Spatial Variations in Methane Content and Their Main Controlling Factors of the Deep‐Buried Coalbed in the Nalinhe–Hengshan Area, Ordos Basin

Coal contains mineral matter that will be left as ash after coal is burned. Coal will be referred to as dirty coal if the ash content of the coal is high. High ash content is not preferred by consumers of coal users especially coal fired power plants, because ash content will produce fly ash and bottom ash that cause environmental problem. The process of ash content reduction by solvent extraction would produce coal with very low ash content (near zero) known as ash free coal (AFC). The study of ash content reduction was conducted by using Peranap coals that were taken from stockpile and mine site. The coals were then washed and separated into coals with low and high ash contents. The high ash content of coals from stockpile (46.02%) and mine site (25.02%) were then extracted using solvent. Three kinds of solvent have been tested, namely 1-methyl naphthalene, 1-1-1-methoxy ethoxy acetic acid and N-methyl 2 pyrolidynon. The results indicate that the ash content of coal derived from the stockpile decreased to 0.06% and coal from the mine site decreased to 0.11% by using 1-methyl naphthalene solution with a ratio of coal and solvent of 1: 6 (weight/weight).

Geological prediction models for gas content in marine–terrigenous shale under the effects of reservoir characteristics and in situ geological conditions, were established using methane isothermal adsorption, high temperature/pressure methane isothermal adsorption, total organic carbon, X-ray diffraction, mercury porosimetry, porosity in net confining stress, and field desorption methods. Results indicated that the adsorption capacity of marine–terrigenous shale has a linearly positive correlation with total organic carbon content and maturity. Clay and quartz minerals are the two main components of inorganic minerals in marine–terrigenous shale, with an average content of 54.3% and 36.9%, respectively. Adsorption capacity of marine–terrigenous shale is slightly positive correlated with clay content, while it exponentially decreases with increasing quartz content. The effects of in situ temperature and reservoir pressure on adsorption capacity in marine–terrigenous shale are also significant. The adsorption capacity of marine–terrigenous shale shows a clear decreasing trend as temperature increases, while it increases with increasing reservoir pressure. The porosity of marine–terrigenous shale is characterized by highly stress-sensitive, decreasing exponentially with increasing effective stress, which results in a more complex occurrence of free gas in deep shale reservoirs. In addition, gas saturation for the shale samples was calculated based on the results of field desorption, after which geological prediction models of total gas, adsorbed gas, and free gas were established while considering the coupled effects. Adsorbed gas, free gas, and total gas content all initially increase as burial depth increases, and then eventually decrease. Adsorbed gas content and free gas content have a positive correlation with total organic carbon content and porosity, indicating that the total gas content at different burial depths is mainly controlled by the total organic carbon content and porosity.

Logging evaluation of free-gas saturation and volume content in Wufeng-Longmaxi organic-rich shales in the Upper Yangtze Platform, China

Evaluation of gas content prediction models for deep coal seams: A case study from the Daning–Jixian Block, Eastern Ordos Basin

Micro- and nano-scale pores develop in shale reservoirs, and the associated pore structure controls the occurrence state, gas content, seepage capacity, and micro-migration and accumulation mechanisms of shale gas. For this study, we mainly conducted tests, using field emission-scanning electron microscopy, of the isothermal methane adsorption of powder-sized samples under high temperatures (60–130 °C) and pressures (0–45 MPa), along with methane-saturated nuclear magnetic resonance tests of plug-sized samples under different temperatures (60–100 °C) and pressures (0–35 MPa). These samples were from Longmaxi shale cores from strata at different burial depths from the Zhaotong, Weiyuan, and Luzhou areas. As the burial depth increases, organic pores transform from complex networks to relatively isolated and circular pore-like structures, and the proportion of organic matter-hosted pores increases from 25.0% to 61.2%. The pore size is influenced by the pressure difference inside and outside the pores, as well as the surface tension of organic matter in situ. As the burial depth increases to 4200 m, the main peak of the pore size first increases from 5–30 nm to 200–400 nm and then decreases to 50–200 nm. This work establishes an NMR method of saturated methane on plug-sized samples to test the free gas content and develop a prediction model of shale reservoirs at different burial depths. The gas content of a shale reservoir is influenced by both burial depths and pore structure. When the burial depth of the shale gas reservoir is less than 2000 m, inorganic pores and microfractures develop, and the self-sealing ability of the reservoir in terms of retaining shale gas is weak, resulting in low gas content. However, due to the small pore size of organic pores and the low formation temperature, the content of adsorbed gas increases, accounting for up to 60%. As the burial depth increases, the free gas and total gas content increase; at 4500 m, the total gas content of shale reservoirs is 18.9 m3/t, and the proportion of free gas can be as high as 80%. The total gas content predicted by our method is consistent with the results of the pressure-holding coring technique, which is about twice our original understanding of gas content, greatly enhancing our confidence in the possibility of accelerating the exploration and development of deep shale gas.

