Search Results (12)

Phosphatic bioclastic laminae distributed along bedding planes have been recently discovered within the Jurassic Lianggaoshan Formation shale in the eastern Sichuan Basin. However, their characteristics and potential as shale oil and gas reservoirs remain unclear. To reveal their microscopic pore structure characteristics and development model, this study focuses on samples of phosphatic bioclastic laminae obtained from drilling cores in the Fuxing area of eastern Sichuan. A multi-scale analytical approach was employed, integrating micro-X-ray fluorescence spectroscopy (μ-XRF), field emission scanning electron microscopy (FE-SEM), nitrogen adsorption, nuclear magnetic resonance (NMR), and geochemical analyses. The results indicate that the phosphatic bioclastic laminae are primarily composed of apatite and calcite and formed in a low-energy, anoxic, semi-deep to deep lacustrine environment. They exhibit an average total porosity of 4.84% and an average TOC of 1.99 mg/g. It is 14.7% and 17.8% higher than the clay laminae, and 255.9% and 109.57% higher than the calcareous bioclastic laminae. The pore system is dominated by mesopores and macropores, encompassing multiple pore types including dissolution pores, interparticle pores, interlayer pores, organic matter-hosted pores, and micro-fractures. Notably, a well-connected nanometer-scale pore network developed within fish bone fragments contributes substantially to the storage space. These intervals integrate high organic matter richness with superior reservoir properties, demonstrating typical “source-reservoir integration” characteristics. Their pore structure is synergistically regulated by sedimentary–diagenetic processes, with a core mechanism of primary biogenic pore foundation–late diagenetic dissolution enhancement–micro-fracture connectivity. This study systematically elucidates, for the first time, the reservoir formation mechanism of the phosphatic bioclast-rich laminae in the Lianggaoshan Formation. It confirms their potential as “geological-engineering” dual sweet spots for shale oil and gas exploration, providing a new basis for sweet spot prediction and exploration deployment targeting similar phosphatic bioclastic laminae in the Sichuan Basin and analogous regions. Full article

Conventional material balance methods, typically based on single- or dual-porosity models solvable via single-step linearization, are inadequate for hydraulically fractured shale oil reservoirs due to their pronounced heterogeneity and contrasting interzonal connectivity. Specifically, dual-zone models fail to represent the realistic characteristics of shale oil reservoirs because they treat artificially created hydraulic fractures and natural fractures as equivalent, despite their substantially different properties. To address this gap, this paper proposes a novel three-zone conceptual model, segmenting the reservoir into the matrix zone (MZ), the Weakly Stimulated Zone (WSZ, low-conductivity zone), and the Strongly Stimulated Zone (SSZ, high-conductivity zone). A corresponding three-zone gas injection replenishment material balance model is developed. This model explicitly captures interactions between injected gas and formation fluids and incorporates dynamic variations in pore volume and fluid saturation induced by imbibition. To solve the complexities introduced by the triple-porosity system, a dedicated two-step linearization solution procedure is proposed. Utilizing conventional production performance and basic PVT data, the method enables simultaneous estimation of zone-specific developed reserves and prediction of the Estimated Ultimate Recovery (EUR) through a least squares algorithm. Validation against actual well cases and multi-well statistics confirms that the method provides stable and reliable zonal reserve characterization and EUR forecasting. The results indicate that the MZ contributes the majority of the geological reserves, accounting for >70%. The WSZ contributes approximately 29.5% of the reserves and serves as the primary source for energy replenishment in the shale oil reservoir. In contrast, the SSZ contributes less than 0.5% of the reserves but acts as the dominant channel for flow convergence, controlling the main fluid production pathways. The proposed framework not only offers a practical tool for refined reserve assessment in shale oil reservoirs but also provides a computational basis and decision support for the design and injection parameter optimization of pre-pad CO₂ energy storage fracturing schemes. Full article

