Search Results (289)

The Permian Qixia dolostone in the Central Sichuan Basin is a significant hydrocarbon reservoir of hydrothermal origin, linked to the Emeishan Large Igneous Province and structurally controlled by E–W strike–slip faults. However, how this process controls reservoir quality remains poorly understood. To address this, we integrate core observation, thin-section petrography, XRD analysis, thickness mapping, MICP, and μ-CT to characterize the lithofacies and pore structures of the Qixia Formation in the study area. Six lithofacies are recognized, including mudstone (F1), wackestone (F2), packstone (F3), grainstone (F4), rudstone (F5), and dolostone (F6), and F6 is further divided into three subtypes (F6-1, F6-2, F6-3). Dolostones exhibit superior reservoir quality relative to limestones, and among the dolostone, reservoir quality improves progressively from F6-1 to F6-3 with increasing crystal size and dolomite content. Dolostone distribution is spatially tied to E–W strike–slip faults, and its formation age coincides with documented fault activity, implicating these faults as the primary fluid conduits. Quantitative pore structure analyses further indicates that dolomitization enhanced permeability by enlarging pore–throat radii and improving macropore connectivity, with associated dissolution contributing additional secondary porosity. Full article

Microbially Induced Carbonate Precipitation (MICP) is a biochemical process that promotes the precipitation of calcium carbonate, mainly in the mineral form of calcite, using urease-producing bacteria. This method has numerous applications, particularly in the field of geotechnical engineering when it is adopted for soil improvement or for the consolidation of porous or cracked construction materials such as stone and concrete. One microfluidic platform made of polymethylmethacrylate (PMMA) was designed with multiple channels, and the minerals precipitated were visualized using an optical microscope. The precipitated mineral observed in all channels analyzed formed spherical mineral structures with a core and multiple external rings. The same spherical mineral structures were observed in the biocement layer precipitated on plates of the same material as that of the microfluidic platform and on limestone, following the same treatment protocol. SEM images of pieces of these layers, complemented with EDS and mineral analysis by XRD, have confirmed the existence of multiple layers of minerals with spherical structures, mainly vaterite, precipitated around a nucleation point. Overlapping minerals in both the confined microfluidic channels and the unconstrained plates indicate that overlap results from repeated injections rather than physical confinement. From the tests with the microfluidic devices, these studies revealed that crystallization depends on different factors, namely the size of the channels and the number of Sporosarcina pasteurii cells. The number of injections appeared to affect the number of rings precipitated around the inner core. Substrate effects on spatial distribution or adhesion may still exist but were not detectable in this study and require further investigation. The observation of similar mineralogical structures in both the microfluidic devices and the plates, particularly the limestone, demonstrates that microfluidic systems are effective tools for small-scale visualization of geological processes. Full article

This study investigates the mechanical properties, moisture stability, and environmental safety of microbial-induced carbonate precipitation (MICP)-treated phosphogypsum (PG)-based mixtures (MPGT) for road base utilization. Optimal cementation solution concentrations and bacterial-to-cementation solution ratios were determined via unconfined compressive strength (UCS), California bearing ratio (CBR), and splitting tensile strength tests. Durability was compared with untreated mixtures, and enhancement mechanisms were analyzed using XRD, SEM, and FTIR. Additionally, toxicity leaching tests evaluated environmental safety. Results indicated optimal parameters of 2.0 mol/L cementation solution and a 2:1 bacterial/cementation solution ratio for maximum mechanical strength. Under these conditions, MPGT durability significantly improved compared to untreated mixtures. Mechanism analysis revealed that MICP-generated calcium carbonate coats PG particles and fills voids, enhancing strength and durability. Furthermore, F⁻ and PO₄³⁻ leaching concentrations were significantly reduced. In summary, MICP improves the mechanical performance, durability, and environmental safety of PG-based mixtures, promoting PG recycling in road engineering. Full article

