Geofluids

There is an abundance of tight gas resources in narrow channel sand-bodies from the Jurassic Shaximiao Formation of the Jinqiu gas field in the central Sichuan Basin of China. The architecture of sand group in the study area is undefined, and the spatial distribution of channel sand-bodies is unclear. The complex and inhomogeneous sandstones have a significant impact on the reservoir’s physical properties and the fluid mobility of the reservoir. In this study, data from drilling cores, logs, seismic, and experiment testing were used to investigate the spatial distribution of sand group architecture and the channel types. There are five channel genetic types, including the multiphase superimposed type, deeply incised type, abandoned type, progradational superimposed type, and normal single genetic type. Based on the channel genetic types, the ratio of sandstone and mudstone, the ratio of width to depth, the connectivity ratio of sand-bodies, and the production dynamic characteristics, the channel sand-body connectivity is defined into three types. The connected sand-bodies occur in the multiphase superimposed and deeply incised types of channels, with an average connectivity ratio of 83%, a ratio of sandstone and mudstone larger than 0.9, and a ratio of width and depth larger than 40. Based on the association of sandstone and mudstone and rhythmic structure, the sand group architecture can be divided into three types, including (A) uniform-grain-sequence pure sandstone architecture, (B) positive-grain-sequence thick sandstone and thin mudstone architecture, and (C) positive-grain-sequence thick mudstone and thin sandstone architecture. There is a high content of natural gas in Types A and B of sandstones, with a daily gas production of 29.16×104–47.6×104 m³/day and pressure coefficients of 0.72–1.08. The sand group architecture of the study area is mainly controlled by the channel sinuosity and the ratio of accommodation and sediment supply, and Types A and B of sand group architectures occur with large channel sinuosity of 1.14–1.36 and a large ratio of accommodation and sediment supply of 0.61–2.92. Based on the connectivity degree of channel sand-bodies, the sand group architectures, and production data, the channels of the study area can be divided into three types. Type I channels mainly occur in Sand Groups 6, 8, and 9, and Type II and Type III channels occur in Sand Groups 6 and 7 in the western and southern parts of the study area. The technology of fine characterization for channel sand-bodies on the basis of human–computer interaction and seismic attributes is proposed, and geological modelling of the spatial distribution of sand group architectures and channel types is established. The research results achieve a theoretical breakthrough in the characterization of the sand-body structure of tight sandstone reservoirs in narrow river channels and assist in the efficient exploration and development of tight sandstone gas.

China’s shale gas has undergone nearly 20 years of exploration; unconventional oil and gas geological evaluation theories and research methods have been greatly enriched, but how to quickly, conveniently, and accurately identify the sweet spots of shale gas is still puzzling many researchers. This study focuses on the black shale of the Wufeng–Longmaxi Formation in the southeastern edge of the Sichuan Basin; lithofacies classification, the relationship between lithofacies and depositional environments, and the correlation between lithofacies and shale gas–bearing capacity are discussed. At last, we have established the lithofacies classification criteria; the Wufeng–Longmaxi Formation deposited eight types of lithofacies, which the paleoenvironment during deposition evolved gradually from anaerobic environment to oxygen-poor and oxygen-rich environment. The black high-carbon and high-silicon shale lithofacies and the black carbon-rich and silicon-rich shale lithofacies are rich in organic matter, and they were deposited in high primary productivity, low terrigenous detritus input, and euxinic environment. The black medium-carbon medium-silica shale lithofacies and the black medium-carbon and high-silica shale lithofacies contain organic matter, which are deposited in medium primary productivity, middle terrigenous detritus input, and oxygen-poor and low hydrodynamic environment. The gray–black low-carbon low-silicon clay-rich shale lithofacies, the gray low-carbon and high-silicon shale lithofacies, and the gray–white low-carbon and silicon-rich shale lithofacies are poor in organic matter, which are deposited in a transitional environment of low primary productivity and oxygen poor–oxygen rich. In the analysis of the relationship between organic matter–rich black shale facies and sedimentary environment, it is shown that the enrichment of organic matter is positively correlated with the oxidation–reduction discrimination indicators Ni/Co, U/Th ratio of ancient oceans, and the evaluation indicators Babio and Ba/Al ratios of primary productivity. Only under the favorable sedimentary geochemical conditions and good preservation conditions can deposit lithofacies sections (zones). Based on the optimization of shale gas dessert section and the drilling of horizontal wells, the optimization of favorable black shale lithofacies types and the classification of shale gas dessert section are the key to shale gas exploration. The shale gas–bearing capacity is closely related to lithofacies. Black carbon-rich silicon-rich shale lithofacies and black high-carbon high-silicon shale lithofacies have the best gas-bearing capacity and are favorable lithofacies.

