Sand control mechanism of radial well filled with phase change material in hydrate reservoir

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.

Fracture propagation law of temporary plugging and diversion fracturing in shale reservoirs under completion experiments of horizontal well with multi-cluster sand jetting perforation

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.

Influence of temperature on swelling deformation characteristic of compacted GMZ bentonite-sand mixtures

Laboratory swelling deformation tests were carried out on compacted GMZ bentonite and bentonite-sand mixtures with 30%and 50%sand contents at 20,40,60,80 and 90°C with infiltration of distilled water.Influence of temperature,initial dry density,and quartz sand content on the swelling deformation characteristic of compacted bentonite specimens was analyzed.Results indicate that the swelling deformation process is accelerated,and the maximum swelling strain increases with the increase in temperature,while the maximum swelling strain tends to be stable with increasing temperature.In the meantime,the temperature effects depend on both of the sand content and the initial dry density of the specimens,the increases of the maximum swelling strain induced by increasing temperature,are enlarged by increasing sand content or initial dry density.Adding of quartz sand to bentonite not only influences the integrality of bentonite specimen,but also increase the microfissuring in area on quartz sand,which are advantageous to the heat transfer,leading to the increase of swelling deformation capacity of the specimen.The increased dry density relatively increases the bentonite content,so the swelling property is enhanced.However,no change on mineral composition of bentonite was observed when temperature was changed from 20 to 90°C.

Mechanism analysis and process optimization of sand and plug removal with rotating jet in horizontal well

In the view of the problems existing in horizontal well,such as sand depositing and cleaning difficulty of borehole,a technology with rotating jet suitable to resolution of the problems was presented.Based on liquid solid two-phase flow theory,the analyses on the sand movement law and the swirling field influential factors were conducted.Results show that:1) With the increasing of displacement in horizontal section annulus,swirling field strength increases,and when the displacement is constant,the closer from the nozzle,the stronger the swirling field strength is;2) Head rotating speed and liquid viscosity have little influence on the swirling field strength,but the sand-carrying rate of fluid can increase by increasing liquid viscosity in a certain range;3) Rotating the string and reducing its eccentricity in annulus are conducive for sand migration in the annulus;4) The sand can be suspended and accelerated again and the swirling field strength is enhanced by the helix agitator.Hence,the research results provide the theoretical basis for the design and application of rotating jet tool.

Porothermoelastic response of an oil sand formation subjected to injection and micro-fracturing in horizontal wells

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.

An experimental investigation on the effect of grain size on oil-well sand production

Sand production in oil wells is closely related to the mechanical behavior and petrographical properties of sandstones reservoir. Grain size is one of the main parameters controlling the phenomenon, which is studied in this paper. Large-scale hollow cylindrical synthetic samples with the same rock strength but different grain sizes were tested by an experimental setup in the laboratory. Different external stresses and fluid flow rates were applied to the samples and produced sand was measured continuously. Results show two different trends between sanding stress level and grain size. For the samples with finer grain size （D50〈0.3 mm）, the required confining stress for different sanding levels decreased with an increase in the grain size and for the samples with the coarser grains （D50〉0.3 mm） the required confining stress for different sanding levels dramatically increased with an increase in the grain size. Those two different trends were discussed and explained. The first one was production of individual grains and the second was bigger chunks in the slab form. In samples with large grains, plastic zones around hole were changed to a completely loose zone including interlocked individual grains or cluster of grains. In these samples after breakage of these interlocked zones sand was produced in the form of individual grains and clusters. Contrary to this, for samples with smaller grain size, shear bands were formed around the plastified hole and sand was produced in the form of big chunks or slabs.

Selection of candidate wells for re-fracturing in tight gas sand reservoirs using fuzzy inference

An artificial-intelligence based decision-making protocol is developed for tight gas sands to identify re-fracturing wells and used in case studies. The methodology is based on fuzzy logic to deal with imprecision and subjectivity through mathematical representations of linguistic vagueness, and is a computing system based on the concepts of fuzzy set theory, fuzzy if-then rules, and fuzzy reasoning. Five indexes are used to characterize hydraulic fracture quality, reservoir characteristics, operational parameters, initial conditions, and production related to the selection of re-fracturing well, and each index includes 3 related parameters. The value of each index/parameter is grouped into three categories that are low, medium, and high. For each category, a trapezoidal membership function all related rules are defined. The related parameters of an index are input into the rule-based fuzzy-inference system to output value of the index. Another fuzzy-inference system is built with the reservoir index, operational index, initial condition index and production index as input parameters and re-fracturing potential index as output parameter to screen out re-fracturing wells. This approach was successfully validated using published data.

