Physical Simulation Experiments Research Articles

A novel design of electromagnetic side sealing in twin-roll strip cast-rolling process

In this paper, a novel design of electromagnetic side sealing is proposed to further promote its realization in the field of TRSC. Based on the liquid metal flow under the magnetic field, the magnetic induction intensity for side sealing was obtained. The simulation model of the electromagnetic side sealing is established to research the influence of parameters on the electromagnetic force. The physical simulation experiment is carried out to verify and supplement the model. Then a new type of electromagnetic side sealing structure with improved solenoid coil is designed. Its electromagnetic intensity distribution is more consistent with the theoretical requirements.

Study on the Pressure-Bearing Law of Backfilling Material Based on Three-Stage Strip Backfilling Mining

During strip backfilling mining in coal mines, the backfilling material is the main support structure. Therefore, studying the pressure law of the backfilling material is essential for the safe and efficient mining of coal resources. Based on research into strip backfilling mining at working face number 3216 of the Shanghe Coal Mine, and to smooth transition of overlying strata loads to the backfilling material, this study proposes a three-stage strip backfilling mining method. Based on thin-plate theory, an elastic thin-plate model, a reasonable spacing of strip mining is constructed, and the reasonable mining parameters of “mining 7 m to retain 8 m” at working face number 3216 of the Shanghe Coal Mine are determined. The law of backfilling pressure in three-stage strip backfilling mining is studied through numerical simulation and physical simulation experiments. The results show that field measurement results are basically consistent with the experimental results and numerical simulation results. When three-stage strip backfilling mining is adopted, the stage-one backfilling material is the main bearing body to which the overlying rock load transfers smoothly and gradually, and the structure of the “overburden-coal pillar (or backfilling strip)” in the stope remains stable. In three-stage strip backfilling mining, the overlying rock load is ultimately transferred to the stage-one backfilling material, the stage-two backfilling material is the auxiliary bearing body, and the stage-three backfilling material mainly provides long-term stable lateral support for the stage-one backfilling material.

Experimental Study on Deformation Mechanism of a Utility Tunnel in a Ground Fissure Area

This paper discusses the deformation mechanism of a utility tunnel crossing active ground fissures in Xi’an as observed in a physical model test. The purpose of this work is to confirm the precise effects of ground fissures on utility tunnels. The physical simulation experiment is carried out to measure the earth pressure and the strain relationship of the structure and the structural displacement. The structure appears to have been destroyed by torsion. The structural deformation located in the tunnel’s footwall was more serious than that in the hanging wall. However, at the top of the utility tunnel structure, the earth pressure in the footwall was less than that in the hanging wall. The increased range of the hanging wall at 0.3–1.5 m (the prototype within the range of 22.5 m) and decreased range of the footwall at 0.3–0.8 m (the prototype within the range of 12 m) were basically consistent with changes in the contact pressure at the structure’s bottom. This was roughly consistent with the main deformation zone of ground fissures mentioned in the specification, with the hanging wall at 0–20 m and footwall at 0–12 mm. Displacement meter data shows that the structure tends to deform to the lower right as the utility tunnel is “twisted” clockwise. These observations mark a notable departure from the previously published failure mode of metro tunnels under active ground fissures.

The mechanism of rockburst-outburst coupling disaster considering the coal-rock combination: An experiment study

With the ongoing development of deep mining of coal resources, some coal mine dynamic disasters have exhibited characteristics of both coal-gas outbursts and rockbursts. Therefore, research is required on the mechanism of rockburst-outburst coupling disaster. In this study, the failure characteristics of coal-rock combination structures were investigated using lab-scale physical simulation experiments. The energy criterion of the rockburst-outburst coupling disaster was obtained, and the mechanism of the disaster induced by the gas-solid coupling instability of the coal-rock combination structure was determined. The experimental results indicate that the damage of the coal-rock structure is significantly different from that of a coal body. The influence of the coal-rock structure should be considered in the study of rockburst-outburst coupling disaster. The deformation degree of the roof is controlled by the more significant main role of the gas pressure and the difference in the strength between the rock body and the coal body. The outburst holes and spall characteristics of the coal body after the failure of the coal-rock structure are strongly affected by the difference in strength between the roof and the coal body. The research results provide an in-depth understanding of the mechanism of rockburst-outburst coupling disasters in deep mining.

Study on the movement characteristics of the overlying stratum and surrounding rock control in ultraclose coal seams: A case study

AbstractIn Fucun Coal Mine, the average spacing between the 3upper coal seam (UCS) and 3lower coal seam (LCS) is only 6 m. In the process of mining upper coal, the lower roadway (LR), which is 60 m away from upper pillar, becomes unstable. In order to control the surrounding rock of lower roadway, a physical model experiment and a 3D numerical calculation were performed in this study. The results of physical similarity simulation experiment show that mining of longwall face in UCS will lead to fracturing of key layers at a high elevation (KLHE) far away from the coal seam. The expanded goaf area caused large‐scale fracturing and rotation of the KLHE, which resulted in significant strata pressure behavior in LR. The numerical calculation results show that the LR should be within 19 m of the coal pillar. Finally, a plan which includes a proper location and a supporting system was proposed. The feasibility of the proposed plan is verified by an industrial application.