Understanding how nanocomposite gels regulate pore–throat structures and flow behavior is essential for improving profile control and flow diversion in deep-water tight reservoirs. In this study, a dual-structure-regulated nanocomposite gel (DSRC-NCG) was designed, and its structure–flow coupling behavior during gel injection, curing, and degradation was systematically investigated using multiscale flow configurations, including microfluidic models, artificial cores, and sandpack systems. Microstructural evolution and pore–throat connectivity were characterized using μCT imaging, mercury intrusion porosimetry, nitrogen adsorption, and image-based flow simulations, while macroscopic flow responses were evaluated through permeability variation, dominant-channel evolution, injectivity behavior, and quantitative indices including the structure regulation index (SRI) and pore–flow matching index (HCI). The results show that increasing SiO₂ content induces a progressive optimization of pore–flow matching by refining critical throats and suppressing preferential flow channels, whereas excessive nanoparticle loading leads to aggregation and attenuation of these effects. This study proposes a multiscale structure–flow coupling framework that quantitatively connects pore–throat regulation with macroscopic flow responses during nanocomposite gel injection and degradation. These findings offer mechanistic insights and practical guidance for the design of nanocomposite gels with improved flow-regulation efficiency and reversibility in deep-water tight reservoir applications. Full article

The dynamic process of water depletion plays a critical role in both surface coalbed methane (CBM) development and underground gas extraction, reshaping water–rock interactions and inducing complex permeability responses. Addressing the limited understanding of the coupling mechanism between heterogeneous pore water evolution and permeability during dynamic processes, this study simulates reservoir transitions across four zones (prospective planning, production preparation, active production, and mining-affected zones) via centrifugal experiments. The results reveal a pronounced scale dependence in pore water distribution. During low-pressure stages (0–0.54 MPa), rapid drainage from fractures and seepage pores leads to a ~12% reduction in total water content. In contrast, high-pressure stages (0.54–3.83 MPa) promote water retention in adsorption pores, with their relative contribution rising to 95.8%, forming a dual-structure of macropore drainage and micropore retention. Multifractal analysis indicates a dual-mode evolution of movable pore space. Under low centrifugal pressure, D₋₁₀ and Δα decrease by approximately 34% and 36%, respectively, reflecting improved connectivity within large-pore networks. At high centrifugal pressure, an ~8% increase in D₀−D₂ suggests that pore-scale heterogeneity in adsorption pores inhibits further seepage. A quantitative coupling model establishes a quadratic relationship between fractal parameters and permeability, illustrating that permeability enhancement results from the combined effects of pore volume expansion and structural homogenization. As water saturation decreases from 1.0 to 0.64, permeability increases by more than 3.5 times. These findings offer theoretical insights into optimizing seepage pathways and improving gas recovery efficiency in dynamically evolving reservoirs. Full article

Controlling fluid loss during acid fracturing remains challenging, as acid may partially or completely leak into reservoir pores and fractures, preventing effective flow within the formation and thereby reducing stimulation effectiveness. The acid leakoff mechanism is fundamentally distinct from that of non-reactive pad fluid (fracturing fluid), with the most critical distinction manifested through wall-confined acid-etched wormholes formed during reactive flow processes, which exert a dominant influence on acid filtration behavior. To address this challenge, a modified dual-scale continuum model based on the Brinkman equation was developed. This model establishes a numerical simulation framework for acid fracturing–etching processes in dolomite reservoirs of the Xi Xiangchi Formation. The study systematically reveals acid leakoff patterns at fracture walls under the influence of operational parameters (injection rate, acid concentration, acid viscosity) and reservoir characteristics (porosity heterogeneity). For field operations, medium-viscosity acid initially enhances distal fracture communication, followed by viscosity reduction to promote non-uniform etching. Prioritizing acid concentration over injection rate optimizes fracture connectivity, while minimizing leakoff. In high-porosity reservoirs, process parameters require optimization through acid retardation and leakoff control strategies. Full article

The propagation of seismic waves and ultrasonic waves in rocks is significantly affected by dispersion and attenuation effects. When ultrasonic and seismic waves pass through rocks, the local flow of fluid in microcracks causes a substantial amount of energy attenuation, a phenomenon known as squirt flow. A simple analytical model is proposed in this paper to describe the attenuation and dispersion of isotropic fractured rocks due to squirt flow. Compared to the previous squirt flow model of the pore-crack model, this model adopts crack-to-crack flow configurations and considers the impact of crack connectivity and demonstrates higher accuracy in characterizing squirt-flow-induced wave dispersion and attenuation between cracks. In two complex extended geometric models, precise 3D numerical solutions were used to validate the results derived from the isotropic dual crack squirt flow analytical model, the P-wave modulus prediction error < 1% compared to numerical models. This study can be used for seismic data interpretation in fractured carbonate reservoirs. Full article

