Coal is an important resource with a high content of organic matter in the context of fossil energy and energy engineering. However, previous studies lacked a comprehensive understanding of the effects and underlying mechanisms of the original components on the chemical structure and micromechanical properties of coals. The space of coal skeleton structure to store small molecule compounds and how small molecule compounds affect the strength of coal skeleton structure are two unresolved issues. Here, we investigated the chemical structure and micromechanical properties of original coal (OC) after removing the weakly soluble small molecule compounds (i.e., decarbonized coal (DC) and then strongly soluble small molecules compounds (i.e., skeleton of coal (SC)) using nanoindentation techniques and X-ray diffraction. The results indicate that after removing soluble small molecule compounds, the aliphatic layer interlayer spacing and the aromatic layer interlayer spacing values of coal samples with high hydrogen index decreased, with a more pronounced decrease observed for SC samples. This suggests that coal has a dense, layered microstructure and that weakly and strongly bond soluble small molecule compounds bind the layers together. The removal of soluble small molecule compounds induces the rearrangement of macromolecular aromatic clusters, causing them to stack more closely, leaving the extremely polar soluble molecule compounds and the skeletal structure of the coal. Consequently, the elastic modulus and hardness of the OC decreased. In addition, the creep deformation of the OC increased and a transition from elastic to plastic deformation was observed in the coals. These changes in the mechanical parameters are mainly related to the changes in the chemical structure of the coal. In particular, the DC and SC samples exhibit a decrease in interlayer spacing, which leads to the disintegration of the coal's pile structure and leave behind the main skeletal structure of the coal. This study elucidates the influence of the original components in coal on its mechanical properties from a microscopic mechanism perspective, which will provide important technical support for efficient and clean coal utilization and mining engineering.

The differences between the free and kerogen-bound pristane (Pr) and phytane (Ph) were investigated in six Oligocene–Miocene source rocks from the western Qaidam Basin (Qaidam source rocks) and ten Jurassic coals from the Junggar Basin (Junggar coals) that were deposited under anoxic blackish-saline lacustrine and oxic swamp depositional environments, respectively. The free isoprenoid precursors in the initial bitumen are more sensitive to redox conditions compared with the bound counterparts to kerogen. Similarly, the bound isoprenoid precursors in kerogen with labile bonds (e.g., oxygen‑carbon and sulfur‑carbon bonds) are more influenced by redox conditions than those with stable carbon‑carbon bonds. This leads to different diagenetic reaction routes giving rise to different Pr/Ph between the free isoprenoids in the initial bitumen and bound isoprenoids released from kerogen and between the bound isoprenoids released from kerogen at lower and higher temperature and maturity. For the six Qaidam source rocks, the free isoprenoid precursors (e.g., phytol) in the initial bitumen are more prone to be converted to Ph than the counterparts bound to kerogen, leading to Pr/Ph that increases from substantially lower than 1 for the initial bitumens to increasingly close to 1 for the released oils with increasing temperature and maturity. In contrast, for the ten Junggar coals, the free isoprenoid precursors in the initial bitumen are more prone to be converted to Pr than the counterparts bound to kerogen, leading to Pr/Ph that decreases from greatly higher than 1 for the initial bitumens to increasingly close to 1 for the released oils with increasing temperature and maturity. The Qaidam and Junggar oils that were derived from the Qaidam source rocks and Junggar coals, respectively are substantially different from the initial bitumens but similar to pyrolysates at the bulk oil generation stage of these source rocks and coals on the basis of Pr/n-C17, Ph/n-C18, Pr/Ph and (Pr + Ph)/(n-C17 + n-C18), demonstrating that these oils were mainly generated and expelled from the Qaidam source rocks and Junggar coals, respectively at the bulk oil generation stage.

