A hybrid Stochastic Fractal Search plus Pattern Search （hSFS-PS） based cascade PI-PD controller is suggested in this paper for Automatic Generation Control （AGC） of thermal, hydro and gas power unit based power sy...A hybrid Stochastic Fractal Search plus Pattern Search （hSFS-PS） based cascade PI-PD controller is suggested in this paper for Automatic Generation Control （AGC） of thermal, hydro and gas power unit based power systems in presence of Plug in Electric Vehicles （PEV）. Firstly, a single area multi-source power system consisting of thermal hydro and gas power plants is considered and parameters of Integral （I） controller is optimized by Stochastic FractaI Search （SFS） algorithm. The superiority of SFS algorithm over some recently proposed approaches such as optimal control, differential evolution and teaching learning based optimization techniques is demonstrated by comparing simulation results for the identical power system. To improve the system performance further, Pattern Search （PS） is subsequently employed. The study is further extended for different controllers like PI, PID, and cascaded PI-PD controller and the superiority of cascade PI-PD controller over conventional controllers is demonstrated. Then, cascade PI- PD controller parameters of AGC searched using the proposed hSFS-PS algorithm in presence of plug in electric vehicles. The study is also extended to an interconnected power system. It is seen from the comparative analysis that hSFS-PS tuned PI-PD controller in single and multi-area with multi sources improves the system frequency stability in complicated situations. Lastly, a three area interconnected system with PEVs with dissimilar cascade PI-PD controller in each area is considered and proposed hSFS- PS algorithm is used to tune the controller parameters in presence of nonlinearities like rate constraint of units, dead zone of governor and communication delay.展开更多
High pressure and water-bearing caverns ahead of a karst tunnel face tend to cause geological disasters, such as water and mud bursts. So, the determination of safe thickness of the reserved rock plug is a key technic...High pressure and water-bearing caverns ahead of a karst tunnel face tend to cause geological disasters, such as water and mud bursts. So, the determination of safe thickness of the reserved rock plug is a key technical problem to be solved for karst tunnel construction. Based on the Hoek-Brown nonlinear failure criterion, the minimum safe thickness of rock plug was investigated in the light of the limit analysis theory. On the basis of the proposed failure mode, the expression of the minimum thickness for rock plug was obtained by means of upper bound theorem in combination with variational principle. The calculation results show the influence of each parameter on safe thickness and reveal the damage range of rock plug. The proposed method is verified by comparing the results with those of the drain cavern of Maluqing Tunnel. The research shows that with the increase of compressive strength and tensile strength as well as constant A of Hoek-Brown criterion, the safe thickness decreases, whereas with the increase of cavern pressure, tunnel diameter, and constant B from Hoek-Brown criterion, the safe thickness increases. Besides, the tensile strength, or constants A and B affect the shear failure angle of rock plug structure, but other parameters do not. In conclusion, the proposed method can predict the minimum safe thickness of rock plug, and is useful for water burst study and prevention measures of tunnels constructed in high-risk karst regions.展开更多
The phenomenon of the soil plug usually rising inside the suction foundations during suction penetration was quantitatively described and predicted. The formation process of the soil plug was simulated and calculated ...The phenomenon of the soil plug usually rising inside the suction foundations during suction penetration was quantitatively described and predicted. The formation process of the soil plug was simulated and calculated by DEM （discrete element method） model. The seepage flow, the self-weight of soil, the friction on the chamber wall as well as the suction inside the chamber are considered as the main external forces in the process. The results are compared with a set of laboratory model tests performed by using three soil types （sand, silty clay and clay） in the Bohai Sea area. The heights of soil plug from numerical estimations are lower than those from model test results, mainly because the suction pressure and friction resistance are applied in an ideal way under the numerical simulation.展开更多
The soil plug phenomenon involving the rising of the surface soil inside the bucket chamber under the suction pressure and seepage forces was simulated and calculated by deformable discrete element method (DDEM) model...The soil plug phenomenon involving the rising of the surface soil inside the bucket chamber under the suction pressure and seepage forces was simulated and calculated by deformable discrete element method (DDEM) models. The seepage forces, the effective gravity of soil, the friction on the chamber wall and the suction inside the chamber are considered as the main external forces of DDEM specimen. Three typical types of soil (silty clay, silt and sand) in the Bohai Sea are set as the main environmental conditions in the formation process of soil plug. It is found that the heights of soil plug simulated by DDEM models are 161.85 mm in silty clay, 125.22 mm in silt and 167.56 mm in sand, which are close to model test results and higher than those estimated by discrete element method (DEM). DDEM is an effective method to estimate and predict the heights of soil plug before suction penetration of bucket foundations on site.展开更多
Background: Dry eye syndrome, which affects 10% to 20% of adults, is a disorder of the tear film and is associated with symptoms of ocular discomfort. Smart Plug is a mechanical treatment in which the tear drainage sy...Background: Dry eye syndrome, which affects 10% to 20% of adults, is a disorder of the tear film and is associated with symptoms of ocular discomfort. Smart Plug is a mechanical treatment in which the tear drainage system is blocked in order to aid in the preservation of natural tears on the ocular surface. Purpose: To evaluate the long-term clinical efficacy of Smart Plug in the treatment of aqueous tear deficiency dry eye. Patients and Methods: Retrospective study. Three hundred and two patients with aqueous tear deficiency dry eye were enrolled and all the patients accepted the punctual plug of Smart plug from Jan. 2011 to Jan. 2016. The clinical symptoms, Schirmer’s I test, Fluorescein staining (FL), tear break up time (TBUT), and complications were observed and analyzed. Results: Three hundred and two patients (604 eyes) were treated with Smart Plug (22 cases accepted upper and lower punctual plug, 280 cases only lower punctual plug). There were 109 males (36.1%) and 193 females (63.9%) with a mean age of 44.54 years old (Range from 25 to 83 years). Ten cases required the upper Smart Plug after lower punctual plug insertion because of no significantly improved symptoms. Smart plug was removed in 3 patients (1%) due to tearing. Six patients had mild postoperative tearing and no special treatment was required. Lacrimal canaliculitis occurred postoperatively in 8 cases (2.6%) (6 lower and 2 upper), and the affected plug was removed and treated with topical antibiotic eye drops. The BUT, SIT and FL scores of all patients were significantly improved from (2.11 ± 1.01, 4.20 ± 1.07, 6.06 ± 1.97) to (4.34 ± 1.22, 9.01 ± 1.56, 2.33 ± 1.28) respectively after at least 36 months of follow-up (All P P Conclusion: During a mean follow-up of 4.3 years, Smart plug is an effective method for the treatment of aqueous tear deficiency dry eye in spite of its postoperative complications such as canaliculitis and tearing.展开更多
