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Diagenesis is a series of physical and chemical reactions that take place after deposition. Using cores, thin sections, cathode luminescence, X-ray diffraction, scanning electron microscope, inclusions analysis, geochemical analysis and pore permeability data, the diagenesis, and its influence on the tight sandstone reservoir of Xu 2 member in the southwest Sichuan Basin has been analyzed. The reservoirs of the southwest Sichuan Basin mainly consist of feldspathic feldspathic sandstone, feldspathic feldspathic sandstone, and felsic sandstone, with an average porosity of 3.57% and an average permeability of 0.138·10-3 μm2, which are typical tight sandstone reservoirs. The sandstones in the Xu2 member mainly underwent compaction, dissolution, cementation and accounting, and the specific evolution process is compaction , first-phase fracture, first-phase quartz increase, first-phase calcite cementation, second-phase fracture, feldspar and rock chip dissolution, second-phase quartz increase and silica filling, chlorite cementation or illite cementation, second-phase calcite cementation, dissolution, third-phase quartz increase and silica filling, the third stage of carbonate cementation, carbonate accounting for feldspar and quartz- third stage of tectonic fragmentation, late calcite or quartz cementation into rocks. And the rock formation stage is mainly mesodiagenesis B stage. The secondary pores and microfractures are the main reservoir space in the Xu 2 member sandstone reservoirs. Strong compaction and carbonate cementation are the main reasons for the tight sandstone reservoir, and dissolution and fracture are the main constructional effects for the development of the dominant reservoir. [ABSTRACT FROM AUTHOR]

The microscopic pore throat structure of shale reservoir rocks directly affects the reservoir seepage capacity. The occurrence and flow channels of shale gas are mainly micron–nanometer pore throats. Therefore, to clarify the microstructural characteristics and influencing factors of the deep organic-rich shales, a study is conducted on the marine shale from the Upper Silurian to Lower Ordovician Wufeng–Longmaxi Formation in the southern Sichuan Basin. Petrographic lithofacies division is carried out in combination with petro-mineralogical characteristics, and a high-resolution scanning electron microscope, low-temperature nitrogen and low-temperature carbon dioxide adsorption, and micron-computed tomography are used to characterize the mineral composition and pore structure qualitatively and quantitatively, upon which the influencing factors of the microstructure are further analyzed. The results show that with the increase in burial depth, the total organic carbon content and siliceous mineral content decrease in the Wufeng formation to Long-11 subsection deep shale, while clay mineral content increases, which corresponds to the change in sedimentary environment from anoxic to oxidizing environment. Unexpectedly, the total pore volume of deep shale does not decrease with the increase in burial depth but increases first and then decreases. Using total organic carbon (TOC), siliceous mineral content showed a good correlation with total pore volume and specific surface area, with correlation coefficients greater than 0.7, confirming the predominant role of these two factors in controlling the pore structure of deep shales. This is mainly because the Longmaxi shale is already in the late diagenetic stage, and organic matter pores are generated in large quantities. Clay minerals have a negative correlation with the total pore volume of shale, and the correlation coefficient is 0.7591. It could be that clay minerals are much more flexible and are easily deformed to block the pores under compaction. In addition, the longitudinal heterogeneity of the deep shale reservoir structure in southern Sichuan is also controlled by the thermal effect of the Emei mantle plume on hydrocarbon generation of organic matter and the development of natural microfractures promoted by multistage tectonic movement. Overall, the complex microstructure in the deep shales of the Longmaxi Formation in the southern Sichuan Basin is jointly controlled by multiple effects, and the results of this research provide strong support for the benefit development of deep shale gas in southern Sichuan Basin. [ABSTRACT FROM AUTHOR]

The Permian volcanic reservoir in Sichuan Basin is mainly composed of three types of volcanic rocks (basalt, tuff and breccia), showing an intertwined distribution of their characteristics. The mechanical properties of these rocks, affected by the invasion of water-based drilling fluid, are significantly different, resulting in frequent and complex wellbore instability problems during drilling operations. Thus, using compression tests and scanning electron microscope tests, the mechanical properties and microscopic failure mechanisms of these rocks are studied considering the effect of water absorption, and their implications for wellbore stability are discussed. The results demonstrate the following points. (1) The strength, elastic modulus, cohesion and internal friction angle of basalt are significantly greater than those of tuff and breccia, and these values of tuff are the smallest, but the axial strain of tuff at peak stress is the largest. (2) With the effect of hydration, the elastic deformations of the three kinds of volcanic rocks would weaken, and the plastic deformations are enhanced. These trends for tuff and breccia are more obvious than those of basalt. With the increase in water absorption time, the strength, strains at peak stress, elastic modulus, cohesion and internal friction angle all decrease significantly, but Poisson's ratios change irregularly. (3) The hydration of clay minerals will lead to the surface expansion of mineral particles in these rocks, especially the mineral particles of tuff and breccia will be fragmented and disintegrated to form some loose particle structures in local areas. (4) The collapse mud weight for the tuff well section is the highest, followed by that of the breccia well section and that of the basalt well section, but it decreases most significantly for the breccia well section after water absorption. The collapse mud weights determined by the result of tuff well sections agree with the practical situation. [ABSTRACT FROM AUTHOR]

This paper describes and illustrates the morphological traits of Impatiens zhaojueensis Q. Luo (Balsaminaceae), a new species from the Sichuan Province of southwestern China. Using a scanning electron microscope (SEM), the micromorphological characteristics of its pollen grains and seeds are also described. The new species is closely related to Impatiens baishaensis, but it has larger flowers, obround dorsal petals, somewhat clawed lateral united petals, obround or obround‐dolabriform distal lobes and the ornamentation on the pollen grains has wider meshes. [ABSTRACT FROM AUTHOR]

