Experimental study of the temporary plugging capability of diverters to block hydraulic fractures in high-temperature geothermal reservoirs

The effective plugging of artificial fractures is key to the success of temporary plugging and diverting fracturing technology,which is one of the most promising ways to improve the heat recovery efficiency of hot dry rock.At present,how temporary plugging agents plug artificial fractures under high temperature remains unclear.In this paper,by establishing an improved experimental system for the evaluation of temporary plugging performance at high temperature,we clarified the effects of high temperature,injection rate,and fracture width on the pressure response and plugging efficiency of the fracture.The results revealed that the temporary plugging process of artificial fractures in hot dry rock can be divided into four main stages:the initial stage of temporary plugging,the bridging stage of the particles,the plugging formation stage,and the high-pressure dense plugging stage.As the temperature increases,the distribution distance of the temporary plugging agent,the number of pressure fluctuations,and the time required for crack plugging increases.Particularly,when the temperature increases by 100℃,the complete plugging time increases by 90.7%.

Compact Pneumatic Pulse-Jet Pump with Venturi-Like Reverse Flow Diverter

A compact pneumatic pulse-jet pump with a Venturi-like reverse flow diverter,which consists of a nozzle and diffuser,is designed for lifting and transporting a hazardous fluid through a narrow mounting hole.The pumping performance for a liquid mixture or a liquid-solid mixture is examined in terms of the effects of liquid viscosity,particle mass concentration,lifting height,and compression pressure.Results reveal that the pumping performance of the compact pneumatic pulse-jet pump is controlled by jet inertia and the flow resistance of the riser tube positioned after the diffuser.The capacity of the compact pneumatic pulse-jet pump increases with compression pressure and decreases with liquid viscosity.However,even for a liquid mixture with a high viscosity of 7.38 mPa·s,a pumping capacity of 170.7 L·h-1 was observed.For a liquid mixture,two dimensionless indices of performance were found to be the ratio of Euler numbers Euout/EuDV and the suction factor q.As the liquid-solid mixture was lifted to elevation of 6.74 m by the compact pump,the particle size distributions of the liquid-solid mixture in the tank and from the riser tube outlet were determined by a particle size analyzer and found to coincide well.

Plasma discharge characteristics of segmented diverter strips subject to lightning strike

In order to research segmented diverters for aircraft lightning protection, a transient 2 D multiphysics model based on magnetohydrodynamics theory is proposed to predict the location of the arc plasma discharge and lightning channel, and to simulate the electrothermal behavior.Based on numerical calculation and preliminary analysis, factors that affect the breakdown voltage of the segmented diverter are discussed. The results show that the voltage increase rate of the voltage source, the width of the air gap between metal segments and the geometry of these segments influence the breakdown voltage of the strip. High-voltage tests of the segmented diverter are performed to reveal air breakdown of the strip and redirect the lightning current.Experimental and numerical results are compared to verify the correctness of the numerical model. The ionization of the air gap between metal segments and the breakdown voltage of the strip calculated by the model are qualitatively consistent with experimental results. The breakdown voltage of the segmented diverter is far lower than the lightning voltage. When a lightning strike occurs, the segmented diverter can be quickly ionized to form a plasma channel which can guide the lightning current well.

Effects of Geometric Configurations on the Performance of Reverse Flow Diverters in Reverse Flow Mode

The reverse flow diverter (RFD) consisting of a nozzle and a diffuser is a key component in pneumatic pulse jet pumps. We investigated the effects of suction gap and diffuser configurations on RFD performance during the reverse flow mode. Three suction gap configurations were examined: (1) an axisymmetrical cylinder, (2) a cuboid whose bottom plane had no half-circle groove and was level with the diffuser entrance lower border, and (3) a cuboid with a half-circle groove on the bottom plane. Among them, the second one resulted in the highest RFD pumping capacity. The effect of receiver presence before the diffuser was also examined. RFD pumping efficiency was found to be enhanced in the presence of a receiver before the diffuser when the suction gap length is small and the jet outlet velocity at the nozzle exit is high enough. Based on experimental data, a dimensionless performance curve of the suction factor q versus the ratio of Euler numbers in sections out-out and 0-0 Eu out /Eu 0 was derived. This curve is insensitive to suction gap configurations.