Unique fractal characteristics are significantly controlled by shale lithofacies, mineralogical characteristics, and OM features, which in turn determine reservoir properties and gas-bearing capacity. However, a comprehensive understanding of fractal features has remained insufficient. This study presents a systematic investigation into the full-scale pore size distribution for the Wufeng–Longmaxi shales in Sichuan Basin which employed low-pressure CO₂ adsorption (CO₂GA), N₂ adsorption (N₂GA), and mercury injection capillary pressure (MICP), as well as field emission scanning electron microscope (FE-SEM) techniques. The fractal dimensions of pores across different pressure ranges were revealed by different fractal models. The results demonstrate that the shale pores are dominated by micro- to mesopores and partial extremely larger pores, contributed primarily by organic matter (OM) pores and microcracks, respectively. Fractal dimensions follow a consistent increasing order: D_C < D_N1 < D_N2 < D_M or D_C < D_N1 < D_M < D_N2, suggesting that larger pores with diameters lager than 5 nm are more heterogeneous and complex compared to the pores less than 5 nm (smaller pores). This is because smaller pores are predominantly composed of OM pores, while larger pores comprise a mixture of OM pores, mineral-related pores, and microcracks. Different fractal dimensions, in turn, are influenced by distinct factors. The D_C value exhibits a positive correlation with micropore volume. D_N1 and D_N2 values are positively correlated with the content of brittle minerals and TOC, while they show negative correlations with the content of clay minerals. Notably, D_M values do not demonstrate a significant correlation with shale compositions, primarily owing to the development of microcracks. Fractal dimensions, particularly D_N1 and D_N2, are significantly controlled by the lithofacies of shale. The highest D_N1 and D_N2 values occur in the siliceous shale lithofacies, and the mixed shale lithofacies exhibit moderate D_N1 and D_N2 values, whereas the lowest D_N1 and D_N2 values primarily occur in clay-rich shale lithofacies. Different fractal dimensions show various correlations with shale gas content. The Langmuir volume as well as total gas content exhibit significant correlations with D_N1 and D_N2 values, while they exhibit no obvious correlations with D_C and D_M values. This implies that pores with diameters of 1.8–55 nm serve as primary storage sites for both adsorbed and free gas. The findings can significantly improve the cognition of adsorbed gas and free gas behavior in shale reservoirs. Full article

To facilitate the large-scale recycling of phosphogypsum (PG) as a construction material and mitigate the environmental safety concerns associated with its stockpiling or discharge, this study proposes an innovative approach. The method employs modified (acid-treated) basalt fibers (MBF) synergistically combined with microbially induced carbonate precipitation (MICP) technology for PG solidification. This synergistic MBF–MICP treatment not only enhances the strength and further improves the toughness of the solidified PG but also effectively immobilizes heavy metals within the PG matrix. Bacterial attachment tests conducted on fibers subjected to various pretreatment conditions revealed that the maximum bacterial adhesion occurred on fibers treated with a 1 mol/L acid concentration for 2 h at 40 °C. However, MICP mineralization experiments performed on these pretreated fibers determined the optimal pretreatment conditions for mineralization efficiency to be an acid concentration of 0.93 mol/L, a treatment duration of 0.96 h, and a temperature of 30 °C. Unconfined compressive strength (UCS) tests and calcium carbonate content measurements identified the optimal reinforcement parameters for MBF–MICP-solidified PG as a fiber length of 9 mm and a fiber dosage of 0.4%. Furthermore, comparative analysis demonstrated that the UCS and toughness of MBF–MICP-solidified PG were superior to those of bio-cemented PG specimens treated with unmodified fibers or without any fiber reinforcement. It was found by scanning electron microscopy that there was an obvious phosphogypsum particle-fiber-calcium carbonate precipitation interface in the sample, and the fiber had a bridging effect. Finally, heavy metal leaching tests conducted on the solidified PG confirmed that the leached heavy metal concentrations were below the detection limit, complying with national discharge standards. Full article

This study presents an innovative approach by combining magnetized water (MW) with Bacillus megaterium to improve the sustainability of concrete under various curing conditions. These enhancements contribute directly to reduced cement use and improved durability, both essential factors in sustainable construction. An experimental program with 27 distinct mixes analyzed variables such as the type of water (tap water/TW and two magnetization sequences/MW1 and MW2), bacterial dosage (0%, 2.5%, and 5% relative to cement weight), and curing methods (traditional water curing/C1, thermal shock/C2, freeze–thaw/C3). The primary discovery is a synergistic relationship between MW and bacteria: the MW1 treatment (1.5 T followed by 0.9 T) paired with a 2.5% bacterial dosage significantly improved the mechanical and self-healing properties of the concrete. This combination led to significant improvements in workability and compressive strength, achieving an increase of as much as 46.5% compared to the control. There was also an impressive recovery of strength in pre-cracked specimens, particularly under thermal shock curing (C2), where some healed cubes exceeded the strength of the uncracked ones. On the other hand, a 5% bacterial dosage was less effective, often resulting in reduced returns due to variations in microstructure. SEM and XRD analyses confirmed a more compact matrix and increased calcite precipitation with 2.5% bacteria, illustrating the combined effects of microbial activity and microwave treatment for sustainable concrete. Full article

