Tuha Basin Research Articles

Thirty years’ spatio-temporal evolution of desertification degrees and driving factors in Turpan–Hami Basin, Xinjiang, China

Turpan-Hami (Tuha) Basin is in an extremely arid area, surrounded by mountains and desert with sparse vegetation. It has experienced serious desertification over the past 30 years, resulting in ecological environment and socio-economic issues. To reveal the temporal and spatial evolutions of desertification degrees in Tuha Basin, we first constructed an evaluation system for the desertification degree classification using vegetation and soil-related indices; then long-time series Landsat 5 TM/ Landsat8 OLI images and a C5.0 decision tree (DT) model were used to monitor large-scale desertification from 1990 to 2020. We applied a geographic detector to discover the driving forces between desertification changes and natural and human factors. The results demonstrated that the severe desertification (SD) accounted for the largest desertification degree, and the transitions of various desertification degrees mainly occurred between extremely severe desertification (ESD) and SD, which were considered the most active degrees. Only 9.4 % of Tuha Basin showed an expansion trend in desertification degree, with the most significant expansion occurred in 1990–1995. The proportion of 13.6 % desertification showed a reversion trend, with the most significant reversion occurred in 1995–2010. The main driving factors affecting the evolution of desertification degrees were precipitation and temperature, with the average q value higher than 0.95. Human activity factors such as year-end cropland area and population also impacted the patterns of desertification degree, with the q values of 0.9 and 0.7, respectively. The interactive detection enhanced the driving forces and the interaction between precipitation and other factors played a leading role in desertification degree changes. The results provide scientific data and a basis for desertification control and ecological protection in arid areas.

Extensive carbon cycle between peatland and vegetation: Insights from high net primary productivity of the Middle Jurassic in northwestern China

Peatlands have obvious carbon storage capacity and are crucial in mitigating global climate change. As the end-product of peatlands, coals have preserved a large amount of palaeoenvironmental information. The carbon accumulation rate and the net primary productivity (NPP) of coal-forming peatlands can be used as proxies for recovering palaeoenvironments. A super-thick coal seam (42°35′N, 91°25′E) was developed in the Middle Jurassic Xishanyao Formation in the Shaerhu coalfield in the southern margin of the Tuha (Turpan-Hami) Basin, northwestern China. In this study, we use the time series analysis to identify the periods of Milankovitch orbital cycles in the Gamma-ray curve of this super-thick (124.85 m) coal and then use the obtained cycle periods of 405 ka, 173 ka, 44 ka, 37.6 ka, 22.5 ka to calculate the timeframe of the coal-forming peatlands which ranges from 2703.44 to 2975.11 ka. Considering that the carbon content of the coal seam is 78.32% and the carbon loss during the coalification is about 25.80%, the carbon accumulation rate of the targeted coal seam is estimated to be 58.47–64.34 g C/m2·a, and the NPP is estimated to be 252.28–277.63 g C/m2·a. The main palaeoenvironmental factors controlling the NPP of peatlands are CO2 content, palaeolatitude and palaeotemperature. The reduced NPP values of the palaeo-peatlands in the Shaerhu coalfield can be attributed to the mid-palaeolatitude and/or too low atmospheric CO2 contents. To a certain extent, the NPP of palaeo-peatlands reflects the changes in atmospheric CO2, which can further reveal the dynamic response of the global carbon cycle to climate change. Therefore, predicting the level of NPP in the Middle Jurassic and studying the final destination of carbon in the ecosystem are beneficial to understanding the coal-forming process and palaeoenvironment.

Whole petroleum system in Jurassic coal measures of Taibei Sag in Tuha Basin, NW China

