Deep saline aquifers,characterized by wide distribution,large storage capacity,and low competition with oil and gas resources,are widely regarded as ideal media for geological CO2 storage.This study elucidates the dissolution and diffusion behavior of CO2 in real formation water under complex temperature-pressure conditions is of great significance for improving storage efficiency and ensuring long-term safety.Taking the Jurassic Sangonghe Formation in the Junggar Basin as the research object,a NaHCO3 -type formation water model containing Na+,K+,Ca2+,Mg2+and ions was constructed based on regional geological and hydrochemical data.Molecular dynamics simulations were then performed to systematically investigate the dissolution behavior,density distribution,intermolecular interactions,and diffusion mechanisms of CO2 in formation water under varying temperature and pressure conditions.The simulation results indicate that under isothermal conditions,pressure is the dominant factor controlling CO2 occurrence and dissolution.Low pressure favors rapid dissolution of CO2,moderate pressure enables efficient utilization of storage capacity,and high pressure helps maintain long-term system stability.Under isobaric conditions,elevated temperature markedly enhances CO2 solubility by weakening hydrogen bonding and intensifying molecular thermal motion,thereby promoting uniform dispersion of CO2 molecules and the formation of stable solvation structures.Under coupled temperature-pressure conditions,the CO2 adsorption amount increases significantly with burial depth in the low-pressure interval(approximately 1000～4000 m),indicating a strong promotion of dissolution by pressure increase;in the high-pressure interval(>4000 m),the adsorption continues to increase but with a decreasing rate,reflecting that temperature-induced desorption gradually offsets the promoting effect of pressure.In addition,the diffusion coefficient shows a stratified trend:elevated temperature in shallow zones promotes CO2 molecular migration,whereas high pressure in deep zones significantly suppresses diffusion,with a relatively small overall variation.Comprehensive analysis suggests that the depth interval of 1000～4000 m is the most suitable range for CO2 geological storage,as it ensures both high dissolution efficiency and long-term stability.This study elucidates the microscopic mechanisms of CO2 dissolution and diffusion in formation water under complex temperature-pressure conditions,deepens the understanding of CO2 fluid occurrence and migration in deep geological environments,and provides scientific guidance for evaluating storage potential,selecting suitable storage sites,and designing injection strategies,offering valuable references for CCUS engineering practice.
The deep coalbed methane(CBM)resources(buried deeper than 1500 m)in North China exceed 30 trillion cubic meters,with significant breakthroughs in exploration,making it a new frontier for natural gas production growth.However,it faces key issues,including complex preservation conditions,unclear controls on enrichment and high productivity,and large production variations.In order to clarify the control factors of preservation conditions of deep CBM,the coal quality,lithology combination,and structural preservation characteristics of typical deep CBM exploration wells in North China are systematically analyzed with multidisciplinary analysis methods of geology,geochemistry,and geophysics.This study reveals that the differ-ential preservation of deep CBM is controlled by the dynamic coupling mechanism of adsorption self-sealing,physical property sealing,and structural preservation system:(1)Favorable coal quality is the basis of strong adsorption.Coal with low ash content and a high evolution degree is characterized by a large Langmuir volume,a great critical depth,and strong self-sealing ability.(2)Tightly lithology combination is a barrier to deep free gas dissipation.Limestone and mudstone exhibit low porosity,a small throat radius,and high breakthrough pressure,resulting in good physical sealing conditions and a high total retained gas content.(3)Continuous and stable structural preservation is the key to free gas enrichment.L ate-stage uplift with low amplitude and weak tectonic activity is conducive to free gas accumulation,resulting in a high-pressure coefficient.In summary,areas characterized by deep burial,low-ash coal,limestone/mudstone roof rocks,and structural stability are favorable for deep CBM preservation.The study of differential preservation of deep CBM deepens the understanding of enrichment and high productivity,and provides a theoretical basis for optimizing favorable exploration and development targets.
