Production characteristics and displacement mechanisms of infilling polymer-surfactant-preformed particle gel flooding in post-polymer flooding reservoirs:A review of practice in Ng3 block of Gudao Oilfield

The pilot test of infilling polymer-surfactant-preformed particle gel(PPG)flooding has been successfully implemented after polymer flooding in Ng3 block of Gudao Oilfield in China.However,the production characteristics and displacement mechanisms are still unclear,which restricts its further popularization and application.Aiming at this problem,this paper firstly analyzes the production performance of the pilot test and proposed four response types according to the change of water cut curves,including W-type,U-type,V-type response,and no response.Furthermore,the underlying reasons of these four types are analyzed from the aspects of seepage resistance and sweep efficiency.The overall sweep efficiency of gradual-rising W-type,gradual-decreasing W-type,and early V-type response increases from 0.81 to 0.93,0.55 to 0.89,and 0.94 to 1,respectively.And the sum of seepage resistance along the connection line between production well and injection well for U-type and delayed V-type response increases from 0.0994 to 0.2425,and 0.0677 to 0.1654,respectively.Then,the remaining oil distribution after polymer flooding is summarized into four types on the basis of production and geological characteristics,namely disconnected remaining oil,streamline unswept remaining oil,rhythm remaining oil,and interlayer-controlled remaining oil.Furthermore,the main displacement mechanisms for each type are clarified based on the dimensionless seepage resistance and water absorption profile.Generally,improving connectivity by well pattern infilling is the most important for producing disconnected remaining oil.The synergistic effect of well pattern infilling and polymer-surfactant-PPG flooding increases the dimensionless seepage resistance of water channeling regions and forces the subsequent injected water to turn to regions with streamline unswept remaining oil.The improvement of the water absorption profile by polymer-surfactant-PPG flooding and separated layer water injection contributes to displacing rhythm remaining oil and interlayer-controlled remaining oil.Finally,the paper analyzes the relationships between the remaining oil distribution after polymer flooding and production characteristics of infilling polymer-surfactant-PPG flooding.The study helps to deepen the understanding of infilling polymer-surfactant-PPG flooding and has reference significance for more commercial implementations in the future.

Mechanical mechanism analysis of tension type anchor based on shear displacement method

Based on the fact that the shear stress along anchorage segment is neither linearly nor uniformly distributed, the load transfer mechanism of the tension type anchor was studied and the mechanical characteristic of anchorage segment was analyzed. Shear stress?strain relationship of soil surrounding anchorage body was simplified into three-folding-lines model consisting of elastic phase, elasto-plastic phase and residual phase considering its softening characteristic. Meanwhile, shear displacement method that has been extensively used in the analysis of pile foundation was introduced. Based on elasto-plastic theory, the distributions of displacement, shear stress and axial force along the anchorage segment of tension type anchor were obtained, and the formula for calculating the elastic limit load was also developed accordingly. Finally, an example was given to discuss the variation of stress and displacement in the anchorage segment with the loads exerted on the anchor, and a program was worked out to calculate the anchor maximum bearing capacity. The influence of some parameters on the anchor bearing capacity was discussed, and effective anchorage length was obtained simultaneously. The results show that the shear stress first increases and then decreases and finally trends to the residual strength with increase of distance from bottom of the anchorage body, the displacement increases all the time with the increase of distance from bottom of the anchorage body, and the increase of velocity gradually becomes greater.

Algebraic Solution for the Forward Displacement Analysis of the General 6-6 Stewart Mechanism

The solution for the forward displacement analysis（FDA） of the general 6-6 Stewart mechanism（i.e., the connection points of the moving and fixed platforms are not restricted to lying in a plane） has been extensively studied, but the efficiency of the solution remains to be effectively addressed. To this end, an algebraic elimination method is proposed for the FDA of the general 6-6 Stewart mechanism. The kinematic constraint equations are built using conformal geometric algebra（CGA）. The kinematic constraint equations are transformed by a substitution of variables into seven equations with seven unknown variables. According to the characteristic of anti-symmetric matrices, the aforementioned seven equations can be further transformed into seven equations with four unknown variables by a substitution of variables using the Grobner basis. Its elimination weight is increased through changing the degree of one variable, and sixteen equations with four unknown variables can be obtained using the Grobner basis. A 40th-degree univariate polynomial equation is derived by constructing a relatively small-sized 9 × 9 Sylvester resultant matrix. Finally, two numerical examples are employed to verify the proposed method. The results indicate that the proposed method can effectively improve the efficiency of solution and reduce the computational burden because of the small-sized resultant matrix.

