During the operation of sandy railways, the challenge posed by wind-blown sand is a persistent issue. An in-depth study on the influence of wind-blown sand content on the macroscopic and microscopic mechanical propert...During the operation of sandy railways, the challenge posed by wind-blown sand is a persistent issue. An in-depth study on the influence of wind-blown sand content on the macroscopic and microscopic mechanical properties of the ballast bed is of great significance for understanding the potential problems of sandy railways and proposing reasonable and adequate maintenance and repair strategies. Building upon existing research, this study proposes a new assessment indicator for sand content. Utilizing the discrete element method(DEM) and fully considering the complex interactions between ballast and sand particles, three-dimensional(3D) multi-scale analysis models of sandy ballast beds with different wind-blown sand contents are established and validated through field experiments. The effects of varying wind-blown sand content on the microscopic contact distribution and macroscopic mechanical behavior(such as resistance and support stiffness) of ballast beds are carefully analyzed. The results show that with the increase in sand content, the average contact force and coordination number between ballast particles gradually decrease, and the disparity in contact forces between different layers of the ballast bed diminishes. The longitudinal and lateral resistance of the ballast bed initially decreases and then increases, with a critical point at 10% sand content. At 15% sand content, the lateral resistance is mainly shared by the ballast shoulder. The longitudinal resistance sharing ratio is always the largest on the sleeper side, followed by that at the sleeper bottom, and the smallest on the ballast shoulder. When the sand content exceeds 10%, the contribution of sand particles to stiffness significantly increases, leading to an accelerated growth rate of the overall support stiffness of the ballast bed, which is highly detrimental to the long-term service performance of the ballast bed. In conclusion, it is recommended that maintenance and repair operations should be promptly conducted when the sand content of the ballast bed reaches or exceeds 10%.展开更多
To visually describe the sanding pattern,this study constructs a new particle-scale microstructure model of weakly consolidated formation,and develop the corresponding methodology to simulate the sanding process and p...To visually describe the sanding pattern,this study constructs a new particle-scale microstructure model of weakly consolidated formation,and develop the corresponding methodology to simulate the sanding process and predict sand cavity shape.The microstructure model is a particle-objective model,which focuses on the random sedimentation of every sand grain.In the microstructure,every particle has its own size,sphericity and inclination angle.It is used to simulate the actual structure of cemented granular materials,which considers the heterogeneity and randomness of reservoir properties,provides the initial status for subsequent sanding simulation.With the particle detachment criteria,the microscopic simulation of sanding can be visually implemented to investigate the pattern and cavity shapes caused by sand production.The results indicate that sanding always starts initially from the borehole border,and then extends along the weakly consolidated plane,showing obvious characteristic of randomness.Three typical microscopic sanding patterns,concerning pore liquefaction,pseudo wormhole and continuous collapse,are proposed to illustrate the sanding mechanism in weakly consolidated reservoirs.The nonuniformity of sanding performance depends on the heterogeneous distribution of reservoir properties,such as rock strength and particle size.Finally,the three sanding patterns are verified by visually experimental work.The proposed integrated methodology is capable of predicting and describing the sanding cavity shape of an oil well after long-term sanding production,and providing the focus objective of future sand control measure.展开更多
As an independent sand control unit or a common protective shell of a high-quality screen,the punching screen is the outermost sand retaining unit of the sand control pipe which is used in geothermal well or oil and g...As an independent sand control unit or a common protective shell of a high-quality screen,the punching screen is the outermost sand retaining unit of the sand control pipe which is used in geothermal well or oil and gas well.However,most screens only consider the influence of the internal sand retaining medium parameters in the sand control performance design while ignoring the influence of the plugging of the punching screen on the overall sand retaining performance of the screen.To explore the clogging mechanism of the punching screen,this paper established the clogging mechanism calculation model of a single punching screen sand control unit by using the computational fluid mechanics-discrete element method(CFD-DEM)combined method.According to the combined motion of particles and fluids,the influence of the internal flow state on particle motion and accumulation was analyzed.The results showed that(1)the clogging process of the punching sand control unit is divided into three stages:initial clogging,aggravation of clogging and stability of clogging.In the initial stage of blockage,coarse particles form a loose bridge structure,and blockage often occurs preferentially at the streamline gathering place below chamfering inside the sand control unit.In the stage of blockage intensification,the particle mass develops into a relatively complete sand bridge,which develops from both ends of the opening to the center of the opening.In the stable plugging stage,the sand deposits show a“fan shape”and form a“V-shaped”gully inside the punching slot element.(2)Under a certain reservoir particle-size distribution,The slit length and opening height have a large influence on the permeability and blockage rate,while the slit width size has little influence on the permeability and blockage rate.The microscopic clogging mechanism and its law of the punching screen prevention unit are proposed in this study,which has some field guidance significance for the design of punching screen and sand prevention selection.展开更多
Radial well filled with phase change material has been proposed as a novel sand control method for hydrate exploitation.In order to reveal the sand control mechanism,CFD-DEM coupling method is applied to simulate the ...Radial well filled with phase change material has been proposed as a novel sand control method for hydrate exploitation.In order to reveal the sand control mechanism,CFD-DEM coupling method is applied to simulate the migration,settlement,and blockage processes of sand particles in the radial well.The obtained results indicate that three scenarios have been recognized for sand particles passing through sand control medium,based on the diameter ratio of sand control medium to sand particle(D_(d)):fully passing(D_(d)=8.75-22.5),partially passing and partially blocked(D_(d)=3.18-5.63),and completely blocked(D_(d)=2.18-3.21).After being captured by the sand control medium,sand particles can block pores,which increases fluid flow resistance and causes a certain pressure difference in the radial well.The pressure in the radial well should be lower than the hydrate phase equilibrium pressure during sand control design,for the purpose of promoting hydrate decomposition,and sand capture.The length of the radial well should be optimized based on the reservoir pore pressure,production pressure difference,bottom hole pressure,and the pressure gradient in the radial well.It should be noticed that the sand control medium leads to a decrease in permeability after sand particles captured.Even the permeability is reduced to several hundred millidarcy,it is still sufficient to ensure the effective flow of gas and water after hydrate decomposition.Increasing fluid velocity reduces the blocking capacity of the sand control medium,mainly because of deterioration in bridging between sand particles.展开更多
