The flow behaviors of gas and water in hydrate-bearing sediments(HBS)are significantly affected by the threshold pressure gradient(TPG).During long-term natural gas hydrates(NGHs)mining,there exists creep deformation ...The flow behaviors of gas and water in hydrate-bearing sediments(HBS)are significantly affected by the threshold pressure gradient(TPG).During long-term natural gas hydrates(NGHs)mining,there exists creep deformation in HBS,which significantly alters pore structures,makes the flow path of fluid more complex,and leads to changes in TPG.Thus,clarifying the evolution of TPG in HBS during creep is essential for NGH production,but it also confronts enormous challenges.In this study,based on the nonlinear creep constitutive model,a novel theoretical TPG model of HBS during creep is proposed that considers pore structures and hydrate pore morphology.The established model is validated against experimental data,demonstrating its ability to capture the evolution of TPG and permeability in HBS during creep.Additionally,the relationship between initial hydrate saturation and TPG of HBS during creep is revealed by sensitivity analysis.The creep strain increases with the decrease in initial hydrate saturation,leading to a greater TPG and a lower permeability.The evolution of TPG at the stable creep stage and the accelerated creep stage is primarily controlled by the Kelvin element and visco-plastic element,respectively.This novel proposed model provides a mechanistic understanding of TPG evolution in HBS during creep,and it is of great significance to optimize the exploitation of NGHs.展开更多
Spontaneous imbibition(SI)is an important mechanism for enhancing oil recovery in low-permeability reservoirs.Due to the strong heterogeneity,and the non-Darcy flow,the construction of SI model for lowpermeability res...Spontaneous imbibition(SI)is an important mechanism for enhancing oil recovery in low-permeability reservoirs.Due to the strong heterogeneity,and the non-Darcy flow,the construction of SI model for lowpermeability reservoirs is extremely challenging.Commonly,traditional SI models based on single or averaged capillary tortuosity ignore the influence of heterogeneity of pore seepage channels and the threshold pressure(TP)on imbibition.Therefore,in this work,based on capillary model and fractal theory,a mathematical model of characterizing SI considering heterogeneity of pore seepage channels is established.On this basis,the threshold pressure was introduced to determine the pore radius at which the wetted phase can displace oil.The proposed new SI model was verified by imbibition experimental data.The study shows that for weakly heterogeneous cores with permeability of 0-1 m D,the traditional SI model can characterize the imbibition process relatively accurately,and the new imbibition model can increase the coefficient of determination by 1.05 times.However,traditional model has serious deviations in predicting the imbibition recovery for cores with permeability of 10-50 m D.The new SI model coupling with heterogeneity of pore seepage channels and threshold pressure effectively solves this problem,and the determination coefficient is increased from 0.344 to 0.922,which is increased by2.68 times.For low-permeability reservoirs,the production of the oil in transitional pores(0.01-0.1μm)and mesopores(0.1-1μm)significantly affects the imbibition recovery,as the research shows that when the heterogeneity of pore seepage channels is ignored,the oil recovery in transitional pores and mesopores decreases by 7.54%and 4.26%,respectively.Sensitivity analysis shows that increasing interfacial tension,decreasing contact angle,oil-water viscosity ratio and threshold pressure will increase imbibition recovery.In addition,there are critical values for the influence of these factors on the imbibition recovery,which provides theoretical support for surfactant optimization.展开更多
Field evidence indicates that proppant distribution and threshold pressure gradient have great impacts on well productivity.Aiming at the development of unconventional oil reservoirs in Triassic Chang-7 Unit,Ordos Bas...Field evidence indicates that proppant distribution and threshold pressure gradient have great impacts on well productivity.Aiming at the development of unconventional oil reservoirs in Triassic Chang-7 Unit,Ordos Basin of China,we presented an integrated workflow to investigate how(1)proppant placement in induced fracture and(2)non-linear flow in reservoir matrix would affect well productivity and fluid flow in the reservoir.Compared with our research before(Yue et al.,2020),here we extended this study into the development of multi-stage fractured horizontal wells(MFHWs)with large-scale complicated fracture geometry.The integrated workflow is based on the finite element method and consists of simulation models for proppant-laden fluid flow,fracture flow,and non-linear seepage flow,respectively.Simulation results indicate that the distribution of proppant inside the induced cracks significantly affects the productivity of the MFHW.When we assign an idealized proppant distribution instead of the real distribution,there will be an overestimation of 44.98%in daily oil rate and 30.63%in cumulative oil production after continuous development of 1000 days.Besides,threshold pressure gradient(TPG)also significantly affects the well performance in tight oil reservoirs.If we simply apply linear Darcy’s law to the reservoir matrix,the overall cumulative oil production can be overrated by 77%after 1000 days of development.In general,this research provides new insights into the development of tight oil reservoirs with TPG and meanwhile reveals the significance of proppant distribution and non-linear fluid flow in the production scenario design.展开更多
A dynamic measuring apparatus was developed to investigate the infiltration process of liquid metal into the fibrous preform. 10% （volume fraction） chopped carbon fiber preforms were infiltrated with magnesium alloy...A dynamic measuring apparatus was developed to investigate the infiltration process of liquid metal into the fibrous preform. 10% （volume fraction） chopped carbon fiber preforms were infiltrated with magnesium alloy under different infiltration pressures. The threshold pressure and flow behavior of liquid metal infiltrating into the preforms were calculated and measured. The microstructure of obtained Ct4Mg composites was observed. The results indicate that the measured threshold pressure for infiltration was 0.048 MPa, which was larger than the calculated value. The infiltration rate increased with the increase of infiltration pressure, but the increase amplitude decreased gradually. The tiny pores in the composites could be eliminated by increasing the infiltration pressure. When the infiltration pressure rose to 0.6 MPa, high quality C1/Mg composite was obtained.展开更多
