Tarim Basin Research Articles

Characteristics and controlling factors of the unconformity-related carbonate reservoir: a case study from Sinian Shuiquan Formation, Tarim Basin, northwestern China

Deep-buried marine carbonate reservoirs in the Tarim Basin present challenges for exploration. A regional unconformity in dolomite at the top surface of the Shuiquan Formation makes the carbonate rocks ideal reservoirs. This study determines the unconformity belt distribution, lithology, reservoir space types and the controlling factors of the Shuiquan Formation, to establish a paleokarst development model and predict the favourable exploration targets. By flattening the seismic-event section and tracking truncation points on the seismic profiles, the unconformity area and denudation trends of the Shuiquan Formation are identified. The denudation area appears on a NEE-trending plane as a band with a width of 10–20 km and a thickness that expands from the depression to the slope and uplift. The Sinian Shuiquan Formation developed in a carbonate platform–tidal flat environment. Outcrop, core, well logging, and thin-section observations reveal that the lithology of the Shuiquan Formation consists of crystalline dolomite and granular dolomite, with pore types that include intercrystalline dissolution pores, intercrystalline pores and structural fractures. Unconformity, karstification and tectonic activity with atmospheric freshwater leaching, storage space and communication channels, respectively, are considered crucial factors influencing carbonate reservoir formation in the study area. A prediction model for the carbonate reservoirs in the Tadong area shows that the strong karst belt on the slope is the ideal area for forming a carbonate reservoir.

Prediction of permeability in a tight sandstone reservoir using a gated network stacking model driven by data and physical models

Introduction: Permeability is one of the most important parameters for reservoir evaluation. It is commonly measured in laboratories using underground core samples. However, it cannot describe the entire reservoir because of the limited number of cores. Therefore, petrophysicists use well logs to establish empirical equations to estimate permeability. This method has been widely used in conventional sandstone reservoirs, but it is not applicable to tight sandstone reservoirs with low porosity, extremely low permeability, and complex pore structures.Methods: Machine learning models can identify potential relationships between input features and sample labels, making them a good choice for establishing permeability prediction models. A stacking model is an ensemble learning method that aims to train a meta-learner to learn an optimal combination of expert models. However, the meta-learner does not evaluate or control the experts, making it difficult to interpret the contribution of each model. In this study, we design a gate network stacking (GNS) model, which is an algorithm that combines data and model-driven methods. First, an input log combination is selected for each expert model to ensure the best performance of the expert model and selfoptimization of the hyperparameters. Petrophysical constraints are then added to the inputs of the expert model and meta-learner, and weights are dynamically assigned to the output of the expert model. Finally, the overall performance of the model is evaluated iteratively to enhance its interpretability and robustness.Results and discussion: The GNS model is then used to predict the permeability of a tight sandstone reservoir in the Jurassic Ahe Formation in the Tarim Basin. The case study shows that the permeability predicted by the GNS model is more accurate than that of other ensemble models. This study provides a new approach for predicting the parameters of tight sandstone reservoirs.

Hydrological fluctuations in the Tarim Basin, northwest China, over the past millennium

Abstract Reconstruction of hydrological fluctuations in arid regions has proven challenging due to a lack of reliable chronologic constraints on sparse geological archives. The aim of this study was to establish an independent record of hydrologic changes in the hyper-arid Tarim Basin (TB; northwest China) with high spatiotemporal resolution. We present comprehensive radiocarbon and tree-ring data sets of subfossilized plant remains in the TB compiled from geomorphological investigations of the paleochannels of the Tarim River (TR), the longest endorheic river in China, crossing the world's second-largest shifting sand desert. Results show that the late medieval configuration of the TR basin was characterized by enhanced hydrological connectivity, as indicated by the formation of significant riparian forests in the desert regions at ca. 1170 CE. A distinct low-flow interval (ca. 1500–1650 CE) is identified for the first time, refining the period of a wetter-than-present TB. The present-day organization of streams in the lower TR was proto-formed after the dry period, possibly led by episodic flood-induced diversion. Our study describes the centennial-scale dynamics in the TR flow over the past millennium, offering a robust long-term context for hydrological assessment in the extensive drylands of the Asian interior.