Organic matter (OM) is an important host for uranium in coal-bearing systems, but its molecular response to uranium enrichment remains poorly constrained. Here, coal and carbonaceous-debris samples from the Honghaigou coal-hosted uranium deposit, Yili Basin, were investigated using Rock-Eval, FT-IR, solid-state 13C NMR, and negative-ion ESI FT-ICR MS. To reduce the influence of maturity heterogeneity, the three K3216 carbonaceous-debris samples were used as the main within borehole U-abundance comparison, whereas the anomalously high-Tmax sample K36161C was treated as a supplementary case. Within the comparison among the three K3216 samples, the high-U endpoint showed lower aliphatic‑carbon contributions, higher aromatic- and bridgehead‑carbon contributions, and a greater contribution from highly oxygenated polar formulas than the low-U endpoint. FT-ICR MS results showed that CHO compounds dominated the molecular composition of all three K3216 samples. Compared with the other samples, the high-U sample exhibited a greater contribution from CHO species with high oxygen numbers and DBE values. NO-related signals were more evident in the U-rich samples and were tentatively compatible with nitro-related structures. However, neither their specific structures nor their formation pathways could be established, and non-radiogenic origins could not be excluded. Together, these observations are consistent with a possible U-associated radiolytic overprint superimposed on thermal maturation. Because bulk U concentration was used as an abundance indicator rather than a measurement of absorbed dose, the observed contrasts do not establish a quantitative dose–response relationship. This study provides molecular evidence for evaluating OM reactivity and uranium retention in coal-hosted uranium systems.

The fracture properties and creep behavior of coal and its macerals play a critical role in coal mining and exploration, hydraulic fracturing operations, improving the efficiency of (enhanced) coalbed methane recovery, the implementation of geological carbon sequestration technology, and deep underground coal gasification technology. Previous researchers have mainly focused on micromechanical parameters such as Young's modulus and hardness, while it is currently unclear how organic macerals affect their fracture properties (fracture toughness (K-c), brittleness index (B)) and creep behavior of coal. Here, X-ray diffraction, Raman spectroscopy, and nanoindentation were used to investigate the microstructure, fracture properties and creep behavior of sapropelic and humic coals. Results show that the variation of fracture parameters (K-c and B) is similar to the variation of hardness and Young's modulus for different coal macerals. Humic coal exhibited higher brittleness index and creep parameters (viscoelastic parameters (E-1, E-2, eta(1), and eta(2)), and contact creep modulus (C)) compared to sapropelic coal. In addition, the fracture parameters (K-c and B) and the creep parameters (E-1, E-2, eta(1), eta(2,) C-,C- and creep stress exponent (n)) of coal macerals decrease in the order: inertinite > vitrinite > alginite. This suggests that the sapropelic coal and alginite with lower brittle were more prone to creep. The changes in the microfracture and creep parameters of coal maceral are mainly determined by its chemical structure. This study improves the understanding of the fracture properties and creep behavior in the coal and its matrix at the micro scale, which will provide theoretical guidance for optimizing coal seam fracturing and shed light on the creep mechanism of coal.

Accurate assessment of the mechanical properties of organic matter, clay matrix, and bulk shale during maturation remains a challenge. Here, we aim to assess the mechanical properties of organic-rich shale during maturation using a combination of nanoindentation methods and various geochemical analyses, i.e., mineral composition, mass loss rate, chemical structure of organic matter, and Rock-Eval analyses. Results show that the evolution of mechanical properties of organic matter in shale during maturation can be divided into: the main oil-generation stage, and the condensate oil and gas generation stage. The stiffening of organic matter in the shale is mainly due to increased aromaticity and condensation of aromatic groups. The clay matrix experiences a slight decrease in hardness and Young’s modulus at low maturity levels due to the generation of liquid hydrocarbons. However, overall, the clay matrix becomes stiffer as the shale matures due to shale dehydration, expulsion or cracking of liquid hydrocarbons, transformation of clay minerals, and hardening of organic matter. The Young’s modulus and hardness of bulk shale generally increase with increasing maturity. This is closely related to the hardening of organic matter and clay matrix, as well as the development of the more compact and dense microstructure in the shale.

