Petrophysics of coals directly affects the development of coalbed methane (CBM). Based on the analysis of the representative academic works at home and abroad, the recent progress on petrophysics characteristics was reviewed from the aspects of the scale-span pore-fracture structure, permeability, reservoir heterogeneity, and its controlling factors. The results showed that the characterization of pore-fracture has gone through three stages: qualitative and semiquantitative evaluation of pore-fracture by various techniques, quantitatively refined characterization of pore-fracture by integrating multiple methods including nuclear magnetic resonance analysis, liquid nitrogen, and mercury intrusion, and advanced quantitative characterization methods of pore-fracture by high-precision experimental instruments (focused-ion beam-scanning electron microscopy, small-angle neutron scattering and computed tomography scanner) and testing methods (m-CT scanning and X-ray diffraction). The effects of acoustic field can promote the diffusion of CBM and generally increase the permeability of coal reservoirs by more than 10%. For the controlling factors of reservoir petrophysics, tectonic stress is the most crucial factor in determining permeability, while the heterogeneity of CBM reservoirs increases with the enhancement of the tectonic deformation and stress field. The study on lithology heterogeneity of deep and high-dip coal measures, the spatial storage-seepage characteristics with deep CBM reservoirs, and the optimizing production between coal measures should be the leading research directions.
Tight sandstone reservoirs are generally characterized by complex reservoir quality, non-Darcy flow, and strong heterogeneity. Approaches utilized for evaluating physical property cutoffs of conventional reservoirs maybe inapplicable. Thus, a comprehensive investigation on physical property cutoffs of tight sandstone reservoirs is crucial for the reserve evaluation and successful exploration. In this study, a set of evaluation approaches take advantage of field operations (i.e., core drilling, oil testing, and wireline well logging data), and simulation experiments (i.e., high-pressure mercury injection-capillary pressure (MICP) experiment, oil-water relative permeability experiment, nuclear magnetic resonance (NMR) experiment, and biaxial pressure simulation experiment) were comparatively optimized to determine the physical property cutoffs of effective reservoirs in the Upper Triassic Chang 6, Chang 8 and Chang 9 oil layers of the Zhenjing Block. The results show that the porosity cutoffs of the Chang 6, Chang 8, and Chang 9 oil layers are 7.9%, 6.4%, and 8.6%, and the corresponding permeability are 0.08 mD, 0.05 mD, and 0.09 mD, respectively. Coupled with wireline well logging, mud logging, and oil testing, the cut-off of the thickness of single-layer effective reservoirs are approximately 3.0 m, 3.0 m, and 2.0 m, respectively. Depending on the cutoffs of critical properties, a superimposed map showing the planar distribution of the prospective targets can be mapped, which may delineate the effective boundary of prospective targets for petroleum exploration of tight sandstone reservoirs.
The sandstone of the third member of the Funing Formation (E1f3) in the northern slope zone of the Gaoyou Sag has the typical characteristics of high porosity and ultralow permeability, which makes it difficult for oil to flow. In this study, the lithological characteristics, sedimentary facies, diagenetic characteristics, pore structure, and seepage ability of this sandstone are characterized in detail. Correlation analysis is used to reveal the reason for the sandstone high porosity-low permeability phenomenon in the study area. The results indicate that this phenomenon is controlled mainly by the following three factors: 1) the sedimentary environment is the initial affecting factor, whereby the deposition of a large number of fine-grained materials reduces the primary pores of sandstone. 2) The Funing Formation has undergone strong compaction and cementation, which have led to the removal of most of the primary pores and a reduction in size of the throat channels. 3) Owing to fluid activity during the later stage of diagenesis, sandstone underwent intense dissolution and a large number of particles (feldspar and lithic debris) formed many dissolution pores (accounting for nearly 60% of the total pore space). Among these factors, dissolution has contributed the most to the development of high porosity-low permeability phenomenon. This is mainly attributed to the inhomogeneous dissolution process, whereby the degree of particle dissolution (e.g. feldspar) exceeds that of cementing minerals (clay and carbonate minerals). The secondary dissolution pores have increased the porosity of sandstone in the study area; however, the pore connectivity (permeability) has not been significantly improved, thus resulting in the special high porosity-low permeability characteristics of this sandstone.
Investigation into natural fractures is extremely important for the exploration and development of low-permeability reservoirs. Previous studies have proven that abundant oil resources are present in the Upper Triassic Yanchang Formation Chang 7 oil-bearing layer of the Ordos Basin, which are accumulated in typical low-permeability shale reservoirs. Natural fractures are important storage spaces and flow pathways for shale oil. In this study, characteristics of natural fractures in the Chang 7 oil-bearing layer are first analyzed. The results indicate that most fractures are shear fractures in the Heshui region, which are characterized by high-angle, unfilled, and ENE-WSW-trending strike. Subsequently, natural fracture distributions in the Yanchang Formation Chang 7 oil-bearing layer of the study area are predicted based on the R/S analysis approach. Logs of AC, CAL, ILD, LL8, and DEN are selected and used for fracture prediction in this study, and the R(n)/S(n) curves of each log are calculated. The quadratic derivatives are calculated to identify the concave points in the R(n)/S(n) curve, indicating the location where natural fracture develops. Considering the difference in sensitivity of each log to natural fracture, gray prediction analysis is used to construct a new parameter, fracture prediction indicator K, to quantitatively predict fracture development. In addition, fracture development among different wells is compared. The results show that parameter K responds well to fracture development. Some minor errors may probably be caused by the heterogeneity of the reservoir, limitation of core range and fracture size, dip angle, filling minerals, etc.
