Geofluids最新文献

Microbially induced carbonate precipitation (MICP) has been utilized as a new method to improve loess soil strength. In this study, we investigated the influence of the main parameters on the shear strength of MICP-treated loess specimens. Initially, culture media with different formulas and pH values were examined to identify the most efficient medium for loess soil. To explore the shear behavior of MICP-treated loess under general stress levels, unconfined compressive strength (UCS) tests and triaxial tests relevant to the compression strength and vertical loads were performed on MICP-treated loess with different calcium sources, cementation concentrations, and curing periods. Subsequently, calcium chloride was selected as the optimal calcium source based on the ultimate strength of the MICP-treated loess. The effective cementation concentration in the loess soil was between 1.0 and 1.25 M. The ultimate strength of the MICP-treated loess was 3.6 times of the untreated loess. The stress-strain curves indicate that a higher cementing effect can be expected with an increase in the curing period. The formation process of calcium carbonate and the micromorphology of the MICP-treated loess samples were examined using scanning electron microscopy. In this study, we present an environmentally friendly technique for improving loess soil strength.

The undesirable effect on the stability for cross-river tunnel faces considering pore water pressure was observed with the consideration of the soil arch effect by using the discrete technology for the first time. In light of the upper bound of plastic theory, an improved failure mechanism of the deep-buried tunnel face was established. A new discrete technology approach taking account into the soil arching effect was proposed to estimate the stability for cross-river tunnel faces subjected to pore water pressure. The presented approach is validated by comparing with the existing solutions as well as showing great improvements. After verification, based on the failure mechanism, this paper discusses the impact of the changing water level and the soil parameters on the normalized supporting pressure and meanwhile analyzes the variation of the shape of collapsing domain of soils ahead of the tunnel face considering the soil arching effect. The results illustrate that soils with the bigger friction angle form the arch more easily during excavation, and with higher water height, the soil arching effect appears not as obvious as expected, particularly on those soils with the smaller friction angle.

The temperature field beneath a roadbed is asymmetrically distributed, which causes uneven settlement, longitudinal cracking, and even sliding and collapse, as well as other diseases of frozen soil roadbeds. Most roads in alpine mountain regions are half-filled and half-excavated. The degree and direction of the temperature gradient are utilized as variables in a numerical simulation to examine the deformation properties of coarse-grained frozen soil. The findings demonstrate that (1) coarse-grained frozen soil has a nonlinear connection between strength and the lowest temperature, with strength increasing with decreasing temperature and decreasing under the influence of the temperature gradient. (2) When an arbitrary temperature field acts on frozen soil, its monolithic character diminishes, its shear strength and maximum strength decrease as the angle θ increases, and the distribution of the shear zone takes the form of an X. (3) An asymmetrical shear zone forms when the direction of the temperature gradient θ deviates from 0°. The degree of asymmetry in the ground deformation and the angle of inclination of the shear zone are positively related to θ.

The Urho Formation in the Lower Permian System at the Junggar Basin in China commonly develops zeolite cements. The presence of zeolite minerals in various states of occurrence and uneven distribution in glutenite reservoirs makes it indeterminate to interpret the well logging response characteristics such as acoustic, resistivity, radioactivity, and nuclear magnetic resonance (NMR). This poses significant challenges for the evaluation of well loggings in glutenite reservoirs containing laumontite and the determination of oil and gas reserves. In this study, through petrophysics experiments such as whole-rock X-ray diffraction, conventional petrophysical properties, mercury injection, and electron microprobe analysis, the characteristics of glutenite reservoirs containing laumontite and the well logging response mechanisms were analyzed from the perspectives of mineral composition of rocks, geochemical characteristics, and principle of loggings. A multimineral optimization method was used to calculate the laumontite content. The results indicate that in the study area, the cementation of zeolite minerals dominated by laumontite suppresses the pore development in the reservoir, which is a crucial factor in the formation of complex pore structures and low-porosity low-permeability reservoirs. Since laumontite exhibits a water-bearing framework structure with numerous micropores and crystal water, the laumontite-bearing glutenite reservoirs are characterized by low natural gamma radiation, low density, high neutron porosity, and high electrical resistivity. The acoustic interval transit time shows no significant differences, while the NMR T₂ spectrum exhibits a short relaxation time.