Polymetallic enrichment layers are commonly found at the base of the Lower Cambrian and extensively distributed across the Upper Yangtze Platform, yet their genetic models remain controversial. This study systematically collected samples from a typical section in the southeastern Chongqing region for mineral, organic, and inorganic analyses. It investigates the relationship between the abundance of various trace metal elements and organic matter at the base of the Niutitang Formation, as well as the vertical distribution characteristics of organic carbon isotopes and organic matter features. The results indicate that the Niutitang Formation shale exhibits a distinct three-part structure from bottom to top. Various metal elements are enriched in the lower interval, showing a close correlation between the abundance of polymetallic elements and the carbon isotopes of shale organic matter. The middle interval contains the highest TOC value and the lowest Ti/Al ratio, while the upper interval shows a significant decrease in organic matter abundance, with a clear positive correlation between the excess silicon content and Ti/Al ratio. Additionally, the mixing effect of deep-sea upwelling is the primary control on the formation of polymetallic enrichment layers in the lower interval, followed by the adsorption of organic matter under anoxic conditions. The sedimentary environment of the upper interval of the Niutitang Formation trends toward oxidation, with paleoclimate shifting toward colder and drier conditions, exhibiting aeolian sedimentary features that are unfavorable for the enrichment of trace metal elements. Consequently, upwelling is a key factor in the enrichment and mineralization of trace metal elements at the base of the Lower Cambrian in the Upper Yangtze region.

Asphaltene is one of the main fractions in expelled and retained oils of shales, but its generation, expulsion, and solidification with increasing thermal maturity are still unknown. In this study, low-maturated G1 and G3 Triassic Chang7 shale samples were drilled from the Guo43 well, located in the Northwest margin of the Ordos Basin. These shale samples were adopted for conducting artificial simulation experiments in a semi-closed system to assess their oil generation and expulsion character at different temperatures and various closure capacity conditions. Several shale bulk columns of G1 and G3 shales were made for each temperature point ranging from 320°C to 500°C with a temperature gradient of 20°C. Raw shale samples were settled in autoclaves and heated from 250°C to presetting temperatures with an increasing temperature gradient of 1°C/min and held for 24 h. At the temperature increase stage, the fluid expulsion pipeline which was linked to the system was closed for the G1 shale and open for the G3 shale; at the constant temperature stage, the pipeline was kept open for both shale samples to allow expulsion of generated fluids. A comparison study was conducted to investigate the features of expelled oils and retained oils of artificially maturated G1 and G3 shales to illustrate the effect of the impaction of closure capacity and accompanied fluid pressure on pyrolysis. The results showed that the moderate closure capacity during the heat simulation experiments dramatically decreased the maximum value of the oil expulsion ratio, but increased the production ratio of expelled asphaltenes. The trends of retained oils of G3 shale samples and expelled asphaltenes of G1 shale samples suggested that the solidification of asphaltenes in shale samples processed in Ro ranged from 0.92% to 1.35%. A surge of expelled light hydrocarbons was attributed partially to the discharge of adsorbed and occluded hydrocarbons in solidified asphaltenes.

鄂尔多斯盆地上三叠统延长组长7段富有机质页岩是这一区域页岩油、致密油的主要烃源岩,其生排烃特征是石油勘探开发的关键问题.采取鄂尔多斯盆地西南缘三叠系延长组长7段低熟(Ro=0.55％)页岩岩心样品(TOC=3.59％),设置不同模拟温度(300～570℃),开展原岩岩心柱状样品的半封闭体系生排烃模拟实验,获得了不同成熟度梯度的页岩模拟样品残余及排出烃类.利用低熟煤样标定各模拟温度点的成熟度(0.60％