Objective: this study is mainly to analyze the effect of pregnancy and oxytocin in the treatment of postpartum bleeding diseases. Methods: the study object, number and group division method are: in our cure postpartum...Objective: this study is mainly to analyze the effect of pregnancy and oxytocin in the treatment of postpartum bleeding diseases. Methods: the study object, number and group division method are: in our cure postpartum bleeding patients, 78 cases and random method, and as the name of the reference group, as another group, 39 cases of study group in the treatment of the accepted scheme for oxytocin, 39 cases of reference group in treatment received oxytocin, after the following indicators of two groups recorded analysis, respectively for quality of life, postpartum bleeding, clinical efficacy and shrinkage intensity, incidence of adverse reactions, etc. Results: in the clinical efficacy evaluation, the research group with total response rate was 94.87%, higher than the reference group with a total response rate of 71.79% (P <0.05);In the comparison of the improvement of quality of life in the study group and the reference group, it showed that the above indicators improved after the treatment. However, the obvious improvement was the research group (P <0.05);In the comparison of adverse reactions: the study group with total incidence of 5.13% was lower compared with the reference group with total incidence of 20.51% (P <0.05);The evaluation of the contractions intensity between the groups showed that the contractions were not improved significantly in the study group (P <0.05);In the statistics of the treatment satisfaction of the study group and the reference group, it is known that in the study group where the total satisfaction score was (95.65 ± 1.75) points was higher than the total satisfaction score was (76.54 ± 0.65) points (P <0.05);In the comparison of postpartum bleeding in the second group, the study group improved better after receiving treatment (P <0.05). Conclusion: the treatment of pregnancy plug and oxytonin is more effective in the treatment of postpartum bleeding patients, and can reduce the probability of adverse reactions, improve the situation of postpartum bleeding and weak contractions, and significantly improve the treatment satisfaction and quality of life.展开更多
During drilling operations in deep fractured tight gas reservoirs,lost circulation of working fluid frequently occurs due to the formationʼs low pressure-bearing capacity.Adding lost circulation materials(LCMs)to dril...During drilling operations in deep fractured tight gas reservoirs,lost circulation of working fluid frequently occurs due to the formationʼs low pressure-bearing capacity.Adding lost circulation materials(LCMs)to drilling fluids is the most common method for controlling lost circulation.Among these,granular LCMs are widely used,but the application frequency of flaky LCMs has been increasing annually due to their unique morphology.However,the migration and plugging behavior of flaky LCMs within fractures,and the mechanisms enhancing the pressure-bearing capacity of the plugging zone are not well understood.Therefore,this study conducted visual plugging experiments and dynamic fracture plugging experiments to evaluate the plugging mode and pressure-bearing capacity of the plugging slurry with various particle sizes and concentrations of flaky LCMs.The experimental results demonstrate that the fracture plugging process can be divided into four stages:uniform flow stage of the plugging slurry,formation and development stage of the bridging area,formation and development stage of the plugging area,and pressure-bearing stage of the plugging zone.The inclusion of flaky LCMs notably reduces the duration of stages 1 and 2,while simultaneously increasing the proportion of the plugging zone and enhancing its surface porosity.Flaky LCMs reduce the effective fracture width through“interception”and“co-bridging”modes,thus improving plugging zone formation efficiency.Appropriate particle size and concentration of flaky LCMs increase the area and length of the plugging zone.This reduces the fracture width increment caused by injection pressure and enhances frictional force between the plugging zone and fracture surface,thereby improving the pressure-bearing capacity of the plugging zone.However,excessively high concentrations of flaky LCMs result in decreased structural stability of the plugging zone,and excessively large particle sizes increase the risk of plugging outside fracture inlet.The recommended concentration of flaky LCMs in the plugging slurry is 2%–3%,with a particle size 1.2 to 1.5 times that of the bridging granular LCMs and not exceeding twice the fracture width.This study provides a theoretical foundation for selecting LCMs and designing plugging formulations for field applications.展开更多
The stress corrosion cracking(SCC)performance of the sealed Alloy 690 plugs was investigated in 350℃deoxygenated concentrated alkaline solution.Sealing was used to expose only the inner surface of the plug,preventing...The stress corrosion cracking(SCC)performance of the sealed Alloy 690 plugs was investigated in 350℃deoxygenated concentrated alkaline solution.Sealing was used to expose only the inner surface of the plug,preventing direct contact between the tube sheet and the concentrated alkaline solution.After exposure for 1000 h,several intergranular cracks were observed on the inner wall of the plugs.Stress corrosion cracks primarily appear in some regions on the inner wall,which are highly deformed and advanced along the random grain boundary.The internal oxide layer formed in the high-temperature alkaline solution was not dense;it comprised a composite oxide with multiple layers.The outermost layer consisted of Fe-Cr-Ni oxide particles,and beneath it was an uneven Ni-rich layer,followed by a thin Cr-rich layer closest to the matrix.High kernel average misorientation in the heavily deformed region and a lack of chromium carbide contributed to crack initiation and propagation of Alloy 690 plug in hot concentrated alkaline solutions.展开更多
Temporary plugging and diversion fracturing(TPDF)is widely used to promote the uniform and complex distribution of multi-clustered hydraulic fractures(HFs)in a horizontal well of the unconventional formations.However,...Temporary plugging and diversion fracturing(TPDF)is widely used to promote the uniform and complex distribution of multi-clustered hydraulic fractures(HFs)in a horizontal well of the unconventional formations.However,the migration behavior of temporary plugging agent(TPA),as a function of the concentration and particle size of TPA and cluster-perforation numbers,etc.,determining the effectiveness of this technique,remains unclear.Therefore,this study conducted innovatively a series of TPDF simulation experiments on transparent polymethyl methacrylate(PMMA)specimens(cubic block of 30 cm×30 cm×30 cm)to explore visually the migration behavior of TPA in multi-clustered HFs in a horizontal well.A laboratory hydraulic sandblasting perforation completion technique was implemented to simulate the multi-cluster perforations.All the distributions of wellbore,perforations,HFs,and TPA can be seen clearly inside the PMMA specimen post the experiment.The results show that there are four characteristic plugging positions for the TPA:mouth of HF,middle of HF,tip of HF,and the intersection of