Sedimentary characteristics and model of seasonal deltaic sandstone: a case study on the continental red bed from the Cretaceous Baxigai Formation, Tarim Basin, NW China

Seasonal delta is a sandy fan-shaped sedimentary system formed by seasonal river flooding in continental basins. Modern sedimentary finds that seasonal deltas mainly develop in an arid-semi-arid climate environment with gentle terrain. However, the study of seasonal deltas in ancient rock records is still insufficient, leading to misinterpretations as other sedimentary systems, which poses challenges to the correct understanding of the origin and spatial distribution of sand body deposits. In this study, the red bed deposits of the Cretaceous Baxigai Formation in the west of the Tabei Uplift were selected as the research object. Based on core observation and description, a comprehensive analysis of the sedimentary environment, sedimentary characteristics and sedimentary model of the Baxigai Formation was carried out using data such as well-logging and analytical testing, combined with modern depositional characteristics. Research shows that the sedimentary sequence of the Baxigai Formation red bed developed a seasonal delta sedimentary system in the arid climate. The seasonal delta deposits provide an opportunity to understand the influencing of river flow and total sedimentary loading vary greatly on the sedimentary model, sedimentary mechanism, and distribution of sand bodies in arid climates. The sedimentary process of the seasonal delta in the Baxigai Formation was controlled by the dual-stage sedimentation process in an arid paleoclimate. During the flood period, the supercritical flow sedimentary structures are widely developed in the major distributary channels, and the distributary channels migrate and bifurcate frequently. On the delta plain, crevasse channels are formed through the avulsion of major distributary channels. During the dry period, due to the consumption of water seepage and evaporation transfer, terminal distributary channels are abandoned, crevasse channels are not developed, and the sediment is exposed. The density of the distributary channels is reduced, and the total sedimentary loading is low. The distributary channels sand body is the skeleton sand body of the seasonal delta. This study is of great significance for accurately explaining the formation process of seasonal deltas and provides a useful reference for further exploration and deployment of oil and gas reservoirs and paleogeographic reconstruction in the study area.

Meteoric water effect of diagenesis processes in deep carbonate reservoirs

As the world’s main oil and gas resource, the deep carbonate reservoir has great exploration-development potential. However, it is difficult to make development and exploration due to its complex diagenesis processes. During the formation of carbonate reservoirs, the effect of meteoric water forms karst holes for oil and gas reservoirs, but the complex internal mechanism severely restricts the exploration and development of carbonate reservoirs. This paper takes the deep carbonate reservoirs in the Tarim Basin as the research object, studies the diagenesis processes in deep carbonate reservoirs through geological survey, analyzes the effect of meteoric water on porosity and mineral changes in carbonate reservoirs at different diagenetic stages by using laboratory test, theoretical analysis, and numerical simulation research methods. The numerical simulation method is used to simulate the porosity changes and mineral evolution of reservoirs in different diagenetic stages, and the conclusion is drawn that meteoric water has an impact on reservoir minerals and porosity. The results show that the carbonate reservoirs in the Tarim Basin have high porosity and good permeability, and the reservoirs have experienced deposition, compaction, dissolution, and hydrothermal stages, and have experienced meteoric water effects for a long time, resulting in rock dissolution, regenerative precipitation and chemical reaction; Quartz and feldspar minerals are the most in the sample through laboratory tests, the content of quartz decreased first, then increased and decreased, and the content of chlorite and mica changed little during the whole diagenesis processes. With the injection of organic acid, the porosity of the reservoir increases, with the continuous increase of temperature and pressure, the porosity decreases. After the second injection of organic acid, the porosity increases continuously, and finally, the porosity decreases. TOUGHREACT is used to simulate the static reaction of water and rock, simulating six diagenetic stages. With the injection of organic acid, the porosity increases continuously and then reaches equilibrium. The sudden increase in temperature and pressure leads to an increase in porosity, and the porosity of the reservoir changes little during the second injection of organic acid, and the porosity decreases in the final stage. The research results provide theoretical data support for guiding oil and gas exploration in deep carbonate reservoirs.