To systematically review the research progress of intelligent fracturing technology in unconventional oil and gas reservoirs,by integrating machine learning algorithms(e.g.,random forest and gradient boosting),the embedded discrete fracture model(EDFM),fiber-optic/microseismic monitoring technologies,and smart equipment,this study analyzes technological breakthroughs and application cases in key aspects such as reservoir parameter prediction,fracture propagation simulation,and real-time control.Results demonstrate that the random forest and gradient boosting models demonstrated optimal performance in permeability prediction(R²>0.92).The EDFM-AI workflow reduces fracture parameter calibration errors to 6.8%.Fiber-optic monitoring technology achieves sub-millimeter resolution in fracture detection.The intelligent early-warning system predicts sand plugging risks 30 seconds in advance(accuracy above 85%).Intelligent fracturing technology significantly enhances res-ervoir modification efficiency and production,but challenges such as small-sample generalization,multi-source data fusion,and equipment autonomy require further resolution.Establishing a closed-loop technical system encompassing"reservoir evaluation,optimized design,fracture monitoring,anomaly prediction,and equipment control",and promote the development of intelligent and precise fracturing processes.
Reflection waveform inversion(RWI)exploits reflected-wave information in seismic data to update the deep back-ground velocity model.By alternately inverting for the migration and tomographic components,RWI not only improves the accu-racy of deep velocity model updates but also alleviates the cycle-skipping problem to a certain degree.However,RWI generally requires seismic data with a high signal-to-noise ratio(SNR)and has so far achieved its most successful applications in marine environments.In contrast,land seismic data are often degraded by poor receiver coupling,rugged topography,environmental noise,and strong surface-wave interference,making it difficult to acquire continuous and high-SNR reflection waveforms,which severely limits the applicability of RWI to land data.To address these challenges,this study employs Kirchhoff pre-stack time migration to identify characteristic reflection layer and extract their corresponding common-image gathers(CIGs).The extracted events are then reverse migrated to reconstruct reflected-wave data with enhanced SNR.The reconstructed data are subsequently incorporated into RWI and validated using both synthetic and field data examples.The results demonstrate that the proposed method significantly improves the accuracy of deep background velocity model updates.Furthermore,the strong consistency between the migrated images and the corresponding CIGs confirms the reliability and effectiveness of the reconstructed reflection data for RWI applications.Overall,this method offers a new feasible solution for applying RWI to land seismic data.
The Linxing gas field was selected as the research object,where weak bedding planes represent typical features and significantly influence hydraulic fracture propagation.This study provides valuable insights on hydraulic fracture propagation in bedded shale formations and offers guidance for optimizing fracturing techniques.The characteristics of shale featuring bedding planes were examined by utilizing rock mechanics experiments and direct shear tests.Considering the cementation strength and friction properties of bedding planes,a computational subroutine was developed to characterize the contact behavior for bedding planes.A 3D Finite Element Method-Cohesive Zone Model(FEM-CZM)has been established for multi-field coupling analysis of stress-damage-fluid flow,specifically incorporating bedding planes.This model incorporates a contact constitutive relationship that accounts for both friction and cementation strength of the bedding.A comprehensive and systematic quantitative analysis is conducted to investigate the influence of various factors on bedding shear slip and the propagation of hydraulic fractures.These factors include the initial opening of bedding fractures,friction coefficient,cementation strength,number of bedding planes surrounding the wellbore,and fracturing operation parameters.The results indicate that the presence of weakly bonded bedding planes leads to complex fracture propagation patterns involving both tensile and shear fractures.Bedding plane apertures serve as preferential flow pathways for fracturing fluid,significantly inhibiting fracture propagation.When the bedding aperture increases to 300 μm,the fractures are unable to cross bedding planes,which limits the fracture scale.Compared to the bonding strength,the bedding friction coefficient plays a more dominant role in determining whether fractures penetrate.Higher friction coefficients facilitate the penetration,regardless of whether the bedding planes are bonded or not.The penetration probability increases exponentially as the friction coefficient rises.In contrast,with lower friction coefficients and weakly bonded bedding planes,fractures are intercepted,while higher cementation strength allows for effective penetration.Furthermore,with a rise in the number of bedding planes,the shear fractures along these beddings expands considerably,which results in a more intricate fracture pattern.The shear failure of multiple bedding planes restricts the development of tensile-dominated fractures,which reduces the efficiency of reservoir stimulation.Optimizing fracturing fluid injection,increasing high-viscosity fracturing fluid volumes,and raising injection rates can enhance vertical fracture propagation and improve the stimulated reservoir area.Further validation of the influence of bedding planes on fracture propagation is provided by analyzing distributed temperature sensing(DTS)profiles,as well as the post-fracturing performance in Linxing.