A proposed design of flow diverter and it’s hemodynamic validation

Flow diverter intervention is a cutting-edge treatment for intracranial aneurysms by altering the flow field and reducing the pressure in the aneurysm sac.However,the rupture rate and complications rate are still high.In this study,a new design of flow diverter based on Bernoulli’s equation was proposed and hemodynamics evaluation of it was conducted.The numerical model of a patient specific internal carotid aneurysm was established based on computed tomography scan images(Model C).The aneurysm models with normal diverter(ND)and local stenosed diverter(LSD)were modified from the patient-specific model.The blood flow characteristics were obtained and analyzed by numerical simulation while the in vitro experiments were conducted using three-dimensional printed silicone models and pressure measurement system.In both ND and LSD models,the blood flow into the aneurysm have been significantly blocked by the diverters and the pressure in the aneurysm sac have been decreased.The pressure drop and the wall shear stress on the aneurysm wall in the LSD model are higher than that in the ND model.The oscillatory shear index and relative residence time in the aneurysm wall of LSD are lower than that in the ND model.The pressure measurement in the vitro experiment also qualitatively verified the results of pressure comparison in the numerical simulation.In conclusion,the simulation results and in vitro experiments verified that diverter can certainly reduce the pressure in the aneurysm,and the newly design diverter with local stenosis can strengthening this effect.

Computational methods applied to analyze the hemodynamic effects of flow-diverter devices in the treatment of cerebral aneurysms:Current status and future directions

Flow diverter(FD)devices have been widely employed to treat cerebral aneurysms.Despite the well-documented clinical benefits,considerable inter-patient variability in clinical outcome has been reported,which implies the necessity of patient-specifically evaluating hemodynamic changes following FD treatment,especially those associated with posttreatment intra-aneurysmal thrombus formation or complications.Computational fluid dynamics(CFD)methods,owing to the advantages in hemodynamic quantification,cost,and flexibility over traditional in vivo measurement or in vitro experiment methods,have increasingly become a major means for addressing hemodynamic problems related to FD treatment.Relevant CFD-based studies have extensively demonstrated that the results of hemodynamic computation can reasonably explain the clinical outcomes in different patient cohorts and provide useful insights for guiding the selection or optimization of FD devices.Nevertheless,CFD models are inherently unable to predict FD implantation-induced mechanical changes in the walls of aneurysm and its parent artery.In addition,the boundary conditions of most existing CFD models were not fully personalized for purpose of simplicity or due to the difficulty of measuring flow velocity in nearaneurysm regions,which may however considerably compromise the fidelity of the models in reproducing in vivo hemodynamics.To address these issues,the following studies would be expected:(1)perform fluid structure interaction simulations to explore the associations between wall stress/tension and posttreatment adverse vascular remodeling or aneurysm rupture,and(2)develop geometrical multiscale models based on available in vivo data to generate patient-specific boundary conditions for CFD models localized to aneurysm regions.

Hemodynamic analysis for endovascular treatment in small unruptured intracranial aneurysms:a matched comparison study of flow diverter versus LVIS

Background:We compared the treatment of small unruptured intracranial aneurysms(UIAs)with flow diverter and LVIS-assisted coiling to determine the effects of hemodynamic changes caused by different stent and coil packing in endovascular treatment.Methods:Fifty-one UIAs in 51 patients treated with pipeline embolization device(PED)were included in this study and defined as the PED group.We matched controls 1:1 and enrolled 51 UIAs who were treated with LVIS stent,which were defined as the LVIS group.Computational fluid dynamics were performed to assess hemodynamic alterations between PED and LVIS.Clinical analysis was also performed between these two groups after the match.Results:There was no difference in procedural complications between the two groups(P=0.558).At the first angiographic follow-up,the complete occlusion rate was significantly higher in the LVIS group compared with that in the PED group(98.0%vs.82.4%,P=0.027).However,during the further angiographic follow-up,the complete occlusion rate in the PED group achieved 100%,which was higher than that in the LVIS group(98.0%).Compared with the LVIS group after treatment,cases in the PED group showed a higher value of velocity in the aneurysm(0.03±0.09 vs.0.01±0.01,P=0.037)and WSS on the aneurysm(2.32±5.40 vs.0.33±0.47,P=0.011).Consequently,the reduction ratios of these two parameters also showed statistical differences.These parameters in the LVIS group showed much higher reduction ratios.However,the reduction ratio of the velocity on the neck plane was comparable between two groups.Conclusions:Both LVIS and PED were safe and effective for the treatment of small UIAs.However,LVIS-assisted coiling produced greater hemodynamic alterations in the aneurysm sac compared with PED.The hemodynamics in the aneurysm neck may be a key factor for aneurysm outcome.