Magma-driven thermal convection dolomitization of the Lower-Middle Ordovician strata caused by Mg sourced from underlying Cambrian dolomites in the Tarim Basin, China

Thermal convection arises due to a density gradient between geothermally heated formation water within the underlying strata and the water in the overlying strata. The thermal convection model has long been accepted as a stable and long-lived flow mechanism for dolomitization, which can affect large volumes of rock. This study investigates the dolomitization of the Lower-Middle Ordovician strata in the Tarim Basin using petrological evidence, geochemical data, and the Calculation of Mg2+ flux. The Ordovician dolomites occurred in several types, including 1) individual dolomite crystals; 2) patchy dolomites; 3) layered-massive dolomites; 4) cement dolomites in pores and fractures. The dolomite content decreases vertically with decreasing burial depth. Geochemically, the dolomitizing fluids of the Ordovician carbonates are suggested as deep-formation water slightly influenced by hydrothermal fluids, with an obvious genetic connection with the underlying Cambrian dolomites. In addition, mass balance calculations were conducted to help identify the Mg2+ sources, supporting that the Mg-rich dolomitizing fluids were derived largely from the underlying strata. Large volumes of Mg-rich fluids were released when the underlying contemporaneous Cambrian dolomites were physically and chemically compacted. The released fluids were driven by heat from a high-temperature Early Ordovician magma chamber and migrated upward through fractures and/or permeable strata due to hydrothermal convection. These processes caused thermal convection dolomitization of the overlying Ordovician limestones from bottom to top. This study explains how these widespread dolomites developed in the Ordovician strata of the Tarim Basin, which can help identify the locations of the oil-gas reservoir rocks. In addition, this revised thermal convection model highlights the contribution of Mg-rich fluids derived from the underlying dolomites, and the circulation of fluids may have been driven by the heat from a magmatic source. This model is believed to be of significance to areas affected by abnormal geothermal activities.

An Analysis of the Instability Conditions and Water Vapor Transport Characteristics during a Typical Rainstorm in the Tarim Basin

In order to deepen the understanding of the occurrence mechanism and water vapor transport characteristics of the heavy rain process in the extreme arid region of Xinjiang, a rare heavy rain process in the Tarim Basin during the period of 18–22 July 2021 was comprehensively analyzed by using multi-source data. The results show that the upper tropospheric South Asian high was distributed in a “west-high-east-low” pattern during the rainstorm process, and the rainstorm area was located on the right side of the upper jet stream entrance area, while the middle-level Iranian high pressure, Baikal high pressure and Central Asian low pressure formed a “two-highs and one-low” circulation situation. The coupling of the high and low air jets and the strong vertical upward motion provided favorable dynamic conditions. Rainstorm water vapor mainly comes from the Mediterranean Sea, Central Asia and the Indian Ocean, and it enters the basin in four paths: west, east to west, west to east, and southwest and south. The water vapor mainly flows into the middle layer of the western boundary and the southern boundary and the lower layer of the eastern boundary, and it flows out from the middle and upper layer of the eastern boundary. The negative moist potential vorticity region at a low level has a strong indicator significance for the occurrence and development of heavy rain, and the superposition of positive and negative moist potential vorticity regions at vertical height is conducive to the occurrence and development of heavy rain.

Quantitative Prediction of the Development and Opening Sequence of Fractures in an Ultradeep Carbonate Reservoir: A Case Study of the Middle Ordovician in the Shunnan Area, Tarim Basin, China