Considering the complementarity of synchrotron radiation SAXS and nano-CT in the pore structure detection range, synchrotron radiation SAXS and nano-CT methods were combined to characterize the nano- to micro-pore structure of two bituminous coal samples. In mesopores, the pore size distribution curves exhibit unimodal distribution and the average pore diameters are similar due to the affinity of metamorphic grades of the two samples. In macropores, the sample with higher mineral matter content, especially clay mineral content, has a much higher number of pores. The fractal dimensions representing the pore surface irregularity and the pore structure heterogeneity were also characterized by synchrotron radiation SAXS and nano-CT. The fractal dimensions estimated by both methods for different pore sizes show consistency and the sample with smaller average pore diameters has a more complex pore structure within the full tested range.
The positive S-isotopic excursion of carbonate-associated sulfate (δ34SCAS) is generally in phase with the Steptoean positive carbon isotope excursion (SPICE), which may reflect widespread, global, transient increases in the burial of organic carbon and pyrite sulfate in sediments deposited under large-scale anoxic and sulphidic conditions. However, carbon-sulfur isotope cycling of the global SPICE event, which may be controlled by global and regional events, is still poorly understood, especially in south China. Therefore, the δ13CPDB, δ18OPDB,δ34SCAS, total carbon (TC), total organic carbon (TOC) and total sulfate (TS) of Cambrian carbonate of Waergang section of Hunan Province were analyzed to unravel global and regional controls on carbon-sulfur cycling during SPICE event in south China.
The δ34SCAS values in the onset and rising limb are not obviously higher than that in the preceding SPICE, meanwhile sulfate (δ34SCAS) isotope values increase slightly with increasing δ13CPDB in rising limb and near peak of SPICE (130–160 m). The sulfate (δ34SCAS) isotope values gradually decrease from 48.6‰ to 18‰ in the peak part of SPICE and even increase from 18‰ to 38.5% in the descending limb of SPICE. The abnormal asynchronous C-S isotope excursion during SPICE event in the south China was mainly controlled by the global events including sea level change and marine sulfate reduction, and it was also influenced by regional events such as enhanced siliciclastic provenance input (sulfate), weathering of a carbonate platform and sedimentary environment. Sedimentary environment and lithology are not the main reason for global SPICE event but influence the δ13CPDB excursion-amplitude of SPICE. Sea level eustacy and carbonate platform weathering probably made a major contribution to the δ13CPDB excursion during the SPICE, in particularly, near peak of SPICE. Besides, the trilobite extinctions, anoxia, organic-matter burial and siliciclastic provenance input also play an important role in the onset, early and late stage of SPICE event.
As one of the most devastating tropical cyclones over the western North Pacific Ocean, Super Typhoon Lekima (2019) has caused a wide range of heavy rainfall in China. Based on the CMA Multi-source merged Precipitation Analysis System (CMPAS)-hourly data set, both the temporal and spatial distribution of extreme rainfall is analyzed. It is found that the heavy rainfall associated with Lekima includes three main episodes with peaks at 3, 14 and 24 h after landfall, respectively. The first two rainfall episodes are related to the symmetric outburst of the inner rainband and the persistence of outer rainband. The third rainfall episode is caused by the influence of cold, dry air from higher latitudes and the peripheral circulation of the warm moist tropical storm. The averaged rainrate of inner rainbands underwent an obvious outburst within 6 h after landfall. The asymmetric component of the inner rainbands experienced a transport from North (West) quadrant to East (South) quadrant after landfall which was related to the storm motion other than the Vertical Wind Shear (VWS). Meanwhile the outer rainband in the vicinity of three times of the Radius of Maximum Wind (RMW) was active over a 12-h period since the decay of the inner rainband. The asymmetric component of the outer rainband experienced two significant cyclonical migrations in the northern semicircle.