Deep coalbed methane (CBM) is a crucial resource for ensuring energy security. Despite some successful localized deep CBM developments, the unclear understanding of gas content and gas occurrence state remains a key obstacle to the comprehensive development of deep CBM. This study utilizes data from pressure‐preserved coring and wireline coring gas content tests, isothermal adsorption tests, and well test temperature and pressure data to establish a methodological model. This model corrects the gas content obtained from wireline coring and determines the gas occurrence state. The gas content, including adsorbed and free gas content, and gas/water saturation were calculated, and the controlling factors were analyzed. The results reveal that the high values of total gas content and adsorbed gas content are concentrated in the southwestern part of the study area. The adsorption capacity of the coal, influenced by its degree of metamorphism, is identified as the primary factor affecting the total gas content and adsorbed gas content. Furthermore, the high values of free gas content are primarily concentrated at the northwestern edge of the study area. The main factors affecting the porosity difference of free gas are coal metamorphism type and inertinite content. Areas affected by magmatic thermal metamorphism and those with high inertinite content tend to have higher porosity. Additionally, pressure, rather than temperature, is identified as the main factor determining the density of free gas. These findings provide a relatively simple indirect method for obtaining deep CBM content and occurrence state, particularly for studying the free gas content in deep coal seams. This approach is aimed at offering theoretical support for the development of deep CBM in the middle Linxing block.

The exploration and development of deep marine shale gas has made significant breakthroughs, but factors influencing gas contents of deep marine shale are elusive, and quantitative prediction methods of gas content needs to be refined urgently. In this study, the deep marine shale of Longmaxi Formation in Luzhou area was taken as an example, vitrinite reflectance analysis, kerogen microscopy experiment, TOC content analysis, mineral composition analysis, gas content measurement, isothermal adsorption experiment, physical property analysis and argon ion polishing scanning electron microscopy experiment were carried out to find out factors affecting the gas content of deep marine shale, and a gas content prediction model has been worked out. Conclusions below have been reached: the content of adsorbed gas is mainly affected by Ro, TOC content, porosity, water saturation, clay mineral content, formation temperature and pressure; the content of free gas is mainly controlled by porosity, water saturation, formation temperature and pressure; according to the prediction models, the adsorbed gas content, free gas content and total gas content of each well were quantitatively calculated, and the study area was divided into Class I (with a total gas content ≥ 11 m3/t), Class II (with a total gas content between 9 m3/t and 11 m3/t), and Class III (with a total gas content < 9 m3/t) gas-bearing areas.

Quantitative characterization of the evolution of in-situ adsorption/free gas in deep coal seams: Insights from NMR fluid detection and geological time simulations

Co-pyrolysis of low ash content of coconut shell (CNS) and cashew nuts shells (CCS), and high ash content rice husk (RH) blends was performed using thermal gravimetric analysis (TGA). RH was blended with both CCS and CNS at 0, 30, 60, and 100% RH by mass. Results showed that CCS and CNS have low ash contents of 2.7 and 1.5%, respectively, while RH has high ash content of 26.7% on dry basis. TGA under nitrogen gas study was carried out at three heating rates of 10, 15, and 20 K/min. It was observed that the increase of CCS/CNS increased decomposition rates of blends. For example, RH increased from 6 to 7.7%/min when CNS was added. Furthermore, addition of low ash content leads to high decrease of maximum decomposition rates compared to high-high or low-low ash blends. Synergistic analysis has found out that a positive effect is observed when CNS/CCS is added to RH. The decrease of maximum decomposition temperature of 60–63°C compared to other studies of 10°C for all low and 40° for all high ashes is of great advantage. Flynn-Wall-Ozawa (FWO), Kissinger-Akahra-Sunose (KAS), and DAEM kinetic model analysis for 0.1 ≤ α ≤ 0.75 were used between 315 and 840°C. FWO model gave activation energy of 85, 70, and 75 kJ/mol, for RH, CNS, and CCS, respectively. Addition of low ash content biomass reduced activation energy of RH, activation energy of RH was reduced from 85 to 72 kJ/mol when CNS was added. RH requires high energy than the rest, example, RH needed 66.29 kJ/mol of energy compared to 51% of CNS and 56 kJ/mol for CCS. The entropy results were negative which implies a different orientation of molecules from origin samples properties. The Gibbs-free energies were positive and thus non-spontaneous process. Empirical models generated using SB model indicated that kinetics depends on reaction order and acceleration mechanism rather than diffusion and nuclei growth. Kinetically, the blending of high and low ash content biomass leads to high decrease of operating temperature and activation energy compared to low-low or high-high ash content blends. It has been recommended to further study on quality and quantity of product from such blends and the possibility of pre-treatment methods such as microwaves to improve pyrolysis of such blend.