Summary Quantitative prediction of reservoir tectonic fracture development characteristics, opening pressures, and opening sequences is critical in the exploration and development of oil- and gas-bearing reservoirs and thus has received widespread attention. Using numerical simulations of the paleostress field during the formation of tectonic fractures and the rock fracture criterion, we predict the development and occurrence of fractures in the Middle Ordovician Yijianfang Formation in the Shunnan region of the Tarim Basin, China. The local paleostress fields reflected by the mechanical properties and occurrence of tectonic fractures obtained from core descriptions, acoustic emission (AE) experiments, paleomagnetic experiments, sound velocity measurements, and borehole breakouts were used to determine the regional paleostress and in-situ stress. We established a geomechanical model by combining the mechanical parameters of the rocks with the finite element method (FEM), optimizing the boundary conditions with a self-adaptive constraint algorithm, and conducting numerical simulations of the in-situ stresses. Fracture occurrence and numerical simulation results of the in-situ stress field were used to determine the opening pressure (Pk) and opening sequence of the fractures. The level of fracture development decreases away from the strike-slip fault in the study area. Fracture development is positively correlated with the Young’s modulus, paleostress difference, and paleostress difference coefficient of the rock. The direction of the maximum horizontal principal stress is from north-northeast (NNE) to northeast (NE). Initially, shear fractures and tensional fractures oriented NNE 30°–35° and NE 40°–45°, respectively, open during the water injection process. Pk is positively correlated with the horizontal stress difference coefficient and the angle between the fracture strike and the maximum horizontal principal stress. At the structural highs (burial depths shallower than 6450 m) and the structural lows (burial depths deeper than 6450 m), the burial depth correlates negatively and positively with Pk, respectively. This investigation of the development, occurrence, Pk, and opening sequence of tectonic fractures and their principal controlling factors will have a positive impact on the future exploration and production opportunities of similar fractured reservoirs.

Molecular and Carbon Isotopic Compositions of Crude Oils from the Kekeya Area of the Southwest Depression, Tarim Basin: Implications for Oil Groups and Effective Sources

Molecular and stable carbon isotopic compositions of 32 crude oils from the Kekeya area of the Southwest Depression, Tarim Basin, were analyzed comprehensively to clarify oil groups and trace oil sources. The results indicate that lacustrine shale sequences within the Upper-Middle Permian Pusige Formation (P3–2p) are the major effective oil sources; the thermal maturation effects exert the crucial impact on geochemical compositions of crude oils. In the Kekeya structural belt, crude oils produced from the Lower-Neogene, Middle-Paleogene and Middle-Cretaceous sandstone reservoirs were generated mainly from deeply buried P3–2p at the late-to-high maturity stage. These condensates are depleted in terpanes, steranes and triaromatic steranes and enriched in adamantanes and diamantanes. The evaluated thermal maturity levels of crude oils by terpanoids and steranes are generally lower than that of diamondoids, implying at least two phases of oil charging. In the Fusha structural belt, oils produced from the Lower-Jurassic reservoirs (J1s) of Well FS8 were generated from the local P3–2p at the middle to late mature stage. On the contrary, these oils are relatively rich in molecular biomarkers such as terpanes and steranes and depleted in diamondoids with only adamantanes detectable. The P3–2p-associated oils can migrate laterally from the Kekeya to Fusha structural belt, but not to the location of Well FS8. The Middle-Lower Jurassic (J1–2) lacustrine shales as the major oil sources are limited to the area around Well KS101 in the Kekeya structural belt. Crude oils originated from J1–2 and P3–2p can mix together within the Cretaceous reservoirs of Well KS101 by presenting the concurrence of high concentrations of terpane and sterane biomarkers and diamondoids as well as 2–4% 13C-enriched n-alkanes than those of P3–2p derived oils. This study provides a better understanding of hydrocarbon sources and accumulation mechanisms and hence petroleum exploration in this region.

Multi-Factor Controlling Diversity of the Ordovician Hydrocarbon Phase in the Tazhong I Block, Tarim Basin, NW China

The distribution characteristics and main controlling factors of hydrocarbon phases in deep strata from petroliferous basins are important for the evaluation of oil–gas resources and decision-making regarding exploration. The distribution characteristics and controlling factors of the Ordovician hydrocarbon phases are systematically analyzed in the Tazhong I block, Tarim Basin, NW China. The results show that the Ordovician reservoirs in the Tazhong I block are characterized as multi-phase reservoirs with a lateral co-existence of condensates, normal oil reservoirs, and heavy oil reservoirs. From east to west, gas-rich in the fault belt and oil-rich in the platform area are presented. Meanwhile, there are regular variations in the geochemical characteristics of the Ordovician hydrocarbon, showing decreasing trends in the gas/oil ratio (GOR), wax contents, dryness coefficients, methane contents, and methane carbonate isotope values (δ13C1) and an increasing trend in oil densities. Because the same Cambrian–Lower Ordovician source for the Ordovician hydrocarbon is observed in the Tazhong I block, the regular variations in the hydrocarbon phases and geochemical characteristics can be interpreted as records of gas invasion, biodegradation, multi-stage filling, thermal cracking, and thermochemical sulfate reduction (TSR) rather than controlled by the source rock organofacies. This indicated that different kinds of secondary processes for a diversity of the hydrocarbon phase can appear in one region. Our re-construction of the Ordovician hydrocarbon accumulation model in the Tazhong I block encourages future exploration to target gas reservoirs in the fault belt and oil reservoirs in the platform area.