Estimating horizontal winds in and around typhoons is important for improved monitoring and prediction of typhoons and mitigating their damages. Here, we present a new algorithm for estimating typhoon winds using multiple satellite observations and its application to Typhoon Soulik (2018). Four kinds of satellite remote sensing data, along with their relationship to typhoon intensity, derived statistically from hundreds of historical typhoon cases, were merged into the final product of typhoon wind (MT wind): 1) geostationary-satellite-based infrared images (IR wind), 2) passive microwave sounder (MW wind), 3) feature-tracked atmospheric motion vectors, and 4) scatterometer-based sea surface winds (SSWs). The algorithm was applied to two cases (A and B) of Typhoon Soulik and validated against SSWs independently retrieved from active microwave synthetic aperture radar (SAR) and microwave radiometer (AMSR2) images, and vertical profiles of wind speed derived from reanalyzed data and dropsonde observations. For Case A (open ocean), the algorithm estimated the realistic maximum wind, radius of maximum wind, and radius of 15 m/s, which could not be estimated using the reanalysis data, demonstrating reasonable and practical estimates. However, for Case B (when the typhoon rapidly weakened just before making landfall in the Korean Peninsula), the algorithm significantly overestimated the parameters, primarily due to the overestimation of typhoon intensity. Our study highlights that realistic typhoon winds can be monitored continuously in real-time using multiple satellite observations, particularly when typhoon intensity is reasonably well predicted, providing timely analysis results and products of operational importance.
During the coalbed methane (CBM) exploitation, the reservoir permeability can be affected by the effective stress that varies with the reservoir fluid pressure, which is a complex, dynamic and significant engineering problem. To analyze the response characteristics of the pore-fracture system by the changing stress, this work simulated reservoir and fluid pressures during the exploitation by adjusting confining pressure and displacement pressure. Stress sensitivity experiments under different effective stresses were conducted to systematically study the stage variation characteristics of porosity and permeability of coal. The results show that the permeability decreases exponentially with the increase in effective stress, consistent with previous studies. However, the porosity shows a V-shaped trend, which is different from the traditional understanding that it would decrease continuously with rising effective stress. These variation characteristics (of porosity and permeability above) therefore result in a phased porosity sensitivity of coal permeability (PPS). Moreover, the stress sensitivity of the samples was evaluated using the permeability damage rate method (MPDR) and the stress sensitivity coefficient method (MCSS), both of which showed that it ranges from the degree of strong to extremely strong. When the effective stress is lower than 5–6 MPa, the stress sensitivity of the coal reservoir drops rapidly with effective stress rising; when it is higher than 5–6 MPa, the change in stress sensitivity tends to flatten out, and the stress sensitivity coefficient (CSS) goes down slowly with rising effective stress. Finally, suggestions are proposed for the drainage scheme of CBM wells based on the experimental results.
Shale gas is a relatively clean-burning fossil fuel, produced by hydraulic fracturing. This technology may be harmful to the environment; therefore, environmentally friendly methods to extract shale gas have attracted considerable attention from researchers. Unlike previous studies, this study is a comprehensive investigation that uses systematic analyses and detailed field data. The environmental challenges associated with shale gas extraction, as well as measures to mitigate environmental impacts from the source to end point are detailed, using data and experience from China’s shale gas production sites. Environmental concerns are among the biggest challenges in practice, mainly including seasonal water shortages, requisition of primary farmland, leakage of drilling fluid and infiltration of flowback fluid, oil-based drill cuttings getting buried underground, and induced seismicity. China’s shale gas companies have attempted to improve methods, as well as invent new materials and devices to implement cleaner processes for the sake of protecting the environment. Through more than 10-year summary, China’s clean production model for shale gas focuses on source pollution prevention, process control, and end treatment, which yield significant results in terms of resource as well as environmental protection, and can have practical implications for shale gas production in other countries, that can be duplicated elsewhere.
Gaofen-3 (GF-3) is the first Chinese spaceborne multi-polarization synthetic aperture radar (SAR) instrument at C-band (5.43 GHz). In this paper, we use data collected from GF-3 to observe Super Typhoon Lekima (2019) in the East China Sea. Using a VH-polarized wide ScanSAR (WSC) image, ocean surface wind speeds at 100m horizontal resolution are obtained at 21:56:59 UTC on 8 August 2019, with the maximum wind speed, 38.9 m·s−1. Validating the SAR-retrieved winds with buoy-measured wind speeds, we find that the root mean square error (RMSE) is 1.86 m·s−1, and correlation coefficient, 0.92. This suggests that wind speeds retrieved from GF-3 SAR are reliable. Both the European Centre for Medium-Range Weather Forecasts (ECMWF) fine grid operational forecast products with spatial resolution, and China Global/Regional Assimilation and Prediction Enhance System (GRAPES) have good performances on surface wind prediction under weak wind speed condition (<24 m·s−1), but underestimate the maximum wind speed when the storm is intensified as a severe tropical storm (>24 m·s−1). With respect to SAR-retrieved wind speeds, the RMSEs are 5.24 m·s−1 for ECMWF and 5.17 m·s−1 for GRAPES, with biases of 4.16 m·s−1 for ECMWF and 3.84 m·s−1 for GRAPES during Super Typhoon Lekima (2019).