Reservoir characteristics and source rock geochemistry are essential for petroleum system investigation as they reveal reservoir quality and hydrocarbon generation capability, respectively. The primary Karama oil field reservoir of Abu El Gharadig Basin is the limestone-sand-shale Abu Roash G (AR/G) Member. This study examines AR/G, analyzes source rocks for maturity and organic elements, and defines the main reservoir lithotypes and evaluates reservoir properties. Five well log datasets and an AR/F pyrolysis analysis on another well were used in this study to characterize the AR/G’s 168-foot effective thickness and assess the AR/F source-rock maturation. The effective porosity is up to 30%. The highest shale concentration was 24% in central and western parts of the field. Therefore, drilling development wells in this area, especially east and north, demands caution. The composition and vertical and lateral lithofacies variations of the defined reservoir in the Karama field region are a significant control of its petrophysical properties. The pyrolysis of AR/F revealed 1.32–5.84% content of organic matter. That content qualifies AR/F as a hydrocarbon source if thermal maturity is reached. Type I and type II kerogen in the Abu Roash F Member suggests oil production. The Abu Roash G Member and Upper Bahariya (UB) formation produce oil and gas due to their own type II and III kerogen. GC biomarker data suggests that the research area is predominantly maritime, with most samples showing environmental degradation. The area under consideration has one reservoir, AR/G, and three members of source rocks in AR/F&G and UB. AR/G electrofacies revealed various lithotypes and flow units.

The transport of sulfate-bearing brines is closely relevant to mineralization of sulfide deposits as metal-sulfate complexes exist in hydrothermal fluids. Liquid-liquid phase separation evidently occurs in various metal-sulfate systems with transport and precipitating different from homogeneous fluids. Previous studies have revealed a new species with a Raman peak at ~1020 cm^-1 in rich concentration phase of liquid-liquid phase separated MgSO₄ solution, and it was interpreted as chain structure polymers. Ab initio molecular dynamics simulations (AIMD) and autocorrelation functions for frequency calculation have been performed to disclose the speciation. The results show that more Mg²⁺ ions surrounding a SO₄^2- anion lead to higher wavenumber of Raman peaks, which indicates the formation of complicate clusters with ion associations similar to kieserite. Besides, the splitting peaks of v-980 Raman bands at ~980, 990, and 1005 cm^-1 in homogeneous solution represent more monodentate Mg-Os (Os: O of SO₄^2-) associations instead of certain species, which favors the formation of prenucleation clusters. Furthermore, bidentate Mg-SO₄ ligand is less stable than monodentate ligands at 543 K by applying free energy calculations. Our findings give atomic level recognition of concentrated phase in liquid-liquid phase separated MgSO₄ fluids and theoretical explanation of the 980 cm^-1 Raman peak shifting, which will further inspire understandings on nucleation processes of hydrated sulfate minerals and Raman spectra resolving of other sulfate systems.

Broken rock masses with the complexity and concealment widely exist in nature such as underground mine, collapse column, and zone. It is extremely difficult to model fracture networks and to simulate water diffusion for broken rock masses. To explore a reasonable fracture network model for broken rock masses, a new method for modeling a two-dimensional planar fracture network model is proposed in this paper. It includes packer test, empirical relationship, fractal width description, and symmetric expansion modeling. Then, the fluid-solid coupling is used to simulate the diffusion properties of water in the two-dimensional planar fracture network model. It is found that the diffusion velocities v_max and v_min do not appear in the fracture widths λ_max and λ_min. It indicates that the fracture widths λ_max and λ_min in the fracture network model for broken rock mass have little impact on the diffusion velocity. Furthermore, the fracture distribution pattern in the fracture network model is an important factor affecting the diffusion velocities v_max and v_min. The simulation results of water diffusion in the currently proposed model are almost consistent with the actual process of the packer test. Also, the validity of the two-dimensional planar fracture network model is verified by comparing the simulation results with the existing research.

