Buried coastal sandstones would be of high-quality hydrocarbon reservoirs.Controlled by deposition and diagenesis,coastal sandstones mixed with muddy and calcareous materials are usually low in porosity and permeabili...Buried coastal sandstones would be of high-quality hydrocarbon reservoirs.Controlled by deposition and diagenesis,coastal sandstones mixed with muddy and calcareous materials are usually low in porosity and permeability and small in layer thickness.These impermeable inte rlayers act as baffles and barriers between flow units and are crucial in hydrocarbon development.Donghe Sandstone in the Hade Oilfield of Tarim Basin,NW China,belongs to coastal clastic reservoirs of high oil productivity.Following nearly 30 years of development,the distribution of remaining hydrocarbon resources is affected by the muddy,calcareous,and marlaceous interlayers.Taking the Donghe Sandstone as an example,a quantitative recognition method of interlayers in coastal sandstone reservoirs is proposed in this paper.Based on cores from 26 wells,the sensitive conventional log curves of different interlayers,namely the natural gamma-ray(GR),density(DEN),compensated neutron(CNL),and acoustic(AC),are extracted by the Extreme Gradient Boosting(XGBoost).Multi-mineral model(MMM)is used to calculate continuous curves for muddy,sandy,and calcareous contents by the mentioned sensitive logs.A set of quantitative standard system is established for identifying muddy,calcareous,and marlaceous interlayers based on their respective contents.The types of inte rlayers are identified across all vertical wells.The interlayers exhibit lateral continuity at the top of each bed-set.Interlayers are currently more developed in the slope region than in the coastal region.Muddy and marlaceous interlayers are more developed at high relative sea-level,while calcareous interlayers are more developed at low relative sea-level.The extended interlayers at the top of BS6 lead to two different oil-water contacts in the Donghe Sandstone.The proposed quantitative recognition method for interlayers provides valuable insights into the exploitation potential of petroleum systems in the Donghe Sandstone of the Hade Oilfield.The flexible and easy-to-use method can be applied to other marine sandstone reservoirs or similar formations.展开更多
In cold regions,rock structures will be weakened by freeze-thaw cycles under various water immersion conditions.Determining how water immersion conditions impact rock deterioration under freeze-thaw cycles is critical...In cold regions,rock structures will be weakened by freeze-thaw cycles under various water immersion conditions.Determining how water immersion conditions impact rock deterioration under freeze-thaw cycles is critical to assess accurately the frost resistance of engineered rock.In this paper,freeze-thaw cycles(temperature range of-20℃-20℃)were performed on the sandstones in different water immersion conditions(fully,partially and non-immersed in water).Then,computed tomography(CT)tests were conducted on the sandstones when the freeze-thaw number reached 0,5,10,15,20 and 30.Next,the effects of water immersion conditions on the microstructure deterioration of sandstone under freezethaw cycles were evaluated using CT spatial imaging,porosity and damage factor.Finally,focusing on the partially immersed condition,the immersion volume rate was defined to understand the effects of immersion degree on the freeze-thaw damage of sandstone and to propose a damage model considering the freeze-thaw number and immersion degree.The results show that with increasing freeze-thaw number,the porosities and damage factors under fully and partially immersed conditions increase continuously,while those under non-immersed condition first increase and then remain approximately constant.The most severe freeze-thaw damage occurs in fully immersed condition,followed by partially immersed condition and finally non-immersed condition.Interestingly,the freeze-thaw number and the immersion volume rate both impact the microstructure deterioration of the partially immersed sandstone.For the same freeze-thaw number,the damage factor increases approximately linearly with increasing immersion volume rate,and the increasing immersion degree exacerbates the microstructure deterioration of sandstone.Moreover,the proposed model can effectively estimate the freeze-thaw damage of partially immersed sandstone with different immersion volume rates.展开更多
To investigate the effect of saturation on the storage-dissipation properties and failure characteristics of red sandstone,as well as the energy mechanism of rockburst prevention by water,a series of uniaxial compress...To investigate the effect of saturation on the storage-dissipation properties and failure characteristics of red sandstone,as well as the energy mechanism of rockburst prevention by water,a series of uniaxial compression and uniaxial loading–unloading tests were conducted under five saturation levels.The effect of saturation on the mechanical properties and elastic energy density was analyzed,and a method for obtaining peak energy density was proposed.The effect of saturation on the energy evolution was examined,and the energy mechanism of water in preventing rockburst was revealed.The results indicate that an increase in saturation of red sandstone decreases the input energy density,elastic energy density,dissipated energy density,peak strength and peak strain;the compaction phase of the stress–strain curve becomes shorter;the failure mode transitions from X-conjugate oblique shear to single oblique shear;the variation in the debris ejection trajectory is as follows:radiation→X-ray→oblique upward parabola→horizontal parabola→oblique downward parabola;the degree of failure intensity and fragmentation is decreased gradually.Elastic energy density is interconnected with both saturation and stress but independent of the loading path.Saturation exhibits a dual effect on the energy storage property,i.e.,increasing saturation increases the energy storage efficiency and reduces the energy storage capacity.The ratio of peak elastic energy density to peak input energy density remains constant irrespective of saturation levels.Water prevents rockburst by decreasing the energy storage capacity of surrounding rock,alleviating the stress of surrounding rock to reduce energy storage,and elevating the energy release threshold of high-energy surrounding rock.The findings of this study contribute to understanding the effect of water on rock failure from an energy perspective,as well as provide theoretical guidance for rockburst prevention by water in deep tunnels.展开更多
A novel fractional elastoplastic constitutive model is proposed to accurately characterize the deformation of sandstone under true-triaxial stress states.This model is founded on the yield function and the fractional ...A novel fractional elastoplastic constitutive model is proposed to accurately characterize the deformation of sandstone under true-triaxial stress states.This model is founded on the yield function and the fractional flow rule.The yield function includes parameters that govern the evolution of yield surface,enabling an accurate description of three-dimensional stress states.The direction of plastic flow is governed by the two different fractional orders,which are functions of the plastic internal variable.Additionally,a detailed process is proposed for identifying the yield function parameters and fractional orders.Subsequently,the relationship between the fractional order and the direction of plastic flow in the meridian and deviatoric planes is examined,characterized by the dilation angle and the plastic deflection angle,respectively.The non-orthogonal flow rule,also referred to as the fractional flow rule,allows for a border range of plastic deflection and dilation angles compared to the orthogonal flow rule,thereby significantly enhancing its applicability.The validity and accuracy of proposed model are verified by comparing the analytical solution of the constitutive model with the experimental data.A comparison between the non-orthogonal flow rule and orthogonal flow rule is conducted in both the deviatoric and meridian planes.The further comparison of the stress-strain curves for the non-orthogonal and orthogonal flow rules demonstrates the superiority of the fractional constitutive model.展开更多
The tight sandstone reservoirs in the first sub-member of Chang 7 member(Chang 71)of Triassic Yanchang Formation in the Jiyuan area,Ordos Basin,show significant variations in microscopic pore-throat structure(PTS)and ...The tight sandstone reservoirs in the first sub-member of Chang 7 member(Chang 71)of Triassic Yanchang Formation in the Jiyuan area,Ordos Basin,show significant variations in microscopic pore-throat structure(PTS)and fluid mobility due to the influences of the northeast and northwest dual provenance systems.This study performed multiple experimental analyses on nine samples from the area to determine the petrological and petrophysical properties,as well as the PTS characteristics of reservoirs in different provenance-controlled regions.On this basis,the pore-throat size distribution(PSD)obtained from high-pressure mercury injection(HPMI)was utilized to convert the NMR movable fluid T2spectrum,allowing for quantitative characterization of the full PSD and the occurrence characteristics of movable fluids.A systematic analysis was conducted on the primary controlling factors affecting fluid mobility in the reservoir.The results indicated that the lithology in the eastern and western regions is lithic arkose.The eastern sandstones,being farther from the provenance,exhibit higher contents of feldspar and lithic fragments,along with the development of more dissolution pores.The reservoir possesses good petrophysical properties,low displacement pressure,and high pore-throat connectivity and homogeneity,indicating strong fluid mobility.In contrast,the western sandstones,being nearer to the provenance,exhibit poor grain sorting,high contents of lithic fragments,strong compaction and cementation effects,resulting in poor petrophysical properties,and strong pore-throat heterogeneity,revealing weak fluid mobility.The range of full PSD in the eastern reservoir is wider than that in the western reservoir,with relatively well-developed macropores.The macropores are the primary space for occurrence of movable fluids,and controls the fluid mobility of the reservoir.The effective porosity of movable fluids(EPMF)quantitatively represents the pore space occupied by movable fluids within the reservoir and correlates well with porosity,permeability,and PTS parameters,making it a valuable parameter for evaluating fluid mobility.Under the multi-provenance system,the eastern and western reservoirs underwent different sedimentation and diagenesis processes,resulting in differential distribution of reservoir mineral components and pore types,which in turn affects the PTS heterogeneity and reservoir quality.The composition and content of reservoir minerals are intrinsic factors influencing fluid mobility,while the microscopic PTS is the primary factor controlling it.Low clay mineral content,welldeveloped macropores,and weak pore-throat heterogeneity all contribute to the storage and seepage of reservoir fluids.展开更多