Unilateral self-locking mechanism for inchworm in-pipe robot

A unilateral self-locking mechanism(USM) was proposed to increase the tractive ability of the inchworm in-pipe robots for pipeline inspection.The USM was basically composed of a cam,a torsional spring and an axis.The self-locking and virtual work principles were applied to studying the basic self-locking condition of the USM.In order to make the cooperation between the crutch and telescopic mechanism more harmonical,the unlocking time of the USM was calculated.A set of parameters were selected to build a virtual model and fabricate a prototype.Both the simulation and performance experiments were carried out in a pipe with a nominal inside diameter of 160 mm.The results show that USM enables the robot to move quickly in one way,and in the other way it helps the robot get self-locking with the pipe wall.The traction of the inchworm robot can rise to 1.2 kN,beyond the limitation of friction of 0.497 kN.

Mechanisms of oil displacement by ASP-foam and its influencing factors

ASP-foam （ASPF） is a system prepared by injecting natural gas into the conventional alkali- surfactant-polymer （ASP） system. Foam can be formed in the porous media by the interaction of gas and surfactant in the ASP system. With the ASPF system, oil recovery is improved as the interfacial tension （IFT） is reduced to a relatively low level, and the swept volume is enlarged. In this paper, four surfactants were evaluated and characterized by IFT between ASP system and oil and the foaming performance. AI- kyl benzene sulfonate （ORS-41） was chosen as the surfactant to best reduce IFT between displacement fluids and oil and improve the foaming performance. The mechanisms of ASPF flooding were studied in this paper, the results show that the ASPF flooding not only enlarges the swept volume but also enhances the displacement efficiency. The effects of reservoir heterogeneity, the gas-liquid ratio of ASPF system, and the concentrations of polymer and surfactant on the displacement efficiency were studied. A field trial of ASPF flooding has also been conducted. Both the laboratory results and the field trial results show that the ASPF flooding can significantly increase the oil recovery, with a 30% increase in the proportion of the original oil in place recovered compared with water flooding.

A Piezoelectric Friction-Inertial Linear Motor Based on Piezoelectric Single-Crystal Cymbal Displacement Amplification Mechanism

Piezoelectric friction-inertial motor is known for its promise for a long-range and high-resolution motion.The movement of the slider/rotor of the motor is achieved by stick-slip effect.We report a relaxor-based-ferroelectric-single-crystal cymbal actuator and a miniature piezoelectric friction-inertial linear motor(abbreviated as PFILM)fabricated with the cymbal actuator.The cymbal actuator is fabricated with a 10 mm diameter disk of 0.70Pb(Mg_(1/3)Nb_(2/3))O_3-0.30PbTiO_3 single crystal.The displacement of the cymbal actuator increases almost proportionally from 0to 23μm with driving voltage up to 500 V,and the minimal hysteresis is observed.The cymbalPFILM with 20 mm motion range works under driving voltage frequency of ca.100 Hz to ca.5kHz,the fastest speed is obtained with 3.5kHz and the no-load speed is 14mm/s and the maximum thrust force is 98 mN.Compared with a PFILM based on multilayer piezoelectric ceramic,the proposed motor has a larger stroke under DC/quasistatic input voltage in fine motion mode,but a smaller driving force in long-travel mode due to lower resonance frequency.