Research on Water Invasion Law and Control Measures for Ultradeep, Fractured, and Low-Porosity Sandstone Gas Reservoirs: A Case Study of Kelasu Gas Reservoirs in Tarim Basin

The exploitation of ultradeep, fractured, and low-porosity gas reservoirs often encounters challenges from water invasion, exacerbated by the presence of faults and fractures. This is particularly evident in the Kelasu gas reservoir group, located in the Kuqa Depression of the Tarim Basin. The complexity of the water invasion patterns in these reservoirs demands a thorough investigation to devise effective water control measures. To elucidate the water invasion patterns, a combined approach of large-scale physical modeling and discrete fracture numerical simulations was adopted. These models allowed for the identification and categorization of water invasion behaviors in various gas reservoirs. Furthermore, production dynamic analysis was utilized to tailor water control strategies to specific invasion patterns. The large-scale physical simulation experiment revealed that water invasion in gas reservoirs is primarily influenced by high-permeability channels (faults + fractures), and that the gas production rate serves as the key factor governing gas reservoir development. The range of gas extraction rates spans from 3% to 5%. As the gas extraction rate increases, the extraction intensity diminishes and the stable production duration shortens. On the basis of the changes in the water breakthrough time and water production rate, a 2% gas extraction rate is determined as the optimal rate for the model. The embedded discrete fracture numerical simulation model further supports the findings of the physical simulation experiments and demonstrates that ① this type of gas reservoir exhibits typical nonuniform water invasion patterns, controlled by structural location, faults, and degree of crack development; ② the water invasion patterns of gas reservoirs can be categorized into three types, these being explosive water flooding and channeling along faults, uniform intrusion along fractures, and combined intrusion along faults and fractures; ③ drawing from the characteristics of water invasion in various gas reservoirs, combined with production well dynamics and structural location, a five-character water control strategy of “prevention, control, drainage, adjustment, and plugging” is formulated, with the implementation of differentiated, one-well, one-policy governance. The study concludes that a proactive approach, prioritizing prevention, is crucial for managing water-free gas reservoirs. For water-bearing reservoirs, a combination of three-dimensional water plugging and drainage strategies is recommended. These insights have significant implications for extending the productive lifespan of gas reservoirs, enhancing recovery rates, and contributing to the economic and efficient development of ultradeep, fractured, and low-porosity gas reservoirs.

Molecular transformations of heteroatomic organic compounds in crude oils caused by biodegradation and subsequent thermal maturation: Insights from ESI FT-ICR MS

The Tarim and Junggar basins are major petroliferous sedimentary deposits in China. Some oil reservoirs in these basins experienced superimposed secondary alterations including early biodegradation followed by thermal maturation/alteration (SSA-B&M). Heteroatomic polar organic compounds in crude oil are significantly influenced by SSA-B&M, which play a vital role in understanding the evolutionary history of oil reservoir. However, research on such alterations is limited. The present study employed negative and positive ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) to investigate the molecular transformations of heteroatomic organic compounds in crude oils resulting from SSA-B&M. The findings indicate that biodegradation leads to an enrichment of naphthenic acids, while subsequent cyclization, aromatization and thermal cracking reactions enhances the aromaticity of the pyrolysis products of all the oil samples with varying degree of biodegradation. Notably, highest aromaticity was observed for the crude oil that has been most severely altered by biodegradation. During early and moderate stages of biodegradation, the abundances of O2 compounds (molecules contain two oxygen atoms) representing carboxylic acids were continuously increasing. However, at severe biodegradation levels, fatty acids with 1 double bond equivalents (DBE) underwent degradation, while the naphthenic acids were further enriched. Subsequently, during maturation, O2 compounds with 1 to 5 DBE experienced a steady decline in abundance. The naphthenic acids mainly experienced aromatization, while the fatty acids were partly decarboxylized and cracked thereby forming new n-alkanes. Biodegradation led to modification in neutral nitrogen compounds with 3 to 4 condensed rings (DBE = 9–12) and long alkyl side chains, while the impact on basic nitrogen compounds was relatively minimal. After subsequent thermal maturation, both neutral and basic nitrogen compounds with long alkyl side chains underwent cracking, while those with shorter alkyl side chains and higher degrees of condensation tended to remain relatively unchanged. Finally, two new indices were defined and tested to correctly evaluate the maturation and biodegradation level for crude oils that have experienced SSA-B&M.

