To analyze the differences in the transport and distribution of different types of proppants and to address issues such as the short effective support of proppant and poor placement in hydraulically intersecting fract...To analyze the differences in the transport and distribution of different types of proppants and to address issues such as the short effective support of proppant and poor placement in hydraulically intersecting fractures,this study considered the combined impact of geological-engineering factors on conductivity.Using reservoir production parameters and the discrete elementmethod,multispherical proppants were constructed.Additionally,a 3D fracture model,based on the specified conditions of the L block,employed coupled(Computational Fluid Dynamics)CFD-DEM(Discrete ElementMethod)for joint simulations to quantitatively analyze the transport and placement patterns of multispherical proppants in intersecting fractures.Results indicate that turbulent kinetic energy is an intrinsic factor affecting proppant transport.Moreover,the efficiency of placement and migration distance of low-sphericity quartz sand constructed by the DEM in the main fracture are significantly reduced compared to spherical ceramic proppants,with a 27.7%decrease in the volume fraction of the fracture surface,subsequently affecting the placement concentration and damaging fracture conductivity.Compared to small-angle fractures,controlling artificial and natural fractures to expand at angles of 45°to 60°increases the effective support length by approximately 20.6%.During hydraulic fracturing of gas wells,ensuring the fracture support area and post-closure conductivity can be achieved by controlling the sphericity of proppants and adjusting the perforation direction to control the direction of artificial fractures.展开更多
To accurately analyze proppant transport in rough intersecting fractures and elucidate the interaction mechanisms among liquid,particles,and rough walls,this study reconstructed a numerical model of fractures in inhom...To accurately analyze proppant transport in rough intersecting fractures and elucidate the interaction mechanisms among liquid,particles,and rough walls,this study reconstructed a numerical model of fractures in inhomogeneous reservoirs with varying brittleness index(BI).Various auto-correlation Gaussian rough fracture models were created using Matlab to assess roughness through the fractal dimension method.This research innovatively combined Boolean operations to establish three-dimensional rough fracture models,incorporating(Computational Fluid Dynamics)CFD-DEM(Discrete Element Method)with a bidirectional method for cosimulation.The proppant transport in fractures was categorized into three zones based on the difference in the turbulent kinetic energy.Artificially induced fracture roughness increases fluid retention and turbulence,causing plugging effects and limiting proppant flow into branch fractures.Additionally,compared with the superior deposition and significant support effects of the spherical proppant,the low-sphericity proppant traveled farther under fracturing fluid,inducing more pronounced plugging near curved fracture intersections;the variation in fracture intersection angles primarily impacted the wall shear stress within the flow field,indicating smaller angles led to higher shear energy at the intersection.Compared with the intersection angle of 30°,the height and area deposited in the 90 branch fracture increased by 52.25%and 65.33%,respectively:notably,injecting proppant from smaller to larger particles(S:M:L)and a low velocity effectively ensured fracture conductivity near the wellbore at joint roughness coefficient(JRC)≥46 while achieving satis-factory placement in the branch fracture,making it a recommended approach.展开更多
Shale gas production involves complex gas-water two-phase flow,with flow patterns in proppant-filled fractures playing a critical role in determining production efficiency.In this study,3D geometric models of 40/70 me...Shale gas production involves complex gas-water two-phase flow,with flow patterns in proppant-filled fractures playing a critical role in determining production efficiency.In this study,3D geometric models of 40/70 mesh ceramic particles and quartz sand proppant clusters were elaborated using computed tomography(CT)scanning.These models were used to develop a numerical simulation framework based on the lattice Boltzmann method(LBM),enabling the investigation of gas-water flow behavior within proppant-filled fractures under varying driving forces and surface tensions.Simulation results at a closure pressure of 15 MPa have revealed that ceramic particles exhibit a simpler and more porous internal structure than quartz sand of the same size.Under identical flow conditions,ceramic proppants demonstrate higher fluid replacement efficiency.Replacement efficiency increases with higher porosity,greater driving force,and lower surface tension.Furthermore,fluid displacement is strongly influenced by pore geometry:flow is faster in straighter and wider channels,with preferential movement through larger pores forming dominant flow paths.The replacement velocity exhibits a characteristic time evolution,initially rapid,then gradually decreasing,correlating positively with the development of these dominant channels.展开更多
Fracture conductivity is a key factor to determine the fracturing effect.Optimizing proppant particle size distribution is critical for ensuring efficient proppant placement within fractures.To address challenges asso...Fracture conductivity is a key factor to determine the fracturing effect.Optimizing proppant particle size distribution is critical for ensuring efficient proppant placement within fractures.To address challenges associated with the low-permeability reservoirs in the Lufeng Oilfield of the South China Sea—including high heterogeneity,complex lithology,and suboptimal fracturing outcomes—JRC(Joint Roughness Coefficient)was employed to quantitatively characterize the lithological properties of the target formation.A CFD-DEM(Computational Fluid Dynamics-Discrete Element Method)two-way coupling approach was then utilized to construct a fracture channel model that simulates proppant transport dynamics.Theproppant particle size under different lithology was optimized.Theresults show that:(1)In rough fractures,proppant particles exhibit more chaotic migration behavior compared to their movement on smooth surfaces,thereby increasing the risk of fracture plugging;(2)Within the same particle size range,for proppants with mesh sizes of 40/70 or 20/40,fracture conductivity decreases as roughness increases.In contrast,for 30/50 mesh proppants,conductivity initially increases and then decreases with rising roughness;(3)Under identical roughness conditions,the following recommendations apply based on fracture conductivity behavior relative to proppant particle size:When JRC<46,conductivity increases with larger particle sizes,with 20/40 mesh proppant recommended;When JRC>46,conductivity decreases as particle size increases;40/70 mesh proppant is thus recommended to maintain effective conductivity;At JRC=46,conductivity first increases then decreases with increasing particle size,making 30/50mesh the optimal choice.Theresearch findings provide a theoretical foundation for optimizing fracturing designs and enhancing fracturing performance in the field.展开更多
Ceramic spheres,typically with a particle diameter of less than 0.8 mm,are frequently utilized as a critical proppant material in hydraulic fracturing for petroleum and natural gas extraction.Porous ceramic spheres wi...Ceramic spheres,typically with a particle diameter of less than 0.8 mm,are frequently utilized as a critical proppant material in hydraulic fracturing for petroleum and natural gas extraction.Porous ceramic spheres with artificial inherent pores are an important type of lightweight proppant,enabling their transport to distant fracture extremities and enhancing fracture conductivity.However,the focus frequently gravitates towards the low-density advantage,often overlooking the pore geometry impacts on compressive strength by traditional strength evaluation.This paper numerically bypasses such limitations by using a combined finite and discrete element method(FDEM)considering experimental results.The mesh size of the model undergoes validation,followed by the calibration of cohesive element parameters via the single particle compression test.The stimulation elucidates that proppants with a smaller pore size(40μm)manifest crack propagation evolution at a more rapid pace in comparison to their larger-pore counterparts,though the influence of pore diameter on overall strength is subtle.The inception of pores not only alters the trajectory of crack progression but also,with an increase in porosity,leads to a discernible decline in proppant compressive strength.Intriguingly,upon crossing a porosity threshold of 10%,the decrement in strength becomes more gradual.A denser congregation of pores accelerates crack propagation,undermining proppant robustness,suggesting that under analogous conditions,hollow proppants might not match the strength of their porous counterparts.This exploration elucidates the underlying mechanisms of proppant failure from a microstructural perspective,furnishing pivotal insights that may guide future refinements in the architectural design of porous proppant.展开更多