Based on the latest results of near-source exploration in the Middle and Lower Jurassic of the Tuha Basin, a new understanding of the source rocks, reservoir conditions, and source-reservoir-cap rock combinations of the Jurassic Shuixigou Group in the Taibei Sag is established using the concept of the whole petroleum system, and the coal-measure whole petroleum system is analyzed thoroughly. The results are obtained in three aspects. First, the coal-measure source rocks of the Badaowan Formation and Xishanyao Formation and the argillaceous source rocks of the Sangonghe Formation in the Shuixigou Group exhibit the characteristics of long-term hydrocarbon generation, multiple hydrocarbon generation peaks, and simultaneous oil and gas generation, providing sufficient oil and gas sources for the whole petroleum system in the Jurassic coal-bearing basin. Second, multi-phase shallow braided river delta–shallow lacustrine deposits contribute multiple types of reservoirs, e.g. sandstone, tight sandstone, shale and coal rock, in slope and depression areas, providing effective storage space for the petroleum reservoir formation in coal-measure strata. Third, three phases of hydrocarbon charging and structural evolution, as well as effective configuration of multiple types of reservoirs, result in the sequential accumulation of conventional-unconventional hydrocarbons. From high structural positions to depression, there are conventional structural and structural-lithological reservoirs far from the source, low-saturation structural-lithological reservoirs near the source, and tight sandstone gas, coal rock gas and shale oil accumulations within the source. Typically, the tight sandstone gas and coal rock gas are the key options for further exploration, and the shale oil and gas in the depression area is worth of more attention. The new understanding of the whole petroleum system in the coal measures could further enrich and improve the geological theory of the whole petroleum system, and provide new ideas for the overall exploration of oil and gas resources in the Tuha Basin.

Three Decades of Oasis Transition and Its Driving Factors in Turpan–Hami Basin in Xinjiang, China: A Complex Network Approach

As a predominant ecosystem-providing area and distinctive landscape in arid regions, an oasis plays an important role in maintaining land stability, human production, and daily activities. Studying the dynamics of oasis and its driving factors is vital to supporting arid regions’ sustainable development. As a typical mountain–desert–oasis landscape, the Turpan–Hami (Tuha) Basin, located in Xinjiang, China, includes complex interactions among different land types. For this study, we revealed the spatio-temporal patterns and transition processes of the oasis using a complex network method between 1990 and 2020 in the Tuha Basin. In the oasis transition network, the degree value, betweenness centrality, and average path length were calculated to express the transition relationship, key oasis type, and oasis structural stability, respectively. Six factors related to climate change and human actives were selected to investigate the driving forces behind oasis transitions, including the average temperature and precipitation in the growing season, the total power of agricultural machinery (TAMP), the production of raw coal (PRC), the total output value of the plantation industry (TPI), and the population (Pop). Our results show that the oasis area of the Tuha Basin, including the natural oasis and artificial oasis, all grew from 1990 to 2020, with the natural oasis expanding more than the artificial oasis. The transitions between oasis types became more frequent as the area of oasis land types increased throughout the study period. Grassland acted as the most important oasis type in the network, with the highest betweenness centrality, but its importance declined due to the increasing complexity of the oasis transition network from 1990 to 2020. The transitions between oasis types became simpler, and the oasis structural stability decreased. Through driving force analysis, the oasis changes showed a positive correlation with the temperature (p-value < 0.05, r = 0.88), and urbanization and industrialization factors prompted transitions to built-up areas and cropland from grassland and shrubland. In summary, our results suggest that to create a harmonious symbiotic relationship between the natural environment in dryland and human activities, preventing grassland degradation and excessive reclamation of land cover is an available way. Meanwhile, the protection of shrubland and water resources is also important. This study provided reference and theory support for promoting the sustainable development of oases.

Effect of Matrix Characteristic and the Pore‐Throat Limit for Water Imbibition in Early Jurassic Tight Sandstone Reservoir of the Tuha Basin

Spontaneous imbibition (SI) is a fundamental mechanism for improving the production efficiency of tight sandstone reservoirs. Matrix characteristic plays important roles in the SI process, but how these factors affect SI and the limit pore‐throat size of effective driving force in the tight sandstone of the Tuha Basin has not been firmly established. Thus, a series of experiments (FE‐SEM, QEMSCAN, XRD, CT, and SI) of four tight sandstone core samples were conducted under laboratory conditions in the Tuha Basin. The results show that quartz and plagioclase feldspar are the main detrital minerals, while illite and illite/smectite (I/S) are the predominant clay minerals of those sandstone samples, and they have a micro‐nano (<2 μm) to meso‐macro (>10 μm) pores, but the micro‐nano pore performance disconnected, and during SI process, fluid enters small and meso‐macro‐size pores simultaneously. However, small pores play a dominant role in the initial stage (with steep imbibition slopes), while meso‐macro pores predominate in the second stage (with shallow imbibition slopes), and the limit pore‐throat value of the tight sandstone is around 9.1 μm in the Tuha Basin, beyond which the SI will be weakened. Though the mineral composition and its wettability will be changed with fluid environment (especially for clay minerals), the small pores (formed by clay minerals) always play a dominant role than meso‐macro‐size pores (mainly formed by quartz and plagioclase feldspar) in SI process. These observations can improve our understanding of fluid–reservoir interaction in the Tuha Basin’s tight sandstone reservoir and provide guidance for improving oil and gas recovery.

