Search Results (1,817)

Shale oil is a vital strategic resource in China. Developing shale oil using CO₂ not only enhances oil recovery but also contributes to achieving Chinese “dual carbon” goals. Given the challenges of insufficient number of fractures, inadequate vertical stimulation volume, and poor reservoir mobility associated with horizontal well fracturing, this study proposes a method for CO₂ flooding based on radial borehole fracturing in a single well to achieve long-term carbon sequestration. To this end, a multi-component numerical model is built to analyze the production capacity of radial borehole fracturing. This study analyzed the impacts of non-Darcy flow, diffusion, and adsorption mechanisms on CO₂ migration and sequestration. It also compared the applicability of continuous CO₂ flooding and CO₂ huff-and-puff under different matrix permeabilities. The results indicate that (1) CO₂ flooding using radial borehole fracturing can achieve long-term oil production and carbon sequestration. (2) Under low permeability conditions, the liquid non-Darcy effect retards the flow of oil and CO₂, while diffusion and adsorption facilitate CO₂ sequestration in the reservoir. The impact on carbon sequestration is ranked as follows: non-Darcy effect > adsorption > diffusion. (3) High-permeability reservoirs are more suitable for carbon sequestration and should utilize continuous CO₂ flooding. For low-permeability reservoirs (<0.001 mD), huff-and-puff should be employed to mobilize the reservoir around fractures and achieve carbon sequestration. The findings of this study are expected to provide new methods and a theoretical basis for efficient and economical carbon sequestration in shale oil reservoirs. Full article

Efficient development of bottom-water reservoirs is seriously affected by low recovery due to the rapid rise in water content in horizontal wells. In order to cope with this problem, a number of water control devices (including ICD and AICD) have been installed in horizontal wellbores in recent years. These are used in conjunction with packers to achieve the effect of balancing the fluid production profile and controlling water in sections. As an alternative to packers, the method of horizontal-well gravel packing has been widely used. This technique utilizes the permeability of gravel to block axial flow in the annulus of the horizontal wellbore, and uses water control devices for the purpose of sectional flow restriction. In this paper, a coupled method of numerical simulation of the production dynamics of gravel-packed water-control completions in horizontal wells in bottom-water reservoirs is proposed, which can consider multi-phase flows in porous media, in layers packed with gravel particles, and in water control devices simultaneously. In order to obtain the blocking capacity of the layer packed with gravel, we built an experimental setup of the same size as the borehole and annulus of a horizontal well, tested the permeability of the layer using Darcy’s law, and applied it to a coupled numerical simulation model. After comparison with actual well examples, it was proved that the coupled numerical simulation model has good accuracy, and can be used to carry out production predictions for gravel-packed water-control completions in horizontal wells in bottom-water reservoirs. The study also provides field engineers with a design tool for parameter optimization using a different water control method. Full article

Hot-point thermal drills are among the simplest and most compact tools for drilling boreholes in ice by melting. They are widely used in glaciological and geophysical research, including subsurface access on Earth and planetary missions. This study focuses on electrically heated hot-point drills. It presents a comparative review of four analytical models commonly used to describe thermal penetration into ice. Our theoretical processing and computation allow for the analysis and optimization of the drilling performance of thermal drill heads. The predictive accuracy of the adapted model was evaluated through comparison with experimental data obtained using the RECAS-200 thermal sonde. Based on the analysis of various sources and calculations using the modified model, a set of recommendations is proposed for early-stage estimation of drilling parameters and assessment of thermal drilling efficiency in the design of hot-point drills for autonomous and resource-constrained missions. Full article

In the context where the surrounding rock of deep coal mine roadways is in a complex mechanical environment of “three highs and one disturbance”, mining disturbances are prone to cause instability and damage to the roadways, and the severe deformation of the south wing main roadway caused by mining disturbances in the 2404 working face of a certain mine in the Jiaoping Mining Area restricts safe production. In order to reduce the deformation and damage of the south wing main roadway affected by long-term dynamic pressure, this study proposes a determination method of key rock strata for top cutting pressure relief and the pressure-relief method along the stress transmission path of the south wing main roadway. It completes the design and field test of the hydraulic fracturing scheme for the hard roof of the 2404 transportation roadway, and evaluates the pressure-relief effect through means such as pressure curves, mine pressure manifestation laws, and borehole observation. The results show that hydraulic fracturing significantly weakens the strength of the roof rock strata, forms through cracks between the pressure-relief holes, reduces the average working resistance of the support by 18% after fracturing, and reduces the average pressure step distance of the roof by 34%. During the mining process, the stress variation range of the coal pillar is small, and there is no obvious deformation or damage to the surrounding rock and support structure of the south wing main roadway. It effectively cuts off the stress transmission path of the hard roof and controls the deformation of the roadway, providing technical support for the control of surrounding rock in deep dynamic pressure roadways. Full article