To explore the penetration resistance of calcareous sand media,penetration tests have been conducted in the velocity range of 200-1000 m/s using conical-nosed projectiles with a diameter of 14.5 mm.Further,a pseudo fl...To explore the penetration resistance of calcareous sand media,penetration tests have been conducted in the velocity range of 200-1000 m/s using conical-nosed projectiles with a diameter of 14.5 mm.Further,a pseudo fluid penetration model applicable to the penetration of rigid projectiles in sand media is established according to the approximate flow of compacted sand in the adjacent zone of penetration.The correlation between the impedance function of projectile-target interaction and the internal friction features of pseudo fluid is clarified,and the effects of sand density,cone angle of nose-shaped projectile,and dynamic hardness on the penetration depth are investigated.The results verify the feasibility,wide applicability,and much lower error(with respect to the experimental data)of the proposed model as compared to the Slepyan hydrodynamic model.展开更多
This study conducted temporary plugging and diversion fracturing(TPDF)experiments using a true triaxial fracturing simulation system within a laboratory setting that replicated a lab-based horizontal well completion w...This study conducted temporary plugging and diversion fracturing(TPDF)experiments using a true triaxial fracturing simulation system within a laboratory setting that replicated a lab-based horizontal well completion with multi-cluster sand jetting perforation.The effects of temporary plugging agent(TPA)particle size,TPA concentration,single-cluster perforation number and cluster number on plugging pressure,multi-fracture diversion pattern and distribution of TPAs were investigated.A combination of TPAs with small particle sizes within the fracture and large particle sizes within the segment is conducive to increasing the plugging pressure and promoting the diversion of multi-fractures.The addition of fibers can quickly achieve ultra-high pressure,but it may lead to longitudinal fractures extending along the wellbore.The temporary plugging peak pressure increases with an increase in the concentration of the TPA,reaching a peak at a certain concentration,and further increases do not significantly improve the temporary plugging peak pressure.The breaking pressure and temporary plugging peak pressure show a decreasing trend with an increase in single-cluster perforation number.A lower number of single-cluster perforations is beneficial for increasing the breaking pressure and temporary plugging peak pressure,and it has a more significant control on the propagation of multi-cluster fractures.A lower number of clusters is not conducive to increasing the total number and complexity of artificial fractures,while a higher number of clusters makes it difficult to achieve effective plugging.The TPAs within the fracture is mainly concentrated in the complex fracture areas,especially at the intersections of fractures.Meanwhile,the TPAs within the segment are primarily distributed near the perforation cluster apertures which initiated complex fractures.展开更多
The study of flow behaviour of water-sand mixtures in fractured rocks is of great necessity to understand the producing mechanism and prevention of water inrush and sand gushing accidents.A self-developed seepage test...The study of flow behaviour of water-sand mixtures in fractured rocks is of great necessity to understand the producing mechanism and prevention of water inrush and sand gushing accidents.A self-developed seepage test system is used in this paper to conduct laboratory experiments in order to study the influence of the particle size distribution,the void ratio,and the initial mass of Aeolian sand on the flow behavior.It is concluded that the water flow velocity is insensitive to the initial mass of the Aeolian sand but increases with the power exponent in the Talbot formula and the specimen height.The outflow of the Aeolian sand increases with the power exponent in the Talbot formula,the specimen height,and the initial mass of the Aeolian sand.Besides,the outflow of the Aeolian sand changes exponentially with the water flow velocity.Finally,it is found that the fractured specimen has a maximum sand filtration capacity beyond which the outflow of the Aeolian sand significantly increases with the initial mass of the Aeolian sand.展开更多
The purpose of this paper is to study the critical sand starting velocity and transformation law of flow pattern based on gas-water-sand three-phase flow in an inclined pipe.Firstly,the indoor simulation experiment sy...The purpose of this paper is to study the critical sand starting velocity and transformation law of flow pattern based on gas-water-sand three-phase flow in an inclined pipe.Firstly,the indoor simulation experiment system of gas-water-sand three-phase flow was used to test the conversion law of flow pattern based upon the different gas void fraction.Secondly,the influence of slug bubbles on sand migration was investigated according to distinctive hole deviation angles,gas void fraction and sand concentration.Finally,the critical sand starting velocity was tested based on dissimilar hole deviation angles,gas void fraction,sand concentration and sand particle size,and then the influence of the abovementioned key parameters on the sand starting velocity was debated based on the force analysis of the sand particles.The experimental results illustrated that when the gas void fraction was less than 5%,it was bubbly flow.When it increased from 5%to 30%,the bubbly flow and slug flow coexisted.When it was between 30%and 50%,the slug flow and agitated flow coexisted.When it reached 50%,it was agitated flow.Providing that the hole deviation angle was 90°,the phenomenon of overall migration and wavelike migration on the surface of sand bed was observed.On the contrary,the phenomenon of rolling and jumping migration was recognized.The critical sand starting velocity was positively correlated with the hole deviation angle and sand particle size,but negatively associated with the gas void fraction and sand concentration.This research can provide a certain reference for sand-starting production in the field of petroleum engineering.展开更多
In order to explore the influence of sandstone architecture on waterflooding mechanisms using the architecture method,and taking as an example the M-I layer of the Kumkol oilfield in the South Turgay Basin,Kazakhstan,...In order to explore the influence of sandstone architecture on waterflooding mechanisms using the architecture method,and taking as an example the M-I layer of the Kumkol oilfield in the South Turgay Basin,Kazakhstan,we portrayed the architecture features of different types of sandstones and quantitatively characterized heterogeneities in a single sand body in meandering river facies.Based on the waterflooding characteristics of point bar sand and overbank sand according to waterflooded interpretation results in 367 wells and numerical simulation results of well groups,we finally analyzed the remaining oil potential of the meandering river sandstone and pointed out its development directions at the high water cut stage.The result shows that because lateral accretion shale beds are developed inside single sand bodies,the point bar sand is a semi-connected body.The overbank sand is thin sandstone with poor connectivity,small area and fast lateral changes.The heterogeneity of the overbank sand is stronger than the point bar sand.The sandstone architectures control the waterflooding characteristics.In meandering river sandstones,the bottom of the point bar sand is strongly waterflooded,while the top of the point bar sand and most of the overbank sand are only weakly waterflooded or unflooded.The thickness percentage of unflooded zone and weakly waterflooded zone in point bar sand is 40％,and the remaining oil in its top part is the main direction for future development.展开更多
