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Fan J.,China University of Mining and Technology | Feng R.,Southern Illinois University Carbondale | Wang J.,Chongqing Institute of Geology and Mineral Resources | Wang Y.,China University of Mining and Technology
Rock Mechanics and Rock Engineering | Year: 2017

Geological sequestration of CO2 in coal seams is of significant interest to both academia and industry. A thorough laboratory investigation of mechanical and flow behaviors is crucial for understanding the complex response of coalbeds to CO2 injection-enhanced coalbed methane recovery (CO2-ECBM) operation. In this work, systematic experiments were carried out on cylindrical coal core specimens under different uniform confining stresses. The coal deformation caused by variations in effective stress as well as the sorption-induced matrix swelling/shrinkage was monitored. The competitive gas sorption characteristics and permeability evolution during the process of methane displacement by CO2 were also investigated. The measured volumetric strain results indicate that sorption-induced strain is the dominant factor in the coal deformation. The relationship between the volumetric strain and the adsorbed gas volume has been revealed to be a linear function. Experimental results obtained under different stress conditions suggest that higher confining stress suppresses the increase in both volumetric strain and the adsorbed gas volume. Furthermore, both methane displacement and CO2 injection are reduced when applying higher confining stresses. In addition, the permeability enhancement is heavily suppressed at higher confining stress. At a certain confining stress, a characteristic “U-shaped” trend of permeability is presented as a function of decreasing pore pressure. This study contributes to the understanding of coal deformation and its impact on permeability evolution under uniformly stressed condition, which has practical significance for CO2 sequestration and CO2-ECBM operation in the Qinshui basin. © 2017 Springer-Verlag Wien

Yuan S.D.,Chinese Academy of Geological Sciences | Yuan S.D.,China University of Geosciences | Zhang D.L.,Central South University | Shuang Y.,Chongqing Institute of Geology and Mineral Resources
Acta Petrologica Sinica | Year: 2012

The Xintianling tungsten deposit is a large-sized skarn and vein-type tungsten-molybdenum polymetallic deposit located in southern Hunan Province, which is genetically associated with the early stage hornblende-biotite monzonitic granite of Qitianling pluton. Direct Re-Os dating on molybdenites collected from the skarn and quartz-vein type ore in the Xintianling deposit have been carried out, to better understand the age of mineralization. The results show that the Re-Os dating of one molybdenite sample collected from skarn- type ore yields a 187Re- 187 Os model age of 159.1 ± 1.9Ma, and six molybdenite samples collected from quartz-vein-type ore yield 187Re- 187Os model ages ranging from 159.1 ± 1.9Ma to 160.2 ±2.9Ma, with an average of 159.4 ± 1.3Ma, and give an isochron age of 161.7 ±9.3Ma (2σ) , with an initial 187Os of 0.6 ±2.3 ( MSWD =0.051). Comparison of the Re-Os ages with published Ar-Ar date ( 157.1 ± 0.3Ma) on iron mica and Rb-Sr date( 157.4 ± 3.2Ma) on quartz indicates that the timing of skarnization and tungsten- molybdenum mineralization are identical within error. Therefore, we can constrain the absolute age of tungsten-molybdenum mineralization in the Xintianling deposit at ca.161.7 ∼ 157.IMa. These ages are consistent with the SHRIMP zircon U-Pb ages (163 ∼ 160Ma) of the early stage hornblende-biotite monzonitic granite. Based on previous studies, it is suggested that the mineralization of the Xintianling W-Mo deposit is spatially and temporally related to the early stage hornblende-biotite monzonitic granite of Qitianling pluton.While the Furong tin deposit located in southern part of Qitianling pluton may be closely related to the late stage biotite monzonitic granite. The emplacement of the Qitianling A-type granite and associated tungsten-tin polymetallic mineralization is a continuous evolution process, which are the products of large-scale mineralization of the Nanling in Middle-Late Jurassic (150 ∼160Ma). Under the tectonic setting of Mesozoic lithospheric extension, asthenosphere upwelling along deep fault, intensive mantle-crust interaction processes probably provide not only the high heat flow, but also part mantle-derived material for large-scale W-Sn-polymetallic mineralization in this area.