BACKGROUND Low back pain(LBP)is a common condition with large burden worldwide.Exposure to prolonged sitting with a flexed lumbar posture has been suggested in the literature to be a potential risk factor for self-rep...BACKGROUND Low back pain(LBP)is a common condition with large burden worldwide.Exposure to prolonged sitting with a flexed lumbar posture has been suggested in the literature to be a potential risk factor for self-reported LBP.No study has previously investigated whether exposure to prolonged flexed sitting posture provokes discomfort/pain and decreased interspinous pressure pain thresholds for healthy young men and women without back pain,despite this being a suggested risk factor for LBP.AIM To investigate whether sitting in a prolonged flexed lumbar posture provokes discomfort and lowers interspinous pressure pain thresholds in the lumbar spine for healthy young men and women without previous LBP.METHODS This is a an observational before and after study of 26 participants(13 men,13 women)between 20-35 years old.Algometry was used to examine the pain threshold for pressure applied between spinous processes of the lumbar spine L1-L5.Pressure algometer measures were performed in prone before and after participants were instructed to sit in a fully flexed posture for a maximum of 15 min or until discomfort was experienced in the low back(Borg CR10=7/10).Wilcoxon signed-rank test was used for analyze values from the before and after test conditions.Mann-Whitney U test was used to investigate potential gender difference.RESULTS Fully flexed lumbar spine sitting posture up to 15 min provoked temporary discomfort but the proportion of participants experiencing discomfort 7/10 in the low back was 62%.For all pain pressure threshold locations tested,there was a significant difference for the study population with moderate-large decreased(r=-0.56)pressure pain threshold after exposure to prolonged flexed sitting posture(P<0.01).Comparisons between gender did not show any significant difference.CONCLUSION The result showed that exposure to fully flexed lumbar sitting posture for up to 15 min produced temporary discomfort in the low back in young healthy adults with no previous history of LBP and significantly reduced lumbar interspinous pressure pain thresholds.No gender-based differences were observed.展开更多
The threshold pressure gradient and formation stress-sensitive effect as the two prominent physical phenomena in the development of a low-permeable reservoir are both considered here for building a new coupled moving ...The threshold pressure gradient and formation stress-sensitive effect as the two prominent physical phenomena in the development of a low-permeable reservoir are both considered here for building a new coupled moving boundary model of radial flow in porous medium. Moreover, the wellbore storage and skin effect are both incorporated into the inner boundary conditions in the model. It is known that the new coupled moving boundary model has strong nonlinearity. A coordinate transformation based fully implicit finite difference method is adopted to obtain its numerical solutions. The involved coordinate transformation can equivalently transform the dynamic flow region for the moving boundary model into a fixed region as a unit circle, which is very convenient for the model computation by the finite difference method on fixed spatial grids. By comparing the numerical solution obtained from other different numerical method in the existing literature, its validity can be verified. Eventually, the effects of permeability modulus, threshold pressure gradient, wellbore storage coefficient, and skin factor on the transient wellbore pressure, the derivative, and the formation pressure distribution are analyzed respectively.展开更多
The flow behavior in porous media with threshold pressure gradient(TPG) is more complex than Darcy flow and the equations of motion, and outer boundary and inner boundary with TPG are also different from Darcy flow fo...The flow behavior in porous media with threshold pressure gradient(TPG) is more complex than Darcy flow and the equations of motion, and outer boundary and inner boundary with TPG are also different from Darcy flow for unsteady flow of a producing well in a reservoir. An analytic method to solve this kind of problem is in a need of reestablishment. The classical method of Green's function and Newman product principle in a new way are used to solve the unsteady state flow problems of various shapes of well and reservoir while considering the TPG. Four Green's functions of point, line, band and circle while considering the TPG are achieved. Then, two well models of vertical well and horizontal well are built and simultaneously the function to calculate the moving boundary of each well model is provided. The results show that when considering TPG the pressure field is much different, which has a sudden pressure change, with a moving boundary in it. And the moving boundary of each well model increases with time but slows down rapidly, especially when the TGP is large.展开更多
This paper studies the transient pressure of percolation during one production and one shutting in one dimension porous media with threshold pressure gradient, the differential equations are derived and solved with nu...This paper studies the transient pressure of percolation during one production and one shutting in one dimension porous media with threshold pressure gradient, the differential equations are derived and solved with numerical computation. Basing on numerical solution, it is analyzed that: 1. the relation between the steady pressure at well bore (or at endpoint) and threshold pressure gradient, shut-in time, and the corresponding formulae are derived; 2, the regulation of transient pressure peak. The result is very useful and will help experiments and applications in the development of low permeability reservoirs with threshold pressure gradient.展开更多
The flowing mechanism of a low permeability gas reservoir is different from a conventional gas reservoir,especially for that with higher irreducible water saturation the threshold pressure gradient exists. At present,...The flowing mechanism of a low permeability gas reservoir is different from a conventional gas reservoir,especially for that with higher irreducible water saturation the threshold pressure gradient exists. At present,in all the deliverability equation,the additional pressure drop caused by the threshold pressure gradient is viewed as constant,but this method has big error in the practical application. Based on the non-Darcy steady flow equation,the limited integral of the additional pressure drop is solved in this paper and it is realized that the additional pressure drop is not a constant but has something to do with production data,and a new deliverability equation is derived,with the relevant processing method for modified isochronal test data. The new deliverability equation turns out to be practical through onsite application.展开更多
A new method for determining two key parameters(threshold pressure and permeability)for fabricating metal matrix composites was proposed based on the equation-solving method.An infiltration experimental device was dev...A new method for determining two key parameters(threshold pressure and permeability)for fabricating metal matrix composites was proposed based on the equation-solving method.An infiltration experimental device was devised to measure the infiltration behavior precisely with controllable infiltration velocity.Two experiments with alloy Pb-Sn infiltrating into Al2O3 preform were conducted independently under two different pressures so as to get two different infiltration curves.Two sets of coefficients which are functions of threshold pressure and permeability can be obtained through curve fitting method.By solving the two-variable equation set,two unknown variables were determined.It is shown that the determined threshold pressure and permeability are very close to the calculated ones and are also verified by another independent infiltration experiment.The proposed method is also feasible to determine the key infiltration parameters for other metal matrix composite systems.展开更多
