Experimental investigation of water absorption and its significance on pore network connectivity in mudstone from Silurian Longmaxi Formation, Sichuan basin

In this study, a test was carried out on organic carbon, sulfur content, major and trace elements of 24 shale samples from fresh outcrop sections in Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation, Shuanghe Town, Changning County, Sichuan Basin. Moreover, this study analyzed the vertical variation characteristics of major and trace element contents and their relationship with sea-basin paleo-sedimentary environment and explored the major controlling factors for organic matter enrichment in Ordovician-Silurian shale of Sichuan Basin. Research results show that the organic carbon content is higher (2.2%-7.76%)in the reservoir intervals about 20 m above Wufeng Formation to the bottom of Longmaxi Formation, then decreased upwards to stable value of 0.81%-1.83%. Major components of shale include SiO2(55.67%), Al2O3(10.13%)and CaO (9.51%). The contents of TiO2and SiO2are lower at the bottom of profile and then increased upwards, indicating the increased input of terrigenous clastics. The SiO2and CaO contents of organic-rich shale are apparently higher than those of organic-poor shale, but the contents of Al2O3, Fe2O3and TiO2are lower. Meanwhile, redox sensitive elements (Mo, U, V, Ni, Co, Cr)and nutritional elements Ba are significantly enriched in the organic-rich interval. Ni/Co, V/Cr, U/Th and the degree of pyritization(DOPT) indicate that Wufeng Formation presents large changes in water mass redox conditions, dominated by suboxic and anoxic conditions. The water mass at the bottom of Longmaxi Formation has a higher reducibility than Wufeng Formation, indicating a euxinic environment with certain content of H2S. However, normal oxygen enrichment environment exists in the middle and upper part. The contents of P and excess Ba (Baxs) in shale demonstrate a higher productivity in the sedimentary stage of Wufeng Formation-Longmaxi Formation, while TOC content has a positive correlation with redox proxies, suggesting that the changes in organic matter content is predominantly controlled by redox environment. The cross plots of Mo/TOC and DOPTshow that redox condition and water retention is the major controlling factor for trace element enrichment in Longmaxi Formation shale and Wufeng Formation, respectively. Organic matter enrichment in Longmaxi Formation is mainly controlled by the degree of seawater anoxic resulting from the rise and fall of sea level. However, anoxic environment in Wufeng Formation caused by water retention leads to favorable preservation of organic matter. © 2015, Editorial Office of ACTA PETROLEI SINICA. All right reserved.

The statistical discrepancy of physical properties of summer precipitation clouds over the Qinghai-Xizang Plateau,Sichuan Basin and their transition region were analyzed,based on July and August Cloud Sat products from 2008 to 2010. At the same time,four examples from Cloud Sat,FY- 2D TBB data and surface precipitation products were also analyzed to discuss howthe different physical properties lead to the different precipitation of summer precipitation clouds over studying regions. The results showed that:( 1) As to the macrophysical properties of clouds,the main precipitation clouds of the Qinghai-Xizang Plateau were Cu and Ci,lowlevel clouds accounted for the largest proportion,it were Ns and Ci in Sichuan Basin and transition region. Compared with Basin,the clouds base was higher and top was lower in Plateau,it could rain while convection will not deep enough. In three regions,single layer cloud was easier to rain than multilayer one.( 2) As for the microphysical properties of clouds,the main precipitation clouds of the Qinghai-Xizang Plateau was ice cloud,mixed cloud was second,the least was liquid water cloud,mixed cloud accounted for the largest proportion in Sichuan Basin. The clouds were mostly at the beginning of lifetimes in statistics,although the differences were not obvious,the effective radius and distribution width parameter of cloud ice particles over the Qinghai-Xizang Plateau were bigger and wider than those in the other two regions. Their number concentration were similarly,that could quicken the cold cloud processes. It was slower to developed ice cloud processes in Sichuan Basin than that in the QinghaiXizang Plateau.

The dataset includes the measured gas permeability data of sample L1P and L1V under different pressure conditions (confining pressure and pore pressure), in the comment you will find the fitted results of response surface model (RSM). All data was measured by PoroPDP-200 full-automatic instrument (Core Lab, USA) based on pressure pulse decay technique, with nitrogen as the probing gas.Sampling site is Heye Village, Shuanghe Town, Changning County, Sichuan Province (Latitude: 28.392287 * Longitude: 104.887276).

