Qinshui Basin Research Articles

Clumped isotopes constrain thermogenic and secondary microbial methane origins in coal bed methane

Methane is an economic energy resource and potent greenhouse gas. Distinguishing secondary microbial methane from thermogenic gas is important for natural gas exploration and consideration of subsurface microbial activity in the global carbon cycle, but remains challenging. To understand controls on methane origins in natural gas systems, we investigated the methane clumped isotopologue distributions in the Qinshui Basin high-thermal maturity coal bed methane (CBM) reservoir. Here, near-equilibrium clumped isotopologues distribution (Δ13CH3D and Δ12CH2D2) inferred a temperature interval of 21.6–252.3 °C. The high-temperature thermodynamic equilibrium most likely represents original thermogenic CBM characteristics during coalification. The low-temperature equilibrium clumped isotopologue distributions suggest microbial alteration to CH4 isotopic bond ordering by increased enzymatically catalyzed isotopic exchange. The independent constraints from clumped isotopes, integrated with other geochemical and genomic evidence, confirm notable secondary microbial methane from biodegradation in the highly mature reservoir. Thus, methane clumped isotopes can be used as unequivocal tracers to distinguish secondary microbial methane from thermogenic gases and hence provide the ability to incorporate them separately into global methane budgets.

Matrix Compression and Pore Heterogeneity in the Coal-Measure Shale Reservoirs of the Qinshui Basin: A Multifractal Analysis

The application of high-pressure fluid induces the closure of isolated pores inside the matrix and promotes the generation of new fractures, resulting in a compressive effect on the matrix. To examine the compressibility of coal-measure shale samples, the compression of the coal–shale matrix in the high-pressure stage was analyzed by a low-pressure nitrogen gas adsorption and mercury intrusion porosimetry experiment. The quantitative parameters describing the heterogeneity of the pore-size distribution of coal-measure shale are obtained using multifractal theory. The results indicate that the samples exhibit compressibility values ranging from 0.154 × 10−5 MPa−1 to 4.74 × 10−5 MPa−1 across a pressure range of 12–413 MPa. The presence of pliable clay minerals enhances the matrix compressibility, whereas inflexible brittle minerals exhibit resistance to matrix compression. There is a reduction in local fluctuations of pore volume across different pore sizes, an improvement in the autocorrelation of PSD, and a mitigation of nonuniformity after correction. Singular and dimension spectra have advantages in multifractal characterization. The left and right spectral width parameters of the singular spectrum emphasize the local differences between the high- and low-value pore volume areas, respectively, whereas the dimensional spectrum width is more suitable for reflecting the overall heterogeneity of the PSD.

Geological controls on distribution of carbon isotope of CBM in Zhengzhuang Block, Qinshui Basin, China

Isotope geochemical experiments were conducted on coalbed methane (CBM) from the Zhengzhuang (ZZ) block to understand its formation history and aggregation pattern in the southern Qingshui Basin. The study analyzed the correlation between methane carbon isotope (δ13C1) and factors such as burial depth, gas content, tectonics, and hydrodynamic conditions in 3# coal seam of the Shanxi Formation and 15# coal seam of the Taiyuan Formation. The findings reveal that the δ13C1 values of CBM in 15# coal seam (average −29.4‰), which is at a greater depth, are slightly higher than those in 3# coal seam (average −30.0‰). Positive correlations were observed between δ13C1, gas content, and burial depth. Variations in tectonic and hydrodynamic conditions between 3# and 15# seams account for differences in the spatial distribution of δ13C1 values. Geochemical data, including drainage water analysis, suggest the presence of a potential hidden structure in the northwestern region. Since the Cenozoic Era, gas reservoirs in the area have undergone restructuring, with δ13C1 influenced mainly by desorption, diffusion, transport, and water-solvation effects. The study's results provide valuable insights for applying CBM δ13C1 data in exploration and production.