To elucidate the mechanism by which supercritical CO_(2)(SCCO_(2))-water-shale interactions during CO_(2)energized fracturing influence proppant embedment in lacustrine shale,shale samples from the Bohai Bay Basin wer...To elucidate the mechanism by which supercritical CO_(2)(SCCO_(2))-water-shale interactions during CO_(2)energized fracturing influence proppant embedment in lacustrine shale,shale samples from the Bohai Bay Basin were selected for SCCO_(2)-water-shale interaction experiments.X-ray diffraction(XRD),SEM large-area high-resolution imaging,automated mineral identification and characterization system(AMICS),and nanoindentation tests were employed to examine the micro-mechanical damage mechanisms of fracture surfaces and the evolving patterns of proppant embedment characteristics.The results reveal that:Prolonged interaction time reduces the contents of dolomite,feldspar,and clay minerals,while quartz content increases,with dolomite showing the most pronounced dissolution effect.As interaction time increases,the hardness and elasticity modulus of shale follow a power-law decay pattern,with the peak degradation rate occurring at 1 d,followed by a gradual decline of degradation velocity.Increasing interaction time results in growth in both the number and depth of embedment pits on the sample surface.After more than 3 d of interaction,clustered proppant embedment is observed,accompanied by the formation of deep embedment pits on the surface.展开更多
Fiber is highly escapable in conventional slickwater,making it difficult to form fiber-proppant agglomerate with proppant and exhibit limited effectiveness.To solve these problems,a novel structure stabilizer(SS)is de...Fiber is highly escapable in conventional slickwater,making it difficult to form fiber-proppant agglomerate with proppant and exhibit limited effectiveness.To solve these problems,a novel structure stabilizer(SS)is developed.Through microscopic structural observations and performance evaluations in indoor experiments,the mechanism of proppant placement under the action of the SS and the effects of the SS on proppant placement dimensions and fracture conductivity were elucidated.The SS facilitates the formation of robust fiber-proppant agglomerates by polymer,fiber,and quartz sand.Compared to bare proppants,these agglomerates exhibit reduced density,increased volume,and enlarged contact area with the fluid during settlement,leading to heightened buoyancy and drag forces,ultimately resulting in slower settling velocities and enhanced transportability into deeper regions of the fracture.Co-injecting the fiber and the SS alongside the proppant into the reservoir effectively reduces the fiber escape rate,increases the proppant volume in the slickwater,and boosts the proppant placement height,conveyance distance and fracture conductivity,while also decreasing the proppant backflow.Experimental results indicate an optimal SS mass fraction of 0.3%.The application of this SS in over 80 wells targeting tight gas,shale oil,and shale gas reservoirs has substantiated its strong adaptability and general suitability for meeting the production enhancement,cost reduction,and sand control requirements of such wells.展开更多
The gas production of deep coalbed methane wells in Linxing-Shenfu block decreases rapidly,the water output is high,the supporting effect is poor,the effective supporting fracture size is limited,and the migration mec...The gas production of deep coalbed methane wells in Linxing-Shenfu block decreases rapidly,the water output is high,the supporting effect is poor,the effective supporting fracture size is limited,and the migration mechanism of proppant in deep coal reservoir is not clear at present.To investigate the migration behavior of proppants in complex fractures during the volume reconstruction of deep coal and rock reservoirs,an optimization test on the conductivity of low-density proppants and simulations of proppant migration in complex fractures of deep coal reservoirs were conducted.The study systematically analyzed the impact of various fracture geometries,proppant types and fracturingfluid viscosities on proppant distribution.Furthermore,the study compared the outcomes of dynamic proppant transport experiments with simulation results.The results show that the numerical simulation is consistent with the results of the proppant dynamic sand-carrying experiment.Under the conditions of low viscosity and large pumping-rate,a high ratio of 40/70 mesh proppant can facilitate the movement of the proppant to the depths of fractures at all levels.The technical goal is to create comprehensive fracture support within intricate trapezoidal fractures in deep coal and rock reservoirs without inducing sand plugging.The sand ratio is controlled at 15%–20%,with a proppant combination ratio of 40/70:30/50:20/40=6:3:1.Proppant pumping operations can effectively address the issue of poor support in complex fractures in deep coal formations.The research results have been successfully applied to the development of deep coalbed methane in the Linxing-Shenfu block,Ordos Basin.展开更多
The stability and mobility of proppant packs in hydraulic fractures during hydrocarbon production are numerically investigated by the lattice Boltzmann-discrete element coupling method(LB-DEM).This study starts with a...The stability and mobility of proppant packs in hydraulic fractures during hydrocarbon production are numerically investigated by the lattice Boltzmann-discrete element coupling method(LB-DEM).This study starts with a preliminary proppant settling test,from which a solid volume fraction of 0.575 is calibrated for the proppant pack in the fracture.In the established workflow to investigate proppant flowback,a displacement is applied to the fracture surfaces to compact the generated proppant pack as well as further mimicking proppant embedment under closure stress.When a pressure gradient is applied to drive the fluid-particle flow,a critical aperture-to-diameter ratio of 4 is observed,above which the proppant pack would collapse.The results also show that the volumetric proppant flowback rate increases quadratically with the fracture aperture,while a linear variation between the particle flux and the pressure gradient is exhibited for a fixed fracture aperture.The research outcome contributes towards an improved understanding of proppant flowback in hydraulic fractures,which also supports an optimised proppant size selection for hydraulic fracturing operations.展开更多
A three-dimensional reconstruction of rough fracture surfaces of hydraulically fractured rock outcrops is carried out by casting process,a large-scale experimental setup for visualizing rough fractures is built to per...A three-dimensional reconstruction of rough fracture surfaces of hydraulically fractured rock outcrops is carried out by casting process,a large-scale experimental setup for visualizing rough fractures is built to perform proppant transport experiments.The typical characteristics of proppant transport and placement in rough fractures and its intrinsic mechanisms are investigated,and the influences of fracture inclination,fracture width and fracturing fluid viscosity on proppant transport and placement in rough fractures are analyzed.The results show that the rough fractures cause variations in the shape of the flow channel and the fluid flow pattern,resulting in the bridging buildup during proppant transport to form unfilled zone,the emergence of multiple complex flow patterns such as channeling,reverse flow and bypassing of sand-carrying fluid,and the influence on the stability of the sand dune.The proppant has a higher placement rate in inclined rough fractures,with a maximum increase of 22.16 percentage points in the experiments compared to vertical fractures,but exhibits poor stability of the sand dune.Reduced fracture width aggravates the bridging of proppant and induces higher pumping pressure.Increasing the viscosity of the fracturing fluid can weaken the proppant bridging phenomenon caused by the rough fractures.展开更多