To thoroughly investigate the mechanisms behind coal and gas outbursts in folded structural areas, we conducted similarity simulation experiments using a custom-built apparatus designed to replicate these structures. The objective was to analyze the stress distribution characteristics of coal rock masses under horizontal structural stress within folded zones. The experimental outcomes reveal that, under horizontal loading, shear cracks progressively develop along layer directions within the anticline wing, anticline axis, and syncline axis, evolving continuously along the interlayer direction. In these folded structures, horizontal stress consistently remains compressive, with the highest compressive stress concentrations observed at the anticline axis, followed by the wings and turning points of the anticline, and the lowest in the syncline axis area. The stress coefficient (k) in the anticline axis reached values as high as 3.18, while the syncline axis exhibited much lower stress concentrations, with k values of 0.66. Vertically, the anticline axis and its wings primarily experience tensile stress, whereas the syncline and its wings mainly undergo vertical compressive stress. The anticline axis region, subjected to horizontal structural stress, tends to develop tension cracks, which adversely affect gas retention. The combination of horizontal tension and vertical tensile stress in this region reduces the risk of coal and gas outbursts. Conversely, the syncline axis area, experiencing triaxial compressive stress, exhibits a higher degree of stress concentration and superior gas sealing capacity, rendering it more vulnerable to coal and gas outbursts. These findings provide essential insights for refining coal mining methodologies in fold structures, particularly for addressing the safety challenges posed by coal and gas outbursts.

Rock masses characterized by X-type joints are prevalent in cold region rock engineering projects. A precise understanding of the mechanical mechanisms governing the fracture initiation strength of these jointed rock masses after experiencing freeze–thaw damage is paramount for ensuring the safety and stability of associated engineering structures. Leveraging the mutual constraint relationship between the displacements at the tips of intersecting joints under compressive shear conditions, a computational approach has been developed to determine the stress intensity factor at the tip of the main joint, taking into account the interference effects arising from both main and subjoints. Furthermore, the fine-grained defects within the rock mass are abstracted as elliptical microcracks, and deterioration equations for rock cohesion and fracture toughness under freeze–thaw cycling are derived using frost heave theory. Taking into account the mutual interference effects between main and subjoints, as well as the degradation of rock mechanical properties caused by freeze–thaw cycles, a computational approach for determining the initiation strength of X-type jointed rock masses has been developed. The validity of this method has been confirmed through rigorous model testing. The findings reveal that the wing cracks in X-type jointed rock masses predominantly propagate along the tips of the main joints, while the extension of subjoints is constrained. When the X-joints have the same inclination, the initiation strength of the subjoint exceeds that of the single-joint rock mass when its inclination is less than the main joint’s but is lower when the subjoint’s inclination exceeds that of the main joint. The interference effect between oppositely inclined intersecting joints enhances the initiation strength of the rock mass, with the maximum occurring when the subjoint is at an inclination of 120°. When the freezing time is less than 18 h and the temperature is below −16°C, variations in both time and temperature are more sensitive in affecting the initiation strength of the X-jointed rock mass. Rocks with a high elastic modulus and low tensile strength experience a greater rate of freeze–thaw damage, and brittle rocks are more susceptible to frost heaving failure.

Although various fractal flow models have recently been developed to investigate pressure responses of fractured vertical wells, almost all of the existing fractal models ignore the quadratic gradient term (QGT), which makes them violate mass conservation. In this paper, fractal theory is introduced to develop a nonlinear flow model of fractured vertical wells with stimulated reservoir volume (SRV). The QGT is reserved so that the present model fully obeys material balance. Function transforms are used to linearize the nonlinear flow model, and then, Laplace transform and Laplace numerical inversion algorithm are employed to derive the pressure solution. Type curves are provided to analyze the flow characteristic and identify the flow regimes. The effects of some parameters on the pressure responses are discussed in detail. It is found that the existence of the QGT leads to the decrease of the pressure drop, especially at a large nonlinear coefficient and a large time scale. Fractal parameters and SRV radius not only affect type curves but also affect the relative error caused by neglecting the QGT.