HFs.Small particle size TPA tends to migrate to the fracture tip for plugging,while large particle size TPA tends to plug at the fracture mouth.The migration of the TPA is influenced obviously by the morphology of the fracture wall.A smooth fracture wall is conducive to the migration of the TPA to the far end of HFs,but not conducive to generating the plugging zone and HF diversion.In contrast,a"leaf vein"fracture of rough wall is conducive to generating the plugging layer and the diversion of HFs,but not conducive to the migration of the TPA to the far end of HFs.The migration ability of TPA in a"shell"pattern is intermediate between the two above cases.Increasing TPA concentration can encourage TPA to migrate more quickly to the characteristic plugging position,and thereby to promote the creation of effective plugging and subsequently the multi-stage diversion of the HFs.Nevertheless,excessive concentration may cause the TPA to settle prematurely,affecting the propagation of the HFs to the far end.Increasing the number of clusters to a certain extent can encourage TPA to migrate into the HFs and form plugging,and promote the diversion.An evaluation system for the migration ability of granular TPA has been established,and it was calculated that when there is no plugging expectation target,the comprehensive migration ability of small particle size TPA is stronger than that of large particle size TPA.This research provides theoretical foundation for the optimization of temporary plugging parameters.展开更多
This study investigates the load-bearing capacity of open-ended pipe piles in sandy soil, with a specific focus on the impact of soil plug constraints at four levels(no plug, 25% plug, 50% plug, and full plug). Levera...This study investigates the load-bearing capacity of open-ended pipe piles in sandy soil, with a specific focus on the impact of soil plug constraints at four levels(no plug, 25% plug, 50% plug, and full plug). Leveraging a dataset comprising open-ended pipe piles with varying geometrical and geotechnical properties, this research employs shallow neural network(SNN) and deep neural network(DNN) models to predict plugging conditions for both driven and pressed installation types. This paper underscores the importance of key parameters such as the settlement value,applied load, installation type, and soil configuration(loose, medium, and dense) in accurately predicting pile settlement. These findings offer valuable insights for optimizing pile design and construction in geotechnical engineering,addressing a longstanding challenge in the field. The study demonstrates the potential of the SNN and DNN models in precisely identifying plugging conditions before pile driving, with the SNN achieving R2 values ranging from0.444 to 0.711 and RMSPE values ranging from 24.621% to 48.663%, whereas the DNN exhibits superior performance, with R2 values ranging from 0.815 to 0.942 and RMSPE values ranging from 4.419% to 10.325%. These results have significant implications for enhancing construction practices and reducing uncertainties associated with pile foundation projects in addition to leveraging artificial intelligence tools to avoid long experimental procedures.展开更多
Milling bridge plugs in shale gas wells with severe casing deformation often leads to the accumulation of cuttings,increasing the risk of stuck drill bits.Friction in the wellbore further complicates tool deployment i...Milling bridge plugs in shale gas wells with severe casing deformation often leads to the accumulation of cuttings,increasing the risk of stuck drill bits.Friction in the wellbore further complicates tool deployment into the horizontal section,posing challenges to efficient plug drilling and achieving wellbore access to the target layer.This paper integrates the theory of positive displacement motors and models their actual working characteristics to study the milling of bridge plugs in severely deformed horizontal wells.It examines the effects of coiled tubing diameter and wall thickness on the bending load of horizontal sections and discusses key technical requirements,including the timing of plug drilling,extending the run in the horizontal section,parameter control,and real-time field analysis.Field practices have shown that after casing deformation occurs,priority should be given to drilling out the bridge plugs below the point of deformation.The primary factors contributing to stuck drills in deformed wells include smaller mill shoe sizes and larger cuttings sizes.Short well-washing cycles and targeted cuttings removal can effectively reduce sticking risks.If sticking occurs,high-tonnage pulling should be avoided.Instead,releasing the stick through up-anddown string motion,combined with high-volume nozzle spraying and annulus pumping,is recommended.The selection of coiled tubing should consider diameter,wall thickness,and steel grade to handle complex situations.Larger diameters,thicker walls,and low-frequency,multi-head hydraulic oscillators are more effective for unlocking horizontal sections.This approach can reduce the risk of drill sticking and solve the problem of horizontal section lock-ups,offering a reliable solution for smooth drilling and efficient production in wells with severe casing deformation.展开更多
Resin plugging agents play a pivotal role in addressing casing damage in oil and gas fields.However,the widespread use of epoxy resin is constrained by its high cost and non-renewable origin,while plant-based resins o...Resin plugging agents play a pivotal role in addressing casing damage in oil and gas fields.However,the widespread use of epoxy resin is constrained by its high cost and non-renewable origin,while plant-based resins often suffer from inadequate mechanical properties,which limit their effectiveness in such applications.This study introduces BEOPA,an innovative,renewable,high-strength resin plugging agent derived from epoxidized soybean oil(ESO)and enhanced with bisphenol A-type benzoxazine(BZ).In this study,the synthesis process,reactionmechanism,and application performance of this novelmaterial are systematically presented,explored and optimized.It is shown that the optimal formulation of BEOPA includes 41.4 wt%ESO,24.8 wt%BZ,24.8 wt%methylhexahydrophthalic anhydride(MHHPA),8.2 wt%styrene(ST),and 0.8 wt%N,N-dimethylbenzylamine(BDMA),yielding an impressive compressive strength of 93.7 MPa.The integration of ESO and BZ creates an intricate and robust double crosslinking network,significantly enhancing material strength and durability.BEOPA exhibits a tunable curing time,ranging from 0.5 to 15 h,with viscosities below 300 mPa⋅s at 25℃and 75mPa⋅s at 50℃.Furthermore,it demonstrates exceptional thermal stability within the 100℃-150℃range,even in environments with mineral salt concentrations as high as 43,330 mg/L.Remarkably,BEOPA achieves superior plugging performance,sustaining breakthrough pressures exceeding 29.7 MPa in 1 mm crack cores.展开更多