Lacustrine shale oil resources in China are abundant, with remarkable exploration breakthroughs being achieved. Compared to marine shale oil in North America, efficient exploration of lacustrine shale oil is more difficult; thus, selecting favorable layer and optimization zone for horizontal wells is more important. In this study, based on systematic coring of approximately 500 m fine-grained deposits of the Kong 2 Member, combining laboratory tests and log data, source rock geochemistry and reservoir physical properties, the favorable rock fabric facies for oil accumulation was analyzed and classified. First, the dominant lithologic facies, organic facies, and bed combination facies were determined based on mineral composition from logging, total organic content (TOC), and sedimentary structure. Secondly, 10 fabric facies were classified by combining these three facies, with 4 fabric facies were found to have high TOC content, high total hydrocarbon, and strong fluorescence features, indicating good shale oil enrichment. Thirdly, the distribution of the upon good fabric facies was identified to be located at the top of the Kong 2 Member, with evidences of seismic resistivity inversion, thermal maturity, structure depth, and strata thickness. And the favorable facies were found to be stably distributed lateral at the area of about 100 km2. High oil flow has been detected at this layer within this area by several wells, including horizontal wells. The exploratory study of fabric facies classification and evaluation provides a new research idea for lacustrine shale oil exploration and effectively promotes breakthroughs in lacustrine shale oil exploration in Bohai Bay Basin.
Natural fractures are of crucial importance for oil and gas reservoirs, especially for those with ultralow permeability and porosity. The deep-marine shale gas reservoirs of the Wufeng and Longmaxi Formations are typical targets for the study of natural fracture characteristics. Detailed descriptions of full-diameter shale drill core, together with 3D Computed Tomography scans and Formation MicroScanner Image data acquisition, were carried out to characterize microfracture morphology in order to obtain the key parameters of natural fractures in such system. The fracture type, orientation, and their macroscopic and microscopic distribution features are evaluated. The results show that the natural fracture density appears to remarkably decrease in the Wufeng and Longmaxi Formations with increasing the burial depth. Similar trends have been observed for fracture length and aperture. Moreover, the natural fracture density diminishes as the formation thickness increases. There are three main types of natural fractures, which we interpret as (I) mineral-filled fractures (by pyrite and calcite), i.e., veins, (II) those induced by tectonic stress, and (III) those formed by other processes (including diagenetic shrinkage and fluid overpressure). Natural fracture orientations estimated from the studied natural fractures in the Luzhou block are not consistent with the present-day stress field. The difference in tortuosity between horizontally and vertically oriented fractures reveals their morphological complexity. In addition, natural fracture density, host rock formation thickness, average total organic carbon and effective porosity are found to be important factors for evaluating shale gas reservoirs. The study also reveals that the high density of natural fractures is decisive to evaluate the shale gas potential. The results may have significant implications for evaluating favorable exploration areas of shale gas reservoirs and can be applied to optimize hydraulic fracturing for permeability enhancement.
High- and low-rank coalbed methane (CBM) are both important fields of CBM development in China, but their formation and production mechanisms differ considerably. The adsorption/desorption behavior of high- and low-rank coals under the coupling of coal–water–gas was investigated using two series of samples. Coal samples from Zhangjiamao (ZJM) coal mine, Ordos basin, and Sihe (SH) coal mine, Qinshui basin, were tested by isothermal adsorption–desorption experiment, natural imbibition experiment, nuclear magnetic resonance, mercury injection porosimetry, contact angle test, and permeability test. Isothermal adsorption and desorption experiments under dry, equilibrium water, and saturated water, were performed to explore the differences between the adsorption and desorption characteristics. The results show that the wettability and permeability of the ZJM low-rank coal sample was considerably higher than that of the SH high-rank coal sample. The imbibition process of the ZJM sample exhibited a high imbibition rate and high total-imbibition volume, whereas the SH sample exhibited a slow imbibition rate and low total-imbibition volume. The ZJM sample had a complex pore structure and diverse pore-size distribution with a lower mercury withdrawal efficiency at 59.60%, whereas the SH sample had a relatively uniform pore-size distribution with a higher mercury withdrawal efficiency at 97.62%. The response of adsorption and desorption of the ZJM sample to water was more significant than that of the SH sample. The desorption hysteresis of the ZJM sample was stronger than that of the SH sample and was more prominently affected by water, which was consistent with its strong wettability and complex pore-throat configuration. A comprehensive adsorption and desorption mode was constructed for high- and low-rank coal samples under coal–water–gas coupling condition. The research results are important to enrich the geological theory of high- and low-rank CBM and to guide efficient CBM recovery.