Supercritical CO_(2)(SC-CO_(2))fracturing stands out a promising waterless stimulation technique in the development of unconventional resources.While numerous studies have delved into the inducedfracture mechanism of ...Supercritical CO_(2)(SC-CO_(2))fracturing stands out a promising waterless stimulation technique in the development of unconventional resources.While numerous studies have delved into the inducedfracture mechanism of SC-CO_(2),the small scale of rock samples and synthetic materials used in many studies have limited a comprehensive understanding of fracture propagation in unconventional formations.In this study,cubic tight sandstone samples with dimensions of 300 mm were employed to conduct SC-CO_(2)fractu ring experiments under true-triaxial stre ss conditions.The spatial morphology and quantitative attributes of fracture induced by water and SC-CO_(2)fracturing were compared,while the impact of in-situ stress on fracture propagation was also investigated.The results indicate that the SCCO_(2)fracturing takes approximately ten times longer than water fracturing.Furthermore,under identical stress condition,the breakdown pressure(BP)for SC-CO_(2)fracturing is nearly 25%lower than that for water fracturing.A quantitative analysis of fracture morphology reveals that water fracturing typically produces relatively simple fracture pattern,with the primary fracture distribution predominantly controlled by bedding planes.In contrast,SC-CO_(2)fracturing results in a more complex fracture morphology.As the differential of horizontal principal stress increases,the BP for SC-CO_(2)fractured rock exhibits a downward trend,and the induced fracture morphology becomes more simplified.Moreover,the presence of abnormal in-situ stress leads to a further increase in the BP for SC-CO_(2)fracturing,simultaneously enhancing the development of a more conductive fracture network.These findings provide critical insights into the efficiency and behavior of SC-CO_(2)fracturing in comparison to traditional water-based fracturing,offering valuable implication for its potential applications in unconventional reservoirs.展开更多
Rock residual strength,as an important input parameter,plays an indispensable role in proposing the reasonable and scientific scheme about stope design,underground tunnel excavation and stability evaluation of deep ch...Rock residual strength,as an important input parameter,plays an indispensable role in proposing the reasonable and scientific scheme about stope design,underground tunnel excavation and stability evaluation of deep chambers.Therefore,previous residual strength models of rocks established were reviewed.And corresponding related problems were stated.Subsequently,starting from the effects of bedding and whole life-cycle evolution process,series of triaxial mechanical tests of deep bedded sandstone with five bedding angles were conducted under different confining pressures.Then,six residual strength models considering the effects of bedding and whole life-cycle evolution process were established and evaluated.Finally,a cohesion loss model for determining residual strength of deep bedded sandstone was verified.The results showed that the effects of bedding and whole life-cycle evolution process had both significant influences on the evolution characteristic of residual strength of deep bedded sandstone.Additionally,residual strength parameters:residual cohesion and residual internal friction angle of deep bedded sandstone were not constant,which both significantly changed with increasing bedding angle.Besides,the cohesion loss model was the most suitable for determining and estimating the residual strength of bedded rocks,which could provide more accurate theoretical guidance for the stability control of deep chambers.展开更多
Understanding the storage mechanisms in CO_(2)flooding is crucial,as many carbon capture,utilization,and storage(CCUS)projects are related to enhanced oil recovery(EOR).CO_(2)storage in reservoirs across large timesca...Understanding the storage mechanisms in CO_(2)flooding is crucial,as many carbon capture,utilization,and storage(CCUS)projects are related to enhanced oil recovery(EOR).CO_(2)storage in reservoirs across large timescales undergoes the two storage stages of oil displacement and well shut-in,which cover mul-tiple replacement processes of injection-production synchronization,injection only with no production,and injection-production stoppage.Because the controlling mechanism of CO_(2)storage in different stages is unknown,the evolution of CO_(2)storage mechanisms over large timescales is not understood.A math-ematical model for the evaluation of CO_(2)storage,including stratigraphic,residual,solubility,and mineral trapping in low-permeability tight sandstone reservoirs,was established using experimental and theoret-ical analyses.Based on a detailed geological model of the Huaziping Oilfield,calibrated with reservoir permeability and fracture characteristic parameters obtained from well test results,a dynamic simulation of CO_(2)storage for the entire reservoir life cycle under two scenarios of continuous injection and water-gas alternation were considered.The results show that CO_(2)storage exhibits the significant stage charac-teristics of complete storage,dynamic storage,and stable storage.The CO_(2)storage capacity and storage rate under the continuous gas injection scenario(scenario 1)were 6.34×10^(4)t and 61%,while those under the water-gas alternation scenario(scenario 2)were 4.62×10^(4)t and 46%.The proportions of stor-age capacity under scenarios 1 and 2 for structural or stratigraphic,residual,solubility,and mineral trap-ping were 33.36%,33.96%,32.43%,and 0.25%;and 15.09%,38.65%,45.77%,and 0.49%,respectively.The evolution of the CO_(2)storage mechanism showed an overall trend:stratigraphic and residual trapping first increased and then decreased,whereas solubility trapping gradually decreased,and mineral trapping continuously increased.Based on these results,an evolution diagram of the CO_(2)storage mechanism of low-permeability tight sandstone reservoirs across large timescales was established.展开更多
Taking the second member of the Xujiahe Formation of the Upper Triassic in the Xinchang structural belt as an example,based on data such as logging,production,seismic interpretation and test,a systematic analysis was ...Taking the second member of the Xujiahe Formation of the Upper Triassic in the Xinchang structural belt as an example,based on data such as logging,production,seismic interpretation and test,a systematic analysis was conducted on the structural characteristics and evolution,reservoir diagenesis and densification processes,and types and stages of faults/fractures,and revealing the multi-stage and multi-factor dynamic coupled enrichment mechanisms of tight gas reservoirs.(1)In the early Yanshan period,the paleo-structural traps were formed with low-medium maturity hydrocarbons accumulating in structural highs driven by buoyancy since reservoirs were not fully densified in this stage,demonstrating paleo-structure control on traps and early hydrocarbon accumulation.(2)In the middle-late Yanshan period,the source rocks became mature to generate and expel a large quantity of hydrocarbons.Grain size and type of sandstone controlled the time of reservoir densification,which restricted the scale of hydrocarbon charging,allowing for only a small-scale migration through sand bodies near the fault/fracture or less-densified matrix reservoirs.(3)During the Himalayan period,the source rocks reached overmaturity,and the residual oil cracking gas was efficiently transported along the late-stage faults/fractures.Wells with high production capacity were mainly located in Type I and II fault/fracture zones comprising the late-stage north-south trending fourth-order faults and the late-stage fractures.The productivity of the wells was controlled by the transformation of the late-stage faults/fractures.(4)The Xinchang structural belt underwent three stages of tectonic evolution,two stages of reservoir formation,and three stages of fault/fractures development.Hydrocarbons mainly accumulated in the paleo-structure highs.After reservoir densification and late fault/fracture adjustment,a complex gas-water distribution pattern was formed.Thus,it is summarized as the model of“near-source and low-abundance hydrocarbon charging in the early stage,and differential enrichment of natural gas under the joint control of fault-fold-fracture complex,high-quality reservoirs and structural highs in the late stage”.Faults/fractures with well-coupled fault-fold-fracture-pore are favorable exploration targets with high exploration effectiveness.展开更多
Understanding the mesoscopic tensile fracture damage of rock is the basis of evaluating the deterioration process of mechanical properties of heat-damaged rock. For this, tensile tests of rocks under high-temperature ...Understanding the mesoscopic tensile fracture damage of rock is the basis of evaluating the deterioration process of mechanical properties of heat-damaged rock. For this, tensile tests of rocks under high-temperature treatment were conducted with a ϕ75 mm split Hopkinson tension bar (SHTB) to investigate the mesoscopic fracture and damage properties of rock. An improved scanning electron microscopy (SEM) experimental method was used to analyze the tensile fracture surfaces of rock samples. Qualitative and quantitative analyses were performed to assess evolution of mesoscopic damage of heat-damaged rock under tensile loading. A constitutive model describing the mesoscopic fractal damage under thermo-mechanical coupling was established. The results showed that the high temperatures significantly reduced the tensile strength and fracture surface roughness of the red sandstone. The three-dimensional (3D) reconstruction of the fracture surface of the samples that experienced tensile failure at 900 °C showed a flat surface. The standard deviation of elevation and slope angle of specimen fracture surface first increased and then decreased with increasing temperature. The threshold for brittle fracture of the heat-damaged red sandstone specimens was 600 °C. Beyond this threshold temperature, local ductile fracture occurred, resulting in plastic deformation of the fracture surface during tensile fracturing. With increase of temperature, the internal meso-structure of samples was strengthened slightly at first and then deteriorated gradually, which was consistent with the change of macroscopic mechanical properties of red sandstone. The mesoscopic characteristics, such as the number, mean side length, maximum area, porosity, and fractal dimension of crack, exhibited an initial decline, followed by a gradual increase. The development of microcracks in samples had significant influence on mesoscopic fractal dimension. The mesoscopic fractal characteristics were used to establish a mesoscopic fractal damage constitutive model for red sandstone, and the agreement between the theoretical and experimental results validated the proposed model.展开更多