Pore-Fracture System Distribution Heterogeneity by Using the T2 Spectral Curve under a Centrifugal State

In this paper, 12 sandstone samples are collected from the Taiyuan Formation in Qinshui Basin, and sample types using the T2 spectral under LF-NMR saturation and centrifugation conditions are classified. Moreover, single and multifractal models were used to calculate fractal parameters of saturated and centrifugal T2 spectra, and the correlation between different fractal parameters, pore structure, T2cutoff value, and pore permeability parameters was studied. The results are as follows. (1) According to the T2 spectrum curves under centrifugation and saturation conditions, all the samples can be divided into three types. There are significant differences in the uniform pore size distribution. However, the non-uniformity of small pore distribution in type B samples is stronger than that of other types, while heterogeneity of large pore distribution is weaker than that of different types. The centrifugal T2 spectrum curve exhibits both single-fold and multifractal characteristics. The results of a single fractal by using a centrifugal T2 spectrum are consistent with those of a saturated T2 spectrum, indicating that single fractal features by using centrifugal and saturated T2 spectra are consistent. Unlike the single fractal parameters, the correlation between the saturation and centrifugal T2 spectrum’s multifractal parameters is weak. This suggests that the physical significance conveyed by the centrifugal T2 spectrum’s multifractal parameters differs from that of the saturated T2 spectrum.

Impacts and Countermeasures of Present-Day Stress State and Geological Conditions on Coal Reservoir Development in Shizhuang South Block, Qinshui Basin

Impacts and Countermeasures of Present-Day Stress State and Geological Conditions on Coal Reservoir Development in Shizhuang South Block, Qinshui Basin

Applying 3D geological modeling to predict favorable areas for coalbed methane accumulation: a case study in the Qinshui Basin

Applying 3D geological modeling to predict favorable areas for coalbed methane accumulation: a case study in the Qinshui Basin

Analysis of Carboniferous‐Permian coal‐accumulating environment and coalbed methane enrichment in the southern Qinshui Basin

Analysis of Carboniferous‐Permian coal‐accumulating environment and coalbed methane enrichment in the southern Qinshui Basin

Occurrence and Favorable Enrichment Environment of Lithium in Gaoping Coal Measures: Evidence from Mineralogy and Geochemistry

The Carboniferous-Permian coal measure strata in the Qinshui Basin exhibit highly lithium (Li) enrichment, with substantial exploitation potential. To further explore the enrichment mechanism of lithium in coal measure strata, the No. 15 coal of the Taiyuan Formation from the Gaoping mine is taken as the research object, and its mineralogical and geochemistry characteristics are evaluated using optical microscopy, X-ray diffraction, scanning electron microscopy, inductively coupled plasma mass spectrometry, X-ray fluorescence, and infrared spectral. The results show that the No. 15 coal is semi-anthracite coal with low moisture, low ash, low volatility, and high sulfur. Organic macerals are primarily vitrinite, followed by inertinite, and liptinite is rare; the inorganic macerals (ash) are dominated by clay minerals (predominantly kaolinite, cookeite, illite, and NH4-illite), calcite, pyrite, quartz, siderite, gypsum, and zircon. The average Li content in the coal is 66.59 μg/g, with higher content in the coal parting (566.00 μg/g) and floor (396.00 μg/g). Lithium in coal occurs primarily in kaolinite, illite, cookeite, and is closely related to titanium-bearing minerals. In addition, Li in organic maceral may occur in liptinite. The No. 15 coal was formed in the coastal depositional system, and the deposition palaeoenvironment is primarily a wet–shallow water covered environment in open swamp facies; the plant tissue preservation index is poor, and aquatic or herbaceous plants dominate the plant type. The reducing environment with more terrestrial detritus, an arid climate, and strong hydrodynamic effects is favorable for Li enrichment in coal. The results have important theoretical significance for exploring the enrichment and metallogenic mechanisms of Li in coal.

Multi-Scale Characterization of Pores and Fractures in Coals with Different Coal-Body Structures from the Jincheng Mine, Qinshui Basin, Northern China

The Qinshui Basin is located in the southeast of Shanxi Province, China. It is one of the most abundant coal resources from Permo-Carboniferous North China. It is rich in coal and coalbed methane resources. However, the accumulation of coalbed methane is complex and the enrichment law has not been fully understood because of the high heterogeneity of coal reservoirs in the Qinshui Basin. The examination of dissimilarities between tectonically deformed coals (TDCs) and primary coals at multiple scales holds paramount importance in advancing our understanding of the occurrence and flow patterns of coalbed methane, and in providing guidance for exploration efforts. In the present study, the samples from the Jincheng Mine, Qinshui Basin, were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), CO2 gas adsorption and 3D X-ray micro-computed tomography. The results showed that the dominant minerals in coal were illite, kaolinite, and calcite, with minor amounts of quartz and ankerite. In comparison to primary coal, tectonism could increase the microfractures density of type A (the fracture of width ≥ 5 μm and length > 10 mm) in TDCs. In CO2 gas adsorption in mylonite coal, it was observed that the volume of micropores (<2 nm) was significantly reduced leading to a decrease in gas adsorption capacity. The result of Micro-CT scanning revealed that the minerals occurred as veins in primary coal, but as irregular aggregates in TDCs. Moreover, tectonism had a staged impact on fracture structure, which was initially closed in cataclastic coal and then formed into granulated coal during the tectonic evolution. The effects of tectonism on coal structure had an impact on the connectivity of micropores at the micrometer scale by the destruction of the pore throat structure, increasing the heterogeneity of the reservoir. These findings help to better understand the changes in TDC structure at different scales for developing effective strategies for coalbed methane exploration and production.