The production of shale gas plays an important role in the global oil/gas industries, which is considered to approach about 1/3 of the total natural gas production at 2040. In recent years, Wufeng–Longmaxi Formation shale in Sichuan Basin has become a key target of gas development in China. The detection of high-quality gas-producing areas based on the relation between pore structure, mineralogy and elastic properties is the main research direction. However, the effects of depositional environment and diagenetic processes are rarely considered in the studies of these petrophysical properties. We select core samples from the two boreholes to perform X-ray diffraction experiments together with another set of cores from the target formation to obtain scanning electron microscope images and ultrasonic velocities. The mineralogy, pore structure and elastic properties are analyzed. The formation is divided into two sections based on the reservoir characteristics and sedimentary environments. Then, we study the different diagenetic processes of the upper and lower sections. Three-dimensional rock-physics templates of the shale in the two sections are built by using equivalent medium theories and elastic attributes. The templates are calibrated with the samples and well-log data. A 2D survey line and a 3D seismic block of the upper and lower sections are selected, respectively, to map the mineral component, porosity and microcrack density. The good match between the predictions and log interpretation and actual gas content reports suggests that the rock-physics template based on differential diagenesis can be effectively used for further interpretation of seismic inversion results. [ABSTRACT FROM AUTHOR]

Objective The perforated corrosion sample of a natural gas gathering pipeline in Sichuan was studied to determine its failure reason. Methods The failure samples were tested by direct-reading spectrometer, optical microscope, X-ray diffractometer, scanning electron microscope and EDS, and the corrosion condition was analyzed. Results (1) A large number of corrosion pits can be seen on the inner surface of the pipeline. The matrix of the pipeline was ferrite plus pearlite, and the weld seam was acicular ferrite. Its metallurgical quality, chemical composition and mechanical properties meet the national standard requirements. (2) The corrosion products were FeS and FeCO3. (3) SRB existed in the gas field water. Conclusions The cause of pipeline perforation is the result of SRB, H2S, CO2 and other factors. [ABSTRACT FROM AUTHOR]

As one of the most important energy sources in the world today, shale gas has attracted extensive research. Numerous scholars agreed that the organic matter (OM) pores in shale provide the main space which benefits effective gas occurrence. However, the connectivity provided by OM pores is more important in the development process than their reservoir properties. A comprehensive portrayal of the 3D connectivity of the OM pores is elaborated in this study. The Lower Silurian Longmaxi shale samples were selected as the research subject. The shale samples are subjected to focused ion beam scanning electron microscope, helium ion microscope observation experiments, 2D microscopic characterization of OM pores, and 3D segmentation extraction. The results indicate that the connectivity of shale is mainly contributed by OM pores. The OM pores have the advantageous structural characteristics of large number per unit area, evenly distributed, regular pore morphology, and large pore size relative to the mineral matrix pores. The OM pores structure in shale is complex with a network structure of small pores nested in large pores, which can increase the adsorption capacity of gas. Besides, the small pores nested in large pores can act as a throat to significantly improve the connectivity. OM pores in the pyrobitumen are interconnected in 3D space, providing the main channels for gas percolation in the shale reservoir. [ABSTRACT FROM AUTHOR]

The Da'anzhai Member of the Jurassic Ziliujing formation in central Sichuan is a typical tight-oil reservoir with porosity and permeability less than 2% and 0.1 × 10–3 μm2, respectively. Fractures in this formation are well developed in micro- and nano-scale. However, the factors that control the fracture distribution are unclear. Additionally, the uncomprehensive and ineffective identification and evaluation of fractures in the early stage of tight-oil development makes it difficult to meet the requirements of tight-oil development. In our work, we used cores, thin sections, and a scanning electron microscope (SEM) to study the influence of the microscopic rock composition, including the shelly grains, calcite grains, and clastic grains, on the fracture development. We found that the microscopic composition of shelly grains and calcite grains separately control the development of inter-shelly fractures and shelly fractures, and intergranular fractures, and tectonic fractures. Except for a small number of dissolution fractures found in mudstone, the fractures are not well developed in the formations with clastic grains. According to the characteristics of the development degree of fracture and the resolution of the well-logs, the fractures are divided into large scale, small scale, and micro-scale. By a newly established level-by-level constraints method, we systematically identified the scale, occurrence, filling characteristics, and development degree of fractures in the Da'anzhai member by well-logs. Moreover, a quantitative model is also proposed for identifying the angles and development degree of fractures. The results show that the scale of fractures can be effectively identified by the shapes and values of resistivity logs; the occurrence, development, and filling characteristics of fractures can be semi-quantitatively evaluated by the relative amplitude difference between the matrix resistivity (Rb) and formation resistivity (RT). The results are consistent with the interpretation results by formation micro-resistivity imaging (FMI) log, which further demonstrates that the level-by-level constraint method by conventional well-logs can be used to systematically and effectively predict the fracture characteristics in tight-oil reservoirs. [ABSTRACT FROM AUTHOR]