Oil and condensate reservoirs frequently experienced later gas charging and cap gas leakage. The influences of these two processes on diamondoid concentrations and compositions are not well documented. To investigate these issues, quantitative GC, GC-MS and GC-IRMS analyses were performed on 24 condensates from the Kekeya Field of gas condensate in the Southwestern Depression of the Tarim Basin, northwestern China. Only normal oils filled the reservoirs of this field prior to gas charging. Based on biomarker concentrations and carbon isotopic composition of individual n-alkanes, these oils were derived from multiple source rocks within the Permian and Middle-Lower Jurassic strata within the early to late window of oil generation. Diamondoid concentrations and compositions of condensates were mainly controlled by the gas that subsequently charged the reservoirs and the extents of cap gas leakage. Two deeper condensates KS101C2 and KS101C3 at 6651-6835 m have extremely high concentrations of 4- + 3-methyldiamantanes (4 + 3MD) in the range of 2523-4296 ppm and very low ratios of adamantane/diamantane (A/D) and methyladamantanes/methyldiamantanes (MAs/MDs) in the ranges of 0.10-0.11 and 0.28-0.33, respectively, demonstrating that these reservoirs were charged by the primary gas with high diamondoid concentration that was generated from very deeply buried source rocks at post mature stage in combination with extensive leakage of the cap gas (the secondary gas). The shallower condensate K2C2 at 3319-3326 m has a moderate 4 + 3MD concentration of 18 ppm and very low ratios of A/D and MAs/MDs of 0.00 and 0.19, respectively, demonstrating that this reservoir was charged by the secondary gas in combination with extensive leakage of the cap gas (the third-generation gas). The shallower condensate KX3C at 3765-3820 m has a lower 4 + 3MD concentration of 9 ppm but very high ratios of A/D and MAs/MDs of 8.60 and 16.73, respectively, demonstrating that this reservoir was charged by the third-generation gas with or without minor cap gas leakage. The other twenty condensates have 4 + 3MD concentrations in the range of 7-23 ppm and ratios of A/D and MAs/MDs in the ranges of 0.60-5.29 and 2.18-12.18, respectively, demonstrating that these reservoirs were charged by the secondary or/and third-generation gases with different extents of cap gas leakage. Furthermore, cap gas leakage influenced alkyladamantane ratios of MAI, DMAI-1, TMAI-1, TMAI-2 and EAI but not the alkyldiamantane ratios of MDI, DMDI-1 and DMDI-2 for maturity and source.

Confined pyrolysis experiments (gold capsules), quantitative flash pyrolysis-gas chromatography (Py-GC) and Rock-Eval analysis were performed on ten coals from the Junggar Basin and seven coals from the Kuqa Depression, Tarim Basin, northwestern China. The maximum yields of liquid components in confined pyrolysis experimnets (MCP Sigma C8+), which reflect oil potentials, have close correlations with the yields of n-alkanes + n-alkenes (FP Sigma n-C7+) in flash Py-GC, but have poor correlations with Rock-Eval QI ((S1 + S2)/TOC) values. Thus, oil potentials of coals can be better predicted on the basis of FP Sigma n-C(7+ )yields from flash Py-GC analysis. Coals with FP Sigma n-C7+ yield >10.4 mg/g TOC can generate MCP Sigma C8+, yield >similar to 22.5 mg/g TOC or oil yield >similar to 40 mg/g TOC in confined pyrolysis or in natural systems and are effective oil source rocks. Although both Py-GC and Rock-Eval are open systems, the yields of total liquid components (FP Sigma C7+) obtained from flash Py-GC have poor correlations with, and are substantially lower than, Rock-Eval Ql. In contrast, FP Sigma C7+ values have much better correlations with oil potentials (MCP Sigma C8+). Coals with higher oil potentials (MCP Sigma C8+) generate higher amounts of liquid components detected in flash Py-GC (FP Sigma C7+) than those with lower oil potentials but similar Rock-Eval Ql. The correlations for parameters with gas to oil ratios (GOR) in confined pyrolysis are increasingly better in the sequence of Rock-Eval QI, H/C atomic ratios, MCP Sigma C8+, FP Sigma n-C7+ and FP Sigma n-C7+/Sigma C7+ ratios. GOR of petroleum generated from coals within oil generative window can be reasonably predicted on the basis of FP Sigma n-C7+/Sigma C7+ ratio from flash Py-GC analysis. (C) 2020 Elsevier Ltd. All rights reserved.