This study undertook verification of the applicability and accuracy of wind data measured using a WindCube V2 Doppler Wind Lidar (DWL). The data were collected as part of a field experiment in Zhoushan, Zhejiang Province (China), which was conducted by Shanghai Typhoon Institute of China Meteorological Administration during the passage of Super Typhoon Lekima (2019). The DWL measurements were compared with balloon-borne GPS radiosonde (GPS sonde) data, which were acquired using balloons launched from the DWL location. Results showed that wind speed measured by GPS sonde at heights of<100 m is unreliable owing to the drift effect. Optimal agreement (at heights of>100 m) was found for DWL-measured wind speed time-averaged during the ascent of the GPS sonde from the ground surface to the height of 270 m (correlation coefficient: 0.82; root mean square (RMS): 2.19 m·s−1). Analysis revealed that precipitation intensity (PI) exerts considerable influence on both the carrier-to-noise ratio and the rate of missing DWL data; however, PI has minimal effect on the wind speed bias of DWL measurements. Specifically, the rate of missing DWL data increased with increasing measurement height and PI. For PI classed as heavy rain or less (PI<12 mm·h−1), the DWL data below 300 m were considered valid, whereas for PI classed as a severe rainstorm (PI>90 mm·h−1), only data below 100 m were valid. Up to the height of 300 m, the RMS of the DWL measurements was nearly half that of wind profile radar (WPR) estimates (4.32 m·s−1), indicating that DWL wind data are more accurate than WPR data under typhoon conditions.
Regarding CO2 enhanced shale gas recovery, this work focuses on changes in the multiphase (free/adsorbed) CH4 in the process of CO2 enhanced shale gas recovery, by utilizing a rigorous numerical model with real geological parameters. This work studies nine injection well (IW) and CH4 production well (PW) combinations of CO2 to determine the influence of IW and PW locations on the dynamic interaction of multiphase CH4 during 10000 d of CO2 injection. The results indicate that the content of both the adsorbed CH4 and free CH4 is strongly variable before (and during) the CO2-CH4 displacement. In addition, during the simulation process, the proportion of the adsorbed CH4 among all extracted CH4 phases dynamically increases first and then tends to stabilize at 70%–80%. Moreover, the IW-PWs combinations significantly affect the outcomes of CO2 enhanced shale gas recovery – for both the proportion of adsorbed/free CH4 and the recovery efficiency. A longer IW-PW distance enables more adsorbed CH4 to be recovered but results in a lower efficiency of shale gas recovery. Basically, a shorter IW-PWs distance helps recover CH4 via CO2 injection if the IW targets the bottom layer of the Wufeng-Longmaxi shale formation. This numerical work expands the knowledge of CO2 enhanced gas recovery from depleted shale reservoirs.
The terminal settling velocity (TSV) calculation of drops and other spherical objects in fluid medium is a classical problem, which has important application values in many fields such as the study of cloud and precipitation processes, the evaluation of soil erosion, and the determination of fluid viscosity coefficient etc. In this paper, a new explicit approximation model of TSV is established, which combines the theoretical solution of N-S equation about fluid motion around spherical objects and the statistical regression of solution dimensionless coefficients with measurement data. This new model can adapt to different values of drop parameters and medium parameters in a large range of Re. By this model, the relative and absolute calculation errors of TSV are in range of −3.42%–+4.34% and −0.271 m/s–+0.128 m/s respectively for drop radius 0.005–2.9 mm. Their corresponding root mean square values are 1.77% and 0.084 m/s respectively, which are much smaller than that of past theoretical and empirical models.
There were significant discrepancies in the intensity estimations of Super Typhoon Lekima (2019) among the China Meteorological Administration (CMA), the United States Joint Typhoon Warning Center (JTWC), and the Japan Meteorological Agency (JMA) data sets, with a maximum difference of over 12 m/s and 16 m/s between the JTWC data set and the CMA and JMA data sets, respectively. During the intensification phase, disagreement on the maximum sustained wind (MSW) between these agencies was due to the use of different conversion tables for the current intensity number (CI) estimated by Dvorak technique-MSW. In addition, CI discrepancies and different available observational data were also important contributors to the different intensities estimated during the Lekima’s decay phase before landfall. The ability of various methods to minimize these discrepancies was evaluated in this study. Both the linear factor multiplication method and the remapping method using the same CI-MSW conversion table have substantially abilities to reduce intensity discrepancies, with the latter method being more effective. However, these improvements only hold for the intensification phase in the ocean. The CMA data set had more complete and accurate intensity estimations when Lekima made landfall in China. After its landfall, the intensity estimate of the CMA was comparable to that of the JMA, which differed greatly from that of the JTWC.