Comparison of oil displacement mechanisms and performances between continuous and dispersed phase flooding agents

To compare the oil displacement mechanisms and performances of continuous phase flooding agent(traditional polymer solution) and dispersed phase flooding agent(particle-type polymer SMG dispersion), the particle phase separation of SMG dispersion migrating in pores was simulated by using the microfluidic technology. Theoretically guided by the tree fork concentration distribution of red cells in biological fluid mechanics, the concentration distribution mathematical model of SMG in different pores is established. Furthermore, the micro and macro physical simulation experiments of continuous and dispersed phase flooding agents were carried out. The results show that the continuous flooding agent enters all the swept zones and increases the flow resistance in both larger and small pores. On the contrary, the particle phase separation phenomenon occurs during the injection process of dispersed flooding agent. The SMG particles gather in the larger pore to form bridge blinding, and the carrier fluid displace oil in the small pore. Working in cooperation, the SMG particle and carrier fluid drive the residual oil in the low permeability layers step by step and achieve the goal of enhanced oil recovery. The laboratory experimental results indicate that, the oil increment and water reduction effect of dispersed flooding agent is much better than that of continuous flooding agent, which is consistent with the field test results.

Characteristics and displacement mechanisms of the dispersed particle gel soft heterogeneous compound flooding system

Considering high temperature and high salinity in the reservoirs, a dispersed particle gel soft heterogeneous compound(SHC) flooding system was prepared to improve the micro-profile control and displacement efficiency. The characteristics and displacement mechanisms of the system were investigated via core flow tests and visual simulation experiments. The SHC flooding system composed of DPG particles and surfactants was suitable for the reservoirs with the temperature of 80-110 °C and the salinity of 1×10~4-10×10~4 mg/L. The system presented good characteristics: low viscosity, weak negatively charged, temperature and salinity resistance, particles aggregation capacity, wettability alteration on oil wet surface, wettability weaken on water wet surface, and interfacial tension(IFT) still less than 1×10^(-1) mN/m after aging at high temperature. The SHC flooding system achieved the micro-profile control by entering formations deeply and the better performance was found in the formation with the higher permeability difference existing between the layers, which suggested that the flooding system was superior to the surfactants, DPG particles, and polymer/surfactant compound flooding systems. The system could effectively enhance the micro-profile control in porous media through four behaviors, including direct plugging, bridging, adsorption, and retention. Moreover, the surfactant in the system magnified the deep migration capability and oil displacement capacity of the SHC flooding system, and the impact was strengthened through the mechanisms of improved displacement capacity, synergistic emulsification, enhanced wettability alteration ability and coalescence of oil belts. The synergistic effect of the two components of SHC flooding system improved oil displacement efficiency and subsequently enhanced oil recovery.

A New Type of Continuously Variable Displacement Mechanism Used for Hydraulic Motors

A continuously variable displacement mechanism, which is composed of a hydraulic control valve with mechanical-positional feedback to camshaft, was designed for changing the displacement of traditional camshaft connecting-rod low speed high torque (LSHT) hydraulic motor continuously. The new type of continuously variable displacement mechanism is simple and easy to be made. The structure and principle of a continuously variable displacement mechanism was introduced. The mathematic model of the continuously variable displacement mechanism was set up and its static and dynamic characteristics were analyzed with the help of computer simulation. It can be seen that the cam ring on camshaft of the traditional LSHT hydraulic motor can stop at any position between minimum and maximum eccentricity, according to an input fluid pressure signal. And it can also stay anywhere stably through self-adjusting. Besides, it can work stabilized when load impact or oil leakage exists.

DIRECT DISPLACEMENT OF PARALLEL MECHANISM WITH WAVELET NETWORK

A new method solution for the direct displacement of parallel mechanism, wavelet network method, is proposed. Comparing with the classical analytical and numerical methods, this method can be extended to any parallel mechanism with any selected degree of freedom and configuration. A wavelet network suiting to approach multi-input and multi-output system is constructed. The network is optimized by analyzing the sparseness of input data and selecting the fitting wavelets by orthogonalization method according to the output data. Then it is applied to solve the direct displace- ment of a general six-degree-of-freedom parallel mechanism as a numerical example. For comparison purposes, a BP neural network is also used for this problem. Simulation results show that the wavelet network performs better than BP neural network. In addition, the wavelet network learns much faster than BP network.