Coal gangue, as a predominant solid byproduct of the global coal industry, poses severe environmental challenges because of its massive accumulation and low utilization rate. This review systematically synthesizes and analyzes published experimental and analytical studies on the dual-pathway utilization of coal gangue in concrete, including Pathway 1 (aggregate substitution) and Pathway 2 (cementitious activity activation). While the application of coal gangue aggregates is traditionally limited by their inherent high porosity and lower mechanical strength than those of natural aggregates, this review demonstrates that performance barriers can be effectively overcome. Through multiscale modification strategies—including surface densification, biological mineralization (MICP), and matrix synergy—the interfacial defects are significantly mitigated, allowing for feasible substitution in structural concrete. Conversely, for the mineral admixture pathway, controlled thermal activation is identified as a key process to optimize the phase transformation of kaolinite, thereby significantly enhancing pozzolanic reactivity and long-term durability. According to reported studies, the partial replacement of natural aggregates or cement with coal gangue can reduce CO₂ emissions by approximately tens to several hundreds of kilograms per ton of coal gangue utilized, depending on the substitution level and activation strategy, highlighting its considerable potential for carbon reduction in the construction sector. Nevertheless, challenges related to energy-intensive activation processes and variability in raw gangue composition remain. These limitations indicate the need for future research focusing on low-carbon activation technologies, standardized classification of coal gangue resources, and long-term performance validation under realistic service environments. Based on the synthesized literature, this review discusses hierarchical utilization concepts and low-carbon activation approaches as promising directions for promoting the sustainable transformation of coal gangue from an environmental liability into a carbon-reduction asset in the construction industry. Full article

Aeolian sand in arid mining regions is highly susceptible to wind erosion, posing serious threats to ecological stability and surface engineering safety. To enhance its resistance, this study applied the microbially induced carbonate precipitation (MICP) technique and conducted wind tunnel experiments combined with SEM and XRD analyses to examine the effects of cementing solution type and concentration, bacteria-to-cementation-solution ratio (B/C ratio), and spraying volume on the wind erosion behavior of MICP-treated aeolian sand. Results show that the cementing solution type and concentration jointly control erosion resistance. The MgO-based system exhibited the best performance at a B/C ratio of 1:2, reducing erosion loss by 47.2% compared with the CaCl₂ system, while a 1.0 mol/L concentration further decreased loss by 97.4% relative to 0.5 mol/L. Increasing the spraying volume from 0.6 to 1.2 L/m² reduced erosion loss by 70–99%, and a moderate B/C ratio (1:2) ensured balanced microbial activity and uniform CaCO₃ deposition. Microstructural observations confirmed that MICP strengthened the sand through CaCO₃ crystal attachment, pore filling, and interparticle bridging, forming a dense surface crust with enhanced integrity. From a symmetry perspective, the microbially induced mineralization process promotes a more symmetric and spatially uniform distribution of carbonate precipitates at particle contacts and within pore networks. This symmetry-enhanced microstructural organization plays a key role in improving the macroscopic stability and wind erosion resistance of aeolian sand. Overall, MICP improved wind erosion resistance through a coupled biological induction–chemical precipitation–structural reconstruction mechanism, providing a sustainable approach for eco-friendly sand stabilization and wind erosion control in arid mining regions. Full article

Urease, a metalloenzyme widely present in various organisms, catalyzes the hydrolysis of urea to ammonia and CO₂ and has been extensively utilized in studies and applications of microbially induced calcium carbonate precipitation (MICP). While microbially induced calcium carbonate precipitation (MICP) and silicate mineral bio-weathering are both important biogeochemical processes mediated by microorganisms, and their coupling has been verified in some geological environments, the potential role of urease (a key enzyme in MICP) in mineral weathering remains unreported. In this study, Bacillus velezensis LB002 served as the urease gene donor for the construction of a Bacillus subtilis strain with heterologous overexpression of urease genes. The effects of this engineered strain and the wild-type strain on serpentine weathering and secondary mineral formation were compared. The results showed that the urease activity of the overexpression strain was approximately 3.8 times higher than that of the wild-type strain, and the release of Mg²⁺ during serpentine weathering increased by 17 mg/L. XRD and SEM-EDS analyses revealed that the wild-type strain promoted the formation of vaterite as a secondary mineral, whereas the overexpression strain induced the precipitation of both vaterite and magnesium-containing calcite. These findings demonstrate that urease plays a synergistic role in mineral weathering and that urease overexpression significantly enhances the release of Mg²⁺ from serpentine and the formation of magnesium-containing calcite. Full article