Based on the statistical data of 26 outburst prone coal seams in China, this paper presents the relationship among the threshold gas pressure in coal and gas outburst and the volatile content and hardness of coal by m...Based on the statistical data of 26 outburst prone coal seams in China, this paper presents the relationship among the threshold gas pressure in coal and gas outburst and the volatile content and hardness of coal by mathematical statistics. The threshold value of gas pressure for outburst pmin in MPa may be calculated by formula Pmin =5(0. 1+0. 07Kf), where / is the hardness and V the volatile content (%) of a soft bed. In China, the value of Pmin of some outburst prone coal seams ranges from 0. 57 to 0. 1 MPa.展开更多
The aim is to evaluate the influence of oral contraceptive intake and menstrual cycle on the electrical activity and pressure pain threshold from anterior temporal and masseter muscles. Twenty-eight women on reproduct...The aim is to evaluate the influence of oral contraceptive intake and menstrual cycle on the electrical activity and pressure pain threshold from anterior temporal and masseter muscles. Twenty-eight women on reproductive age were selected, 13 OC users and 15 nonusers. They were weekly submitted to electromyography and algometry of the anterior temporal and masseter muscles during three consecutive menstrual cycles. Electrical activities at rest position and PPTs of temporal and masseter muscles were not affected by menstrual cycle or by OCs uses. Comparison between groups demonstrated that working side electrical activity was increased in OC users in both muscles, except during lutheal phase for the anterior temporal. However, comparison within weeks did not demonstrate statistical difference. It was suggested that, in healthy women, oral contraceptive use may influence electrical activity, but different phases of the cycle may not.展开更多
Threshold pressure gradient has great importance in efficient tight gas field development as well as for research and laboratory experiments.This experimental study is carried out to investigate the threshold pressure...Threshold pressure gradient has great importance in efficient tight gas field development as well as for research and laboratory experiments.This experimental study is carried out to investigate the threshold pressure gradient in detail.Experiments are carried out with and without back pressure so that the effect of pore pressure on threshold pressure gradient may be observed.The trend of increasing or decreasing the threshold pressure gradient is totally opposite in the cases of considering and not considering the pore pressure.The results demonstrate that the pore pressure of tight gas reservoirs has great influence on threshold pressure gradient.The effects of other parameters like permeability and water saturation,in the presence of pore pressure,on threshold pressure gradient are also examined which show that the threshold pressure gradient increases with either a decrease in permeability or an increase in water saturation.Two new correlations of threshold pressure gradient on the basis of pore pressure and permeability,and pore pressure and water saturation,are also introduced.Based on these equations,new models for tight gas production are proposed.The gas slip correction factor is also considered during derivation of this proposed tight gas production models.Inflow performance relationship curves based on these proposed models show that production rates and absolute open flow potential are always be overestimated while ignoring the threshold pressure gradients.展开更多
Purpose: Memory has been identified as an important protective feature to prevent future injury, but its role has yet to be ascertained. The current study aimed to determine whether there was a difference in pressure ...Purpose: Memory has been identified as an important protective feature to prevent future injury, but its role has yet to be ascertained. The current study aimed to determine whether there was a difference in pressure pain threshold (PPT) responses between participants with a prior history of injury of lower extremity injury (PSI) and those without (NPSI) when exposed to 1) experimental mechanical pain, 2) short-term memory recall of a painful stimulus, or 3) long-term memory of the pain associated with a prior injury. Subjects and Methods: The study used a pretest-posttest quasi-experimental design. A convenience sample of 59 pain-free participants was recruited from an urban university. Twenty-nine PSI and 30 NPSI were stratified into two groups based on their injury history with PPT values measured at baseline and immediately following each of the three experimental conditions. A repeated measure ANCOVA analysis was conducted for each condition to determine whether there was a difference in PPT responses between the two groups. Results: There was a statistically significant difference in PPT values between the two groups when exposed to experimental pain, F(1,57) = 6.010, p = 0.017, partial η<sup>2</sup> = 0.095 and with long-term pain memory, F(1,57) = 4.886, p = 0.031, partial η<sup>2</sup> = 0.079. There was no statistically significant difference between groups with short-term pain memory, F(1,57) = 3.925, p = 0.052, partial η<sup>2</sup> = 0.064. Conclusions: These findings suggest that pain processing may be altered by pain memory, highlighting the role of experience and memory in the rehabilitation process.展开更多
Objective: to explore the risk factors of diabetic nephropathy caused by diabetic patients and the critical value of blood pressure that patients need to control. Methods: 74 patients with diabetic nephropathy who rec...Objective: to explore the risk factors of diabetic nephropathy caused by diabetic patients and the critical value of blood pressure that patients need to control. Methods: 74 patients with diabetic nephropathy who received treatment in our hospital from March 2019 to March 2020 were selected. After the patients were admitted to our hospital, the medical staff first thoroughly understood the patient's physical condition. The 74 patients were divided into group F as a reference and group Y for observation according to the patient's condition. The patients in group F were determined to have the disease as non-diabetic nephropathy according to the clinical detection standard. Group Y patients were identified as diabetic nephropathy patients according to the clinical diagnostic criteria. The clinical data of the patients were analyzed in detail. The patient's age, onset course and related indicators were recorded and compared. The risk factors of diabetic nephropathy were determined based on regression analysis. The protective factor is high density lipoprotein, and other factors are irrelevant. The critical blood pressure values of the patients were 137.6mmhg and 78.01mmhg respectively. Conclusion: the analysis of the risk factors of diabetic nephropathy. The risk factors of diabetic nephropathy should be controlled scientifically and the critical value of blood pressure should be strictly controlled to delay the development of the patient's condition.展开更多