Sand production and high water content in oil wells are two major challenges that restrict high and stable production in loose sandstone reservoirs.In this paper,nano SiO_(2),coupling agent triethoxysilane,phenolic re...Sand production and high water content in oil wells are two major challenges that restrict high and stable production in loose sandstone reservoirs.In this paper,nano SiO_(2),coupling agent triethoxysilane,phenolic resin and n-octanol were used to synthesize the main agent SCA-2.Hexamethylenetetramine and vinyl carbonate were selected to prepare the curing agent YGA-1,which was then compounded with SCA-2 to develop a sand fixation and water plugging system.Firstly,single-factor experiments were conducted to determine the optimal concentrations of SCA-2 and YGA-1,subsequently,the system’s sand fixation and water blocking performance were evaluated.Finally,a pilot test was carried out in the mining site.Experimental results showed that the optimal formula composition of the system was 10%SCA-2+5%YGA-1.The gelation time of the system was 180 minutes and the viscosity after gelation could reach 108.4 mPa·s.When the dosage of the drug system was 0.6 PV,the sand production rate remained below 0.08%.Dual-tube parallel experiments showed that the sand fixation and water plugging system had a water flow channel plugging rate of 87.5%,while the oil flow channel plugging rate was only 11.3%,indicating minimal damage to the oil-bearing reservoir.The field test showed that after the measures taken in Well M of X oilfield,the sand free oil recovery period exceeded 360 days,the water content decreased by 5.0%and the cumulative oil production increased by 7092 m^(3).This study provides new ideas for efficient development of loose sandstone reservoirs.展开更多
With the discovery of ultra-deepwater and ultra-shallow large natural gas reservoirs in the South China Sea,unconsolidated sandstone reservoirs have once again become a focal point of research.In response to the uncle...With the discovery of ultra-deepwater and ultra-shallow large natural gas reservoirs in the South China Sea,unconsolidated sandstone reservoirs have once again become a focal point of research.In response to the unclear controlling factors and the need for connectivity evaluation of unconsolidated sandstone reservoirs in the Ledong formation of the Lingshui A area in the Qiongdongnan Basin,this study employs a range of experimental techniques,namely,cast thin sections,scanning electron microscopy,Xray diffraction mineral analysis,laser granulometry,and nuclear magnetic resonance(NMR),to investigate the microstructural characteristics of these reservoirs.The primary objective is to elucidate the controlling mechanisms behind pore-throat variability and to identify how sedimentary factors,mineral composition,and gas hydrate occurrence modes collectively influence pore-throat structural characteristics.Guided by fractal theory,a multidimensional analysis of pore-throat modal characteristics is conducted using a combination of image analysis,mercury intrusion capillary pressure,and NMR techniques.Furthermore,connectivity evaluation factors(CEFs)are constructed based on reservoir parameters to quantitatively assess reservoir connectivity and to establish connectivity evaluation standards.Results indicate that sedimentary factors are the principal determinants of pore-throat differences in the study area.Coarse grains,low clay content,and enhanced reservoir porosity contribute to improved permeability.At the microscopic level,variations in mineral composition also play a critical role.Higher quartz content and reduced clay mineral content,particularly illite and chlorite,are associated with excellent reservoir properties.By contrast,diagenesis exhibits a limited effect on reservoir quality.The gas hydrate occurrence state is characterized as a pore suspension type,exhibiting a relatively uniform pore-throat distribution.This load-bearing hydrate type may enhance pore-throat heterogeneity.Pore-throat modes are classified into three types:bimodal,multimodalⅠ,and multimodalⅡ.The bimodal hydrate occurrence state is dominated by the pore suspension type and characterized by low sorting coefficients,reduced fractal dimensions,increased uniform pore-throat structures,and improved reservoir connectivity.Five key reservoir parameters are selected,forming the basis of the CEFs,which comprehensively characterize reservoir connectivity.Ultimately,a connectivity evaluation standard and a microscopic connectivity model for typical unconsolidated sandstones in the South China Sea are established,providing critical guidance for future reservoir development strategies.展开更多
This research employs micro-CT scanning technology to analyze the porosity,pore fractal dimension,and spatial variability of sandstone preheated to 600℃ and subsequently cooled in water at varying temperatures(20℃,6...This research employs micro-CT scanning technology to analyze the porosity,pore fractal dimension,and spatial variability of sandstone preheated to 600℃ and subsequently cooled in water at varying temperatures(20℃,60℃,100℃).The study investigates the mechanisms by which various factors influence thermal shock damage,focusing on the effects of cooling water temperature and the boiling phase transition.The objective is to develop a method for characterizing thermal shock damage that considers spatial variability.The findings indicate that thermal shock damage is limited to a shallow depth beneath the surface,with increased severity near the surface.The boiling phase transition significantly enhances the convective heat transfer coefficient,resulting in substantially higher thermal shock damage when cooled with 100℃ boiling water compared to 20℃ and 60℃ water.Furthermore,for the entire specimen,heating damage exceeds thermal shock damage,and the influence of thermal shock diminishes as specimen size increases.This study addresses the limitations of traditional methods for assessing thermal shock damage that disregard spatial variability and provides practical guidance for engineering projects to manage thermal shock damage more effectively.展开更多
The presence of clay coatings on the surfaces of quartz grains can play a pivotal role in determining the porosity and permeability of sandstone reservoirs,thus directly impacting their reservoir quality.This study em...The presence of clay coatings on the surfaces of quartz grains can play a pivotal role in determining the porosity and permeability of sandstone reservoirs,thus directly impacting their reservoir quality.This study employs a multiphase-field model of syntaxial quartz cementation to explore the effects of clay coatings on quartz cement volumes,porosity,permeability,and their interrelations in sandstone formations.To generate various patterns of clay coatings on quartz grains within three-dimensional(3D)digital sandstone grain packs,a pre-processing toolchain is developed.Through numerical simulation experiments involving syntaxial overgrowth cementation on both single crystals and multigrain packs,the main coating parameters controlling quartz cement volume are elucidated.Such parameters include the growth of exposed pyramidal faces,lateral encasement,coating coverage,and coating pattern,etc.The coating pattern has a remarkable impact on cementation,with the layered coatings corresponding to fast cement growth rates.The coating coverage is positively correlated with the porosity and permeability of sandstone.The cement growth rate of quartz crystals is the lowest in the vertical orientation,and in the middle to late stages of evolution,it is faster in the diagonal orientation than in the horizontal orientation.Through comparing the simulated results of dynamic evolution process with the actual features,it is found that the simulated coating patterns after 20 d and 40 d show clear similarities with natural samples,proving the validity of the proposed three-dimensional numerical modeling of coatings.The methodology and findings presented contribute to improved reservoir characterization and predictive modeling of sandstone formations.展开更多
Existing sandstone rock structure evaluation methods rely on visual inspection,with low efficiency,semi-quantitative analysis of roundness,and inability to perform classified statistics in particle size analysis.This ...Existing sandstone rock structure evaluation methods rely on visual inspection,with low efficiency,semi-quantitative analysis of roundness,and inability to perform classified statistics in particle size analysis.This study presents an intelligent evaluation method for sandstone rock structure based on the Segment Anything Model(SAM).By developing a lightweight SAM fine-tuning method with rank-decomposition matrix adapters,a multispectral rock particle segmentation model named CoreSAM is constructed,which achieves rock particle edge extraction and type identification.Building upon this,we propose a comprehensive quantitative evaluation system for rock structure,assessing parameters including particle size,sorting,roundness,particle contact and cementation types.The experimental results demonstrate that CoreSAM outperforms existing methods in rock particle segmentation accuracy while showing excellent generalization across different image types such as CT scans and core photographs.The proposed method enables full-sample,classified particle size analysis and quantitative characterization of parameters like roundness,advancing reservoir evaluation towards more precise,quantitative,intuitive,and comprehensive development.展开更多
High-altitude cold regions exhibit complex geological and environmental conditions,fostering steep rock slopes with macroscopic joints and mesoscopic freeze-thaw(F-T)damage.Cyclic loading further exacerbates rock inst...High-altitude cold regions exhibit complex geological and environmental conditions,fostering steep rock slopes with macroscopic joints and mesoscopic freeze-thaw(F-T)damage.Cyclic loading further exacerbates rock instability,yet the fracture mechanisms and load response relationships remain poorly understood.This study prepared intact and fractured sandstone specimens,subjected them to F-T cycles and graded loading-unloading,and monitored their structural evolution via X-ray computed tomography.First,the progressive failure process was investigated from both qualitative morphologic features and quantitative void parameters.The results showed that intact and fractured sandstone instability behaviors are determined by F-T damage and joint arrangement,respectively.However,both indicate that precursory localization of failure can only be detected when heterogeneous damage exists in advance.Furthermore,the void parameters of undamaged intact sandstone exhibit power-law acceleration,while damaged sandstones are characterized by a trend of initial decrease followed by an increase.Subsequently,a damage constitutive model for freeze-thawed fractured sandstone under graded loading-unloading was established.This model is based on the Lemaitre strain equivalence hypothesis and defines the coupled damage variable through multivariable indicators.In this framework,the material damage induced by fractures and F-T is unified and characterized by void parameters;while the load-induced damage is integrated with the energy linear allocation law and defined by damage energy.Thus,the stress-strain theoretical relationship is depicted,and the model is validated as reliable.Finally,a conceptual model of rock damage due to F-T and loading-unloading was proposed by combining the microscopic testing results from X-ray diffraction and scanning electron microscopy.展开更多