Field evidence indicates that proppant distribution and threshold pressure gradient have great impacts on well productivity.Aiming at the development of unconventional oil reservoirs in Triassic Chang-7 Unit,Ordos Bas...Field evidence indicates that proppant distribution and threshold pressure gradient have great impacts on well productivity.Aiming at the development of unconventional oil reservoirs in Triassic Chang-7 Unit,Ordos Basin of China,we presented an integrated workflow to investigate how(1)proppant placement in induced fracture and(2)non-linear flow in reservoir matrix would affect well productivity and fluid flow in the reservoir.Compared with our research before(Yue et al.,2020),here we extended this study into the development of multi-stage fractured horizontal wells(MFHWs)with large-scale complicated fracture geometry.The integrated workflow is based on the finite element method and consists of simulation models for proppant-laden fluid flow,fracture flow,and non-linear seepage flow,respectively.Simulation results indicate that the distribution of proppant inside the induced cracks significantly affects the productivity of the MFHW.When we assign an idealized proppant distribution instead of the real distribution,there will be an overestimation of 44.98%in daily oil rate and 30.63%in cumulative oil production after continuous development of 1000 days.Besides,threshold pressure gradient(TPG)also significantly affects the well performance in tight oil reservoirs.If we simply apply linear Darcy’s law to the reservoir matrix,the overall cumulative oil production can be overrated by 77%after 1000 days of development.In general,this research provides new insights into the development of tight oil reservoirs with TPG and meanwhile reveals the significance of proppant distribution and non-linear fluid flow in the production scenario design.展开更多
Low-permeability reservoirs are generally characterized by low porosity and low permeability.Obtaining high production using the traditional method is technologically challenging because it yields a low reservoir reco...Low-permeability reservoirs are generally characterized by low porosity and low permeability.Obtaining high production using the traditional method is technologically challenging because it yields a low reservoir recovery factor.In recent years,hydraulic fracturing technology is widely applied for efficiently exploiting and developing low-permeability reservoirs using a low-viscosity fluid as a fracturing fluid.However,the transportation of the proppant is inefficient in the low-viscosity fluid,and the proppant has a low piling-up height in fracture channels.These key challenges restrict the fluid(natural gas or oil)flow in fracture channels and their functional flow areas,reducing the profits of hydrocarbon exploitation.This study aimed to explore and develop a novel dandelion-bionic proppant by modifying the surface of the proppant and the fiber.Its structure was similar to that of dandelion seeds,and it had high transport and stacking efficiency in low-viscosity liquids compared with the traditional proppant.Moreover,the transportation efficiency of this newly developed proppant was investigated experimentally using six different types of fracture models(tortuous fracture model,rough fracture model,narrow fracture model,complex fracture model,large-scale single fracture model,and small-scale single fracture model).Experimental results indicated that,compared with the traditional proppant,the transportation efficiency and the packing area of the dandelion-based bionic proppant significantly improved in tap water or low-viscosity fluid.Compared with the traditional proppant,the dandelionbased bionic proppant had 0.1-4 times longer transportation length,0.3-5 times higher piling-up height,and 2-10 times larger placement area.The newly developed proppant also had some other extraordinary features.The tortuosity of the fracture did not influence the transportation of the novel proppant.This proppant could easily enter the branch fracture and narrow fracture with a high packing area in rough surface fractures.Based on the aforementioned characteristics,this novel proppant technique could improve the proppant transportation efficiency in the low-viscosity fracturing fluid and increase the ability of the proppant to enter the secondary fracture.This study might provide a new solution for effectively exploiting low-permeability hydrocarbon reservoirs.展开更多
With the increasing global demand for oil and gas,the development of unconventional resources such as shale gas is becoming ever more important.The key to developing unconventional oil and gas resources lies in horizo...With the increasing global demand for oil and gas,the development of unconventional resources such as shale gas is becoming ever more important.The key to developing unconventional oil and gas resources lies in horizontal wells with multistage fracturing technology.In the process of horizontal well segmentation fracturing,the distribution of the proppant among multiple clusters has a significant influence on the fracturing effect.However,the influence of various factors on the entry of proppant into the perforation and then into the fracture along the wellbore is unclear.In this paper,based on the flow characteristics of proppants in fracturing fluids,we investigate the wellboreeperforation proppant transport using a Eulerian multiphase flow model.The effect of different factors on proppant entry into the perforation in horizontal wells is studied.We first verify that the computational fluid dynamics model satisfies the accuracy requirements for studying the sandcarrying efficiency of proppants in a perforation cluster.Second,the effects of the proppant size,proppant density,fracturing fluid viscosity,perforation diameter,and fracturing fluid flow rate on the proppant transport efficiency are investigated.Finally,a mathematical model of the sand-carrying efficiency is established by multivariate nonlinear fitting.The results show that the proppant size has a more significant effect on proppant settling at low wellbore flow rates.Increasing the diameter of the proppant particles can accelerate proppant settling.Higher wellbore flow rates tend to reduce the sand-carrying efficiency,although using a low-density proppant can mitigate the effect of the wellbore flow rate.At low wellbore flow rates,increasing the perforation size makes it easier for the proppant to enter bottom perforations.Increasing the fluid viscosity helps to distribute the proppant evenly between perforations in different directions,but this effect diminishes as the flow rate increases.Finally,a formula for the wellbore sand-carrying efficiency is obtained and validated,providing a basis for optimizing the distribution of the proppant in the perforation.The results from this paper enhance our understanding of the sand and fluid feeding patterns of each perforation cluster and provide direction for improving the construction process and enhancing the fracture inflow capacity.展开更多
Crushing and embedment are two critical downhole proppant degradation mechanisms that lead to a significant drop in production outputs in unconventional oil/gas stimulation projects. These persistent production drops ...Crushing and embedment are two critical downhole proppant degradation mechanisms that lead to a significant drop in production outputs in unconventional oil/gas stimulation projects. These persistent production drops due to the non-linear responses of proppants under reservoir conditions put the future utilization of such advanced stimulation techniques in unconventional energy extraction in doubt. The aim of this study is to address these issues by conducting a comprehensive experimental approach. According to the results, whatever the type of proppant, all proppant packs tend to undergo significant plastic deformation under the first loading cycle.Moreover, the utilization of ceramic proppants(which retain proppant pack porosity up to 75%), larger proppant sizes(which retain proppant pack porosity up to 15.2%) and higher proppant concentrations(which retain proppant pack porosity up to 29.5%) in the fracturing stimulations with higher in-situ stresses are recommended to de-escalate the critical consequences of crushing associated issues. Similarly, the selection of resin-coated proppants over ceramic and sand proppants may benefit in terms of obtaining reduced proppant embedment.In addition, selection of smaller proppant sizes and higher proppant concentrations are suggested for stimulation projects at depth with sedimentary formations and lower in-situ stresses where proppant embedment predominates. Furthermore, correlation between proppant embedment with repetitive loading cycles was studied.Importantly, microstructural analysis of the proppant-embedded siltstone rock samples revealed that the initiation of secondary induced fractures. Finally, the findings of this study can greatly contribute to accurately select optimum proppant properties(proppant type, size and concentration) depending on the oil/gas reservoir characteristics to minimize proppant crushing and embedment effects.展开更多
Workers involved in hydraulic fracking processes are exposed to various types of chemicals and dusts in their workplaces, such as proppants, which hold open the fissures created in the fracking process. Recently, cera...Workers involved in hydraulic fracking processes are exposed to various types of chemicals and dusts in their workplaces, such as proppants, which hold open the fissures created in the fracking process. Recently, ceramic proppants have been developed that may be less hazardous to workers than traditional proppants. Pulmonary function testing of workers producing ceramic proppant was used to assess the potential inhalation hazards of ceramic proppant. 100 male workers from a producer of ceramic proppant were evaluated with pulmonary function test data collected and evaluated using The American Thoracic Society (ATS) acceptability criteria. A comparison group was selected from the Third National Health and Nutrition Examination Survey (NHANES III) spirometry laboratory subset. No pulmonary function deficits were found in the worker group in comparison to the NHANES III population. Mean FEV1 and FVC values in workers were 3.8 and 4.8 liters respectively, and were greater as compared to the NHANES III population of similar demographics. An FEV1/FVC ratio of less than 0.8, when compared to the NHANES III group, produced an odds ratio of 0.44 in worker group, indicating less risk of preclinical pulmonary dysfunction. Overall, exposure to ceramic proppant was not found to produce an adverse impact on pulmonary function in workers engaged in the manufacture of ceramic proppant.展开更多
