Comparison of pore characteristics in the coal and shale reservoirs of Taiyuan Formation, Qinshui Basin, China

Coal and shale are both unconventional gas reservoirs. Comparison of pore characteristics in shale and coal would help understand organic pore structure in shale and investigate co-exploration of shale gas and coalbed methane in coal bearing strata. In this study, five shale samples and three coal samples of Taiyuan Formation were collected from Qinshui Basin, China. High pressure mercury injection, scanning electronic microscopy, and fractal theory have been used to compare pore characteristics in shale and coal. The results show that pore volumes in coal are much larger than that in shale, especially pores 3-100 nm. In coal, there are many semi-closed pores in micro pores （〈10 nm） and transition pores （10-100 nm）. On the contrary, micro pores and transition pores are mainly with open pores in shale. The fractal curves show that pores larger than 65 nm in coal and shale reservoir both have obvious self-similarity and the fractal dimension values in shale and coal are similar. But the fractal characteristics of pores smaller than 65 nm in shale reservoir are quite different from that in coal.

Nanoscale pore morphology and distribution of lacustrine shale reservoirs:Examples from the Upper Triassic Yanchang Formation,Ordos Basin

Pore structure plays an important role in the gas storage and flow capacity of shale gas reservoirs. Fieldemission environmental scanning electron microscopy（FE-SEM） in combination with low-pressure carbon dioxide gas adsorption（CO2GA）,nitrogen gas adsorption（N2GA）,and high-pressure mercury intrusion（HPMI） were used to study the nanostructure pore morphology and pore-size distributions（PSDs） of lacustrine shale from the Upper Triassic Yanchang Formation,Ordos Basin. Results show that the pores in the shale reservoirs are generally nanoscale and can be classified into four types： organic,interparticle,intraparticle,and microfracture. The interparticle pores between clay particles and organic-matter pores develop most often,l with pore sizes that vary from several to more than 100 nm. Mercury porosimetry analysis shows total porosities ranging between 1.93 and 7.68%,with a mean value of 5.27%. The BET surface areas as determined by N2 adsorption in the nine samples range from 10 to 20 m2/g and the CO2 equivalent surface areas（2 nm）vary from 18 to 71 m2/g. Together,the HPMI,N2 GA,and CO2 GA curves indicate that the pore volumes are mainly due to pores 100 nm in size. In contrast,however,most of the specific surface areas are provided by the micropores. The total organic carbon（TOC） and clay minerals are the primary controls of the structures of nanoscale pores（especially micropores and mesopores）. Micropores are predominantly determined by the content of the TOC,and mesopores are possibly related to the content of clay minerals,particularly the illite-montmorillonite mixed-layer content.

Prospect Conceiving of Joint Research and Development of Shale Gas and Coalbed Methane in China

Inspired by successful development of shale gas in USA and influenced by hydrocarbon resources shortage currently, China has strengthened shale gas research and accelerated its exploration process. In order to enrich coalbed methane (CBM) and shale gas geological theory and promote their development process, this paper compared shale gas with CBM in accumulation, distribution, reservoir and production. It expatiated on the background and significance of the combined research and development, and analyzed the geological foundation and future prospects. Our investigation demonstrated that there are many sets of coal-bearing strata in Shanxi formation of Permian system in Ordos in North China, Longtan formation of Upper Permian and Xujiahe formation of Upper Triassic in Southern Yangtze region, Xishanyao formation of Middle Jurassic in Turpan-Hami Basin and Junggar Basin in Northwest China, and Shahezi formation of Cretaceous in Songliao Basin in northeast China. In these regions, shales which are interbeded with coal seams have the characters of big thickness, continuous distribution, high content of organic matter, good parent material and high maturity, accord with the basic geological conditions to format shale gas and CBM reservoir and composite gas reservoir, thus form appropriate regions and layers to carry out joint research and exploration with good prospects for development.

Sedimentary environment and major controlling factors of organic matter-rich shale from the Wufeng-Longmaxi formation in eastern Sichuan Basin,China