There are various sedimentary structures developed in the black shales of the Upper Ordovician Wufeng Formation and the Lower Silurian Longmaxi Formation in Luzhou area, southern Sichuan Basin, southwestern China. In order to evaluate the controlling effects of sedimentary structures on the key parameters of shale reservoir properties, collected classification of sedimentary structures, scanning electron microscope observation, analysis of shale fabric and porosity characteristics, low‐pressure nitrogen adsorption, methane isothermal adsorption, and conventional triaxial compression test were carried out based on shale samples from Wells A‐H1, B‐H1, C‐H1 and D‐H1 in the study area. The sedimentary structures recorded in these shales are categorized into five types: homogeneous bedding, weak horizontal bedding, strong horizontal bedding, discontinuous ripple bedding, and gravel‐bearing massive bedding. In general, the palaeo‐hydrodynamics and oxygen content of water columns were weak when homogeneous bedding shale was deposited. The organic matter is the most abundant and the total organic carbon content is up to 4.01% on average. The average quartz content is 43.5%, and the brittleness index is the highest. The porosity and adsorption capacity were the highest, with an average of 4.57% and 79.5 scf/ton, respectively. Combined with its mechanical properties of low Poisson's ratio and high Young's modulus, homogeneous bedding sedimentary structure is associated with the shale units possessing the highest organic matter abundance, the strongest reservoir property, and the best fracability, which is the priority target for exploration and development of the Wufeng to lower Longmaxi Formation in the Sichuan Basin, southwestern China. [ABSTRACT FROM AUTHOR]

This study investigated the effects of microfabric and laminae on the pore structure and gas transport pathways of the Silurian Longmaxi shales from Sichuan Basin. 23 shale samples with varied lithofacies were comprehensively investigated by mineralogy, organic geochemistry, pycnometry, and low-pressure nitrogen adsorption analysis. The fabric and laminae of these samples were identified using petrographic microscope and scanning electron microscopy. Permeabilities were measured using the nonsteady-state method on both perpendicular and parallel to bedding shales. The effective pore diameter controlling gas transport was estimated from gas slippage factors obtained in permeability measurements. These values were also compared to those calculated using the Winland equation. Siliceous shales studied are faintly laminated to nonlaminated and have larger porosity and specific surface area. Argillaceous/siliceous mixed shales are well laminated, whereas argillaceous shales contain many oriented clay flakes along the lamination. Both porosity and surface area are positively correlated with TOC content. Unlike most conventional reservoirs, there is a negative correlation between porosity and permeability values of the samples studied. Permeabilities parallel to bedding, ranging from 0.4 to 76.6 μD, are in control of the oriented clay flakes and silty microlaminae. Permeability anisotropy values of the shales vary between 1.3 and 49.8. Samples rich in oriented clay flakes and microlaminated fabric have relatively larger permeability and permeability anisotropy values. The effective transport pore diameters derived from gas slippage measurements are slightly lower than those calculated from the Winland equation. However, both methods have shown that the effective transport pore diameters of argillaceous shales (averaging 552 nm) are significantly higher than siliceous shales (averaging 198 nm), which underlines the control of microfabric, rather than porosity, on gas transport pathways of the shales studied. [ABSTRACT FROM AUTHOR]

BACKGROUND: Organic matter is the most important component in shale, and organic pore is an important reservoir space of shale gas. Scanning electron microscope (SEM), the mainstream microscopic analysis and detection technology, has become an important means of shale research. The comprehensive study of organic matter is gradually becoming an important part of shale gas exploration and development. OBJECTIVES: To summarize the microscopic morphology of organic matter in organic shale of the Longmaxi Formation and discuss its hydrocarbon generation and reservoir ability according to its internal structure and composition characteristics. METHODS: The organic shale of the Longmaxi Formation in Sichuan Basin and its periphery were polished with argon ion, and the samples were examined by high resolution field emission scanning electron microscope under the condition of low voltage and close working distance. RESULTS: There were three main microscopic forms of organic matter in the organic shale of the Longmaxi Formation, which were structure-type sedimentary organic matter, differentiated symbiotic organic matter and interstitial migration organic matter. The structural sedimentary organic matter formed in the stage of sedimentation and early diagenetic evolution, and retained some biological structure characteristics or sedimentary directional structure. Differentiated symbiotic organic matter interacted with clay minerals and underwent evolutionary differentiation, forming a 'granitic structure' similar to that in magmatic rocks. On the other hand, the interstitial migration organic matter was formed in the high evolution stage of late diagenetic organic matter, and the liquid hydrocarbon filled in the intergranular of authigenic minerals, and the surrounding minerals had euhedral characteristics. The shale of the Longmaxi Formation was dominated by organic matter pores-rich interstitial migration organic matter and differentiated symbiotic organic matter, which were the high-quality gas parent materials of the Longmaxi Formation shale, with high reservoir performance. CONCLUSIONS: The research results provide deep-level micro-information for the theory of shale gas formation and the evaluation of exploration and development in the Longmaxi Formation in China. [ABSTRACT FROM AUTHOR]

Organic matter (OM) pores are recognized to be the most important pore type in gas shales in the Ordovician Wufeng-Silurian Longmaxi Formation in the Sichuan Basin, China. However, the effects of the type and origin of organic matter on pore development in OM remain controversial. In this study, detailed scanning electron microscope (SEM) analysis of siliceous shales was conducted for core samples from the Wufeng-Longmaxi Formation, taken from five shale gas wells in the Southeast Sichuan Basin. In addition to bitumen, several types of morphologically distinct organic macerals were identified. Due to the high maturity (vitrinite reflectance (R o) > 2.2%) and compaction of the sample, confirming the origin of some OM types was difficult. However, each OM type is characterized by distinct pore features: (1) the pores in bitumen are normally well developed, with circular or irregular shapes; (2) spherical kerogen contains uneven pores, with irregular and angular pores at the periphery and few pores in the core; (3) algal fragments may have angular pores, the distribution and structure of which are influenced by the initial structure of the organic matter; (4) bacteria-like aggregates represent the accumulation of numerous microbial granules, and contain residual pores; (5) graptolites are relatively tight and usually have few or no pores. The findings indicate that bitumen and algal fragments are the most favourable hydrocarbon-generating organisms for OM pore development. Notably, organic matter originating from different biological sources can influence the extent, shape, and structure of the pores. Some organic pores are recognized as remained pores of sedimentary stage, which may be previously regarded as pores formed during the gas generation period. • Detailed description of pore characteristics of bitumen and different macerals. • The initial structures of organic matter influence pore shapes, distribution and structure according to SEM analysis. • Some irregular angular pores are recognized to be residual pores formed at sedimentary stage. [ABSTRACT FROM AUTHOR]

