Distribution Of Rocks Research Articles

Numerical simulation of thermo‐solid coupling under the condition of unidirectional heating of underground coal gasification overlying rock

AbstractIn order to study the variation law of temperature and stress of overlying rock under the thermal solid coupling condition of underground coal gasification (UCG), the coal measure sandstone samples were heated in one direction, the variation law of temperature and thermal stress was analyzed, and the experiment was analyzed using the numerical simulation software COMSOL. The temperature field, stress field, and volume strain distribution of rock mass are obtained. The results show that in the heating stage of the heating plate, the temperature curve of each measuring point changes rapidly and the temperature rises rapidly, and due to the decrease of the heating rate of the heating plate, the change rate of thermal stress tends to decrease. In the circumferential region of the lower end face, stress stretching occurs and the radial strain is the largest. Under the constraint of unidirectional heating, the temperature distribution of rock along the height direction is obvious. The principal stress is mainly concentrated near the lower end face of the specimen. The research results are helpful to study the thermal damage and fracture characteristics of overlying sandstone of UCG from the perspective of thermal solid coupling.

Detrital zircon U[sbnd]Pb geochronology of modern river sediment in the Eastern Pamir Syntaxis and its implications for the formation of the Pamir and growth of the Tibetan Plateau

The Eastern Pamir Syntaxis links the western Tibetan Plateau with the western syntaxis of the Himalayan-Tibetan orogen. Quantifying temporal and spatial variations in uplift rates for the Eastern Pamir Syntaxis is critical for understanding the growth of the Himalayan-Tibetan orogen. To better understand these variations, we report n = 285 new detrital zircon UPb ages from sediments in modern rivers of the Eastern Pamir Syntaxis. When compared with previous work, our data, with a major age mode around ∼107 Ma, indicate that siliciclastic sediments in the Taxkorgan River were primarily derived from Cretaceous rocks. Whereas a less prominent age mode around ∼13 Ma suggests that Miocene rocks made an important sediment contribution to the Taxkorgan River. The other notable age modes are in the range of 200–300 Ma and 600–800 Ma. Our data suggest that detrital zircon UPb signatures for rivers draining the Eastern Pamir Syntaxis change significantly from south to north, and the influence of Cretaceous proto-sources gradually diminishes northward. Because Tibetan sutures are traceable into the Pamir, these data help define the distribution of late Early Cretaceous rocks associated with the closure of the Meso-Tethys within the Pamir. These data support the establishment of the modern-like river pattern in the Eastern Pamir Syntaxis contemporaneous with activity on the Kongur Extensional System in the northeast Pamir.

Use of machine learning technology to model the distribution of lithotypes in the Permo-Carboniferous oil deposit of the Usinskoye field

Permo-Carboniferous oil deposit of the Usinskoye field is characterized by an extremely complex type of the void space with intense cross-sectional distribution of cavernous and fractured rock. In this study, for this production site, the process of 3D geological modeling has been implemented. At the first stage, it provided for automated identification of reservoir volumes by comparing the data of core and well logging surveys; at the second stage, identification of rock lithotypes according to Dunham classification is performed on the basis of comparison of thin sections examination and well logging data. A large array of factual information enables the use of machine learning technology on the basis of Levenberg – Marquardt neural network apparatus toward achievement of our research goals. The prediction algorithms of reservoir and rock lithotype identification using well logging methods obtained on the basis of the training samples are applied to the wells without core sampling. The implemented approach enabled complementing the 3D geological model with information about rock permeability and porosity, taking into account the structural features of the identified lithotypes. For the Permo-Carboniferous oil deposit of the Usinskoye field, the volumetric zoning of the distribution of different rock lithotypes has been established. Taking into account the lithotypes identified based on machine learning algorithms, density and openness of fractures were determined, and fracture permeability in the deposit volume was calculated. In general, during the implementation, the machine learning errors remained within 3-5 %, which suggests reliability of the obtained predictive solutions. The results of the research are incorporated in the existing 3D digital geological and process model of the deposit under study.

