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Phased-array radar (PAR) technology offers the flexibility of sampling the storm and clear-air regions with different update times. As such, the radial velocity from clear-air regions, typically with a lower signal-to-noise ratio, can be measured more accurately. In this work, observing system simulation experiments are conducted to explore the potential value of assimilating clear-air radial velocity observations to improve numerical prediction of supercell thunderstorms. Synthetic PAR observations of a splitting supercell are assimilated at different life cycle stages using an ensemble Kalman filter. Results show that assimilating environmental clear-air radial velocity can reduce wind errors in the near-storm environment and within the precipitation region. Improvements in the forecast are seen at different stages, especially for the forecast after 30 min. After assimilating clear-air radial velocity observations, the probabilities of updraft helicity and precipitation within the corresponding swaths of the truth simulation increase up to 30%–40%. Additional diagnostics suggest that the more accurate track forecast, stronger vertical motion, and better-maintained supercell can be attributed to the better analysis and prediction of the mean environmental winds and linear and nonlinear dynamic forces. Consequently, assimilating clear-air radial velocity produces accurate storm structure (rotating updrafts), updraft size, and storm track, and improves the surface accumulated precipitation forecast. The performance of forecasts with a higher frequency of assimilating clear-air radial velocity does not show systematic improvement. These results highlight the potential of assimilating clear-air radial velocity observations to improve numerical weather prediction forecasts of supercell thunderstorms.

Single nucleotide polymorphisms (SNPs), known as the third-generation molecular markers, are becoming popular in molecular ecology studies. The rapid development of next generation sequencing technologies allow identifying large numbers of SNP markers that can be used in conservation genetics. Based on the genome resequencing dataset of Crested ibis (Nipponia nippon), we developed 31 polymorphic SNP markers using the restriction-site associated DNA (RAD) sequencing. The minor allele frequency per locus varied from 0.176 to 0.485, while the observed and expected heterozygosity varied from 0.118 to 0.794 and from 0.295 to 0.507, respectively. Three loci showed significant departures from Hardy–Weinberg equilibrium. These SNP markers could be useful in future population genetic analysis of Crested ibis.

Differences in rainfall budgets between convective and stratiform regions of a torrential rainfall event were investigated using high-resolution simulation data produced by the Weather Research and Forecasting (WRF) model. The convective and stratiform regions were reasonably separated by the radar-based convective–stratiform partitioning method, and the three-dimensional WRF-based precipitation equation combining water vapor and hydrometeor budgets was further used to analyze the rainfall budgets. The results showed that the magnitude of precipitation budget processes in the convective region was one order larger than that in the stratiform region. In convective/stratiform updraft regions, precipitation was mainly from the contribution of moisture-related processes, with a small negative contribution from cloud-related processes. In convective/ stratiform downdraft regions, cloud-related processes played positive roles in precipitation, while moisture-related processes made a negative contribution. Moisture flux convergence played a dominant role in the moisture-related processes in convective or stratiform updraft regions, which was closely related to large-scale dynamics. Differences in cloud-related processes between convective and stratiform regions were more complex compared with those in moisture-related processes. Both liquid- and ice-phase microphysical processes were strong in convective/stratiform updraft regions, and ice-phase processes were dominant in convective/stratiform downdraft regions. There was strong net latent heating within almost the whole troposphere in updraft regions, especially in the convective updraft region, while the net latent heating (cooling) mainly existed above (below) the zero-layer in convective/stratiform downdraft regions.

This paper puts forward a new method to predict the net-tension strength of single blot joint based on the Finite Fracture Mechanics (FFM) model. Instead of using the tensile strength and fracture toughness of the laminates, only the properties of the 0° ply are used to obtain the failure stress and critical crack length by considering the relation between mode I fracture toughness of laminates and that of 0° ply. While the tensile strength of the 0° ply can be easily obtained through uniaxial tensile tests, the size effect law of double edge notched specimens is incorporated for the determination of the crack resistance curve of the ply. After validating the proposed method by the experimental results of central-notched IM7/8552 laminates, a 3D finite element model is established and the secondary bending is taken into consideration to find the maximum stress distribution of 0° ply around the bolt hole of the single bolt joint. It is concluded that the predicted strength by the semi-analytical method suits well with the experimental results. The secondary bending and the crack resistance curve, which can be seen as improvements of the Finite Fracture Mechanics model, have an influence on the predicted value.