Proppant plays a critical role in the exploitation of oil and gas,especially in the development of nonconventional oil and gas resources.Proppants are small spheres that have adequate strength to withstand high closur...Proppant plays a critical role in the exploitation of oil and gas,especially in the development of nonconventional oil and gas resources.Proppants are small spheres that have adequate strength to withstand high closure stresses to keep cracks open;therefore,hydrocarbon fows smoothly into the wellbore.However,traditional proppants are prone to settling in hydraulic fracturing operations,which seriously afects the operation efect.To this end,ultralow-weight proppants have been extensively employed in the petroleum industry.One of the widespread forms of ultralow-weight proppant application in the oil and gas industry is related to light density.Ultralow-weight proppants will provide substantial fow paths with a considerably high propped surface area and remarkably reduce fne generation and scaling.This paper presents a comprehensive review of over 50 papers published in the past several decades on ultralow-weight proppants.The purpose of this study is to provide an overview of the current ultralow-weight proppant development status in raw materials,manufacturing process,performance characteristics,hydrophobic and lipophilic capabilities,and feld application to promote the research of new ultralow-weight proppants.Lastly,this study analyzes the current challenges and emphasizes the development direction of fractured proppants.展开更多
Hydraulic fracturing is a key technology for the development of unconventional hydrocarbon resources.The proppant placement morphology determines the fracture conductivity,thus affecting the reservoir stimulation effe...Hydraulic fracturing is a key technology for the development of unconventional hydrocarbon resources.The proppant placement morphology determines the fracture conductivity,thus affecting the reservoir stimulation effect.In this paper,the proppant migration and placement within complex fractures was studied by considering the fracture wall roughness through computational fluid mechanics-discrete element method(CFD-DEM)in numerical simulation,which is a key approach to study the proppant migration and placement.The results show that the proppant placement non-uniformity,proppant migration capacity,and proppant volume filled in the far-end and the secondary branched fracture are enhanced within the rough fracture compared with those within smooth fractures.The proppant migration capacity is increased within the fracture at low inclination angles(<60°)and low approach angles(<90°),and the proppant placement area is larger in the inclined fracture than that in the vertical fracture.The rise of injection rate and fracturing fluid viscosity causes more proppants migrate to far-end or secondary fractures,resulting in a non-proppant area within the near-wellbore fracture.An increase by 1.3 times in the injection rate and 3 times in the fracturing fluid viscosity leads to a decrease by 26.6%and 27%,respectively,in the proppant placement area within the near-wellbore fracture.The staged injection with small size proppants followed by large size proppants increases the proppant placement area in the primary fracture by 13%-26%,and that with large size proppants followed by small size proppants increases the proppant placement area by 19%-25%,which is due to that the latter method facilitates filling of the secondary branched fracture.The injection location mainly affects the proppant filling degree within the near-wellbore fractures.Compared with the upper injection,the middle and lower injection is not beneficial to filling of proppants within the near-wellbore fracture.展开更多
Hydraulic fracturing is a crucial stimulation for the development of deep shale gas reservoirs.A key challenge to the effectiveness of hydraulic fracturing is to place small proppants in complex narrow fractures reaso...Hydraulic fracturing is a crucial stimulation for the development of deep shale gas reservoirs.A key challenge to the effectiveness of hydraulic fracturing is to place small proppants in complex narrow fractures reasonably.The experiments with varied particle and fluid parameters are carried out in a narrow planar channel to understand particle transport and distribution.The four dimensionless parameters,including the Reynold number,Shields number,density ratio,and particle volume fraction,are introduced to describe the particle transport in narrow fractures.The results indicate that the narrow channel probably induces fluid fingers and small particle aggregation in a highly viscous fluid,leading to particle settlement near the entrance.The low viscous fluid is beneficial to disperse particles further into the fracture,especially in the high-speed fluid velocity.The linear and natural logarithmic laws have relationships with dimensionless parameters accurately.The multiple linear regression method developed two correlation models with four dimensionless parameters to predict the bed equilibrium height and covered area of small particles in narrow fractures.The study provides fundamental insight into understanding small size proppant distribution in deep reservoirs.展开更多
The distribution of proppant injected in hydraulic fractures significantly affects the fracture conductivity and well performance.The proppant transport in thin fracturing fluid used during hydraulic fracturing in the...The distribution of proppant injected in hydraulic fractures significantly affects the fracture conductivity and well performance.The proppant transport in thin fracturing fluid used during hydraulic fracturing in the unconventional reservoirs is considerably different from fracturing fluids in the conventional reservoir due to the very low viscosity and quick deposition of the proppants.This paper presents the development of a three-dimensional Computational Fluid Dynamics(CFD)modelling technique for the prediction of proppant-fluid multiphase flow in hydraulic fractures.The proposed model also simulates the fluid leak-off behaviour from the fracture wall.The Euler-Granular and CFD-Discrete Element Method(CFD-DEM)multiphase modelling approach has been applied,and the equations defining the fluid-proppant and inter-proppant interaction have been solved using the finite volume technique.The proppant transport in hydraulic fractures has been studied comprehensively,and the computational modelling results of proppant distribution and other flow properties are in good agreement with the published experimental study.The parametric study is performed to investigate the effect of variation in proppant size,fluid viscosity and fracture width on the proppant transport.Smaller proppants can be injected early,followed by larger proppants to maintain high propping efficiency.This study has enhanced the understanding of the complex flow phenomenon between proppant and fracturing fluid and can play a vital role in hydraulic fracturing design.展开更多
Proppant is a key material in the hydraulic fracturing process,which has been widely used in unconventional oil exploitation.Normal proppants are easy to sedimentate and accumulate at the entrance of shale fracture,wh...Proppant is a key material in the hydraulic fracturing process,which has been widely used in unconventional oil exploitation.Normal proppants are easy to sedimentate and accumulate at the entrance of shale fracture,which will block the diversion of water,oil and gas.Coated proppants(CPs) are fabricated by coating resin on normal ceramic proppants through a simple method,which is dramatically enhanced the supporting properties in shale fracture and easy to scale up.Compared with uncoated ceramic proppants,the self-suspension ability of CPs is ~11 times higher,which are able to migrate and distribute farther and deeper inside the fracture.At the same time,Coating enhanced the 23.7% of adhesive force in maximum,which makes the CPs easier to adhere on the fracture surface to supportthe shale fracture.Besides,the liquid conductivity of CPs is 60% higher than uncoated ceramic proppants at13.6 MPa pressure.This method is expected to fabricated varieties of proppantsfor shale fracture supporting to improve the exploration of unconventional oil and gas resources.展开更多
基金funded by the project of the Major Scientific and Technological Projects of CNOOC in the 14th Five-Year Plan(No.KJGG2022-0701)the CNOOC Research Institute(No.2020PFS-03).