Comparative assessment of mechanical and chemical fluid diversion techniques during hydraulic fracturing in horizontal wells

The application of fluid diversion during hydraulic fracturing is an evolving technology and has become popular amongst E&P operators over the past few years.The primary objective of the fluid diversion is to improve hydraulic fracturing treatment by increasing stimulated reservoir volume and improving hydrocarbon recovery.This is possible by achieving any of the following objectives:creating uniform distribution of treatment slurry within the target zone;treating unstimulated and under-stimulated zones;or by increasing fracture density by creating a complex fracture network.The fluid diversion application is also helpful in decreasing the number of stages(by increasing stage length)for multi-stage plug-n-perf(PnP)fracturing treatment.It is also applied to prevent fracture-driven interactions between adjacent wells,which is currently a major issue,especially in shale.In addition,for successful refracturing treatment,the diverter application is essential for isolating the existing fractures and redirecting the treatment slurry to the desired unstimulated zones.The diversion methods can be broadly categorized into the mechanical and chemical diversion.Several established mechanical diversion techniques are frac plugs,expandable casing patches,expandable liners,swellable packers,straddle packer assembly,sand plugs,frac sleeves,perforation ball sealers,and limited entry technique.The different chemical diversion techniques are particulates,fibers,gels,surfactants,perforation pods,and composite diverting.This paper describes the current status of established mechanical and chemical diverter technologies and examines their comparative advantages and challenges.Various techniques are suitable for diverter application,but the technique is selected based on the desired objective and conditions of the wellbore and reservoir.The general guidelines for selecting diversion techniques and operational considerations are also provided in the paper.The diagnosis of diversion treatment plays an essential role in diversion technique selection and optimization of selection parameters for the subsequent treatments.Therefore,the application of conventional surface pressure monitoring techniques and advanced diagnostic tools to evaluate diversion effectiveness are briefly described.Presently no standard laboratory testing method is established for the performance evaluation of diverting agents.Therefore,researchers have implemented various laboratory methods,which are briefly summarized in the paper.Significant insight into the diversion technology and guidelines for its selection and successful implementation is provided to help engineers to increase the effectiveness of hydraulic fracturing treatments.The limitations of individual diversion techniques are clarified,which provide the future scope of research for improvement in various diversion technologies.

Unraveling the mechanisms underlying lake expansion from 2001 to 2020 and its impact on the ecological environment in a typical alpine basin on the Tibetan Plateau

Yanhu Lake basin(YHB)is a typical alpine lake on the northeastern Tibetan Plateau(TP).Its continuous expansion in recent years poses serious threats to downstream major projects.As a result,studies of the mechanisms underlying lake expansion are urgently needed.The elasticity method within the Budyko framework was used to calculate the water balance in the Yanhu Lake basin(YHB)and the neighboring Tuotuo River basin(TRB).Results show intensification of hydrological cycles and positive trends in the lake area,river runoff,precipitation,and potential evapotranspiration.Lake expansion was significant between 2001 and 2020 and accelerated between 2015 and 2020.Precipitation increase was the key factor underlying the hydrological changes,followed by glacier meltwater and groundwater.The overflow of Yanhu Lake was inevitable because it was connected to three other lakes and the water balance of all four lakes was positive.The high salinity lake water diverted downstream will greatly impact the water quality of the source area of the Yangtze River and the stability of the permafrost base of the traffic corridor.