Shale gas content is the key parameter for shale gas potential evaluation and favorable area prediction. Therefore, it is very important to determine shale gas content accurately. Generally, we use the US Bureau of Mines (USBM) method for coal reservoirs to calculate the gas content of shale reservoirs. However, shale reservoirs are different from coal reservoirs in depth, pressure, core collection, etc. This method would inevitably cause problems. In order to make the USBM method more suitable for shale reservoirs, an improved USBM method is put forward on the basis of systematic analysis of core pressure history and temperature history during shale gas degassing. The improved USBM method modifies the calculation method of the gas loss time, and determines the temperature balance time of water heating. In addition, we give the calculation method of adsorption gas content and free gas content, especially the new method of calculating the oil dissolved gas content and water dissolved gas content that are easily neglected. We used the direct method (USBM and the improved USBM) and the indirect method (including the calculation of adsorption gas, free gas and the dissolved gas method) to calculate the shale gas content of 16 shale samples of the Triassic Yanchang Formation in the Southeastern Ordos Basin, China. The results of the improved USBM method show that the total shale gas content is high, with an average of 3.97 m3/t, and the lost shale gas content is the largest proportion with an average of 62%. The total shale gas content calculated by the improved USBM method is greater than that of the USBM method. The results of the indirect method show that the total shale gas content is large, with an average of 4.11 m3/t, and the adsorption shale gas content is the largest proportion with an average of 71%. The oil dissolved shale gas content which should be paid attention to accounts for about 7.8%. The discrepancy between the direct method and indirect method is reduced by using the improved USBM method, and the improved USBM method could be more practical and accurate than the USBM method.

In our previous investigation on grain quality of Chinese spring sown wheat (Triticum aestivum L.), we sampled two sites from Inner Mongolia and got primary result of location effect on grain quality. To map out the regional planning of quality of spring wheat grown in Inner Mongolia, we need to study the effects of genotype, location, and their interaction on wheat quality systematically under different eco-regions. In the present experiment, we used 9 cultivars including strong (4), medium (3), and weak (2) gluten types, to evaluate main wheat quality traits including grain hardness, protein content, mixograph properties and starch pasting parameters. All cultivars were sown at 6 representative locations in Inner Mongolia with completely randomized block design in 2003 and 2004. The results indicated that all of the wheat quality traits tested were significantly influenced by genotype and location effects, and were also significantly affected by genotype by location interaction effect except for grain pro- tein content. The group of cultivars with strong gluten strength was characterized by high protein and ash content, high Zeleny sedimentation value, strong mixograph performance, medium flour yield, and good starch pasting parameters; the group of culti-vars with moderate gluten strength was characterized by high flour yield and strong mixograph properties, but low ash content and poor starch pasting quality; while the group of cultivars with weak gluten strength was characterized by high ash content, good starch pasting parameters, but low grain hardness, protein content, flour yield, and sedimentation value, as well as weak mixograph properties. Significant differences for all quality parameters across locations were observed. Samples collected from Wuhai generally showed high ash content, strong mixograph performance, but low grain hardness and sedimentation value, and poor starch pasting parameters. Samples from Hangjinhouqi had high flour yield, medium starch pasting parameters and mixograph properties, but low protein content and sedimentation value. Samples from Hohhot expressed high grain hardness, protein and ash content, sedimentation value, and strong mixograph properties, but poor milling quality and starch pasting pa- rameters; samples from Chifeng had medium values for all the traits; samples from Tongliao had high grain hardness and protein content, good starch pasting parameters, medium to strong mixograph properties, and medium for the other traits. Samples from Eerguna showed high protein content and sedimentation value, but weak mixograph properties. Based on the above information, Hohhot and Wuhai were the most suitable regions while Eerguna was not the suitable region for the production of cultivars with strong or medium strong gluten strength. It also showed that all the 6 locations were not suitable for the production of cultivars with weak gluten strength. The results provided some basic information for wheat breeding as well as quality wheat production zoning in Inner Mongolia.

Investigations Into the Nature of Phosphorus in Soil Humic Acids Using 31P NMR Spectroscopy

Experimental study on gas content of adsorption and desorption in Fuling shale gas field

Characteristics of particulate matter generated in pressurized coal combustion for high-efficiency power generation system

Gas occurrence characteristics in marine-continental transitional shale from Shan23 sub-member shale in the Ordos Basin: Implications for shale gas production