Methods for horizontal well spacing calculation in tight gas reservoirs are still adversely affected by the complexity of related control factors,such as strong reservoir heterogeneity and seepage mechanisms.In this s...Methods for horizontal well spacing calculation in tight gas reservoirs are still adversely affected by the complexity of related control factors,such as strong reservoir heterogeneity and seepage mechanisms.In this study,the stress sensitivity and threshold pressure gradient of various types of reservoirs are quantitatively evaluated through reservoir seepage experiments.On the basis of these experiments,a numerical simulation model(based on the special seepage mechanism)and an inverse dynamic reserve algorithm(with different equivalent drainage areas)were developed.The well spacing ranges of Classes I,II,and III wells in the Q gas field are determined to be 802–1,000,600–662,and 285–400 m,respectively,with their average ranges as 901,631,and 342.5 m,respectively.By considering both the pairs of parallel well groups and series well groups as examples,the reliability of the calculation results is verified.It is shown that the combination of the two models can reduce errors and provide accurate results.展开更多
In exploration for tight oil, the content and saturation of hydrocarbon in the tight reservoir is a key factor for evaluating the reserve. Therefore, it is necessary to study the geological history of hydrocarbon accu...In exploration for tight oil, the content and saturation of hydrocarbon in the tight reservoir is a key factor for evaluating the reserve. Therefore, it is necessary to study the geological history of hydrocarbon accumulation and the tight oil charging process. However, kinetic models used for petroleum development are not applicable for petroleum exploration. In this study, a static resistance model[ is proposed after analyzing resistances in ultra-slow flow in porous media. Using this model, the disco^atinuous pattern of oil charging is reproduced through incompressible Navier-Stokes equations, the phase field method and the finite element method. This study also explains macroscopic percolation behavior with microscopic flow mechanisms and discusses some issues in ultra-slow flow in a micro/nano pore-throat network. The resistance analysis reveals that capillary resistance and dissipation resistance are dominant factors in the mechanism of oil accumulation in tight reservoirs. Numerical simulations show that pressure thresholds exist and result in discontinuous oil charging. Generally, it is proven that the static model is more applicable than kinetic models in describing oil accumulation in tight reservoirs.展开更多
In this paper, the mechanism for fluid flow at low velocity in a porous medium is analyzed based on plastic flow of oil in a reservoir and the fractal approach. The analytical expressions for flow rate and velocity of...In this paper, the mechanism for fluid flow at low velocity in a porous medium is analyzed based on plastic flow of oil in a reservoir and the fractal approach. The analytical expressions for flow rate and velocity of non-Newtonian fluid flow in the low permeability porous medium are derived, and the threshold pressure gradient （TPG） is also obtained. It is notable that the TPG （J） and permeability （K） of the porous medium analytically exhibit the scaling behavior J ~ K-D＇r/（l＋Or）, where DT is the fractal dimension for tortuous capillaries. The fractal characteristics of tortuosity for capillaries should be considered in analysis of non-Darcy flow in a low permeability porous medium. The model predictions of TPG show good agreement with those obtained by the available expression and experimental data. The proposed model may be conducible to a better understanding of the mechanism for nonlinear flow in the low permeability porous medium.展开更多
Based on the non-Darcy flow characteristics of surfactant flooding in the low permeability oilfield, considering the changes of threshold pressure and influence of surfactant on convection, diffusion, adsorption and r...Based on the non-Darcy flow characteristics of surfactant flooding in the low permeability oilfield, considering the changes of threshold pressure and influence of surfactant on convection, diffusion, adsorption and retention, a mathematical model is established for a three-dimensional, two-phase, three-component surfactant flooding. A new treatment for the changes of threshold pressure and a novel correction method for the relative permeability curve in the process of surfactant flooding are derived, which enhances the matching degree between the mathematical model and field practice. The mathematical model was used to perform the numerical simulation study for a pilot test of surfactant flooding in Chao 45 Block of Daqing Oilfield, a proper injection plan was optimized. After the optimized plan was carried out in oilfield, the desirable effects, like pressure-reducing, injection rate increase, and the increase of oil recovery, were achieved. The average oil increase for single well reaches 37%, the ratio of cost to revenue is above 1：4, so the economic effect of scale is promising.展开更多
After analyzing many studies of fluid flow theory of multi-porous media in low and extra-low permeability reservoirs and the numerical simulation of non-Darcy flow, we found that a negative flow rate occurs in the exi...After analyzing many studies of fluid flow theory of multi-porous media in low and extra-low permeability reservoirs and the numerical simulation of non-Darcy flow, we found that a negative flow rate occurs in the existing non-Darcy flow equation, which is unreasonable. We believe that the existing equation can only be considered as a discriminant to judging Darcy flow or non-Darcy flow, and cannot be taken as a fluid flow governing equation of multi-porous media. Our analysis of the experimental results shows that the threshold pressure gradient(TPG) of low and extra-low permeability reservoirs is excessively high, and does not conform to fluid flow through multi-porous media in the actual reservoir situation. Therefore, we present a reasonable TPG ranging from 0.006 to 0.04 MPa/m at the well depth of 1500 m and oil drainage distance of 500 m. The results of our study also indicate that the non-Darcy flow phenomenon will disappear when the TPG reaches a certain value. In addition, the TPG or non-Darcy flow in low and extra-low permeability reservoirs does not need to be considered in the productivity prediction and reservoir numerical simulation. At present, the black oil model or dual-porous media is suitable for simulating low and extra-low permeability reservoirs.展开更多
基金supported by the Guangdong Basic and Applied Basic Research Foundation(Grant No.2022A1515110376)the Open Research Fund of National Center for International Research on Deep Earth Drilling and Resource Development,Ministry of Science and Technology(Grant No.DEDRD-2023-04)the Fundamental Research Funds for the Central Universities,China University of Geosciences(Grant No.107-G1323523046).