Hydrocarbon accumulation in deep ancient carbonate–evaporite assemblages

The Ediacaran–Ordovician strata within three major marine basins (Tarim, Sichuan, and Ordos) in China are analyzed. Based on previous studies focusing on the characteristics of the Neoproterozoic–Cambrian strata within the three major basins (East Siberian, Oman, and Officer in Australia) overseas, the carbonate–evaporite assemblages in the target interval are divided into three types: intercalated carbonate and gypsum salt, interbedded carbonate and gypsum salt, and coexisted carbonate, gypsum salt and clastic rock. Moreover, the concept and definition of the carbonate–evaporite assemblage are clarified. The results indicate that the oil and gas in the carbonate–evaporite assemblage are originated from two types of source rocks: shale and argillaceous carbonate, and confirmed the capability of gypsum salt in the saline environment to drive the source rock hydrocarbon generation. The dolomite reservoirs are classified in two types: gypseous dolomite flat, and grain shoal & microbial mound. This study clarifies that the penecontemporaneous or epigenic leaching of atmospheric fresh water mainly controlled the large-scale development of reservoirs. Afterwards, burial dissolution transformed and reworked the reservoirs. The hydrocarbon accumulation in carbonate-evaporite assemblage can be categorized into eight sub-models under three models (sub-evaporite hydrocarbon accumulation, supra-evaporite hydrocarbon accumulation, and inter-evaporite hydrocarbon accumulation). As a result, the Cambrian strata in the Tazhong Uplift North Slope, Maigaiti Slope and Mazatag Front Uplift Zone of the Tarim Basin, the Cambrian strata in the eastern-southern area of the Sichuan Basin, and the inter-evaporite Ma-4 Member of Ordovician in the Ordos Basin, China, are defined as favorable targets for future exploration.

Evolution and Application of Sealing Ability of Gypsum Caprocks under Temperature‐Pressure Coupling: An Example of the ZS5 Well in the Tazhong Area of the Tarim Basin

AbstractGypsum caprocks' sealing ability is affected by temperature‐pressure coupling. Due to the limitations of experimental conditions, there is still a lack of triaxial stress‐strain experiments that simultaneously consider changes in temperature and pressure conditions, which limits the accuracy of the comprehensive evaluation of the brittle plastic evolution and sealing ability of gypsum rocks using temperature pressure coupling. Triaxial stress‐strain tests were utilized to investigate the differences in the evolution of the confinement capacity of gypsum rocks under coupled temperature‐pressure action and isothermal‐variable pressure action on the basis of sample feasibility analysis. According to research, the gypsum rock's peak and residual strengths decrease under simultaneous increases in temperature and pressure over isothermal pressurization experimental conditions, and it becomes more ductile. This reduces the amount of time it takes for the rock to transition from brittle to plastic. When temperature is taken into account, both the brittle–plastic transformation's depth limit and the lithological transformation of gypsum rocks become shallower, and the evolution of gypsum rocks under variable temperature and pressure conditions is more complicated than that under isothermal pressurization. The sealing ability under the temperature‐pressure coupling is more in line with the actual geological context when the application results of the Well #ZS5 are compared. This provides a theoretical basis for precisely determining the process of hydrocarbon accumulation and explains why the early hydrocarbon were not well preserved.