Dai S.,China University of Mining and Technology | Wang X.,China University of Mining and Technology | Zhou Y.,Yunnan Institute of Coal Geology Prospection | Hower J.C.,University of Kentucky | And 4 more authors.
Chemical Geology | Year: 2011

Silicic and alkali intra-seam tonsteins were discovered earlier in southwestern China. This paper reports new data on the geochemical and mineralogical compositions of tonsteins from the Songzao Coalfield, Chongqing, southwestern China, and provides new insights into the origin and distribution of the minerals and elements present. Three types of tonsteins (silicic, mafic, and alkali) were identified based on their lateral correlation over a large coalfield area and the overall similarity of corresponding mineralogical and chemical compositions. The clay minerals in most tonsteins of different sources and the mafic tuffs in the lower portion of the late Permian are dominated by kaolinite or are mainly composed of mixed layers of illite and smectite. The silicic tonsteins contain high quartz while the mafic tonsteins and mafic tuffs have high contents of anatase. All the tonsteins and tuffs contain pyrite, attributed to the seawater influences. The mafic tonsteins and tuffs have higher pyrite contents, probably due to the higher Fe derived from mafic volcanic ashes. The mafic tonsteins and tuffs are enriched in Sc, V, Cr, Co, and Ni, similar to the normal clay sediments in the southwestern China, indicating similar sources. The alkali tonsteins are characterized by high contents of Nb, Ta, Zr, Hf, REEs (rare earth elements), and Ga. The TiO2/Al2O3 values are 0.02-0.08 for alkali, <0.02 for silicic, and >0.10 for mafic tonsteins and mafic tuffs, indicating different magma sources. Mafic tuffs and alkali tonsteins are enriched in rare earth elements, and silicic tonsteins contain a lowest REE but have the highest fractionation between light REE and heavy REE. Tonsteins and tuffs may be at the periphery of the Emeishan Large Igneous Province and probably resulted from a waning activity of the plume. They were probably derived from different mantle sources that were underwent not only low-degree partial melting but also fluid fractionation and contamination by lithospheric mantle. Their source magmas had an alkali-basalt composition and were similar to that of ocean island basalt. © 2010 Elsevier B.V.

Song X.-X.,China University of Mining and Technology | Song X.-X.,Taiyuan University of Technology | Tang Y.-G.,China University of Mining and Technology | Li W.,Taiyuan University of Technology | And 2 more authors.
Meitan Xuebao/Journal of the China Coal Society | Year: 2013

Nine standard coal samples from different coalbeds of Zhongliangshan southern coal mine in Huayingshan coalfield were tested using the low-temperature nitrogen adsorption method to study the fractal characteristics of adsorption pores (pore diameter <100 nanometers) and the relationship between fractal dimension and the gas adsorption capacity of tectonic coal. The results of both the low-temperature nitrogen adsorption and desorption show that different deformed coal has different adsorption characteristics under relative pressures between 0.5-1.0.Based on the results, the fractal dimension D of tectonic coal was studied using the fractal Frenkel-Halsey-Hill (FHH) method. The results demonstrate that the fractal dimension D can represent the variation characteristics of pore structure and pore surface area of tectonic coal. The higher fractal dimension D, the more micropores, the more irregular specific coal surface, and the higher heterogeneity of pore structure. The gas storage capacity of coal can be represented by the fractal dimension D, and the gas adsorption capacity of coal increases with the increasing of fractal dimension D. Therefore, the higher fractal dimension and the more homogeneous pore structure resulting from strong tectonic deformation, indicate that the coal has a higher gas adsorption capacity.

Han H.,China University of Petroleum - Beijing | Li D.,Chongqing Institute of Geology and Mineral Resources | Ma Y.,China University of Petroleum - Beijing | Cheng L.,Chongqing Institute of Geology and Mineral Resources | And 3 more authors.
Shiyou Xuebao/Acta Petrolei Sinica | Year: 2013