Over the past decade, the application of Tunnel Boring Machines (TBMs) in tunnel construction has increased significantly. During the construction process, numerous unfavorable geological structures, especially water-conducting structures, are encountered. The commonly used Tunnel Seismic Prediction (TSP) method often cannot accurately interpret water-conducting features, while resistivity methods are sensitive to low-resistivity bodies, which are frequently associated with water channels. Due to the limited space and the surrounding pipe lining near the tunnel face, as well as the difficulty in drilling boreholes under TBM construction conditions, this paper proposes a novel electrode arrangement method that replaces rigid electrodes with flexible electrodes installed on the sidewalls. This approach overcomes the difficulty of deploying traditional electrodes downward in TBM tunnels. A simple direct current resistivity configuration was employed for field testing during the construction of the Guiyang Metro Line 3 TBM tunnel, and the results were compared with those from the Tunnel Seismic Prediction (TSP) method. The experimental results demonstrate that the improved DC resistivity method achieves high detection accuracy for water-conducting structures within a range of 30 m, showing strong consistency with the TSP detection results. This validates the feasibility and accuracy of the method, effectively addressing the challenges associated with traditional electrode deployment in TBM tunnels while compensating for the limited response of seismic methods to water-bearing structures. However, the effectiveness near the tunnel face remains suboptimal, with insufficient current distribution—an area requiring improvement, potentially by increasing forward current supply or further optimizing the electrode layout. Additionally, the study highlights the limitations of relying solely on a single advanced prospecting method. It suggests adopting an integrated approach, primarily based on seismic methods supplemented by electrical methods, to enable joint detection and interpretation, thereby minimizing the risk of accidents during construction. Full article

In extended-reach wells, cuttings bed formation in high-deviation sections presents a major challenge for hole cleaning and borehole stability. This study analyzes the morphological and mechanical behavior of cuttings beds, focusing on particle size distribution and repose angle as key indicators of accumulation behavior. The modeling approach considers dominant interparticle forces, including buoyancy and cohesion, while neglecting secondary microscale forces for clarity. A theoretical model is developed to predict repose angles under both rolling and sliding regimes and is calibrated through laboratory-scale experiments using simulated drilling fluid with field-representative rheological properties. Results show that cohesive effects are negligible when cuttings are of similar size but exhibit higher densities. Laboratory measurements reveal that the repose angle of cuttings beds varies between 23.9° and 31.7°, with increasing polyacrylamide (PAM) concentration and particle size contributing to steeper repose angles. Additionally, the rolling repose angle is found to be relatively stable, ranging from 25° to 30°, regardless of fluid or particle property variations. These findings provide a predictive framework and practical guidelines for optimizing hole cleaning strategies and designing more effective models in extended-reach drilling. Full article

The Variscan and Mesozoic basement are covered by Neogene and Quaternary sediments belonging to the Guadalquivir foreland Basin (southern Spain). This study explores the subsurface of the northern margin of its westernmost sector using the HVSR method, recording seismic noise at 334 stations between the mouths of the Guadiana and the Guadalquivir rivers, near Doñana National Park. Fundamental frequency and basement measurements enabled the estimation of an empirical formula for basement depth: h = 80.16·f₀^−1.48. Five distinct HVSR responses were obtained: (a) low-frequency peaks, indicating deep substratum; (b) high-frequency peaks, shallow bedrock; (c) broad peaks, potential critical zones (3D-2D effects, suggesting faults); (d) double peaks (marshlands); and (e) no peaks, near-outcropping bedrock. The soil fundamental frequencies range from 0.23 to 18 Hz, with bedrock depth ranges from 1 to 5 m in the northwest to over 600 m in the southeast. Borehole data correlate strongly with HVSR-derived results, with typical discrepancies of only a few tens of meters, likely due to the presence of non-geological basement acting as a mechanical basement. Although the possibility of ancient fluvial terraces of the Guadalquivir River contributing to abrupt slope changes is considered, H/V spectra with broad peaks suggest tectonic origins. This study presents the first regional three-dimensional model of the basin basement over an area exceeding 2300 km², revealing a horst-and-graben system formed by foreland deformation linked to the westward advance of the Rif-Betic orogenic front. Full article