The major controlling factors of organic matter and its enrichment model of the black shale from the Wufeng-Longmaxi Formation were explored by investigating the vertical variation characteristics,as well as major element and trace element abundances in the Wuxi Bailu section.The results show that the sedimentary tectonic setting of the Wufeng-Longmaxi Formation in the north-east margin of the upper Yangtze platform is located on the active continental margin,which is a passive continental margin and continental island arc.The parent rock in the source area is mainly felsic volcanic rocks mixed with small amounts of sedimentary recycling materials.Due to increased plate activity and a drop in sea levels,terrigenous pyroclastic input increased.The palaeoclimate was semi-humid,and a robust dysoxic-reduction environment and a high level of palaeoproductivity,causing the formation of the organic-rich shale in the Wufeng Formation.At the base of the Longmaxi Formation,the sedimentary water body was affected by global transgression,showing a strong anoxic-reductive environment,and the paleoclimate was a warm and humid condition.The palaeoproductivity level was high,resulting in the formation of organic shale.Due to the sea level drop at the top of the Longmaxi Formation,the sedimentary water was in an oxic-reduced environment,but the input of terrigenous pyroclastic matter increased.Because the paleoclimate was warm and humid and the palaeoproductivity level was high,organic-rich shale was formed.The findings demonstrate that terrigenous clastic input circumstances,palaeoproductivity conditions,and paleo-redox conditions had the greatest influence on the enrichment of organic matter in the Wufeng-Longmaxi Formation.Thus,organic matter enrichment was controlled by multiple paleoenvironmental factors.

Influence of liquid water on coalbed methane adsorption:An experimental research on coal reservoirs in the south of Qinshui Basin

Using Isothermal Adsorption/Desorption System Model IS-100 and Electrohydraulic Servo Rock System Model MTS815 as the main apparatuses and collecting samples from the major coal reservoirs in the south of Qinshui Basin, a hot point region of coalbed methane exploration, the paper carries out systematical comparisons of the isothermal adsorption experimental data for injection water coal samples, equilibrium moisture samples and dry coal samples, probes and establishes an experimental method of injection water coal sample preparation and isothermal experiment to simulate real reservoir conditions, and then summaries the experimental regulations and discusses the mechanism of liquid water influencing coal methane adsorption. Results of the experiment indicate that: The Langmuir volume of injection water coal samples is notably larger than that of equilibrium moisture samples, as well as larger than or equivalent to that of dry coal samples; the Langmuir pressure of injection water coal samples is the highest, the next is equilibrium moisture samples, while the dry samples is the lowest, of which the experimental results of injection water samples to simulate real reservoir conditions are more close to the fact. Under the conditions of in-position reservoirs, liquid water in coals has evident influence on methane adsorption ability of coal matrix, which can increase the adsorbability of coal and make the adsorption regulation fit to Langmuir model better. Its major reason is the increase of wetting coal matrix adsorbability. The above experimental results overthrow the conventional cognition that liquid water has no influence on coalbed methane adsorption, which may lead to an improvement of the coalbed methane isothermal adsorption experimental method and of the reliability of coalbed methane resource evaluation and prediction.

Ultrawide-bandgap(6.14 eV)(AlGa))_(2)O_(3)/Ga_(2)O_(3)heterostructure designed by lattice matching strategy for highly sensitive vacuum ultraviolet photodetection

One judiciously designed strategy of utilizing an ultrathin but conductive Ga_(2)O_(3):Si nanolayer to prepare(AlGa)_(2)O_(3)crystalline film is demonstrated.Benefiting from the existence of Ga_(2)O_(3):Si nanolayer,a high-quality(Al_(0.68)Ga_(0.32))_(2)O_(3)sesquioxide film with 68 at.%aluminum was epitaxially grown on sapphire substrates,which was characterized by high-resolution transmission electron microscopy,X-ray photoelectron spectroscopy and X-ray diffraction.Its bandgap was broadened to 6.14 eV,and a vacuum ultraviolet(VUV)(AlGa)_(2)O_(3)/Ga_(2)O_(3):Si photodetector was subsequently fabricated.The detector exhibits a pretty high on-off ratio of about 10^(3),an open-circuit voltage of 1.0 V and a responsivity of 8.1 mA W^(-1) at 0 V bias voltage.The performances imply that the proposed strategy is valuable for improving the quality and also adjusting the bandgap of(AlGa)_(2)O_(3)sesquioxides,which is expected to facilitate their application in VUV photodetection.

Raman tensor of graphite:Symmetry of G,D and D′phonons

Graphite is a natural highly-anisotropic layered material formed by stacking in the direction perpendicular to two-dimensional(2D)graphene monolayers.As an anisotropic material,graphite is characterized by its extraordinary optical response[1].For example,the Raman scattering effect of graphite is both complex and intriguing to be an important window for peeping through its physical properties[1].