Microstructure and anisotropic swelling behaviour of compacted bentonite/sand mixture

Pre-compacted elements （disks, tutus） of bentonite/sand mixture are candidate materials for sealing plugs of radioactive waste disposal. Choice of this material is mainly based on its swelling capacity allowing all gaps in the system to be sealed, and on its low permeability. When emplaced in the gallery, these elements will start to absorb water from the host rock and swell. Thereby, a swelling pressure will develop in the radial direction against the host rock and in the axial direction against the support structure. In this work, the swelling pressure of a small scale compacted disk of bentonite and sand was experimentally studied in both radial and axial directions. Different swelling kinetics were identified for different dry densities and along different directions. As a rule, the swelling pressure starts increasing quickly, reaches a peak value, decreases a little and finally stabilises. For some dry densities, higher peaks were observed in the radial direction than in the axial direction. The presence of peaks is related to the microstructure change and to the collapse of macro- pores. In parallel to the mechanical tests, microstructure investigation at the sample scale was conducted using microfocus X-ray computed tomography （BCT）. Image observation showed a denser structure in the centre and a looser one in the border, which was also confirmed by image analysis. This structure heterogeneity in the radial direction and the occurrence of macro-pores close to the radial boundary of the sample can explain the large peaks observed in the radial swelling pressure evolution. Another interesting result is the higher anisotropy found at lower bentonite dry densities, which was also analysed by means ofμCT observation of a sample at low bentonite dry density after the end of test. It was found that the macro-pores, especially those between sand grains, were not filled by swelled bentonite, which preserved the anisotropic microstructure caused by uniaxial compression due to the absence of microstructure collapse.

Effects of fluid flow rate and viscosity on gravel-pack plugging and the optimization of sand-control wells production

Series of experiments were performed to simulate the invasion of formation sand into and the plugging process of gravel-pack at different viscosities and flowing rates of fluid.Two types of formation sands with the medium size of 0.10 mm and 0.16 mm and the quartz sand and ceramsite of 0.6-1.2 mm were used in the experiments.A new viscosity-velocity index(the product of fluid viscosity and velocity)was put forward to characterize the influencing mechanism and law of physical property and flow condition of formation fluid on gravel-pack plugging,and a new method to optimize the production rate of wells controlling sand production with gravel-packing was proposed.The results show that the permeability of formation sand invaded zone and final permeability of plugged gravel-pack have negative correlations with viscosity and flow velocity of fluid,the higher the flow velocity and viscosity,the lower the permeability of formation sand invaded zone and final permeability of plugged gravel-pack will be.The flow velocity and viscosity of fluid are key factors affecting plugging degree of the gravel zone.The viscosity-velocity index(v-v index)can reflect the flow characteristics of fluid very well and make it easier to analyze the plugging mechanism of gravel zone.For different combinations of fluid viscosity and flow velocity,if the v-v index is the same or close,their impact on the final gravel permeability would be the same or close.With the increase of the v-v index,the permeability of plugged gravel zone decreases first,then the reduction rate slows down till the permeability stabilizes.By optimizing production and increasing production step by step,the optimal working scheme for sand-control well can reduce the damage to gravel-pack zone permeability caused by sand-carrying fluid effectively,and increase well productivity and extend the sand control life.

Data-driven casting defect prediction model for sand casting based on random forest classification algorithm

The complex sand-casting process combined with the interactions between process parameters makes it difficult to control the casting quality,resulting in a high scrap rate.A strategy based on a data-driven model was proposed to reduce casting defects and improve production efficiency,which includes the random forest(RF)classification model,the feature importance analysis,and the process parameters optimization with Monte Carlo simulation.The collected data includes four types of defects and corresponding process parameters were used to construct the RF model.Classification results show a recall rate above 90% for all categories.The Gini Index was used to assess the importance of the process parameters in the formation of various defects in the RF model.Finally,the classification model was applied to different production conditions for quality prediction.In the case of process parameters optimization for gas porosity defects,this model serves as an experimental process in the Monte Carlo method to estimate a better temperature distribution.The prediction model,when applied to the factory,greatly improved the efficiency of defect detection.Results show that the scrap rate decreased from 10.16% to 6.68%.