Formation and distribution of coal measure source rocks in the Eocene Pinghu Formation in the Pinghu Slope of the Xihu Depression, East China Sea Shelf Basin

Formation and distribution of coal measure source rocks in the Eocene Pinghu Formation in the Pinghu Slope of the Xihu Depression, East China Sea Shelf Basin

Geochemical characteristics of source rocks and gas exploration direction in Shawan Sag, Junggar Basin, China

In recent years, significant advancements have been achieved in the exploration of natural gas around Shawan Sag in the Junggar Basin. However, the geochemical characteristics and distribution of source rocks in the center of the sag have yet to be thoroughly researched, and there is a lack of understanding regarding the evolution history of hydrocarbon generation and the characteristics of each set of source rocks. This has posed limitations on future exploration and development initiatives in the area. The study focused on source rock samples from the uplift zone and conducted a comprehensive evaluation through seismic and hydrocarbon generation thermal simulation experiments. This allowed for clarification of the product characteristics of source rocks in different strata and pointing out the direction for future natural gas exploration. The results showed the presence of four sets of well-developed source rocks in Shawan Sag, characterized by their extensive thickness, wide distribution, and deep burial, laying a material foundation for oil and gas accumulation in peripheral structures. The Carboniferous and Jiamuhe Formation source rocks have high organic matter abundance, but the quality is poor and the potential for generating hydrocarbons is low, leading mainly to the generation of dry gas. On the other hand, the Fengcheng Formation and Lower Wuerhe Formation source rocks have high organic matter abundance and good quality, and are highly mature, resulting in high potential for generating hydrocarbons. The δ13C1-RO regression equation of natural gas in Shawan Sag was established, and the carbon isotope distribution patterns of ethane generated from source rocks in different layers were identified, providing a foundation for determining the maturity of natural gas and correlating the sources of gas in surrounding structures. The west slope of Shawan Sag has favorable preservation conditions and is located on a hydrocarbon migration pathway, similar to the slope of Mahu Sag. This area also has favorable geological conditions for the formation of large lithologic reservoirs, making it a key field for gas exploration in the study area moving forward.

Prediction of gas–water relative permeability in tight rock from movable fluid distribution with nuclear magnetic resonance

The measurement of the relative permeability in tight rock is challenging due to its ultralow permeability and the time-consuming nature of the experiments. Studying the movable and unmovable fluid distribution and establishing a reliable relative permeability prediction model is an urgent problem to be solved. This paper used nuclear magnetic resonance (NMR) to investigate movable and unmovable water distribution in tight sandstone under different centrifugal forces. A new method for predicting gas–water relative permeability in tight rock is established based on movable fluid distribution using the capillary bundle model. The results show that the distribution of movable and unmovable fluids is strongly influenced by the tight rock's pore size distribution and structure. The unmovable fluid saturation increases as the tight rock's permeability and median radius decrease. The nonlinear correlation between the NMR relaxation time and the pore throat size obtained from high-pressure mercury intrusion can be used to derive the pore size of the fluid distribution in tight rocks. The ratio of the movable fluid thickness to pore throat size increases near linearly with the logarithm of the pore throat size. The proposed mathematical model for the prediction of gas-water relative permeability based on movable fluid distribution is verified by comparing with the normalized relative permeability curve measured from experiments. This new model offers an alternative method of estimating the gas–water relative permeability when measurement is unavailable due to the ultralow permeability of the core samples.