文摘To analyze the differences in the transport and distribution of different types of proppants and to address issues such as the short effective support of proppant and poor placement in hydraulically intersecting fractures,this study considered the combined impact of geological-engineering factors on conductivity.Using reservoir production parameters and the discrete elementmethod,multispherical proppants were constructed.Additionally,a 3D fracture model,based on the specified conditions of the L block,employed coupled(Computational Fluid Dynamics)CFD-DEM(Discrete ElementMethod)for joint simulations to quantitatively analyze the transport and placement patterns of multispherical proppants in intersecting fractures.Results indicate that turbulent kinetic energy is an intrinsic factor affecting proppant transport.Moreover,the efficiency of placement and migration distance of low-sphericity quartz sand constructed by the DEM in the main fracture are significantly reduced compared to spherical ceramic proppants,with a 27.7%decrease in the volume fraction of the fracture surface,subsequently affecting the placement concentration and damaging fracture conductivity.Compared to small-angle fractures,controlling artificial and natural fractures to expand at angles of 45°to 60°increases the effective support length by approximately 20.6%.During hydraulic fracturing of gas wells,ensuring the fracture support area and post-closure conductivity can be achieved by controlling the sphericity of proppants and adjusting the perforation direction to control the direction of artificial fractures.
文摘To accurately analyze proppant transport in rough intersecting fractures and elucidate the interaction mechanisms among liquid,particles,and rough walls,this study reconstructed a numerical model of fractures in inhomogeneous reservoirs with varying brittleness index(BI).Various auto-correlation Gaussian rough fracture models were created using Matlab to assess roughness through the fractal dimension method.This research innovatively combined Boolean operations to establish three-dimensional rough fracture models,incorporating(Computational Fluid Dynamics)CFD-DEM(Discrete Element Method)with a bidirectional method for cosimulation.The proppant transport in fractures was categorized into three zones based on the difference in the turbulent kinetic energy.Artificially induced fracture roughness increases fluid retention and turbulence,causing plugging effects and limiting proppant flow into branch fractures.Additionally,compared with the superior deposition and significant support effects of the spherical proppant,the low-sphericity proppant traveled farther under fracturing fluid,inducing more pronounced plugging near curved fracture intersections;the variation in fracture intersection angles primarily impacted the wall shear stress within the flow field,indicating smaller angles led to higher shear energy at the intersection.Compared with the intersection angle of 30°,the height and area deposited in the 90 branch fracture increased by 52.25%and 65.33%,respectively:notably,injecting proppant from smaller to larger particles(S:M:L)and a low velocity effectively ensured fracture conductivity near the wellbore at joint roughness coefficient(JRC)≥46 while achieving satis-factory placement in the branch fracture,making it a recommended approach.
文摘Shale gas production involves complex gas-water two-phase flow,with flow patterns in proppant-filled fractures playing a critical role in determining production efficiency.In this study,3D geometric models of 40/70 mesh ceramic particles and quartz sand proppant clusters were elaborated using computed tomography(CT)scanning.These models were used to develop a numerical simulation framework based on the lattice Boltzmann method(LBM),enabling the investigation of gas-water flow behavior within proppant-filled fractures under varying driving forces and surface tensions.Simulation results at a closure pressure of 15 MPa have revealed that ceramic particles exhibit a simpler and more porous internal structure than quartz sand of the same size.Under identical flow conditions,ceramic proppants demonstrate higher fluid replacement efficiency.Replacement efficiency increases with higher porosity,greater driving force,and lower surface tension.Furthermore,fluid displacement is strongly influenced by pore geometry:flow is faster in straighter and wider channels,with preferential movement through larger pores forming dominant flow paths.The replacement velocity exhibits a characteristic time evolution,initially rapid,then gradually decreasing,correlating positively with the development of these dominant channels.
基金funded by China NationalOffshore Oil Corporation(CNOOC)14th Five-Year Plan Major Science and Technology Project:Research on Integrated Geological Engineering Technology for Fracturing and Development of Offshore Low-Permeability Reservoirs(Grant NO.KJGG2022-0701).Mao Jiang,Chengyong Peng,JiangshuWu and Xuesong Xing.https://www.cnooc.com.cn.
文摘Fracture conductivity is a key factor to determine the fracturing effect.Optimizing proppant particle size distribution is critical for ensuring efficient proppant placement within fractures.To address challenges associated with the low-permeability reservoirs in the Lufeng Oilfield of the South China Sea—including high heterogeneity,complex lithology,and suboptimal fracturing outcomes—JRC(Joint Roughness Coefficient)was employed to quantitatively characterize the lithological properties of the target formation.A CFD-DEM(Computational Fluid Dynamics-Discrete Element Method)two-way coupling approach was then utilized to construct a fracture channel model that simulates proppant transport dynamics.Theproppant particle size under different lithology was optimized.Theresults show that:(1)In rough fractures,proppant particles exhibit more chaotic migration behavior compared to their movement on smooth surfaces,thereby increasing the risk of fracture plugging;(2)Within the same particle size range,for proppants with mesh sizes of 40/70 or 20/40,fracture conductivity decreases as roughness increases.In contrast,for 30/50 mesh proppants,conductivity initially increases and then decreases with rising roughness;(3)Under identical roughness conditions,the following recommendations apply based on fracture conductivity behavior relative to proppant particle size:When JRC<46,conductivity increases with larger particle sizes,with 20/40 mesh proppant recommended;When JRC>46,conductivity decreases as particle size increases;40/70 mesh proppant is thus recommended to maintain effective conductivity;At JRC=46,conductivity first increases then decreases with increasing particle size,making 30/50mesh the optimal choice.Theresearch findings provide a theoretical foundation for optimizing fracturing designs and enhancing fracturing performance in the field.
基金the financial support provided by Tianfu Yongxing Laboratory Organized Research Project Funding(No.2023CXXM01)the ARC linkage program(No.LP200100420).
文摘Ceramic spheres,typically with a particle diameter of less than 0.8 mm,are frequently utilized as a critical proppant material in hydraulic fracturing for petroleum and natural gas extraction.Porous ceramic spheres with artificial inherent pores are an important type of lightweight proppant,enabling their transport to distant fracture extremities and enhancing fracture conductivity.However,the focus frequently gravitates towards the low-density advantage,often overlooking the pore geometry impacts on compressive strength by traditional strength evaluation.This paper numerically bypasses such limitations by using a combined finite and discrete element method(FDEM)considering experimental results.The mesh size of the model undergoes validation,followed by the calibration of cohesive element parameters via the single particle compression test.The stimulation elucidates that proppants with a smaller pore size(40μm)manifest crack propagation evolution at a more rapid pace in comparison to their larger-pore counterparts,though the influence of pore diameter on overall strength is subtle.The inception of pores not only alters the trajectory of crack progression but also,with an increase in porosity,leads to a discernible decline in proppant compressive strength.Intriguingly,upon crossing a porosity threshold of 10%,the decrement in strength becomes more gradual.A denser congregation of pores accelerates crack propagation,undermining proppant robustness,suggesting that under analogous conditions,hollow proppants might not match the strength of their porous counterparts.This exploration elucidates the underlying mechanisms of proppant failure from a microstructural perspective,furnishing pivotal insights that may guide future refinements in the architectural design of porous proppant.