Nursing care of 22 patients with complex intracranial aneurysms treated with flow-diverting stents:A retrospective study

Objective:To summarize the nursing treatment of patients who underwent implantation of a blood flow diverter to treat complex intracranial aneurysms.Methods:Data from 22 patients with complex aneurysms,diagnosed at an interventional center for blood flow diverter implantation between February 2015 and February 2016,treated in the Henan Provincial People’s Hospital(Zhengzhou,China),were retrospectively analyzed.Nursing methods,including preoperative,intraoperative,and postoperative care,were analyzed.Results:All 22 patients underwent successful surgery,with no related complications or hospital mortality,and were cured in hospital.Conclusion:Interventional flow diverter therapy for patients with complex intracranial aneurysms is a new technology,and involves intensive care by nursing staff and appears to be a promising new treatment method.

Self-consistent diverted tokamak equilibria with nonzero edge current

The semi-analytical method, previously used to construct model double-null and single-null diverted tokamak equi- libria （Bingren Shi, Plasma Phys. Control Fusion 50 （2008） 085006, 51 （2009） 105008, Nucl. Fusion 51 （2011） 023004）, is extended to describe diverted tokamak equilibria with nonzero edge current, including the Pfirsch Schliiter（PS） cur- rent. The PS current density is expressed in a way suitable to describe a diverted tokamak configuration in the near separatrix region. The model equilibrium is expressed by only two terms of the exact separable solutions of the Grad Shafranov equation, one of which is governed by a homogeneous ordinary differential equation, and the other by an inhomogeneous one. The particular merits of such a model configuration are that the internal region inside the separa- trix and a suitable scrape-off layer can be simultaneously described by this exact solution. To investigate the physics in the region near the X-point, the magnetic surfaces can be satisfactorily described by approximate hyperbolic curves.

Combinational Optimization of Strut Placement for Intracranial Stent Using a Realistic Aneurysm

Stent insertion for cerebral aneurysm has been studied using ideal and realistic aneurysms in recent years. Stent insertion aims at reducing the flow in an aneurysm. To minimize the average velocity in an aneurysm, we applied optimization to the strut position in a realistic aneurysm based on computational fluid dynamics. The result shows the effect on velocity reduction of strut placement in the inflow area.

Fatal Outcome after Delayed Pipeline Embolization Device Migration for the Treatment of a Giant Superior Cerebellar Artery Aneurysm: Technical Note for Complication Avoidance

Purpose: Flow diversion is a relatively novel technique to treat some intracranial aneurysms. With new techniques, unusual complications can occur. We described a case of Pipeline Embolization Device (PED) migration, strategy for its recognition, and a technical point to prevent its occurrence. Publication of these rare events is important to make physicians aware of potential complications. Methods: A patient with a previously coiled giant superior cerebellar aneurysm presented with brainstem compression symptoms. Imaging verified progressive aneurysm growth. A decision was made to treat the aneurysm with PED. Results: Development of new neurologic symptoms prompted a computed tomography that showed hydrocephalus. An angiogram also showed recanalization of the aneurysm secondary to upward migration/retraction of the flow diverter. A ventriculo-peritoneal shunt was implemented and planning for placement of a second flow diverter was made. Unfortunately, the patient expired while waiting for the endovacular intervention. Conclusions: PED migration may occur even after correct placement of the device. Early recognition of this complication is essential. When clinical changes occur, it is paramount that this uncommon, but potentially deadly, complication is suspected. Appropriate sizing and deployment technique are important for the long-term stability of the device.

Predictive factors for anastomotic leakage after laparoscopic colorectal surgery

Every colorectal surgeon during his or her career is faced with anastomotic leakage(AL); one of the most dreaded complications following any type of gastrointestinal anastomosis due to increased risk of morbidity, mortality, overall impact on functional and oncologic outcome and drainage on hospital resources. In order to understand and give an overview of the AL risk factors in laparoscopic colorectal surgery, we carried out a careful review of the existing literature on this topic and found several different definitions of AL which leads us to believe that the lack of a consensual, standard definition can partly explain the considerable variations in reported rates of AL in clinical studies. Colorectal leak rates have been found to vary depending on the anatomic location of the anastomosis with reported incidence rates ranging from 0 to 20%, while the laparoscopic approach to colorectal resections has not yet been associated with a significant reduction in AL incidence. As well, numerous risk factors, though identified, lack unanimous recognition amongst researchers. For example, the majority of papers describe the risk factors for left-sided anastomosis, the principal risk being male sex and lower anastomosis, while little data exists defining AL risk factors in a right colectomy. Also, gut microbioma is gaining an emerging role as potential risk factor for leakage.