Sand production is one of the major problems in sandstone reservoirs. Different mechanical and chemical methods have been proposed to control sand production. In this paper, we propose a chemical method based on using...Sand production is one of the major problems in sandstone reservoirs. Different mechanical and chemical methods have been proposed to control sand production. In this paper, we propose a chemical method based on using polyacrylamide/chromium triacetate hydrogel to investigate sand production in a synthetic sandpack system. To this end, a series of bulk experiments including the bottle test and rheological analysis along with compression tests were conducted. Experimental results indicated that the compressive strength of the sandpack was increased as much as 30 times by injecting 0.5 pore volume of hydrogel. Also, it was found that the increases in cross-linker and polymer concentrations exhibited a positive impact on the compressive strength of the sandpack, mostly by cross-linker concentration(48 psi). Hydrogel with a higher value of cross-linker could retain its viscoelastic properties against the strain which was a maximum of 122% for 0.5 weight ratio of cross-linker/polymer. The presence of salts, in particular divalent cations, has a detrimental effect on the hydrogel stability. The maximum strain value applied on hydrogel in the presence of CaCl_2 was only about 201% as compared to 1010% in the presence of distilled water. Finally, thermogravimetric analysis and its derivative showed that the hydrogel could retain its structure up to 300 °C. The results of this study revealed the potential application of the hydrogel to control sand production.展开更多
Stimulation of unconsolidated formations via horizontal wells has seen its vast implementation in the recent development of heavy oil reservoir to save the time and cost of preheating the reservoir before the steam-as...Stimulation of unconsolidated formations via horizontal wells has seen its vast implementation in the recent development of heavy oil reservoir to save the time and cost of preheating the reservoir before the steam-assisted gravity drainage(SAGD)process.A mathematical approach was proposed in this research that fully couples the hydraulic,mechanical and thermal responses of unconsolidated sandstone formations and also applies failure criteria for describing either shear dilation or tensile parting mechanism that generates microcracks.The approach was implemented to predict the porothermoelastic response of a pair of SAGD wells subject to injection and subsequent micro-fracturing using hot water.It was found that the predicted bottom hole pressures(BHPs)match closely with the field observed data.An elliptical dilation zone developed around the dual wells with relatively high pore pressure,porosity,permeability and temperature,implying good interwell hydraulic communication between both wells.The activation of microcracks dramatically accelerated the dissipation of pore pressure across the entire formation depth and also facilitated heat convection in between the dual wells,though to a lesser extent.In summary,the approach provides a convenient means to assist field engineers in the optimization of injection efficiency and evaluation of interference among multiple horizontal wells.展开更多
Water–sand flow triggered by rainfall is the dominant mechanism for instability and failure of sand slopes. To further analyze the stability state of sand on a slope under different rainfall conditions, the initiatio...Water–sand flow triggered by rainfall is the dominant mechanism for instability and failure of sand slopes. To further analyze the stability state of sand on a slope under different rainfall conditions, the initiation conditions and flow characteristics of water–sand flows are studied. Based on the theory of equilibrium forces and hydrological dynamics, a 1：100-scale analog model is built and verified with field observation data. The results indicate three dynamic stabilization stages of the sand slope under different weather conditions： dry sand, wet sand, and water–sand flow. Water–sand flows are triggered easilyunder short duration and heavy rainfall conditions. The rainfall threshold required to initiate water–sand flow is 4.14 mm/h. Rainfall amount and duration required to initiate water–sand flow decrease with fine sand content increasing. A sand head that develops at the front of the water–sand flow results in a flow along the edge of the sand debris flow and a ‘‘tree root’’ flow morphology. Modelingresults are consistent with theoretical analysis and field observations.展开更多
Based on seismic and logging data,taking the downthrow fault nose of Binhai fault in Qikou Sag as the object of study,we analyzed fault characteristics,sand body distribution,fault-sand combinations and hydrocarbon ac...Based on seismic and logging data,taking the downthrow fault nose of Binhai fault in Qikou Sag as the object of study,we analyzed fault characteristics,sand body distribution,fault-sand combinations and hydrocarbon accumulation to reveal the hydrocarbon enrichment law in the fault-rich area of fault depression lake basin.The results show that the Binhai Cenozoic fault nose is characterized by east-west zoning,the main part of the western fault segment is simple in structure,whereas the broom-shaped faults in the eastern segment are complex in structure,including several groups of faults.The difference of fault evolution controls the spatial distribution of sand bodies.The sand bodies are in continuous large pieces in the downthrow fault trough belt along the Gangdong Fault in the middle segment of the fault nose,forming consequent fault-sand combination;whereas the fault activity period of the eastern part of the fault nose was later,and the sand bodies controlled by paleogeomorphology are distributed in multi-phase north-south finger-shaped pattern,forming vertical fault-sand combination pattern matching with the fault.The configuration between faults and sand bodies,and oil sources and caprocks determine the vertical conductivity,plane distribution and vertical distribution of oil and gas.Two oil and gas accumulation modes,i.e.single main fault hydrocarbon supply-fault sand consequent matching-oil accumulation in multi-layers stereoscopically and fault system transportation-fault sand vertical matching-oil accumulation in banded overlapping layers occur in the middle and eastern segments of the fault nose respectively,and they control the difference of oil and gas distribution and enrichment degree in the Binhai fault nose.展开更多
Gas injection is the second largest enhanced oil recovery process, next only to the thermal method used in heavy oil fields. To increase the extent of the reservoir contacted by the injected gas, the gas is generally ...Gas injection is the second largest enhanced oil recovery process, next only to the thermal method used in heavy oil fields. To increase the extent of the reservoir contacted by the injected gas, the gas is generally injected intermittently with water. This mode of injection is called water-alternating-gas (WAG). This study deals with a new immiscible water alternating gas (IWAG) EOR technique, “hot IWAG” which includes combination of thermal, solvent and sweep techniques. In the proposed method CO2 will be superheated above the reservoir temperature and instead of normal temperature water, hot water will be used. Hot CO2 and hot water will be alternatively injected into the sand packs. A laboratory test was conducted on the fractured and conventional sand packs. Slugs of water and CO2 with a low and constant rate were injected into the sand packs alternatively; slug size was 0.05 PV. Recovery from each sand pack was monitored and after that hot water and hot CO2 were injected alternatively under the same conditions and increased oil recovery from each sand pack and breakthrough were measured. Experimental results showed that the injection of hot WAG could significantly recover residual oil after WAG injection in conventional and fractured sand packs.展开更多
Based on the cores from 47 wells and logging data of 130 wells,the main types of sand bodies in the shallow water delta of the Chang 8_(2) sub-member in the Triassic Yanchang Formation,Longdong Area,Ordos Basin were c...Based on the cores from 47 wells and logging data of 130 wells,the main types of sand bodies in the shallow water delta of the Chang 8_(2) sub-member in the Triassic Yanchang Formation,Longdong Area,Ordos Basin were comprehensively analyzed,the distribution characteristics of sand bodies more than 20 m thick were identified,and the genetic types of the thick sand bodies were sorted out.In this region,thick-bed sand bodies can be divided into two types according to the shape and position:type 1 is the sand body in wide strip and is distributed between the average high water mark and the average low water mark;type 2 is distributed on both sides of the average low water mark and is in irregular lump shape.Based on the principle of the volume distribution of sediments and the change rule of accommodation space,the genetic models of two types of thick-bed sand bodies in the Chang 8_(2) sub-member are superimposed distributary channel sand bodies in high accommodation space and superimposed composite sand bodies in low accommodation space.展开更多