To address the challenge of determining the borehole layout scheme in the practical application of high-pressure gas expansion rock breaking, this study takes the excavation of the safety passage at Kaixuan Road Station on the North Extension Line 2 of Chongqing Metro Line 18 as the engineering background. The rock-breaking capacity was evaluated by analyzing the damaged zone volume caused by gas expansion using FLAC3D 6.0 numerical simulation software, and vibration monitoring was conducted for the historical buildings on the surface. This study revealed the following: (1) When the borehole depth is 1.2 m and the charge length is 0.6 m, the optimal angle is 70°, with the optimal vertical and horizontal spacing between holes being 1200 mm and 2000 mm, respectively. (2) The numerical simulations indicated that by adjusting the charge density, the optimized sandstone borehole network parameters could be applied to mudstone strata, and the rock-breaking effect was similar. The difference in the volume of the damaged zones obtained in the two strata was less than 3%. (3) The vibration analysis demonstrated that the peak particle velocity generated by high-pressure gas expansion rock fracturing at the ancient building directly above was 0.06316 cm/s, which was lower than the threshold value of 0.1 cm/s and approximately 67.95% lower than that of explosive blasting. Furthermore, when the tunnel depth exceeded 29 m, the vibration velocity of surface structures remained within the safety range. The results verified the feasibility of applying the same borehole network parameters to different strata, providing theoretical support for the practical application of high-pressure gas expansion rock fracturing technology in engineering projects. Full article

Despite its potential danger, site amplification effects are often neglected in seismic hazard analysis. Appropriate amplification factors can be determined from shear wave velocity, but impracticality in in situ measurements leads to reliance on regional correlation with geotechnical parameters such as SPT N-value. Modified power law and logarithmic equations were derived from past correlation studies to determine V_s30 values for each borehole location in the City of Manila. V_s30 profiles were spatially interpolated using the inverse-distance weighted and thin-spline methods to approximate the variation in shear wave velocities and add more detail to the existing contour map for soil profile classification across Metro Manila. Statistical analysis of the interpolated models indicates percentage differences ranging from 0 to 10% with a normalized root mean square error of nearly 5%. Generated equations and geospatial models in the study may be used as a basis for a seismic microzonation model for Metro Manila, considering other geological and geophysical layers. Full article

This study presents an integrated geomechanical modeling framework for predicting multi-scale fracture networks and their activity in the Longmaxi Formation shale reservoir, northern Luzhou region, southeastern Sichuan Basin—an area shaped by complex, multi-phase tectonic deformation that poses significant challenges for resource prospecting. The workflow begins with quantitative characterization of key mechanical parameters, including uniaxial compressive strength, Young’s modulus, Poisson’s ratio, and tensile strength, obtained from core experiments and log-based inversion. These parameters form the foundation for multi-phase finite element simulations that reconstruct paleo- and present-day stress fields associated with the Indosinian (NW–SE compression), Yanshanian (NWW–SEE compression), and Himalayan (near W–E compression) deformation phases. Optimized Mohr–Coulomb and tensile failure criteria, coupled with a multi-phase stress superposition algorithm, enable quantitative prediction of fracture density, aperture, and orientation through successive tectonic cycles. The results reveal that the Longmaxi Formation’s high brittleness and lithological heterogeneity interact with evolving stress regimes to produce fracture systems that are strongly anisotropic and phase-dependent: initial NE–SW-oriented domains established during the Indosinian phase were intensified during Yanshanian reactivation, while Himalayan uplift induced regional stress attenuation with limited new fracture formation. The cumulative stress effects yield fracture networks concentrated along NE–SW fold axes, fault zones, and intersection zones. By integrating geomechanical predictions with seismic attributes and borehole observations, the study constructs a discrete fracture network that captures both large-scale tectonic fractures and small-scale features beyond seismic resolution. Fracture activity is further assessed using friction coefficient analysis, delineating zones of high activity along fold–fault intersections and stress concentration areas. This principle-driven approach demonstrates how mechanical characterization, stress field evolution, and fracture mechanics can be combined into a unified predictive tool, offering a transferable methodology for structurally complex, multi-deformation reservoirs. Beyond its relevance to shale gas development, the framework exemplifies how advanced geomechanical modeling can enhance resource prospecting efficiency and accuracy in diverse geological settings. Full article