The exploitation and exploration of shale gas is of great values to solve the energy problem. Taking the shale from Silurian Longmaxi formation in Sichuan Basin as an example, its geological characteristics and reservoir chemical reaction under the action of fracturing fluid were analyzed, and moreover, a series of data determination and fracturing fluid chemical reaction experiments were carried out. The results showed that the average total organic carbon value of shale in the study area was 4.79%, the kerogen type was type I, the ratio of aliphatic structure to aromatic structure was smaller than 1, the average RO value was 2.15%, the content of clay mineral in the mineral composition was high, the average porosity was 3.16%, and the average permeability was 0.036 × 103 μm2, which was conducive to shale gas generation; under the action of fracturing fluid, the sulfate mineral in the shale dissolved, clay mineral expanded, and the pore volume and specific surface area reduced. The results verify that the research area has shale gas mining value, and this study makes some contributions to further study the optimization of fracturing fluid and improve exploitation technology.

The pore structure of shale plays key role in oil and gas storage capacity and accumulation. Twelve representative samples were selected from Triassic Yanchang Formation in the Ordos Basin and Silurian Longmaxi Formation in the Sichuan Basin with different ages, depositional settings, and maturities to analyze shale pore structure using focused ion beam-scanning electron microscopy and high-pressure mercury intrusion capillary porosimetry. The results show that the pores of lacustrine shale with maturity Ro < 1.3% from the Triassic Yanchang Formation were predominantly composed of pores with pore throat diameter of larger than 30 µm. The pores of marine shale with maturity Ro > 1.3% from the Silurian Longmaxi Formation were predominantly composed of pores with pore throat diameter of smaller than 100 nm. For the porosity, the average porosity of low-mature lacustrine shale is 2.4%, while the average porosity of high-mature marine shale is 1.5%. For the pore type, intergranular inorganic pores predominantly occurred between mineral particles in the lacustrine shale, while the marine shale mainly developed organic pores with pore throat diameters ranging from 5 to 200 nm. Compared to the low-mature lacustrine shale, macropores of high-mature marine shale are less developed and micropores dominant. Importantly, brittle minerals (quartz, feldspar, and carbonate minerals) mainly affect the pore structure of lacustrine shale, while organic matter mainly affects the pore structure of marine shale.

This paper discusses the main factors affecting generation and accumulation of shale gas in the Qiongzhusi and Longmaxi formations in and around the Sichuan Basin, China, based on case studies and comparative analysis of sedimentary environments, lithological associations, basic parameters of shale gas, roof and floor conditions and carrier systems. Both the Qiongzhusi and Longmaxi Formations contain good-quality thick shale strata with high TOC, brittle minerals contents, and gas contents. The accumulation of shale gas is affected by the transport systems and the preservation conditions, especially the roof and floor lithology. The overlying strata of the Longmaxi Formation is tight and thick mudstone and muddy siltstone. The underlying strata of the Longmaxi Formation is tight and thick limestone. Both overlying and underlying strata all have low porosity and low permeability, which acts as a good roof and floor for shale gas preservation and subsequent mass fracturing reformation. Overlying strata of Qiongzhusi formation and Longmaxi is similar and served as a good roof. But the underlying stratum of the Qiongzhusi Formation is a regional reservoir that usually contains aquifers; theredore, it isn't a good floor for shale gas preservation. As a result of these conditions, the Longmaxi Formation has better shale gas accumulation conditions than that of the Qiongzhusi Formation.

Dispositional characteristics of Ordovician Wufeng Formation and Silurian Longmaxi Formation in Sichuan Basin and its adjacent areas

Five planetary boundary layer (PBL) parameterization schemes [Yonsei University (YSU), Mellor–Yamada–Janjic (MYJ), Mellor–Yamada–Nakanishi–Niino Level 2.5 (MYNN2), Shin-Hong (SH), and the asymmetric convective model, version 2 (ACM2)] in the Weather Research and Forecast model (WRF v4.0), were used to simulate all well-developed Southwest China vortex (SWCV) processes in the eastern Sichuan basin in 2016. Each level of precipitation prediction was verified, and the L-band radiosonde data with temporal resolution of 1 s were used to reveal the fine structure of the PBL during a midday. The differences between the observation and simulation are assessed, and the reasons are discussed based on the characteristics of the turbulence algorithm used in each scheme. Finally, the parameter of turbulence intensity was adjusted for the ACM2 scheme to improve the structure of the PBL that influences the simulation of the precipitation in the eastern Sichuan basin. The results show that the ACM2 and YSU schemes show a relatively better TS performance. Compared with other schemes, ACM2 has fewer false alarms. The attribute of ACM2 that can modify local or nonlocal algorithms according to the stability of the surrounding environment seems to be more suitable for the Sichuan basin precipitation simulation than the other schemes. However, all PBL schemes show a high false-alarm rate in the prediction of the SWCV precipitation, especially when the precipitation is heavy. The sounding data with 1 s temporal and 3 m spatial resolution further show that all the PBL schemes predict a higher PBL height compared with that of the observations, which means that the simulation has a stronger mixing intensity compared with that of the real atmosphere. By parameter adjustment, using the ACM2 scheme with reduced mixing intensity, the potential temperature and humidity structure in PBL are more aligned with the observations. Further, the potential temperature of the low PBL is low, humidity is high, and false alarm reports of heavy precipitation are reduced, which leads to an improvement regarding the precipitation simulation in the Sichuan basin. The different characters of the PBL schemes that are used in the simulation of the SWCV mainly lead to different positions of the vortex and precipitation intensity. Essentially, these characters are derived from a local or nonlocal attribute and the intensity of vertical mixing. A selection based on regional features of a research object is the key to the accurate simulation of a PBL structure and precipitation process.