基金Supported by the National Natural Science Foundation of China(52425402,52204021,52404038)Scientific Research Fund of China University of Petroleum(Beijing)(2462022BJRC002).
文摘To elucidate the mechanism by which supercritical CO_(2)(SCCO_(2))-water-shale interactions during CO_(2)energized fracturing influence proppant embedment in lacustrine shale,shale samples from the Bohai Bay Basin were selected for SCCO_(2)-water-shale interaction experiments.X-ray diffraction(XRD),SEM large-area high-resolution imaging,automated mineral identification and characterization system(AMICS),and nanoindentation tests were employed to examine the micro-mechanical damage mechanisms of fracture surfaces and the evolving patterns of proppant embedment characteristics.The results reveal that:Prolonged interaction time reduces the contents of dolomite,feldspar,and clay minerals,while quartz content increases,with dolomite showing the most pronounced dissolution effect.As interaction time increases,the hardness and elasticity modulus of shale follow a power-law decay pattern,with the peak degradation rate occurring at 1 d,followed by a gradual decline of degradation velocity.Increasing interaction time results in growth in both the number and depth of embedment pits on the sample surface.After more than 3 d of interaction,clustered proppant embedment is observed,accompanied by the formation of deep embedment pits on the surface.
文摘Fiber is highly escapable in conventional slickwater,making it difficult to form fiber-proppant agglomerate with proppant and exhibit limited effectiveness.To solve these problems,a novel structure stabilizer(SS)is developed.Through microscopic structural observations and performance evaluations in indoor experiments,the mechanism of proppant placement under the action of the SS and the effects of the SS on proppant placement dimensions and fracture conductivity were elucidated.The SS facilitates the formation of robust fiber-proppant agglomerates by polymer,fiber,and quartz sand.Compared to bare proppants,these agglomerates exhibit reduced density,increased volume,and enlarged contact area with the fluid during settlement,leading to heightened buoyancy and drag forces,ultimately resulting in slower settling velocities and enhanced transportability into deeper regions of the fracture.Co-injecting the fiber and the SS alongside the proppant into the reservoir effectively reduces the fiber escape rate,increases the proppant volume in the slickwater,and boosts the proppant placement height,conveyance distance and fracture conductivity,while also decreasing the proppant backflow.Experimental results indicate an optimal SS mass fraction of 0.3%.The application of this SS in over 80 wells targeting tight gas,shale oil,and shale gas reservoirs has substantiated its strong adaptability and general suitability for meeting the production enhancement,cost reduction,and sand control requirements of such wells.
基金Specific grant number KJGG2022-1002YFKey Technologies for Exploration and Development of Onshore Unconventional Natural Gas in CNOOC’s“14th Five-Year Plan”Major Science and Technology Project.
文摘The gas production of deep coalbed methane wells in Linxing-Shenfu block decreases rapidly,the water output is high,the supporting effect is poor,the effective supporting fracture size is limited,and the migration mechanism of proppant in deep coal reservoir is not clear at present.To investigate the migration behavior of proppants in complex fractures during the volume reconstruction of deep coal and rock reservoirs,an optimization test on the conductivity of low-density proppants and simulations of proppant migration in complex fractures of deep coal reservoirs were conducted.The study systematically analyzed the impact of various fracture geometries,proppant types and fracturingfluid viscosities on proppant distribution.Furthermore,the study compared the outcomes of dynamic proppant transport experiments with simulation results.The results show that the numerical simulation is consistent with the results of the proppant dynamic sand-carrying experiment.Under the conditions of low viscosity and large pumping-rate,a high ratio of 40/70 mesh proppant can facilitate the movement of the proppant to the depths of fractures at all levels.The technical goal is to create comprehensive fracture support within intricate trapezoidal fractures in deep coal and rock reservoirs without inducing sand plugging.The sand ratio is controlled at 15%–20%,with a proppant combination ratio of 40/70:30/50:20/40=6:3:1.Proppant pumping operations can effectively address the issue of poor support in complex fractures in deep coal formations.The research results have been successfully applied to the development of deep coalbed methane in the Linxing-Shenfu block,Ordos Basin.
基金Funding support from Heilongjiang"Open Competition"project(Grant No.DQYT2022-JS-758)is greatly acknowledgedFinancial support from the National Natural Science Foundation of China(Grant Nos.52304025 and 52174025)is acknowledged+1 种基金supports from Northeast Petroleum University and Guangdong Basic and Applied Basic Research Foundationsupport from the Heilongjiang Touyan Innovation Team Program.
文摘The stability and mobility of proppant packs in hydraulic fractures during hydrocarbon production are numerically investigated by the lattice Boltzmann-discrete element coupling method(LB-DEM).This study starts with a preliminary proppant settling test,from which a solid volume fraction of 0.575 is calibrated for the proppant pack in the fracture.In the established workflow to investigate proppant flowback,a displacement is applied to the fracture surfaces to compact the generated proppant pack as well as further mimicking proppant embedment under closure stress.When a pressure gradient is applied to drive the fluid-particle flow,a critical aperture-to-diameter ratio of 4 is observed,above which the proppant pack would collapse.The results also show that the volumetric proppant flowback rate increases quadratically with the fracture aperture,while a linear variation between the particle flux and the pressure gradient is exhibited for a fixed fracture aperture.The research outcome contributes towards an improved understanding of proppant flowback in hydraulic fractures,which also supports an optimised proppant size selection for hydraulic fracturing operations.
基金Supported by National Key Research and Development Program of China(2022YFE0137200)Outstanding Youth Natural Science Fund of Shaanxi Province(2022JC-37)+2 种基金Innovation Capability Support Program of Shaanxi(2023-CX-TD-31)Natural Science Basic Research Project of Shaanxi Province(2024JC-YBQN-0381)National Natural Science Foundation of China(51874240,52204021)。
文摘A three-dimensional reconstruction of rough fracture surfaces of hydraulically fractured rock outcrops is carried out by casting process,a large-scale experimental setup for visualizing rough fractures is built to perform proppant transport experiments.The typical characteristics of proppant transport and placement in rough fractures and its intrinsic mechanisms are investigated,and the influences of fracture inclination,fracture width and fracturing fluid viscosity on proppant transport and placement in rough fractures are analyzed.The results show that the rough fractures cause variations in the shape of the flow channel and the fluid flow pattern,resulting in the bridging buildup during proppant transport to form unfilled zone,the emergence of multiple complex flow patterns such as channeling,reverse flow and bypassing of sand-carrying fluid,and the influence on the stability of the sand dune.The proppant has a higher placement rate in inclined rough fractures,with a maximum increase of 22.16 percentage points in the experiments compared to vertical fractures,but exhibits poor stability of the sand dune.Reduced fracture width aggravates the bridging of proppant and induces higher pumping pressure.Increasing the viscosity of the fracturing fluid can weaken the proppant bridging phenomenon caused by the rough fractures.
基金The authors gratefully acknowledge the financial supports from the National Science Foundation of China under Grant 52274027 as well as the High-end Foreign Experts Recruitment Plan of the Ministry of Science and Technology China under Grant G2022105027L.
