Tight sand gas is an important unconventional gas resource occurring widely in different petroleum basins. In coal-bearing formations of the Upper Triassic in the Sichuan Basin and the Carboniferous and Permian in the...Tight sand gas is an important unconventional gas resource occurring widely in different petroleum basins. In coal-bearing formations of the Upper Triassic in the Sichuan Basin and the Carboniferous and Permian in the Ordos Basin, coal measure strata and tight sandstone constitute widely distributed source-reservoir assemblages and form the basic conditions for the formation of large tight sand gas fields. Similar to most tight gas basins in North America, the Sichuan, and Ordos Basins, all experienced overall moderate uplift and denudation in Meso- Cenozoic after earlier deep burial. Coal seam adsorption principles and actual coal sample simulation experiment results show that in the course of strata uplift, pressure drops and desorption occurs in coal measure strata, resulting in the discharge of substantial free gas. This ac- counts for 28 %-42 % of total gas expulsion from source rocks. At the same time, the free gases formerly stored in the pores of coal measure source rocks were also dis- charged at a large scale due to volumetric expansion re- sulting from strata uplift and pressure drop. Based on experimental data, the gas totally discharged in the uplift period of Upper Paleozoic in the Ordos Basin, and Upper Triassic Xujiahe Formation in the Sichuan Basin is calcu- lated as （3-6） × 10^5 m^3/km^2. Geological evidence for gasaccumulation in the uplift period is found in the gas reservoir analysis of the above two basins. Firstly, natural gas discharged in the uplift period has a lighter carbon isotope ratio and lower maturity than that formed in the burial period, belonging to that generated at the early stage of source rock maturity, and is absorbed and stored in coal measure strata. Secondly, physical simulation experiment results at high-temperature and high-salinity inclusions, and almost actual geologic conditions confirm that sub- stantial gas charging and accumulation occurred in the uplift period of the coal measure strata of the two basins. Diffusive flow is the main mode for gas accumulation in the uplift period, which probably reached 56 × 10^12 m^3 in the uplift period of the Xujiahe Formation of the Sichuan Basin, compensating for the diffusive loss of gas in the gas reservoirs, and has an important contribution to the formation of large gas fields. The above insight has promoted the gas resource extent and potential of the coal measure tight sand uplift area; therefore, we need to reassess the areas formerly believed unfavorable where the uplift scale is large, so as to get better resource potential and exploration prospects.展开更多
Background： During tile last 3 decades, China has dramatic changes of the dietary pattern among its citizens, particularly in urban cities. This study aimed to determine the nutrient intake status and factors associa...Background： During tile last 3 decades, China has dramatic changes of the dietary pattern among its citizens, particularly in urban cities. This study aimed to determine the nutrient intake status and factors associated with nutrient intakes of urban Chinese pregnant women now-a-day. Methods： The multistage stratified random sampling method was applied in the cross-sectional study. 479 women in three trimesters of pregnancy from eight cities of China were recruited. Nutrient intakes were evaluated with one 24 h dietary recall, and compared with the Chinese Dietary Reference Intakes （DRIs） 2013 tbr available nutrients. Results： Most pregnant women had imbalanced macronutrient distribution with excessive energy derived from fat. Intakes of Vitamin A, B, calcium, magnesium, and selenium were below Chinese Recommended Nutrient Intake （RNI） and Estimated Average Requirements （EARs） in all trimesters. Most pregnant women took more tblic acid in the first trimester with a significant decrease in the second and third trimester （P 〈 0.05）. Shortfall in iron intake was tbund in the third trimester whereas some women may be at the risk of excessive iron intake. Intakes of thiamin met RNI in the first trimester but were below EAR in all trimesters. Trimester phasing was positively associated with most nutrients （P 〈 0.05）. Prepregnancy body mass index was inversely associated with energy, tht, Vitamin C, and calcium intake （P 〈 0.05）. Educational level and household income were positively associated with folic acid intake （P 〈 0.05）. Conclusions： Cunent prenatal dietary choices of urban pregnant women in China are imbalanced in the nutrient intake when compared with national DRIs 2013, particularly in intakes of energy derived from fat and micronutrients. Appropriate dietary advice to pregnant women should promote a balanced diet with emphasis on avoidance of foods of high fat content and incorporation of t＇oods that are good sources of the key micronutrients that are usually lacking in a regular pregnancy diet. Further research is needed to understand the eating habits and food patterns that contribute to this imbalanced diet in order to be able to effectively improve prenatal women＇s nutrient intake status.展开更多
