Search

Treating peat soil foundations around Dianchi Lake and Erhai Lake in Yunnan is a complex problem in practical engineering projects. Peat soil solely reinforced with ordinary cement (OPC) does not satisfy demand. This study aims to solidify soil to achieve better mechanical properties. The preparation of peat soil incorporates a humic acid (HA) reagent into cohesive soil, and cement and ultra-fine cement (UFC) are mixed by stirring to prepare cement soil samples. They are then immersed in fulvic acid (FA) solution to simulate cement soil in the actual environment. X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and pores and cracks analysis system (PCAS) tests are used to study the impact of the UFC on the microscopic pore structure of cement soil in a peat soil environment. The unconfined compressive strength (UCS) test is used for verification. The microscopic test results indicate that incorporating UFC enhances the specimen's micropore structure. The XRD test results show the presence of C–S–H, C–A–S–H, and C–A–H. SEM and PCAS tests show that the UFC proportion increases by between 0% and 10%, and the percentage reduction in the macropore volume is the largest, at 38.84%. When the UFC admixture is 30%, the cumulative reduction in the percentage of macropore volume reaches 71.55%. The MIP test results show that the cumulative volume greater than 10 µm in pore size decreases from 7.68% to 0.17% with an increase in the UFC proportion. The UCS test results show that the maximum strength growth of cement soil is 12.99% when the UFC admixture is 0–10%. Incorporating UFC to form a compound curing agent solves the problem of the traditional reinforcement treatment of peat soil foundation being undesirable and decreases the amount of cement. This study provides practical guidance for reducing carbon emissions in actual projects. [ABSTRACT FROM AUTHOR]

Using fracturing fluids to modify coal seams to boost their permeability is an essential way to address the technical challenges of the resourceful and efficient extraction of coalbed methane from coal reservoirs in China. However, some current fracturing fluids are toxic or corrosive and pollute groundwater resources, which becomes one of the obstacles to the development of fracturing and penetration technology. Five new types of composite clean fracturing fluids were developed in this paper with Yunnan anthracite coal in China as the research object. The changing rules of functional groups and pore structures, which have a vital influence on gas adsorption and permeability of the treated coal samples, were systematically explored through infrared spectroscopy and low-temperature nitrogen adsorption experiments, and the highly efficient, environmentally friendly, and safe fracturing fluids that are suitable for the experimental coal seams were preferred. The new fracturing fluid effectively reduces the structure of aliphatic hydrocarbon and the structure of oxygen-containing functional groups, improves aromaticity, and lowers the adsorption capacity of coal for methane. Meanwhile, it simplifies the pore structure of coal and improves the average pore diameter. The research results are essential to the clean production and efficient exploitation of coalbed methane resources and safe coal production. • Five new clean fracturing fluids was prepared. • Analyze the effect of different clean fracturing fluids on coal microstructure. • Explored the mechanism of action of clean fracking fluids on coal. • Determined the optimal ratio of clean fracturing fluid. [ABSTRACT FROM AUTHOR]

Hydrothermal and thermal upgrading techniques are promising coal drying methods that enable the utilization of low rank coals. In this study, Zhaotong (ZT) lignite from the Yunnan province of China was hydrothermally upgraded at 150–300 °C and thermally upgraded at 200–500 °C; then, the correlation between the changes in the physical and chemical structures and the moisture readsorption characteristics were investigated. The maturity of lignite was improved by the upgrading treatment. The main hydrophilic oxygen-containing groups, including hydroxyl and carboxyl, were effectively removed as the upgrading temperature increased. In addition, the removal of hydroxyl groups was more remarkable during hydrothermal upgrading. Irreversible changes occurred in the pore structure of the treated lignites; the specific surface area and total pore volume first increased and then decreased with hydrothermal upgrading, whereas the specific surface area and total pore volume continually increased with thermal upgrading as the temperature increased. In addition, the gel-like structure of the lignite experienced violent shrinkages and collapses. The moisture readsorption performance was effectively inhibited under the synergy effects of the physicochemical structure such that the moisture readsorption ratio ( MRR ) and moisture holding capacity (MHC) decreased continuously with the increasing upgrading temperature. An MHC model built through multiple linear regressions proved suitable to describe the moisture readsorption of the upgraded lignites. [ABSTRACT FROM AUTHOR]

In order to study pore structure and fractal characteristics of the organic-rich marine shale, fourteen shale samples from Lower Cambrian Qiongzhusi formation in Malong block of eastern Yunnan province were investigated by organic geochemical analysis (total organic carbon content analysis and thermal maturity analysis), X-ray diffraction (XRD) analysis, porosity and permeability tests, field emission scanning electron microscopy (FE-SEM), low-pressure nitrogen adsorption and methane adsorption experiments. Fractal dimensions D 1 and D 2 (at relative pressure of 0–0.5 and 0.5–1, respectively) were obtained from the nitrogen adsorption data using the fractal Frenkel–Halsey–Hill (FHH) method. Not only have the relationships among pore structure parameters of shale, the relationships between TOC content, mineral compositions, pore structure parameters and fractal dimensions been discussed, but also the significance of two fractal dimensions D 1 and D 2 and the impact of fractal dimensions on adsorption capacity have been investigated. The results showed that fourteen shale samples have TOC content ranging from 1.25% to 7.72%, two fractal dimensions both increase with the increasing TOC content, and gradually come to a standstill—the curves present the shape of “parabola”. The major mineralogical compositions of shales are quartz and clay minerals, the quartz contents are between 25.5% and 42.7%, the clay contents are between 26.6% and 44.2%. Fractal dimension D 1 has a negative correlation with quartz contents and a positive correlation with clay minerals contents, but fractal dimension D 2 has no apparent relationship with quartz and clay minerals contents. The specific surface area is in the range of 4.98 m 2 /g–19.66 m 2 /g, the total pore volume is between 0.00479 cm 3 /g and 0.01765 cm 3 /g, and the average pore diameter is between 3.37 nm and 6.02 nm. Two fractal dimensions increase with the increasing surface area and pore volume, and also increase with the decreasing average pore diameter because of the complicated pore surface and structure of small pores. Further investigation indicates that D 1 represents fractal characteristics from the irregular pore surface, while D 2 represents fractal characteristics related to the complicated pore structure, and shale samples with larger fractal dimensions have higher methane adsorption capacity. Therefore fractal analysis is helpful to have a better understanding of pore structure and adsorption capacity of marine shale. [ABSTRACT FROM AUTHOR]