Colostomy is a simple and effective procedure for severe chronic radiation proctitis

AIM: To assess the efficacy and safety of diverting colostomy in treating severe hemorrhagic chronic radiation proctitis(CRP). METHODS: Patients with severe hemorrhagic CRP who were admitted from 2008 to 2014 were enrolled into this study. All CRP patients were diagnosed by a combination of pelvic radiation history, clinical rectal bleeding, and endoscopic findings. Inclusion criteria were CRP patients with refractory bleeding with moderate to severe anemia with a hemoglobin level < 90 g/L. The study group included patients who were treated by diverting colostomy, while the control group included patients who received conservative treatment. The remission of bleeding was defined as complete cessation or only occasional bleeding that needed no further treatment. The primary outcome was bleeding remission at 6 mo after treatment. Quality of life beforetreatment and at follow-up was evaluated according to EORTC QLQ C30. Severe CRP complications were recorded during follow-up.RESULTS: Forty-seven consecutive patients were enrolled, including 22 in the colostomy group and 27 in the conservative treatment group. When compared to conservative treatment, colostomy obtained a higher rate of bleeding remission(94% vs 12%), especially in control of transfusion-dependent bleeding(100% vs 0%), and offered a better control of refractory perianal pain(100% vs 0%), and a lower score of bleeding(P < 0.001) at 6 mo after treatment. At 1 year after treatment, colostomy achieved better remission of both moderate bleeding(100% vs 21.5%, P = 0.002) and severe bleeding(100% vs 0%, P < 0.001), obtained a lower score of bleeding(0.8 vs 2.0, P < 0.001), and achieved obvious elevated hemoglobin levels(P = 0.003), when compared to the conservative treatment group. The quality of life dramatically improved after colostomy, which included global health, function, and symptoms, but it was not improved in the control group. Pathological evaluation after colostomy found diffused chronic inflammation cells, and massive fibrosis collagen depositions under the rectal wall, which revealed potential fibrosis formation. CONCLUSION: Diverting colostomy is a simple, effective and safe procedure for severe hemorrhagic CRP. Colostomy can improve quality of life and reduce serious complications secondary to radiotherapy.

Visco-elastic Properties of VES Diverting Acid for Carbonate Reservoirs

Storage modulus and loss modulus is the main performance index of visco-elastic properties.In this paper the storage modulus and loss modulus of a new diverting acid and their influencing factors were systematically investigated.Besides,the constitutive equations of the diverting acid at different temperatures were elicited from shearing experiments,which show that the visco-elastic surfactant(VES)acid system is a non-Newtonian power law fluid at low temperature and a Newtonian fluid at high temperature.The storage modulus and loss modulus at different temperatures,pH,and VES content in the acid are critical for the design of acid stimulation for oil well,especially when the VES acid is used in this field only on trial and the basic data are in urgent needed for the design and construction of the acidification stimulation.

Quantitative investigation of multi-fracture morphology during TPDF through true tri-axial fracturing experiments and CT scanning