Aiming at the problems of borehole shrinkage and pipe sticking caused by creep in salt-gypsum rock formations during deep well drilling, multi-field coupling creep experiments on deep salt-bearing gypsum mudstone were carried out. Furthermore, a nonlinear creep constitutive model was constructed based on the Drucker–Prager criterion, and the critical value of liquid column pressure for borehole shrinkage was determined through numerical simulation. Experiments show that at 140 °C, salt-gypsum rock is mainly subjected to brittle failure with single shear fracture, while at 180 °C, multiple sets of cross-cutting shear bands form, shifting to plastic flow-dominated composite failure. The coupling effect of confining pressure and deviatoric stress is temperature-dependent; the critical deviatoric stress is independent of confining pressure at 140 °C, but decreases significantly with increasing confining pressure at 180 °C, revealing that salt-gypsum rock is more prone to plastic flow under high temperatures and confining pressure. The creep constitutive equation was further determined, and fitting parameters show that the stress exponent m = 2–5 and the time exponent n decrease linearly with the increase in deviatoric stress, and the model can accurately describe the characteristics of three-stage creep. The numerical simulation found that there is a nonlinear relationship between the drilling fluid density and borehole shrinkage; the shrinkage rate exceeds 1.47% when the density is ≤2.0 g/cm³, and the expansion amount is >1.0 mm when ≥2.4 g/cm³. The critical safe density range is 2.1–2.3 g/cm³, which is consistent with the field data in the Bayan area. The research results provide an experimental basis and quantitative method for the dynamic regulation of drilling fluid density in deep gypsum rock formations, and have engineering guiding significance for preventing borehole wall instability. Full article

Real-time monitoring of the pile foundation pouring status is the key to ensuring the quality and reliability of cast-in-place bored pile foundation structures. In response to the technical challenge of difficult real-time monitoring and accurate evaluation of pile top morphology during concrete pouring, this paper proposes a method for detecting the cast-in-place bored pile top surface based on full waveform inversion. Firstly, a coupling equation between concrete sound waves and viscoelastic waves inside the borehole is constructed, forming a full waveform inversion method that considers multiple parameters of the complex environment inside the borehole. Subsequently, a pile top flatness factor that simultaneously considers the elevation and undulation characteristics of the pile top is constructed to achieve a comprehensive evaluation of the elevation between the center position and the center peripheral position of the bored pile top. Finally, the feasibility and accuracy of the proposed method are verified through indoor experiments. The results indicate that the detection method proposed in this article can not only accurately reflect the actual elevation of the pile top, ensuring the accuracy of the measurement data, but also achieve a comprehensive evaluation of the quality of the pile top considering the differences in the center and edge positions of the pile top, which can provide a new analysis method for quality control of bored piles. Full article

This study presents a novel approach to the parametrization of 3D PETRO FACIES and SEISMO FACIES using supervised and unsupervised learning, supported by a coherent structural and stratigraphic framework, to enhance understanding of the presence of hydrocarbons in the Dzików–Uszkowce region. The prediction relies on selected seismic attributes and well logging data, which are essential in hydrocarbon exploration. Three-dimensional seismic data, a crucial source of information, reflect the propagation velocity of elastic waves influenced by lithological formations and reservoir fluids. However, seismic response similarities complicate accurate seismic image interpretation. Three-dimensional seismic data were also used to build a structural–stratigraphic model that partitions the study area into coeval strata, enabling spatial analysis of the machine learning results. In the 3D seismic model, PETRO FACIES classification achieved an overall accuracy of 80% (SD = 0.01), effectively distinguishing sandstone- and mudstone-dominated facies (RT1–RT4) with F1 scores between 0.65 and 0.85. RESERVOIR FACIES prediction, covering seven hydrocarbon system classes, reached an accuracy of 70% (SD = 0.01). However, class-level performance varied substantially. Non-productive zones such as HNF (No Flow) were identified with high precision (0.82) and recall (0.84, F1 = 0.83), while mixed-saturation facies (HWGS, BSWGS) showed moderate performance (F1 = 0.74–0.81). In contrast, gas-saturated classes (BSGS and HGS) suffered from extremely low F1 scores (0.08 and 0.12, respectively), with recalls as low as 5–7%, highlighting the model’s difficulty in discriminating these units from water-saturated or mixed facies due to overlapping seismic responses and limited training data for gas-rich intervals. To enhance reservoir characterization, SEISMO FACIES analysis identified 12 distinct seismic facies using key attributes. An additional facies (facies 13) was defined to characterize gas-saturated sandstones with high reservoir quality and accumulation potential. Refinements were performed using borehole data on hydrocarbon-bearing zones and clay volume (VCL), applying a 0.3 VCL cutoff and filtering specific facies to isolate zones with confirmed gas presence. The same approach was applied to PETRO FACIES and a new RT facie was extracted. This integrated approach improved mapping of lithological variability and hydrocarbon saturation in complex geological settings. The results were validated against two blind wells that were excluded from the machine learning process. Knowledge of the presence of gas in well N-1 and its absence in well D-24 guided verification of the models within the structural–stratigraphic framework. Full article