Titanium alloy has been increasingly applied in aviation industry due to its superior performance. However, the titanium alloy structures are less studied. This work investigates the structural behavior of Ti6Al4V titanium alloy stiffened panels under in-plane shear load by experiments and numerical analysis. After the shear tests, the buckling instability, the post-buckling process and the failure mechanism of the specimen were obtained. The Finite Element (FE) models were established with the subsequent validation verification. A parametric analysis was implemented to study the influence of stringer thickness and stringer height on the behavior of the stiffened panels. The results show that after the initial local buckling on the skin, the buckling mode jumps several times with the increase of load. The stringers twist when the load reaches a certain level, and finally the structure damages due to the plastic deformation and the global buckling. The shear clip has little effect on the buckling and failure loads. Compared to the relatively large effect on the buckling load, the influence of the stringer thickness and stringer height on the failure load is neglectable. According to the parametric analysis, the stringer thickness influences the final buckling mode and failure mode, while the stringer height affects the buckling mode transformation. Keywords: Buckling, Finite Element Method (FEM), In-plane shear loading, Stiffened panel, Stringer height, Stringer thickness, Titanium alloys

Idealized simulations are conducted using the Cloud Model version 1 (CM1) to explore the mechanism of tropical cyclone (TC) genesis from a preexisting midtropospheric vortex that forms in radiative–convective equilibrium. With lower-tropospheric air approaching near saturation during TC genesis, convective cells become stronger, along with the intensifying updrafts and downdrafts and the larger area coverage of updrafts relative to downdrafts. Consequently, the low-level vertical mass flux increases, inducing vorticity amplification above the boundary layer. Of interest is that while surface cold pools help organize lower-tropospheric updrafts, genesis still proceeds, only slightly delayed, if subcloud evaporation cooling and cold pool intensity are drastically reduced. More detrimental is the disruption of near saturation through the introduction of weak vertical wind shear. The lower-tropospheric dry air suppresses the strengthening of convection, leading to weaker upward mass flux and much slower near-surface vortex spinup. We also find that surface spinup is similarly inhibited by decreasing surface drag despite the existence of a nearly saturated column, whereas larger drag accelerates spinup. Increased vorticity above the boundary layer is followed by the emergence of a horizontal pressure gradient through the depth of the boundary layer. Then the corresponding convergence resulting from the gradient imbalance in the frictional boundary layer causes vorticity amplification near the surface. It is suggested that near saturation in the lower troposphere is critical for increasing the mass flux and vorticity just above the boundary layer, but it is necessary yet insufficient because the spinup is strongly governed by boundary layer dynamics.

The rainfall processes during the formation of tropical cyclone (TC) Durian (2001) were investigated quantitatively using the three-dimensional (3D) WRF-based precipitation equation. The rain rate (PS) decreased slightly as the TC approached to formation, and then increased as Durian began to intensify. The rate of moisture-related processes (QWV) in the equation contributed around 80% to PS before TC genesis, and made more contribution during and after TC genesis. The rate of hydrometeor-related processes (QCM) contributed about 20% before TC formation, followed by less contribution during and after TC formation. QWV were dominated by the 3D moisture flux advection rate (QWVA), while the surface evaporation rate (QWVE) also played an important role. Just before TC genesis, moisture from QWVA and QWVE helped the local atmosphere moisten (negative QWVL). QCM were determined by the 3D hydrometeor advection rates (QCLA and QCIA) and the local change rates of hydrometeors (QCLL and QCIL). During TC formation, QCM largely decreased and then reactivated as Durian began to intensify, accompanied by the development of TC cloud. Both the height and the strength of the net latent heating center associated with microphysical processes generally lowered before and during TC genesis, resulting mainly from lessening deposition and condensation. The downward shift of the net latent heating center induced a more bottom-heavy upward mass flux profile, suggesting to promote lower-tropospheric convergence in a shallower layer, vorticity amplification and TC spin-up.

