Geofluids最新文献

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.

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.

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.

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.