Desorption experiments were performed on Lower Cambrian shale cores from the northeastern Sichuan Basin, China and desorbed gas was obtained for analyses of its chemical composition and stable carbon isotope. The results showed that methane (CH4) content of the desorbed gas ranges from 96.39%to 98.83%, while amounts of other gaseous hydrocarbons are pretty small. With increase of desorption time and cumulative amounts of the desorbed gas, contents of individual gas compounds vary regularly, which may result from a different adsorption capacity of shales to individual gas compounds. Stable carbon isotopic values of methane (δ13C1) and ethane (δ13C2) in the desorbed shale gas range from -32.20‰ to -29.50‰ and -37.70‰ to -36.60‰, respectively. All of the desorbed gas samples are characterized by a "reversed" order of carbon isotope, which may result from mixture of two gases generated from cracking of liquid hydrocarbons at high maturity and kerogen pyrolysis at the early hydrocarbon-generating stage. With increase of desorption time, about 2.3‰ of carbon isotopic fractionation occurs in δ13C1. This fractionation of δ13C1 may be attributed to a diffusion effect of gas during desorption process.

Ma W.,Chengdu University of Technology | Liu S.,Chengdu University of Technology | Huang W.,China National Petroleum Corporation | Zhang C.,China National Petroleum Corporation | Zeng X.,Chongqing Institute of Geology and Mineral Resources
Xinan Shiyou Daxue Xuebao/Journal of Southwest Petroleum University | Year: 2012

The study area (western Hubei-eastern Chongqing) was a transitional zone between steep detachment fold belt in eastern Sichuan and block-basement fault-fold belt in western Hunan-Hubei. There the deformation is relatively weak, and oil & gas geological preservation condition was better than surrounding areas. Based on the well drilling and field data, employing the petrology, thin section, SEM and organic geochemical analysis, we studied the characteristics of the macro and micro Silurian reservoir rocks and their oil & gas prospection. The results show that: the main lithology of Longmaxi Formation was black carboniferous shale, deep gray (gray) shale and silty mudstone. The micro-reservoir spaces were highly developed including intergranular dissolution pores of clay minerals, dissolution pores in feldspar and quartz, microfratures and so on. Source rocks with high quality were developed east to the belt of Well Jianshen 1 and Lengshuixi. And the microporosity and microfractures were very rich in Silurian. The Silurian Hanjiadian Formation gas reservoir belonged to tight gas. Based on the Well Jianshen 1 gas reservoir characteristics and the existing drilling analysis data, we conclude that Shizhu composite anticline, Lichuan and Huaguoping composite syncline are fully equipped with tight gas and shale gas exploration potential.

Gao Y.,China University of Petroleum - Beijing | Xiao L.-Z.,China University of Petroleum - Beijing | Xie Q.-M.,Chongqing Institute of Geology and Mineral Resources
Zhongguo Shiyou Daxue Xuebao (Ziran Kexue Ban)/Journal of China University of Petroleum (Edition of Natural Science) | Year: 2014

In the Phillips-Twomey method, it is essential to find a suitable regular parameter r. The selection of the parameter r remains practically difficult, and is often biased by researcher's subjectivity. Finding a suitable regular parameter r in using Phillips-Twomey method to inverse nuclear magnetic resonance (NMR) logging transverse relaxation time was focused on. The way to finding the suitable r was based on the compromise criterion in BG theory and the r minimal criterion. The inversed transverse relaxation time was also assessed through the resolution matrix and the covariance matrix. Digital simulation and core analysis show that the approach in determining the regular parameter r of the Phillips-Twomey inverse method works very well for the inverse of NMR transverse relaxation time. Core analysis also shows that this method is better than the classical SVD method without subjective bias.

Xia L.,China University of Petroleum - Beijing | Luo D.,China University of Petroleum - Beijing | Luo D.,Chongqing Institute of Geology and Mineral Resources
Journal of Natural Gas Science and Engineering | Year: 2014

Target depth is a key measure of the commercial viability of a shale gas prospect. Although much research has been conducted in the shale gas techno-economic appraisal field, no reports are available on the economic critical depth (ECD) of shale gas resources. The present work aims at establishing a model for calculating the ECD using the break-even analysis-the reverse of calculating the net present value (NPV)-such that the break-even ECD occurs at zero NPV. The ECD is sensitive to production uncertainty, depending on the initial production (IP) rate and the production decline rate. Examples indicate that these have a marked effect on ECD based on current technology, gas price and exploitation policy, with the IP rate having the more pronounced effect. When the IP rate varies between 2.5 and 5.5 × 104 m3/day based on the fitted production decline trend from a pilot area in China, the corresponding ECD varies from 898 m to 3997 m. The ECD is thus able to rule out non-commercial shale gas prospects quickly. © 2014 Elsevier B.V.