To evaluate the characteristics of microorganisms and the origin of organic matter of the Wufeng Formation and Longmaxi Formation (WF-LMX) in Sichuan Basin (South China), the type and number of microorganisms were determined in this study using scanning electron microscope (SEM) microphotographs and microbial extraction. The contribution of various microorganisms to organic matter was analyzed in combination with the data of biomarkers and total organic carbon (TOC). It can be deduced from the paleogeography and pristine/phytane (Pr/Ph) ratio that the microorganisms of WF-LMX resided in 60 m–200 m deep shelf with anoxic bottom water. From SEM microphotographs and microbial microscopy analysis, it was demonstrated that the microorganisms in the WF-LMX can be divided into 3 types: planktonic algae (mainly including acritarchs and green algae), fungi, and benthic algae. Acritarchs were the most common microorganisms in the WF-LMX with the average relative content of 60.5%. The average relative contents of benthic algae, fungi, and green algae were 17.6%, 18.0% and 3.9%, respectively. Since the acritarchs and green algae in the Wufeng Formation and the Longmaxi Formation basically belong to planktonic algae, the relative content of planktonic algae in them is about 64.4%. The strata of WF-LMX can be divided into 3 sections based on the distribution characteristics of various microorganisms. The relative content of acritarchs gradually decreased upwards, while that of benthic algae gradually increased. The multiple proxies of biomarkers proved that the planktonic algae was the main source of organic matter in the WF-LMX. Combining the statistical data of microorganisms, it was considered that the organic matter in WF-LMX was mainly derived from acritarchs, which might be the components of planktonic algae. The fungi had a significant contribution to the organic matter in organic-rich layers (TOC > 2.0%) rather than in organic-poor layers, while green algae and benthic algae made little contribution to the organic matters in WF-LMX. • Main microorganisms include acritarchs, fungi, benthic algae, and green algae. • Acritarchs were the most common microorganisms and might be from planktonic algae. • Eucaryon, especially planktonic algae, was the main source of organic matter. • Fungi had a marked contribution to the organic matter in organic-rich layers. [ABSTRACT FROM AUTHOR]

The siliceous Wufeng-Longmaxi Formation is the main shale gas play in China. It contains a large amount of silica, which has been reported to be of biogenic origin. The previous evidences for a biogenic origin include the presence of siliceous skeletal debris resembling organisms, such as sponge spicules, various parameters, such as the ratios of Al/(Al + Fe + Mn) and Si/(Si + Fe + Al + Ca), and a number of different correlations, such as a positive relationship of silica content with total organic matter (TOC). However, these evidences, especially various parameters and correlations, become unpersuasive when comparing Wufeng-Longmaxi Formation siliceous shale with other shale in these parameters and correlations. A series of petrographic thin section and scanning electron microscope (SEM) observations, elemental analysis, TOC analysis and mineral composition analysis were conducted to verify the unpersuasiveness of the existing evidences, and then propose new evidences to demonstrate the abundance of biogenic silica in Wufeng-Longmaxi siliceous shale. It is shown that siliceous ellipsoids are a better mark of biogenic silica in Wufeng-Longmaxi siliceous shale than sponge spicule, radiolarian and foraminifera. Except for the Barium (Ba) concentration, most elemental composition data cannot be used to distinguish biogenic silica from silica with an airborne volcanic ash origin. Furthermore, the poor crystal morphology of the silica in Wufeng-Longmaxi siliceous shale was a clear difference from the airborne volcanic ash-derived silica in Lucaogou Formation and hydrothermal silica in Nutitang and Doushantuo formations. Hence, the crystal morphology can be considered as a distinguishing feature for biogenic silica. • Siliceous ellipsoids are better marks of biogenic silica than sponge spicule, radiolarian and foraminifera. • Most elemental parameters cannot be readily used to distinguish biogenic silica. • The silica crystal morphology is an obvious recognition mark of biogenic silica. [ABSTRACT FROM AUTHOR]

With the global success of the commercial exploration and development of shale oil and gas, research interest in the structure of shale pore, the gas and oil storage carrier, is increasing. However, current studies on shale organic pore are insufficient. Based on this, the basic parameters of Wufeng-Longmaxi shale in Sichuan Basin were tested and shale samples were observed using optical and electron microscopes. In the Changning and Weiyuan areas, CO 2 , N 2 adsorption and mercury intrusion porosimetry (MIP) experiments were conducted on shale samples with different total organic carbon (TOC) content. In this study, we termed the organic matter (OM) with fixed form as formed OM, and the OM without fixed form as amorphous OM, rather than the amorphous OM in the conventional context, which only exists when the maturity of shale is less than 1.0%. The results showed that: (1) formed and amorphous OM can be distinguished under optical and electron microscopes. The formed OM was mainly graptolite, while the amorphous OM could be subdivided into bitumen and micrinite. Under reflected light, bitumen appeared gray-black, while micrinite exhibited certain fluorescence. Under the electron microscope, bitumen showed larger particles than micrinite; (2) there were abundant organic pores in graptolite and bitumen. The organic pores in graptolites were significantly smaller than those in bitumen. Due to the limitation associated with the scanning electron microscope (SEM) resolution, we did not observe organic pores in micrinite, which indicated that the organic pore size in micrinite is smaller than that in bitumen; (3) there were obvious differences in the development of organic pore. In different areas, the relationship between shale porosity and TOC content varied greatly, which was related to the shale gas preservation conditions. Microscopically, there were also several reasons for the developmental differences of organic pore. Among them, inorganic minerals contribute to the preservation of organic pore by filling these pores or forming rigid spatial skeletons, which is an important reason for the micro-difference of organic pore development; (4) The SEM image processing results showed that the organic pore of Wufeng-Longmaxi shale in the Sichuan Basin mainly occurs in the range of mesopore. By comparing the pore size distribution curves of shale samples in the Changning and Weiyuan areas, it is concluded that the organic pore size of shale in the Changning area is primarily 4–10 nm and that in the Weiyuan area it is primarily 2–20 nm. • Micrinite and bitumen were distinguished by optical and electron microscopes. • Supporting effect of inorganic minerals is beneficial for the preservation of organic pore. • The organic pore size of Wufeng-Longmaxi shale is mainly in the range of mesopore. [ABSTRACT FROM AUTHOR]