Confined pyrolysis experiments (gold capsules) were performed to determine the yields and kinetic features for petroleum formation for seven coal samples with hydrogen index (HI) ranging from 57 to 278 mg HC/g TOC and maturities of 0.58-0.74 %Ro from coal pits within Triassic-Jurassic strata in the Kuqa Depression, China. Gases and liquid yields were measured at regular intervals as the sealed tubes were heated at 2 and 20 degrees C/h and total thermal stress calculated as a vitrinte reflectance equivalent (%Re) using Easy%Ro. The total confined pyrolysate yields of oil and gaseous hydrocarbons at 1.19-1.50 %Re only account for a portion (38-53%) of the releasable moieties in measured by Rock-Eval (open) pyrolysis, suggesting that a substantial portion of (47-62%) of these moieties was rearranged and incorporated into polyaromatic residual solids. At maturities >1.87 %Re, the solid residues of the seven coals have very similar gas generative potentials (Sigma C1-5), which are substantially higher than their quality index (QI = (S1 + S2)/TOC) with differences ranging from 20 to 40 mg/g TOC. This result can be mainly ascribed to the differences both in methane formation mechanisms and final thermal stress levels between open (2.25 %Re) and confined pyrolysis (4.44 %Re). Only a minor portion of gaseous hydrocarbons (similar to 32% and 44% for the Jurassic and Triassic coals, respectively) was generated up to 2.19 %Re while the major portion was generated at higher maturities. Under a heating rate of 5 degrees C/My, the Jurassic and Triassic coals are modeled to become effective gas source rocks with gas yield (Sigma C1-5) > 20 mg/g TOC at maturities of >1.76 %Re and 1.59 %Re, respectively. The abundant gaseous hydrocarbons found in the Kuqa Depression can be mainly ascribed to the high maturities of coal source rocks (>2.0 %Ro), in combination with excellent seal of thick salt and gypsum for the gas reservoirs. (C) 2019 Elsevier Ltd. All rights reserved.

对位于不同构造位置的两条下寒武统牛蹄塘组页岩采石场剖面进行了垂向系统采样研究,并进行了有机地球化学、矿物学及孔隙度测试.酉阳丹泉剖面富有机质层段集中在牛蹄塘组下部,厚度在25 m以上,总有机碳含量(TOC)均大于5.65％,遵义松林剖面仅对下部富有机质页岩进行采样,但基于富有机质层段地球化学垂向变化趋势可进行对比研究.结果表明,页岩微孔体积主要由有机孔提供,且基本不受构造作用影响.松林剖面TOC值越高,伊利石含量越低,介孔体积越小;而构造稳定区页岩介孔体积除部分样品与松林剖面重合外,仍有部分样品介孔体积明显偏高,说明构造位置的差异对页岩介孔具有明显的影响.宏孔体积在TOC大于6.4％时有减小的趋势,但不同构造位置的两剖面样品受构造应力差异影响不明显.构造应力对孔隙的影响主要与岩石的力学性质及伊利石矿物孔的保存能力有关.

中扬子地区页岩气勘探潜力巨大,但页岩发育机制研究相对滞后.选取宜昌地区临湘组、五峰组和龙马溪组25个样品开展了总有机碳(TOC)和主、微量元素测试,重点调查古生产力、沉积环境和陆源输入等指标与富有机质页岩发育的关系.研究发现:五峰组和龙马溪组下段为富有机质层段,过量硅为生物来源;微量元素中P/Ti、Ba/Al和过量钡等古生产力指标与TOC无关,这可能与P、Ba沉积后期的损耗有关;过量铜、过量镍和过量锌构建的古生产力替代系数与TOC呈正相关性,表明高生产力与富有机质页岩的发育密不可分,这与前人的认识有很大不同;氧化还原敏感元素U、V和Mo在五峰组和龙马溪组下段相对富集,且V、Mo与TOC有良好正相关性,表明还原沉积环境是富有机质页岩发育的必要条件;陆源输入指标Al2 O3在龙马溪组上段最高,且TOC与Al、Ti和Th呈负相关关系,表明陆源输入增加对有机质具有稀释效应.综上所述,高古生产力、还原沉积环境和较低的陆源输入有利于海相富有机质页岩的发育.