Organic Geochemical Features of the Upper Paleozoic Coal-Bearing Deposits in Ordos Basin, North-Central China

The exploration of hydrocarbon resources plays a critical role in fulfilling the world’s increasing demand for energy. In this regard, the distribution and source rock characteristics of coal measure stratum in the whole basin are important and must be studied. However, systematic research has not been conducted yet. In this study, organic geochemical data, drilling data, and fieldwork were used to examine the source rock distribution of the Upper Paleozoic stratum. The results revealed that Upper Paleozoic coal-bearing rock series are mostly present in the Benxi, Taiyuan, and Shanxi formations, and mudstones and coals are formed frequently in tidal flat deposits. The layers of the coal and mudstone are primarily thick on the western sides, eastern sides, and northern sides, thin in the middle region, and gradually thinner from north to south. The source rocks are mostly enriched in the east and west of the basin. The results of the Rock-Eval pyrolysis analysis indicated that the overwhelming majority of the coal comprises excellent source rocks, all limestones are poor source rocks, and most mudstones are good–excellent source rocks. The kerogen type of most of the rock samples is type Ⅲ, suggesting typical “gas source” kerogen. Humus is derived from terrestrial organism and aquatic algae remnants, indicating a diversified parent material input. These results evidence that studied source rocks are at the postmature-dry gas stage.

Importance of shear dilation to two-phase flow in naturally fractured geological media: A numerical study using zero-thickness interface elements

In this paper, a hydro-mechanical coupling model is proposed to investigate the geomechanical effects on two-phase flow in fractured rocks. The discrete fracture model (DFM) and modified Barton-Bandis's model are used to model two-phase fluid flow and mechanical behavior of fractures, respectively. The coupled problem is solved by a mixed finite volume/finite element method, together with the fixed-stress split algorithm. Our model is able to capture the complex coupled behavior induced by the interaction between pore pressure and in-situ stress loadings. Then the proposed model is applied to investigate the two-phase flow behaviors in the fracture networks with different fracture configurations under various in-situ stress conditions. The results illustrate significant influences of shear dilation on the hydraulic properties of fractured rock. With the increase of differential stress, fracture aperture gradually increases due to shear dilation, which accordingly enhances the equivalent permeability of the fractured medium. The degree of shear dilation is highly dependent on the fracture orientation and length distribution. Consequently, channelized flow is formed through the dilated fractures, which results in early water breakthrough and reduces the water sweep efficiency. This study highlights the necessity of considering hydro-mechanical coupling effect for accurate prediction of saturation distributions in fractured rocks.

Study on soil-rock slope instability at mesoscopic scale using discrete element method

Soil-rock mixtures (S-RM) are pervasive in nature and are heterogeneous media with continuous and discrete properties. The S-RM slope has become one of the fundamental geological environments for engineering activities due to the constant growth of engineering construction. In this study, a slope system was constructed based on the discrete element method (DEM) to analyze the micro-scale phenomena of rock-wrapping in the slope shear band and the micro-scale mechanisms, including force chains and anisotropy, under the ultimate load-bearing state. The results indicate that the slope ultimate bearing capacity increased with rock content and angularity but decreased with aspect ratio and was also affected by the spatial distribution of rocks. During the slope destabilization process, there were at least four modes of rock-wrapping movement in the shear band, and the variability of soil and rock movement caused the irregularity of shear surface in the S-RM slope. The disturbance range of slope shear dilatation was heavily influenced by rock content and angularity, and the aspect ratio was an important factor in determining the morphological characteristics of shear dilatation. The content, distribution, and shape of rocks influenced the regularity of the distribution of force chains and the anisotropy of a slope.

Tectono-sedimentary characteristics and controlling factors of the lower-middle Cambrian gypsum-salt rocks in the Tarim Basin, Northwest China