Experimental investigation on stable displacement mechanism and oil recovery enhancement of oxygen-reduced air assisted gravity drainage

The effects of gravity,capillary force,and viscous force on the migration characteristics of oil and gas interface in oxygen-reduced air-assisted gravity drainage(OAGD)were studied through a two-dimensional visualization model.The effects of bond number,capillary number and low-temperature oxidation on OAGD recovery were studied by long core displacement experiments.On this basis,the low-temperature oxidation number was introduced and its relationship with the OAGD recovery was established.The results show that the shape and changing law of oil and gas front are mainly influenced by gravity,capillary force and viscous force.When the bond number is constant(4.52×10-4),the shape of oil-gas front is controlled by capillary number.When the capillary number is less than 1.68×10-3,the oil and gas interface is stable.When the capillary number is greater than 2.69×10-2,the oil and gas interface shows viscous fingering.When the capillary number is between 1.68×10-3 and 2.69×10-2,the oil and gas interface becomes capillary fingering.The core flooding experiments results show that for OAGD stable flooding,before the gas breakthrough,higher recovery is obtained in higher gravity number and lower capillary number.In this stage,gravity is predominant in controlling OAGD recovery and the oil recovery could be improved by reducing injection velocity.After gas breakthrough,higher recovery was obtained in lower gravity and higher capillary numbers,which means that the viscous force had a significant influence on the recovery.Increasing gas injection velocity in this stage is an effective measure to improve oil recovery.The low-temperature oxidation number has a good correlation with the recovery and can be used to predict the OAGD recovery.

The Description of Oil Displacement Mechanism in Steam Injection of Multi-Field Synergy with Exergy Transfer

Steam injection is a most effective way for improving heavy oil recovery efficiency, and it has academic and practical significance for the mechanism of multi-field synergy oil displacement. Mechanism of “diversified” oil displacement which is obtained by traditional study methods in the exploitation territory of oil and gas fields has both respective roles and mutual cross shortages. To describe and analyze the displacement process of multi-field coupling with exergy transfer can simplify this kind of problem by introducing a unified goal-driving exergy. It needs to use the method of theoretical modeling, numerical simulation and experimental validation to study the basic law of exergy transfer in the oil displacement process of multi-field synergy, make a thorough research for the flooding process of steam injection with exergy transfer theory and reveal the oil displacement mechanism in steam injection of multi-field synergy. Thus the theory instruction and technical support can be provided to improve reservoirs producing degree and extraction ratio.

A Study on Propagation Mechanism of Fracture Systems in Rock Masses by Discontinuity Displacement Method

The main task of fracture mechanics of rock masses is the study on the propagating mechanism of fractures in rock masses , which can be efficiently conducted by discontinuty displacement (DD) numerical evaluation . Firstly ,the element stress and displacement are analysed and the principle and steps of the numerical calculation of stress intensity factor and fracture extension force are introduced .The numerical results of parallel and echelon fracture systems ,which are compared with real field fractures .are presented. Finally . a simple engineering application example is presented .

The mechanism of hydraulic fracturing assisted oil displacement to enhance oil recovery in low and medium permeability reservoirs

Aiming at the technology of hydraulic fracturing assisted oil displacement which combines hydraulic fracturing,seepage and oil displacement,an experimental system of energy storage and flowback in fracturing assisted oil displacement process has been developed and used to simulate the mechanism of percolation,energy storage,oil displacement and flowback of chemical agents in the whole process.The research shows that in hydraulic fracturing assisted oil displacement,the chemical agent could be directly pushed to the deeper area of the low and medium permeability reservoirs,avoiding the viscosity loss and adhesion retention of chemical agents near the pay zone;in addition,this technology could effectively enlarge the swept volume,improve the oil displacement efficiency,replenish formation energy,gather and exploit the scattered residual oil.For the reservoir with higher permeability,this measure takes effect fast,so to lower cost,and the high pressure hydraulic fracturing assisted oil displacement could be adopted directly.For the reservoir with lower permeability which is difficult to absorb water,hydraulic fracturing assisted oil displacement with surfactant should be adopted to reduce flow resistance of the reservoir and improve the water absorption capacity and development effect of the reservoir.The degree of formation energy deficit was the main factor affecting the effective swept range of chemical agents.Moreover,the larger the formation energy deficit was,the further the seepage distance of chemical agents was,accordingly,the larger the effective swept volume was,and the greater the increase of oil recovery was.Formation energy enhancement was the most important contribution to enhanced oil recovery(EOR),which was the key to EOR by the technology of hydraulic fracturing assisted oil displacement.