In the Southeastern Ordos Basin, the Chang 2 low-permeability sandstone reservoir of the Triassic Yanchang Formation is a typical heterogeneous reservoir. Quantitatively characterizing and analyzing its complex pore throat structure has become crucial for enhancing storage and production in the study area. The pore throat structure is a key factor influencing reservoir properties. To achieve this, a comprehensive suite of analytical techniques was employed, including cast thin section (CTS), scanning electron microscopy (SEM), cathodoluminescence (CL), X-ray diffraction (XRD), and mercury intrusion capillary pressure (MICP). This study quantitatively characterizes the pore size distribution of reservoirs in the Southeast Ordos Basin. Based on fractal theory, it clarifies the complexity of the pore throat structure and the degree of microscopic heterogeneity at different scales. Finally, this study reveals the correlation between fractal dimensions and storage and permeability capacities and analyzes the controlling factors. The findings indicate that the predominant lithotype in the study area is fine-grained feldspar sandstone, which develops pore types such as intergranular pores, dissolution pores, and microfractures. Based on the shapes of mercury injection curves and pore throat structural parameters, and in conjunction with SEM images, the samples are categorized into three types. Type I samples exhibit good pore throat connectivity and are characterized by a lattice model. Type II samples are characterized by a tubular pore throat model. Type III samples have poor pore throat connectivity and are characterized by an isolated model. The pore throat network of low-permeability sandstone is primarily composed of micropores (pore throat radius r < 0.1 μm), mesopores (0.1 < r < 1.0 μm), and macropores (r > 1.0 μm). The complexity of the reservoir pore throat structure was quantitatively characterized by fractal theory. The total fractal dimension (D) of all the samples is between 2 and 3, which indicates that the reservoir has capillary fractal characteristics. The average fractal dimension of micropores (D1) is 2.57, while that for mesopores (D2) and macropores (D3) is slightly higher, at an average of 2.68. This suggests that micropores have higher self-similarity and homogeneity. The fractal dimensions D1, D2, and D3 of the three types of reservoirs all exhibit a negative correlation with porosity and permeability. This shows that the more complex the pore throat structure is, the worse the storage and seepage capacity of the reservoir. For type I samples, the correlation of D3 with pore throat structural parameters such as entry pressure, skewness, and maximum mercury saturation is better than that of D2 and D1. For type II and type III samples, D2 shows a significant correlation with pore throat structural parameters. This indicates that the heterogeneity and complexity of mesopores are key factors influencing the pore throat structure of poor-quality reservoirs. Different mineral compositions have varying effects on the fractal characteristics of pore structures. Quartz, feldspar, and clay exert both negative and positive dual impacts on reservoir quality by altering the pore throat structure and the diagenetic processes. The mineral content exhibits a complex quadratic relationship with the fractal dimension. Moreover, micropores are more significantly influenced by the mineral content. The study of the relationship between the fractal dimension and physical properties, pore throat structural parameters, and mineral composition can improve the understanding of the reservoir quality of low-permeability reservoirs. This provides a theoretical basis for exploration and improving the recovery rate in the study area. Full article

Soil hydraulic properties are mainly governed by the soil’s heterogeneity, anisotropy, and discontinuous structural characteristics, primarily when connected soil macropores characterize the structures. Therefore, researchers must document reliable hydrological models to elucidate how the soil medium affects the movement of soil water. This study, utilizing a field-scale staining tracer test, distinguishes between matrix flow and preferential flow areas in the seepage field of Xi’an loess. The Xi’an loess’s soil water characteristic curve (SWCC) was explored through field investigations and laboratory analyses. A dual-permeability model that couples matrix and macropore flow was developed using the Hydrus-2D model, enabling simulations of water migration under varying initial soil water content, rainfall intensity, and crack width. The results showed that (1) The SWCC of macropores in the preferential flow area exhibits a bimodal distribution, and the Fredlund & Xing model is applied for sectional fitting to obtain the corresponding soil water characteristic parameters. (2) Initial soil water content and rainfall intensity significantly influence water distribution, while crack width has a relatively minor effect. (3) The cumulative flux under the preferential flow is significantly higher than in the matrix area, and the wetting front depth increases with higher initial water content and rainfall intensity. This study reveals the key characteristics of preferential flow and moisture migration in the matrix zone and their influencing factors in loess. It constructs a two-domain infiltration model by integrating loess’s diverse structural characteristics and pore morphology. This model provides a theoretical basis and technical support for simulating preferential flow and studying the moisture dynamics of loess profiles. Full article