Due to their excellent sealing capacity, gypsum-salt rocks are often associated with hydrocarbon accumulations. In the Tarim Basin (Northwest China), exploration activity has demonstrated that the Cambrian gypsum-salt rocks played a key role in the development of hydrocarbon plays, but there is still a lack of research on them. This study utilizes geological data coming from outcrops, well logs, rock cores, and seismic reflection profiles to quantify the distribution and tectono-sedimentary characteristics of the Cambrian gypsum-salt rocks in the Tarim Basin, and decipher the controlling factors governing their deposition. The gypsum-salt rocks are present in the Lower Cambrian Wusonger and the Middle Cambrian Awatage Formations, which are distributed around the Aman and Awati depressions, two structures inherited from the Ediacaran intracontinental rift, and the Bachu uplift. These Formations are mainly composed of salt, gypsum, gypsum halite, gypsum dolomite and gypsum mudstone, and are usually deposited in medium-thin beds. The total and single layer thicknesses of gypsum-salt rocks in the north of Bachu uplift are greater than that in the south. These lithofacies can be associated with different environments of deposition, with the Bachu uplift interpreted as supratidal sabkhas and evaporation lagoons and the Aman-Awati depressions as large-scale evaporation salt basins with a bull's eye architecture of halite-gypsum-dolomite. Carbon and oxygen isotopes indicate an overall fall in relative sea level from the late Early Cambrian to the Middle Cambrian in the Tarim Basin, accompanied by higher-frequency oscillations. Influenced by this continuous decline of sea level, the eastern platform margin transformed from gentle ramp to progradational rimmed margin and blocked the water exchange between the open sea and the platform. The southwest side of the platform was characterized by a stable gentle ramp margin, which was flooded by seawater during rise of sea level. In addition, the development of the intraplatform shoals further provided morphological barriers for the lagoons in the Bachu-Tazhong uplift belt. The Aman-Awati depressions continued to subside during the Early and Middle Cambrian and became the main loci of salt deposition, whereas the depressions and half grabens formed under the tensile tectonic regime in the Bachu-Tazhong uplift belt controlled the development of evaporation lagoons and gypsum-salt flats. This study constrained the distribution and evolution of gypsum-salt caprocks, and thus provide new insights for the sub-salt and inter-salt hydrocarbon exploration in the Tarim Basin.

Quantifying Magnetic Resonance Effects Due to Solid–Fluid Interactions on Confined Water within Quartz-Lined Nanopores via Molecular Dynamics Simulations

Nuclear magnetic resonance (NMR) relaxation time provides valuable information about properties of fluid and solid surfaces within rocks; however, the complexity of rock samples makes it difficult to quantify the effect of solid–fluid interactions on NMR measurements. Additionally, the ability of 2 MHz NMR equipment to probe nanopores is limited, while detailed analyses of fluid NMR properties in nanopores are possible through molecular dynamics (MD) simulations. We performed atomistic MD simulations to quantify the effect of solid–fluid interactions on confined water within hydroxylated slit and cylindrical quartz-lined rock pores (slit width and cylinder radius from 1 to 9 nm). NMR properties along with density profiles and mean-squared displacements (MSD) were calculated to quantify the effect of solids on relaxation times. MD results indicate that the surface chemistry of slit and cylindrical pores causes differences in density profiles and NMR properties of water confined in silica nanopores. Structural features present in density profiles are important to interpret both MSD and NMR relaxation properties. Intramolecular correlation times are shorter than intermolecular correlation times except when water is confined inside a 1 nm slit pore. These results highlight the importance of pore size on the solid–fluid interactions at the nanoscale. Layer analysis of confined water shows that NMR relaxation times of central layers in small nanopores are not the same as bulk relaxation time. This difference originates an overestimation of pore-size distributions of tight rocks from NMR measurements via Brownstein–Tarr’s equation. Furthermore, relaxation times of water layers indicate that the effect of solid surfaces on NMR relaxation times in a 3 nm slit pore is 15.32% of those in a 9 nm slit pore.