Water is usally thought of a limiting factor for the restoration of semi-arid ecosystem. In the growing season of 2006, a study was conducted to determine the effects of modeling precipitation on seasonal patterns in ...Water is usally thought of a limiting factor for the restoration of semi-arid ecosystem. In the growing season of 2006, a study was conducted to determine the effects of modeling precipitation on seasonal patterns in concentrations of soil-available nitrogen and to describe the seasonal patterns in soil nitrogen availability and seasonal variation in the rates of net nitrogen mineralization of topsoil at Daqinggou ecological station in Keerqin sand lands, Inner Mongolia Autonomous Region, China. Manipulation of water （80 mm） was designed to be added to experiment plots of sandy grasslands in dry season. Water addition （W） treatment and control （CK） treatment were separately taken in six replications and randomly assigned in 12 plots （4 m×4 m for each） with 2-m buffers betweens. Results showed that the content of soil inorganic nitrogen and net nitrogen mineralization rate were not affected by adding water in sandy grassland of Keerqin sand lands. Net ni- trogen mineralization rates ranged from 0.5μg·g^-1,month^-1 to 4 μg.g^-1.month^-1. The highest values of soil inorganic nitrogen and net nitrogen mineralization occurred on October 15 in control plots. The seasonal changes of soil inorganic nitrogen contents exhibited ＂V＂ shape pattern that was related to seasonal patterns of soil ammonium-N （ascending trend） and nitrate-N transformation （descending trend）.展开更多
The oil sands deposits in the Western Canada Sedimentary Basin （WCSB） comprise of at least 85% of the total immobile bitumen in place in the world and are so concentrated as to be virtually the only such deposits th...The oil sands deposits in the Western Canada Sedimentary Basin （WCSB） comprise of at least 85% of the total immobile bitumen in place in the world and are so concentrated as to be virtually the only such deposits that are economically recoverable for conversion to oil. The major deposits are in three geographic and geologic regions of Alberta： Athabasca, Cold Lake and Peace River. The bitumen reserves have oil gravities ranging from 8 to 12° API, and are hosted in the reservoirs of varying age, ranging from Devonian （Grosmont Formation） to Early Cretaceous （Mannville Group）. They were derived from light oils in the southern Alberta and migrated to the north and east for over 100 km during the Laramide Orogeny, which was responsible for the uplift of the Rocky Mountains. Biodegradation is the only process that transforms light oil into bitumen in such a dramatic way that overshadowed other alterations with minor contributions. The levels of biodegradation in the basin increasing from west （non-biodegraded） to east （extremely biodegraded） can be attributed to decreasing reservoir temperature, which played the primary role in controlling the biodegradation regime. Once the reservoir was heated to approximately 80℃, it was pasteurized and no biodegradation would further occur. However, reservoir temperature could not alone predict the variations of the oil composition and physical properties. Compositional gradients and a wide range ofbiodegradation degree at single reservoir column indicate that the water-leg size or the volume ratio of oil to water is one of the critical local controls for the vertical variations ofbiodegradation degree and oil physical properties. Late charging and mixing of the fresh and degraded oils ultimately dictate the final distribution of compositions and physical properties found in the heavy oil and oil sand fields. Oil geochemistry can reveal precisely the processes and levels that control these variations in a given field, which opens the possibility of model-driven prediction of oil properties and sweet spots in reservoirs.展开更多
Tight sands are abundant in nanopores leading to a high capillary pressure and normally a low fluid injectivity.As such,spontaneous imbibition might be an effective mechanism for improving oil recovery from tight sand...Tight sands are abundant in nanopores leading to a high capillary pressure and normally a low fluid injectivity.As such,spontaneous imbibition might be an effective mechanism for improving oil recovery from tight sands after fracturing.The chemical agents added to the injected water can alter the interfacial properties,which could help further enhance the oil recovery by spontaneous imbibition.This study explores the possibility of using novel chemicals to enhance oil recovery from tight sands via spontaneous imbibition.We experimentally examine the effects of more than ten different chemical agents on spontaneous imbibition,including a cationic surfactant(C12 TAB),two anionic surfactants(0242 and 0342),an ionic liquid(BMMIM BF4),a high pH solution(NaBO2),and a series of house-made deep eutectic solvents(DES3-7,9,11,and 14).The interfacial tensions(IFT)between oil phase and some chemical solutions are also determined.Experimental results indicate that both the ionic liquid and cationic surfactant used in this study are detrimental to spontaneous imbibition and decrease the oil recovery from tight sands,even though cationic surfactant significantly decreases the oil-water IFT while ionic liquid does not.The high pH NaBO2 solution does not demonstrate significant effect on oil recovery improvement and IFT reduction.The anionic surfactants(O242 and O342)are effective in enhancing oil recovery from tight sands through oil-water IFT reduction and emulsification effects.The DESs drive the rock surface to be more water-wet,and a specific formulation(DES9)leads to much improvement on oil recovery under counter-current imbibition condition.This preliminary study would provide some knowledge about how to optimize the selection of chemicals for improving oil recovery from tight reservoirs.展开更多
基金supported by the National Natural Science Foundation of China (Grant No. 52372425)the Fundamental Research Funds for the Central Universities (Science and Technology Leading Talent Team Poject) Grant No. 2022JBXT010。
文摘During the operation of sandy railways, the challenge posed by wind-blown sand is a persistent issue. An in-depth study on the influence of wind-blown sand content on the macroscopic and microscopic mechanical properties of the ballast bed is of great significance for understanding the potential problems of sandy railways and proposing reasonable and adequate maintenance and repair strategies. Building upon existing research, this study proposes a new assessment indicator for sand content. Utilizing the discrete element method(DEM) and fully considering the complex interactions between ballast and sand particles, three-dimensional(3D) multi-scale analysis models of sandy ballast beds with different wind-blown sand contents are established and validated through field experiments. The effects of varying wind-blown sand content on the microscopic contact distribution and macroscopic mechanical behavior(such as resistance and support stiffness) of ballast beds are carefully analyzed. The results show that with the increase in sand content, the average contact force and coordination number between ballast particles gradually decrease, and the disparity in contact forces between different layers of the ballast bed diminishes. The longitudinal and lateral resistance of the ballast bed initially decreases and then increases, with a critical point at 10% sand content. At 15% sand content, the lateral resistance is mainly shared by the ballast shoulder. The longitudinal resistance sharing ratio is always the largest on the sleeper side, followed by that at the sleeper bottom, and the smallest on the ballast shoulder. When the sand content exceeds 10%, the contribution of sand particles to stiffness significantly increases, leading to an accelerated growth rate of the overall support stiffness of the ballast bed, which is highly detrimental to the long-term service performance of the ballast bed. In conclusion, it is recommended that maintenance and repair operations should be promptly conducted when the sand content of the ballast bed reaches or exceeds 10%.