Lost circulation critically jeopardizes drilling safety and efficiency,and remains an unresolved challenge in oil and gas engineering.In this paper,by utilizing the self-developed dynamic plugging apparatus and synthe...Lost circulation critically jeopardizes drilling safety and efficiency,and remains an unresolved challenge in oil and gas engineering.In this paper,by utilizing the self-developed dynamic plugging apparatus and synthetic cores containing large-scale fractures,experimental research on the circulation plugging of different materials was conducted.Based on the D90 rule and fracture mechanical aperture model,we analyze the location of plugging layer under dynamic plugging mechanism.By setting different parameters of fracture width and injection pressure,the laws of cyclic plugging time,pressure bearing capacity and plugging layers formation were investigated.The results show that the comprehensive analysis of particle size and fracture aperture provides an accurate judgment of the entrance-plugging phenomenon.The bridging of solid materials in the leakage channel is a gradual process,and the formation of a stable plug requires 2–3 plug-leakage cycles.The first and second cyclic plugging time was positively correlated with the fracture width.Different scales of fractures were successfully plugged with the bearing pressure greater than 6 MPa,but there were significant differences in the composition of the plugging layer.The experimental results can effectively prove that the utilized plugging agent is effective and provides an effective reference for dynamic plugging operation.展开更多
Multi-stage and multi-cluster fracturing(MMF)is a crucial technology in unconventional oil and gas development,aiming to enhance production by creating extensive fracture networks.However,achieving uniform expansion o...Multi-stage and multi-cluster fracturing(MMF)is a crucial technology in unconventional oil and gas development,aiming to enhance production by creating extensive fracture networks.However,achieving uniform expansion of multi-cluster hydraulic fractures(HFs)in MMF remains a significant challenge.Field practice has shown that the use of temporary plugging and diversion fracturing(TPDF)can promote the balanced expansion of multi-cluster HFs.This study conducted TPDF experiments using a true triaxial fracturing simulation system setting a horizontal well completion with multi-cluster jetting perforations to investigate the equilibrium initiation and extension of multi-cluster fractures.The influence of key parameters,including cluster spacing,fracturing fluid viscosity,differential stress,and fracturing fluid injection rate,on fracture initiation and propagation was systematically examined.The results indicate that while close-spaced multi-cluster fracturing significantly increases the number of HFs,it also leads to uneven extension of HFs in their propagation.In contrast,TPDF demonstrates effectiveness in mitigating uneven HF extension,increasing the number of HFs,and creating a larger stimulated reservoir volume,ultimately leading to improved oil and gas well productivity.Moreover,under conditions of high differential stress,the differential stress within the formation exerts a stronger guiding effect in HFs,which are more closely aligned with the minimum principal stress.Low-viscosity fluids facilitate rapid and extensive fracture propagation within the rock formation.High-volume fluid injection,on the other hand,more comprehensively fills the formation.Therefore,employing lowviscosity and high-volume fracturing is advantageous for the initiation and extension of multi-cluster HFs.展开更多
Gamma-ray imaging systems are powerful tools in radiographic diagnosis.However,the recorded images suffer from degradations such as noise,blurring,and downsampling,consequently failing to meet high-precision diagnosti...Gamma-ray imaging systems are powerful tools in radiographic diagnosis.However,the recorded images suffer from degradations such as noise,blurring,and downsampling,consequently failing to meet high-precision diagnostic requirements.In this paper,we propose a novel single-image super-resolution algorithm to enhance the spatial resolution of gamma-ray imaging systems.A mathematical model of the gamma-ray imaging system is established based on maximum a posteriori estimation.Within the plug-and-play framework,the half-quadratic splitting method is employed to decouple the data fidelit term and the regularization term.An image denoiser using convolutional neural networks is adopted as an implicit image prior,referred to as a deep denoiser prior,eliminating the need to explicitly design a regularization term.Furthermore,the impact of the image boundary condition on reconstruction results is considered,and a method for estimating image boundaries is introduced.The results show that the proposed algorithm can effectively addresses boundary artifacts.By increasing the pixel number of the reconstructed images,the proposed algorithm is capable of recovering more details.Notably,in both simulation and real experiments,the proposed algorithm is demonstrated to achieve subpixel resolution,surpassing the Nyquist sampling limit determined by the camera pixel size.展开更多
Two types of ultra-high-temperature resistant water-based drilling fluid additives were designed and developed:an ultra-high-temperature resistant salt-tolerant polymer fluid loss reducer,and an ultra-high-temperature...Two types of ultra-high-temperature resistant water-based drilling fluid additives were designed and developed:an ultra-high-temperature resistant salt-tolerant polymer fluid loss reducer,and an ultra-high-temperature resistant micro-nano plugging agent.An ultra-high-temperature resistant water-based drilling fluid system meeting the requirements of ultra-deep well drilling was established.Laboratory test and field application were employed for performance evaluation.The ultra-high-temperature and high-salt resistant polymer fluid loss reducer exhibits a mesh-like membrane structure with numerous cross-linking points,and its high-temperature and high-pressure(HTHP)loss was 28.2 m L after aging at 220℃under saturated salt conditions.The ultra-high-temperature resistant micro-nano plugging agent adaptively filled mud cake pores/fractures through deformation,thus reducing the fluid loss.At elevated temperatures,it transitioned to a viscoelastic state to effectively cement the rock on wellbore wall and enhanced wall stability.The ultra-high-temperature resistant water-based drilling fluid system with a density of 1.6 g/cm^(3)exhibits excellent rheological properties at high temperature and high pressure.Its HTHP fluid loss at 220℃was only 9.6 m L.It maintains a stable performance under high-temperature and high-salt conditions,with a sedimentation factor below 0.52 after holding at high temperature for 7 d,and generates no H_(2)S gas after aging,demonstrating good lubricity and safety.This drilling fluid system has been successfully applied in the 10000-meter ultra-deep well of China,Shenditake 1,in Tarim Oilfield,ensuring the well's successful drilling to a depth of 10910 m.展开更多
Plugging agent treatment and acid stimulation have completely different mechanisms for improving injection profiles. In this paper, a hybrid procedure is introduced to reduce the damage of the plugging agent to low a...Plugging agent treatment and acid stimulation have completely different mechanisms for improving injection profiles. In this paper, a hybrid procedure is introduced to reduce the damage of the plugging agent to low and medium permeability zones and the penetration radius of acid into high permeability zones. The procedure is: First inject plugging agent to block high permeability zones, and then inject acid to remove plugging agent damage from the low and medium permeability zones and stimulate them. To perform this procedure successfully, three kinds of plugging agents, namely strong strength plugging agent for the wells with fractures or high permeability streaks, weak gel for those with thick layer in which serious heterogeneity exists, temporary plugging agent for those in which the absorption ability of high permeability zones needs maintaining, were screened out for use in different reservoirs. Several acid systems were evaluated to be compatible with the three kinds of plugging agents. The objectives of this paper are:(1)To show the screen results about the compatible plugging agent and acid; 2 To show how to optimize the operation process;(3)To tell some experience gained ( ) from the oilfield applications of this technique. From Jan. 2001 to Dec. 2002, 46 operations using this procedure were carried out in Weicheng and Mazhai Oilfields of SINOPEC. Results show that the average benefit/cost ratio is over 3.5. Experience acquired from these applications was summarized in the paper.展开更多