The impact of mid- and upper-level dry air, represented by low relative humidity (RH) values, on the genesis of tropical cyclone (TC) Durian (2001) in the South China Sea was investigated by a series of numerical experiments using the Weather Research and Forecasting model. The mid-level RH was lowered in different regions relative to TC Durian (2001)’s genesis location. Results suggest that the location of dry air was important to Durian (2001)’s genesis and intensification. The rapid development of the TC was accompanied by sustained near-saturated mid- and upper-level air, whereas low humidity decelerated its development. Water vapor budget analysis showed that moisture at mid and upper levels was mainly supplied by the vertical convergence of moisture flux and the divergence terms, and consumed by the condensation process. The horizontal convergence of moisture flux term supplied moisture in the air moistening process but consumed moisture in the air drying process. With a dryer mid- and upper-level environment, convective and stratiform precipitation were both inhibited. The upward mass fluxes and the diabatic heating rates associated with these two precipitation types were also suppressed. Generally, convection played the dominant role, since the impact of the stratiform process on vertical mass transportation and diabatic heating was much weaker. The vorticity budget showed that the negative vorticity convergence term, which was closely related to the inhibited convection, caused the vorticity to decrease above the lower troposphere in a dryer environment. The negative vorticity tendency is suggested to slow down the vertical coherence and the development rate of TCs.

Radar data assimilation is an important method for short-term convection forecasting or nowcasting. To improve the short-term (mainly 0–3 h) precipitation forecasts for severe convective storms, an analysis nudging (Newtonian relaxation) based hydrometeor and latent heat nudging (HLHN) technique was developed to effectively assimilate radar reflectivity data in a Weather Research and Forecasting (WRF)-based real time four-dimensional data assimilation and short-term forecasting system (RTFDDA). The purpose of this study is to investigate the performance of the RTFDDA system with radar data assimilation (RTFDDA-RDA) with rapid-cycling forecasting applications for Shenzhen, a subtropical coastal metropolis in southern China. The RTFDDA-RDA system was run to produce hindcasts for ten severe convective storm events occurred in Guangdong region during the 2017 rainy season. Results show that, through nudging cloud hydrometeors retrieved from radar reflectivity and the associated latent heat release, RTFDDA-RDA is able to produce the meso- and convective-scale features of the convective storms in a good accuracy and improve the short-term precipitation forecasting of the convective storms. Subjective and statistical evaluation results demonstrate that RTFDDA-RDA presents a reasonable capability for forecasting convective systems with improving the initial conditions and resulting in significant improvements of precipitation forecasting skills, especially for the 0–3-h nowcasting range. The sensitivity experiments on different latent heating schemes show that, the convective-stratiform separated heating scheme has the best performance of forecasts. Finally, intercomparison of different radar data assimilation approaches will be conducted in future.

Summary Keshen is a high-pressure/high-temperature (HP/HT) tight-sandstone gas reservoir with reservoir pressure greater than 110 MPa and temperature more than 175°C. The sandstone is hard, with unconfined compressive strength (UCS) greater than 100 MPa. Given the HP/HT nature and natural-fracture systems in the reservoir, with aid of stimulation, many wells produced at a high rate, with the mean value exceeding 500 000 m3/d. In the last few years, many production wells in this reservoir experienced severe sanding issues that contradicted the conventional understanding that sanding would not occur in such hard rock. The sanding wells exhibited large fluctuations of production rate and wellhead pressure, erosion of chokes and nozzles, and eventually major or even complete loss of production. A solution to address the sanding issues was urgently needed because they had caused a major decline in production and resulted in significant economic loss. Because of the unconventional nature of the sanding issues, the typical sanding-prediction methods dependent on evaluating rock failure were not adequate to reveal the underlying sanding mechanism and develop a viable operational solution. To this end, a new work flow was formulated and applied to this study. The work flow started with detailed data mining on the large amount of drilling, completion, stimulation, and production data of more than 51 wells from this reservoir to investigate possible relationships of drilling practices, completion options, and production schedules to the occurrence and severity of sanding issues. The analysis revealed that downhole flow velocity and production drawdown were the two major controlling factors in the occurrence of sand production. Further geomechanics simulation and particle-migration simulation with a multiphase dynamic flow simulator confirmed that the production drawdown would cause failure of the rock near the wellbore and the gas flow could transport the sand debris to the wellbore and lift it up to the surface. In addition, the fluctuation of production rate was caused by blockage because of the accumulation of sand particles in the wells and production tubing that were flushed out after downhole-pressure buildup. Using the analysis, the threshold of flow velocity and the threshold of drawdown were identified, and these thresholds can be used in the reservoir management to effectively address the sanding issues. The experience in Keshen shows that sanding is possible in HP/HT high-productivity sandstone gas reservoirs, even in an extremely hard formation, which overturns some prior conceptions on sanding. The information shared from this paper could attract the attention of those operating similar HP/HT tight-sandstone reservoirs around the world.