We conducted a chemical and isotopic study of oilfield waters from Ordovician limestone reservoirs in the Tazhong oilfield (Tarim Basin, China) to trace the origin and evolution of the waters, and to demonstrate their possible relationship with hydrocarbon charging. The elemental chemistry (Cl, Br, SO4, I, K, Na, Ca, Mg, and Sr) and multiple isotopic compositions (δD, δ18O, 87Sr/86Sr, and 129I/I) of the oilfield waters were determined. The results show that these oilfield waters contain basinal brines that infiltrated in three stages, along with a lesser contribution from meteoric water. The meteoric water appears to have infiltrated downwards during the late Silurian and Carboniferous. The earliest brine had very low I contents (<5.65 mg/L) and migrated upwards from organic-poor Cambrian to Lower Ordovician dolostones during the Late Ordovician. The second brine had high I contents (>50 mg/L), was derived from Cambrian argillaceous source rocks, and migrated upwards into Ordovician reservoirs. This stage was related to the main period of migration of crude oils out of the source rocks into reservoirs during the Silurian and Devonian. Both of these brines incorporated constant levels of fissiogenic 129I from the limestone reservoir rocks (11.8–47.0 atom/μL). Finally, brine with very low I contents, but higher 129I (106–491 atom/μL), began to migrate upwards and infiltrate reservoirs. Given the relatively high fissiogenic 129I, this stage may have occurred during the late Cenozoic, and was associated with migration of dry gas from the same source rocks. Our results, combined with those of a previous study of other oilfields in the basin, suggest that the evolutionary of oilfield waters can be used to constrain hydrocarbon accumulation events, and both of which were ultimately controlled by regional tectonism and local geological factors.

Semi-closed heat simulation experiments were conducted on cylindrical samples, and a series of residue samples of Chang7 shale heated to different temperature were acquired to characterize the evolution and controlling factors of shale reservoir structure. Low pressure adsorption experiments with carbon dioxide and nitrogen as the adsorbents were conducted to characterize the evolution of shale nanopores. Mercury intrusion capillary pressure (MICP) and He-Hg porosities of the raw and residue shale columns were measured to study the evolution of porosities with increasing maturity. Also, the morphology of nanopores and microfractures of Argon ion polished shales was examined using scanning electron microscopy. Decreasing trends of micro- and meso-pores with increasing temperature were mainly caused by masking or occupation of pores by generated oil and bitumens during the oil generation stage. Then the specific surface areas (SSAs) and volumes of micro- and meso-pores increase dramatically with increasing temperature as further nanopores were formed through secondary cracking of the generated oil and bitumens. Destruction of nanopores occurred at the over-maturation stage, and caused decreasing trends of SSAs and volumes of micro-pore, meso-pore and macro-pore from 450 degrees C, 489 degrees C and 500 degrees C, respectively. Shale porosity showed a generally positive correlation with temperature, suggesting that macro-pores and micro-fractures were the predominant reservoirs. That was also observed with focused ion beam scanning electron microscopy. The insights into the evolution of shale nanopores presented in this study are generally in accordance with previous research in North America and China on the properties of these structures in shales at different maturation level.

At high maturities,strong alterations in the chemical and isotopic compositions of natural gases can be caused by both thermal cracking and TSR (thermochemical sulfate reduction) processes,which will bring about difficulties in identifying the gas source.By considering that the temperature range of TSR reaction is identical to that of peak generation of condensates,n-heptane and toluene were selected as model compounds to conduct simulation experiments in a temperature programmed furnace,to reveal the characteristics of TSR behavior for saturated and aromatic hydrocarbons and to discriminate the effects of thermal cracking from TSR processes on natural gas.The results illustrate that:1.toluene is intensively involved in TSR reaction at high temperatures,implying that TSR of aromatic hydrocarbons under geological conditions should not be ignored;2.TSR processes can lead to the 13C enrichment of hydrocarbon gases significantly;and 3.according to the differences in yields and carbon isotopes of methane between the blank group and the TSR group,it can be deduced that methane does not directly take part in TSR reaction in these experiments,methane evolution is possibly due to the effect of TSR on its precursors.These findings can provide a reference to evaluate the TSR behaviors of light hydrocarbons under geological conditions and improve our understandings toward the different effects of thermal cracking and TSR processes on natural gas.