Taking the carbonate of the Majiagou Formation in the Ordos Basin as an example, this paper introduces a method for predicting the S-wave velocity of carbonate based on rock physics modeling. By analyzing the samples in the study area, we can find that the carbonate reservoirs in the study area have the following characteristics: (1) The lithology of the Majiagou Formation in the Ordos Basin is relatively complex, mainly composed of dolomite, lime dolomite, dolomitic limestone, gypsum, and gypsum-bearing dolomite. The pore types include intergranular pores formed by dolomitization, intergranular dissolution pores formed by dissolution, and fractures. (2) Due to the diverse types and complex distribution of rock-forming minerals, there are always some rock samples whose matrix modulus is beyond the upper or lower limits. Those were calculated using the Voigt–Reuss–Hill (VRH) average method. (3) The pore structure of carbonate is very complex due to diagenesis. Based on the influence of pore shape characteristics on rock elastic parameters, pore shapes are divided into three types using the pore aspect ratio. Among them, the aspect ratio of intergranular pores is the largest, while that of the fracture pores is the smallest, and the aspect ratio of intergranular dissolved pores falls between the two. Therefore, the accuracy of predicting S-wave velocity in this area based on traditional rock physics modeling methods is low. In this paper, we will introduce a new model that is aimed at improving the traditional rock physics model. The first improvement is based on a variable matrix modulus, which can be used for matrix modeling to mitigate the influence of uneven mineral distribution. The second enhancement involves quantitatively characterizing the impact of different pore aspect ratios on the S-wave velocity of carbonate rocks, using a porous differential equivalent medium (DEM) model.

The optimization of coal dust management in fluidized mining environments is of paramount importance, yet it is currently impeded by a gap in understanding chemical dust suppression mechanisms. This study combines indoor experiments with molecular simulation to investigate the mechanisms by which three anionic surfactants with different hydrophilic and hydrophobic groups (SDBS, SDS, and SLS) influence coal wettability. Using hydrophobic bituminous coal as the experimental subject, basic physical and chemical properties are analyzed through proximate analysis, XRD, and FTIR. The effect of different surfactants on coal wettability is characterized based on sedimentation experiments, while the coal–surfactant–water three-phase model examines the equilibrium adsorption configuration, water molecule diffusion coefficient, and interaction energy in different adsorption systems. The surface free energy of coal dust and its components is measured before and after surfactant adsorption, verifying the adsorption-wetting mechanism of surfactants at the coal–water interface. Results show that anionic surfactants enhance wettability through a bidirectional adsorption mechanism at the coal–water interface: the hydrophobic tail adheres to the coal surface via van der Waals forces, while the hydrophilic head faces the water phase, driven by electrostatic and hydrogen bonding interactions. This coordinated adsorption process alters water diffusion and the surface free energy of coal, thereby improving wettability. SDBS, due to its benzene ring, significantly amplifies the bidirectional adsorption effect, achieving the most substantial improvement in coal dust wettability. The findings provide a robust theoretical framework for developing dust control strategies in fluidized mining operations, advancing the field toward more efficient and sustainable mining practices.

Using changes in ground temperature to reflect the flow status of groundwater is one of the methods for predicting mine water inrush. In this study, in order to make this method suitable for different geological conditions, an improved method for predicting mine water inrush is established based on the theories of heat transfer and nonlinear water flow in fractal porous media. A water inrush judging criterion based on the critical pressure gradient of nonlinear flow is first established. Then, an internal structural model of the crushed rocks and a mathematical model of nonlinear flow in crushed rocks are derived based on the fractal theory. Finally, a thermal, hydraulic, and mechanical (THM) coupling model is established to study the nonlinear water inrush process and temperature changes. The improved method is established based on the numerical simulation results of the THM coupling model. Results show that the water inrush judging criterion can simultaneously consider the water-resisting capacity of intact and crushed rocks and quantitatively calculate the water-resisting capacity of crushed rocks compared with the traditional method. The improved method is suitable for different cases with different water-resisting capacities, ground temperature change ranges and gradients, and aquifer water pressures, which can improve the applicability of using ground temperature to predict mine water inrush.

Composite aquiclude rock is an important part of the water barrier layer of coal seam floor, and its mechanical properties and failure characteristics have an important impact on the safety of coal seam mining. In order to explore the uniaxial compression failure characteristics and mechanical properties of composite aquiclude rocks, the mineral composition and microstructure of the composite cement rock were measured by XRD and SEM. Using a WAW-1000D electrohydraulic servo universal test system, uniaxial compression tests were carried out on samples of four structural types, namely, mudstone/siltstone, mudstone/fine sandstone, fine sandstone/siltstone, and siltstone/mudstone/fine sandstone composites soaked in saline water with various immersion periods and pH values. The experimental results show that the failure of composite rock samples was mainly concentrated in the mudstone part. With the increased proportion of soft rock in the structure, the rock samples exhibited changes in tensile, X-shaped conjugate inclined plane shear, and single inclined plane shear failure modes. The overall compressive strength of composite rock samples decreased with immersion time, and their failure mode shifted from shear to tensile with increasing immersion time. The strength-weakening effect of high-salinity water with different acidity and alkalinity on composite rock samples was significant. The increased pH promoted the tensile failure-shear failure-tensile failure evolution. The results of this study can provide important experimental data and theoretical basis for the stability control of composite aquiclude rock in coal mining.