Overpressure characteristics and geological origin of the paleogene in Baiyun Sag, Pearl River Mouth Basin

The accurate understanding of the origin of overpressure is the basis of formation pressure research and the core work of determining the distribution of formation pore pressure in drilling design. The deep water area of Baiyun Sag in the Pearl River Mouth Basin in the northern margin of the South China Sea has been proved to be a hydrocarbon rich depression. In recent years, overpressure has been encountered in the middle and deep layers, but the geological origin of the overpressure in the deep water area are still unclear. Therefore, the pore pressure profile of the Baiyun Sag was evaluated using the data of drilling and seismic velocity, and the relationship between overpressure and the generation mechanism was established. Most of the surrounding and shallow strata of Baiyun Sag show normal pressure, while the middle and deep strata generally show overpressure, with the maximum pressure coefficient up to 1.55. The overpressure zone mainly develops from the middle of Zhujiang Formation to the upper member of Enping Formation. The mudstone resistivity and density values of the two typical Wells deviated from the normal trend. The density showed a constant trend with the increase of depth, while the resistivity showed a certain degree of reversal. The upper layer of the overpressure zone showed abnormally high resistivity values, corresponding to the overgland and transition zone formed by high carbonate content. There is no obvious increase of porosity in the overpressured sandstone strata of Baiyun sag, which does not have the characteristics of undercompaction. The velocity in the overpressure section of the two Wells varies greatly, and the density is basically unchanged or slightly decreased. It is concluded that the overpressure is caused by fluid expansion from hydrocarbon-generation. The large-scale and long-term fluid expansion caused by hydrocarbon generation and expulsion of source rocks provides the power source for the formation of overpressure in Baiyun sag. The distribution of effective source rocks has a controlling effect on the distribution range of overpressure. The tight sandstone strata in the Zhuhai, Wenchang and Enping formations become the cover layer of the overpressure system in the longitudinal direction.

VES Geoelectrical Method for Identification of Aquifer Depth in Coastal Area of North Lombok Regency, Indonesia: Implications for the Sustainable Utilization of Water Resources

Measurement of the resistivity value distribution of subsurface rocks has been carried out in Mumbul Sari Village, Bayan District, North Lombok, which is one of the drought-prone areas in NTB Province, Indonesia. This research was conducted to identify the presence of groundwater aquifer layers in the study area based on the distribution of resistivity values. Data collection was carried out at two measurement points, namely the MBLS-1 Point with a track length of 700 m and the MBLS-2 Point with a length of 750 m. Data processing was carried out using IP2WIN Software to obtain a one-dimensional subsurface cross-sectional model, then interpreted using a resistivity log to make it easier to draw information on the subsurface point of measurement. Based on the distribution of resistivity values, it is known that the geological layers in the study area consist of pumice tuff, silty silt, sandy silt, and lava. The inversion results from the IP2WIN software show that the depth of the aquifer zone at Point MBLS-1 is 15.6 – 70.2 m with a resistivity value of 90.3 Ωm and a thickness of 54.5 m, while at Point MBLS-2 it is located at a depth of 21.9 – 86.1 m with a resistivity value of 112 Ωm and a thickness 64.3m. The aquifer zone at both measurement points is interpreted as a sandy silt layer. Groundwater drilling is recommended at the MBLS-1 point to a depth of 70 m and at the MBLS-2 point to a depth of 86 m. The geological structure that forms the boundary of the aquifer zone is a layer of compact and hard lava, so for groundwater utilization in the study area, it is recommended to use drilled wells to a depth of 70 – 86 m which is the lower limit of the aquifer layer.

Deciphering complexity of block-faulted topography – Insights from morphometric variables, drainage patterns and river profiles (Orlickie-Bystrzyckie Mountains Block, Central Europe)