Phase Behavior of Fluid Composition in Coalbed Methane Wells Pre- and Post-Workover: An Examination of the Panzhuang Block, Qinshui Basin, Shanxi, China

Phase Behavior of Fluid Composition in Coalbed Methane Wells Pre- and Post-Workover: An Examination of the Panzhuang Block, Qinshui Basin, Shanxi, China

Investigation into the variation characteristics and influencing factors of coalbed methane gas content in deep coal seams

Gas saturation is a critical parameter for the selection and development of coalbed methane, as well as a key indicator reflecting the challenges in coalbed methane development and productivity evaluation of coalbed methane wells. As one of the significant factors influencing gas saturation, gas content plays a vital role in comprehensively investigating coal pore properties to fully comprehend the process and conditions of methane adsorption and desorption. In this study, 3# and 15# coals from Qinshui Basin, China was selected as research subjects. The experimental evaluation encompassed an examination of composition, pore characteristics, permeability characteristics of coal, rock mechanical parameters while discussing the impact of temperature and pressure on coal's adsorption and desorption capacity. The mineral characteristics analysis revealed that vitrinite is the main component with varying percentages and reflectance values in both 3# and 15# coal seams. The gas content and methane concentration in the 15# coal seam are higher than those in the 3# coal seam. The relationship between gas content within a coal seam and burial depth depends on achieving a balance between positive pressure effects caused by overburden stress exertion on gases trapped within pores under high pressures during burial history versus negative temperature effects due to cooling during geological processes over time. Predictions were made regarding deep-coal gas content which holds significant implications for accurately understanding variations in desorption behavior along with optimizing fracturing engineering.

Optimized Random Forest Method for 3D Evaluation of Coalbed Methane Content Using Geophysical Logging Data.

Accurate evaluation of coalbed methane (CBM) content is crucial for effective exploration and development. Traditional gas content measurement methods based on laboratory analysis of drill core samples are costly, whereas geophysical logging methods offer a cost-effective alternative by providing continuous high-resolution profiles of rock layer physical properties. However, the relationship between CBM content and geophysical logging data is complex and nonlinear, necessitating an advanced prediction method. This study focuses on the No. 3 coal seam in the Shizhuang South Block of the Qinshui Basin, utilizing geophysical logging data and 148 sets of laboratory core samples. We employed the Random Forest (RF) method optimized with a simulated annealing-genetic algorithm (SA-GA) to develop the SA-GA-RF model for evaluating CBM content. The model's performance was validated using test data and new CBM well data, and it was applied to calculate the vertical gas content profiles of No. 3 coal seam across 128 wells. The SA-GA-RF model demonstrated an average relative error of 13.13% in the test data set, outperforming Backpropagation Neural Network (BPNN), Least Squares Support Vector Machine (LSSVM), Extreme Learning Machine (ELM), and multivariate regression (MR) methods. The model also exhibited strong generalizability in new wells and improved model-building efficiency compared to traditional cross-validation grid search methods. The construction of a three-dimensional CBM content model, incorporating well coordinates and elevation data, allowed for detailed identification of high gas content areas and layers. This three-dimensional model offers a more precise characterization than traditional two-dimensional isopleth maps, providing valuable insights for CBM exploration, reserve evaluation, and production optimization.