Migration and accumulation mechanisms and main controlling factors of tight oil enrichment in a continental lake basin

Based on the typical dissection of various onshore tight oil fields in China,the tight oil migration and accumulation mechanism and enrichment-controlling factors in continental lake basins are analyzed through nuclear magnetic resonance(NMR)displacement physical simulation and Lattice Boltzmann numerical simulation by using the samples of source rock,reservoir rock and crude oil.In continental lake basins,the dynamic forces driving hydrocarbon generation and expulsion of high-quality source rocks are the foundational power that determines the charging efficiency and accumulation effect of tight oil,the oil migration resistance is a key element that influences the charging efficiency and accumulation effect of tight oil,and the coupling of charging force with pore-throat resistance in tight reservoir controls the tight oil accumulation and sweet spot enrichment.The degree of tight oil enrichment in continental lake basins is controlled by four factors:source rock,reservoir pore-throat size,anisotropy of reservoir structure,and fractures.The high-quality source rocks control the near-source distribution of tight oil,reservoir physical properties and pore-throat size are positively correlated with the degree of tight oil enrichment,the anisotropy of reservoir structure reveals that the parallel migration rate is the highest,and intralayer fractures can improve the migration and accumulation efficiency and the oil saturation.

Analysis of displacement damage effects on the charge-coupled device induced by neutrons at Back-n in the China Spallation Neutron Source

Displacement damage effects on the charge-coupled device(CCD)induced by neutrons at the back-streaming white neutron source(Back-n)in the China Spallation Neutron Source(CSNS)are analyzed according to an online irradiation experiment.The hot pixels,random telegraph signal(RTS),mean dark signal,dark current and dark signal non-uniformity(DSNU)induced by Back-n are presented.The dark current is calculated according to the mean dark signal at various integration times.The single-particle displacement damage and transient response are also observed based on the online measurement data.The trends of hot pixels,mean dark signal,DSNU and RTS degradation are related to the integration time and irradiation fluence.The mean dark signal,dark current and DSNU2 are nearly linear with neutron irradiation fluence when nearly all the pixels do not reach saturation.In addition,the mechanisms of the displacement damage effects on the CCD are demonstrated by combining the experimental results and technology computer-aided design(TCAD)simulation.Radiation-induced traps in the space charge region of the CCD will act as generation/recombination centers of electron-hole pairs,leading to an increase in the dark signal.

Analytical solutions for the restraint effect of isolation piles against tunneling-induced vertical ground displacements

This paper presents a simplified elastic continuum method for calculating the restraint effect of isolation piles on tunneling-induced vertical ground displacement,which can consider not only the relative sliding of the pile‒soil interface but also the pile rowesoil interaction.The proposed method is verified by comparisons with existing theoretical methods,including the boundary element method and the elastic foundation method.The results reveal the restraining mechanism of the isolation piles on vertical ground displacements due to tunneling,i.e.the positive and negative restraint effects exerted by the isolation piles jointly drive the ground vertical displacement along the depth direction from the original tunneling-induced nonlinear variation situation to a relatively uniform situation.The results also indicate that the stiffness of the pile‒soil interface,including the pile shaft‒surrounding soil interface and pile tip-supporting soil interface,describes the strength of the pile‒soil interaction.The pile rows can confine the vertical ground displacement caused by the tunnel excavation to the inner side of the isolation piles and effectively prevent the vertical ground displacement from expanding further toward the outer side of the isolation piles.