Raman spectroscopy regulation in van der Waals crystals

Raman spectroscopy is a versatile tool widely used for comprehensive probing of crystal information. However,generally when applied in narrow-band-gap van der Waals crystals, it is liable to form a "bug," especially in transition-metal-dichalcogenides(TMDs). That is, several resonant Raman-scattering(RS) modes will inevitably appear in the Raman spectra with strong intensity, interfering with the desired signal of optical-phonon modes.Here, we propose cross-sectional polarized Raman scattering capable of regulating the intensity of RS modes in accordance with quasi-sinusoidal rules. Typically, for MoS_2 and WS_2, when the polarization vector of excited light is along the c axis of the crystal, all RS modes are nearly completely "expunged" from the Raman spectra. The mechanism is that the absorption of most TMDs with a space group of R_(3m)for the light polarized along the c axis is infinitesimal, thus forming a small coupling intensity of electronic states excited optically and acoustic-phonon modes at point M, which in turn restrain the appearance of RS modes. The regulating strategy proposed can be applied to other van der Waals crystals so as to obtain a high signal-to-noise ratio Raman spectrum.

Raman tensor of layered WS2

Recently,van der Waals layered materials,such as MoS2,WS2,MoSe2 and WSe2,have attracted extensive attention due to their unique properties and potential applications in(optoelectronic)electronic devices[1].Similar to graphene,the atoms of van der Waals materials in the layer are connected by covalent bonds,and the van der Waals’force is applied between the layers[2].However,compared with graphene,van der Waals materials exhibit more excellent performance in sensors.

Pore structure complexity and its significance to the petrophysical properties of coal measure gas reservoirs in Qinshui Basin,China

The pore structure of continuous unconven-tional reservoirs(CURs)in coal measures was investigated using different technologies for 29 samples(9 coal samples,9 shale samples,and 11 sandstone samples)from Qinshui Basin,China.Results show that coals have relatively high porosities and permeabilities ranging from 4.02%to 5.19%and 0.001 to 0.042 mD,respectively.Micropores(<2 nm)are well-developed in coals and contribute to the majority of pore volume(PV)and specific surface area(SSA).The porosities and permeabilities are between 1.19%-4.11%,and 0.0001-0.004 mD of sand-stones with a predominance of macropores(>50 nm).However,shales are characterized by poorly petrophysical properties with low porosity and permeability.Macropores and mesopores(2-50 nm)are well-developed in shales compared with micropores.For coals,abundant organic matters are expected to promote the development of micropores,and clay minerals significantly control the performance of mesopores.For shales and sandstones,micropores are mainly observed in organic matters,whereas clay minerals are the important contributor to mesopores.Moreover,micropore SSA significantly deter-mines the adsorption capacity of CURs and sandstones have the best pore connectivity.The permeability of CURs is positively associated with the macropore PV since macropores serve as the main flow paths for gas seepage.Additionally,we also proposed that effective porosity has a significant effect on the permeability of CURs.The findings of this study could enhance the understanding of the multiscale pore structure of CURs and provide insights into the mechanisms that control gas storage,transport,and subsequent co-production for continuous unconventional natural gas(CUNG)in the Qinshui Basin and other coal-bearing basins worldwide.

Near vacuum-ultraviolet aperiodic oscillation emission of Al N films

An accurate measurement of the refractive index is necessary for the optical design of both deep ultraviolet laser diodes and light-emitting diodes. Generally, the refractive indices along different crystallographic axes of anisotropic thin films are measured using variable angle spectroscopic ellipsometry.However, there are still some limitations concerning this method. Here we proposed a potential method to measure the band edge refractive index of wide bandgap semiconductor. An aperiodic oscillation emission phenomenon due to the Fabry-Perot effect was observed in the fluorescence spectrum of an AlN film with a thickness of 1500 nm. Based on the characteristics of the fluorescence spectrum and the definition of Fabry-Perot effect, we obtained the ordinary refractive index of the AlN thin film near the band edge directly. This refractive index measurement method is a supplement to the variable angle ellipsometry,and it is a more direct and effective method for transferred film and thinner samples to measure the fluorescence spectrum.

Laser tuning in AlN single crystals

In the fields of trace gas detection,electric field detection,visible optical communication,and beyond,laser tuning technology plays an increasingly important role,as shown in Fig.S1.Following the miniaturization of optoelectronic devices,it is desirable to integrate a large number of lasers with different wavelengths into one chip[1].However,the dynamic wavelength allocation efficiency of fixedwavelength laser is quite low,which greatly limits the monolithic integration of optoelectronics systems.Therefore,the development of laser wavelength tuning technology is urgent and crucial to the efficiency of optoelectronics[2–7].Raman scattering is a physical phenomenon that can be explained by mature normal form[8,9].However,most studies only pay attention to the fact that Raman spectrum is a non-destructive material characterization method with fingerprint identification characteristics,while its essential feature of inelastic scattering is always ignored[10].The natural frequency shift characteristics indicate the possibility of Raman scattering as a feasible method to realize laser wavelength tuning[11–13].