Under the background of the “dual carbon” target, exploring the pathway of efficient geological storage and high energy utilization of CO₂ is a hot issue in CO₂ emission reduction research. Under the coupling effect of high geopathic stress in deep rock layers and thermal stress generated during the geological sequestration of CO₂, CO₂ infiltration into coal rock changes the ambient temperature around the rock, while thermal diffusion effects cause damage to the rock and influence fracture expansion. In the present study, CO₂-water–rock coupling test system and characterization of fissure surface roughness were conducted to analyze the rock’s mechanical properties, damage, and fracture evolution. Modeling of the equivalent fissure was employed to reveal the heat transfer mechanism between the rock matrix and CO₂. The results obtained illustrate that the rock samples coupled with CO₂ exhibited remarkable changes in mechanical properties. These changes include an increase in the number of pores, enhanced inter-pore connectivity, and a planar type of surface roughness in the fissures, ultimately resulting in an increase in conductivity. Conversely, the remaining rock samples displayed poor mechanical properties and surface fracture connectivity. As pressure decreased, the heat transfer coefficient decreased from 86.9 W/m²·K to 57.5 W/m²·K, accompanied by a temperature drop from 33.6 °C to 30.6 °C, demonstrating a proportional relationship between pressure and the heat transfer coefficient. Furthermore, the flow rate gradually increased with the rise in CO₂ pressure, indicating denser flow lines with faster flow rates. At 15 MPa, CO₂ exhibits enhanced mobility. Full article

Based on the statistical self-similar fractal characteristics of the microstructure of porous media, the total flow rate and permeability of Newtonian fluids in the rough fracture network and rough matrix pores are derived, respectively. According to the connection structure between fractures and pores, the permeability analysis model of fluids in a matrix-embedded fracture network is established. The comparison between the predicted values of the model and the experimental data shows that the predicted values of the permeability of the rough fracture network and the rough matrix pores decrease with the increase in the relative roughness of the fractures and matrix pores, and are lower than the experimental data. Meanwhile, the predicted total flow rate of a rough fractured dual porous media is lower than that of a smooth fractal model and experimental data. In addition, it is also found that the larger the average inclination angle and the relative roughness of the fracture network, the smaller the permeability of the fractured dual porous media, and the relative roughness of the fracture network has a far greater influence on fluid permeability in the fractured dual porous media than the relative roughness of the matrix pores. Full article

The study of unconventional reservoirs has gained increasing attention with the deepening of exploration and development especially in deep-buried tight sandstone reservoirs. We could not obtain the accurate elastic parameters of reservoirs using the conventional rock physics model, since tight sandstone reservoirs have the characteristics of strong heterogeneity, complex lithology and storage space. In order to better describe tight sandstone reservoirs, we improved the traditional tight sandstone rock physics model by combining the dual-connected pore model and the linear slip model. Since the combined modeling process subtly considers four characteristics including the diversity of tight sandstone matrix minerals, the irregularities of pores structure, the connectivity between pores, and the anisotropy caused by fractures, multiple reservoir characteristic parameters can be derived from the limited logging information by the improved model. These reservoir characteristic parameters could account for the difference of diagenesis, which are useful to distinguish different pore types and eliminate ineffective reservoirs. The practical application shows that the improved model can extract microscopic reservoir information hidden in the logging data more effectively than the traditional model. It provides a reliable tool for identifying effective reservoirs in tight sandstone. Full article

The gas permeability of a porous material is a key property determining the impact of the material in an application such as filter/separation techniques. In the present study, aerogels of cellulose scaffolds were designed with a dual pore space system consisting of macropores with cell walls composing of mesopores and a nanofibrillar network. The gas permeability properties of these dual porous materials were compared with classical cellulose aerogels. Emulsifying the oil droplets in the hot salt–hydrate melt with a fixed amount of cellulose was performed in the presence of surfactants. The surfactants varied in physical, chemical and structural properties and a range of hydrophilic–lipophilic balance (HLB) values, 13.5 to 18. A wide range of hierarchical dual pore space systems were produced and analysed using nitrogen adsorption–desorption analysis and scanning electron microscopy. The microstructures of the dual pore system of aerogels were quantitatively characterized using image analysis methods. The gas permeability was measured and discussed with respect to the well-known model of Carman–Kozeny for open porous materials. The gas permeability values implied that the kind of the macropore channel’s size, shape, their connectivity through the neck parts and the mesoporous structures on the cell walls are significantly controlling the flow resistance of air. Adaption of this new design route for cellulose-based aerogels can be suitable for advanced filters/membranes production and also biological or catalytic supporting materials since the emulsion template method allows the tailoring of the gas permeability while the nanopores of the cell walls can act simultaneously as absorbers. Full article