文摘The flow behaviors of gas and water in hydrate-bearing sediments(HBS)are significantly affected by the threshold pressure gradient(TPG).During long-term natural gas hydrates(NGHs)mining,there exists creep deformation in HBS,which significantly alters pore structures,makes the flow path of fluid more complex,and leads to changes in TPG.Thus,clarifying the evolution of TPG in HBS during creep is essential for NGH production,but it also confronts enormous challenges.In this study,based on the nonlinear creep constitutive model,a novel theoretical TPG model of HBS during creep is proposed that considers pore structures and hydrate pore morphology.The established model is validated against experimental data,demonstrating its ability to capture the evolution of TPG and permeability in HBS during creep.Additionally,the relationship between initial hydrate saturation and TPG of HBS during creep is revealed by sensitivity analysis.The creep strain increases with the decrease in initial hydrate saturation,leading to a greater TPG and a lower permeability.The evolution of TPG at the stable creep stage and the accelerated creep stage is primarily controlled by the Kelvin element and visco-plastic element,respectively.This novel proposed model provides a mechanistic understanding of TPG evolution in HBS during creep,and it is of great significance to optimize the exploitation of NGHs.
基金supported by China Natural Science Foundation(Grant No.52274053)Beijing Natural Science Foundation(Grant No.3232028)Open Fund of State Key Laboratory of Offshore Oil Exploitation(Grant No.CCL2021RCPS0515KQN)。
文摘Spontaneous imbibition(SI)is an important mechanism for enhancing oil recovery in low-permeability reservoirs.Due to the strong heterogeneity,and the non-Darcy flow,the construction of SI model for lowpermeability reservoirs is extremely challenging.Commonly,traditional SI models based on single or averaged capillary tortuosity ignore the influence of heterogeneity of pore seepage channels and the threshold pressure(TP)on imbibition.Therefore,in this work,based on capillary model and fractal theory,a mathematical model of characterizing SI considering heterogeneity of pore seepage channels is established.On this basis,the threshold pressure was introduced to determine the pore radius at which the wetted phase can displace oil.The proposed new SI model was verified by imbibition experimental data.The study shows that for weakly heterogeneous cores with permeability of 0-1 m D,the traditional SI model can characterize the imbibition process relatively accurately,and the new imbibition model can increase the coefficient of determination by 1.05 times.However,traditional model has serious deviations in predicting the imbibition recovery for cores with permeability of 10-50 m D.The new SI model coupling with heterogeneity of pore seepage channels and threshold pressure effectively solves this problem,and the determination coefficient is increased from 0.344 to 0.922,which is increased by2.68 times.For low-permeability reservoirs,the production of the oil in transitional pores(0.01-0.1μm)and mesopores(0.1-1μm)significantly affects the imbibition recovery,as the research shows that when the heterogeneity of pore seepage channels is ignored,the oil recovery in transitional pores and mesopores decreases by 7.54%and 4.26%,respectively.Sensitivity analysis shows that increasing interfacial tension,decreasing contact angle,oil-water viscosity ratio and threshold pressure will increase imbibition recovery.In addition,there are critical values for the influence of these factors on the imbibition recovery,which provides theoretical support for surfactant optimization.
基金The authors gratefully acknowledge the financial supports from the National Science Foundation of China under Grant 52274027 as well as the High-end Foreign Experts Recruitment Plan of the Ministry of Science and Technology China under Grant G2022105027L.
文摘Field evidence indicates that proppant distribution and threshold pressure gradient have great impacts on well productivity.Aiming at the development of unconventional oil reservoirs in Triassic Chang-7 Unit,Ordos Basin of China,we presented an integrated workflow to investigate how(1)proppant placement in induced fracture and(2)non-linear flow in reservoir matrix would affect well productivity and fluid flow in the reservoir.Compared with our research before(Yue et al.,2020),here we extended this study into the development of multi-stage fractured horizontal wells(MFHWs)with large-scale complicated fracture geometry.The integrated workflow is based on the finite element method and consists of simulation models for proppant-laden fluid flow,fracture flow,and non-linear seepage flow,respectively.Simulation results indicate that the distribution of proppant inside the induced cracks significantly affects the productivity of the MFHW.When we assign an idealized proppant distribution instead of the real distribution,there will be an overestimation of 44.98%in daily oil rate and 30.63%in cumulative oil production after continuous development of 1000 days.Besides,threshold pressure gradient(TPG)also significantly affects the well performance in tight oil reservoirs.If we simply apply linear Darcy’s law to the reservoir matrix,the overall cumulative oil production can be overrated by 77%after 1000 days of development.In general,this research provides new insights into the development of tight oil reservoirs with TPG and meanwhile reveals the significance of proppant distribution and non-linear fluid flow in the production scenario design.