The adsorption, diffusion, and aggregation of methane from coal are often studied based on slit or carbon nanotube models and isothermal adsorption and thermodynamics theories. However, the pore morphology of the slit model involves a single slit, and the carbon nanotube model does not consider the molecular structure of coal. The difference of the adsorption capacity of coal to methane was determined without considering the external environmental conditions by the molecular structure and pore morphology of coal. The study of methane adsorption by coal under single condition cannot reveal its mechanism. In view of this, elemental analysis, FTIR spectrum, XPS electron energy spectrum, 13C NMR, and isothermal adsorption tests were conducted on the semi-anthracite of Changping mine and the anthracite of Sihe Mine in Shanxi Province, China. The grand canonical Monte Carlo (GCMC) and molecular dynamics simulation method was used to establish the coal molecular structure model. By comparing the results with the experimental test results, the accuracy and practicability of the molecular structure model are confirmed. Based on the adsorption potential energy theory and aggregation model, the adsorption force of methane on aromatic ring structure, pyrrole nitrogen structure, aliphatic structure, and oxygen-containing functional group was calculated. The relationship between pore morphology, methane aggregation morphology, and coal molecular structure was revealed. The results show that the adsorption force of coal molecular structure on methane is as follows: aromatic ring structure (1.96 kcal/mol) > pyridine nitrogen (1.41 kcal/mol) > pyrrorole nitrogen (1.05 kcal/mol) > aliphatic structure (0.29 kcal/mol) > oxygen-containing functional group (0.20 kcal/mol). In the long and narrow regular pores of semi-anthracite and anthracite, methane aggregates in clusters at turns and aperture changes, and the adsorption and aggregation positions are mainly determined by the aromatic ring structure, the positions of pyrrole nitrogen and pyridine nitrogen. The degree of aggregation is controlled by the interaction energy and pore morphology. The results pertaining to coal molecular structure and pore morphology on methane adsorption and aggregation location and degree are conducive to the evaluation of the adsorption mechanism of methane in coal.
Nowadays, autonomous driving has been attracted widespread attention from academia and industry. As we all know, deep learning is effective and essential for the development of AI components of Autonomous Vehicles (AVs). However, it is challenging to adopt multi-source heterogenous data in deep learning. Therefore, we propose a novel data-driven approach for the delivery of high-quality Spatio-Temporal Trajectory Data (STTD) to AVs, which can be deployed to assist the development of AI components with deep learning. The novelty of our work is that the meta-model of STTD is constructed based on the domain knowledge of autonomous driving. Our approach, including collection, preprocessing, storage and modeling of STTD as well as the training of AI components, helps to process and utilize huge amount of STTD efficiently. To further demonstrate the usability of our approach, a case study of vehicle behavior prediction using Long Short-Term Memory (LSTM) networks is discussed. Experimental results show that our approach facilitates the training process of AI components with the STTD.
Gas and water distribution is discontinuous in tight gas reservoirs, and a quantitative understanding of the factors controlling the scale and distribution of effective reservoirs is important for natural gas exploration. We used geological and geophysical explanation results, dynamic and static well test data, interference well test and static pressure test to calculate the distribution and characteristics of tight gas reservoirs in the H8 Member of the Shihezi Formation, Sulige gas field, Ordos Basin, northwest China. Our evaluation system examines the scale, physical properties, gas-bearing properties, and other reservoir features, and results in classification of effective reservoirs into types I, II, and III that differ greatly in size, porosity, permeability, and saturation. The average thickness, length, and width of type I effective reservoirs are 2.89, 808, and 598 m, respectively, and the porosity is>10.0%, permeability is>10 × 10–3µm2, and average gas saturation is>60%. Compared with conventional gas reservoirs, tight gas effective reservoirs are small-scale and have low gas saturation. Our results show that the scale of the sedimentary system controls the size of the dominant microfacies in which tight gas effective reservoirs form. The presence of different types of interbeds hinders the connectivity of effective sand body reservoirs. The gas source conditions and pore characteristics of the reservoirs control sand body gas filling and reservoir formation. The physical properties and structural nature of the reservoirs control gas–water separation and the gas contents of effective reservoirs. The results are beneficial for the understanding of gas reservoir distribution in the whole Ordos Basin and other similar basins worldwide.
Retrospectively evaluating the efficacy of revegetation practices is helpful in planning and implementing future ecosystem restoration programs (ERP). Having a good understanding of how human activities can affect vegetation cover, both before and after ERP, is particularly important in sandstorm hotspot areas. The Beijing–Tianjin Sandstorm Source Region (BTSSR) is one such area. We conducted an investigation into vegetation dynamics within the BTSSR. This was done using remote sensing data in conjunction with climate data sets and land use data spanning the 1982–2014 period. The relationships between climatic factors (such as precipitation and temperature), and vegetative change were modeled using a neural network method. By a process of residual analysis, the proportions of human-induced vegetative change both before and after the ERP were established. Our results show that: 1) before the ERP (1982–2000), 40.96% of the study area exhibited significantly progressive vegetation changes (p<0.05). This proportion decreased to encompass only 20.23% of the study area in the period following the ERP (2001–2014). 2) 89.55% of the study area showed signs of human-induced vegetation degradation before the ERP. Between 2001 and 2014 however, following ERP, this figure fell to only 27.78%. 3) ERP implementation led to visible improvements in vegetative conditions within the BTSSR, especially in areas where ecological restoration measures were directly and anthropogenically applied. These results highlight the benefits that positive human action (i.e., revegetation initiatives implemented under the framework of an ERP) have brought to the BTSSR.