文摘A hybrid Stochastic Fractal Search plus Pattern Search （hSFS-PS） based cascade PI-PD controller is suggested in this paper for Automatic Generation Control （AGC） of thermal, hydro and gas power unit based power systems in presence of Plug in Electric Vehicles （PEV）. Firstly, a single area multi-source power system consisting of thermal hydro and gas power plants is considered and parameters of Integral （I） controller is optimized by Stochastic FractaI Search （SFS） algorithm. The superiority of SFS algorithm over some recently proposed approaches such as optimal control, differential evolution and teaching learning based optimization techniques is demonstrated by comparing simulation results for the identical power system. To improve the system performance further, Pattern Search （PS） is subsequently employed. The study is further extended for different controllers like PI, PID, and cascaded PI-PD controller and the superiority of cascade PI-PD controller over conventional controllers is demonstrated. Then, cascade PI- PD controller parameters of AGC searched using the proposed hSFS-PS algorithm in presence of plug in electric vehicles. The study is also extended to an interconnected power system. It is seen from the comparative analysis that hSFS-PS tuned PI-PD controller in single and multi-area with multi sources improves the system frequency stability in complicated situations. Lastly, a three area interconnected system with PEVs with dissimilar cascade PI-PD controller in each area is considered and proposed hSFS- PS algorithm is used to tune the controller parameters in presence of nonlinearities like rate constraint of units, dead zone of governor and communication delay.
基金Project(2013CB036004)supported by the National Basic Research Program of ChinaProject(51378510)supported by the National Natural Science Foundation of ChinaProject(CX2014B069)supported by Hunan Provincial Innovation Foundation for Postgraduate,China
文摘High pressure and water-bearing caverns ahead of a karst tunnel face tend to cause geological disasters, such as water and mud bursts. So, the determination of safe thickness of the reserved rock plug is a key technical problem to be solved for karst tunnel construction. Based on the Hoek-Brown nonlinear failure criterion, the minimum safe thickness of rock plug was investigated in the light of the limit analysis theory. On the basis of the proposed failure mode, the expression of the minimum thickness for rock plug was obtained by means of upper bound theorem in combination with variational principle. The calculation results show the influence of each parameter on safe thickness and reveal the damage range of rock plug. The proposed method is verified by comparing the results with those of the drain cavern of Maluqing Tunnel. The research shows that with the increase of compressive strength and tensile strength as well as constant A of Hoek-Brown criterion, the safe thickness decreases, whereas with the increase of cavern pressure, tunnel diameter, and constant B from Hoek-Brown criterion, the safe thickness increases. Besides, the tensile strength, or constants A and B affect the shear failure angle of rock plug structure, but other parameters do not. In conclusion, the proposed method can predict the minimum safe thickness of rock plug, and is useful for water burst study and prevention measures of tunnels constructed in high-risk karst regions.
基金SUPPORTED BY NATIONAL NATURAL SCIENCE FOUNDATION OF CHINA ( NO. 50079016).
文摘The phenomenon of the soil plug usually rising inside the suction foundations during suction penetration was quantitatively described and predicted. The formation process of the soil plug was simulated and calculated by DEM （discrete element method） model. The seepage flow, the self-weight of soil, the friction on the chamber wall as well as the suction inside the chamber are considered as the main external forces in the process. The results are compared with a set of laboratory model tests performed by using three soil types （sand, silty clay and clay） in the Bohai Sea area. The heights of soil plug from numerical estimations are lower than those from model test results, mainly because the suction pressure and friction resistance are applied in an ideal way under the numerical simulation.
基金Supported by National Natural Science Foundation of China(50079016) .
文摘The soil plug phenomenon involving the rising of the surface soil inside the bucket chamber under the suction pressure and seepage forces was simulated and calculated by deformable discrete element method (DDEM) models. The seepage forces, the effective gravity of soil, the friction on the chamber wall and the suction inside the chamber are considered as the main external forces of DDEM specimen. Three typical types of soil (silty clay, silt and sand) in the Bohai Sea are set as the main environmental conditions in the formation process of soil plug. It is found that the heights of soil plug simulated by DDEM models are 161.85 mm in silty clay, 125.22 mm in silt and 167.56 mm in sand, which are close to model test results and higher than those estimated by discrete element method (DEM). DDEM is an effective method to estimate and predict the heights of soil plug before suction penetration of bucket foundations on site.
文摘Background: Dry eye syndrome, which affects 10% to 20% of adults, is a disorder of the tear film and is associated with symptoms of ocular discomfort. Smart Plug is a mechanical treatment in which the tear drainage system is blocked in order to aid in the preservation of natural tears on the ocular surface. Purpose: To evaluate the long-term clinical efficacy of Smart Plug in the treatment of aqueous tear deficiency dry eye. Patients and Methods: Retrospective study. Three hundred and two patients with aqueous tear deficiency dry eye were enrolled and all the patients accepted the punctual plug of Smart plug from Jan. 2011 to Jan. 2016. The clinical symptoms, Schirmer’s I test, Fluorescein staining (FL), tear break up time (TBUT), and complications were observed and analyzed. Results: Three hundred and two patients (604 eyes) were treated with Smart Plug (22 cases accepted upper and lower punctual plug, 280 cases only lower punctual plug). There were 109 males (36.1%) and 193 females (63.9%) with a mean age of 44.54 years old (Range from 25 to 83 years). Ten cases required the upper Smart Plug after lower punctual plug insertion because of no significantly improved symptoms. Smart plug was removed in 3 patients (1%) due to tearing. Six patients had mild postoperative tearing and no special treatment was required. Lacrimal canaliculitis occurred postoperatively in 8 cases (2.6%) (6 lower and 2 upper), and the affected plug was removed and treated with topical antibiotic eye drops. The BUT, SIT and FL scores of all patients were significantly improved from (2.11 ± 1.01, 4.20 ± 1.07, 6.06 ± 1.97) to (4.34 ± 1.22, 9.01 ± 1.56, 2.33 ± 1.28) respectively after at least 36 months of follow-up (All P P Conclusion: During a mean follow-up of 4.3 years, Smart plug is an effective method for the treatment of aqueous tear deficiency dry eye in spite of its postoperative complications such as canaliculitis and tearing.