• Trace elements are innovatively used in the study of hydrothermally altered pyrobitumen. • Hydrothermal minerals cause enrichment of some trace elements in altered pyrobitumen. • The enrichment of trace elements varies with the optical texture change of pyrobitumen. • The hydrothermal activity is not limited to the vicinity of deep faults. The hydrothermal activity in the Ediacaran Dengying (DY) Formation in central Sichuan has modified the reservoirs and paleo-oil reservoirs; however, these modifications are not specific due to the challenges in recovering the hydrothermal scale. This paper classified pyrobitumen in the DY Formation into five categories by optical textures and analyzed the physical structure and trace element composition of the different pyrobitumen using scanning electron microscope, reflectance, and trace elements. Finally, the responses of the trace element concentrations and optical textures of the pyrobitumen to hydrothermal alteration were discussed and used to restore the hydrothermal scale in the central Sichuan Basin. The results show that isotropic, fine-grained, medium-grained, coarse-grained mosaic, and fibrous pyrobitumen develop in the DY Formation. As the optical texture of the pyrobitumen changes from isotropic to mosaic to fibrous, the order degree of aromatic lamella in pyrobitumen gradually increases, the maturity, the maximum reflectance, and the bireflectance of pyrobitumen gradually increase. Except for isotropic pyrobitumen, anisotropic pyrobitumen is subject to varying degrees of hydrothermal alteration. The hydrothermal alteration on pyrobitumen is primarily in the form of material exchange, precipitating illite, salt, and barium-enriched minerals in pyrobitumen pores and enriching some elements (Ba, Cr, Nb, and Sr) in the pyrobitumen. As the optical texture changes from isotropic to mosaic to fibrous, the element enrichment degree gradually increases. Medium-grained mosaic, coarse-grained mosaic, and fibrous pyrobitumen are widely observed in central Sichuan. Therefore, hydrothermal modification on the DY reservoirs and paleo-oil reservoirs is not limited to the deep faults but widely develop in central Sichuan, and should be an essential part of the further study of hydrocarbon accumulation. [ABSTRACT FROM AUTHOR]

The resistivity anisotropy of shale has a non-negligible effect on resistivity logs. Many studies have shown that the macroscale factors of shale anisotropy are depositional environment, compaction process, and diagenesis process, and the microscale factors mainly include lamination, orientation of clay minerals, and microfractures. However, the mechanism of laminations, pores, organic matters, pyrite and clay minerals driving resistivity anisotropy remains unclear. In this research, experiments and simulations were performed to investigate the characteristics and mechanism of the resistivity anisotropy of shale. Two sets of shale samples were collected at different inclination angles from the Lower Silurian Longmaxi Formation in the Pengshui area, southeastern Sichuan Basin, China. Core sample resistivities were measured in several water saturation states established using imbibition, pressurized saturation and centrifuge methods. Scanning electron microscopy, thin sections, X-ray diffraction, the mercury injection capillary method, and N 2 adsorption were also performed. Resistivity simulations were applied to three-dimensional models derived from the microimages. The results of the experiments and simulations show that Longmaxi shale has strong resistivity anisotropy. The resistivity anisotropy coefficient (λ) of Longmaxi shale ranged from 1.3699 to 2.1623. Longmaxi shale has a strong lamination structure. In the submillimeter scale, strawberry-like pyrite (3.8%–10.2%, v /v) aggregates in elongated strips with an extension direction consistent with the horizontal direction. Due to the differential compaction, the clay minerals (21.1%–26.4%, v /v) also tend to be parallel to the formation bedding. The most obvious directional distribution of pores occured in the organic pores. Most interparticle pores between detrital minerals did not exhibit anisotropic characteristics. Because of the horizontal distribution of lamination, pyrite, clay minerals and organic pores, a higher resistivity is measured in the vertical direction than in the horizontal direction. • Lamination, distribution of minerals and pores affect shale resistivity anisotropy. • Large quartz and feldspar grains in laminae block vertical flow of electricity. • Accumulation of strawberry-like pyrite decreases horizontal resistivity of shale. • Organic pore exhibits more horizontal distribution characteristics than other pores. [ABSTRACT FROM AUTHOR]