The bearing capacity of traditional prestressed high-strength concrete (PHC) pipe pile is hampered by the poor mechanical properties of surrounding soil in soft soil areas, and the PHC nodular pile can improve the behavior of pile foundation in soft soils. The PHC nodular pile installation process will induce larger disturbance to the surrounding soil compared to the PHC pipe pile, and there is little research on the installation effect of the PHC nodular pile. In this paper, the coupled Eulerian-Lagrangian (CEL) finite element method was adopted to simulate the penetration process of PHC nodular piles and pipe piles in soft soil. The radial stress and displacement in soil induced by the PHC nodular pile and pipe pile and the soil resistance at different parts of the PHC nodular pile were analyzed. The simulation results showed that the penetration resistance of the PHC nodular pile was larger than that of the PHC pipe pile. The penetration resistance of PHC nodular piles was mainly provided by the pile shaft resistance. The uplift height of soil surface caused by the PHC nodular pile and pipe pile penetration was approximately the same. The influence range of compaction effect for PHC nodular pile and pipe pile was both concentrated on 10R (R is the pile diameter).

As one of the comprehensive exploration techniques for underground geological resources, surface geochemical methods could play an important role in geothermal exploration, which requires detailed and systematic investigations. In this study, we take the Shiba geothermal basin in Huizhou, China, as the research object and apply surface geochemical testing methods to analyze the intrinsic relationship between the geothermal system and the surface soil. The contents of soil gases and elements are mainly determined, among which hydrogen (H2) and radon (Rn) show three obvious negative anomalies, corresponding to three positive anomalies of soil elements (Fe, U, Cr, V, Cu, and As) that are easy to migrate. The largest negative and positive anomalies correspond to the surface above the fault, which is related to the dominant channel from underground to the surface and is caused by the gas loss effect and the dissolution and migration of inorganic ions. However, the effects of the surface environment and organisms cannot be ignored. Only when the geothermal system has a significant impact on a certain geochemical parameter could the anomaly be manifested in the surface soil. Otherwise, most of the geothermal information, including thermal conduction, will be covered by surface factors. After surface geochemical anomalies related to the geothermal system have been identified, anomaly patterns (especially the top anomaly pattern) can be preliminarily established, which can be used for geothermal exploration. Furthermore, based on the empirical regional geothermal formula, the temperature and depth of the Shiba geothermal system are evaluated at 170°C and 4500 m, respectively, indicating that surface geochemical methods have a good practical prospect in the prediction of geothermal resources.

There have been many M≥3.0 earthquakes in and around the Jiangling Depression in history, and the stress variation can directly affect the preparation of surrounding earthquakes. This paper innovatively uses the variation characteristics of Jingzhou well water level and GNSS data to analyze the stress variation in the Jiangling Depression. The results show that (1) the long-term decline trend of Jingzhou well water level has little correlation with rainfall and is mainly from deep source, which is different from the recharge source of the surrounding water system. The long-term decline trend of Jingzhou well water level is mainly affected by the tension state of the region. (2) The strain rate in the northern part of the study area is relatively high, and the tension state in the NNW direction is dominant. The slope of HBJM-HBJL stations baseline time series is positive, indicating that the NNW-SSE is in a tension state as a whole, which is consistent with the trend of Jingzhou well water level. (3) Jingzhou well water level and GNSS baseline time series have good synchronization, which directly reflects that the stress field in and around Jiangling Depression is in a state of tension in recent years. There have been many ≥ 3.0 earthquakes in and around the Jiangling depression in history. In the future, it is worth noting when the stress–strain state of the study area changes.

In recent years, breakthroughs in deep hydrocarbon exploration have been continuously achieved in the Tarim Basin of China. The Ordovician carbonate stratum has been shown to contain vast oil and gas resources. However, challenges remain in understanding the seismic response characteristics and accurately identifying the hydrocarbon reservoirs. These challenges can be attributed to factors including the significant burial depth of the target layers and complex geologic structures. To effectively support hydrocarbon exploration and resource assessment in the Tarim Basin, this study focused on the following three aspects in Region Y. First, according to the analysis of prestack amplitude versus offset (AVO) characteristics in well-adjacent seismic traces and seismic forward modeling, we demonstrated that different fluid-filled reservoirs have distinctly different AVO characteristics. This means that the hydrocarbon reservoirs in the study area can be identified by AVO inversion. Second, based on the theory that seismic waves exhibit amplitude attenuation and velocity dispersion when propagating through fluid-filled media, the seismic dispersion AVO inversion technique was developed to obtain equations for the attributes of primary (P) and shear (S) seismic wave dispersion. Finally, this technique was applied in Region Y and further verified using actual drilling data from single wells and well profiles. The application results demonstrate that hydrocarbon reservoirs can be effectively identified using this technique and provide a technical reference for reservoir identification in other areas of the Tarim Basin. The AVO characteristic analysis is the prerequisite for the successful application of this method; the key is to find accurate inversion equations and parameters to recognize the AVO response patterns in the study area.