Ma Y.,China University of Petroleum - Beijing | Zhong N.,China University of Petroleum - Beijing | Li D.,Chongqing Institute of Geology and Mineral Resources | Pan Z.,CSIRO | And 2 more authors.
International Journal of Coal Geology | Year: 2015

Gas shales with a high gas content were encountered in the Lower Cambrian Lujiaping Formation in the northeast part of the upper Yangtze area, China. In this area, the tectonic condition is complex and the organic matter is over-matured, so conventional oil and gas exploration have not previously been considered. During a recent shale gas exploration, canister-desorbed gas contents of more than 1m3/t were detected from 490 to 825m depth, with a maximum value of 3.18m3/t at 762m. Hence to understand the mechanism of preservation of the gas is important. The gas shales have a total organic carbon (TOC) content of between 0.44% and 6.91%, and vitrinite-like macerals reflectance (Ro) between 3.3% and 4.3% with type II kerogen. The porosity of 22 gas shale samples ranges between 0.4% and 2.29%, and their permeability is between 6.9×10-5 and 3.8×10-1mD. To investigate the shale's pore structure and its relation to gas storage behavior, we studied the microscopic mechanism of gas preservation using a combination of pore characterization techniques, including focused ion beam-scanning electron microscope (FIB-SEM) imaging, and comparison of gas sorption and free gas storage capacity.Folding, thrusting and subsequent rapid uplifting movements occurred after most of the dry gas had been originally generated, and the present gas is a mixture originated from the cracking of liquid hydrocarbons at high maturity and kerogen pyrolysis in the early hydrocarbon-generation phase. SEM observations, combined with low temperature gas adsorption and mercury injection capillary pressure analyses, show that pores within the organic matter or the mineral particles in the Lujiaping Shale are rare, while the nanometer-sized pores (1-4nm) between organic matter and clay mineral particles, especially in cleavage domains, are greatly developed. Thus the gas in these shales is mainly adsorbed gas due to the limited free gas storage space. This is unlike most other shale gas reservoirs, pores within the organic matter and pores between or within mineral particles are dominant. Moreover, the desorbed gas content correlates well with TOC content and the microporous and mesoporous specific surface area determined by low temperature CO2 and N2, respectively, suggesting that the nanometer-sized pores associated with the organic matter make up the fundamental storage space for this shale. The calculations based on FIB-SEM observation showed that the nanometer-sized intergranular pores have large specific surface areas, with their small pore throat diameters resulting in high capillary pressure. These characteristics have contributed to the preservation of shale gas in this complex tectonic area. © 2014 Elsevier B.V.

Xia L.,China University of Petroleum - Beijing | Luo D.,China University of Petroleum - Beijing | Luo D.,Chongqing Institute of Geology and Mineral Resources | Yuan J.,China University of Petroleum - Beijing
Journal of Natural Gas Science and Engineering | Year: 2015

Although there have been discussions regarding the commercial prospect of shale gas in China, no quantitative and convincing analysis regarding its economic viability has been reported. This research aims to explore the future of the shale gas industry in China using a single-well model. This model is established with the DCF (Discounted cash flow) method aiming at getting an average or representative reflection of the economic viability of shale gas. In the model based on data mainly from pilot areas in Sichuan Basin, three scenarios are conducted to discuss the current economy, the short-term prospect, and the future of the shale gas industry. Under the current technological and economic conditions, China's shale gas resources are not worth an investment. However, in the near future, several sweet-spots are promising, particularly with the expectation of higher gas prices and lower drilling and completion costs (D&C costs). Although the sweet-spots are promising, it is difficult to achieve the goal of large-scale development according to the known information if mainly relying on current policy, unless there are sufficient sweet-spots. Hence, we hold a cautiously optimistic attitude towards the future of the shale gas industry. We suggest that the government should spend more on supporting resource surveys and exploration in the initial stages. After identifying the resource status, a more comprehensive development plan with systemic policies conformed to the resource status is warranted, including encouragement of technical innovations, a system for mature shale gas technical service markets, and a market-oriented price. © 2015 Elsevier B.V.

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