Characterization of the pore size distribution of tight sandstone is of great significance for the effective development of tight oil resources. This paper analyzed the fractal characteristics of pore spaces of tight sandstones from the Yanchang Formation in the Ordos Basin of China with NMR and rate-controlled porosimetry (RCP). A new NMR fractal analysis method that considers the movable fluid distribution was proposed. Compared with the conventional NMR fractal analysis metrics, the fractal dimensions of the pore spaces occupied by completely movable fluid and partially movable fluid have stronger correlations with the tight sandstone petrophysical properties. This work shows that the fractal dimensions of pore spaces with partially movable and completely movable fluids are negatively correlated with the permeability and reservoir quality index (RQI), and as the fractal dimensions approach 3, the tight sandstone petrophysical properties become less favorable. The fractal dimensions of the pore spaces detected by RCP were calculated with three different fractal models, the thermodynamic model, the 3D capillary model, and the wetting phase model. The research results show that compared with the results of the other two fractal models, the fractal dimensions obtained from the 3D capillary model can be used to more accurately evaluate tight sandstone petrophysical properties, and the calculated fractal dimensions are strongly negatively correlated to the pore radius, sorting coefficient, skewness, and permeability. The fractal dimensions obtained from the thermodynamic model have no obvious relationship with the tight sandstone properties, and the wetting phase model gives opposite fractal analysis results, so these two fractal models are not recommended for fractal analysis of tight sandstone pore size distributions via RCP. Finally, the models for predicting tight sandstone permeability with NMR and RCP were evaluated and screened.

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Dietary sorghum distillery residue (SDR) showed antioxidant and blood thinning effects on grey mullet during winter, but inhibited their growth. The objective of this study was to establish a preliminary treatment of the dietary SDR with polyethylene glycol (PEG), a tannin-binding agent, to enhance growth and blood antioxidant capacity of grey mullet ( Mugil cephalus ) feed. The feeding trial was carried out from June to November. The water temperature was between 25 and 30 degrees C; the specific growth rate of mullet was reduced significantly by feeding diet containing 20% SDR in comparison to fish fed the control diet or diet containing 20% SDR and PEG. In the period of October-November, the water temperature decreased to 19-25 degrees C; the specific growth rates of the 20% SDR-PEG group and the 20% SDR group were 0.13 and 0.19% day(-1), respectively, significantly higher than those fed the control diet (0.07% day(-1)). Feeding with 20% SDR or 20% SDR-PEG diets resulted in prolonged lag phase of low-density lipoprotein (LDL) oxidation compared to fish fed the control diet. The total antioxidant capacity of the plasma of the grey mullet fed 20% SDR-PEG was 1.24 mmol/L, significantly higher than those in the fish fed 20% SDR diet (0.84 mmol/L) or the control (0.72 mmol/L). In vivo observations found that preliminary treatment of SDR with PEG eliminated the endogenous undesirable growth inhibitory factors but maintained its protective effects against LDL oxidation in blood and improved the total antioxidant capacity and cold adaptation of grey mullet. The ethanol extract of SDR contained 31.9 +/- 7.8 mg/g gallic acids equivalent. The concentration needed to scavenge 50% of the DPPH radicals (IC(50)) was 0.86 mg/mL. Increased gallic acid equivalent and decreased IC(50) of DPPH scavenging activity of SDR fed to fish increased the total antioxidant capacity in blood plasma of grey mullet significantly.

Gas flooding is a promising way to enhance oil recovery in unconventional oil reservoirs, but accurate identification of the distributions of movable and residual oil during gas flooding is difficult. In this study, the movable and residual oil distributions of tight conglomerate oil reservoirs during gas flooding are monitored with low-field nuclear magnetic resonance (NMR). The NMR T 2 spectra are converted into pore throat size distributions using a nonlinear conversion method in conjunction with high-pressure mercury intrusion, and then the lower limit of the pore throat size of movable oil under different pressure differences is determined. In addition, a mathematical model is proposed to predict the lower limit of the pore throat size of movable oil during gas flooding based on the capillary tube model and the fractal characteristics of pore structures in conglomerates. The research studies show that the model prediction results are very close to the results measured from experiments. The lower limit of the pore throat size of movable oil decreases with the increasing pressure difference of gas injection and decreasing core permeability. This study will be beneficial for characterizing residual oil distribution after gas flooding in unconventional oil reservoirs.

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