During the exploitation of sandstone gas reservoirs,natural fractures near the wellbore affect water infiltration and pore evolution;however,the impact mechanisms of these fractures remain unclear.This study utilized ...During the exploitation of sandstone gas reservoirs,natural fractures near the wellbore affect water infiltration and pore evolution;however,the impact mechanisms of these fractures remain unclear.This study utilized real-time nuclear magnetic resonance(RT-NMR)technology to investigate the influence of near-wellbore fracture angle(a)at 0°,15°,30°,and 45°on water infiltration,migration patterns,and pore evolution mechanisms during water injection.Throughout the experiments,T_(2)curves and magnetic resonance imaging(MRI)were monito red in real time during the water injection process.The pore evolution and water infiltration were translated by the evolution of T_(2)curves and MRI.The results show that increasing injection pressure(P_(inj))transforms adsorption pores into seepage pores,leading to enhanced pore damage.Pore damage predominantly occurs during the rapid pressurization stage and is concentrated around the near-wellbore fracture.The maximum infiltration area and rate were observed at α=0°,while the minimum values occurred at α=45°,which can be attributed to the significant influence of a on water infiltration and migration pathways.The increasing inclination of the infiltration front with a is attributed to the fact that the rate of water infiltration along the fracture wall is always higher than that at the fracture tip.In field fracturing,it is recommended to adjust the perforation direction to align with the natural fracture orientation and optimize pressurization strategies by reducing the slow pressurization duration while extending the rapid pressurization stage.These findings can provide important guidance for setting fracturing sections and optimizing injection parameters in sandstone gas reservoir exploitation.展开更多
Gas explosions in coal mine goafs are associated with the roof rock fracturing.An experimental system was established to investigate the potential for electrical ignition induced by sandstone fracturing.The electrical...Gas explosions in coal mine goafs are associated with the roof rock fracturing.An experimental system was established to investigate the potential for electrical ignition induced by sandstone fracturing.The electrical responses,luminescent emissions,and ignition characteristics during tensile and compressive failure of sandstones were analyzed in methane/air premixed gas environments.Results indicate that the application of mechanical loading induces the emergence of electrical signals on rock surfaces and in the surrounding atmosphere.This phenomenon is attributed to the generation,accumulation,and subsequent release of free charges during the deformation and fracture within the sandstone.Compressive failure proved to be more conducive to free charge generation than tensile failure,owing to more crack connections.Furthermore,a precipitous increase in surface and external voltages was observed during complete fracturing,a consequence of electron emission from crack tips within the rock structure.Moreover,the ionization induces luminous emissions owing to the collision of energetic electrons released from gas molecules in methane/air mixtures.A strong positive correlation(R2=0.9429)was identified between luminescence intensity and the magnitude of electrical discharge resulting from rock fracture.Notably,such discharge by rock fracturing can be capable of igniting the premixed gas,particularly when the quartz content exceeds 61%.Piezoelectric effects and crack propagation are crucial mechanisms in the causal chain of the charge generation,discharge,and ionization triggered by rock fractures.Based on the above laboratory results,electric ignition of the transient roof fracturing caused by stress mutations can serve as a new potential ignition source for gas explosions in the goaf.These results offer new insights into the prevention and control of gas explosions.展开更多
As an efficient monitoring and prediction tool,chemical tracers have been widely applied in reservoir characterization,production monitoring,water resources monitoring,and various other fields.Chemical tracer technolo...As an efficient monitoring and prediction tool,chemical tracers have been widely applied in reservoir characterization,production monitoring,water resources monitoring,and various other fields.Chemical tracer technology is characterized by high efficiency,high precision,relatively simple operational procedures,and low cost.Owing to the limitations of existing tracers,such as minimal options,limited transport efficiency,and complex detection methods,this study used fluorescein isothiocyanate and a ruthenium complex(Ru(phen_(3))^(2+))to synthesize 50 nm multi-color fluorescent silica nanoparticle tracers using an improved St ober method based on fluorescence resonance energy transfer(FRET).Due to the FRET between the two compounds,the synthesized tracer exhibited the characteristics of multi-color fluorescence,and its fluorescent color varied with the mixing ratio of the two precursor solutions.The fluorescence intensity of the synthesized tracer was significantly higher than that of the monochromatic fluorescent nano-tracer.Fourier-transform infrared spectroscopy,ultraviolet spectrophotometry,and fluorescence spectrometry were used to characterize the structure,maximum absorption wavelength,and fluorescence characteristics of the synthesized tracer,respectively.The experimental results show that the synthesized tracer has a maximum absorption wavelength of 450 nm and an emission wavelength of 576 nm.Under field emission scanning electron microscopy,the tracer appears as uniformly spherical particles with a size of 50±5 nm.It exhibited good dispersibility and fluorescence characteristics in reservoir environments that varied in temperature(25-85°C)and salinity(1000-10000 mg/L).The effects of environmentally sensitive clay minerals,tracer particle size,injection concentration,fluid salinity,and flow rate on the transport characteristics(retention)of tracers in sandstone cores were studied using 12 sets of tracer breakthrough experiments.The experimental results showed that increased sensitivity to clay minerals,salinity,and tracer particle size were not conducive to tracer migration in the core.In contrast,increased tracer injection concentration and flow rate were beneficial to tracer migration in the core.展开更多
Three sandstone specimens common in rock engineering were selected to study the differences in the mechanical properties of rocks with different lithologies.The development and expansion of the internal cracks in the ...Three sandstone specimens common in rock engineering were selected to study the differences in the mechanical properties of rocks with different lithologies.The development and expansion of the internal cracks in the specimens were observed by combining the simulation system with the acoustic emission system.Through the combination of dynamic and static stresses,the deformation and damage of rocks under deep rock excavation and blasting were simulated.As the results show,the acoustic emission events of specimens with different lithologies under combined static and dynamic cyclic loading can be roughly divided into three phases:weakening,stabilizing,and surging periods.In addition,the acoustic emission characteristics of specimens with different lithologies show general consistency in different compression phases.The degree of fragmentation of specimens increases with the applied stress level;therefore,the stress level is one of the important factors influencing the damage pattern of specimens.The acoustic emission system was used to simulate the deformation and damage of rocks subjected to deep rock body excavation and engineering blasting.Cyclic dynamic perturbations under sinusoidal waves with a frequency of 5 Hz,a loading rate of 0.1 mm/min,a cyclic amplitude of 5 MPa,and a loading rate of 0.1 mm/min were applied to the three rock samples during the experiments.Among them,the fine-grained sandstones are the most sensitive to the sinusoidal cyclic perturbation,followed by the muddy siltstone and the medium-grained sandstones.On this basis,the acoustic emission energy release characteristics were analyzed,and the waveform characteristics in the damage evolution of the specimen under dynamic perturbation were studied by extracting the key points and searching for the main frequency eigenvalues.展开更多
基金funded by the National Natural Science Foundation of China(No.42202113)。
文摘Buried coastal sandstones would be of high-quality hydrocarbon reservoirs.Controlled by deposition and diagenesis,coastal sandstones mixed with muddy and calcareous materials are usually low in porosity and permeability and small in layer thickness.These impermeable inte rlayers act as baffles and barriers between flow units and are crucial in hydrocarbon development.Donghe Sandstone in the Hade Oilfield of Tarim Basin,NW China,belongs to coastal clastic reservoirs of high oil productivity.Following nearly 30 years of development,the distribution of remaining hydrocarbon resources is affected by the muddy,calcareous,and marlaceous interlayers.Taking the Donghe Sandstone as an example,a quantitative recognition method of interlayers in coastal sandstone reservoirs is proposed in this paper.Based on cores from 26 wells,the sensitive conventional log curves of different interlayers,namely the natural gamma-ray(GR),density(DEN),compensated neutron(CNL),and acoustic(AC),are extracted by the Extreme Gradient Boosting(XGBoost).Multi-mineral model(MMM)is used to calculate continuous curves for muddy,sandy,and calcareous contents by the mentioned sensitive logs.A set of quantitative standard system is established for identifying muddy,calcareous,and marlaceous interlayers based on their respective contents.The types of inte rlayers are identified across all vertical wells.The interlayers exhibit lateral continuity at the top of each bed-set.Interlayers are currently more developed in the slope region than in the coastal region.Muddy and marlaceous interlayers are more developed at high relative sea-level,while calcareous interlayers are more developed at low relative sea-level.The extended interlayers at the top of BS6 lead to two different oil-water contacts in the Donghe Sandstone.The proposed quantitative recognition method for interlayers provides valuable insights into the exploitation potential of petroleum systems in the Donghe Sandstone of the Hade Oilfield.The flexible and easy-to-use method can be applied to other marine sandstone reservoirs or similar formations.