Studying complex pore structures is the key to understanding the mechanism of shale gas accumulation. FIB-SEM (focused ion beam-scanning electron microscope) is the mainstream and effective instrument for imaging nanopores in gas shales. Based on this technology, 2D and 3D characteristics of shale samples from Lower Silurian Longmaxi formation in southern Sichuan Basin were investigated. 2D experimental results show that the pores in shale are nanometer-sized, and the structure of those nanopores can be classified into three types: organic pores, inorganic pores and micro fractures. Among the three types, organic pores are dominantly developed in the OM (organic matter) with three patterns such as continuous distributed OM, OM between clay minerals and OM between pyrite particles, and the size of organic pores range from 5 nm to 200 nm.Inveresly, inorganic pores and micro fractures are less developed in the Longmaxi shales. 3D digital rocks were reconstructed and segmented by 600 continuous images by FIB cutting and SEM imaging simultaneously. The pore size distribution and porosity can be calculated by this 3D digital core, showing that its average value is 32 nm and porosity is 3.62%.The 3D digital porosity is higher than its helium porosity, which can be regarded as one important parameter for evaluation of shale gas reserves. The 2D and 3D characterized results suggest that the nanometer-sized pores in organic matter take up the fundamental storage space for the Longmaxi shale. These characteristics have contributed to the preservation of shale gas in this complex tectonic area. [ABSTRACT FROM AUTHOR]

Impatiens menghuochengensis Q Luo. (Balsaminaceae), a new species from Shimian county in southwestern Sichuan province, China, is described and illustrated. It is similar to I. tortisepala J. D. Hooker, but differs in having stem unbranched in lower portion; lateral sepals transparent, obliquely ovate; dorsal petal with central columnar cristate swelling; lateral united petals with distal lobes oblong-dolabriform, apically retuse; lower sepal saccate with purple-red veins, abruptly narrowed at belly into an incurved spur 20-25 mm. The morphological characteristics and surface patterning of the seeds and pollen of the new species are examined under SEM and compared with those of I. tortisepala. [ABSTRACT FROM AUTHOR]

Organic matter (OM)-hosted pores play important roles in controlling the porosity and gas content of gas shales. However, the control of organic pore development and preservation remains poorly understood, partly because of the inability to distinguish OM types under the scanning electron microscope (SEM). In this study, seven over-mature Wufeng-Longmaxi Shale samples (equivalent vitrinite reflectance 1.93%–3.07%) were investigated with organic petrography and scanning electron microscope to study the origin of OM and development of organic pores in this black shale succession. Correlative light and electron microscopy was employed to examine pore development in individual macerals. Organic petrographic observations show that OM in these over-mature black shales is dominated by pyrobitumen and graptolites (> 90 vol% of total OM based on point counting). Pyrobitumen mainly occurs as matrix bitumen in the fine-grained matrix, and also as a mixture with clay minerals and fossil cavity infillings. Vitrinite-like particles are minor constituents of OM in the Wufeng-Longmaxi Shale, and their average reflectance, reflectance distribution, and morphology suggest that they may be derived from graptolite fragments lacking diagnostic features and acritarchs. OM type critically controls the development of organic pores. Organic pores primarily occur in pyrobitumen, whereas other macerals are mostly non-porous when examined under the SEM. Results of this study provided important insights into OM thermal evolution and organic pore development in source-rock reservoirs, calling for a critical appraisal of OM in black shales with organic petrography in addition to SEM. • Maceral composition in the over-mature Wufeng-Longmaxi Shale was studied. • Maceral control on organic pore development was analyzed. • Organic matter mainly consists of pyrobitumen and graptolites. • Oil-prone alginite does not exist in the Wufeng-Longmaxi Shale. • Organic pores are primarily hosted by pyrobitumen. [ABSTRACT FROM AUTHOR]

This paper documents depositional structures and their reservoir characteristics in the Wufeng–Longmaxi shale from outcrops and cores using thin sections, X-ray powder diffraction (XRD) analysis, carbon–sulfur analyzer, helium porosimeter, decay permeameter, and focused ion beam scanning electron microscope (FIB-SEM). In the study area, clayey and silty laminae abound in the shale. Clayey laminae are rich in bedding parallel fractures, microfractures, and organic pore networks. Silty laminae are rich in isolated inorganic pores and limited amounts of bedding non-parallel fractures. Various inter-lamination of clayey and silty laminae form five depositional structure types which are closely related to the ancient hydrodynamics, paleoredox condition, and sedimentation rate and have significant impacts on shale fractures, microfractures, pore types, pore-size distribution, and porosity. For the paper lamination (PL) and grading lamination composed of siltstone and claystone (GL-SC), organic pores account for 71.6% and 61.4% of the total, and dense bedding parallel and non-parallel fractures intersect to form connective networks. In the interlaminated lamination composed of siltstone and claystone (IL), grading lamination composed of claystone (GL-C) and structureless beds (SB), organic pores merely account for 20% to 51.8% of the total and minor isolated bedding parallel fractures occur. Among five depositional structure types, the PL and GL-SC have the highest porosity, permeability, TOC content, siliceous content, organic pore proportions, and ratios of horizontal to vertical permeability, which help them become shale gas exploration and development targets. [ABSTRACT FROM AUTHOR]