As a typical representative of soft capping, primary vegetation capping has both protective and destructive effects on earthen city walls. Addressing its detrimental aspects constitutes the central challenge of this project. Because the integration of MICP technology with plants offered advantages, including soil solidification, erosion resistance, and resilience to dry–wet cycles and freeze–thaw cycles, the application of MICP technology to root–soil composites was proposed as a potential solution. Employing a combined approach of RF-RFE-CV modeling and microscopic imaging on laboratory samples from the Western City Wall of the Jinyang Ancient City in Taiyuan, Shanxi Province, China, key factors and characteristics in the mineralization process of Sporosarcina pasteurii were quantified and observed systematically to define the optimal pathway for enhancing urease activity and calcite yield. The conclusions were as follows. The urease activity of Sporosarcina pasteurii was primarily regulated by three key parameters with bacterial concentration, pH value, and the intensity of urease activity, which required stage-specific dynamic control throughout the growth cycle. Bacterial concentration consistently emerged as a high-importance feature across multiple time points, with peak effectiveness observed at 24 h (1.127). pH value remained a highly influential parameter across several time points, exhibiting maximum impact at around 8 h (1.566). With the intensity of urease activity, pH exerted a pronounced influence during the early cultivation stage, whereas inoculation volume gained increasing importance after 12 h. To achieve maximum urease activity, the use of CASO AGAR Medium 220 and the following optimized culture conditions was recommended: an activation culture time of 27 h, an inoculation age of 16 h, an inoculation volume of 1%, a culture temperature of 32 °C, an initial pH of 8, and an oscillation speed of 170 r/min. Furthermore, to maximize the yield of CaCO₃ in output and the yield of calcite in CaCO₃, the following conditions and procedures were recommended: a ratio of urea concentration to Ca²⁺ concentration of 1 M:1.3 M, using the premix method of Sporosarcina pasteurii, quiescent reaction, undisturbed filtration, and drying at room-temperature in the shade environment. Full article

The Qingshankou Formation shale in the Changling Sag of the Songliao Basin represents a typical lacustrine pure-shale reservoir, characterized by high organic matter abundance, high maturity, high clay mineral content, and strong heterogeneity. To elucidate the pore structure and heterogeneity of this shale, a comprehensive suite of analytical techniques—including X-ray diffraction (XRD), scanning electron microscopy (SEM), high-pressure mercury intrusion porosimetry (MICP), and low-temperature nitrogen adsorption—was employed to investigate its pore types and fractal characteristics systematically. On this basis, lithofacies classification and FHH fractal modeling were conducted to quantitatively assess the complexity of pore–throat structures and their influence on reservoir properties. The results indicate that shale-dominated lithofacies (Types A–C) exhibit higher surface fractal dimensions (D₁ = 2.51–2.58) and structural fractal dimensions (D₂ = 2.73–2.81), corresponding to low porosity, low permeability, and high displacement pressure. In contrast, carbonate- and clastic-dominated lithofacies (Types D–G) display lower fractal dimensions, suggesting more regular pore–throat structures and better connectivity. Overall, both D₁ and D₂ show negative correlations with porosity and permeability but positive correlations with displacement pressure, and are negatively correlated with TOC content, reflecting the intrinsic coupling among pore–throat complexity, reservoir capacity, and organic matter abundance. These findings reveal that the Qingshankou shale reservoir has undergone a geometric evolutionary pathway of “shale compaction → siltstone transition → carbonate porosity reconstruction.” The fractal dimensions effectively characterize the reservoir heterogeneity and pore–throat connectivity, providing a new theoretical basis for the quantitative characterization, classification, and potential prediction of continental shale oil reservoirs. Full article

Microbially induced calcium carbonate precipitation (MICP) is recognized as a promising, environmentally sustainable technology with diverse applications in environmental engineering. A bibliometric analysis of 5373 publications indexed in Web of Science from 2005 to 2024 was conducted using CiteSpace and VOSviewer to identify research trends and hotspots in biomineralization and calcium carbonate (CaCO₃) studies. The results showed exponential growth in publications, increasing from 96 in 2004 to 397 in 2024 and spanning 91 interdisciplinary research areas. China, United States of America, and Germany were identified as the leading contributors. Research evolution was categorized into five distinct phases, progressing from initial crystal formation investigations to the current emphasis on underlying microbial mechanisms. Trend analysis revealed four emerging research hotspots: interfaces (0.22), crystal morphology (0.18), amorphous calcium carbonate (0.05), and bacteria (0.02). Mechanisms of MICP across bacteria, fungi, and algae were examined, revealing diverse metabolic pathways, including urea hydrolysis, denitrification, and photosynthesis. These findings suggest a paradigm shift in research toward microbial diversity and the role of extracellular polymeric substances. This shift provides valuable insights for developing sustainable biotechnological applications in environmental remediation. Full article