The recovery of the Middle-Late Triassic prototype basin in the western Tuha basin-eastern Junggar Basin

Based on the data of mud logging, well logging and seismic data, the erosion thickness and original sedimentary thickness of the Middle-Late Triassic prototype basin in the west of Turpan-Hami Basin-Zhundong area were restored and analyzed. The erosion thickness of the Middle-Upper Triassic was calculated by the seismic stratigraphic thickness trend method, and the prototype basin was analyzed by combining the original sedimentary thickness. The results show that the erosion thickness in the west of Turpan-Hami Basin is 0m-600 m, which decreases first and then increases from north to south and then decreases. The erosion thickness of the Middle-Upper Triassic strata in the Zhundong area is 0m-400m, which increases first and then decreases from south to north. The maximum original thickness of the Middle-Upper Triassic strata in the western Tuha Basin is 1400 m in the front of the Bogda Mountain, which is thickened from north to south. The original thickness of the Middle-Upper Triassic strata in the eastern Junggar Basin generally increases from north to south. Bogda Mountain and its adjacent areas show a quasi-plainization process of cutting high and filling low. The scope of Taibei depression and Tainan depression further expanded, the sedimentary center moved southward, the Pubei low uplift became the denudation area, and the Keyayi depression and the Toksun depression developed. Beisantai uplift and Shaqi uplift in the north of Zhundong area are developed and their scope is expanding, and Zhundong depression area is developed in the south.

Petrogenesis of Early Permian basalts in the Turpan-Hami basin, NW China: Implications for the spatial limits of the Tarim mantle plume

Controversies remain as to the area of the Tarim Large Igneous Province (TLIP), in particular, the relationship between extensive Permian magmatism in the Central Asian Orogenic Belt (CAOB) and the activity of Tarim plume. Here we report the geochronological, mineralogical and geochemical characteristics of the Permian basalts from the Turpan-Hami (Tu-Ha) basin, located in southwestern CAOB. LA-ICP-MS zircon U-Pb dating yielded an age of 298.4 ± 2.6 Ma, temporally close to that of the Tarim plume. The basalts could be classified into lower porphyritic basalt with phenocrysts of plagioclase, olivine, minor clinopyroxene, and upper aphyric basalts. Geochemically, the former is characterized by relatively higher Na2O + K2O (3.97–5.13 wt%), low (La/Yb)N (∼2) and depleted Sr-Nd values [εNd(t)= +8.2 to +8.7; (87Sr/86Sr)i = 0.7032–0.7034], whereas the latter have lower Na2O + K2O (4.19–4.43 wt%) content, higher (La/Yb)N (∼4–6) and more enriched Sr-Nd values [εNd(t)= +4.6 to +6.2; (87Sr/86Sr)i = 0.7033–0.7048]. The compositional variation of plagioclase phenocrysts and pressure estimation (∼7kbar) indicate that Tu-Ha magmas were stored and evolved in a lower crustal magma chamber which experienced at least one-time magma replenishment. The estimated mantle potential temperature (1270–1480 °C) in Tu-Ha basin is similar to MOR, with no obvious thermal anomaly. Furthermore, higher Na/Ti ratio of quartz-normative Tu-Ha basalts suggest a shallower melting depth for Tu-Ha basin than central area of TLIP, which against a typical plume model. These characteristics alongside regional geologic records collectively suggest that the formation of Permian Tu-Ha basalts is more closely linked post-orogenic extension, implying that the extensive Permian magmatism in the CAOB is unrelated to the Tarim plume.