Numerical simulation on sand sedimentation and erosion characteristics around HDPE sheet sand barrier under different wind angles

For the safety of railroad operations,sand barriers are utilized to mitigate wind-sand disaster effects.These disasters,characterized by multi-directional wind patterns,result in diverse angles among the barriers.In this study,using numerical simulations,we examined the behavior of High Density Polyethylene(HDPE)sheet sand barriers under different wind angles,focusing on flow field distribution,windproof efficiency,and sedimentation erosion dynamics.This study discovered that at a steady wind speed,airflow velocity varies as the angle between the airflow and the HDPE barrier changes.Specifically,a 90°angle results in the widest low-speed airflow area on the barrier’s downwind side.If the airflow is not perpendicular to the barrier,it prompts a lateral airflow movement which decreases as the angle expands.The windproof efficiency correlates directly with this angle but inversely with the wind’s speed.Notably,with a wind angle of 90°,wind speed drops by 81%.The minimum wind speed is found at 5.1H(the sand barrier height)on the barrier’s downwind side.As the angle grows,the barrier’s windproof efficiency improves,extending its protective reach.Sedimentation is most prominent on the barrier’s downwind side,as the wind angle shifts from 30°to 90°,the sand sedimentation area on the barrier’s downwind side enlarges by 14.8H.As the angle grows,sedimentation intensifies,eventually overtakes the forward erosion and enlarges the sedimentation area.

Experimental and simulation research on hollow AZ31 magnesium alloy three-channel joint by hot extrusion forming with sand mandrel

Magnesium alloy is one of the lightest metal structural materials.The weight is further reduced through the hollow structure.However,the hollow structure is easily damaged during processing.In order to maintain the hollow structure and to transfer the stresses during the high temperature deformation,the sand mandrel is proposed.In this paper,the hollow AZ31 magnesium alloy three-channel joint is studied by hot extrusion forming.Sand as one of solid granule medium is used to fill the hollow magnesium alloy.The extrusion temperatures are 230℃ and 300℃,respectively.The process parameters(die angle,temperature,bottom thickness,sidewall thickness,edge-to-middle ratio in bottom,bottom shape)of the hollow magnesium alloy are analyzed based on the results of experiments and the finite element method.The results are shown that the formability of the hollow magnesium alloy will be much better when the ratio of sidewall thickness to the bottom thickness is 1:1.5.Also when edge-to-middle ratio in bottom is about 1:1.5,a better forming product can be received.The best bottom shape in these experiments will be convex based on the forming results.The grain will be refined obviously after the extrusion.Also the microstructures will be shown as streamlines.And these lines will be well agreement with the mold in the corner.

Flow field, sedimentation, and erosion characteristics around folded linear HDPE sheet sand fence: Numerical simulation study

Wind and sand hazards are serious in the Milan Gobi area of the Xinjiang section of the Korla Railway. In order to ensure the safe operation of railroads, there is a need for wind and sand protection in heavily sandy areas. The wind and sand flow in the region is notably bi-directional. To shield railroads from sand, a unique sand fence made of folded linear high-density polyethylene(HDPE) is used, aligning with the principle that the dominant wind direction is perpendicular to the fence. This study employed field observations and numerical simulations to investigate the effectiveness of these HDPE sand fences in altering flow field distribution and offering protection. It also explored how these fences affect the deposition and erosion of sand particles. Findings revealed a significant reduction in wind speed near the fence corner;the minimum horizontal wind speed on the leeward side of the first sand fence(LSF) decreased dramatically from 3 m/s to 0.64 m/s. The vortex area on the LSF markedly impacted horizontal wind speeds. Within the LSF, sand deposition was a primary occurrence. As wind speeds increased, the deposition zone shrank, whereas the positive erosion zone expanded. Close to the folded corners of the HDPE sand fence, there was a notable shift from the positive erosion zone to a deposition zone. Field tests and numerical simulations confirmed the high windproof efficiency(WE) and sand resistance efficiency(SE) in the HDPE sand fence. Folded linear HDPE sheet sand fence can effectively slow down the incoming flow and reduce the sand content, thus achieving good wind and sand protection. This study provides essential theoretical guidance for the design and improvement of wind and sand protection systems in railroad engineering.

Establishment of tensile failure induced sanding onset prediction model for cased-perforated gas wells

Sand production is a challenging issue in upstream oil and gas industry,causing operational and safety problems.Therefore,before drilling the wells,it is essential to predict and evaluate sanding onset of the wells.In this paper,new poroelastoplastic stress solutions around the perforation tunnel and tip based on the Mohr-Coulomb criterion are presented firstly.Based on the stress models,a tensile failure induced sanding onset prediction model for cased-perforated gas wells is derived.Then the analytical model is applied to field data to verify its applicability.The results from the perforation tip tensile failure induced sanding model are very close to field data.Therefore,this model is recommended for forecasting the critical conditions of sand production analysis.Such predictions are necessary for providing technical support for sand control decision-making and predicting the production condition at which sanding onset occurs.

