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The characterization of the pore structure of tight sandstones is of great importance for the exploration and development of tight oil reservoirs. However, little attention has been given to the geometrical features of pores with various scales, which implies that the effect of pores on the fluid flow and storage capacity is still ambiguous and presents a significant challenge to the risk assessment of tight oil reservoirs. This study investigates the pore structure characteristics of tight sandstones by applying thin section petrography, scanning electron microscopy, nuclear magnetic resonance, fractal theory, and geometric analysis. The results indicate that the tight sandstones have a binary pore system, consisting of small pores and combine pores. A shuttlecock model expresses the shape of the small pore. The radius of the small pore is comparable to the throat radius, and the connectivity of the small pore is poor. A spiny spherical model describes the shape of the combine pore. The connectivity of the combine pore is good, and the pore radius is larger than the throat radius. The most significant contribution to the storage space of the tight sandstones is attributed to the small pores, while permeability is primarily controlled by the combine pores. The heterogeneity of the combine pore has a strong positive correlation with flow capacity, which is associated with the multiple throats of the combine pores that developed during diagenesis. Therefore, the sandstones that are dominated by combine pores and are located near the source rocks represent the most favorable area for the exploitation and development of tight sandstone reservoirs.

Background: Many researchers have focused on exploring the association between patients’ nutritional status and clinical outcomes with some easy-to-reach indicators, especially in some carcinoma with high incidence. However, there was little attention on sarcomas and the objective of this study was to evaluate the prognostic value of some innovative nutrition associated indexes on patients with high grade osteosarcoma receiving surgical excision. Method: We retrospectively included patients’ clinical characteristics diagnosed as high grade osteosarcomas histologically receiving surgical excision from January 2008 to June 2018. Body mass index (BMI), Glasgow prognostic score (GPS), systematic inflammatory index (SII), and controlling nutritional (CONUT) score were calculated as nutritional associated factors to evaluate their prognostic value. The primary outcome was overall survival (OS) while the secondary outcome was the postoperative length of hospitalization. The relationship between clinical features and outcomes were performed by Cox and logistic regression analysis, respectively. The independent prognostic factors were chosen to construct predicted model whose internal and external accuracy were validated by concordance index (C-index), Brier score, and calibration plots.Results: High score of GPS predicted worse OS [HR (95% CI): 3.122 (1.982-4.918) versus 2.208 (1.014-4.804)] and higher rank of CONUT predicted poorer prognosis [HR (95% CI): 2.573 (1.616-4.097)] independently. The CONUT score was selected as the only prognostic factor on the length of hospitalization [HR (95% CI): 2.137 (1.270-3.596)]. The nomogram plots were used to visualize the results of predicted models whose performance was evaluated from the aspects of calibration and discrimination. Conclusion: Our study suggested prognostic value of nutritional assessment indexes including GPS and CONUT score that appropriate preoperative intervention which could optimize patients’ nutrition associated indicators may improve prognosis on patients with high grade osteosarcoma receiving surgical excision.Level of evidence: Level Ⅲ, prognostic study