文摘Objective: this study is mainly to analyze the effect of pregnancy and oxytocin in the treatment of postpartum bleeding diseases. Methods: the study object, number and group division method are: in our cure postpartum bleeding patients, 78 cases and random method, and as the name of the reference group, as another group, 39 cases of study group in the treatment of the accepted scheme for oxytocin, 39 cases of reference group in treatment received oxytocin, after the following indicators of two groups recorded analysis, respectively for quality of life, postpartum bleeding, clinical efficacy and shrinkage intensity, incidence of adverse reactions, etc. Results: in the clinical efficacy evaluation, the research group with total response rate was 94.87%, higher than the reference group with a total response rate of 71.79% (P <0.05);In the comparison of the improvement of quality of life in the study group and the reference group, it showed that the above indicators improved after the treatment. However, the obvious improvement was the research group (P <0.05);In the comparison of adverse reactions: the study group with total incidence of 5.13% was lower compared with the reference group with total incidence of 20.51% (P <0.05);The evaluation of the contractions intensity between the groups showed that the contractions were not improved significantly in the study group (P <0.05);In the statistics of the treatment satisfaction of the study group and the reference group, it is known that in the study group where the total satisfaction score was (95.65 ± 1.75) points was higher than the total satisfaction score was (76.54 ± 0.65) points (P <0.05);In the comparison of postpartum bleeding in the second group, the study group improved better after receiving treatment (P <0.05). Conclusion: the treatment of pregnancy plug and oxytonin is more effective in the treatment of postpartum bleeding patients, and can reduce the probability of adverse reactions, improve the situation of postpartum bleeding and weak contractions, and significantly improve the treatment satisfaction and quality of life.
基金support from the National Natural Science Foundation of China(Grant No.52274009).
文摘During drilling operations in deep fractured tight gas reservoirs,lost circulation of working fluid frequently occurs due to the formationʼs low pressure-bearing capacity.Adding lost circulation materials(LCMs)to drilling fluids is the most common method for controlling lost circulation.Among these,granular LCMs are widely used,but the application frequency of flaky LCMs has been increasing annually due to their unique morphology.However,the migration and plugging behavior of flaky LCMs within fractures,and the mechanisms enhancing the pressure-bearing capacity of the plugging zone are not well understood.Therefore,this study conducted visual plugging experiments and dynamic fracture plugging experiments to evaluate the plugging mode and pressure-bearing capacity of the plugging slurry with various particle sizes and concentrations of flaky LCMs.The experimental results demonstrate that the fracture plugging process can be divided into four stages:uniform flow stage of the plugging slurry,formation and development stage of the bridging area,formation and development stage of the plugging area,and pressure-bearing stage of the plugging zone.The inclusion of flaky LCMs notably reduces the duration of stages 1 and 2,while simultaneously increasing the proportion of the plugging zone and enhancing its surface porosity.Flaky LCMs reduce the effective fracture width through“interception”and“co-bridging”modes,thus improving plugging zone formation efficiency.Appropriate particle size and concentration of flaky LCMs increase the area and length of the plugging zone.This reduces the fracture width increment caused by injection pressure and enhances frictional force between the plugging zone and fracture surface,thereby improving the pressure-bearing capacity of the plugging zone.However,excessively high concentrations of flaky LCMs result in decreased structural stability of the plugging zone,and excessively large particle sizes increase the risk of plugging outside fracture inlet.The recommended concentration of flaky LCMs in the plugging slurry is 2%–3%,with a particle size 1.2 to 1.5 times that of the bridging granular LCMs and not exceeding twice the fracture width.This study provides a theoretical foundation for selecting LCMs and designing plugging formulations for field applications.
基金financially supported by the National Science and Technology Major Project(2019YFB1900904)the National Natural Science Foundation of China(52271060 and 51771107)Independent Research and Development Project of State Key Laboratory of Advanced Special Steel(SKLASS)Shanghai University(2022-Z00)
文摘The stress corrosion cracking(SCC)performance of the sealed Alloy 690 plugs was investigated in 350℃deoxygenated concentrated alkaline solution.Sealing was used to expose only the inner surface of the plug,preventing direct contact between the tube sheet and the concentrated alkaline solution.After exposure for 1000 h,several intergranular cracks were observed on the inner wall of the plugs.Stress corrosion cracks primarily appear in some regions on the inner wall,which are highly deformed and advanced along the random grain boundary.The internal oxide layer formed in the high-temperature alkaline solution was not dense;it comprised a composite oxide with multiple layers.The outermost layer consisted of Fe-Cr-Ni oxide particles,and beneath it was an uneven Ni-rich layer,followed by a thin Cr-rich layer closest to the matrix.High kernel average misorientation in the heavily deformed region and a lack of chromium carbide contributed to crack initiation and propagation of Alloy 690 plug in hot concentrated alkaline solutions.
基金supported by the National Natural Science Foundation of China Joint Fund for Enterprise Innovation and Development,Enrichment Mechanism and Stereoscopic Development of Shale Oil in Continental Rift Basins(No.U24B6002).