Alternanthera philoxeroides is an alien invasive species, which can cause substantial damage to the local ecosystem by secreting allelochemicals. The objective of the present study was to appraise the effects of root extracts of the invasive plant Alternanthera philoxeroides on soil enzyme and native microbial community. Urease activity was measured using the phenol sodium hypochlorite colorimetric method, sucrase activity was determined by 3, 5-dinitrosalicylic acid colorimetric method, catalase activity was determined using the KMnO4 titration method and alkaline phosphatase activity was determined by the disodium phenyl phosphate colorimetric method. The soil microbial community was investigated by pyrosequencing of the 16S rRNA gene. Results showed that the alkaline phosphatase, sucrase and urease activities were all significantly lower than that of the control treatment. The structure of the soil microbial community in the treatments with root extracts addition clearly differed from that of t...

Cadmium (Cd) is a toxic non-essential element accumulated easily in living organisms due to its non-biodegradable nature. A slight increase in Cd levels will threaten the health of terrestrial and aquatic organisms. Therefore, Cd contamination and its effects on the ecosystems and organisms have become a major topic of eco-toxicological research. The present study investigated the eco-toxicological effects of Cd-supplemented diet on some life history traits and specific enzyme activities of carboxylesterase (CarE), glutathione S-transferase (GST), acetylcholinesterase (AChE) and cytochrome P450 monooxygenases (P450s) in the cotton bollworm, Helicoverpa armigera. The results showed that Cd significantly decreased larval survival, pupation and emergence, and reduced body mass of the sixth instar larvae, pupae, adult moths and female fecundity. Cd-supplemented diet also delayed the development of larvae and pupae and shortened the life span of the cotton bollworm moth. In addition, dietary Cd inhibit...

The blue sheep is an endemic species to the Qinghai-Tibet Plateau and surrounding regions. It has been regarded as having 2 subspecies: Pseudois nayaur nayaur and P. n. szechuanensis. However, such a classification remains controversial. Herein, we analyze 10 microsatellite loci and part of the mitochondrial control region for clarification in such taxonomic debates. We use samples from 168 individuals from 6 geographic populations covering almost all the distribution areas of the species in China to carry out comparisons. Phylogenetic trees derived from both the microsatellite and mitochondrial markers combined with the discriminant analysis of principal components (DAPC) and the STRUCTURE analysis reveal that the individuals in the Helan Mountains are well grouped with a distinct evolutionary lineage and are significantly different from the other populations of P. n. szechuanensis according to Fst values, implying that this isolated population should be categorized as a valid subspecies; namely, Pseudois nayaur alashanicus. The isolation-by-distance (IBD) analysis shows a significant positive relationship between genetic and geographical distances among the populations.