The migration law of proppants in slick water during fracturing is of great significance for field fracturing. A large-scale visualized experimental device was utilized to test sand patterns for varying injection parameter combinations, and sensitivity parameters of proppant settlement are analyzed. Experimental results showed that when the viscosity of fluid is 5 mPa.s, proppants with 70–140 mesh and 8% sand ratio were used, the slick water for fracture initiation had a good sand-carrying capacity, and there was no sand bank formed at the entrance of the fracture but the spreading of sands in fractures was insufficient. When slick water with a lower viscosity of 10 mPa.s, the proppant of 40–70 mesh and 10% sand ratio were used, massive proppants were filled within the fractures, and a high sand bank was formed in the deep of the fracture, while a poor-filling effect appeared at the entrance of fracture. When the higher viscosity slick water of 20 mPa.s, proppants with 20–40 mesh and 20% sand ratio were used; with the growth of pump-in rate, the distance between the sand front and fracture entrance increased, the height of the bank is lower, and the balance height stayed the same for various fracturing fluid and proppant combination. The injection parameters affected the sand bank patterns and made diverse bank shapes, which made it essential to modify the fracturing fluid and proppant combination in the field to improve the conductivity at the entrance of the fracture.

This paper is aimed at introducing a method for the division of development units of thick carbonate reservoirs. This method consists of eight steps, ranked according to impact weight, each of which is independent but intrinsically linked. When there is a conflict between studies in different steps, the results of the previous step take precedence. (1) Pressure is the most important and reliable data. When the wells with an abnormal pressure gradient in the same interval account for more than 60%, further division of the reservoir is appropriate. (2) Baffles are the second most important and reliable basis. When there are continuous baffles or poor reservoirs that encounter more than 80% wells, it is appropriate to further divide reservoirs. (3) Without the two mentioned above, but with an unconformity surface or discontinuity surface between two sequences, it is appropriate to treat these two sequences as two development units. (4) Without the three mentioned above, if the permeability above and below the sequence boundary differs by 10 or more times, reservoirs above and below the sequence boundary are appropriate as distinct development units. (5) When the thickness, continuity, distribution pattern, and microstructure of two adjacent sequences are significantly different, it is appropriate to treat these two sequences as two development units. (6) If the development units are based on sequences, check for homogeneity within the stratigraphy. If depositional facies or physical property discontinuities are present, the sequence would be reconsidered for subdivision. (7) The reserves in each development unit should account for more than 20% of that of the whole reservoir. (8) When the division of the development units is complete, it needs to be examined to ensure that there is a consistent structure, fluid property, and free water level. If inconsistencies exist, then subdivision is considered. The method was successfully applied to A oilfield, Central Arabian Basin, in combination with the cores, cast thin sections, regular or special core analysis, wireline logging data from 450 wells, formation pressure from 63 wells, and more than 100 wells with a production logging test. The Mishrif reservoir was divided into four development units, in which different well patterns and well types were deployed. The improved development effect proves that the division of development units for thick bioclastic limestone reservoir is reasonable.

Wufeng–Longmaxi Formation and Qiongzhusi Formation are the significant shale gas exploration strata in China. The former has made a major breakthrough, and the exploration of the latter is restricted. At present, it shows good exploration potential in the Qiongzhusi Formation. Based on the field outcrop and core logging data, the production data from drilled shale gas wells and previous research results combined with the determination of organic matter content, laser Raman spectroscopy of organic matter, X-ray diffraction experiments, and field emission scanning electron microscopy observations. This study compares the geological conditions and control factors of shale gas enrichment and high yield in the Wufeng–Longmaxi Formation and Qiongzhusi Formation and clarifies the enrichment mode of two sets of shale gas reservoirs. The results show that the organic geochemical conditions of two sets of shale reservoirs are similar, about 0.5%~4.5%. The quartz content of Wufeng–Longmaxi Formation shale (42.5%) is more than that of Qiongzhusi Formation (34.1%~40.2%), and the feldspar content (6.4%) is less than that of Qiongzhusi Formation (20.5~27.3%). The inorganic pores of the Qiongzhusi Formation are more developed than those of the Wufeng–Longmaxi Formation, and the pore size of inorganic pores can reach 100 nm~1 μm. Both of them have good preservation conditions. The enrichment of shale gas in the Wufeng–Longmaxi Formation is controlled by hydrocarbon generation reservoir-preservation conditions, and the enrichment of shale gas in the Qiongzhusi Formation is mainly controlled by geological structure. It is of great significance to clarify the enrichment control factors of the Qiongzhusi Formation for effectively guiding the continuous exploration and development of the Qiongzhusi Formation. Shale gas exploration in the Qiongzhusi Formation has a very large prospect, which is expected to exceed the Longmaxi Formation.