The lamellation fractures in marine shales are important to the accumulation and preservation of shale gas, whose characteristics and controlling factors are still unclear. This paper focus on the characteristics descriptions and controlling factor analyses based on core observations, thin sections, and scanning electron microscope (SEM) experiments. The marine shales of Paleozoic Wufeng Formation and Longmaxi Formation in the Fuling Area of Eastern Sichuan Basin are taken as an instance. The lamellation fractures are occurring along the direction of the lamellations, partially of them curved, bifurcated, and converged. The apertures of fractures typically range from 1 to 500 μm. Only a few (<1%) lamellation fractures are filled with quartz, calcite, pyrite, and bitumen. After a series of analyses, developments of lamellation fractures are controlled by total organic carbon (TOC), brittle minerals, laminae, and pyrite. (1) The organic matters control the formation and evolution of lamellation fractures by generating gas and resulting in overpressure. An increase in the TOC content of 1% can increase the lamellation fracture density by 0.26 cm-1. (2) Brittle minerals, especially authigenic quartz, is also an important controlling factor to the development of lamellation fractures. When BI increases by 10%, the lamellation fracture density increases by 19%. (3) Besides, siliceous and carbonate laminae in the shale are more suitable for lamellation fractures to develop. When the laminae density is smaller than 4 cm−1, it is easier to develop lamellation fractures with higher laminae density. However, too densely-distributed laminae will suppress the formation of lamellation fractures. (4) Higher pyrite content is good for the development of lamellation fractures. Lamellation fracture density will increase by 9%, with pyrite content increased by 1%. For the shale at the bottom of the Wufeng Formation - Longmaxi Formation, lamellation fractures develop extensively due to the high TOC and pyrite content, great brittleness, and moderate laminae density. The density of lamellation fractures decreases from the bottom to the top. • Quantitative characterize about development characteristics of the lamellation fractures. • The lamellation fractures is controlled by brittle mineral, TOC, laminae and pyrite. • TOC is the main one that affects the development of lamellation fractures. • Clarify vertical distribution characteristic of lamellation fractures in the Wufeng-longmaxi Fm. [ABSTRACT FROM AUTHOR]

Abstract: The effects of mechanical activation on the hydrochloric acid leaching performance of Panxi ilmenite from Sichuan province of China were investigated. The unactivated and mechanically activated ilmenites were characterized using X-ray diffraction (XRD), particle size analysis, and Scanning Electron Microscope (SEM) techniques to determine the structural changes of Panxi ilmenite during the mechanical activation process. The results show that mechanical activation elevated the calcium, magnesium and iron extraction of Panxi ilmenite irreversibly which mostly attributes to the lattice disorder of Panxi ilmenite. All the results show that a great amount of magnesium in Panxi ilmenite uniformly substitutes for iron in the structure of ilmenite, while a minority magnesium exists in gangue minerals, and calcium more likely exists in gangue minerals. The sites of magnesium, calcium and iron in ilmenite would not be redistributed during the treatment of mechanical activation. [Copyright &y& Elsevier]

Complex geology and fracturing operations have led to frequent sand production problem in the shale gas well. Sand production brings huge engineering risks and seriously affects the normal production of the shale gas well. In order to study the property and source of the yielded sand, sand samples in three production periods of flowback, production test and gas production are collected from Sichuan Basin of China. Combining the methods of particle size analysis, microscope observation, scanning electron microscope, CT scanning, infrared spectroscopy and energy dispersive spectrum analysis, the multi-scale structure and composition characteristics of the yielded sand from different production periods were investigated. Results show that the sand size is the largest in the production test period and the smallest in the gas production period. The large-size sand is blocky in the flowback period, while it is flaky in the period of production test and gas production. The roundness of sand becomes worse as the sand size decreasing. Sand composition has the characteristics of fracturing proppant and shale mineral. Cementing material between large-size sands has the network structure and the higher content of aluminum and iron. Organic chemicals are found to be adhered to the sand surface in all three periods. Both shale fracture and proppant failure can generate particles that provide the material source for sand production. This research provides the source of the yielded sand and a theoretical guidance for the sand production mechanism. [ABSTRACT FROM AUTHOR]

The relative sea-level fluctuations play a vital role in the organic matter enrichment of black shales across the world. The Wufeng-Lower Longmaxi shales deposited during the Late Ordovician to Early Silurian stage are accompanied by the global transgression and regression, whereas the role of relative sea-level changes on organic matter accumulation has been rarely discussed. In this study, we integrated TOC content, X-ray diffraction (XRD) mineralogical composition, thin section and scanning electron microscope (SEM) images, elemental geochemical data, and petrographic features of pyrite framboids to investigate the varying paleoenvironmental conditions and the effect of relative sea-level changes on organic matter accumulation under a robust sequence stratigraphic framework. Based on detailed petrographic observations and mineralogical analysis, six major lithofacies are identified in the Wufeng-Lower Longmaxi formations, including siliceous mudstone, clay-rich siliceous mudstone, siliceous-argillaceous mixed shale, silty mudstone, siltstone, and bentonite. TOC content is generally higher in the transgressive systems tracts (relative sea-level rise stage) than in the highstand systems tracts and falling stage systems tract (relative sea-level fall stage). Multiple geochemical proxies indicate contrasting paleoenvironmental changes between relative sea-level rise and fall stage. Relative sea-level rise resulted in elevated productivity, predominantly anoxic conditions, low detrital flux, and moderate water mass restriction, as indicated by high biogenic Si content, high Mo-EF (enrichment factor of element Mo), small-sized pyrite framboids, low Al content and moderate Mo/TOC ratio. On the contrary, relative sea-level fall generally resulted in decreased productivity, dysoxic conditions, increased detrital flux, and strongly restricted conditions. The correlations between TOC content and geochemical proxies suggest that organic matter accumulation was a combined effect of paleoproductivity, paleoredox conditions, detrital influx, and water mass restriction. The variation of these factors was strongly influenced by relative sea-level fluctuations related to Hirnantian glaciation and regional tectonic movements during the Late Ordovician-Early Silurian transitional stage. • Biogenic barium is not a reliable paleoproductivity proxy for the Longmaxi Formation. • The paleoenvironmental conditions are contrasting between relative sea-level rise and fall stage. • Relative sea-level rise is favorable for OM accumulation. • OM accumulation model is established within sequence stratigraphic framework. [ABSTRACT FROM AUTHOR]