基金funding support from the National Natural Science Foundation of China(Grant No.12172019).
文摘In cold regions,rock structures will be weakened by freeze-thaw cycles under various water immersion conditions.Determining how water immersion conditions impact rock deterioration under freeze-thaw cycles is critical to assess accurately the frost resistance of engineered rock.In this paper,freeze-thaw cycles(temperature range of-20℃-20℃)were performed on the sandstones in different water immersion conditions(fully,partially and non-immersed in water).Then,computed tomography(CT)tests were conducted on the sandstones when the freeze-thaw number reached 0,5,10,15,20 and 30.Next,the effects of water immersion conditions on the microstructure deterioration of sandstone under freezethaw cycles were evaluated using CT spatial imaging,porosity and damage factor.Finally,focusing on the partially immersed condition,the immersion volume rate was defined to understand the effects of immersion degree on the freeze-thaw damage of sandstone and to propose a damage model considering the freeze-thaw number and immersion degree.The results show that with increasing freeze-thaw number,the porosities and damage factors under fully and partially immersed conditions increase continuously,while those under non-immersed condition first increase and then remain approximately constant.The most severe freeze-thaw damage occurs in fully immersed condition,followed by partially immersed condition and finally non-immersed condition.Interestingly,the freeze-thaw number and the immersion volume rate both impact the microstructure deterioration of the partially immersed sandstone.For the same freeze-thaw number,the damage factor increases approximately linearly with increasing immersion volume rate,and the increasing immersion degree exacerbates the microstructure deterioration of sandstone.Moreover,the proposed model can effectively estimate the freeze-thaw damage of partially immersed sandstone with different immersion volume rates.
基金supported by the National Natural Science Foundation of China(52104133,52304227)the Natural Science Foundation of Hunan Province(2021JJ40465,2023JJ40548)the Opening Foundation of the State Key Laboratory of Mining Response and Disaster Prevention and Control in Deep Coal Mines(SKLMRDPC20KF03).
文摘To investigate the effect of saturation on the storage-dissipation properties and failure characteristics of red sandstone,as well as the energy mechanism of rockburst prevention by water,a series of uniaxial compression and uniaxial loading–unloading tests were conducted under five saturation levels.The effect of saturation on the mechanical properties and elastic energy density was analyzed,and a method for obtaining peak energy density was proposed.The effect of saturation on the energy evolution was examined,and the energy mechanism of water in preventing rockburst was revealed.The results indicate that an increase in saturation of red sandstone decreases the input energy density,elastic energy density,dissipated energy density,peak strength and peak strain;the compaction phase of the stress–strain curve becomes shorter;the failure mode transitions from X-conjugate oblique shear to single oblique shear;the variation in the debris ejection trajectory is as follows:radiation→X-ray→oblique upward parabola→horizontal parabola→oblique downward parabola;the degree of failure intensity and fragmentation is decreased gradually.Elastic energy density is interconnected with both saturation and stress but independent of the loading path.Saturation exhibits a dual effect on the energy storage property,i.e.,increasing saturation increases the energy storage efficiency and reduces the energy storage capacity.The ratio of peak elastic energy density to peak input energy density remains constant irrespective of saturation levels.Water prevents rockburst by decreasing the energy storage capacity of surrounding rock,alleviating the stress of surrounding rock to reduce energy storage,and elevating the energy release threshold of high-energy surrounding rock.The findings of this study contribute to understanding the effect of water on rock failure from an energy perspective,as well as provide theoretical guidance for rockburst prevention by water in deep tunnels.
基金sponsored by the National Natural Science Foundation of China(Grant No.42141010).
文摘A novel fractional elastoplastic constitutive model is proposed to accurately characterize the deformation of sandstone under true-triaxial stress states.This model is founded on the yield function and the fractional flow rule.The yield function includes parameters that govern the evolution of yield surface,enabling an accurate description of three-dimensional stress states.The direction of plastic flow is governed by the two different fractional orders,which are functions of the plastic internal variable.Additionally,a detailed process is proposed for identifying the yield function parameters and fractional orders.Subsequently,the relationship between the fractional order and the direction of plastic flow in the meridian and deviatoric planes is examined,characterized by the dilation angle and the plastic deflection angle,respectively.The non-orthogonal flow rule,also referred to as the fractional flow rule,allows for a border range of plastic deflection and dilation angles compared to the orthogonal flow rule,thereby significantly enhancing its applicability.The validity and accuracy of proposed model are verified by comparing the analytical solution of the constitutive model with the experimental data.A comparison between the non-orthogonal flow rule and orthogonal flow rule is conducted in both the deviatoric and meridian planes.The further comparison of the stress-strain curves for the non-orthogonal and orthogonal flow rules demonstrates the superiority of the fractional constitutive model.
文摘The tight sandstone reservoirs in the first sub-member of Chang 7 member(Chang 71)of Triassic Yanchang Formation in the Jiyuan area,Ordos Basin,show significant variations in microscopic pore-throat structure(PTS)and fluid mobility due to the influences of the northeast and northwest dual provenance systems.This study performed multiple experimental analyses on nine samples from the area to determine the petrological and petrophysical properties,as well as the PTS characteristics of reservoirs in different provenance-controlled regions.On this basis,the pore-throat size distribution(PSD)obtained from high-pressure mercury injection(HPMI)was utilized to convert the NMR movable fluid T2spectrum,allowing for quantitative characterization of the full PSD and the occurrence characteristics of movable fluids.A systematic analysis was conducted on the primary controlling factors affecting fluid mobility in the reservoir.The results indicated that the lithology in the eastern and western regions is lithic arkose.The eastern sandstones,being farther from the provenance,exhibit higher contents of feldspar and lithic fragments,along with the development of more dissolution pores.The reservoir possesses good petrophysical properties,low displacement pressure,and high pore-throat connectivity and homogeneity,indicating strong fluid mobility.In contrast,the western sandstones,being nearer to the provenance,exhibit poor grain sorting,high contents of lithic fragments,strong compaction and cementation effects,resulting in poor petrophysical properties,and strong pore-throat heterogeneity,revealing weak fluid mobility.The range of full PSD in the eastern reservoir is wider than that in the western reservoir,with relatively well-developed macropores.The macropores are the primary space for occurrence of movable fluids,and controls the fluid mobility of the reservoir.The effective porosity of movable fluids(EPMF)quantitatively represents the pore space occupied by movable fluids within the reservoir and correlates well with porosity,permeability,and PTS parameters,making it a valuable parameter for evaluating fluid mobility.Under the multi-provenance system,the eastern and western reservoirs underwent different sedimentation and diagenesis processes,resulting in differential distribution of reservoir mineral components and pore types,which in turn affects the PTS heterogeneity and reservoir quality.The composition and content of reservoir minerals are intrinsic factors influencing fluid mobility,while the microscopic PTS is the primary factor controlling it.Low clay mineral content,welldeveloped macropores,and weak pore-throat heterogeneity all contribute to the storage and seepage of reservoir fluids.