Streamflow abrupt change and the driving factors in glacierized basins of Tarim Basin, Northwest China

A climate transition towards warm–wet conditions in Northwest China has drawn much attention. With continuous climate change and universal glacier degradation, increasing water-related hazards and vulnerability have become one of the important problems facing the Tarim Basin. However, the impacts of the climate transition on streamflow abrupt change and extreme hydrological events were less discussed, especially in glacial basins. In the present study, the discharge datasets in four glacial basins of Tarim Basin from 1979 to 2018 were constructed using the GRU-GSWAT+ model first. The differences in streamflow characteristics, the shift of hydrological extreme pattern, and potential changes of the controlling factors before and after the abrupt changes were investigated. The results indicated that the abrupt change point (ACP) in streamflow occurred in 2000 in the Qarqan River Basin, 2002 in the Weigan River Basin, and 1994 in the Aksu River Basin and the Yarkant River Basin. A general decrease in streamflow before the ACP has shifted to a notable upward trend in the Qarqan River Basin and the Aksu River Basin, while minor upward fluctuations were observed in other basins. Moreover, the hydrological characteristics in extreme events vary dramatically before and after the ACPs, characterized by a pronouncing shift from drought-dominant pattern to wet events dominated pattern. The driven climate factors have been altered after the ACPs with notable spatial heterogeneity, in which temperature remained as the dominant role in meltwater-dominated basins while the influence of precipitation has increased after the ACPs, whereas the sensitivity of temperature on streamflow change has been enhanced in basins dominated by precipitation such as the Qarqan River Basin. Owing to the evident warming–wetting trend and glacier compensation effect, both the inter-annual and intra-annual streamflow fluctuations can be efficiently smoothed in basins with a high glacier area ratio (GAR). These findings provide a further understanding of the abrupt change in streamflow under the exacerbated climate and glacier change in mountainous arid regions.

Hydrocarbon Generation and Accumulation in the Eastern Kuqa Depression, Northwestern China: Insights from Basin and Petroleum System Modeling

The eastern Kuqa Depression in the northern Tarim Basin, NW China, is rich in oil and gas. However, recent exploration has been hindered by a lack of knowledge on the evolution of the petroleum system. To address this, we conducted hydrocarbon generation and accumulation modeling using both the 2Dmove and PetroMod2017 software for a complex tectonic extrusion section in the Kuqa Depression. The results show that the source rocks in the northern slope zone became mature quite early at around 170 Ma, but the thermal maturity evolution stagnated subsequently because of tectonic extrusion and uplift. The source rocks in the central anticline zone, the southern slope zone, and the deep sag zone were of overall low maturity during the Jurassic to Paleogene but rapidly became mature to highly mature with the deposition of the Neogene Jidike and Kangcun formations. The main hydrocarbon generation periods are in the late Neogene and Quaternary, and the main hydrocarbon generation stratum is the lower Jurassic Yangxia formation. The amount of cumulative hydrocarbon generation gradually increases for carbonaceous mudstone, mudstone, and coal source rocks. Sourced from source rocks mainly in the northern slope zone, oil and gas migrated to anticlinal traps along sandstone transport layers and faults. Recent discoveries, such as the Tudong-2 gas field in the central anticline zone, underscore the richness of this region in petroleum resources. Some gas fields were also predicted in lithologic traps in the southern slope zone and the deep sag zone, as well as in fault-related traps in the northern part of the northern slope zone.

Dominant circulation pattern and moving path of the Mongolian Cyclone for the severe sand and dust storm in China

Severe sand and dust storm (SDS) is one of the major meteorological disasters in northern China. During 2000–2023, a total of 37 severe SDS events were monitored by the China Meteorological Administration and 34 of them occurred in the boreal spring (March to May). In this study, the 34 cases are analyzed to reveal their spatio-temporal features. The results indicate that there are two high-frequency centers. One is located in the Tarim Basin in northwestern China and the other is located in the central-western part of Inner Mongolia in northern China. In the 21st century, the duration of the severe SDS shows a clear interannual variation with an average of 3.5 days in 2000–2006, 2.7 days in 2007–2015 and 4.6 days in 2016–2023, respectively. Moreover, it occurs mainly in early spring in the third period, whereas it can occur throughout spring in the first and second periods. The composition of the general circulations for these 34 cases indicates that the simultaneous dominant pattern is a “positive-negative-positive” wave structure in the mid-high latitudes of Asia, with a cyclonic circulation (a deep trough) over the southern part of Russia to Mongolia, a major anticyclonic circulation (a ridge) over the eastern Europe to the west of Central Asia and a secondary anticyclonic center over northeastern China to the Korea Peninsula and Japan. The “positive-negative-positive” pattern enhanced the Mongolian Cyclone by increasing the zonal pressure gradients to both its west and east sides. Both the composition and typical case studies indicate that the eastward movement of the Mongolian Cyclone plays a dominant role in causing the severe SDS.