The Orlickie-Bystrzyckie Mountains Block (OBMB) is a medium-size, transboundary morphostructure within the Sudetes range in Central Europe, subject to non-uniform uplift in the late Cenozoic. Geologically, it consists of Variscan basement and Permian to Cretaceous sedimentary cover. This paper attempts to unravel its morphotectonic history and decipher the spatial pattern of uplift and erosional response, using several complementary, quantitative approaches to characterize topography. The focus is on: (1) general relief properties captured by selected topographic variables; (2) fault-generated escarpments, which define the eastern and northern limits of the study area; (3) drainage patterns and its peculiarities; (4) diversity of longitudinal river profiles and valley morphology. A LiDAR-based high-resolution digital terrain model was the primary source of elevation data. An important component of the study was examination of the role of lithological diversity on relief properties. A statistical approach generally revealed a secondary role of the rock factor and provided a foundation to interpret the macro-topography of the OBMB in terms of tectonic controls. Based on geomorphometric characteristics and information about the distribution of sedimentary rocks, which can be used as marker horizons to identify vertical displacements, four major and one secondary centres of surface uplift have been recognized. They are all asymmetric, being bounded by distinct fault-generated escarpments on one side and sloping gently in the opposite direction. Erosional response to uplift has been variable and includes, apart from simple incision into rising crustal blocks, the origin of epigenetic-antecedent water gaps, drainage diversions, headward erosion, and captures. This study also reveals that morphometric indices routinely used to extract the tectonic signal from landform patterns do not necessarily provide consistent information.

Dynamic response characteristics and damage rule of graphite ore rock under different strain rates

In the process of mining graphite mine, rock mass is often subjected to dynamic loads such as blasting or mechanical crushing, which involves dynamic responses of different strain rates, and blasting and crushing effect are affected by the rock dynamic properties and damage specials. The dynamic response characteristics and damage rule of graphite ore rock under different strain rates are very important but rarely studied in the past. To study these issues and provide support for graphite ore rock mining, the dynamic compression tests of graphite ore rock under five kinds of impact pressures were designed and carried out by using the Split Hopkinson Pressure Bar (SHPB) test system, combining with the high-speed photography system and crushing screening tests. The dynamic characteristics, crushing process, crushing mode, crushing form and fragmentation distribution of the graphite ore rock under different strain rates were analyzed. The results show that the dynamic characteristics of the graphite ore rock have obvious strain rate effect. The hardening coefficient (DIF) is positively correlated with the cubic root of strain rate, and the softening factor (K) is negatively correlated with the cubic root of strain rate. Shear failure mainly occurs in the graphite ore rock under impact load, and the crushing process can be divided into five stages, they are compaction, crack initiation, crack expansion and penetration, fragmentation collision and fragmentation fall. In addition, the crushed blocks are mainly triangular pyramid (or cone-like) fine granular and powder. The broken fragments of the graphite ore rock are in accord with the fractal geometry characteristics. That is, the average broken particle size (dS) decreases linearly with the increase of strain rate, and the fractal dimension (Da) increases weakly with the increase of strain rate. Based on D-P fracture criterion and Weibull distribution model, the dynamic damage constitutive model of the graphite ore rock was established, and the correlation between strain rate and Weibull distribution parameters (m and F0) was used to reasonably modify the damage constitutive model. The modified damage constitutive model curve is in good agreement with the experimental curve, which can basically reflect the strain rate effect of the dynamic characteristics of the graphite ore rock and the evolution characteristics of the dynamic stress–strain curve at different stage.

Crustal Structures of the Qimantagh Metallogenic Belt in the Northern Tibetan Plateau from Magnetotelluric Data and Their Correlation to the Distribution of Mineral Deposits

Crustal structure and fluid or melt originating in the deep crust and mantle are critical in regional magmatic mineral systems. However, the crustal structure and the processes that entrain and focus fluids from a deep-source region to a metallogenic belt remain relatively undisclosed. We present a magnetotelluric (MT) study of the eastern Qimantagh Metallogenic Belt (QMB) in the northern Tibetan Plateau. Data from 33 MT stations in two sections and 7 dispersed stations are acquired using a surface electromagnetic prospecting (SEP) system in frequency band ranges from 320 Hz to 0.00034 Hz. Data are converted by Bostick conversion and two-dimensional (2D) nonlinear conjugate gradient inversion. Our MT results reveal the geoelectrical crustal structure of the QMB, which consists of a southern low-resistivity domain that reflects the Kumukuri rift, a high-resistivity middle domain that represents the southern QMB in the central Kunlun belt, and a northern low-resistivity domain that covers the northern QMB and southwestern Qaidam block. We present a comprehensive tectonic and geophysical model of QMB based on the MT interpretation and geological analysis. We infer the high-resistivity domain as a reflection of a rigid crust and detached lithospheric mantle, this belt separate the QMB into northern and southern QMB. Most of the mineral deposits are found in the northern low-resistivity domain of QMB. Our study and findings provide an understanding of the tectonic evolution of the northern Tibetan Plateau, the crustal structure that controls the temporal and spatial distribution of magmatic rocks, and the geological signature associated with mineral deposits.