Indoleacetic acid (IAA) is a plant growth regulator that plays an important role in plant growth and development, and participates in the regulation of abiotic stress. To explore the effect of IAA on cadmium toxicity in Cinnamomum camphora, an indoor potted experiment was conducted with one-year-old C. camphora seedlings. The influence of IAA on cadmium accumulation, net photosynthetic rates, respiration, photosynthetic pigments (chlorophyll a, chlorophyll b, total chlorophyll and carotenoids), osmoregulatory substances (proline, soluble sugar and soluble protein) and the malondialdehyde content in C. camphora leaves treated with 30 mg kg−1 cadmium was analysed with or without the addition of 10 mg kg−1 IAA. Cadmium accumulation in the leaves of C. camphora with the addition of exogenous IAA was significantly higher than accumulation during cadmium stress without additional IAA (ca 69.10% after 60 days' incubation). During the culture period, the net photosynthetic rate in C. camphora leaves subjected to cadmium stress without the addition of IAA was up to 24.31% lower than that of control plants. The net photosynthetic rate in C. camphora leaves subjected to cadmium stress and addition of IAA was up to 30.31% higher than that of leaves subjected to cadmium stress without the addition of IAA. Chlorophyll a, total chlorophyll and carotenoid contents in the cadmium-stressed leaves without the addition of IAA were lower than those in the control treatment. The presence of IAA increased the chlorophyll a, total chlorophyll and carotenoid contents relative to the cadmium stress without the addition of IAA. The respiration rate and concentrations of proline, soluble sugar, soluble protein and malondialdehyde in C. camphora leaves subjected to cadmium stress without the addition of IAA were higher than those in the control. The addition of IAA reduced the respiration rate, and the concentrations of proline, soluble sugar, soluble protein and malondialdehyde in C. camphora leaves when compared with the cadmium stress without the addition of IAA. These results indicate that exogenous IAA improves photosynthetic performance and the growth environment of C. camphora by enhancing the net photosynthetic rate, increasing concentrations of osmoregulatory substances, removing reactive oxygen radicals and eliminating potential damage, thereby reducing the toxic effects of cadmium on C. camphora.

KS is a tight-sandstone and high-pressure-high-temperature (HPHT) gas reservoir in northwest China. It is characterized by a depth of more than 6000 m, temperature over 175°C, and pore pressure over 110 MPa. Despite the high unconfined compressive strength (UCS) of sandstone, almost half of the wells encountered sanding issues. The sanding wells exhibited low production rate, nozzle and pipeline erosion, sanding up, and even permanent closure. Investigating the sanding mechanism and developing solutions for sanding prevention are urgent needs due to the economic loss of low production. An integrated sanding study was conducted to investigate the sanding mechanism. The entire sanding process was analyzed, including stress field alteration during production, rock failure, softening, and sand grain migration. First, wells with sanding issues were identified through production characteristics and field observation. After this, analysis of laboratory tests was performed to better understand the tight-sandstone properties, especially UCS, the softening parameter, and residual strength. Based on the tests, an elastoplastic damage model was proposed to delineate rock failure and sanding behavior. Then, a finite element model was built to simulate the damage of a perforation hole with field data, including hole diameter and length, rock stiffness and strength, drawdown, depletion, and so on. More simulation scenarios were performed to investigate the continuous sanding, transient sanding, and water hammer effect. Grain migration in perforation holes and in pipelines was also studied. It was revealed that shear failure of perforation hole induced by drawdown and depletion was the root cause of sanding problem. Meanwhile, it was also confirmed that erosion and water hammer effect had very limited effect on sanding. Use of the elastoplastic damage model for the simulation of perforation hole failure enabled predicting the sand amount and determining the critical drawdown and depletion for sanding. In the end, an approach to identifying wells with high sanding risk and the key factors behind the sanding were provided, and sanding prevention suggestions were proposed. The new elastoplastic damage model explains the sanding mechanism in a tight-sandstone reservoir and enables evaluating the sand volume, which has rarely been published previously. Laboratory tests, field observation, and numerical simulation were combined effectively to investigate the sanding issue. By utilizing the model, producers can find the key factors behind sanding issues, prevent sanding with a better production strategy, and avoid the economic loss, which are critical for the long-term exploration and production of this area.

The formation of Typhoon Durian (2001) was simulated well by the Weather Research and Forecasting model. The vorticity field was separated into three scales: small scale (L 120 km), where L is wavelength. During the formation, small-scale vorticity anomalies, associated with convection, aggregated radially inward and rotated anticlockwise. The system-scale vorticity field presented a distinct mid-level vortex before genesis, and then a well-organized low-level vortex. The spectral power of the low-level vorticity at the small scale barely changed, while that at the system scale continued to grow steadily. The vorticity growth or spin-up of the near-surface tropical cyclone embryo was mainly due to the convergence of vertical vorticity flux at the planetary boundary layer. The positive (negative) effect of vorticity flux convergence at lower (middle-to-upper) levels appears to cause the shift of system-scale vorticity center from the middle to lower troposphere.