Hydraulic fracturing has been a common treatment to enhance well productivity, especially in tight oil and gas reservoirs. Studying the pressure response characteristics of fractured reservoir has been a hot topic due to the significant contribution of fractures to conductivity enhancement. Because of the difficulty in describing the flow problems in vertical fractured well and the lack of related literatures, a novel method to determine the bottom-hole pressure of a vertical well with multiple fractures based on Newman product method is proposed in this paper. First, the physical model and corresponding mathematical model are established. Then, the solution of bottom-hole pressure can be obtained through Laplace transformation. Sequentially, the validations of computational method and computational codes contain are presented. From the view of curve fitting and interpretation results, the calculations in this paper are in good agreement with the previous numerical results and our computation method is reliable. Next, a group of typical curves are generated to analyze the flow regimes. And a series of curves are generated to demonstrate effects of key parameters on curve shape. The results indicate that increasing the fracture wings, fracture intersection angle, and fracture length uniformity can enhance the well productivity. Lastly, a case study is exhibited to show the application of the proposed method.

Aiming at the problems of safety production cost caused by the increase of mining face width and pressure mining in Xizhuo Coal Mine in Chenghe Mining area, a mechanical model of floor plastic slip failure is established based on the theory of plastic slip line, and the difference between it and the traditional floor failure model is analyzed. The damaged contour line of the support stress and lateral support stress on the bottom plate through the advancing direction of the working face is the intersection line of a straight line and an arc line. The failure of the floor caused by lateral supporting stress is the failure of the floor again on the basis of the failure of the floor in the advancing direction of the working face, and there is a superimposed failure area. The analysis of the failure form of the stope floor by this mechanical model is closer to the engineering practice. By using “ultrasonic detection method + stress monitoring inverse analysis method,” the measured data such as disturbance failure depth and distribution law of large mining width working face were obtained. The test method used in this paper is relatively rare in the monitoring of the depth of floor disturbance failure at home and abroad. Considering that the traditional pressure water test method has disadvantages such as easy collapse hole, long period, and large error in monitoring the failure rule of deep floor rock mass, the embedded stress monitoring and reverse analysis method and ultrasonic detection method are used to successfully collect and real-time monitor the data of rock floor before, during and after mining in the lower part of wide mining face of Xizhuo Coal Mine for the first time, and several effective data are obtained, which solves the three-part “spatial-time” all-round floor disturbance and failure law field measurement which cannot be realized by traditional testing technology. By comparing the results of theoretical analysis, field measurement, and numerical simulation, the law and depth of floor disturbance failure of a 240-m wide mining face in the Chenghe mining area are obtained for the first time, which provides scientific guidance for floor water disaster induced by coal seam mining under similar conditions in the future and has an important reference role for the prevention and control of Ordovician ash water disaster in coal mining. It provides important technical parameters for the safe setting of the effective water barrier layer and the selection and timing of the grouting layer of the floor, which can bring considerable economic and social benefits. The research results have important popularization value.

This study analyzes the depositional regime and textural properties of the sediments from the Shitalakshya River in Bangladesh, enabling us to comprehend how these sediments evolved in a river environment. For this investigation, 30 representative samples were taken from the Shitalakshya River, and their textures were analyzed. The cumulative frequency curve is obtained by using semilog graph paper to plot particle size (in phi scale) against cumulative percent. The statistical parameters such as median (Md), mode (Mo), mean (MZ), standard deviation (σi), skewness (SKi), and kurtosis (KG) were calculated using the percentile of phi values (1%, 5%, 16%, 25%, 50%, 75%, 84%, and 95%). The cumulative curves show that the sediments are deposited through the traction population (1.90%), saltation population (75.64%), and suspension population (22.46%). The median value varies between 0.7Ø and 4.85Ø, with an average of 2.738Ø indicating coarse sand to coarse silt. The analyzed samples have unimodal, bimodal, and polymodal distribution, which indicates the sediments are carried by different tributaries and distributaries in the Sitalakshya River system. The range of 1.46Ø–4.05Ø represented by the observed mean value suggests sand with medium to extremely fine grains. Most of the sediments indicate moderate sorting, which is shown by the standard deviation (sorting), which ranges from 0.399Ø to 1.48Ø. The skewness value ranges between −0.01Ø and 0.66Ø, suggesting near symmetrical skewed, while the kurtosis value ranges from 0.54Ø to 1.87Ø, indicating the sediments are 20% leptokurtic, 20% mesokurtic, and 60% platykurtic. According to the CM plot, the Shitalakshya River is mostly deposited in the area between the rolling and suspension fields, indicating a transportation regime of saltation. The scatter plots of skewness versus sorting and graphic mean versus sorting indicate that the sediments fall within the river sand zone. The energy process discriminant functions of the sediments show that they were deposited by a fluvial process.