Microscopic Analysis of Cementitious Sand and Gravel Damming Materia

The mechanical properties of cementitious sand and gravel damming material have been experimentally determined by means of microscopic SEM(Scanning Electron Microscopy)image analysis.The results show that the combination of fly ash and water can fill the voids in cemented sand and gravel test blocks because of the presence of hydrated calcium silicate and other substances;thereby,the compactness and mechanical properties of these materials can be greatly improved.For every 10 kg/m^(3) increase in the amount of cementitious material,the density increases by about 2%,and the water content decreases by 0.2%.The amount of cementitious material used in the sand and gravel in these tests was 80-110 kg/m^(3),the water-binder ratio was 1-1.50.Moreover,the splitting tensile strength was 1/10 of the compressive strength,and the maximum strength was 7.42 MPa at 90 d.The optimal mix ratio has been found to be 50 kg of cement,60 kg of fly ash and 120 kg of water(C50F60W120).The related dry density was 2.6 g/cm^(3),the water content was 6%,and the water-binder ratio was 1.09.

Experimental research on the mixed sand ratio and initial dry density of weathered sand improved expansive soil free load swelling rate

In this paper, through the indoor free load swelling rate test, expansive soil in a section of a first- class highway reconstruction project in Yichang City was studied. It emphatically analyzed the interrelations among free load swelling rate, non-load time, the proportion of mixed sand and initial dry density. Experimen- tal studies have shown that： Free load swelling deformation is mainly divided into three stages of rapid expan- sion, slow expansion and final stability; when the initial dry density is constant, free load swelling rate of the weathered sand modified soil will reduce rapidly before they slow down with the increase of sand proportion, and weathered sand modified soil free load swelling rate is not sensitive to the large amount of sand mixed; in the same mixed sand ratio, weathered sand modified soil free load swelling rate increases rapidly with the in- crease of initial dry density, there is a good linear correlation between them. To take appropriate control of the initial dry density during the expansive soil subgrade construction helps to reduce its swelling deformation and ensures the stability of the embankment.

SAND: An Additive for Stabilzation of Swelling Clay Soils

An experimental program carried out in this study seeks to understand the physical mechanisms of stabilization of an expansive soil by adding an inert material (sand) at various forms;mixing and intercalation layers of sand. The first aim of the study is to analyze the effect of stabilization on the variation of soil consistency. The results show a marked improvement in soil consistency. Then a study of the effect of the additives on the variation of the swelling in order to solve the lifting structures caused by this phenomenon is carried out. It can be seen that the addition of sand is capable of reducing the swelling action. We complete the study using an ultrasonic device, measuring the propagation velocities of ultrasonic pulse through the tested clay samples. This shows a change occurring in the porosity of the clay when sand is added to it. As a result some interesting conclusions concerning the expansive soil-material amendment are drawn.

The Reduction in the Swelling Potential of the Foundation Ground of Togblécopéin Togo by the Stabilization with Binders and Sands

The present study aims at helping to search for preventive solutions to pathologies of constructions in Togblécopé in Togo, by the reduction in the withdrawal and swelling of foundation grounds through their stabilization. Togblécopé’s clay taken from 1 m, 2 m and 3 m deep, and mixed with four binding materials (cement, sea sand, silty sand and lime). Tests of identification and free swelling with odometer are carried out on pure and stabilized materials. What emerges from these tests is that the limits of liquidity and plasticity are rising along with the rate of stabilizers while the index of plasticity is falling. Cement and lime cause a reduction in the index value of plasticity by almost 50%. The more the sand’s grain size, the more the reduction in the plasticity index. The swelling potential is reduced by 60% for cement and lime, 30% for sea sand and 20% for silty sand. The present study is a contribution to the reduction in deflations from 20% to 60% of some parts of constructions in order to limit cracks.

Effect analysis of biomineralization for solidifying desert sands

The sand-dust weather has become an environmental hazard in the world.However,it is still a challenge to control sandstorms and decrease sand-dust weather.The biomineralization technology for solidifying desert sands has been developed as a novel method in recent years.In this study,the wind erosion tests and verification tests of the sand solidification system were conducted via a series of laboratory experiments.The effects of sand barriers,injecting volume and concentration of the biochemical solution in the sandstorm protection were studied.Moreover,a field test of 60,000 square metres was conducted in the solidification area on both sides of the Wuma Highway in the Tengri Desert.The biomineralization technique was used to solidify sand to prevent the wind from blowing quicksand onto the newly built highway and causing accidents.Results demonstrated that the biomineralization sand solidification method had a good solidification==effect,improved the survival rate,and promoted the growth of plants in the desert.This innovative biomineralization technology is an environmentally responsible technology to control sandstorm disasters.

Study on the clogging mechanism of punching screen in sand control by the punching structure parameters

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.