A set of kinetic energy (KE) budget equations associated with four horizontal flow components was derived to study the KE characteristics during the genesis of Tropical Cyclone (TC) Durian (2001) in the South China Sea using numerical simulation data. The genesis process was divided into three stages: the monsoon trough stage (stage 1), the midlevel mesoscale convective vortex (MCV) stage (stage 2), and the establishment stage of the TC vortex (stage 3). Analysis showed that the KE of the symmetric rotational flow (SRF) was the largest and kept increasing, especially in stages 2 and 3, representing the symmetrization process during TC genesis. The KE of the SRF was mainly converted from the KE of the symmetric divergent flow (SDF), largely transformed from the available potential energy (APE). It was found that vortical hot towers (VHTs) emerged abundantly, aggregated, and merged within the MCV region in stages 1 and 2. From the energy budget perspective, massive moist-convection-produced latent heat was concentrated and accumulated within the MCV region, especially in stage 2, and further warmed the atmosphere, benefiting the accumulation of APE and the transformation from APE to KE. As a result, the midlevel circulation (or MCV) grew strong rapidly. In stage 3, the intensity and number of VHTs both decreased. However, affected by increasing lower-level inward radial wind, latent heat released by the organized convection, instead of disorganized VHTs in the first two stages, continuously contributed to the strengthening of the surface TC circulation as well as the warm core.

Based on the governing equations for water species in the Weather Research and Forecasting (WRF) model, a three-dimensional WRF-based surface precipitation equation was obtained and applied to investigate the surface rainfall processes of a torrential rain event. Sensitivity experiments were performed to further explore roles of surface evaporation in the heavy rainfall event. The results show that the contributions of moisture-related processes to precipitation (QWV, including water vapor local change (QWVL), surface evaporation (QWVE), moisture advection (QWVA), and so on) dominate the torrential rain event, while the contributions of cloud-related processes (QCM) also play indispensable roles whose maximum net contributions could exceed 20%. QWVA dominates the budget of water vapor, while QWVL and QWVE play smaller but by no means negligible roles in the event. Sensitivity experiments show that the changes of surface evaporation affect both moisture-related processes and cloud-related processes, and then influence the intensity and regional redistribution of precipitation. Surface evaporation favors the accumulation of convective available potential energy and enhances the instability of atmosphere, being prone to the development of convective systems. Meanwhile, it also affects the development of vertical motions and cloud systems. Thus accurate estimation of surface evaporation is necessary for accurate simulation and forecast of surface precipitation.

High-resolution data of a torrential rainfall event in Sichuan, China, simulated by the WRF model, were used to analyze the cloud microphysical differences with precipitation intensity. Six-hourly accumulated rainfall was classified into five bins based on rainfall intensity, and the cloud microphysical characteristics and processes in different bins were studied. The results show that: (1) Hydrometeor content differed distinctly among different bins. Mixing ratios of cloud water, rain water, and graupel enhanced significantly and monotonously with increasing rainfall intensity. With increasing precipitation intensity, the monotonous increase in cloud water number concentration was significant. Meanwhile, number concentrations of rain water and graupel increased at first and then decreased or increased slowly in larger rainfall bins. (2) With precipitation intensity increasing, cloud microphysical conversion processes closely related to the production of rainwater, directly (accretion of cloud wat...

An extreme rainfall event in the coastal metropolitan city of Guangzhou, China is simulated by the Weather Research and Forecasting (WRF) model using three bulk microphysics schemes to explore the capability to reproduce the observed precipitation features by these schemes and their differences. The detailed comparison among the three runs in terms of radar reflectivity, precipitation, thermodynamic fields and microphysical processes are conducted. Results show that all the simulations can reproduce the two main heavy rainfall centers in Guangzhou and the first convection initiation. The accumulated precipitation in the simulation using the WSM6 scheme performs better than the others in terms of intensity and distribution compared to observations. The weaker accumulated precipitation in the second heavy rainfall center in the simulations using the Thompson and Morrison schemes result from their more dispersed precipitation distributions dominated by the cold pool intensity and distribution. The latent heating from the water vapor condensation dominates the convection initiation and storm development. The latent cooling from the rain water evaporation dominates the cold pool intensity and distribution, which influences the storm moving and subsequent convection propagation, and finally the intensity and distribution of surface precipitation. Sensitivity experiments of the latent heat confirm the dominant roles of latent heating/cooling, especially the water vapor condensation heating and rain water evaporation cooling, in the differences of the thermodynamic fields, storm development, convection propagation and surface precipitation among the three simulations.