Characteristics of dust aerosols and identification of dust sources in Xinjiang, China

Changes in atmospheric particulate matter content directly affect the Earth-atmosphere system balance and climate change and indirectly affect the environment and ecology. Therefore, this matter is receiving increasing attention. A typical arid area with a fragile ecological environment and frequent dust activities, Xinjiang, China, was investigated using Moderate Resolution Imaging Spectroradiometer (MODIS) daily aerosol optical thickness and Ångström wavelength exponent data to obtain the temporal and spatial distribution characteristics of long-term dust aerosols over 20 years. The frequency of occurrence was calculated to accurately identify anthropogenic and natural sources, and data, such as wind speed, were superimposed to quantitatively estimate dust aerosol emissions. The factors that influenced dust aerosol emissions are discussed. The results show that the distribution of dust aerosols in South and North Xinjiang is obviously different, and the average dust aerosol optical depth (DOD) in spring is higher than that in other seasons. The sources of natural dust have little variation and are primarily located in Lop Nur, on the edges of the Taklamakan and Gurbantunggut deserts, in the central Tuha Basin, and in dried-up lakes. The sources of anthropogenic dust are mainly distributed in the farmland areas of the oasis plain and the impact fan plain. Natural dust aerosols are dominant in Xinjiang, with high natural dust emissions in spring. Changes in anthropogenic dust aerosols are caused by production activities, and the annual average anthropogenic dust emissions account for 8% of the total dust emissions. Precipitation can promote a reduction in natural dust emissions. Topography has an obvious effect on the formation and transportation of dust aerosols, which manifests as the frequent occurrence of dust in the basin. The population density data and Defense Meteorological Satellite Program/Operational Linescan System (DMSP/OLS) nighttime light data reveal, that the intensity of human activities has a great impact on anthropogenic dust aerosols. This study provides support for research on how aerosols affect climate and environmental changes in Xinjiang.

Geochemical characteristics and exploration potential of Jurassic coal-formed gas in northwest China

Jurassic coal-measure strata are widely developed in Northwest China and mainly distributed in the Tarim Basin, Junggar Basin, Qaidam Basin, and Tuha Basin. The Jurassic coal-formed gas resources are abundant. Although the Jurassic strata in Northwest China have similar tectonic and sedimentary environments, the geochemical characteristics of the coal-formed gas formed in Northwest China have both similarities and differences. Therefore, analyzing and summarizing the geochemical characteristics and exploration potential of the coal-formed gas in the Jurassic petroleum systems in different basins are of great significance for searching for different types of coal-formed gases. Through comprehensive comparison and analysis, it is believed that the drying coefficient of Jurassic coal-formed gases in western China present three types: namely the single peak type of wet gas, the double peak type wet gas-dry gas and the single peak type dry gas; the distribution range of δ13C1 is large, corresponding to the sequence of source rocks from low maturity to over-mature; the partial isotopic inversion of C2 and C3 is mainly caused by the mixed source and biological actions; source rock maturity is the main reason causing the geochemical differences of natural gases in different regions. The Jurassic coal-formed gas in Northwest China has large exploration potential, and the exploration degree of structural gas reservoirs is relatively high. The structural-lithological and lithological gas reservoirs, as well as the main exploration reservoir types for Jurassic coal-formed gas in Northwest China; the Jurassic system in the Kuqa Depression of Tarim Basin, Cretaceous-Jurassic system in the southern margin of the Junggar Basin, the Jurassic high maturity coal-formed gas in the Tuha Basin and the Jurassic high maturity–post-mature coal-formed gas in the Qaidam Basin have great exploration potential, which are important exploration fields for Jurassic coal-formed gas in Northwest China in the future.

Geothermal field and deep thermal structure of the Tianshan‐Altun region

AbstractThis paper analyses the characteristics of geothermal gradient and terrestrial heat flow in the Tianshan‐Altun region on the basis of available published data, such as geothermal gradient, measured temperature during oil test producing, rock thermophysics, and heat flow. Based on the steady‐state heat conduction equation, this paper has set up a 3D model by adopting basin modelling method to carry out deep temperature field simulation, with the aim to determine deep thermal structural parameters, the lithospheric thermal thickness, and the crustal contribution rate to the terrestrial heat flow. The geological section of Golmud‐Ejin Banner and the geological section of West Kunlun‐Tarim‐Tianshan were selected to represent the regional temperature and its thermal structure. The results show that the Tianshan‐Altun region has a low temperature geothermal field (averaging temperature gradient 2.2 °C/100 m, heat flow 56.3 mW/m2). The Qaidam Basin has the highest value (averaging 3.2 °C/100 m, 57.4 mW/m2). The lithospheric thermal thickness of the Tianshan‐Altun region is between 110 and 210 km. There are great differences of lithospheric thermal thickness on both sides of the Altun‐Tagh Fault. The west has thicker thermal lithospheric thickness (160–210 km) than the east (110–180 km). The contribution rate of the crust to the terrestrial heat flow decreases in the following order: the Qaidam Basin, the Jiudong Basin, the Jungger Basin, the Tarim Basin, and the Tuha Basin. Sedimentary basins have higher temperature and thinner thermal lithosphere than tectonic orogens when at the same depth. It can be observed that great thermal differences exist on both sides of the Altun‐Tagh Fault. There are relative similarities of low temperature, deeper thermal structure, and thicker lithospheric thermal thickness among the Tarim Basin, the Junggar Basin, and the Yining Basin in a wide geological area because of their shared deep geological basement. The Qaidam Basin and the Hexi Corridor Basin, which are located to the east of Altun‐Tagh Fault, have higher thermal background.