基金funded by the National Natural Scientific Foundation of China(Nos.52304008,52404038,52474043)the China Postdoctoral Science Foundation(No.2023MD734223)+1 种基金the Key Laboratory of Well Stability and Fluid&Rock Mechanics in Oil and Gas Reservoir of Shaanxi Province(No.23JS047)the Youth Talent Lifting Program of Xi'an Science and Technology Association(No.959202413078)。
文摘Supercritical CO_(2)(SC-CO_(2))fracturing stands out a promising waterless stimulation technique in the development of unconventional resources.While numerous studies have delved into the inducedfracture mechanism of SC-CO_(2),the small scale of rock samples and synthetic materials used in many studies have limited a comprehensive understanding of fracture propagation in unconventional formations.In this study,cubic tight sandstone samples with dimensions of 300 mm were employed to conduct SC-CO_(2)fractu ring experiments under true-triaxial stre ss conditions.The spatial morphology and quantitative attributes of fracture induced by water and SC-CO_(2)fracturing were compared,while the impact of in-situ stress on fracture propagation was also investigated.The results indicate that the SCCO_(2)fracturing takes approximately ten times longer than water fracturing.Furthermore,under identical stress condition,the breakdown pressure(BP)for SC-CO_(2)fracturing is nearly 25%lower than that for water fracturing.A quantitative analysis of fracture morphology reveals that water fracturing typically produces relatively simple fracture pattern,with the primary fracture distribution predominantly controlled by bedding planes.In contrast,SC-CO_(2)fracturing results in a more complex fracture morphology.As the differential of horizontal principal stress increases,the BP for SC-CO_(2)fractured rock exhibits a downward trend,and the induced fracture morphology becomes more simplified.Moreover,the presence of abnormal in-situ stress leads to a further increase in the BP for SC-CO_(2)fracturing,simultaneously enhancing the development of a more conductive fracture network.These findings provide critical insights into the efficiency and behavior of SC-CO_(2)fracturing in comparison to traditional water-based fracturing,offering valuable implication for its potential applications in unconventional reservoirs.
基金Projects(2024YFC3013801,2022YFC3004602)supported by the National Key R&D Program of ChinaProjects(U23B2093,52034009)supported by the National Natural Science Foundation of China。
文摘Rock residual strength,as an important input parameter,plays an indispensable role in proposing the reasonable and scientific scheme about stope design,underground tunnel excavation and stability evaluation of deep chambers.Therefore,previous residual strength models of rocks established were reviewed.And corresponding related problems were stated.Subsequently,starting from the effects of bedding and whole life-cycle evolution process,series of triaxial mechanical tests of deep bedded sandstone with five bedding angles were conducted under different confining pressures.Then,six residual strength models considering the effects of bedding and whole life-cycle evolution process were established and evaluated.Finally,a cohesion loss model for determining residual strength of deep bedded sandstone was verified.The results showed that the effects of bedding and whole life-cycle evolution process had both significant influences on the evolution characteristic of residual strength of deep bedded sandstone.Additionally,residual strength parameters:residual cohesion and residual internal friction angle of deep bedded sandstone were not constant,which both significantly changed with increasing bedding angle.Besides,the cohesion loss model was the most suitable for determining and estimating the residual strength of bedded rocks,which could provide more accurate theoretical guidance for the stability control of deep chambers.
基金supported by the National Key Research and Development Program of China(2022YFE0206700).
文摘Understanding the storage mechanisms in CO_(2)flooding is crucial,as many carbon capture,utilization,and storage(CCUS)projects are related to enhanced oil recovery(EOR).CO_(2)storage in reservoirs across large timescales undergoes the two storage stages of oil displacement and well shut-in,which cover mul-tiple replacement processes of injection-production synchronization,injection only with no production,and injection-production stoppage.Because the controlling mechanism of CO_(2)storage in different stages is unknown,the evolution of CO_(2)storage mechanisms over large timescales is not understood.A math-ematical model for the evaluation of CO_(2)storage,including stratigraphic,residual,solubility,and mineral trapping in low-permeability tight sandstone reservoirs,was established using experimental and theoret-ical analyses.Based on a detailed geological model of the Huaziping Oilfield,calibrated with reservoir permeability and fracture characteristic parameters obtained from well test results,a dynamic simulation of CO_(2)storage for the entire reservoir life cycle under two scenarios of continuous injection and water-gas alternation were considered.The results show that CO_(2)storage exhibits the significant stage charac-teristics of complete storage,dynamic storage,and stable storage.The CO_(2)storage capacity and storage rate under the continuous gas injection scenario(scenario 1)were 6.34×10^(4)t and 61%,while those under the water-gas alternation scenario(scenario 2)were 4.62×10^(4)t and 46%.The proportions of stor-age capacity under scenarios 1 and 2 for structural or stratigraphic,residual,solubility,and mineral trap-ping were 33.36%,33.96%,32.43%,and 0.25%;and 15.09%,38.65%,45.77%,and 0.49%,respectively.The evolution of the CO_(2)storage mechanism showed an overall trend:stratigraphic and residual trapping first increased and then decreased,whereas solubility trapping gradually decreased,and mineral trapping continuously increased.Based on these results,an evolution diagram of the CO_(2)storage mechanism of low-permeability tight sandstone reservoirs across large timescales was established.
基金Supported by the National Natural Science Foundation of China(42302141).
文摘Taking the second member of the Xujiahe Formation of the Upper Triassic in the Xinchang structural belt as an example,based on data such as logging,production,seismic interpretation and test,a systematic analysis was conducted on the structural characteristics and evolution,reservoir diagenesis and densification processes,and types and stages of faults/fractures,and revealing the multi-stage and multi-factor dynamic coupled enrichment mechanisms of tight gas reservoirs.(1)In the early Yanshan period,the paleo-structural traps were formed with low-medium maturity hydrocarbons accumulating in structural highs driven by buoyancy since reservoirs were not fully densified in this stage,demonstrating paleo-structure control on traps and early hydrocarbon accumulation.(2)In the middle-late Yanshan period,the source rocks became mature to generate and expel a large quantity of hydrocarbons.Grain size and type of sandstone controlled the time of reservoir densification,which restricted the scale of hydrocarbon charging,allowing for only a small-scale migration through sand bodies near the fault/fracture or less-densified matrix reservoirs.(3)During the Himalayan period,the source rocks reached overmaturity,and the residual oil cracking gas was efficiently transported along the late-stage faults/fractures.Wells with high production capacity were mainly located in Type I and II fault/fracture zones comprising the late-stage north-south trending fourth-order faults and the late-stage fractures.The productivity of the wells was controlled by the transformation of the late-stage faults/fractures.(4)The Xinchang structural belt underwent three stages of tectonic evolution,two stages of reservoir formation,and three stages of fault/fractures development.Hydrocarbons mainly accumulated in the paleo-structure highs.After reservoir densification and late fault/fracture adjustment,a complex gas-water distribution pattern was formed.Thus,it is summarized as the model of“near-source and low-abundance hydrocarbon charging in the early stage,and differential enrichment of natural gas under the joint control of fault-fold-fracture complex,high-quality reservoirs and structural highs in the late stage”.Faults/fractures with well-coupled fault-fold-fracture-pore are favorable exploration targets with high exploration effectiveness.
基金supported by The National Natural Science Foundation of China(Grant Nos.12272411 and 42007259).
文摘Understanding the mesoscopic tensile fracture damage of rock is the basis of evaluating the deterioration process of mechanical properties of heat-damaged rock. For this, tensile tests of rocks under high-temperature treatment were conducted with a ϕ75 mm split Hopkinson tension bar (SHTB) to investigate the mesoscopic fracture and damage properties of rock. An improved scanning electron microscopy (SEM) experimental method was used to analyze the tensile fracture surfaces of rock samples. Qualitative and quantitative analyses were performed to assess evolution of mesoscopic damage of heat-damaged rock under tensile loading. A constitutive model describing the mesoscopic fractal damage under thermo-mechanical coupling was established. The results showed that the high temperatures significantly reduced the tensile strength and fracture surface roughness of the red sandstone. The three-dimensional (3D) reconstruction of the fracture surface of the samples that experienced tensile failure at 900 °C showed a flat surface. The standard deviation of elevation and slope angle of specimen fracture surface first increased and then decreased with increasing temperature. The threshold for brittle fracture of the heat-damaged red sandstone specimens was 600 °C. Beyond this threshold temperature, local ductile fracture occurred, resulting in plastic deformation of the fracture surface during tensile fracturing. With increase of temperature, the internal meso-structure of samples was strengthened slightly at first and then deteriorated gradually, which was consistent with the change of macroscopic mechanical properties of red sandstone. The mesoscopic characteristics, such as the number, mean side length, maximum area, porosity, and fractal dimension of crack, exhibited an initial decline, followed by a gradual increase. The development of microcracks in samples had significant influence on mesoscopic fractal dimension. The mesoscopic fractal characteristics were used to establish a mesoscopic fractal damage constitutive model for red sandstone, and the agreement between the theoretical and experimental results validated the proposed model.