To explore the population-genetics characteristics of Mycobacterium tuberculosis (MTB) prevailing at the Sichuan basin of China. A total of 413 MTB strains collected from Sichuan basin were genotyped by large sequence polymorphism (LSP) and 15 loci variable number tandem repeat (VNTR). Difference between the distribution of lineage population was analyzed by χ(2)-test and the discriminatory ability of each VNTR locus was evaluated under the Hunter-Gaston Discriminatory Index (HGI). Both phylogeny on population level and genetic structure were demonstrated through N-J tree and the Minimal Spanning Tree (MST). Genetic differentiation of different lineage strains was analyzed by Analysis of Molecular Variance (AMOVA). Time of the Most Recent Common Ancestor (TMRCA) was calculated based on the Bayesian model. Four hundred and thirteen MTBs were divided into two major lineages, in which the Beijing lineage accounted for 56.2% (232/413) and the Euro-American lineage for 43.8% (181/413). There was no significant difference of population distribution between the two lineages (P > 0.05). The N-J tree of Beijing lineage MTB presented distinctly "star-like" and 72.4% strains were grouped to one clonal complex in MST. The Euro-American lineages MTB presented "branch-like" in N-J tree and were grouped into multiple clonal complexes in MST. There was significant genetic differentiation in Beijing lineage MTBs between Chongqing and Sichuan (FST = 0.018 91, P < 0.05), but not in the Euro-American lineage MTB (FST = 0.005 19, P > 0.05). TMRCA of the largest clonal complex in Euro-American lineage MTB appeared to be 723 (95% CI: 517-946) years. Both Beijing lineage and Euro-American lineage MTBs were competitively prevalent in the Sichuan basin. There was some difference noticed between the two lineages referring to genetic differentiation. The invasion of Euro-American lineages MTB to the basin area might be associated with a war occurred in this area about 720 years ago.

Factors controlling microfractures in black shale: A case study of Ordovician Wufeng Formation–Silurian Longmaxi Formation in Shuanghe Profile, Changning area, Sichuan Basin, SW China

Data for: Organic geochemistry of the Upper Triassic T3x5 source rocks and the hydrocarbon generation and expulsion characteristics in Sichuan Basin, Central China

Mechanisms of shale gas generation and accumulation in the Ordovician Wufeng-Longmaxi Formation, Sichuan Basin, SW China

The study of noble gases and reactive gases (i.e., CO2, N2 and CH4) in crustal reservoirs can help better understand the origin, migration and accumulation processes of crustal fluids in the subsurface environment, which provide further insights into fluid dynamics underground. This PhD thesis develops noble gas isotopes as geochemical tools in crustal fluid studies. Study sites have been selected to cover different types of geofluids, including geothermal fluids in Krafla, Iceland and natural gases in the Sichuan Basin, China. Following a short introduction to the research background, objectives and thesis layout are presented in Chapter 1 and Chapter 2 gives a literature review on the application of noble gases as powerful geochemical tools in hydrothermal and hydrocarbon systems. Chapter 3 describes a noble gas extraction and purification system, interfaced to a multi-collector NGX noble gas mass spectrometer (Isotopx), which is constructed particularly for this study. The detailed description of each section in sample preparation system, as well as gas sampling, extraction, purification and separation protocols is provided. Temperatures of 50 K and 95 K can be used as the optimal releasing temperatures for He and Ne on the cryotrap in sample prepline. The temperature of 210 K is tested to be the optimal temperature for releasing Ar and Kr but keeping Xe being trapped onto the charcoal trap in the prepline. Chapter 4 characterizes noble gas and stable isotope data of hydrothermal fluid system in Krafla, Iceland. Stable isotope results indicate that CO2 in the samples is considered to be magmatic in origin, with δ13C (CO2) ranging between -7.99 and -3.86 ‰. Modelling results show that processes of boiling and steam separation have occurred during the circulation of geothermal fluids in the shallow crust in the Krafla field. Air addition, possibly introduced by groundwater re-injection, has had a significant effect on the geochemical signatures of Krafla geothermal fluids as well. Chapter 5 focuses on using noble gas isotopes to trace the interaction between hydrocarbon and groundwater systems in the central Sichuan Basin, China. Twenty-six natural gas samples were collected from the Anyue and Weiyuan gas fields in the central Sichuan basin, China for stable isotope and noble gas isotope determination. Noble gases together with stable carbon isotopic parameter (Δδ 13C1-2) can be an effective tool to differentiate the occurrence of two distinct genetic groups of natural gases in the central Sichuan basin. Elemental fractionations of noble gases in samples from the western area (coal-derived gas) can be well explained by solubility-controlled Rayleigh fractionation model with relatively less effect of mass-dependent fractionation process. However, noble gas elemental and isotopic compositions in samples from the eastern area can be interpreted as a mixing effect of solubility-controlled and mass-dependent fractionation processes. This thesis further develops noble gases as a versatile tool in the study of crustal fluids. It is the first-time noble gas isotopes are used in understanding fluid dynamics in natural gas reservoirs in China. This work has demonstrated a huge potential to apply the noble gas tool in basin studies in China and Asian geology in general.