Surface and deep subsurface geological structural trends, stratigraphic features, and reservoir charac-teristics play important roles in assessment of hydrocarbon potential. Here, an approach that integrates digital elevation modelling, seismic interpretation, seismic attributes, three-dimensional (3D) geological structural modeling predicated on seismic data interpretation, and petrophysical analysis is presented to visualize and analyze reservoir structural trends and determine residual hydrocarbon potential. The digital elevation model is utilized to provide verifiable predictions of the Dhulian surface structure. Seismic interpretation of synthetic seismograms use two-way time and depth contour models to perform a representative 3D reservoir geological structure evaluation. Based on Petrel structural modeling efficiency, reservoir development indexes, such as the true 3D structural trends, slope, geometry type, depth, and possibility of hydrocarbon prospects, were calculated for the Eocene limestone Chorgali, upper Paleocene limestone Lockhart, early Permian arkosic sandstone Warcha, and Precambrian Salt Range formations. Trace envelope, instantaneous frequency, and average energy attribute analyses were utilized to resolve the spatial predictions of the subsurface structure, formation extrusion, and reflector continuity. We evaluated the average porosity, permeability, net to gross ratio, water saturation, and hydrocarbon saturation of early Eocene limestone and upper Paleocene limestone based on the qualitative interpretation of well log data. In summary, this integrated study validates 3D stratigraphic structural trends and fault networks, facilitates the residual hydrocarbon potential estimates, and reveals that the Dhulian area has a NE to SW (fold axis) thrust-bounded salt cored anticline structure, which substantiates the presence of tectonic compression. The thrust faults have fold axes trending from ENE to WSW, and the petrophysical analysis shows that the mapped reservoir is of good quality and has essential hydrocarbon potential, which can be exploited economically.
Rare earth elements and yttrium (REY) in coal deposits are considered promising alternative sources for these resources owing to their increasing global demand. This paper reports the geochemical characteristics of REY in the Late Permian coals from an underground K1a seam section of the Zhongliangshan coalfield in Chongqing, southwestern China. The mineralogy, degree of enrichment, distribution patterns, modes of occurrence, and sediment origin of REY were investigated. Compared with the average of world coals, the concentration of REY in the K1a coals were normal, dominated by light REY (LREY), with less medium and heavy REY (MREY, HREY). The fractionation degree of the MREY and HREY are higher than that of LREY in most K1a coal samples, deduced from the mixed enrichment type of REY, mainly including M-H-type, and a few L-M type and H-type. In addition, the combination of anomalies of Ce, Eu, Gd, and Al2O3/TiO2 parameters, the terrigenous materials in the K1a coal were derived from the felsic-intermediate rocks at the top of the Emeishan basalt sequence, and the samples were affected by seawater intrusion during early peat accumulation. Although the minerals primarily consist of kaolinite, illite, pyrite, and small amounts of quartz, calcite and anatase, REY are correlated with ash yield, SiO2, and Al2O3, revealing that the REY mainly occur in aluminosilicate minerals, especially kaolinite and illite. Meanwhile, REY positively relate to P2O5 and Zr, which may exist in phosphate-containing minerals or zircon. Furthermore, most samples in the K1a coal or ash do not reach the cut-off grade for the beneficial recovery of REY. With the exception of central Guizhou, southwestern Chongqing, and the junction of western Guizhou and northeastern Yunnan, the REY content in coals from southwestern China are high, and its by-products are suitable as potential REY sources.
The predictions for Super Typhoon Lekima (2019) have been evaluated from official forecasts, global models, regional models and ensemble prediction systems (EPSs) at lead times of 1–5 days. Track errors from most deterministic forecasts are smaller than their annual mean errors in 2019. Compared to the propagation speed, the propagation direction of Lekima (2019) was much easier to determine for the official agency and numerical weather prediction (NWP) models. The National Centers for Environmental Prediction Global Ensemble Forecast System (NCEP-GEFS), Japan Meteorological Agency Global Ensemble Prediction System (JMA-GEPS) and Meteorological Service of Canada Ensemble System (MSC-CENS) are underdispersed, and the Shanghai Typhoon Institute Typhoon Ensemble Data Assimilation and Prediction System (STI-TEDAPS) is overdispersed, while the ensemble prediction system from European Centre for Medium-Range Weather Forecasts (ECMWF) shows adequate dispersion at all lead times. Most deterministic forecasting methods underestimated the intensity of Lekima (2019), especially for the rapid intensification period after Lekima (2019) entered the East China Sea. All of the deterministic forecasts performed well at predicting the first landfall point at Wenling, Zhejiang Province with a lead time of 24 and 48 h.