The Bangxi–Chenxing suture zone is an essential area from which information about the closure history of the eastern Paleo-Tethys Ocean can be obtained. The Darongshan granitoid, which is adjacent to this suture, lies among the widely distributed granitic rocks and few basic rocks in the southern Guangxi Province. Herein, we report the petrogeochemistry, zircon U–Pb ages, and zircon Hf isotopic data of the Darongshan pluton in this region. The LA-ICP-MS U–Pb zircon analysis indicates that the Darongshan pluton had formed at 249.9 ± 2.6 Ma. The Darongshan granites are silica-rich (SiO₂ = 65.68–72.91 wt%, mean = 69.89 wt%) with high Na₂O contents (Na₂O = 0.46–6.58 wt%, mean = 3.49), relatively high Mg (Mg^# = 35.12–73.31, mean = 57.73), and an average Fe₂O₃^T+TiO₂+MnO+MgO of 4.96. These features are similar to those of the Mg-andesitic/dioritic rock- (MA-) like tonalite–trondhjemite–granodiorites (TTGs). Chemical analyses show that all rocks are enriched in large-ion lithophile elements (Rb, Th, and U) and light rare earth elements, with weak negative Eu anomalies (Eu/Eu^∗ = 0.27–0.67), and Ta, Nb, and Ti depletion, with typical arc-like affinity. The zircon Hf isotopic results show zircon  _ƐHf(t) values ranging from -18.2 to -7.4 and the T_DM2 model ages 1.74–2.41 Ga. The petrogeochemistry and zircon Hf isotopic signatures indicate the magma generation of the Darongshan granitoid with fluid/melt released from the subducted slab and the fluid/melt assimilated and mixed with the mantle peridotite during ascent. Combining previous extant information on Permo–Triassic subduction/collision-related magmatism in the Bangxi–Chenxing with that of the Jinshajiang–Ailaoshan–Song Ma suture zones, the Darongshan granitoid is interpreted as a magmatic formation that was generated in an active continental margin arc environment during the subduction of the Early Indosinian eastern Paleo-Tethys Ocean and the South China Block, further supporting the idea that closure occurred during the Middle–Late Triassic.

Superheated steam flow during multipoint steam injection technology has a good effect on improving the steam absorption profile of heavy oil thermal recovery wells, enhancing the production degree of horizontal section of thermal recovery wells, and enhancing oil recovery. Based on the structure of multipoint steam injection horizontal string, considering the characteristics of variable mass flow, pressure drop of steam-liquid two-phase flow, and throttling pressure difference of steam injection valve in the process of steam injection, this paper establishes the calculation model of various parameters of multipoint steam injection horizontal wellbore and calculates the distribution of steam injection rate, temperature, pressure gradient, and dryness along the section of multipoint steam injection in horizontal wellbore. The results show that the temperature and pressure decrease gradually from heel to toe, and the steam dryness decreases gradually. Considering the influence of throttle pressure difference of steam injection valve and pressure drop of gas-liquid two-phase flow in the wellbore, the traditional calculation model of steam injection thermodynamic parameters is optimized, and the optimization of wellbore structure and steam injection parameters is an effective method to achieve uniform steam injection in horizontal wells. The steam injection uniformity of horizontal wells can be effectively improved by adjusting the steam injection valve spacing and steam injection parameters. When the steam injection volume is 200 m³/d and the steam injection valve spacing is 20 m, a more stable steam injection effect can be obtained. The findings of this study can help for better understanding of improving the uniformity of steam injection and enhancing the recovery factor.

A laboratory model of a single pile embedded in Nanyang expansive soil and subjected to water infiltration is applied in this study to examine the interaction between the expansive soil and pile foundation upon water infiltration. The soil matric suction decreases as a result of the rising soil-water content. The amount of soil ground heave reaches its peak of 10.7 mm after 200 hours of water infiltration. As matric suction decreases, pile shaft friction also declines, which causes more of the load at the pile head to be carried by the pile base resulting in more pile settlements. A new numerical simulation method is provided to simulate this issue by coupling the subsurface flow, soil deformation, and hygroscopic swelling to investigate the expansive soil-pile response upon water infiltration. From the numerical simulation model, hygroscopic strain arises as a result of elevated moisture levels resulting from the entry of water, and due to ground heave and the mobilization of lateral soil swelling, the shear stress at the interface between the soil and the pile gradually increases over time. It reaches its maximum value of 4420 Pa at upper depths around 200 hours after the infiltration. The comparison between the lab model testing data and the numerical model results demonstrates a good level of concurrence.