The origin and secondary alteration of dissolved gas in oil: A case study from the western Tu-Ha Basin, China

The Tu-Ha Basin is a typical Jurassic coal-derived petroliferous basin in western China. Seventeen natural gas samples were collected from the Jurassic Sanjianfang and Qiketai Formations, the Cretaceous Tugulu Formation, and the Paleogene Shanshan Formation to analyze the source and secondary alteration of natural gas. The natural gas samples were characterized by molecular and stable carbon (δ13C) and hydrogen (δD) isotope compositions. The results indicate that the natural gases are wet gases, in which methane is the main alkane component. Nitrogen (N2) and carbon dioxide (CO2) are the two non-hydrocarbons. The N2 values (>12%) are relatively higher, which increase rapidly at the burial depth of 1500–2000 m. Some natural gases have suffered secondary alteration at this depth. The natural gases are thermal genetic coal-derived gases (humic gas), coming from the Jurassic coal measure source rocks, which are chiefly in the low mature to early mature stage. Nitrogen in the shallow is chiefly derived from the atmosphere, while nitrogen at the deeper burial depth is mainly derived from the thermal decomposition of organic matter (OM). The shallow natural gas samples have the heaviest carbon isotope composition of ethane (δ13C2) and a carbon isotope sequence of (δ13C1 < δ13C2 > δ13C3 > δ13n-C4 < δ13i-C4), which is mainly caused by the biodegradation. The higher nitrogen content illustrates that a large amount of surface water is running into the reservoirs. Water washing occurs in the reservoirs, which decreases the molecular methane content and increases the amount of heavier hydrocarbons at 1500–2000 m depth.

Tomographic velocity analysis and wave-equation depth migration in an overthrust terrain: A case study from the Tuha Basin, China

Although the structures associated with overthrust terrains form important targets in many basins, accurately imaging remains challenging. Steep dips and strong lateral velocity variations associated with these complex structures require prestack depth migration instead of simpler time migration. The associated rough topography, coupled with older, more indurated, and thus high-velocity rocks near or outcropping at the surface often lead to seismic data that suffer from severe statics problems, strong head waves, and backscattered energy from the shallow section, giving rise to a low signal-to-noise ratio that increases the difficulties in building an accurate velocity model for subsequent depth migration. We applied a multidomain cascaded noise attenuation workflow to suppress much of the linear noise. Strong lateral velocity variations occur not only at depth but near the surface as well, distorting the reflections and degrading all deeper images. Conventional elevation corrections followed by refraction statics methods fail in these areas due to poor data quality and the absence of a continuous refracting surface. Although a seismically derived tomographic solution provides an improved image, constraining the solution to the near-surface depth-domain interval velocities measured along the surface outcrop data provides further improvement. Although a one-way wave-equation migration algorithm accounts for the strong lateral velocity variations and complicated structures at depth, modifying the algorithm to account for lateral variation in illumination caused by the irregular topography significantly improves the image, preserving the subsurface amplitude variations. We believe that our step-by-step workflow of addressing the data quality, velocity model building, and seismic imaging developed for the Tuha Basin of China can be applied to other overthrust plays in other parts of the world.