Construction of ecological security pattern based on InVEST-Conefor-MCRM: A case study of Xinjiang, China

Constructing ecological security patterns (ESP) effectively maintains ecosystems' green, healthy, and sustainable development. The InVEST model and Conefor software were utilized in this study to pinpoint ecological sources (eco-sources) through a blend of landscape connectivity and the importance of ecosystem services (IES); the ecological resistance surface was constructed by synthesizing the gravity model and minimum cumulative resistance model (MCRM), extracted ecological corridors (eco-corridors) and nodes. Ultimately, the research in this study built the ESP for Xinjiang. The findings showed that: (1) 14 eco-sources were identified in Xinjiang, spanning an area of 2.13 × 105 km2; 32 eco-corridors were extracted, including 9 important and 23 general eco-corridors, comprising a total length of 1.26 × 104 km; identified 46 ecological nodes(eco-nodes); (2) the size of important and more important patches of ecosystem services in Xinjiang was 2.82 × 105 km2, which accounted for a relatively small size, and the value of ecosystem services was generally average. The overall level of landscape connectivity in the primary eco-sources was high, but the spatial distribution was uneven; (3) the ecological resistance values in Xinjiang vary significantly, with high-level resistance surfaces primarily located in the Junggar Basin and Tarim Basin and low-level resistance covering most of Xinjiang's natural ecological reserves and other areas. The study's findings can provide some references for constructing ESP at the provincial scale and in arid and semiarid regions and for planning spatial ecological restoration in Xinjiang.

Microfacies, geometry and growth phases of microbial mound in Gucheng area, Southeastern Tarim Basin, China

Microfacies, geometry and growth phases of microbial mound in Gucheng area, Southeastern Tarim Basin, China

Using seismic methods to detect connectivity of fracture networks controlled by strike-slip faults in ultra-deep carbonate reservoirs: A case study in northern tarim basin, China

Ordovician tight carbonate rocks in the Tarim Basin are typically ultra-deep, with targets deeper than 7000 m. The fracture networks associated with strike-slip faults are the primary reservoir space. Fracture intensity near faults is higher than in wall rock areas and decreases with distance from faults. Based on the relationships of fracture network with the structure of strike-slip faults imaged by seismic data, adjacent to faults (in the ‘fault wall’) there are small-scale wall damage zones (SML SC WALL DMG ZONE) having fault widths is less than 250m, length less than 5 km; large-scale damage zones (LRG SC WALL DMG ZONE) having fault widths are greater than 250m, lengths greater than 5 km; intersection damage zones (INT DMG ZONEs), linking damage zones (LINK DMG ZONEs), overlapping zones between the linking damage zones and intersection damage zones (OL ZONE LINK INT DMG ZONEs).Increasing fracture intensity can be incorporated into fracture network models using well data and seismic data. We used the bounding box and scan line methods to evaluate fracture network connectivity and predict flow. The reliability of the results was verified by interference well tests. The fracture network connectivity based on the bounding box and scan line method is consistent with interference well test data, demonstrating that the bounding box and scan line method can effectively evaluate fracture network connectivity. The fracture network connectivity ranges from high to low in this order: overlapping zones between linking and intersecting zones, linking, intersecting, and large- and small parallel zones. Based on outcrop pattern and 3D discrete element simulation results we infer that connectivity is caused by stress concentration and perturbation in the evolution of strike-slip fault. The LINK DMG ZONE raises the displacement gradient and causes local rotation of the stress field, resulting in increased intensity, complex fracture directions, and high connectivity of fractures. The slip gradient of the INT DMG ZONE grows significantly due to stress perturbations, culminating in more fractures and increased connectivity. The OL ZONE LINK INT DMG ZONE generates more complex fracture networks with better connectivity.