基金financially supported by the National Natural Science Foundation of China(Grant No.51774307,52074331,42002182)partially supported by Major Special Projects of CNPC,China(ZD2019-184)。
文摘To visually describe the sanding pattern,this study constructs a new particle-scale microstructure model of weakly consolidated formation,and develop the corresponding methodology to simulate the sanding process and predict sand cavity shape.The microstructure model is a particle-objective model,which focuses on the random sedimentation of every sand grain.In the microstructure,every particle has its own size,sphericity and inclination angle.It is used to simulate the actual structure of cemented granular materials,which considers the heterogeneity and randomness of reservoir properties,provides the initial status for subsequent sanding simulation.With the particle detachment criteria,the microscopic simulation of sanding can be visually implemented to investigate the pattern and cavity shapes caused by sand production.The results indicate that sanding always starts initially from the borehole border,and then extends along the weakly consolidated plane,showing obvious characteristic of randomness.Three typical microscopic sanding patterns,concerning pore liquefaction,pseudo wormhole and continuous collapse,are proposed to illustrate the sanding mechanism in weakly consolidated reservoirs.The nonuniformity of sanding performance depends on the heterogeneous distribution of reservoir properties,such as rock strength and particle size.Finally,the three sanding patterns are verified by visually experimental work.The proposed integrated methodology is capable of predicting and describing the sanding cavity shape of an oil well after long-term sanding production,and providing the focus objective of future sand control measure.
文摘As an independent sand control unit or a common protective shell of a high-quality screen,the punching screen is the outermost sand retaining unit of the sand control pipe which is used in geothermal well or oil and gas well.However,most screens only consider the influence of the internal sand retaining medium parameters in the sand control performance design while ignoring the influence of the plugging of the punching screen on the overall sand retaining performance of the screen.To explore the clogging mechanism of the punching screen,this paper established the clogging mechanism calculation model of a single punching screen sand control unit by using the computational fluid mechanics-discrete element method(CFD-DEM)combined method.According to the combined motion of particles and fluids,the influence of the internal flow state on particle motion and accumulation was analyzed.The results showed that(1)the clogging process of the punching sand control unit is divided into three stages:initial clogging,aggravation of clogging and stability of clogging.In the initial stage of blockage,coarse particles form a loose bridge structure,and blockage often occurs preferentially at the streamline gathering place below chamfering inside the sand control unit.In the stage of blockage intensification,the particle mass develops into a relatively complete sand bridge,which develops from both ends of the opening to the center of the opening.In the stable plugging stage,the sand deposits show a“fan shape”and form a“V-shaped”gully inside the punching slot element.(2)Under a certain reservoir particle-size distribution,The slit length and opening height have a large influence on the permeability and blockage rate,while the slit width size has little influence on the permeability and blockage rate.The microscopic clogging mechanism and its law of the punching screen prevention unit are proposed in this study,which has some field guidance significance for the design of punching screen and sand prevention selection.
基金sponsored by National Natural Science Foundation of China (Grand No.52204024,52074332)CNPC Innovation Found (Grant No.2021DQ02-1006)Fundamental Research Funds for the Central Universities (No.2-9-2023-049)。
文摘Radial well filled with phase change material has been proposed as a novel sand control method for hydrate exploitation.In order to reveal the sand control mechanism,CFD-DEM coupling method is applied to simulate the migration,settlement,and blockage processes of sand particles in the radial well.The obtained results indicate that three scenarios have been recognized for sand particles passing through sand control medium,based on the diameter ratio of sand control medium to sand particle(D_(d)):fully passing(D_(d)=8.75-22.5),partially passing and partially blocked(D_(d)=3.18-5.63),and completely blocked(D_(d)=2.18-3.21).After being captured by the sand control medium,sand particles can block pores,which increases fluid flow resistance and causes a certain pressure difference in the radial well.The pressure in the radial well should be lower than the hydrate phase equilibrium pressure during sand control design,for the purpose of promoting hydrate decomposition,and sand capture.The length of the radial well should be optimized based on the reservoir pore pressure,production pressure difference,bottom hole pressure,and the pressure gradient in the radial well.It should be noticed that the sand control medium leads to a decrease in permeability after sand particles captured.Even the permeability is reduced to several hundred millidarcy,it is still sufficient to ensure the effective flow of gas and water after hydrate decomposition.Increasing fluid velocity reduces the blocking capacity of the sand control medium,mainly because of deterioration in bridging between sand particles.