The rainfall forecast performance of the Tropical Cyclone (TC) version Model of Global and Regional Assimilation PrEdiction System (GRAPES-TCM) of the China Meteorological Administration for landfalling Super Typhoon Lekima (2019) is studied by using the object-oriented verification method of conti-guous rain area (CRA). The major error sources and possible reasons for the rainfall forecast uncertainties in different landfall stages (including near landfall and moving further inland) are compared. Results show that different performance and errors of rainfall forecast exist in the different TC stages. In the near landfall stage the asymmetric rainfall distribution is hard to be simulated, which might be related to the too strong forecasted TC intensity and too weak vertical wind shear accompanied. As Lekima moves further inland, the rain pattern and volume errors gradually increase. The Equitable Threat Score of the 24 h forecasted rainfall over 100 mm declines quickly with the time-length over land. The diagnostic analysis shows that there exists an interaction between the TC and the mid-latitude westerlies, but too weak frontogenesis is simulated. The results of this research indicate that for the current numerical model, the forecast ability of persistent heavy rainfall is very limited, especially when the weakened landing TC moves further inland.
The sharp increase in the demand for lithium (Li) for high-energy-storage battery materials due to its high specific energy and low negative chemical potential render Li a geopolitically significant resource. It is urgent to develop a low-cost, efficient method to improve lithium extraction. Herein, Li ion (Li+) adsorption in coal-bearing strata kaolinite (CSK) was studied. The effects of pre-activation acid leaching (meta-kaolinite/H2SO4, MK-HS) and dimethyl sulfoxide intercalation (coal-bearing strata kaolinite/dimethyl sulfoxide, CSK-DMSO) on the Li+ adsorption capacity were studied under the same adsorption conditions. The results indicated that the adsorption was completed in 60 min under alkaline conditions (pH = 8.5), a high solution concentration (400 mg/L), and a low dosage (1 g/100 mL); and the comprehensive adsorption capacity is MK-HS > CSK-DMSO > CSK. Furthermore, the DMSO intercalation caused the interlayer spacing of the CSK to increase, which provided more space for Li+ to enter and increase the adsorption capacity. After thermal pre-activation and acid leaching, structural failure and lattice collapse resulted in the presence of more micropores in the MK-HS, which resulted in a 10-fold increase in its specific surface area and caused coordination bond changes (Al(VI) to Al(IV)) and leaching of aluminum (Al) from the lattice. It is proposed that these structural changes greatly improve the activity of CSK so that Li+ cannot only adsorb onto the surface and between the layers but can also enter the lattice defects, which results in the MK-HS having the best adsorption performance. Combined with the adsorption kinetics analysis, the adsorption methods of CSK and two modified materials include physical adsorption and chemical adsorption. In this study, the adsorption capacity of CSK and its modified products to Li were explored, providing a new option for the reuse of CSK and the extraction of Li.
This paper uses pollen climate analysis and coexistence analysis to systematically analyze the climatic evolution of the Shahejie Formation in the Chezhen Depression, Bohai Bay Basin, eastern China and discusses the relationship between palaeoclimatic evolution and lake level rise. The results show that the sedimentary period of the Shahejie Formation in the Chezhen Depression had an overall temperature change trend from hot to cold and simultaneously experienced a dry and wet balance–wet–dry and wet balance–wet transition process. The climatic parameters of the Shahejie Formation in the Chezhen Depression include a mean annual temperature of 8.1°C−15.1°C, a mean coldest monthly temperature of −0.1°C−2°C, a mean warmest monthly temperature of 18.6°C−28°C, a mean annual precipitation of 389−1164 mm, a wettest monthly precipitation amount of 215−262 mm, and a driest monthly precipitation amount of 8−48 mm. Climate change is believed to affect the rise and fall of lake levels to some extent. The quantitative reconstruction of these climatic parameters allows researchers to more intuitively understand the geological background of the Chezhen Depression and guide the exploration and development of oil and gas resources.
Most coal reservoirs show high gas content with relatively low desorption efficiency, which restricts the efficiency of coalbed methane (CBM) extraction and single-well productivity. This review highlights the desorption hysteresis mechanism and its controlling factors as well as methods and models to reveal desorption hysteresis and potential solutions. Methane adsorption and desorption can be recorded by both gravimetric and volumetric experiments. Although different adsorption models are used, desorption is generally considered with the Langmuir model. Desorption hysteresis is influenced by the petrophysical composition, thermal maturity, pore structure distribution of the coal, reservoir temperature, and moisture and water content. Methods for calculating desorption hysteresis include the area index, hysteresis index and introduction of a hysteresis factor and a hysteresis coefficient. Molecular dynamics simulations of methane desorption are mainly based on theories of kinetics, thermodynamics, and potential energy. The interaction forces operating among coal, water, and methane molecules can be calculated from microscopic intermolecular forces (van der Waals forces). The desorption hysteresis mechanism and desorption process still lack quantitative probe methodologies, and future research should focus on coal wettability under the constraints of liquid content, potential energy adjustment mechanism, and quantitative analysis of methane desorption rates. Further research is expected to reveal the desorption kinetics of methane through the use of the solid–liquid–gas three-phase coupling theory associated with the quantitative analysis of methane desorption hysteresis, thereby enhancing the recovery rate and efficiency of CBM wells.