基金Projects(51221001,51275417)supported by the National Natural Science Foundation of ChinaProject(2013AA8011004B)supported by National High Technology Research and Development Program of ChinaProject(CX201011)supported by the Doctorate Foundation of Northwestern Polytechnical University,China
文摘A dynamic measuring apparatus was developed to investigate the infiltration process of liquid metal into the fibrous preform. 10% （volume fraction） chopped carbon fiber preforms were infiltrated with magnesium alloy under different infiltration pressures. The threshold pressure and flow behavior of liquid metal infiltrating into the preforms were calculated and measured. The microstructure of obtained Ct4Mg composites was observed. The results indicate that the measured threshold pressure for infiltration was 0.048 MPa, which was larger than the calculated value. The infiltration rate increased with the increase of infiltration pressure, but the increase amplitude decreased gradually. The tiny pores in the composites could be eliminated by increasing the infiltration pressure. When the infiltration pressure rose to 0.6 MPa, high quality C1/Mg composite was obtained.
文摘BACKGROUND Low back pain(LBP)is a common condition with large burden worldwide.Exposure to prolonged sitting with a flexed lumbar posture has been suggested in the literature to be a potential risk factor for self-reported LBP.No study has previously investigated whether exposure to prolonged flexed sitting posture provokes discomfort/pain and decreased interspinous pressure pain thresholds for healthy young men and women without back pain,despite this being a suggested risk factor for LBP.AIM To investigate whether sitting in a prolonged flexed lumbar posture provokes discomfort and lowers interspinous pressure pain thresholds in the lumbar spine for healthy young men and women without previous LBP.METHODS This is a an observational before and after study of 26 participants(13 men,13 women)between 20-35 years old.Algometry was used to examine the pain threshold for pressure applied between spinous processes of the lumbar spine L1-L5.Pressure algometer measures were performed in prone before and after participants were instructed to sit in a fully flexed posture for a maximum of 15 min or until discomfort was experienced in the low back(Borg CR10=7/10).Wilcoxon signed-rank test was used for analyze values from the before and after test conditions.Mann-Whitney U test was used to investigate potential gender difference.RESULTS Fully flexed lumbar spine sitting posture up to 15 min provoked temporary discomfort but the proportion of participants experiencing discomfort 7/10 in the low back was 62%.For all pain pressure threshold locations tested,there was a significant difference for the study population with moderate-large decreased(r=-0.56)pressure pain threshold after exposure to prolonged flexed sitting posture(P<0.01).Comparisons between gender did not show any significant difference.CONCLUSION The result showed that exposure to fully flexed lumbar sitting posture for up to 15 min produced temporary discomfort in the low back in young healthy adults with no previous history of LBP and significantly reduced lumbar interspinous pressure pain thresholds.No gender-based differences were observed.
基金Project supported by the National Natural Science Foundation of China(Grant No.51404232)the China Postdoctoral Science Foundation(Grant No.2014M561074)the National Science and Technology Major Project,China(Grant No.2011ZX05038003)
文摘The threshold pressure gradient and formation stress-sensitive effect as the two prominent physical phenomena in the development of a low-permeable reservoir are both considered here for building a new coupled moving boundary model of radial flow in porous medium. Moreover, the wellbore storage and skin effect are both incorporated into the inner boundary conditions in the model. It is known that the new coupled moving boundary model has strong nonlinearity. A coordinate transformation based fully implicit finite difference method is adopted to obtain its numerical solutions. The involved coordinate transformation can equivalently transform the dynamic flow region for the moving boundary model into a fixed region as a unit circle, which is very convenient for the model computation by the finite difference method on fixed spatial grids. By comparing the numerical solution obtained from other different numerical method in the existing literature, its validity can be verified. Eventually, the effects of permeability modulus, threshold pressure gradient, wellbore storage coefficient, and skin factor on the transient wellbore pressure, the derivative, and the formation pressure distribution are analyzed respectively.
基金Project(51304220) supported by the National Natural Science Foundation of ChinaProject(3144033) supported by the Beijing Natural Science Foundation,ChinaProject(20130007120014) supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China
文摘The flow behavior in porous media with threshold pressure gradient(TPG) is more complex than Darcy flow and the equations of motion, and outer boundary and inner boundary with TPG are also different from Darcy flow for unsteady flow of a producing well in a reservoir. An analytic method to solve this kind of problem is in a need of reestablishment. The classical method of Green's function and Newman product principle in a new way are used to solve the unsteady state flow problems of various shapes of well and reservoir while considering the TPG. Four Green's functions of point, line, band and circle while considering the TPG are achieved. Then, two well models of vertical well and horizontal well are built and simultaneously the function to calculate the moving boundary of each well model is provided. The results show that when considering TPG the pressure field is much different, which has a sudden pressure change, with a moving boundary in it. And the moving boundary of each well model increases with time but slows down rapidly, especially when the TGP is large.
文摘This paper studies the transient pressure of percolation during one production and one shutting in one dimension porous media with threshold pressure gradient, the differential equations are derived and solved with numerical computation. Basing on numerical solution, it is analyzed that: 1. the relation between the steady pressure at well bore (or at endpoint) and threshold pressure gradient, shut-in time, and the corresponding formulae are derived; 2, the regulation of transient pressure peak. The result is very useful and will help experiments and applications in the development of low permeability reservoirs with threshold pressure gradient.
基金National Basic Research Program of China(2007CB209506)
文摘The flowing mechanism of a low permeability gas reservoir is different from a conventional gas reservoir,especially for that with higher irreducible water saturation the threshold pressure gradient exists. At present,in all the deliverability equation,the additional pressure drop caused by the threshold pressure gradient is viewed as constant,but this method has big error in the practical application. Based on the non-Darcy steady flow equation,the limited integral of the additional pressure drop is solved in this paper and it is realized that the additional pressure drop is not a constant but has something to do with production data,and a new deliverability equation is derived,with the relevant processing method for modified isochronal test data. The new deliverability equation turns out to be practical through onsite application.