文摘Tight sand gas is an important unconventional gas resource occurring widely in different petroleum basins. In coal-bearing formations of the Upper Triassic in the Sichuan Basin and the Carboniferous and Permian in the Ordos Basin, coal measure strata and tight sandstone constitute widely distributed source-reservoir assemblages and form the basic conditions for the formation of large tight sand gas fields. Similar to most tight gas basins in North America, the Sichuan, and Ordos Basins, all experienced overall moderate uplift and denudation in Meso- Cenozoic after earlier deep burial. Coal seam adsorption principles and actual coal sample simulation experiment results show that in the course of strata uplift, pressure drops and desorption occurs in coal measure strata, resulting in the discharge of substantial free gas. This ac- counts for 28 %-42 % of total gas expulsion from source rocks. At the same time, the free gases formerly stored in the pores of coal measure source rocks were also dis- charged at a large scale due to volumetric expansion re- sulting from strata uplift and pressure drop. Based on experimental data, the gas totally discharged in the uplift period of Upper Paleozoic in the Ordos Basin, and Upper Triassic Xujiahe Formation in the Sichuan Basin is calcu- lated as （3-6） × 10^5 m^3/km^2. Geological evidence for gasaccumulation in the uplift period is found in the gas reservoir analysis of the above two basins. Firstly, natural gas discharged in the uplift period has a lighter carbon isotope ratio and lower maturity than that formed in the burial period, belonging to that generated at the early stage of source rock maturity, and is absorbed and stored in coal measure strata. Secondly, physical simulation experiment results at high-temperature and high-salinity inclusions, and almost actual geologic conditions confirm that sub- stantial gas charging and accumulation occurred in the uplift period of the coal measure strata of the two basins. Diffusive flow is the main mode for gas accumulation in the uplift period, which probably reached 56 × 10^12 m^3 in the uplift period of the Xujiahe Formation of the Sichuan Basin, compensating for the diffusive loss of gas in the gas reservoirs, and has an important contribution to the formation of large gas fields. The above insight has promoted the gas resource extent and potential of the coal measure tight sand uplift area; therefore, we need to reassess the areas formerly believed unfavorable where the uplift scale is large, so as to get better resource potential and exploration prospects.
文摘Background： During tile last 3 decades, China has dramatic changes of the dietary pattern among its citizens, particularly in urban cities. This study aimed to determine the nutrient intake status and factors associated with nutrient intakes of urban Chinese pregnant women now-a-day. Methods： The multistage stratified random sampling method was applied in the cross-sectional study. 479 women in three trimesters of pregnancy from eight cities of China were recruited. Nutrient intakes were evaluated with one 24 h dietary recall, and compared with the Chinese Dietary Reference Intakes （DRIs） 2013 tbr available nutrients. Results： Most pregnant women had imbalanced macronutrient distribution with excessive energy derived from fat. Intakes of Vitamin A, B, calcium, magnesium, and selenium were below Chinese Recommended Nutrient Intake （RNI） and Estimated Average Requirements （EARs） in all trimesters. Most pregnant women took more tblic acid in the first trimester with a significant decrease in the second and third trimester （P 〈 0.05）. Shortfall in iron intake was tbund in the third trimester whereas some women may be at the risk of excessive iron intake. Intakes of thiamin met RNI in the first trimester but were below EAR in all trimesters. Trimester phasing was positively associated with most nutrients （P 〈 0.05）. Prepregnancy body mass index was inversely associated with energy, tht, Vitamin C, and calcium intake （P 〈 0.05）. Educational level and household income were positively associated with folic acid intake （P 〈 0.05）. Conclusions： Cunent prenatal dietary choices of urban pregnant women in China are imbalanced in the nutrient intake when compared with national DRIs 2013, particularly in intakes of energy derived from fat and micronutrients. Appropriate dietary advice to pregnant women should promote a balanced diet with emphasis on avoidance of foods of high fat content and incorporation of t＇oods that are good sources of the key micronutrients that are usually lacking in a regular pregnancy diet. Further research is needed to understand the eating habits and food patterns that contribute to this imbalanced diet in order to be able to effectively improve prenatal women＇s nutrient intake status.