The multi-branch horizontal well for coalbed methane (CBM) is a core technical means to achieve efficient CBM extraction, and its productivity is jointly restricted by geological and engineering factors. To accurately grasp the main controlling factors of the productivity of multi-branch horizontal wells and provide a scientific basis for the optimized design of CBM development, this study takes Well W1 in the Wenjiaba Coal Mine of the Zhina Coalfield in Guizhou, China, as an engineering example and comprehensively uses three-dimensional geological modeling and reservoir numerical simulation methods to systematically explore the key influencing factors of the productivity of multi-branch horizontal wells for CBM. This study shows that coal seam thickness, permeability, gas content, and branch borehole size are positively correlated with the productivity of multi-branch horizontal wells. With the simulation time set to 1500 days, when the coal seam thickness increases from 1.5 m to 4 m, the cumulative gas production increases by 166%; when the permeability increases from 0.2 mD to 0.8 mD, the cumulative gas production increases by 123%; when the coal seam gas content increases from 8 m³/t to 18 m³/t, the cumulative gas production increases by 543%; and when the wellbore size increases from 114.3 mm to 177.8 mm, the cumulative gas production increases by 8%. However, the impact of branch angle and spacing on productivity exhibits complex nonlinear trends: when the branch angle is in the range of 15–30°, the cumulative gas production shows an upward trend during the simulation period, while in the range of 30–75°, the cumulative gas production decreases during the simulation period; the cumulative gas production with branch spacing of 100 m and 150 m is significantly higher than that with spacing of 50 m and 200 m. Quantitative analysis through sensitivity coefficients reveals that the coal seam gas content is the most important geological influencing factor, with a sensitivity coefficient of 2.5952; a branch angle of 30° and a branch spacing of 100 m are the optimal engineering conditions for improving productivity, with sensitivity coefficients of 0.2875 and 0.273, respectively. The research results clarify the action mechanism of geological and engineering factors on the productivity of multi-branch horizontal wells for CBM, providing a theoretical basis for the optimized deployment of well locations, wellbore structure, and drilling trajectory design of multi-branch horizontal wells for CBM in areas with similar geological conditions. Full article

This study investigates the uplift and exhumation history of the southern segment of the western margin of the Ordos Basin using low-temperature thermochronology, including zircon (U-Th)/He (ZHe), apatite fission-track (AFT), and apatite (U-Th)/He (AHe) data, combined with thermal history modeling. The study area exhibits a complex structural framework shaped by multiple deformation events, leading to the formation of extensively developed fault systems. Such faulting can adversely affect hydrocarbon preservation. To better constrain the timing of fault reactivation in this area, we carried out an integrated study involving low-temperature thermochronology and burial history modeling. The results reveal a complex, multi-phase thermal-tectonic evolution since the Late Paleozoic. The ZHe ages (291–410 Ma) indicate deep burial and heating related to Late Devonian–Early Permian tectonism and basin sedimentation, reflecting early orogenic activity along the western North China Craton. During the Late Jurassic to Early Cretaceous (165–120 Ma), the study area experienced widespread and differential uplift and cooling, controlled by the Yanshanian Orogeny. Samples on the western side of the fault show earlier and more rapid cooling than those on the eastern side, suggesting a fault-controlled, basinward-propagating exhumation pattern. The cooling period indicated by AHe data and thermal models reflects the Cenozoic uplift, likely induced by far-field compression from the rising northeastern Tibetan Plateau. These findings emphasize the critical role of inherited faults not only as thermal-tectonic boundaries during the Mesozoic but also as a pathway for hydrocarbon migration. Meanwhile, thermal history models based on borehole data further reveal that the study area underwent prolonged burial and heating during the Mesozoic, reaching peak temperatures for hydrocarbon generation in the Late Jurassic. The timing of major cooling events corresponds to the main stages of hydrocarbon expulsion and migration. In particular, the differential uplift since the Mesozoic created structural traps and migration pathways that likely facilitated hydrocarbon accumulation along the western fault zones. The spatial and temporal differences among the samples underscore the structural segmentation and dynamic response of the continental interior to both regional and far-field tectonic forces, while also providing crucial constraints on the petroleum system evolution in this tectonically complex region. Full article