基金funded by the National Natural Science Foundation of China(Grant No.12072371)Jiangsu Natural Science Foundation(Grant No.BK20221528)。
文摘To explore the penetration resistance of calcareous sand media,penetration tests have been conducted in the velocity range of 200-1000 m/s using conical-nosed projectiles with a diameter of 14.5 mm.Further,a pseudo fluid penetration model applicable to the penetration of rigid projectiles in sand media is established according to the approximate flow of compacted sand in the adjacent zone of penetration.The correlation between the impedance function of projectile-target interaction and the internal friction features of pseudo fluid is clarified,and the effects of sand density,cone angle of nose-shaped projectile,and dynamic hardness on the penetration depth are investigated.The results verify the feasibility,wide applicability,and much lower error(with respect to the experimental data)of the proposed model as compared to the Slepyan hydrodynamic model.
基金Supported by the National Natural Science Foundation of China(51974332).
文摘This study conducted temporary plugging and diversion fracturing(TPDF)experiments using a true triaxial fracturing simulation system within a laboratory setting that replicated a lab-based horizontal well completion with multi-cluster sand jetting perforation.The effects of temporary plugging agent(TPA)particle size,TPA concentration,single-cluster perforation number and cluster number on plugging pressure,multi-fracture diversion pattern and distribution of TPAs were investigated.A combination of TPAs with small particle sizes within the fracture and large particle sizes within the segment is conducive to increasing the plugging pressure and promoting the diversion of multi-fractures.The addition of fibers can quickly achieve ultra-high pressure,but it may lead to longitudinal fractures extending along the wellbore.The temporary plugging peak pressure increases with an increase in the concentration of the TPA,reaching a peak at a certain concentration,and further increases do not significantly improve the temporary plugging peak pressure.The breaking pressure and temporary plugging peak pressure show a decreasing trend with an increase in single-cluster perforation number.A lower number of single-cluster perforations is beneficial for increasing the breaking pressure and temporary plugging peak pressure,and it has a more significant control on the propagation of multi-cluster fractures.A lower number of clusters is not conducive to increasing the total number and complexity of artificial fractures,while a higher number of clusters makes it difficult to achieve effective plugging.The TPAs within the fracture is mainly concentrated in the complex fracture areas,especially at the intersections of fractures.Meanwhile,the TPAs within the segment are primarily distributed near the perforation cluster apertures which initiated complex fractures.
基金financially supported by the National Natural Science Foundation of China(Nos.41807209,51778215,51708185,and 51974293)the Young Teacher Foundation of HPU(No.2019XQG-19)+3 种基金the Henan Provincial Youth Talent Promotion Program(No.2020HYTP003)the Jiangsu Province Science Foundation for Youths(No.BK20180658)the Doctor Foundation of Henan Polytechnic University(Nos.B2017-51 and B2017-53)China Postdoctoral Science Foundation(No.2018M632422)。
文摘The study of flow behaviour of water-sand mixtures in fractured rocks is of great necessity to understand the producing mechanism and prevention of water inrush and sand gushing accidents.A self-developed seepage test system is used in this paper to conduct laboratory experiments in order to study the influence of the particle size distribution,the void ratio,and the initial mass of Aeolian sand on the flow behavior.It is concluded that the water flow velocity is insensitive to the initial mass of the Aeolian sand but increases with the power exponent in the Talbot formula and the specimen height.The outflow of the Aeolian sand increases with the power exponent in the Talbot formula,the specimen height,and the initial mass of the Aeolian sand.Besides,the outflow of the Aeolian sand changes exponentially with the water flow velocity.Finally,it is found that the fractured specimen has a maximum sand filtration capacity beyond which the outflow of the Aeolian sand significantly increases with the initial mass of the Aeolian sand.
基金supporting by the Youth Program of National Natural Science Foundation of China(52104012)the China Postdoctoral Science Foundation(2021M693494)+2 种基金the Key Program of the National Natural Science Foundation of China(51734010)the Key Natural Science Projects of Scientific Research Plan in Colleges and Universities of Xinjiang Uygur Autonomous Region(XJEDU2021I028)the Strategic Cooperation Technology Projects of CNPC and CUPB(ZLZX2020-01-01)
文摘The purpose of this paper is to study the critical sand starting velocity and transformation law of flow pattern based on gas-water-sand three-phase flow in an inclined pipe.Firstly,the indoor simulation experiment system of gas-water-sand three-phase flow was used to test the conversion law of flow pattern based upon the different gas void fraction.Secondly,the influence of slug bubbles on sand migration was investigated according to distinctive hole deviation angles,gas void fraction and sand concentration.Finally,the critical sand starting velocity was tested based on dissimilar hole deviation angles,gas void fraction,sand concentration and sand particle size,and then the influence of the abovementioned key parameters on the sand starting velocity was debated based on the force analysis of the sand particles.The experimental results illustrated that when the gas void fraction was less than 5%,it was bubbly flow.When it increased from 5%to 30%,the bubbly flow and slug flow coexisted.When it was between 30%and 50%,the slug flow and agitated flow coexisted.When it reached 50%,it was agitated flow.Providing that the hole deviation angle was 90°,the phenomenon of overall migration and wavelike migration on the surface of sand bed was observed.On the contrary,the phenomenon of rolling and jumping migration was recognized.The critical sand starting velocity was positively correlated with the hole deviation angle and sand particle size,but negatively associated with the gas void fraction and sand concentration.This research can provide a certain reference for sand-starting production in the field of petroleum engineering.
基金funded by the Major Program of PetroChina(2011E-2506)
文摘In order to explore the influence of sandstone architecture on waterflooding mechanisms using the architecture method,and taking as an example the M-I layer of the Kumkol oilfield in the South Turgay Basin,Kazakhstan,we portrayed the architecture features of different types of sandstones and quantitatively characterized heterogeneities in a single sand body in meandering river facies.Based on the waterflooding characteristics of point bar sand and overbank sand according to waterflooded interpretation results in 367 wells and numerical simulation results of well groups,we finally analyzed the remaining oil potential of the meandering river sandstone and pointed out its development directions at the high water cut stage.The result shows that because lateral accretion shale beds are developed inside single sand bodies,the point bar sand is a semi-connected body.The overbank sand is thin sandstone with poor connectivity,small area and fast lateral changes.The heterogeneity of the overbank sand is stronger than the point bar sand.The sandstone architectures control the waterflooding characteristics.In meandering river sandstones,the bottom of the point bar sand is strongly waterflooded,while the top of the point bar sand and most of the overbank sand are only weakly waterflooded or unflooded.The thickness percentage of unflooded zone and weakly waterflooded zone in point bar sand is 40％,and the remaining oil in its top part is the main direction for future development.