基金Project(51575447) supported by the National Natural Science Foundation of ChinaProject supported by Top University around World Visiting Plan for Young Teacher’s Cultivating in NWPU,China
文摘A new method for determining two key parameters(threshold pressure and permeability)for fabricating metal matrix composites was proposed based on the equation-solving method.An infiltration experimental device was devised to measure the infiltration behavior precisely with controllable infiltration velocity.Two experiments with alloy Pb-Sn infiltrating into Al2O3 preform were conducted independently under two different pressures so as to get two different infiltration curves.Two sets of coefficients which are functions of threshold pressure and permeability can be obtained through curve fitting method.By solving the two-variable equation set,two unknown variables were determined.It is shown that the determined threshold pressure and permeability are very close to the calculated ones and are also verified by another independent infiltration experiment.The proposed method is also feasible to determine the key infiltration parameters for other metal matrix composite systems.
文摘Based on the statistical data of 26 outburst prone coal seams in China, this paper presents the relationship among the threshold gas pressure in coal and gas outburst and the volatile content and hardness of coal by mathematical statistics. The threshold value of gas pressure for outburst pmin in MPa may be calculated by formula Pmin =5(0. 1+0. 07Kf), where / is the hardness and V the volatile content (%) of a soft bed. In China, the value of Pmin of some outburst prone coal seams ranges from 0. 57 to 0. 1 MPa.
文摘The aim is to evaluate the influence of oral contraceptive intake and menstrual cycle on the electrical activity and pressure pain threshold from anterior temporal and masseter muscles. Twenty-eight women on reproductive age were selected, 13 OC users and 15 nonusers. They were weekly submitted to electromyography and algometry of the anterior temporal and masseter muscles during three consecutive menstrual cycles. Electrical activities at rest position and PPTs of temporal and masseter muscles were not affected by menstrual cycle or by OCs uses. Comparison between groups demonstrated that working side electrical activity was increased in OC users in both muscles, except during lutheal phase for the anterior temporal. However, comparison within weeks did not demonstrate statistical difference. It was suggested that, in healthy women, oral contraceptive use may influence electrical activity, but different phases of the cycle may not.
基金supported by the National Science Foundation(51674279,51804328)Major National Science and Technology Project(2017ZX05009-001,2017ZX05069,2017ZX05072)+4 种基金Shandong Province Key Research and Development Program(2018GSF116004)Shandong Province Natural Science Foundation(ZR2018BEE008,ZR2018BEE018)Fundamental Research Funds for the Central Universities(18CX02168A)China Postdoctoral Science Foundation(2018M630813)Postdoctoral Applied Research Project Foundation of Qingdao city(BY201802003)。
文摘Threshold pressure gradient has great importance in efficient tight gas field development as well as for research and laboratory experiments.This experimental study is carried out to investigate the threshold pressure gradient in detail.Experiments are carried out with and without back pressure so that the effect of pore pressure on threshold pressure gradient may be observed.The trend of increasing or decreasing the threshold pressure gradient is totally opposite in the cases of considering and not considering the pore pressure.The results demonstrate that the pore pressure of tight gas reservoirs has great influence on threshold pressure gradient.The effects of other parameters like permeability and water saturation,in the presence of pore pressure,on threshold pressure gradient are also examined which show that the threshold pressure gradient increases with either a decrease in permeability or an increase in water saturation.Two new correlations of threshold pressure gradient on the basis of pore pressure and permeability,and pore pressure and water saturation,are also introduced.Based on these equations,new models for tight gas production are proposed.The gas slip correction factor is also considered during derivation of this proposed tight gas production models.Inflow performance relationship curves based on these proposed models show that production rates and absolute open flow potential are always be overestimated while ignoring the threshold pressure gradients.
文摘Purpose: Memory has been identified as an important protective feature to prevent future injury, but its role has yet to be ascertained. The current study aimed to determine whether there was a difference in pressure pain threshold (PPT) responses between participants with a prior history of injury of lower extremity injury (PSI) and those without (NPSI) when exposed to 1) experimental mechanical pain, 2) short-term memory recall of a painful stimulus, or 3) long-term memory of the pain associated with a prior injury. Subjects and Methods: The study used a pretest-posttest quasi-experimental design. A convenience sample of 59 pain-free participants was recruited from an urban university. Twenty-nine PSI and 30 NPSI were stratified into two groups based on their injury history with PPT values measured at baseline and immediately following each of the three experimental conditions. A repeated measure ANCOVA analysis was conducted for each condition to determine whether there was a difference in PPT responses between the two groups. Results: There was a statistically significant difference in PPT values between the two groups when exposed to experimental pain, F(1,57) = 6.010, p = 0.017, partial η<sup>2</sup> = 0.095 and with long-term pain memory, F(1,57) = 4.886, p = 0.031, partial η<sup>2</sup> = 0.079. There was no statistically significant difference between groups with short-term pain memory, F(1,57) = 3.925, p = 0.052, partial η<sup>2</sup> = 0.064. Conclusions: These findings suggest that pain processing may be altered by pain memory, highlighting the role of experience and memory in the rehabilitation process.
文摘Objective: to explore the risk factors of diabetic nephropathy caused by diabetic patients and the critical value of blood pressure that patients need to control. Methods: 74 patients with diabetic nephropathy who received treatment in our hospital from March 2019 to March 2020 were selected. After the patients were admitted to our hospital, the medical staff first thoroughly understood the patient's physical condition. The 74 patients were divided into group F as a reference and group Y for observation according to the patient's condition. The patients in group F were determined to have the disease as non-diabetic nephropathy according to the clinical detection standard. Group Y patients were identified as diabetic nephropathy patients according to the clinical diagnostic criteria. The clinical data of the patients were analyzed in detail. The patient's age, onset course and related indicators were recorded and compared. The risk factors of diabetic nephropathy were determined based on regression analysis. The protective factor is high density lipoprotein, and other factors are irrelevant. The critical blood pressure values of the patients were 137.6mmhg and 78.01mmhg respectively. Conclusion: the analysis of the risk factors of diabetic nephropathy. The risk factors of diabetic nephropathy should be controlled scientifically and the critical value of blood pressure should be strictly controlled to delay the development of the patient's condition.