Two common organic wastes from agriculture (rice straw) and forestry (sawdust) were applied to a petroleum-contaminated soil to estimate their effectiveness in the removal of total petroleum hydrocarbons (TPHs) and polycyclic aromatic hydrocarbons (PAHs). Rice straw was the more effective amendment than the other treatments in reducing TPH contents and addition of sawdust resulted in a significant decrease in PAH removal, particularly high-molecular-weight (5-6 ring) PAHs. Principal coordinates analysis (PCoA) indicates that rice straw treatment separated only the bacterial community but sawdust greatly affected both the soil bacterial and fungal communities. Moreover, the abundance of some petroleum degraders such as the bacteria Sphingomonas, Idiomarina and Phenylobacterium and the fungi Humicola, Wallemia and Graphium was promoted by inputs of the two agricultural and forestry wastes. These results highlight the potential of waste applications in accelerating hydrocarbon biodegradation which may be attributed to the enrichment of keystone taxa that show strong positive associations with hydrocarbon degradation.

Four gramineous energy plants, Miscanthus sacchariflorus, M. floridulus, Phragmites australis, and Arundo donax were grown on copper tailings in the field for four years. Their phytoremediation potential was examined in terms of their effects on the fractions of heavy metals and soil enzyme activities. Results showed that plantation of these four gramineous plants has improved the proportion of organic material (OM)-binding fraction of heavy metals in copper tailings as a whole, and reduced the proportion of exchangeable and residual fractions. In particular, M. sacchariflorus growth improved significantly the proportion of the OM-binding fractions of Cu (1.73 times), Cd (1.71 times), Zn (1.18 times), and Pb (3.14 times) (P < 0.05) and reduced markedly the residual fractions of Cu (64.45%), Cd (82.38%), Zn (61.43%), and Pb (73.41%) (P < 0.05). Except for A. donax, the growth of other three energy plants improved the activity of phosphatase, urease and dehydrogenase in copper tailings to some extent. In particular, the activity of soil phosphatase and urease in planted tailings differed significantly from that of control (P < 0.05). The effect of M. sacchariflorus growth on soil enzyme was the highest, followed by P. australis, M. floridulus, and A. donax. The content of each heavy metal fraction in soil was correlated with soil enzyme activities, especially the content of OM-binding fraction, which correlated significantly with the activities of phosphatase, urease and dehydrogenase in soil. According to the effects of four gramineous plants growth on activity of soil enzymes and fractions of heavy metals, M. sacchariflorus had the optimal effects for phytoremediation. Therefore, M. sacchariflorus was a candidate plant with great potential for the revegetation of heavy metal tailings.