文摘Field evidence indicates that proppant distribution and threshold pressure gradient have great impacts on well productivity.Aiming at the development of unconventional oil reservoirs in Triassic Chang-7 Unit,Ordos Basin of China,we presented an integrated workflow to investigate how(1)proppant placement in induced fracture and(2)non-linear flow in reservoir matrix would affect well productivity and fluid flow in the reservoir.Compared with our research before(Yue et al.,2020),here we extended this study into the development of multi-stage fractured horizontal wells(MFHWs)with large-scale complicated fracture geometry.The integrated workflow is based on the finite element method and consists of simulation models for proppant-laden fluid flow,fracture flow,and non-linear seepage flow,respectively.Simulation results indicate that the distribution of proppant inside the induced cracks significantly affects the productivity of the MFHW.When we assign an idealized proppant distribution instead of the real distribution,there will be an overestimation of 44.98%in daily oil rate and 30.63%in cumulative oil production after continuous development of 1000 days.Besides,threshold pressure gradient(TPG)also significantly affects the well performance in tight oil reservoirs.If we simply apply linear Darcy’s law to the reservoir matrix,the overall cumulative oil production can be overrated by 77%after 1000 days of development.In general,this research provides new insights into the development of tight oil reservoirs with TPG and meanwhile reveals the significance of proppant distribution and non-linear fluid flow in the production scenario design.
基金supported by the Natural Science Foundation of Sichuan“Settlement and Transport Mechanism of Biomimetic Dandelion Proppant in Fracture” (No.23NSFSC5596)the China Postdoctoral Science Foundation (No.2023M742904)。
文摘Low-permeability reservoirs are generally characterized by low porosity and low permeability.Obtaining high production using the traditional method is technologically challenging because it yields a low reservoir recovery factor.In recent years,hydraulic fracturing technology is widely applied for efficiently exploiting and developing low-permeability reservoirs using a low-viscosity fluid as a fracturing fluid.However,the transportation of the proppant is inefficient in the low-viscosity fluid,and the proppant has a low piling-up height in fracture channels.These key challenges restrict the fluid(natural gas or oil)flow in fracture channels and their functional flow areas,reducing the profits of hydrocarbon exploitation.This study aimed to explore and develop a novel dandelion-bionic proppant by modifying the surface of the proppant and the fiber.Its structure was similar to that of dandelion seeds,and it had high transport and stacking efficiency in low-viscosity liquids compared with the traditional proppant.Moreover,the transportation efficiency of this newly developed proppant was investigated experimentally using six different types of fracture models(tortuous fracture model,rough fracture model,narrow fracture model,complex fracture model,large-scale single fracture model,and small-scale single fracture model).Experimental results indicated that,compared with the traditional proppant,the transportation efficiency and the packing area of the dandelion-based bionic proppant significantly improved in tap water or low-viscosity fluid.Compared with the traditional proppant,the dandelionbased bionic proppant had 0.1-4 times longer transportation length,0.3-5 times higher piling-up height,and 2-10 times larger placement area.The newly developed proppant also had some other extraordinary features.The tortuosity of the fracture did not influence the transportation of the novel proppant.This proppant could easily enter the branch fracture and narrow fracture with a high packing area in rough surface fractures.Based on the aforementioned characteristics,this novel proppant technique could improve the proppant transportation efficiency in the low-viscosity fracturing fluid and increase the ability of the proppant to enter the secondary fracture.This study might provide a new solution for effectively exploiting low-permeability hydrocarbon reservoirs.
基金sponsored by the National Natural Science Foundation of China(52074332)the Shandong Provincial Science Fund for Excellent Young Scholars(ZR2020YQ36).
文摘With the increasing global demand for oil and gas,the development of unconventional resources such as shale gas is becoming ever more important.The key to developing unconventional oil and gas resources lies in horizontal wells with multistage fracturing technology.In the process of horizontal well segmentation fracturing,the distribution of the proppant among multiple clusters has a significant influence on the fracturing effect.However,the influence of various factors on the entry of proppant into the perforation and then into the fracture along the wellbore is unclear.In this paper,based on the flow characteristics of proppants in fracturing fluids,we investigate the wellboreeperforation proppant transport using a Eulerian multiphase flow model.The effect of different factors on proppant entry into the perforation in horizontal wells is studied.We first verify that the computational fluid dynamics model satisfies the accuracy requirements for studying the sandcarrying efficiency of proppants in a perforation cluster.Second,the effects of the proppant size,proppant density,fracturing fluid viscosity,perforation diameter,and fracturing fluid flow rate on the proppant transport efficiency are investigated.Finally,a mathematical model of the sand-carrying efficiency is established by multivariate nonlinear fitting.The results show that the proppant size has a more significant effect on proppant settling at low wellbore flow rates.Increasing the diameter of the proppant particles can accelerate proppant settling.Higher wellbore flow rates tend to reduce the sand-carrying efficiency,although using a low-density proppant can mitigate the effect of the wellbore flow rate.At low wellbore flow rates,increasing the perforation size makes it easier for the proppant to enter bottom perforations.Increasing the fluid viscosity helps to distribute the proppant evenly between perforations in different directions,but this effect diminishes as the flow rate increases.Finally,a formula for the wellbore sand-carrying efficiency is obtained and validated,providing a basis for optimizing the distribution of the proppant in the perforation.The results from this paper enhance our understanding of the sand and fluid feeding patterns of each perforation cluster and provide direction for improving the construction process and enhancing the fracture inflow capacity.
文摘Crushing and embedment are two critical downhole proppant degradation mechanisms that lead to a significant drop in production outputs in unconventional oil/gas stimulation projects. These persistent production drops due to the non-linear responses of proppants under reservoir conditions put the future utilization of such advanced stimulation techniques in unconventional energy extraction in doubt. The aim of this study is to address these issues by conducting a comprehensive experimental approach. According to the results, whatever the type of proppant, all proppant packs tend to undergo significant plastic deformation under the first loading cycle.Moreover, the utilization of ceramic proppants(which retain proppant pack porosity up to 75%), larger proppant sizes(which retain proppant pack porosity up to 15.2%) and higher proppant concentrations(which retain proppant pack porosity up to 29.5%) in the fracturing stimulations with higher in-situ stresses are recommended to de-escalate the critical consequences of crushing associated issues. Similarly, the selection of resin-coated proppants over ceramic and sand proppants may benefit in terms of obtaining reduced proppant embedment.In addition, selection of smaller proppant sizes and higher proppant concentrations are suggested for stimulation projects at depth with sedimentary formations and lower in-situ stresses where proppant embedment predominates. Furthermore, correlation between proppant embedment with repetitive loading cycles was studied.Importantly, microstructural analysis of the proppant-embedded siltstone rock samples revealed that the initiation of secondary induced fractures. Finally, the findings of this study can greatly contribute to accurately select optimum proppant properties(proppant type, size and concentration) depending on the oil/gas reservoir characteristics to minimize proppant crushing and embedment effects.