Present-day stress regime, permeability, and fracture stimulations of coal reservoirs in the Qinshui Basin, northern China

Present-day stress regime, permeability, and fracture stimulations of coal reservoirs in the Qinshui Basin, northern China

Research and Application of Treatment Measures for Low-Yield and Low-Efficiency Coalbed Methane Wells in Qinshui Basin

China is rich in high-grade coalbed methane resources, accounting for one-third of the total amount of coalbed methane resources. Qinshui Basin is the main high ranking coalbed methane mining basin in China. In the early stage of CBM development, low-production and low-efficiency wells were formed in the process of block development because of an insufficient understanding of reservoir geological conditions. The existence of low-yield and low-efficiency wells with low output and a poor development benefit seriously restricts the efficient development of coalbed methane. In order to improve the overall development efficiency of coalbed methane fields, how to revitalize low-yield and low-efficiency wells is the main problem facing the development process of coalbed methane. With the deepening understanding of the study area geology, the formation of low-yield and low-efficiency wells has been basically identified. With the advancement of development technology, developers have the ability to retrofit some low-producing and inefficient wells. Low-production and low-efficiency wells are widely distributed. It is difficult to find the criteria for classifying low-producing and low-efficiency wells because of the great differences in geological conditions and reservoir physical properties in different blocks. In addition, the causes of a low-production and low-efficiency well are complex, as the same well is often caused by many reasons, and how to identify the causes of low-production and low-efficiency wells is difficult. In recent decades, developers have studied many methods to retrofit low-production wells, but the retrofit results are not satisfactory. How to choose an economical and efficient reservoir reconstruction method to revitalize low-production and low-efficiency wells is particularly important. This paper starts with the definition of low-production and low-efficiency wells in different blocks, combining an economic evaluation and productivity characteristics to judge whether they are low-production and low-efficiency wells, and defines the distribution of low-production and low-efficiency wells in blocks. The reasons for the formation of low-production and low-efficiency wells are analyzed with the geological characteristics, production dynamic performance, and engineering reconstruction effects. This paper makes a comparative analysis of the current relatively mature low-production and low-efficiency well treatment measures, clearly identifies the advantages and disadvantages of different treatment measures, and takes corresponding stimulation measures for different causes of low-production and low-efficiency wells. The research shows that there are 687 low-production and low-efficiency wells in block A, accounting for 69.4% of the total number of wells, and the low-production and low-efficiency wells account for a relatively large proportion; so, it is necessary to treat them. The main causes of low-production and low-efficiency wells are geology, engineering and drainage systems. The geological reason mainly refers to the low gas production of coalbed methane wells influenced by three factors: resource abundance, faults, and collapse columns. According to the different causes, three treatment measures of large-scale secondary fracturing, temporary plugging, and diversion fracturing and foam fracturing are put forward. The research method in this paper is targeted at different geological conditions so it can be used to guide the treatment of low-yield and low-efficiency wells in other CBM blocks, and it has very important significance for revitalizing the existing low-efficiency CBM assets and improving the development efficiency of CBM.

Fracturing Construction Curves and Fracture Geometries of Coals in the Southern Qinshui Basin, China: Implication for Coalbed Methane Productivity.

Hydraulic fracturing technology has become a common practice to enhance the permeability of coal seams, and its effectiveness significantly impacts the productivity of coalbed methane (CBM) wells. In this study, multiple data sets, including fracturing reports, productivity data, and microseismic monitoring, were utilized to analyze the factors influencing fracturing effectiveness and gas well production at the southern margin of the Qinshui Basin, China, especially the Zhengzhuang and Fanzhuang blocks. Statistics revealed that the fracturing displacement, liquid consumption, and sand consumption were 8 m3/min, 17.69-1386.52 m3 (averaging 728.42 m3), and 28.5-46.1 m3 (averaging 40 m3), respectively. There were differences in the types of fracturing curves among blocks or well groups, and the natural fracture system was identified as the key factor affecting their characteristics. The coal seams with high density of microfractures in Zhengzhuang reduce the fracture threshold of reservoirs during hydraulic fracturing, resulting in a lower fracture response ratio than that of Fanzhuang (71.0 vs 80.3%). Well groups with higher microfracture width in coal seams (Group-ZC and DS) experienced a further reduction in fracture response (averaging 67.2 vs 80.3%), and the connection of hydraulic fractures (HFs) with these high-permeability microfractures lead to an increase in the proportion of fluctuating fracturing curves (averaging 52.2 vs 33.6%). Regional structural features and fracturing effectiveness jointly affected the production of CBM wells. The productivity in Zhengzhuang was lower than that in Fanzhuang due to the highly developed faults and deeply buried coal seams. Shallow coal seams with a high width of microfractures and a low-stress environment were easily supported by a proppant, forming a complex HF network and yielding a high productivity (Group-ZC and DS). For other deeper well groups, proppant migration became unfavorable once high-angle and complex branch HF clusters formed in coal seams, leading to local low-efficiency wells and fluctuating fracturing curves.