Terrestrial shale oil resources in China are abundant. However, its development in China is still in the early stages. And its scale of transformation and production systems is still being explored. Currently, reservoir numerical simulation on shale oil reservoirs faces two main challenges: (1) multiscale flow of matrix–microfracture–hydraulic fractures in shale oil reservoirs and (2) bidirectional coupling of reservoir–wellbore–nozzle systems. This paper proposes a self-flow model for horizontal shale wells that describes multiscale fractures and production controlled by the nozzle. The model integrates the embedded discrete fracture model (EDFM), pipe flow model, and nozzle flow model. The accuracy of the model has been validated through comparisons with other reference models and field data. Then, this study analyzes the effects of different natural fracture densities, horizontal section lengths, number of fracturing stages, and nozzle diameters on the production capacity during the self-flow period. The results indicate that reservoirs with developed natural fractures can enhance the development efficiency during the self-flow period, and appropriate horizontal section lengths and fracturing stages contribute to achieving maximum economic benefits in development. Additionally, smaller nozzle diameters lead to longer self-flow periods and higher cumulative production. The research findings of this paper can be applied to simulate the production of hydraulic fractured horizontal shale wells.

Rammed earth, a commonly used building material in ancient times, differs from natural sedimentary layers in that it is more compact. Buildings constructed from historical rammed earth sites frequently encounter the issue of rainwater erosion. Microbially induced calcium carbonate precipitation (MICP) is commonly applied to sand soil treatment, yet reports on its use for stabilizing rammed earth are scarce. This study focused on the rammed earth of the Shanhaiguan Great Wall and explored the efficacy of MICP in mitigating rain erosion through permeation tests, splash experiments, and scouring trials. The findings indicate that the forms of rain erosion damage under MICP treatment vary across different operational conditions. In laboratory experiments, as the concentration of the cementation solution increases, the amount of calcium carbonate crystals also increases. However, the permeability, splash resistance, and rain erosion resistance initially increase and then decrease. When the cementation solution concentration is 1.0 mol/L, the penetration rate is the highest, lasting 712.55 s. The splash pit rate is the lowest, at only 1.2 mm, and the soil erosion rate is the lowest, at only 4.13%. The rain erosion resistance in the field test exhibit the same trend, and the optimal concentration is 1.2 mol/L. The optimal concentration mechanism involves the aggregation of calcium carbonate crystals at suitable cementation solution concentrations, which begin to fill the soil particle pores, effectively resisting rainwater erosion. At lower concentrations of the cementation solution, calcium carbonate crystals are merely adsorbed by soil particles without blocking the pores. Due to the high compressibility of rammed earth, which results in lower porosity, a higher concentration of the cementation solution leads to rapid pore clogging by excessive calcium carbonate crystals, which accumulate on the surface to form a white crust layer. The MICP technique can effectively alleviate rainwater erosion in rammed earth, and the optimal concentration needs to be tailored to the porosity of the rammed earth. This mechanism was also validated in field scouring experiments on the Shanhaiguan Great Wall’s rammed earth.

The coring data in high water-cut oilfields indicates that the reservoir permeability will change continuously with water flooding, while the existing reservoir numerical simulation software cannot consider the time-varying phenomenon of permeability. With the enhancement of reservoir heterogeneity, the near-wellbore profile control fails to stabilize the oil production and control the water cut. The in-depth profile control has been widely used in oilfields as a new technology, and the types of profile control agents are diverse, with a complex mechanism that cannot be effectively described by the existing conventional numerical simulation software. Considering these two phenomena comprehensively, a new three-dimensional, three-phase, six-component mathematical model that can take into account the time-varying phenomenon of reservoir permeability is proposed for a new kind of in-depth profile control system, namely, the core–shell coagulation system, and an integrated numerical simulation software is developed. The mechanism of the in-depth profile control system can be perfectly demonstrated in the simulator with time-variation of permeability. The results of sensitivity analysis show that the effect is influenced by three factors: the mix slug injecting concentration, the coagulant aid slug volume, and the concentration of the suspension dispersing agent.