基金support of the Iran National Science Foundation(INSF)with Project No.of 95849122
文摘Sand production is one of the major problems in sandstone reservoirs. Different mechanical and chemical methods have been proposed to control sand production. In this paper, we propose a chemical method based on using polyacrylamide/chromium triacetate hydrogel to investigate sand production in a synthetic sandpack system. To this end, a series of bulk experiments including the bottle test and rheological analysis along with compression tests were conducted. Experimental results indicated that the compressive strength of the sandpack was increased as much as 30 times by injecting 0.5 pore volume of hydrogel. Also, it was found that the increases in cross-linker and polymer concentrations exhibited a positive impact on the compressive strength of the sandpack, mostly by cross-linker concentration(48 psi). Hydrogel with a higher value of cross-linker could retain its viscoelastic properties against the strain which was a maximum of 122% for 0.5 weight ratio of cross-linker/polymer. The presence of salts, in particular divalent cations, has a detrimental effect on the hydrogel stability. The maximum strain value applied on hydrogel in the presence of CaCl_2 was only about 201% as compared to 1010% in the presence of distilled water. Finally, thermogravimetric analysis and its derivative showed that the hydrogel could retain its structure up to 300 °C. The results of this study revealed the potential application of the hydrogel to control sand production.
基金the financial support from the National Major Science and Technology Projects of China(Grant No.2017ZX05009-003)the National Natural Science Foundation of China(No.51404281)
文摘Stimulation of unconsolidated formations via horizontal wells has seen its vast implementation in the recent development of heavy oil reservoir to save the time and cost of preheating the reservoir before the steam-assisted gravity drainage(SAGD)process.A mathematical approach was proposed in this research that fully couples the hydraulic,mechanical and thermal responses of unconsolidated sandstone formations and also applies failure criteria for describing either shear dilation or tensile parting mechanism that generates microcracks.The approach was implemented to predict the porothermoelastic response of a pair of SAGD wells subject to injection and subsequent micro-fracturing using hot water.It was found that the predicted bottom hole pressures(BHPs)match closely with the field observed data.An elliptical dilation zone developed around the dual wells with relatively high pore pressure,porosity,permeability and temperature,implying good interwell hydraulic communication between both wells.The activation of microcracks dramatically accelerated the dissipation of pore pressure across the entire formation depth and also facilitated heat convection in between the dual wells,though to a lesser extent.In summary,the approach provides a convenient means to assist field engineers in the optimization of injection efficiency and evaluation of interference among multiple horizontal wells.
基金supported by the National Natural Science Foundation of China (NSFC) (Grants Nos. 41662020 and 41462012)
文摘Water–sand flow triggered by rainfall is the dominant mechanism for instability and failure of sand slopes. To further analyze the stability state of sand on a slope under different rainfall conditions, the initiation conditions and flow characteristics of water–sand flows are studied. Based on the theory of equilibrium forces and hydrological dynamics, a 1：100-scale analog model is built and verified with field observation data. The results indicate three dynamic stabilization stages of the sand slope under different weather conditions： dry sand, wet sand, and water–sand flow. Water–sand flows are triggered easilyunder short duration and heavy rainfall conditions. The rainfall threshold required to initiate water–sand flow is 4.14 mm/h. Rainfall amount and duration required to initiate water–sand flow decrease with fine sand content increasing. A sand head that develops at the front of the water–sand flow results in a flow along the edge of the sand debris flow and a ‘‘tree root’’ flow morphology. Modelingresults are consistent with theoretical analysis and field observations.
基金Supported by the China National Science and Technology Major Project(2016ZX05006).
文摘Based on seismic and logging data,taking the downthrow fault nose of Binhai fault in Qikou Sag as the object of study,we analyzed fault characteristics,sand body distribution,fault-sand combinations and hydrocarbon accumulation to reveal the hydrocarbon enrichment law in the fault-rich area of fault depression lake basin.The results show that the Binhai Cenozoic fault nose is characterized by east-west zoning,the main part of the western fault segment is simple in structure,whereas the broom-shaped faults in the eastern segment are complex in structure,including several groups of faults.The difference of fault evolution controls the spatial distribution of sand bodies.The sand bodies are in continuous large pieces in the downthrow fault trough belt along the Gangdong Fault in the middle segment of the fault nose,forming consequent fault-sand combination;whereas the fault activity period of the eastern part of the fault nose was later,and the sand bodies controlled by paleogeomorphology are distributed in multi-phase north-south finger-shaped pattern,forming vertical fault-sand combination pattern matching with the fault.The configuration between faults and sand bodies,and oil sources and caprocks determine the vertical conductivity,plane distribution and vertical distribution of oil and gas.Two oil and gas accumulation modes,i.e.single main fault hydrocarbon supply-fault sand consequent matching-oil accumulation in multi-layers stereoscopically and fault system transportation-fault sand vertical matching-oil accumulation in banded overlapping layers occur in the middle and eastern segments of the fault nose respectively,and they control the difference of oil and gas distribution and enrichment degree in the Binhai fault nose.
文摘Gas injection is the second largest enhanced oil recovery process, next only to the thermal method used in heavy oil fields. To increase the extent of the reservoir contacted by the injected gas, the gas is generally injected intermittently with water. This mode of injection is called water-alternating-gas (WAG). This study deals with a new immiscible water alternating gas (IWAG) EOR technique, “hot IWAG” which includes combination of thermal, solvent and sweep techniques. In the proposed method CO2 will be superheated above the reservoir temperature and instead of normal temperature water, hot water will be used. Hot CO2 and hot water will be alternatively injected into the sand packs. A laboratory test was conducted on the fractured and conventional sand packs. Slugs of water and CO2 with a low and constant rate were injected into the sand packs alternatively; slug size was 0.05 PV. Recovery from each sand pack was monitored and after that hot water and hot CO2 were injected alternatively under the same conditions and increased oil recovery from each sand pack and breakthrough were measured. Experimental results showed that the injection of hot WAG could significantly recover residual oil after WAG injection in conventional and fractured sand packs.