Keshen is a high-pressure/high temperature (HP/HT) tight-sandstone gas reservoir with reservoir pressure over 110 MPa and temperature over 175°C. The sandstone is very hard, with unconfined compressive strength (UCS) greater than 100 MPa. Given the HP/HT nature and natural fracture system in the reservoir, with aid of stimulation, many wells produced at a very high rate with the mean value exceeding 500,000 m3/d. In the last few years, many production wells in this reservoir experienced severe sanding issues that contradicted the conventional understanding that sanding would not occur in such hard rock. The sanding wells exhibited large fluctuations of production rate and wellhead pressure, erosion of chocks and nozzles, and eventually major or even complete loss of production. A solution to address the sanding issues was urgently needed because the sanding issues had caused a major decline in production and resulted in significant economic loss. Due to the unconventional nature of the sanding issues, the typical sanding prediction methods based on solely on evaluating rock failure were not adequate to reveal the underlying sanding mechanism and develop a viable operational solution to address the sanding issues. To this end, a new workflow was formulated and applied to this study. The workflow started with detailed data mining on the massive amount of drilling, completion, stimulation, and production data from this reservoir to investigate possible relationships of drilling practices, completion options, and production schedules to the occurrence and severity of sanding issues. The analysis revealed that downhole flow velocity and production drawdown were the two major controlling factors in the occurrence of sand production. Further geomechanics simulation and particle migration simulation with a multiphase dynamic flow simulator confirmed that the production drawdown would cause failure of the rock near the wellbore and the gas flow could transport the sand debris to the wellbore and lift it up to the surface. In addition, the fluctuation of production rate was caused by blockage due to accumulation in the wells and production tubing of sand particles that were flushed out after downhole pressure buildup. Based on the analysis, the threshold of flow velocity and the threshold of drawdown were identified, and these thresholds can be used in the reservoir management to address the sanding issues. The experience in Keshen shows that sanding is possible in HP/HT high-productivity sandstone gas reservoirs, even in extremely hard formation, which overturns some prior conceptions on sanding. The information shared from this paper could bring up the attention of those operating similar HP/HT tight sandstone reservoirs around the world.

The main pay of the Keshen gas field is a tight sand formation with very low porosity (2% to 7%) and permeability (0.001md-0.1md). Due to the ultra-deep formation depth and superior high reservoir pressure (greater than 116 MPa) and temperatures (above 160°C), the well construction and field development costs are very high. Therefore, stimulation treatments is essential for achieving sufficiently high production rate and the basis for justifying the costs. Natural fractures (NF) are developed in the reservoir with high heterogeneity which leads to complex production mechanism due to interaction between matrix and NFs, and causes difficulties on stimulation optimization. To better understand the reservoir and optimize the well stimulation, the matrix properties, natural fracture, geomechanical data and stimulation data has been reviewed along with production data. Massive production history matching work has been done to evaluate the NFs. Other dynamic data like the well testing data and pressure data also reviewed to help understand NFs development in the full field scal. Production analysis was conducted to link the rock properties, NFs and wells' performance, and provided full understanding of production controlling factor in this reservoir. The post production analysis helped to understand the efficiency of stimulation. The production behavior for different stimulation strategy also have been illustrated by the simulation models to investigate the impaction on the stimualtion optimization strategy by the interaction between matrix and NFs. The study provided a good understanding of the production mechanism in this kind of natural fractured reservoir and NF's impact on the stimulation efficiency. The heterogeneity of NF results in very different production mechanism given similar matrix petrophysical behavior. Based on production mechanism, each well requires a customized stimulation to maximize the production potential. This study presented a case study for evaluating the production mechanism and highlighted the importance on evaluating the production mechanism on optimizing the stimulation for the naturally fractured tight reservoir.

Activity in the Ordos basin, China, has mostly occurred in the low permeability, clay-rich Chang 7 sandstone and has utilized multi-fractured horizontal wells as the preferred completion technique. To further improve the production potential and increase operational efficiency a dual-well pad site was engineered to trial a pad drilling approach, and to evaluate different completion techniques, utilize integrated workflows, and accelerate the development cycle.The pilot project involved two pads with two horizontal wells each, with the intention to compare the local multistage stimulation practice of using a tubing-conveyed completion method to a wireline-conveyed plug-and-perforation technique. The current tubing-conveyed completion practice impacts the completion efficiency of the well from the standpoints of surface efficiency, engineering workflow, post-fracturing performance, and subsequent commercial performance. The wells completed with the plug-and-perforation technique were completed in a shorter period of time; simultaneous operations enabled flowback water from the first well to be recycled and reused on pumping operations on the second well, further improving the project performance, and first-year cumulative production were 20% higher when compared to surrounding offsets.Three vertical wells were placed between the parallel horizontal wells to enable real-time fracturing monitoring and improve subsurface understanding. To have a more precise microseismic mapping result, the closest vertical well was selected as the monitoring well.The study demonstrates the importance of an integrated approach that accounts for well design, engineering workflow, technology used during the execution, and subsequent evaluation while improving overall productivity. Both the efficiency and production result were breakthroughs in this area.