Extractable organic matter in shales has great significance to shale gas reservoirs during thermal maturation.A semi-closed thermal simulation was conducted on Chang-7 shales at different temperatures to acquire a set of shale samples at a thermal gradiant range from VRo =0.7％ to VRo =3.5％.And extractable organic matter is characterized according to the comparison study of the shale pore characteristics investigated by low-pressure N2 and CO2 adsorption techniques on different scales before and after solvent extraction.The results show that the TOC,S1,S2 and In of the extracted samples tend to decrease significantly with increasing maturity until VRo =2.0％,then generally become stable at higher maturation level.Solvent extraction may cover the micro-pores mainly and dramatically enhance the volumes of meso-and macro-pores,but only slightly enhance the micro-pore volume.In comparison,the increase of specific surface area after solvent extraction may be mostly contributed by micro-pores,and then by meso-pores.

Organic-rich shales from Lower Silurian are widely distributed in the Middle Yangtze region, central China. However, the lack of fundamental data for shale gas reservoirs increases the difficulty.of gas exploration. In this study, 34 core samples were collected to characterize the shale pore structure and conduct a preliminary evaluation of the shale gas reservoir. The TOC (total organic carbon) content of the successively-deposited black shales range from 1.6% to 5.9%, while the total porosity range from 0.5% to 4.2%. The positive correlation between TOC and porosity indicates that TOC is the key factor determining porosity. The major component of the mineral matrix is quartz (content of 21.4%-69.2%), followed by clay minerals (content of 16.7%-44.5%). Field-emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDS) results illustrate that organic matter, mixed with clay minerals, can form an organo-clay complex containing many nanopores. Furthermore, larger organic pores are developed in organo-clay complexes with higher clay content than in those with lower clay content. Correlational analyses between pore volume (or pore surface area) and TOC (or clay content) demonstrate that micropores are associated with organic matter, while mesopores and macropores are probably associated with clay minerals. Many of the clay-related nanopores are organic in nature and are developed in organo-clay complexes containing both organic matter and clay minerals. Overall, the TOC content controls development of nanopores in the shale pore structure, followed by clay content. The DFT-derived PSD indicates that the pore volume is comprised primarily of pores having widths larger than 10 nm, while the surface area is comprised primarily of micropores. When considering the gas in place model and mechanisms of shale gas storage, further shale gas exploration in central China should aim to the deep (>1000 m) and well preserved Longmaxi Shales. (C) 2017 Elsevier Ltd. All rights reserved.

Formation water invasion is common in production wells,which rise concerns about future production potential of hydrocarbon resources.Thus,the preservation regularity of the formation water and the relationship between the reservoir and hosted formation water are very important.A comparative study of the variation of formation waters in Lungu7 (LG7)and Lungu2(LG2)wellblocks are conducted in order to address relationship between the characteristics of formation water and geological setting.These two wellblocks are located at structural location of the Lunnan Oilfield:The LG7 well-block is located at the tectonic high position with Carbonaceous layer partly wedge out,whereas the LG2 wellblock is loca-ted at the tectonic lower position with thicker Carbonaceous layer.The formation water in all producing wells at LG7 well-block have similar chlorine concentration over time,suggesting that the producing wells in LG7 wellbolck have good con-nectivity.On the contrary,the formation water in producing wells at LG2 wellblock are highly variable in composition,in-dicative of poor connectivity of LG2 reservoir.Formation water in LG7 wellblock has higher Cl/Br ratios and coefficient of desulfurization than that in LG2 wellblock.These results show that the carbonate reservoir in LG7 wellblock is more open, and is apparently affected by salt dissolved water compared with that in LG2 wellblock.Thus,it is concluded the reservoir connectivity is controlled by the geological setting.Distance to the wedge line of the Carboniferous layer and the thickness of Carboniferous sand-mudstones have negative correlation of openness and connectivity of the reservior.