Camphora longepaniculata is an endangered evergreen tree listed as National Class II Protected Tree Species in China, highly valued for its medicinal and economic importance. Currently, research on this species has primarily focused on its pharmaceutical properties, while its potential distribution and responses to climate change remain insufficiently explored. In this study, 36 valid occurrence records and 11 environmental variables were utilized to predict its potential distribution and assess its response to future climate scenarios. The MaxEnt model revealed that the current distribution of C. longepaniculata largely aligns with its predicted suitable habitats, with the primary range located in Sichuan Province. Furthermore, this model identified the highly suitable habitats to be predominantly concentrated in Sichuan and Shaanxi Provinces under climate change. Among the environmental variables, annual precipitation (bio12), minimum temperature of the coldest month (bio6), and elevation (dem) were the most influential, collectively contributing over 70% to the model’s predictive accuracy. Future climate projections compared to the current distribution suggest a northward expansion of suitable habitats for C. longepaniculata, although Sichuan Province is predicted to remain the core habitat under future scenarios. Kernel density analysis of occurrence points indicated that the largest concentration of distribution points is near the Sichuan Basin, reinforcing the importance of this region as a stronghold for the species. Based on the results of potential distribution and kernel density analysis, in situ conservation, artificial cultivation, and the establishment of wild protected areas and local germplasm banks are recommended for stable, suitable habitats, such as Sichuan Province and parts of Yunnan and Guizhou Provinces. This study not only sheds light on the potential geographical distribution of C. longepaniculata and its response to climate change but also provides a scientific basis for the development of targeted conservation strategies for this species.

Ultra-deep carbonate reservoirs in the Permian Qixia Formation of the Sichuan Basin, particularly those exceeding 7000m in depth, have emerged as a significant focus for exploration and development. However, production capacities between adjacent wells can vary by up to two orders of magnitude due to the multi-scale heterogeneity of pore connectivity, which poses challenges for accurately predicting well performance. This study utilizes thin-section analysis, high-pressure mercury injection (HPMI), scanning electron microscopy (SEM), and other techniques to investigate pore connectivity in ultra-deep reservoirs. It also explores methods for evaluating the connectivity of multi-scale pore networks in the Qixia Formation. The analysis reveals distinct permeability contribution patterns and connectivity characteristics across different reservoir types. Results indicate that the carbonate reservoirs in the Qixia Formation are predominantly composed of dolomite, with intercrystalline pores, dissolution pores, and fractures constituting the primary pore types. The pore-throat size distribution exhibits significant heterogeneity, as evidenced by a multi-peak distribution curve. Approximately 25% of the reservoirs contain well-connected pores, and a threshold radius (r25) is identified as a key parameter for assessing connectivity. Overall, pore connectivity within the reservoirs is limited, with fractures playing a critical role in linking isolated pore spaces. This study introduces the parameter SHgf, which quantitatively evaluates the connectivity of multi-scale pore networks and distinguishes the abundance of fractures within the reservoir using a boundary value of 7%. By analyzing fluid seepage patterns, a permeability contribution model for the four identified reservoir types is established, providing a robust framework for assessing reservoir connectivity. These findings offer valuable insights for predicting production capacities and optimizing development strategies in ultra-deep carbonate reservoirs.