites exhibit a reversed order. In this study, closed-system Fischer–Tropsch synthesis was conducted at 350°C and 380°C under 30 MPa and 390°C under 30, 100, and 200 MPa, respectively, with magnetite as a catalyst. The results do not show an expected reversed order, even though the features of partially reversed order in carbon isotope values can still be commonly observed. Studies have shown that the essential constraint factor on the carbon isotopic pattern of abiogenic gases is the molar ratio of H2/CO2.

Origin and genetic family of Huhehu oil in the Hailar Basin, northeast China

The Huhehu Sag is one of the most important oil and gas depressions in the Hailar Basin. However, the origin of Huhehu oil is still controversial. Previous studies on source rocks have mainly focused on the Nantun Formation (K1n); a few studies have investigated the Damoguaihe Formation (K1d). Based on the Rock–Eval pyrolysis parameters, 172 drill cutting samples from the Huhehu Sag were analyzed to evaluate their geochemical characteristics. Based on the Rock–Eval data, the mudstones from the first member of the Damoguaihe Formation (K1d1) and the second member of the Nantun Formation (K1n2) have moderate to high hydrocarbon generation potential, while mudstones from the first member of the Nantun Formation (K1n1) have poor to good hydrocarbon generation potential. Additionally, both the K1n1 and K1n2 coal members have poor to fair hydrocarbon generation potential, but the K1n2 coal member has a better generative potential. Fifteen Huhehu oils were collected for molecular geochemical analyses to classify the oils into genetic families and to identify the source rock for each oil using chemometric methods. The Huhehu oils were classified into three groups with different maturity levels using hierarchical cluster analysis and principal component analysis. Group A oils (high maturity) are characterized by relatively moderate ratios of Pr/Ph, Pr/n-C17, and Ph/n-C18, as well as an abundance of C29 steranes, mainly derived from the K1n2 and K1n1 mudstone members. In comparison, group B oils (moderate maturity) have relatively low Pr/Ph ratios, moderate Pr/n-C17 and Ph/n-C18 ratios, and low concentrations of C29 steranes. Group C oils (low maturity) show relatively high ratios of Pr/Ph, Pr/n-C17, and Ph/n-C18, as well as high concentrations of C29 steranes. Furthermore, group B oils derived from the K1d1 mudstone member and group C oils derived from the K1n2 coal member were also identified by principal component analysis score plots. Correlation studies suggest a major contribution from the K1n mudstone Formation and the K1d1 mudstone member to the oils of the Huhehu Sag. So, the Nantun Formation and relatively shallow strata of the Damoguaihe Formation (e.g., the K1d1 member) represent important targets for future oil-reservoir exploration in the Huhehu Sag.