基金Supported by the National Basic Research Program of China (973 Program)(2014CB239000)China Petroleum Scientific Research and Technology Development Project (YJXK2019-16)。
文摘Based on the cores from 47 wells and logging data of 130 wells,the main types of sand bodies in the shallow water delta of the Chang 8_(2) sub-member in the Triassic Yanchang Formation,Longdong Area,Ordos Basin were comprehensively analyzed,the distribution characteristics of sand bodies more than 20 m thick were identified,and the genetic types of the thick sand bodies were sorted out.In this region,thick-bed sand bodies can be divided into two types according to the shape and position:type 1 is the sand body in wide strip and is distributed between the average high water mark and the average low water mark;type 2 is distributed on both sides of the average low water mark and is in irregular lump shape.Based on the principle of the volume distribution of sediments and the change rule of accommodation space,the genetic models of two types of thick-bed sand bodies in the Chang 8_(2) sub-member are superimposed distributary channel sand bodies in high accommodation space and superimposed composite sand bodies in low accommodation space.
基金This paper is supported by the Key Laboratory of Ter-restrial Ecological Process and Regional Ecological Safety in Liaoning Province (06ZDS212SS)the Knowledge Innovation Program of the Chinese Academy of Sciences (07SBS115S3).
文摘Water is usally thought of a limiting factor for the restoration of semi-arid ecosystem. In the growing season of 2006, a study was conducted to determine the effects of modeling precipitation on seasonal patterns in concentrations of soil-available nitrogen and to describe the seasonal patterns in soil nitrogen availability and seasonal variation in the rates of net nitrogen mineralization of topsoil at Daqinggou ecological station in Keerqin sand lands, Inner Mongolia Autonomous Region, China. Manipulation of water （80 mm） was designed to be added to experiment plots of sandy grasslands in dry season. Water addition （W） treatment and control （CK） treatment were separately taken in six replications and randomly assigned in 12 plots （4 m×4 m for each） with 2-m buffers betweens. Results showed that the content of soil inorganic nitrogen and net nitrogen mineralization rate were not affected by adding water in sandy grassland of Keerqin sand lands. Net ni- trogen mineralization rates ranged from 0.5μg·g^-1,month^-1 to 4 μg.g^-1.month^-1. The highest values of soil inorganic nitrogen and net nitrogen mineralization occurred on October 15 in control plots. The seasonal changes of soil inorganic nitrogen contents exhibited ＂V＂ shape pattern that was related to seasonal patterns of soil ammonium-N （ascending trend） and nitrate-N transformation （descending trend）.
文摘The oil sands deposits in the Western Canada Sedimentary Basin （WCSB） comprise of at least 85% of the total immobile bitumen in place in the world and are so concentrated as to be virtually the only such deposits that are economically recoverable for conversion to oil. The major deposits are in three geographic and geologic regions of Alberta： Athabasca, Cold Lake and Peace River. The bitumen reserves have oil gravities ranging from 8 to 12° API, and are hosted in the reservoirs of varying age, ranging from Devonian （Grosmont Formation） to Early Cretaceous （Mannville Group）. They were derived from light oils in the southern Alberta and migrated to the north and east for over 100 km during the Laramide Orogeny, which was responsible for the uplift of the Rocky Mountains. Biodegradation is the only process that transforms light oil into bitumen in such a dramatic way that overshadowed other alterations with minor contributions. The levels of biodegradation in the basin increasing from west （non-biodegraded） to east （extremely biodegraded） can be attributed to decreasing reservoir temperature, which played the primary role in controlling the biodegradation regime. Once the reservoir was heated to approximately 80℃, it was pasteurized and no biodegradation would further occur. However, reservoir temperature could not alone predict the variations of the oil composition and physical properties. Compositional gradients and a wide range ofbiodegradation degree at single reservoir column indicate that the water-leg size or the volume ratio of oil to water is one of the critical local controls for the vertical variations ofbiodegradation degree and oil physical properties. Late charging and mixing of the fresh and degraded oils ultimately dictate the final distribution of compositions and physical properties found in the heavy oil and oil sand fields. Oil geochemistry can reveal precisely the processes and levels that control these variations in a given field, which opens the possibility of model-driven prediction of oil properties and sweet spots in reservoirs.
基金support provided through a NSERC Discovery Grant(No:RES0011227)to T.Babadaglia NSERC Discovery Grant(No:NSERC RGPIN 05394)to H.Li+3 种基金financial supports provided by National Natural Science Foundation of China(No:51874240)National Science and Technology Major Project(No:2016ZX05047003-004)the Key Laboratory Fund of Education Department of Shaanxi Province(No:15JS086)Ph.D.Scholarship from the China Scholarship Council(CSC)(201806450029)for the financial support.
文摘Tight sands are abundant in nanopores leading to a high capillary pressure and normally a low fluid injectivity.As such,spontaneous imbibition might be an effective mechanism for improving oil recovery from tight sands after fracturing.The chemical agents added to the injected water can alter the interfacial properties,which could help further enhance the oil recovery by spontaneous imbibition.This study explores the possibility of using novel chemicals to enhance oil recovery from tight sands via spontaneous imbibition.We experimentally examine the effects of more than ten different chemical agents on spontaneous imbibition,including a cationic surfactant(C12 TAB),two anionic surfactants(0242 and 0342),an ionic liquid(BMMIM BF4),a high pH solution(NaBO2),and a series of house-made deep eutectic solvents(DES3-7,9,11,and 14).The interfacial tensions(IFT)between oil phase and some chemical solutions are also determined.Experimental results indicate that both the ionic liquid and cationic surfactant used in this study are detrimental to spontaneous imbibition and decrease the oil recovery from tight sands,even though cationic surfactant significantly decreases the oil-water IFT while ionic liquid does not.The high pH NaBO2 solution does not demonstrate significant effect on oil recovery improvement and IFT reduction.The anionic surfactants(O242 and O342)are effective in enhancing oil recovery from tight sands through oil-water IFT reduction and emulsification effects.The DESs drive the rock surface to be more water-wet,and a specific formulation(DES9)leads to much improvement on oil recovery under counter-current imbibition condition.This preliminary study would provide some knowledge about how to optimize the selection of chemicals for improving oil recovery from tight reservoirs.