The volume stability of steel slag fine aggregate (SSFA) is poor due to the hydration expansion of f-CaO/f-MgO, which limits its resource utilization. In this paper, a green modification route combining simple boiling water pretreatment with carbonic anhydrase (CA) -mediated microbial mineralization (MICP) was proposed and evaluated from macro–micro multi-scale. Compared with direct carbonization, CA-MICP accelerated CO₂ hydration and carbonate precipitation. Boiling water pretreatment enhanced ion release and pore accessibility, and the two synergistically improved the reaction kinetics. At 0.3 MPa, 100 h boiling pretreatment combined with 12 h microbial mineralization (K8 group) performed best: CO₂ absorption rate reached 4.98%, carbonization rate reached 3.93%; the content of f-CaO and f-MgO decreased to 0.16% and 0.12% (conversion rate 91.82% and 87.43%), respectively. The linear expansion of SSFA mortar decreased to 0.0176% after 55 h of water bath. XRD/FTIR showed that the carbonate peak was enhanced and the O-H characteristics were weakened. The weight loss of TG-DTG at 600–800 °C increased. SEM/BET observed that flake/cluster carbonates filled the pores and increased the interface density. Innovations: For the first time, the synergistic effect of boiling water pretreatment and CA-MICP was verified in the steel slag fine aggregate system, and a feasible process window was given to efficiently convert expansive oxides into stable carbonates, significantly improve volume stability, and provide a feasible path for the high-value utilization of SSFA. Full article

This study examines key bioprocess parameters influencing the reduction in hydraulic conductivity in porous media via Microbially-Induced Calcite Precipitation (MICP), highlighting its relevance to environmental engineering applications such as bio-barriers and landfill liners. Sporosarcina pasteurii was utilized as the ureolytic bacterium to induce calcium carbonate precipitation under controlled laboratory conditions. Experimental variables included bacterial cell density (OD₆₀₀), diameter of glass beads, concentrations of precipitation solution, bentonite, and yeast extract. A total of 42 experimental runs were conducted based on a custom design in Design-Expert software. Hydraulic conductivity was selected as the response variable to evaluate treatment performance. Response surface methodology (RSM) was applied to develop a second-order polynomial model, with statistical analyses indicating a strong model fit (R² = 0.948, adjusted R² = 0.929, predicted R² = 0.868). ANOVA confirmed the significance of the main effects and interactions, particularly those involving glass bead diameter and OD₆₀₀. Among the tested factors, the precipitation solution exhibited the strongest individual effect, while bentonite and yeast extract demonstrated supportive roles. Optimization revealed that a balanced combination of microbial density and chemical inputs minimized hydraulic conductivity to 0.0399 cm/s (≈95% reduction), with an overall desirability score of 1.000. Laboratory-scale experiments demonstrated field-scale applicability, underscoring the potential of biotechnological soil treatment and empirical modeling for developing sustainable low-permeability barriers. Full article

Diagnosing water-phase damage remains challenging because routine petrophysical parameters do not capture capillary hysteresis and pressure-transmission effects. In this study, a standardized, auditable workflow was established to link laboratory descriptors to field-relevant cleanup. Full-curve mercury injection capillary pressure data were acquired and converted using consistent Washburn parameters, from which withdrawal efficiency was computed on the withdrawal branch. A pressure-transmission coefficient was evaluated under unified boundary conditions to complement permeability and porosity. After preprocessing and partial least-squares regression (PLSR) screening, MICP descriptors were clustered by k-means (k = 5) to obtain reservoir Types I–V. Regressions relating WE to permeability and flowback behavior were then used to assess engineering relevance. The results indicate that WE capture hysteretic trapping/back-pressure not contained in permeability or porosity and, when interpreted jointly with PTC, differentiates reservoir types by cleanup propensity. This framework provides a reproducible bridge from laboratory MICP hysteresis to field-scale flowback interpretation. Practical implications include prioritization of gas–wet wettability modification, low-surface-tension systems, and minimized early liquid loading for clusters exhibiting higher WE and lower PTC. Full article