录井评价技术在吐哈红台地区“三低”储集层的应用研究

录井评价技术在吐哈红台地区“三低”储集层的应用研究

B isotopes of Carboniferous‐Permian volcanic rocks in the Tuha basin mirror a transition from subduction to intraplate setting in Central Asian Orogenic Belt

AbstractControversies remain as to the Permian tectonic setting in the Central Asian Orogenic Belt (CAOB), in particular, regarding the triggering of Permian magmatism. To address this issue, we carried out a geochemical study on Dananhu volcanics from the Tuha basin, southwestern CAOB. 40Ar/39Ar analyses for feldspar separates yield a Carboniferous age of 321.2 ± 9.8 Ma for the andesites and a Permian age of 278.9 ± 4.2 Ma for the basalts. Both the andesites and basalts geochemically resemble subduction‐related magmas in aspects of their trace element and Sr‐Nd‐Pb isotopic composition, but they may differ in petrogenesis. The andesites are typical adakites. Their high Cr and Ni contents, and low heavy rare earth element contents, and positive correlation between B/Nb ratios and δ11B values suggest that they were generated by interaction between slab‐derived melts/fluids and the mantle wedge. The Permian basalts are subdivided into two subgroups: alkali and tholeiitic basalts. High Ba/La and Ba/Zr ratios indicate that the source of the alkali basalts has been metasomatized by fluids/melts derived from altered oceanic crust. In contrast, a volatile‐free source metasomatized by sediment‐derived fluids/melts is inferred for the tholeiitic basalts given their high Th/Zr and Th/Ce ratios. Negative correlation between B/Nb and δ11B for the Permian basalts imply that the arc signatures were imposed by previous subduction events, and no direct slab‐derived fluids/melts participated in their petrogenesis. These geochemical characteristics alongside regional geologic records collectively suggest a tectonic shift in the southwestern CAOB from subduction‐related setting during the Late Carboniferous to an intraplate setting during the Early Permian.

Coal-measure source rock characteristics and burial evolution history in the Shisanjianfang Area, Tuha Basin

Shisanjianfang Area in the eastern margin of Taibei Sag, Tuha Basin, is an important region for oil and gas exploration. In this study, a large number of source rock geochemical data were used to analyze the geochemical characteristics of coal-measure source rocks in the Shisanjianfang Area, Tuha Basin, from three aspects, i.e., organic matter abundance, organic matter type, and organic maturity. The results show that the Jurassic Xishanyao Formation (J2x) in the study area has great thickness, continuous distribution, and high source rock maturity, and is the major source rock horizon in the study area. The seismic data are used in combination with 1D and 2D basin simulation technology to study the distribution characteristics of the source rocks in Shisanjianfang Area. The results of the simulation research on the source rock maturity history in the study area indicate the following: (1) The source rocks in the Xishanyao Formation (J2x) have a hydrocarbon generation threshold depth of 1800 m, threshold temperature of 95 °C, and hydrocarbon generation threshold time of about 162 Ma. (2) The Xishanyao Formation (J2x) has a current formation temperature of 50~110 °C and Ro of 0.6~1.1 % in the peak oil generation stage. (3) The source rock maturity in the study area is shown as being higher in the west while lower in the east, and higher in the north while lower in the south, and the favorable exploration area mainly lies in the northwest of the study area. The results of this study could have important implications for the oil and gas exploration in the margins of Xiaocaohu Sag, Tuha Basin.

Formation and accumulation of lower Jurassic tight gas sands field in Kekeya area of Tuha Basin, northwestern China

The lower Jurassic in Kekeya area of Tuha Basin contains great tight gas sand resources. This study reveals the geologic controls on the formation and accumulation of tight gas sand reservoirs in Kekeya area comprehensively and systematically, based on tectonic evolution, depositional setting, source rock characteristics, reservoir properties, charging-accumulation history and mechanisms. Our study reveals that tectonics and depositional systems play important roles in the tight gas sand petroleum system. Located at the thrust fold belt of Tuha Foreland Basin with continuous stratigraphic succession of braided fluvial – deltaic – lacustrine depositional systems, the lower Jurassic in Kekeya area contains favorable petroleum geologic conditions for the tight gas sands field. The source rocks contain abundant organic matters dominated by gas-prone type III kerogens and started generating primarily gas in early burial stage. The tight sand reservoirs are mainly composed of medium to coarse grained feldspathic litharenites with primary reservoir space as remnant interparticle pores, solution enlarged intraparticle pores as well as micro-fractures. The more active burial compactions and chemical diagenesis in coal-bearing stratigraphy along with the fast subsidence rate in Tuha Basin are responsible for the tightness of the sand reservoir. The favorable source – reservoir – seal arrangement along with the right timing of hydrocarbon generation, the developing of overpressure in source rocks as well as faulting and fracturing contribute to the widespread accumulation of tight gas sands in lower Jurassic in Kekeya area. The findings in this study would provide reference and guide for future exploration and development of tight gas sand fields in this area and in other basins.