文摘Workers involved in hydraulic fracking processes are exposed to various types of chemicals and dusts in their workplaces, such as proppants, which hold open the fissures created in the fracking process. Recently, ceramic proppants have been developed that may be less hazardous to workers than traditional proppants. Pulmonary function testing of workers producing ceramic proppant was used to assess the potential inhalation hazards of ceramic proppant. 100 male workers from a producer of ceramic proppant were evaluated with pulmonary function test data collected and evaluated using The American Thoracic Society (ATS) acceptability criteria. A comparison group was selected from the Third National Health and Nutrition Examination Survey (NHANES III) spirometry laboratory subset. No pulmonary function deficits were found in the worker group in comparison to the NHANES III population. Mean FEV1 and FVC values in workers were 3.8 and 4.8 liters respectively, and were greater as compared to the NHANES III population of similar demographics. An FEV1/FVC ratio of less than 0.8, when compared to the NHANES III group, produced an odds ratio of 0.44 in worker group, indicating less risk of preclinical pulmonary dysfunction. Overall, exposure to ceramic proppant was not found to produce an adverse impact on pulmonary function in workers engaged in the manufacture of ceramic proppant.
基金The study was supported by Science Foundation of China University of Petroleum,Beijing(No.2462019YJRC008)National Natural Science Foundation of China(No.52074312).
文摘Proppant plays a critical role in the exploitation of oil and gas,especially in the development of nonconventional oil and gas resources.Proppants are small spheres that have adequate strength to withstand high closure stresses to keep cracks open;therefore,hydrocarbon fows smoothly into the wellbore.However,traditional proppants are prone to settling in hydraulic fracturing operations,which seriously afects the operation efect.To this end,ultralow-weight proppants have been extensively employed in the petroleum industry.One of the widespread forms of ultralow-weight proppant application in the oil and gas industry is related to light density.Ultralow-weight proppants will provide substantial fow paths with a considerably high propped surface area and remarkably reduce fne generation and scaling.This paper presents a comprehensive review of over 50 papers published in the past several decades on ultralow-weight proppants.The purpose of this study is to provide an overview of the current ultralow-weight proppant development status in raw materials,manufacturing process,performance characteristics,hydrophobic and lipophilic capabilities,and feld application to promote the research of new ultralow-weight proppants.Lastly,this study analyzes the current challenges and emphasizes the development direction of fractured proppants.
基金financial support of the National Natural Science Foundation of China(Grant No.52074332)express their gratitude to project ZR2020YQ36 supported by Shandong Provincial Science Fund for Excellent Young Scholars。
文摘Hydraulic fracturing is a key technology for the development of unconventional hydrocarbon resources.The proppant placement morphology determines the fracture conductivity,thus affecting the reservoir stimulation effect.In this paper,the proppant migration and placement within complex fractures was studied by considering the fracture wall roughness through computational fluid mechanics-discrete element method(CFD-DEM)in numerical simulation,which is a key approach to study the proppant migration and placement.The results show that the proppant placement non-uniformity,proppant migration capacity,and proppant volume filled in the far-end and the secondary branched fracture are enhanced within the rough fracture compared with those within smooth fractures.The proppant migration capacity is increased within the fracture at low inclination angles(<60°)and low approach angles(<90°),and the proppant placement area is larger in the inclined fracture than that in the vertical fracture.The rise of injection rate and fracturing fluid viscosity causes more proppants migrate to far-end or secondary fractures,resulting in a non-proppant area within the near-wellbore fracture.An increase by 1.3 times in the injection rate and 3 times in the fracturing fluid viscosity leads to a decrease by 26.6%and 27%,respectively,in the proppant placement area within the near-wellbore fracture.The staged injection with small size proppants followed by large size proppants increases the proppant placement area in the primary fracture by 13%-26%,and that with large size proppants followed by small size proppants increases the proppant placement area by 19%-25%,which is due to that the latter method facilitates filling of the secondary branched fracture.The injection location mainly affects the proppant filling degree within the near-wellbore fractures.Compared with the upper injection,the middle and lower injection is not beneficial to filling of proppants within the near-wellbore fracture.
基金supported by the Chongqing Research Program of Basic Research and Frontier Technology(Grants No.cstc2019jcyjmsxm X0006)Science and Technology Research Program of Chongqing Municipal Education Commission of China(Grant No.KJQN201801530 and KJQN201901511)
文摘Hydraulic fracturing is a crucial stimulation for the development of deep shale gas reservoirs.A key challenge to the effectiveness of hydraulic fracturing is to place small proppants in complex narrow fractures reasonably.The experiments with varied particle and fluid parameters are carried out in a narrow planar channel to understand particle transport and distribution.The four dimensionless parameters,including the Reynold number,Shields number,density ratio,and particle volume fraction,are introduced to describe the particle transport in narrow fractures.The results indicate that the narrow channel probably induces fluid fingers and small particle aggregation in a highly viscous fluid,leading to particle settlement near the entrance.The low viscous fluid is beneficial to disperse particles further into the fracture,especially in the high-speed fluid velocity.The linear and natural logarithmic laws have relationships with dimensionless parameters accurately.The multiple linear regression method developed two correlation models with four dimensionless parameters to predict the bed equilibrium height and covered area of small particles in narrow fractures.The study provides fundamental insight into understanding small size proppant distribution in deep reservoirs.
文摘The distribution of proppant injected in hydraulic fractures significantly affects the fracture conductivity and well performance.The proppant transport in thin fracturing fluid used during hydraulic fracturing in the unconventional reservoirs is considerably different from fracturing fluids in the conventional reservoir due to the very low viscosity and quick deposition of the proppants.This paper presents the development of a three-dimensional Computational Fluid Dynamics(CFD)modelling technique for the prediction of proppant-fluid multiphase flow in hydraulic fractures.The proposed model also simulates the fluid leak-off behaviour from the fracture wall.The Euler-Granular and CFD-Discrete Element Method(CFD-DEM)multiphase modelling approach has been applied,and the equations defining the fluid-proppant and inter-proppant interaction have been solved using the finite volume technique.The proppant transport in hydraulic fractures has been studied comprehensively,and the computational modelling results of proppant distribution and other flow properties are in good agreement with the published experimental study.The parametric study is performed to investigate the effect of variation in proppant size,fluid viscosity and fracture width on the proppant transport.Smaller proppants can be injected early,followed by larger proppants to maintain high propping efficiency.This study has enhanced the understanding of the complex flow phenomenon between proppant and fracturing fluid and can play a vital role in hydraulic fracturing design.
基金supported by National Natural Science Foundation of China(Nos.51875577,51604050)Science Foundationof China University of Petroleum,Beijing(Nos.2462019QNXZ02,2462019BJRC007)Chongqing Science and Technology Innovation Talent Support Program(No.CSTCCXLJRC201712)。
文摘Proppant is a key material in the hydraulic fracturing process,which has been widely used in unconventional oil exploitation.Normal proppants are easy to sedimentate and accumulate at the entrance of shale fracture,which will block the diversion of water,oil and gas.Coated proppants(CPs) are fabricated by coating resin on normal ceramic proppants through a simple method,which is dramatically enhanced the supporting properties in shale fracture and easy to scale up.Compared with uncoated ceramic proppants,the self-suspension ability of CPs is ~11 times higher,which are able to migrate and distribute farther and deeper inside the fracture.At the same time,Coating enhanced the 23.7% of adhesive force in maximum,which makes the CPs easier to adhere on the fracture surface to supportthe shale fracture.Besides,the liquid conductivity of CPs is 60% higher than uncoated ceramic proppants at13.6 MPa pressure.This method is expected to fabricated varieties of proppantsfor shale fracture supporting to improve the exploration of unconventional oil and gas resources.