Assessing the impact of pore‐fracture structures on permeability sensitivity in tectonic coal using computerized tomography scanning

AbstractThe heterogeneity in permeability of coal reservoirs is primarily attributed to the considerable variation in the morphologies and structures of microscopic pore‐fractures, shaped by complex geological processes. This study emphasizes the necessity of understanding the impact and governance of these morphological and structural variations in pore‐fractures across different types of coal bodies on their permeability. Utilizing computerized tomography scanning and three‐dimensional imaging, we examined coal samples from the Datong coalfield in the southeastern Qinshui Basin, Shanxi Province, to characterize the pore‐fracture morphologies and structures distinct to various coal‐body types based on tomographic data. This introduces a methodology for assessing the influence of microscopic pore‐fracture parameters, such as porosity, specific surface area, tortuosity and fractal dimension, on permeability sensitivity. This is achieved through the application of the modified Kozeny–Carman equation and a fractal permeability model. Findings indicate a predominance of slab fractures in raw coal, whereas fragmented coal under weak brittle deformation exhibits small, isolated pore‐fractures with minimal diameter and volume and poor connectivity. In contrast, granular coal subjected to strong brittle deformation features extensive clusters of large pore‐fractures with significant diameter and volume, enhancing connectivity. Moreover, permeability predictions are refined by integrating the modified Kozeny–Carman equation with tomographic data, offering a more precise understanding of the permeability across different coal bodies.

Production of Coal Fines in Deep Coal Seam via Morphologic, Flow-Channel, Mineral Analyses: Evidence from Coalbed Methane Wells in the Qinshui Basin.

During the development of deep coalbed methane (CBM), the production of coal fines is common and suppresses the yield of CBM. This work takes the deep CBM wells in the Qinshui Basin as a case study, and the output, composition, morphology, and sources of coal fines were investigated through scanning electron microscopy, X-ray diffraction, proximate analysis, and particle size measurement including image analysis, laser diffraction, and dynamic light scattering. The results indicate that, in comparison with shallow CBM wells, deep wells produce a greater quantity of coal fines which are darker in color and have smaller particle sizes, with the majority being less than 10 μm. The coal fines exist predominantly as aggregates that contained the iron-bearing and clay minerals. Based on the Liddinger particle settling model, the water production volume required for the coal fines to return to the surface in the Wuxiang block was calculated to be 8.55 m3/d. This work can provide a scientific basis for the prevention and control of coal fines in deep CBM wells.

Division of Main Geological and Engineering Controlling Types of Low-Production Coalbed Methane Well-Blocks and their Stimulation Measures.

At present, the identification of the main factors controlling low-production coalbed methane (CBM) wells and production enhancement measures does not consider geological and reservoir differences between individual wells and the CBM production effect of well groups simultaneously. In view of this, an evaluation index system suitable for use on inefficient well-blocks was established, which involves their geological resource potential, ground stress, coal structure, and comprehensive permeability under engineering influences from a systemic perspective. The main geological engineering types were determined by zoning superposition, and the corresponding stimulation measures were proposed. The evaluation results of the Shizhuang South Block in the Qinshui Basin show that the area of interest can be divided into Class I, II, and III potential areas, of which the Class II potential areas are subdivided into six blocks. In Zone I, the horizontal well infill method is preferred to increase the CBM production from well groups. At the current level of technology, it is difficult to gain economic benefits from Zone III. In Zone II, these stimulation measures such as the infilling method of staged fracturing horizontal wells, refracturing under supplementary injection holes, roof fracturing, the combined method of acidification and secondary fracturing or nitrogen injection and secondary fracturing, the combined method of acidification and controlled displacement secondary fracturing, and controlled displacement repetitive roof fracturing, among others, can be adopted.

Effects of Various Depressurization Paths on Desorption Deformation and Gas Production of Medium-Rank Coal in Qinshui Basin

Effects of Various Depressurization Paths on Desorption Deformation and Gas Production of Medium-Rank Coal in Qinshui Basin

Production characteristics and influencing factors of coalbed methane wells: a case study of the high-ranking coal seam in the southeastern Qinshui Basin, China

Production characteristics and influencing factors of coalbed methane wells: a case study of the high-ranking coal seam in the southeastern Qinshui Basin, China