As the raw material for the production of basalt continuous fibers in Sichuan, basalt glass (BG) and modified basalt glass (MBG) were prepared by the melt quenching method with the basalt and chemically modified basalt, respectively. The crystallization kinetics of BG and MBG were investigated by differential scanning calorimetry (DSC) according to Kissinger methods. The results revealed that it is difficult for both glasses to crystallize at a high temperature. In addition, the crystallization activation energy of MBG is much higher than that of BG, which indicates that MBG is more difficult to crystallize than BG. The crystalline phases seemed to be formed from the surface of the two glasses. The morphologies and crystal structure of the crystalline phases in the heat-treated BG and MBG were analyzed by scanning electron microscope (SEM/EDX) and XRD. It was found that only a small amount of crystalline phase can be observed in the MBG, which indicates that the crystallization ability of the MBG was greatly suppressed. Results of this initial investigation indicate that chemical modification can effectively suppress the crystallization tendency of basalt glass and improve its thermal stability, which opens up an effective way for the industrial scale and stable production of basalt fiber. [ABSTRACT FROM AUTHOR]

A variable sedimentary environment and accumulation process leads to a complex pore structure in deep carbonate gas reservoirs, and the physical properties are quite different between layers. Moreover, some pores and throats are filled with solid bitumen (SB), which not only interferes with reservoir analysis, but also affects efficient development. However, previous studies on SB mainly focused on the accumulation process and reservoir analysis, and there are few reports about the influence on development. In this paper, through scanning electron microscope analysis, SB extraction, gas flow experiments and depletion experiments, and a similar transformation between experimental results and reservoir production, the production characteristics of carbonate gas reservoirs with different pore structures were studied, and the influence of SB on pore structure, reservoir analysis and development were systematically analyzed. The results show that permeability is one of the key factors affecting gas production rate and recovery, and the production is mainly contributed by high-permeability layers. Although the reserves are abundant, the gas production rate and recovery of layers with a low permeability are relatively low. The SB reduces the pore and throat radius, resulting in porosity and permeability being decreased by 4.73–6.28% and 36.02–3.70%, respectively. With the increase in original permeability, the permeability loss rate decreases. During development, the loss rate of gas production rate is much higher than that of permeability. Increasing the production pressure difference is conducive to reducing the influence. SB also reduces the recovery, which leads to the loss rate of gas production being much higher than that of porosity. For reservoirs with a high permeability, the loss rates of gas production rate and the amount produced are close to those of permeability and porosity. Therefore, in the reservoir analysis and development of carbonate gas reservoirs bearing SB, it is necessary and significant to analyze the influence of reservoir types. [ABSTRACT FROM AUTHOR]

• Three lamination types are distinguished in the Upper Ediacaran botryoidal dolostones in Western Yangtze Platform. • EPS and filaments are documented in botryoidal laminae which were previously believed to be abiogenic origin. • Different microbial mineralization types are recognized in different botryoidal laminae. Botryoidal dolostones are abundant in the Second Member of the Upper Ediacaran Dengying Formation in the Western Yangtze Platform. Although they have been extensively discussed as important host rocks for giant gas reservoirs, there is no consensus on the microbial impact on mineralization processes in the botryoidal laminations. Typical botryoidal laminations were studied under optical microscopes and scanning electron microscopes (SEMs) to investigate their origin. There are three macroscopic morphological types of botryoidal lamination: stromatoid lamination, cavity-lining lamination, and spherical-encrusting lamination. These three types of lamination are composed of fibrous and bladed crystals growing perpendicular to the botryoidal laminae, which have hitherto been implicitly considered to be from abiogenic chemical precipitation. There are many lines of new evidence that demonstrate microbial activities in the interbedded dark and bright laminae constituting the laminations. In the dark laminae, euhedral dolomite rhombs are observed sticking to linear and tubular filaments, or wrapped in sheets of extracellular polymeric substances (EPS) with dolomite crystal sizes of generally <5 μm. The bright laminae are dominated by coarser dolomites and connected by radial sheaths and trichomes with dolomite crystal sizes of primarily around 10 μm. Different species of bacteria, which are closely related to the macroscopic morphology of the laminations, are present in both the bright and dark laminae. The results are useful in understanding the origin and formation mechanisms of the Neoproterozoic botryoidal dolostones. The new findings may also shed new light on the occurrence and evolution of early life on Earth in the Precambrian Era. [ABSTRACT FROM AUTHOR]

Multiscale pore structures of shale conjunctionally determine the gas storage and transport properties of gas shale reservoirs. To investigate the complex pore structures and gas transport in the ultra-tight porous media, a combination of petrophysical and scanning measurements is adopted in this study. Five shale samples of the main productive layers from four wells (Long 1 1 sub-members of Longmaxi Formation) in southeast Sichuan Basin, China are analyzed. Based on scanning electron microscope (SEM) image, different types of organic pores and inorganic pores are quantitatively analyzed. A method for identification of organic and inorganic pores from SEM images is developed. And a comparison between the pores identified from SEM and gas adsorption (N 2 and CO 2 adsorption) is conducted. Results show that the main part of inorganic pores are mesopores, and the organic pore size distributions tend to be lognormal with the peak pore size from 10 nm to 30 nm. Results also show that the gas storage space obtained by SEM is several times to several tens of times larger than that obtained by gas adsorption method. The permeability of OM and shale cores is also compared. The permeability is strongly anisotropic and all those samples show a significant non-Darcy effect. Finally, the relationship between the pore structures and gas transport behavior is studied, and the high quality shale samples are identified considering their gas storage and transport behaviors. [ABSTRACT FROM AUTHOR]