Unloading damage patterns of rock slopes in open pit mines and analyses of their mechanisms

The stability of slopes is essential for ensuring safe production in open-pit mines.Analyzing and managing the deformation and failure of the slope rock mass becomes more challenging as the slope height increases.To investigate the damage patterns of slopes with varying heights,three slope models were developed based on a rock slope in Dagushan,China.The deformation failure processes of slopes under the influence of excavation and unloading were analyzed using the base friction test method in combination with digital image technology contrasting.The results supported the following findings:(1)Unloading tensile stress caused lateral partitioning in the slope.Both the foot and top of the slope underwent initial tensile cracks.(2)The destabilization mechanism of unloading deformation in slopes of different heights involved a combination of traction at the foot of the slope or pushing at the top of the slope,followed by accelerated deformation,deceleration creep,and overall destabilization.(3)The unloading damage patterns of slopes at different heights were summarized as follows:compression tension cracking,traction,and slip damage for medium and low slopes;compression tension cracking,traction,and slip failure for the upper part of high slopes;and relaxation tension cracking,pushing,traction,and slip failure for the lower part.Moreover,the upper part of ultra-high slopes exhibited compression tension cracking,traction,and slip failure,while the middle and lower parts displayed relaxation tension cracking,pushing,traction,and slip patterns.Finally,numerical simulations were conducted to verify the results of the test analyses,which demonstrated good consistency.These research results were of great engineering value for proposing effective safety management measures for high slopes.

Evaluation of Visible Losses and Damage to the Ratoon Cane in the Mechanized Harvesting of Sugarcane for Different Displacement Speeds

This study aimed at quantitatively evaluating the sugarcane losses and the damage caused to the ratoon cane while using the Case IH A8800 harvester in different displacement speeds;it was conducted in the municipality of Campos dos Goytacazes, in Rio de Janeiro, Brazil. Three speeds were used as treatment (2 km&middoth-1, 3 km&middoth-1, and 4.5 km&middoth-1), and each treatment was composed of six rows of harvested ratoon, each with a length of 290 m. In order to evaluate the quantitative losses in t&middotha-1 and the percentage of losses, the remaining sugarcane, left on the field after harvesting, was collected. The sampling frame was set to every 50 m, dividing the borders by 40 m;the measurement for each sampling area was of 20 m2, with five repetitions. In order to evaluate the damage caused to the ratoon canes, we chose a visual methodology to classify the damage degrees, ranging from one to four. There was no significant difference in losses when comparing different speeds. Therefore, it is more advantageous and economically viable to use the speed of 4.5 km&middoth-1, which collects more in less time.

Effect of high-energy Ne ions irradiation on mechanical properties difference between Zr_(63.5)Cu_(23)Al_(9)Fe_(4.5)metallic glass and crystalline W

In this paper,high-energy Ne ions were used to irradiate Zr_(63.5)Cu_(23)Al_(9)Fe_(4.5) metallic glass(MG)and crystalline W to investigate their difference in mechanical response after irradiation.The results showed that with the irradiation dose increased,the tensile micro-strain increased,nano-hardness increased from 7.11 GPa to 7.90 GPa and 8.62 GPa,Young’s modulus increased,and H3/E2 increased which indicating that the plastic deformability decreased in crystalline W.Under the same irradiation conditions,the Zr_(63.5)Cu_(23)Al_(9)Fe_(4.5) MG still maintained the amorphous structure and became more disordered despite the longer range and stronger displacement damage of Ne ions in Zr_(63.5)Cu_(23)Al_(9)Fe_(4.5) MG than in crystalline W.Unlike the irradiation hardening and embrittlement behavior of crystalline W,Zr_(63.5)Cu_(23)Al_(9)Fe_(4.5) MG showed the gradual decrease in hardness from 6.02 GPa to 5.89 GPa and 5.50 GPa,the decrease in modulus and the increase in plastic deformability with the increasing dose.Possibly,the irradiation softening and toughening phenomenon of Zr_(63.5)Cu_(23)Al_(9)Fe_(4.5) MG could provide new ideas for the design of nuclear materials.