Micro-occurrence characteristics and charging mechanism in continental shale oil from Lucaogou Formation in the Jimsar Sag, Junggar Basin, NW China.

The micro-occurrence characterization of shale oil is a key geological issue that restricts the effective development of continental shale oil in China. In order to make up for the lack of research in this area, this paper carries out a series of experiments on the shale oil of the Lucaogou Formation using a multi-step extraction method, with the aim of exploring the micro-occurrence types and mechanisms of shale oil in the Lucaogou Formation, as well as exploring its direct connection with production and development. In this paper, shale oil in the reservoir is divided into two categories: free oil and residual oil. The polar substances and OSN compounds are the key factors determining the occurrence state of shale oil. Abundant polar substances and OSN compounds can preferentially react with mineral surfaces (including coordination, complexation, ionic exchange, and so on) to form a stable adsorption layer, making it difficult to extract residual oil in actual exploitation. Free oil is mainly composed of aliphatic hydrocarbons, and its adsorption capacity is related to the length of the carbon chain, i.e. long carbon chain, strong adsorption capacity, and poor movability. Free oil is widely stored in pores and cracks, and that with high mobility can be the most easily extracted, making it the main target at present exploitation. In the current state of drilling and fracturing technology, research should prioritize understanding the adsorption and desorption mechanisms of crude oil, particularly residual oil. This will help optimize exploitation programs, such as carbon dioxide fracturing and displacement, to enhance shale oil production.

A mobile-immobile model for contaminant transport through GCL/AL composite liner: analytical solutions.

The current study focuses on developing alternative formulations (mobile-immobile model) of transient analytical modelling for organic contaminant transport in a composite of geosynthetic clay (GCL) and attenuation layer (AL) system. The Laplace transform method is adopted to derive the solution. The proposed analytical frameworks are validated by two set of benchmarks. The varied examples of organic contaminant transport in the composite liner are evaluated by the proposed solution to discuss the effects of soil properties, flow conditions, adsorption, and mass transfer in mobile and immobile zones on the overall transport of contaminants. Finally, an example case is presented to show the application prospect of the proposed model. The result demonstrated that mass transfer between mobile and immobile may increase the breakthrough time by a factor of 2. This indicates that heterogeneities of clay are a non-negligible part for the performance assessment of the liner system. Péclet number in GCL ([Formula: see text]) is used to investigate the relative importance of advection and diffusion mechanisms. Increasing [Formula: see text] from 0.1 to 1 can lead to an increase of the breakthrough time by a factor of 15. The analytical solutions presented here may also serve as the basic benchmark test tool for alternative numerical studies of contaminants transport in heterogeneous media.

Comparative Study on the Elucidation of Sedimentary Phosphorus Species Using Two Methods, the SMT and SEDEX Methods.

Sedimentary phosphorus (P) forms are important representatives of P sources and their bioavailability as well as the potential of sediments to release P in water. In this study, surface sediments along a transect of the Changjiang Estuary and two transects along the Andong salt marsh in the southwest of Hangzhou Bay were subjected to the elucidation of sedimentary P species using the standards, measurements, and testing (SMT) and sequential extraction (SEDEX) methods. The results showed that the mean sedimentary P forms elucidated by the SMT method were as follows: organic P (OP; ∼11-14 mg/kg; ∼30-45% of total P; TP) > apatite P (∼5-15 mg/kg; ∼21-36% TP) > Fe/Al-P (∼8-14 mg/kg; ∼31-34% TP), with inorganic P (IP) composing 54-70% of TP. The mean sedimentary P forms elucidated by the SEDEX method were as follows: authigenic P (∼54-68 mg/kg; ∼41-46% TP) > extractable P (Ex-P; ∼36-53 mg/kg; ∼28-34%) > Fe-P (∼21-27 mg/kg; ∼13-19%) > OP (∼8.7-13 mg/kg; ∼5-8%) > detrital P (De-P; ∼2 mg/kg; ∼1-2% TP), with IP composed of ∼91-94% TP. These results showed that the SEDEX method elucidated higher concentrations of sedimentary P forms as well as the TP from these coastal sediments although the SMT method had the advantage of being more economic and faster. The results of both the SMT and SEDEX methods showed that the Andong salt marsh and Changjiang Estuary sediments had much bioavailable P. The mean percentages of bioavailable P from the SMT and SEDEX methods were ∼64-74% and 52-56% of TP, respectively, indicating that these sediments were prone to release P to the coastal areas.

An analytical solution to contaminant diffusion in semi-infinite clayey soils with piecewise linear adsorption.

The adsorption of contaminants onto soil particles typically is nonlinear if the contaminant concentration is sufficiently high. A simplified piecewise linear adsorption isotherm consistent with experimental results is proposed as an approximation for nonlinear adsorption behavior. This approximation allows for the use of analytical solution to model solute diffusion of contaminants that exhibit nonlinear adsorption. A moving boundary is introduced to represent significant changes in the retardation factor of clay with an increase in solute concentration. The proposed analytical solutions were validated using experimental data presented in the literature. There is negligible difference between the results obtained by the proposed analytical solution and those obtained by the linear model when C(m)/C(0) reached 0.5. The results also show that the model based on linear adsorption using the initial secant of the Freundlich isotherm leads to significantly lower estimated breakthrough time for the contaminant of interest than that obtained using the proposed model. The earlier breakthrough is due to an under-estimation of the amount of adsorption. The proposed method is relatively simple to apply and can be used for evaluating experimental results and verifying more complex numerical models.