Geochemical Characteristics and Genesis of Pre-jurassic Heavy Oil in Tainan Sag of Tuha Basin

Geochemical Characteristics and Genesis of Pre-jurassic Heavy Oil in Tainan Sag of Tuha Basin

New Reservoir Grading Method for Tight Gas Reservoir – One Case Study in Kekeya Block, Tuha Basin, China

Tight sand reservoir is usually characterized by high heterogeneity and complex pore structure, which makes the permeability calculation a big challenge and leads to difficulties in reservoir classification and productivity evaluation. First, five different Hydraulic Flow Units and respective Porosity-permeability relations were built based on core dataset from Kekeya block, Tuha Basin; and then with BP Neutron Network method, flow unit was classified for un-cored intervals using normalized logging data, and permeability was calculated accordingly. This improved the accuracy of permeability calculation and helped a lot on un-cored reservoir evaluation. In addition, based on porosity, permeability and flow unit type, a new reservoir grading chart was set up by incorporating the testing or production data, which provides important guidance for productivity prediction and reservoir development.

Decadal climate variability and vulnerability of water resources in arid regions of Northwest China

Decadal climate change has evidently posed serious threats and challenges to water resource management across arid regions in China. Thus, vulnerability assessment of water resources has been considered vital to adapt to or cope with the adverse effects of climate change. This paper investigated spatial patterns of decadal climate change and water resources variability in the arid regions of Northwest China based on a GIS analysis. The Budyko hypothesis was used to investigate the climate sensitivity of basin streamflow. A framework was proposed to assess the vulnerability of water resources as a function of exposure, sensitivity, and adaptability. Results indicated that a significant increase in precipitation and water resources (both surface water resources and groundwater recharge) occurred primarily in Xinjiang Province after the 1980s. Water utilization ratio in arid regions was very high, and groundwater abstraction substantially increased as it exceeded the exploitable volume in the Hexi Corridor, the Tuha Basin, and the north of the Tianshan Mountain. Exposure of water resources to drought in arid regions decreased from the 1960s to the 2000s. The sensitivity of water resource response to precipitation changes varied between regions. Water resources were more sensitive to precipitation variability in the river basins in the Hexi Corridor and inner Mongolia. In most arid regions in China, water resources were evaluated with low adaptability and high or severe vulnerability in the 2000s. In the future, the precipitation is projected to increase significantly under the RCP2.6, RCP4.5, and RCP8.5 scenarios. Particularly, water vulnerability will be significantly reduced as the precipitation increases in most river basins under the RCP8.5 scenario. Water resources in the rivers in the Qaidam Basin, the Qinhai Lake Basin, the inner Mongolia, and the north of Kunlun Mountain will have low or medium vulnerability in the 2030s and 2050s. However, in the Tuha Basin and Hexi Corridor, vulnerability will remain severe in the 2050s despite the significant increase in precipitation and implementation of water-saving measures. Hence, measures that will facilitate sustainable water resource management must be identified and implemented.

&amp;lt;sup&amp;gt;40&amp;lt;/sup&amp;gt;Ar/&amp;lt;sup&amp;gt;39&amp;lt;/sup&amp;gt;Ar geochronology of supergene jarosite constraints on weathering front propagation rate in the TuHa basin

Two jarosite samples with visually distinct phases collected from the oxidation zone of the Hongshan Cu-Au deposit in the TuHa Basin are dated by laser ⁴⁰Ar/³⁹Ar incremental heating analysis. To test the age reproducibility of each sample, two aliquots are dated. The results indicate that the dates obtained are reproducible, yielding ages of 7.5 and 8.0 Ma, confirming the suitability of supergene jarosite to ⁴⁰Ar/³⁹Ar geochronology. Combined with published ages, the obtained ⁴⁰Ar/³⁹Ar ages decrease from the top to the bottom of the profile, which records the arrival of a weathering front at that depth, yielding a weathering front propagation rate of 2.92 m/Ma.