Quantitatively unmixing method for complex mixed oil based on its fractions carbon isotopes: A case from the Tarim Basin, NW China

Deep mixed oils with secondary alterations have been widely discovered in the Tarim Basin, but current methods based on biomarkers and isotopes to de-convolute mixed oil cannot calculate the exact mixing proportion of different end-member oils, which has seriously hindered further exploration of deep hydrocarbons in the study area. To solve this problem, we constructed a novel method based on the carbon isotope ( δ 13 C) of the group components to de-convolute mixed liquid hydrocarbons under the material balance principle. The results showed that the mixed oil in the Tazhong Uplift was dominantly contributed at an average proportion of 68% by an oil end-member with heavier δ 13 C that was believed to be generated from the Cambrian-Lower Ordovician source rocks, whereas the mixed oil in the Tabei Uplift was predominantly contributed at an average proportion of 61% by an oil end-member with lighter δ 13 C that was believed to be generated from the Middle-Upper Ordovician source rocks. This indicates that, on the basis of the detailed description of the distribution of effective source rocks, the proposed method will be helpful in realizing differential exploration and further improving the efficiency of deep liquid hydrocarbon exploration in the Tarim Basin. In addition, compared to traditional δ 13 C methods for whole oil and individual n-alkanes in de-convoluted mixed oil, the proposed method has a wider range of applications, including for mixed oils with variations in color and density, indicating potential for promoting the exploration of deep complex mixed oils in the Tarim Basin and even around the world.

Petrogenesis of the Carboniferous Intrusive Rock in the Xiaobaishitou District of East Tianshan, Northwest China: Magma Evolution and Tectonic Significance

AbstractThe Xiaobaishitou gabbro‐diorite pluton comprises a medium‐grained gabbro‐diorite suite and a fine‐grained diorite suite, which intrude the Kawabulag Group in the East Tianshan Orogen of the Central Asian Orogenic Belt (CAOB). A combination of mineral chemistry, zircon U‐Pb age, whole‐rock geochemistry, Sr‐Nd isotopes, and in situ zircon Hf isotopes for newly found gabbro‐diorite from the Xiaobaishitou district in the Central Tianshan Terrane (CTT) is presented to investigate the petrogenesis and tectonic or even crustal evolution of the East Tianshan Orogen. Laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS) zircon U‐Pb analyses indicate that the gabbro‐diorite was formed at 324.7 ± 2.4 Ma. The isolated clinopyroxene formed under higher P‐T‐ƒO2 melt conditions (10.7–14.6 kbar; 1199–1269°C; high ƒO2) than those for the hornblende, plagioclase, and zircon (557–687°C; moderate ƒO2) in the gabbro‐diorite, which reveals a multilevel, magmatic storage system. The gabbro‐diorite is characterized by fractioned REE patterns, enriched LILEs (e.g., Ba and Pb), negative anomalies of HFSEs (e.g., Nb and Ta), and low La/Yb and Sr/Y ratios, which are typically indicative of crustal contamination and accounted for by subduction‐related fluids. The rock also characterized by typical features of high compatible elements (MgO = 3.14–11.65 wt%, Cr = 1–157 ppm, Ni = 6–830 ppm), high Mg# (47 –74), positive ɛHf(t) values (+5.1 to +10.3) and ɛNd(t) values (+2.3 to +4.4). These features suggest that the Xiaobaishitou gabbro‐diorite was most likely derived from metasomatic mantle and contaminated minor crustal components. Taking into account the spatial and temporal distribution of the Carboniferous magmatic rocks in the CTT, we suggest the formation of the Xiaobaishitou gabbro‐diorite was attributed to southward subduction of the Kangguer Ocean.