As an important and universal petrophysics of heavy oil reservoirs, the two-phase flow ability inside porous medium is vital for heavy oil development. Utilizing the laminar flow theory and an ideal pore structure, especially cylinder model, the function of the relative permeability of heavy oil–water with water saturation is derived by incorporating the principles of momentum conservation and the characteristics of Bingham fluids, which was modified by validated experiment. Two-phase relative permeability, considering heavy oil as non-Newtonian fluid, is the function of water saturation, pore size, oil–water viscosity ratio, and yield stress. The results of the validated experiment show that the theoretical values calculated employing the modified equation exhibit better agreement with the experimental values, particularly when the viscosities of two-phase fluid are great. The results of the modified two-phase relative permeability show a decrease in water saturation interval corresponding to the two-phase flow area and a smaller value of permeability at equal two-phase relative permeability. The oil–water viscosity ratio in the hydrophobic pores affects the water-phase relative permeability, although the magnitude of its influence diminishes as the viscosity ratio increases. The behavior of relative permeability in hydrophilic pores is the opposite of that in hydrophobic pores. This work can afford good application prospects for mobility control in multilayered reservoirs through the heterogeneous-phase-composite fluid. The saturations of the remaining oil and irreducible water also play a vital role in the prediction of permeability. The work can afford good application prospects for the flow behavior of Bingham heavy oil in pores with different types of wettability.

In order to understand the resistance loss along the way during multistage high-pressure slurry transportation, the flow state of fly ash slurry in the pipeline was simulated by Fluent software in this paper, and the effects of pipe diameter D, pipe transportation flow rate Q, and fly ash mass concentration Cw on the resistance loss along the pipeline were studied. The fly ash slurry is a non-Newtonian Bingham fluid that moves in a turbulent state in a pipeline. When simulating the flow of fly ash slurry using Fluent software, the mesh type is a mixed mesh of hexahedron and wedge shapes, and the viscous model is selected as realizable k-ε Turbulence Model, with Enhanced-Wall Function (EWF) selected as the wall function, combined with a four-layer boundary layer mesh, which can more accurately capture the details of velocity changes at the wall, thereby improving the accuracy of the model. The inlet of the model is the velocity inlet, and the outlet is the pressure outlet. The coupled algorithm is chosen as the solution method. Under these conditions, the model converges quickly and the calculation accuracy is high. The results show that the resistance loss along the pipeline decreases as a power function with the increase of pipeline diameter, and there is a polynomial relationship between the pipeline flow and the resistance loss along the pipeline, while the mass concentration of fly ash slurry changes linearly with the resistance loss along the pipeline. In addition, three friction coefficient models, namely Blasius formula, Colebrook–White equation, and Wilson–Thomas model, were selected according to the flow characteristics of fly ash slurry. Based on the Blasius formula with the smallest relative calculation error, the Blasius formula was modified by multiple linear regression analysis to improve the accuracy of the frictional resistance coefficient model and to provide help for the design and use of separate layer grouting conveying system.

Hydrothermal geochemical signatures in outcropping rock samples of the super-hot Los Humeros geothermal field were discovered by using an integrated geochemometric study of the mobility of components (major oxides) and trace elements. Chemical component and element mobilities were determined by using the Gresens–Grant equation for mass balances. A spatial distribution of component and element mobility patterns was carried out through the mineral characterization, hydrothermal alteration, and whole-rock elemental analysis. Four alteration assemblages were mainly identified: (i) argillic–silicic; (ii) argillic–sericite; (iii) advance argillic–sulphate acid (alunite or jarosite); and (iv) silicic–carbonate. A clear increasing order of mobility for major oxides such as Fe2O3T, P2O5, K2O, MnO, SiO2, CaO, Al2O3, and MgO and trace elements such as Pb, Th, Sr, Zn, V, Rb, Cr, Cu, and Ba was inferred from hydrothermally altered rocks. The mobility of these components and trace elements showed a geochemical association with a higher contribution of Fe2O3T, CaO, V, Cu, Zn, and Sr and a lower contribution of K2O, Rb, Th, and Cr. The spatial distribution of hydrothermal signatures obtained by tracking the mobilities of major and trace elements in samples collected in a new sector of Los Humeros geothermal field is aligned with NW-SE and NE-SW fault systems. Three areas characterised by a higher permeability were identified, for the first time, from low-cost analyses of rock samples by using energy-dispersive X-ray fluorescence spectrometry. The successful application results obtained from this study provided a new integrated geochemometric method to track high permeability zones for geothermal prospection tasks.