基金the Major Science and Technology Project of Southwest Oil and Gas Field Company(2022ZD01-02).
文摘Methods for horizontal well spacing calculation in tight gas reservoirs are still adversely affected by the complexity of related control factors,such as strong reservoir heterogeneity and seepage mechanisms.In this study,the stress sensitivity and threshold pressure gradient of various types of reservoirs are quantitatively evaluated through reservoir seepage experiments.On the basis of these experiments,a numerical simulation model(based on the special seepage mechanism)and an inverse dynamic reserve algorithm(with different equivalent drainage areas)were developed.The well spacing ranges of Classes I,II,and III wells in the Q gas field are determined to be 802–1,000,600–662,and 285–400 m,respectively,with their average ranges as 901,631,and 342.5 m,respectively.By considering both the pairs of parallel well groups and series well groups as examples,the reliability of the calculation results is verified.It is shown that the combination of the two models can reduce errors and provide accurate results.
基金supported by the Chinese Major National Scientific and Technological Program (2011ZX05001)Chinese Postdoctoral Fund (2013M540114)
文摘In exploration for tight oil, the content and saturation of hydrocarbon in the tight reservoir is a key factor for evaluating the reserve. Therefore, it is necessary to study the geological history of hydrocarbon accumulation and the tight oil charging process. However, kinetic models used for petroleum development are not applicable for petroleum exploration. In this study, a static resistance model[ is proposed after analyzing resistances in ultra-slow flow in porous media. Using this model, the disco^atinuous pattern of oil charging is reproduced through incompressible Navier-Stokes equations, the phase field method and the finite element method. This study also explains macroscopic percolation behavior with microscopic flow mechanisms and discusses some issues in ultra-slow flow in a micro/nano pore-throat network. The resistance analysis reveals that capillary resistance and dissipation resistance are dominant factors in the mechanism of oil accumulation in tight reservoirs. Numerical simulations show that pressure thresholds exist and result in discontinuous oil charging. Generally, it is proven that the static model is more applicable than kinetic models in describing oil accumulation in tight reservoirs.
基金Project supported by the National Natural Science Foundation of China(Grant No.41102080)the Fundamental Research Funds for the Central Universities,China(Grant Nos.CUG130404 and CUG130103)the Fund from the Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education,China University of Geosciences(Wuhan),China(Grant No.TPR-2013-18)
文摘In this paper, the mechanism for fluid flow at low velocity in a porous medium is analyzed based on plastic flow of oil in a reservoir and the fractal approach. The analytical expressions for flow rate and velocity of non-Newtonian fluid flow in the low permeability porous medium are derived, and the threshold pressure gradient （TPG） is also obtained. It is notable that the TPG （J） and permeability （K） of the porous medium analytically exhibit the scaling behavior J ~ K-D＇r/（l＋Or）, where DT is the fractal dimension for tortuous capillaries. The fractal characteristics of tortuosity for capillaries should be considered in analysis of non-Darcy flow in a low permeability porous medium. The model predictions of TPG show good agreement with those obtained by the available expression and experimental data. The proposed model may be conducible to a better understanding of the mechanism for nonlinear flow in the low permeability porous medium.
基金the National Natural Science Foundation of China (Grant No. 50634020)
文摘Based on the non-Darcy flow characteristics of surfactant flooding in the low permeability oilfield, considering the changes of threshold pressure and influence of surfactant on convection, diffusion, adsorption and retention, a mathematical model is established for a three-dimensional, two-phase, three-component surfactant flooding. A new treatment for the changes of threshold pressure and a novel correction method for the relative permeability curve in the process of surfactant flooding are derived, which enhances the matching degree between the mathematical model and field practice. The mathematical model was used to perform the numerical simulation study for a pilot test of surfactant flooding in Chao 45 Block of Daqing Oilfield, a proper injection plan was optimized. After the optimized plan was carried out in oilfield, the desirable effects, like pressure-reducing, injection rate increase, and the increase of oil recovery, were achieved. The average oil increase for single well reaches 37%, the ratio of cost to revenue is above 1：4, so the economic effect of scale is promising.
基金sponsored by National Key Project of Science and Technology of the Ministry of Science and Technology(MOST)(Grant No.2011ZX05043-002)
文摘After analyzing many studies of fluid flow theory of multi-porous media in low and extra-low permeability reservoirs and the numerical simulation of non-Darcy flow, we found that a negative flow rate occurs in the existing non-Darcy flow equation, which is unreasonable. We believe that the existing equation can only be considered as a discriminant to judging Darcy flow or non-Darcy flow, and cannot be taken as a fluid flow governing equation of multi-porous media. Our analysis of the experimental results shows that the threshold pressure gradient(TPG) of low and extra-low permeability reservoirs is excessively high, and does not conform to fluid flow through multi-porous media in the actual reservoir situation. Therefore, we present a reasonable TPG ranging from 0.006 to 0.04 MPa/m at the well depth of 1500 m and oil drainage distance of 500 m. The results of our study also indicate that the non-Darcy flow phenomenon will disappear when the TPG reaches a certain value. In addition, the TPG or non-Darcy flow in low and extra-low permeability reservoirs does not need to be considered in the productivity prediction and reservoir numerical simulation. At present, the black oil model or dual-porous media is suitable for simulating low and extra-low permeability reservoirs.