Prediction of hydrocarbon source rock distribution using logging curves: A case study of Es32 source rock in Nanpu Sag, Huanghua depression, Bohai Bay Basin

The Es3 is the main hydrocarbon source rock system in the Nanpu Sag. Finally, the TOC and hydrocarbon potential of each sub depression of Es3were predicted. The study shows that the hydrocarbon source rocks of Es32 and Es34 sections are mainly of type II2 and type II1 respectively, with good organic matter type and high maturity. Biomarker compound parameters indicate that the Es32 section hydrocarbon source rocks developed in a semi-saline, low to medium terrestrial source organic matter supplied reduction environment with a high algal contribution; the Es34 section hydrocarbon source rocks formed in a freshwater, low terrestrial source supplied reduction environment with a medium-high algal contribution. The multiple linear regression method is more effective than the ΔlgR method in predicting hydrocarbon source rocks in the Nanpu Sag, and the prediction accuracy is higher; the correlation between TOC and S1 + S2 is the best in the model for predicting hydrocarbon potential. The TOC and hydrocarbon potential of the hydrocarbon source rocks in Es31 are generally low; the high value area of TOC and hydrocarbon potential of the hydrocarbon source rocks in Es32 is partly between the No. 1 tectonic zone and No. 5 tectonic zone in Linque sub depression, and the TOC and hydrocarbon potential of the hydrocarbon source rocks in Liunan sub depression are larger; the high value area of TOC and hydrocarbon potential of the hydrocarbon source rocks in Es34 is mainly concentrated in Shichang sub depression.

Depositional environment and hydrocarbon potential of Early Permian coals deposit in the Huanghua Depression, Bohai Bay Basin

The Carboniferous-Permian was an important period for the formation of coal mines and coaly source rocks across the world. Controlled by the paleoclimate, Cathaysia flora, and transitional sedimentary environment of the delta, the Early Permian Shanxi Formation in the Huanghua Depression formed several layers of coal and coaly source rocks that can be explored in the whole depression. However, the development regularity and distribution prediction of high-quality coaly source rocks are still not well understood. The coaly source rocks of the Shanxi Formation in the Huanghua Depression were taken as the research object. With the determination and analysis of organic carbon content, rock pyrolysis, and vitrinite reflectance, we found that the organic matter abundance (i.e., TOC which changed from 20.3 % to 80.0 %), hydrocarbon generation potential (i.e., S1 + S2 which varied from 7.82 mg/g to 208.81 mg/g), and kerogen types (mainly type II2) of the coal were better than carbonaceous mudstone and coaly shale. Maceral component identification indicated that coal and carbonaceous mudstone had more liptinite (i.e. cutinite and sporinite)and hydrogen-rich vitrinite, while coaly shale was mainly composed of hydrogen-poor vitrinite and a small amount of liptinite. The analysis of the ratios of major and trace elements, normal alkanes, and isoparaffin suggested that the paleo-water salinity of coal and carbonaceous mudstone deposition was more than that of part coaly shale. Revealed by the weak reduction of their depositional environment, the development of high-quality coal and carbonaceous mudstone was mostly controlled by the input of oil- and gas-prone organic matter. The formation of high-quality coaly shale was chiefly dominated by a strong reduction environment with an insignificant amount of organic matter input. The formation model of high-quality coaly source rocks was established. This model can be used to predict the distribution of coal mines and coaly source rocks in the Huanghua Depression and Bohai Bay Basin.