文摘Sand production and high water content in oil wells are two major challenges that restrict high and stable production in loose sandstone reservoirs.In this paper,nano SiO_(2),coupling agent triethoxysilane,phenolic resin and n-octanol were used to synthesize the main agent SCA-2.Hexamethylenetetramine and vinyl carbonate were selected to prepare the curing agent YGA-1,which was then compounded with SCA-2 to develop a sand fixation and water plugging system.Firstly,single-factor experiments were conducted to determine the optimal concentrations of SCA-2 and YGA-1,subsequently,the system’s sand fixation and water blocking performance were evaluated.Finally,a pilot test was carried out in the mining site.Experimental results showed that the optimal formula composition of the system was 10%SCA-2+5%YGA-1.The gelation time of the system was 180 minutes and the viscosity after gelation could reach 108.4 mPa·s.When the dosage of the drug system was 0.6 PV,the sand production rate remained below 0.08%.Dual-tube parallel experiments showed that the sand fixation and water plugging system had a water flow channel plugging rate of 87.5%,while the oil flow channel plugging rate was only 11.3%,indicating minimal damage to the oil-bearing reservoir.The field test showed that after the measures taken in Well M of X oilfield,the sand free oil recovery period exceeded 360 days,the water content decreased by 5.0%and the cumulative oil production increased by 7092 m^(3).This study provides new ideas for efficient development of loose sandstone reservoirs.
基金Program‘Geological Reservoir Digital Analogy Study Based on Exploration and Development Data Lake’(No.KJZH2024-2903)。
文摘With the discovery of ultra-deepwater and ultra-shallow large natural gas reservoirs in the South China Sea,unconsolidated sandstone reservoirs have once again become a focal point of research.In response to the unclear controlling factors and the need for connectivity evaluation of unconsolidated sandstone reservoirs in the Ledong formation of the Lingshui A area in the Qiongdongnan Basin,this study employs a range of experimental techniques,namely,cast thin sections,scanning electron microscopy,Xray diffraction mineral analysis,laser granulometry,and nuclear magnetic resonance(NMR),to investigate the microstructural characteristics of these reservoirs.The primary objective is to elucidate the controlling mechanisms behind pore-throat variability and to identify how sedimentary factors,mineral composition,and gas hydrate occurrence modes collectively influence pore-throat structural characteristics.Guided by fractal theory,a multidimensional analysis of pore-throat modal characteristics is conducted using a combination of image analysis,mercury intrusion capillary pressure,and NMR techniques.Furthermore,connectivity evaluation factors(CEFs)are constructed based on reservoir parameters to quantitatively assess reservoir connectivity and to establish connectivity evaluation standards.Results indicate that sedimentary factors are the principal determinants of pore-throat differences in the study area.Coarse grains,low clay content,and enhanced reservoir porosity contribute to improved permeability.At the microscopic level,variations in mineral composition also play a critical role.Higher quartz content and reduced clay mineral content,particularly illite and chlorite,are associated with excellent reservoir properties.By contrast,diagenesis exhibits a limited effect on reservoir quality.The gas hydrate occurrence state is characterized as a pore suspension type,exhibiting a relatively uniform pore-throat distribution.This load-bearing hydrate type may enhance pore-throat heterogeneity.Pore-throat modes are classified into three types:bimodal,multimodalⅠ,and multimodalⅡ.The bimodal hydrate occurrence state is dominated by the pore suspension type and characterized by low sorting coefficients,reduced fractal dimensions,increased uniform pore-throat structures,and improved reservoir connectivity.Five key reservoir parameters are selected,forming the basis of the CEFs,which comprehensively characterize reservoir connectivity.Ultimately,a connectivity evaluation standard and a microscopic connectivity model for typical unconsolidated sandstones in the South China Sea are established,providing critical guidance for future reservoir development strategies.
基金financially supported by the National Natural Science Foundation of China(Grant No.51874207)the Natural Science Foundation of Shanxi Province(Grant Nos.202303021211042 and 202303011222006).
文摘This research employs micro-CT scanning technology to analyze the porosity,pore fractal dimension,and spatial variability of sandstone preheated to 600℃ and subsequently cooled in water at varying temperatures(20℃,60℃,100℃).The study investigates the mechanisms by which various factors influence thermal shock damage,focusing on the effects of cooling water temperature and the boiling phase transition.The objective is to develop a method for characterizing thermal shock damage that considers spatial variability.The findings indicate that thermal shock damage is limited to a shallow depth beneath the surface,with increased severity near the surface.The boiling phase transition significantly enhances the convective heat transfer coefficient,resulting in substantially higher thermal shock damage when cooled with 100℃ boiling water compared to 20℃ and 60℃ water.Furthermore,for the entire specimen,heating damage exceeds thermal shock damage,and the influence of thermal shock diminishes as specimen size increases.This study addresses the limitations of traditional methods for assessing thermal shock damage that disregard spatial variability and provides practical guidance for engineering projects to manage thermal shock damage more effectively.
基金the Helmholtz association for funding the main parts of the modeling and simulation research work under the program“MTET:38.04.04”。
文摘The presence of clay coatings on the surfaces of quartz grains can play a pivotal role in determining the porosity and permeability of sandstone reservoirs,thus directly impacting their reservoir quality.This study employs a multiphase-field model of syntaxial quartz cementation to explore the effects of clay coatings on quartz cement volumes,porosity,permeability,and their interrelations in sandstone formations.To generate various patterns of clay coatings on quartz grains within three-dimensional(3D)digital sandstone grain packs,a pre-processing toolchain is developed.Through numerical simulation experiments involving syntaxial overgrowth cementation on both single crystals and multigrain packs,the main coating parameters controlling quartz cement volume are elucidated.Such parameters include the growth of exposed pyramidal faces,lateral encasement,coating coverage,and coating pattern,etc.The coating pattern has a remarkable impact on cementation,with the layered coatings corresponding to fast cement growth rates.The coating coverage is positively correlated with the porosity and permeability of sandstone.The cement growth rate of quartz crystals is the lowest in the vertical orientation,and in the middle to late stages of evolution,it is faster in the diagonal orientation than in the horizontal orientation.Through comparing the simulated results of dynamic evolution process with the actual features,it is found that the simulated coating patterns after 20 d and 40 d show clear similarities with natural samples,proving the validity of the proposed three-dimensional numerical modeling of coatings.The methodology and findings presented contribute to improved reservoir characterization and predictive modeling of sandstone formations.
基金Supported by the National Natural Science Foundation of China(42372175,72088101)PetroChina Science and Technology Project of(2023DJ84)Basic Research Cooperation Project between China National Petroleum Corporation and Peking University.
文摘Existing sandstone rock structure evaluation methods rely on visual inspection,with low efficiency,semi-quantitative analysis of roundness,and inability to perform classified statistics in particle size analysis.This study presents an intelligent evaluation method for sandstone rock structure based on the Segment Anything Model(SAM).By developing a lightweight SAM fine-tuning method with rank-decomposition matrix adapters,a multispectral rock particle segmentation model named CoreSAM is constructed,which achieves rock particle edge extraction and type identification.Building upon this,we propose a comprehensive quantitative evaluation system for rock structure,assessing parameters including particle size,sorting,roundness,particle contact and cementation types.The experimental results demonstrate that CoreSAM outperforms existing methods in rock particle segmentation accuracy while showing excellent generalization across different image types such as CT scans and core photographs.The proposed method enables full-sample,classified particle size analysis and quantitative characterization of parameters like roundness,advancing reservoir evaluation towards more precise,quantitative,intuitive,and comprehensive development.
基金supported by the National Natural Science Foundation of China(Grant Nos.11972283 and 42277182).