文摘Temporary plugging and diversion fracturing(TPDF)is widely used to promote the uniform and complex distribution of multi-clustered hydraulic fractures(HFs)in a horizontal well of the unconventional formations.However,the migration behavior of temporary plugging agent(TPA),as a function of the concentration and particle size of TPA and cluster-perforation numbers,etc.,determining the effectiveness of this technique,remains unclear.Therefore,this study conducted innovatively a series of TPDF simulation experiments on transparent polymethyl methacrylate(PMMA)specimens(cubic block of 30 cm×30 cm×30 cm)to explore visually the migration behavior of TPA in multi-clustered HFs in a horizontal well.A laboratory hydraulic sandblasting perforation completion technique was implemented to simulate the multi-cluster perforations.All the distributions of wellbore,perforations,HFs,and TPA can be seen clearly inside the PMMA specimen post the experiment.The results show that there are four characteristic plugging positions for the TPA:mouth of HF,middle of HF,tip of HF,and the intersection of HFs.Small particle size TPA tends to migrate to the fracture tip for plugging,while large particle size TPA tends to plug at the fracture mouth.The migration of the TPA is influenced obviously by the morphology of the fracture wall.A smooth fracture wall is conducive to the migration of the TPA to the far end of HFs,but not conducive to generating the plugging zone and HF diversion.In contrast,a"leaf vein"fracture of rough wall is conducive to generating the plugging layer and the diversion of HFs,but not conducive to the migration of the TPA to the far end of HFs.The migration ability of TPA in a"shell"pattern is intermediate between the two above cases.Increasing TPA concentration can encourage TPA to migrate more quickly to the characteristic plugging position,and thereby to promote the creation of effective plugging and subsequently the multi-stage diversion of the HFs.Nevertheless,excessive concentration may cause the TPA to settle prematurely,affecting the propagation of the HFs to the far end.Increasing the number of clusters to a certain extent can encourage TPA to migrate into the HFs and form plugging,and promote the diversion.An evaluation system for the migration ability of granular TPA has been established,and it was calculated that when there is no plugging expectation target,the comprehensive migration ability of small particle size TPA is stronger than that of large particle size TPA.This research provides theoretical foundation for the optimization of temporary plugging parameters.
文摘This study investigates the load-bearing capacity of open-ended pipe piles in sandy soil, with a specific focus on the impact of soil plug constraints at four levels(no plug, 25% plug, 50% plug, and full plug). Leveraging a dataset comprising open-ended pipe piles with varying geometrical and geotechnical properties, this research employs shallow neural network(SNN) and deep neural network(DNN) models to predict plugging conditions for both driven and pressed installation types. This paper underscores the importance of key parameters such as the settlement value,applied load, installation type, and soil configuration(loose, medium, and dense) in accurately predicting pile settlement. These findings offer valuable insights for optimizing pile design and construction in geotechnical engineering,addressing a longstanding challenge in the field. The study demonstrates the potential of the SNN and DNN models in precisely identifying plugging conditions before pile driving, with the SNN achieving R2 values ranging from0.444 to 0.711 and RMSPE values ranging from 24.621% to 48.663%, whereas the DNN exhibits superior performance, with R2 values ranging from 0.815 to 0.942 and RMSPE values ranging from 4.419% to 10.325%. These results have significant implications for enhancing construction practices and reducing uncertainties associated with pile foundation projects in addition to leveraging artificial intelligence tools to avoid long experimental procedures.
基金supported by Major Technology Promotion Project of CNPC,China(No.2022ZT01)Major Field Test Project of CNPC,China(No.2019F-31-04)CNPC Chuanqing Drilling Engineering Company Science and Technology Special Project,China(No.CQ2024B-11-Z2-4).
文摘Milling bridge plugs in shale gas wells with severe casing deformation often leads to the accumulation of cuttings,increasing the risk of stuck drill bits.Friction in the wellbore further complicates tool deployment into the horizontal section,posing challenges to efficient plug drilling and achieving wellbore access to the target layer.This paper integrates the theory of positive displacement motors and models their actual working characteristics to study the milling of bridge plugs in severely deformed horizontal wells.It examines the effects of coiled tubing diameter and wall thickness on the bending load of horizontal sections and discusses key technical requirements,including the timing of plug drilling,extending the run in the horizontal section,parameter control,and real-time field analysis.Field practices have shown that after casing deformation occurs,priority should be given to drilling out the bridge plugs below the point of deformation.The primary factors contributing to stuck drills in deformed wells include smaller mill shoe sizes and larger cuttings sizes.Short well-washing cycles and targeted cuttings removal can effectively reduce sticking risks.If sticking occurs,high-tonnage pulling should be avoided.Instead,releasing the stick through up-anddown string motion,combined with high-volume nozzle spraying and annulus pumping,is recommended.The selection of coiled tubing should consider diameter,wall thickness,and steel grade to handle complex situations.Larger diameters,thicker walls,and low-frequency,multi-head hydraulic oscillators are more effective for unlocking horizontal sections.This approach can reduce the risk of drill sticking and solve the problem of horizontal section lock-ups,offering a reliable solution for smooth drilling and efficient production in wells with severe casing deformation.
基金supported by the National Natural Science Foundation of China(U23B20156,52174033).
文摘Resin plugging agents play a pivotal role in addressing casing damage in oil and gas fields.However,the widespread use of epoxy resin is constrained by its high cost and non-renewable origin,while plant-based resins often suffer from inadequate mechanical properties,which limit their effectiveness in such applications.This study introduces BEOPA,an innovative,renewable,high-strength resin plugging agent derived from epoxidized soybean oil(ESO)and enhanced with bisphenol A-type benzoxazine(BZ).In this study,the synthesis process,reactionmechanism,and application performance of this novelmaterial are systematically presented,explored and optimized.It is shown that the optimal formulation of BEOPA includes 41.4 wt%ESO,24.8 wt%BZ,24.8 wt%methylhexahydrophthalic anhydride(MHHPA),8.2 wt%styrene(ST),and 0.8 wt%N,N-dimethylbenzylamine(BDMA),yielding an impressive compressive strength of 93.7 MPa.The integration of ESO and BZ creates an intricate and robust double crosslinking network,significantly enhancing material strength and durability.BEOPA exhibits a tunable curing time,ranging from 0.5 to 15 h,with viscosities below 300 mPa⋅s at 25℃and 75mPa⋅s at 50℃.Furthermore,it demonstrates exceptional thermal stability within the 100℃-150℃range,even in environments with mineral salt concentrations as high as 43,330 mg/L.Remarkably,BEOPA achieves superior plugging performance,sustaining breakthrough pressures exceeding 29.7 MPa in 1 mm crack cores.