Due to the reservoir heterogeneity and the stress shadow effect, multiple hydraulic fractures within one fracturing segment cannot be initiated simultaneously and propagate evenly, which will cause a low effectiveness of reservoir stimulation. Temporary plugging and diverting fracturing(TPDF) is considered to be a potential uniform-stimulation method for creating multiple fractures simultaneously in the oilfield. However, the multi-fracture propagation morphology during TPDF is not clear now. The purpose of this study is to quantitatively investigate the multi-fracture propagation morphology during TPDF through true tri-axial fracturing experiments and CT scanning. Critical parameters such as fracture spacing, number of perforation clusters, the viscosity of fracturing fluid, and the in-situ stress have been investigated. The fracture geometry before and after diversion have been quantitively analyzed based on the two-dimensional CT slices and three-dimensional reconstruction method. The main conclusions are as follows:(1) When injecting the high viscosity fluid or perforating at the location with low in-situ stress, multiple hydraulic fractures would simultaneously propagate. Otherwise, only one hydraulic fracture was created during the initial fracturing stage(IFS) for most tests.(2) The perforation cluster effectiveness(PCE) has increased from 26.62% during the IFS to 88.86% after using diverters.(3) The diverted fracture volume has no apparent correlation with the pressure peak and peak frequency during the diversion fracturing stage(DFS) but is positively correlated with water-work.(4) Four types of plugging behavior in shale could be controlled by adjusting the diverter recipe and diverter injection time, and the plugging behavior includes plugging the natural fracture in the wellbore, plugging the previous hydraulic fractures, plugging the fracture tip and plugging the bedding.

Growth rate of peeling mode in the near separatrix region of diverted tokamak plasma

An analytical expression of the peeling mode in the near separatrix region of diverted tokamak plasma is derived. It is shown that in diverted plasmas both with single and double X points, though the perturbed potential energy of the unstable peeling mode tends to be large, its growth rate becomes very small due to the even larger kinetic energy. Compared to some recent studies that give qualitatively correct results about this growth rate, our result is directly related with the diverted equilibrium quantities suitable for application to realistic experiments.

Optimization of refracturing timing for horizontal wells in tight oil reservoirs: A case study of Cretaceous Qingshankou Formation, Songliao Basin, NE China

Tight oil reservoirs in Songliao Basin were taken as subjects and a novel idealized refracturing well concept was proposed by considering the special parameters of volume fracturing horizontal wells, the refracturing potential of candidate wells were graded and prioritized, and a production prediction model of refracturing considering the stress sensitivity was established using numerical simulation method to sort out the optimal refracturing method and timing. The simulations show that: with the same perforation clusters, the order of fracturing technologies with contribution to productivity from big to small is refracturing between existent fractured sections, orientation diversion inside fractures, extended refracturing, refracturing of existent fractures; and the later the refracturing timing, the shorter the effective time. Based on this, the prediction model of breakdown pressure considering the variation of formation pressure was used to find out the variation pattern of breakdown pressure of different positions at different production time. Through the classification of the breakdown pressure, the times of temporary plugging and diverting and the amount of temporary plugging agent were determined under the optimal refracturing timing. Daily oil production per well increased from 2.3 t/d to 16.5 t/d in the field test. The research results provide important reference for refracturing optimization design of similar tight oil reservoirs.

Diverting agents in the oil and gas industry:A comprehensive analysis of their origins,types,and applications

During the life of a well,treatments are carried out to boost productivity by stimulating initially unproduced zones.These treatments include hydraulic fracturing,matrix acidization,and acid fracturing,among others.Hydraulic fracturing treatment is generally applied to deeper reservoirs of oil or natural gas for enhanced recovery.By infusing proppant,water,and chemicals under extreme pressure during the fracturing procedure,fissures in and beneath the reservoir layer can be accessed and expanded.Another stimulating procedure,matrix acidization,involves injecting acid down the drilling hole to permeate the rock fissures at stresses lower than the fracture stress.In addition,carbonate reservoir acid fracturing stimulation is commonly used as an acid treatment technique whereby a pressure greater than the formation disintegration pressure or spontaneous fracture closure pressure is used to compress acid into the reservoir.These treatments allow existing wells to sustain hydrocarbon production without new wells being drilled.Diverters,when employed efficiently,can prevent the need to use a rig to provide momentary physical barriers,thus lowering the cost of the workover.Recent improvements in diversion technology make use of a variety of degradable particles that act as momentary bridges,either at the perforation entries or inside the existing fractures.The aim of this study is to introduce different types of mechanical and chemical diverters used to enhance the productivity of wells.This study explains the concepts of different types of diverters and their applications in several formations,it will also help readers to understand the selection procedures based on the suitability and requirements of diverter use by case studies from around the world.