文摘High-altitude cold regions exhibit complex geological and environmental conditions,fostering steep rock slopes with macroscopic joints and mesoscopic freeze-thaw(F-T)damage.Cyclic loading further exacerbates rock instability,yet the fracture mechanisms and load response relationships remain poorly understood.This study prepared intact and fractured sandstone specimens,subjected them to F-T cycles and graded loading-unloading,and monitored their structural evolution via X-ray computed tomography.First,the progressive failure process was investigated from both qualitative morphologic features and quantitative void parameters.The results showed that intact and fractured sandstone instability behaviors are determined by F-T damage and joint arrangement,respectively.However,both indicate that precursory localization of failure can only be detected when heterogeneous damage exists in advance.Furthermore,the void parameters of undamaged intact sandstone exhibit power-law acceleration,while damaged sandstones are characterized by a trend of initial decrease followed by an increase.Subsequently,a damage constitutive model for freeze-thawed fractured sandstone under graded loading-unloading was established.This model is based on the Lemaitre strain equivalence hypothesis and defines the coupled damage variable through multivariable indicators.In this framework,the material damage induced by fractures and F-T is unified and characterized by void parameters;while the load-induced damage is integrated with the energy linear allocation law and defined by damage energy.Thus,the stress-strain theoretical relationship is depicted,and the model is validated as reliable.Finally,a conceptual model of rock damage due to F-T and loading-unloading was proposed by combining the microscopic testing results from X-ray diffraction and scanning electron microscopy.
基金supported by National Natural Science Foundation of China(Nos.52364004,52464005)The Youth Talent Growth Project of Guizhou Provincial Department of Education(No.Qian Jiao Ji[2024]18)+3 种基金Postgraduate Research Fund of Guizhou Province in 2024(No.2024YJSKYJJ067)Basic Research Project of Guizhou University(No.[2023]40)Guizhou Provincial Basic Research Program(Natural Science)(No.Qian Ke He Ji Chu-ZK[2024]Yi Ban011)Research Fund for Talents of Guizhou University(No.Gui Da Ren Ji He Zi(2023)24)。
文摘During the exploitation of sandstone gas reservoirs,natural fractures near the wellbore affect water infiltration and pore evolution;however,the impact mechanisms of these fractures remain unclear.This study utilized real-time nuclear magnetic resonance(RT-NMR)technology to investigate the influence of near-wellbore fracture angle(a)at 0°,15°,30°,and 45°on water infiltration,migration patterns,and pore evolution mechanisms during water injection.Throughout the experiments,T_(2)curves and magnetic resonance imaging(MRI)were monito red in real time during the water injection process.The pore evolution and water infiltration were translated by the evolution of T_(2)curves and MRI.The results show that increasing injection pressure(P_(inj))transforms adsorption pores into seepage pores,leading to enhanced pore damage.Pore damage predominantly occurs during the rapid pressurization stage and is concentrated around the near-wellbore fracture.The maximum infiltration area and rate were observed at α=0°,while the minimum values occurred at α=45°,which can be attributed to the significant influence of a on water infiltration and migration pathways.The increasing inclination of the infiltration front with a is attributed to the fact that the rate of water infiltration along the fracture wall is always higher than that at the fracture tip.In field fracturing,it is recommended to adjust the perforation direction to align with the natural fracture orientation and optimize pressurization strategies by reducing the slow pressurization duration while extending the rapid pressurization stage.These findings can provide important guidance for setting fracturing sections and optimizing injection parameters in sandstone gas reservoir exploitation.
基金supported by the National Natural Science Foundation of China(Nos.52130411,52174219 and 52174220)the Natural Science Foundation of Jiangsu Province(No.BK20240104)the Fundamental Research Funds for the Central Universities(No.2024-11044).
文摘Gas explosions in coal mine goafs are associated with the roof rock fracturing.An experimental system was established to investigate the potential for electrical ignition induced by sandstone fracturing.The electrical responses,luminescent emissions,and ignition characteristics during tensile and compressive failure of sandstones were analyzed in methane/air premixed gas environments.Results indicate that the application of mechanical loading induces the emergence of electrical signals on rock surfaces and in the surrounding atmosphere.This phenomenon is attributed to the generation,accumulation,and subsequent release of free charges during the deformation and fracture within the sandstone.Compressive failure proved to be more conducive to free charge generation than tensile failure,owing to more crack connections.Furthermore,a precipitous increase in surface and external voltages was observed during complete fracturing,a consequence of electron emission from crack tips within the rock structure.Moreover,the ionization induces luminous emissions owing to the collision of energetic electrons released from gas molecules in methane/air mixtures.A strong positive correlation(R2=0.9429)was identified between luminescence intensity and the magnitude of electrical discharge resulting from rock fracture.Notably,such discharge by rock fracturing can be capable of igniting the premixed gas,particularly when the quartz content exceeds 61%.Piezoelectric effects and crack propagation are crucial mechanisms in the causal chain of the charge generation,discharge,and ionization triggered by rock fractures.Based on the above laboratory results,electric ignition of the transient roof fracturing caused by stress mutations can serve as a new potential ignition source for gas explosions in the goaf.These results offer new insights into the prevention and control of gas explosions.
基金funded by the Sichuan Science and Technology Education Joint Fund,including the mechanism and characterization of CO_(2) geological storage and utilization of carbonate reservoirs in the Sichuan Basin to improve the sealing capacity of mudstone caprocks(No.2024NSFSC1981)also supported by the China Petroleum Science and Technology Innovation Fund,including the experiment of acoustic response mechanism of horizontal well fracturing and the research of DAS big data intelligent inversion method(No.2022DQ02-0305)also supported by the National Natural Science Foundation of China'Study on the mechanism of SNPs improving the sealing ability of mudstone caprock in CO_(2) geological storage(No.42272176)。
文摘As an efficient monitoring and prediction tool,chemical tracers have been widely applied in reservoir characterization,production monitoring,water resources monitoring,and various other fields.Chemical tracer technology is characterized by high efficiency,high precision,relatively simple operational procedures,and low cost.Owing to the limitations of existing tracers,such as minimal options,limited transport efficiency,and complex detection methods,this study used fluorescein isothiocyanate and a ruthenium complex(Ru(phen_(3))^(2+))to synthesize 50 nm multi-color fluorescent silica nanoparticle tracers using an improved St ober method based on fluorescence resonance energy transfer(FRET).Due to the FRET between the two compounds,the synthesized tracer exhibited the characteristics of multi-color fluorescence,and its fluorescent color varied with the mixing ratio of the two precursor solutions.The fluorescence intensity of the synthesized tracer was significantly higher than that of the monochromatic fluorescent nano-tracer.Fourier-transform infrared spectroscopy,ultraviolet spectrophotometry,and fluorescence spectrometry were used to characterize the structure,maximum absorption wavelength,and fluorescence characteristics of the synthesized tracer,respectively.The experimental results show that the synthesized tracer has a maximum absorption wavelength of 450 nm and an emission wavelength of 576 nm.Under field emission scanning electron microscopy,the tracer appears as uniformly spherical particles with a size of 50±5 nm.It exhibited good dispersibility and fluorescence characteristics in reservoir environments that varied in temperature(25-85°C)and salinity(1000-10000 mg/L).The effects of environmentally sensitive clay minerals,tracer particle size,injection concentration,fluid salinity,and flow rate on the transport characteristics(retention)of tracers in sandstone cores were studied using 12 sets of tracer breakthrough experiments.The experimental results showed that increased sensitivity to clay minerals,salinity,and tracer particle size were not conducive to tracer migration in the core.In contrast,increased tracer injection concentration and flow rate were beneficial to tracer migration in the core.
基金Open Project of State Key Laboratory for Geomechanics and Deep Underground Engineering in CUMTB,Grant/Award Number:SKLGDUEK2023National Natural Science Foundation of China,Grant/Award Number:52204101Natural Science Foundation of Shandong Province,Grant/Award Number:ZR2022QE137。
文摘Three sandstone specimens common in rock engineering were selected to study the differences in the mechanical properties of rocks with different lithologies.The development and expansion of the internal cracks in the specimens were observed by combining the simulation system with the acoustic emission system.Through the combination of dynamic and static stresses,the deformation and damage of rocks under deep rock excavation and blasting were simulated.As the results show,the acoustic emission events of specimens with different lithologies under combined static and dynamic cyclic loading can be roughly divided into three phases:weakening,stabilizing,and surging periods.In addition,the acoustic emission characteristics of specimens with different lithologies show general consistency in different compression phases.The degree of fragmentation of specimens increases with the applied stress level;therefore,the stress level is one of the important factors influencing the damage pattern of specimens.The acoustic emission system was used to simulate the deformation and damage of rocks subjected to deep rock body excavation and engineering blasting.Cyclic dynamic perturbations under sinusoidal waves with a frequency of 5 Hz,a loading rate of 0.1 mm/min,a cyclic amplitude of 5 MPa,and a loading rate of 0.1 mm/min were applied to the three rock samples during the experiments.Among them,the fine-grained sandstones are the most sensitive to the sinusoidal cyclic perturbation,followed by the muddy siltstone and the medium-grained sandstones.On this basis,the acoustic emission energy release characteristics were analyzed,and the waveform characteristics in the damage evolution of the specimen under dynamic perturbation were studied by extracting the key points and searching for the main frequency eigenvalues.