Shale gas of Longmaxi Formation, in the northeast of the Yunnan Province, has great potentialities but at a relatively immature exploration stage presently. Geological conditions and reservoir pore structure of the Longmaxi shale gas were clearly studied based on our researches. In the study area, the thickness of Longmaxi black shale gradually increases from southeast to northwest and the maximum is more than 120 m. For 46 shale samples from measured profiles, the total organic carbon (TOC) content and mineral composition of the shale gas reservoir were investigated. The TOC content increases from south to north, with an average content of 0.96% and higher TOC content in the lower segment of the Longmaxi Formation. The main minerals are clays and quartz, with an average content of 45.67% and 27.08% respectively. High pressure mercury intrusion (HPMI), low pressure nitrogen gas adsorption (N 2 -GA), carbon dioxide gas adsorption (CO 2 -GA) and scanning electron microscopy (SEM) methods were used to quantitatively and qualitatively analyse the pore structure of the shale gas reservoir. The openness and connectivity of macropores and mesopores gradually decrease from bottom to top in the Longmaxi Formation, and macropores and a few mesopores contribute to the dominant pore volume. Micropores with 0.30–0.40 nm and 0.45–0.60 nm diameters and mesopores of approximately 4 nm in diameter are strongly developed. Interparticle pores (Interp P), intercrystal pores (Interc P), intraparticle pores (Intra P) and organic matter pores (OMP) were observed. The shale porosity is in the range of 1.35–7.49%, with a mean of 3.98%. Porosity generally increases with increasing TOC and clays contents and decreases with increasing carbonate contents. More pore volume and surface area are always developed in shales with high TOC and clays contents and low carbonate contents. The micropore surface area is more developed in shales with high illite/smecnite mixed layers and kaolinite contents, whereas it is less developed in shales with high illite and chlorite contents. Therefore, the Longmaxi shale gas geological conditions are promising in the northeast of Yunnan Province. [ABSTRACT FROM AUTHOR]

The coal and coalbed methane (CBM) resources are abundant in western Guizhou and eastern Yunnan, South China. However, commercial CBM production in this region has not been achieved. Reservoir properties are the prerequisites in determining the possibility of CBM exploration and its development potential. Thus, to help to select the most favorable block and to prioritize CBM development in the study area, a comprehensive program of experimental work has been carried out to study the physical properties of coal reservoirs in different blocks. Experimental results show that the properties of coal reservoir change significantly with respect to coal rank, and the coal rank in the study area is very uneven, with the vitrinite reflectance ( R o ) of coal samples ranging from 0.68% to 3.31%. In detail, low rank coals have well developed seepage pores but undeveloped adsorption pores, resulting in the low adsorption capacity and high porosity and permeability. With burial depth increase, the metamorphic degree and compaction degree of coals grow accordingly, as a result pores and fractures are gradually closed under stress, leading to a sharp reduction of porosity and permeability in medium rank coals. However, most of the high rank coals in the study area have experienced a large number of tectonic thermal events, which not only increased the metamorphism degree and adsorption capacity, but also improved the porosity and permeability of the coal reservoirs. Based on experimental results, the CBM potentials of coal reservoirs in different blocks in the study area were evaluated using multi-objective and multi-level fuzzy optimization model, and the most prospective zones for CBM production were suggested. [ABSTRACT FROM AUTHOR]

The composition of coalbed methane (CBM) in the Enhong syncline of Yunnan China has abnormally high concentrations of heavy hydrocarbon gases (C 2+). The distribution of the C 2+ gases is variable in the syncline, some areas contain high concentration of C 2+ gases from 2.9 to 36.98% which are called "wet gas area", and in some areas, C 2+ gases can't be examined which are called "dry gas area". The reason for the high concentration of C 2+ gases is connected with the coal maceral composition, the barkinites. The barkinites have the oil-prone character and have generated a lot of oil and exsudatinite in the process of coal maturation, which have been observed under the microscope. Accompanied by the oil and exsudatinite, many C 2+ gases are generated from the coal, which can be proved by a large amount of C 2+ gases generated from coal in Enhong syncline during the pyrolysis simulation experiments (Py-Gc). The reason of the uneven distribution of C 2+ gases in the study area may be caused by different degrees of microbial degradation. The gases in the "dry gas area" become drier because of more microbial degradation and presenting biogenic gases character with little wet gas and lighter carbon isotopic methane, while gases in the "wet gas area" keep the character of thermogenic gases. The different degrees of microbial degradation may be caused by different gas preservation conditions such as coal pore structure. Mercury injection experiments show that coals in the "wet gas area" have larger pore specific surface areas and more micropores but fewer macropores. The larger pore volume of micropore and transitional pore may help the coal in the "wet gas area" protect the wet gases, maybe avoid the wet gases being degraded by the microorganisms. • C 2+ gases of coal distribute abnormally high and unevenly in Enhong syncline. • Lots of barkinites may be the material reason of numerous wet gases generated. • Microbial activity and coal pore may impact on the preservation of C 2+ gases. [ABSTRACT FROM AUTHOR]