基金financially supported by National Natural Science Foundation of China(No.52422402)。
文摘Lost circulation critically jeopardizes drilling safety and efficiency,and remains an unresolved challenge in oil and gas engineering.In this paper,by utilizing the self-developed dynamic plugging apparatus and synthetic cores containing large-scale fractures,experimental research on the circulation plugging of different materials was conducted.Based on the D90 rule and fracture mechanical aperture model,we analyze the location of plugging layer under dynamic plugging mechanism.By setting different parameters of fracture width and injection pressure,the laws of cyclic plugging time,pressure bearing capacity and plugging layers formation were investigated.The results show that the comprehensive analysis of particle size and fracture aperture provides an accurate judgment of the entrance-plugging phenomenon.The bridging of solid materials in the leakage channel is a gradual process,and the formation of a stable plug requires 2–3 plug-leakage cycles.The first and second cyclic plugging time was positively correlated with the fracture width.Different scales of fractures were successfully plugged with the bearing pressure greater than 6 MPa,but there were significant differences in the composition of the plugging layer.The experimental results can effectively prove that the utilized plugging agent is effective and provides an effective reference for dynamic plugging operation.
基金funded by the National Natural Science Foundation of China(52104046).
文摘Multi-stage and multi-cluster fracturing(MMF)is a crucial technology in unconventional oil and gas development,aiming to enhance production by creating extensive fracture networks.However,achieving uniform expansion of multi-cluster hydraulic fractures(HFs)in MMF remains a significant challenge.Field practice has shown that the use of temporary plugging and diversion fracturing(TPDF)can promote the balanced expansion of multi-cluster HFs.This study conducted TPDF experiments using a true triaxial fracturing simulation system setting a horizontal well completion with multi-cluster jetting perforations to investigate the equilibrium initiation and extension of multi-cluster fractures.The influence of key parameters,including cluster spacing,fracturing fluid viscosity,differential stress,and fracturing fluid injection rate,on fracture initiation and propagation was systematically examined.The results indicate that while close-spaced multi-cluster fracturing significantly increases the number of HFs,it also leads to uneven extension of HFs in their propagation.In contrast,TPDF demonstrates effectiveness in mitigating uneven HF extension,increasing the number of HFs,and creating a larger stimulated reservoir volume,ultimately leading to improved oil and gas well productivity.Moreover,under conditions of high differential stress,the differential stress within the formation exerts a stronger guiding effect in HFs,which are more closely aligned with the minimum principal stress.Low-viscosity fluids facilitate rapid and extensive fracture propagation within the rock formation.High-volume fluid injection,on the other hand,more comprehensively fills the formation.Therefore,employing lowviscosity and high-volume fracturing is advantageous for the initiation and extension of multi-cluster HFs.
基金supported by the National Natural Science Foundation of China(Grant No.12175183)。
文摘Gamma-ray imaging systems are powerful tools in radiographic diagnosis.However,the recorded images suffer from degradations such as noise,blurring,and downsampling,consequently failing to meet high-precision diagnostic requirements.In this paper,we propose a novel single-image super-resolution algorithm to enhance the spatial resolution of gamma-ray imaging systems.A mathematical model of the gamma-ray imaging system is established based on maximum a posteriori estimation.Within the plug-and-play framework,the half-quadratic splitting method is employed to decouple the data fidelit term and the regularization term.An image denoiser using convolutional neural networks is adopted as an implicit image prior,referred to as a deep denoiser prior,eliminating the need to explicitly design a regularization term.Furthermore,the impact of the image boundary condition on reconstruction results is considered,and a method for estimating image boundaries is introduced.The results show that the proposed algorithm can effectively addresses boundary artifacts.By increasing the pixel number of the reconstructed images,the proposed algorithm is capable of recovering more details.Notably,in both simulation and real experiments,the proposed algorithm is demonstrated to achieve subpixel resolution,surpassing the Nyquist sampling limit determined by the camera pixel size.
基金Supported by the CNPC Science and Technology Project(2022ZG06)Xinjiang Uygur Autonomous Region Science and Technology Innovation Talent Project(2024TSYCCX0061)。
文摘Two types of ultra-high-temperature resistant water-based drilling fluid additives were designed and developed:an ultra-high-temperature resistant salt-tolerant polymer fluid loss reducer,and an ultra-high-temperature resistant micro-nano plugging agent.An ultra-high-temperature resistant water-based drilling fluid system meeting the requirements of ultra-deep well drilling was established.Laboratory test and field application were employed for performance evaluation.The ultra-high-temperature and high-salt resistant polymer fluid loss reducer exhibits a mesh-like membrane structure with numerous cross-linking points,and its high-temperature and high-pressure(HTHP)loss was 28.2 m L after aging at 220℃under saturated salt conditions.The ultra-high-temperature resistant micro-nano plugging agent adaptively filled mud cake pores/fractures through deformation,thus reducing the fluid loss.At elevated temperatures,it transitioned to a viscoelastic state to effectively cement the rock on wellbore wall and enhanced wall stability.The ultra-high-temperature resistant water-based drilling fluid system with a density of 1.6 g/cm^(3)exhibits excellent rheological properties at high temperature and high pressure.Its HTHP fluid loss at 220℃was only 9.6 m L.It maintains a stable performance under high-temperature and high-salt conditions,with a sedimentation factor below 0.52 after holding at high temperature for 7 d,and generates no H_(2)S gas after aging,demonstrating good lubricity and safety.This drilling fluid system has been successfully applied in the 10000-meter ultra-deep well of China,Shenditake 1,in Tarim Oilfield,ensuring the well's successful drilling to a depth of 10910 m.
文摘Plugging agent treatment and acid stimulation have completely different mechanisms for improving injection profiles. In this paper, a hybrid procedure is introduced to reduce the damage of the plugging agent to low and medium permeability zones and the penetration radius of acid into high permeability zones. The procedure is: First inject plugging agent to block high permeability zones, and then inject acid to remove plugging agent damage from the low and medium permeability zones and stimulate them. To perform this procedure successfully, three kinds of plugging agents, namely strong strength plugging agent for the wells with fractures or high permeability streaks, weak gel for those with thick layer in which serious heterogeneity exists, temporary plugging agent for those in which the absorption ability of high permeability zones needs maintaining, were screened out for use in different reservoirs. Several acid systems were evaluated to be compatible with the three kinds of plugging agents. The objectives of this paper are:(1)To show the screen results about the compatible plugging agent and acid; 2 To show how to optimize the operation process;(3)To tell some experience gained ( ) from the oilfield applications of this technique. From Jan. 2001 to Dec. 2002, 46 operations using this procedure were carried out in Weicheng and Mazhai Oilfields of SINOPEC. Results show that the average benefit/cost ratio is over 3.5. Experience acquired from these applications was summarized in the paper.