Infiltration behaviour of dike covers made of dredged material on the Rostock Research dike

The knowledge about the infiltration behaviour of a dike body is an important issue in dike design and flood risk assessment. To reduce the risk of stability failures during flood events, the infiltration rate of a dike should be kept low and the elapsing time to reach the saturated steady state should be long. A number of full-scale physical flood simulation experiments on the Rostock research dike, on which different processed dredged materials were applied in the dike body (cover layers in particular) showed that the infiltration time and rate is much higher as can be expected from comprehensive laboratory test data. To obtain information about the unsaturated/saturated hydraulic soil properties of the installed dredged materials in situ, an automatic multi-objective model calibration method for a minimizing problem is used to reduce the residuals between simulated and observed time series (hydraulic head pressure, suction pressure and rate budget). The measured suction pressure time series of these physical experiments lets us suppose, that it is not possible to simulate the suction pressure behaviour of the installed dredged material using RICHARD’s unsaturated flow equation with a proper water retention function and unsaturated flow conductivity. It seems that the hysteresis effects are negligibly small and the hydraulic behaviour is governed by the inter-aggregate pore structure. In the paper, different back-calculation methods to fit the soil hydraulic parameters to the full-scale measurements are discussed and compared a proposal for the evaluation of the data is provided.

Numerical Simulation for Interaction between the Fracture Surface and the Proppant Column after HiWay Fracturing

HiWay fracturing uses impulse sand to achieve the proppant column supporting the rock wall surface, creating an open flow channel that is more conducive to improving the stimulation effect. The deformation law of the proppant column under the compression of the fracture wall surface is directly related to the effectiveness of the high conductivity fracture. However, the related laboratory physical simulation experiments are challenging to conduct, which restricts the study of the interaction between the fracture surface and the proppant column. In this paper, first, establish the finite element model of the interaction between the fracturing crack and the proppant column, and the variation law of stress-deformation of the crack wall and displacement of the crack wall under the closure stress is analyzed. Furthermore, this paper carries out the quantitative characterization of the active support area of the proppant column. Finally, the accuracy of the simulation results is verified by applying the experimental results of indoor proppant column rock plate compression. The numerical simulation method proposed in this paper can effectively realize the simulation of the interaction between the fracture surface and the proppant column in HiWay fracturing based on real engineering parameters, which lays theoretical and simulation experimental support for improving the effect of channel fracturing stimulation.

Experimental and numerical investigations of accumulated plastic deformation in cement sheath during multistage fracturing in shale gas wells

Sustained Casing Pressure (SCP) has become a serious problem in the development of shale gas fields, which is believed to relate to the multistage fracturing. However, few researches were on this, especially the study of micro-annulus at the interface between the cement sheath and casing, which was one of the mechanisms of the cement sheath integrity failure, and always caused by accumulated plastic deformation. This paper presented experimental and numerical investigations of the emergence and development of plastic deformation occurred at the interface between the cement sheath and casing during multistage fracturing. Mechanical tests and physical simulation experiments were carried out so as to analyze the plastic deformation variation characteristic of the cement sheath under cyclical loading and unloading. 3-D numerical models were established to analyze the emergence and development of the accumulated plastic deformation based on the test results, considering the actual engineering and geological conditions during multistage fracturing in shale gas wells, which presented a new method to calculate the width of the micro-annulus between the cement sheath and casing. The research showed that the numerical results were in accordance with the experimental results. With the increase of cycle times, the accumulated plastic deformation increased, which was the greatest for the first time, and then increased linearly. Decreasing elastic modulus and increasing Poisson's ratio, cohesive force and internal friction angle could facilitate the protection of the cement sheath integrity. Finally, a new cement slurry system was proposed based on the results of study and applied in 5 wells with good effects acquired, none of them showed SCP after fracturing.

Study on Rule of Overburden Failure and Rock Burst Hazard under Repeated Mining in Fully Mechanized Top-Coal Caving Face with Hard Roof

The dynamic disasters caused by the failure of hard roof in the process of mining coal seriously affect the safe production in coal mines. Based on the W1123 mining coal working face of Kuangou coal mine, the physical similar material simulation experiment and acoustic emission (AE) monitoring method are used to study the failure law and AE characteristics of overburden in the process of coal mining. The stress evolution law is revealed through numerical simulation, the dangerous areas and rock burst hazard under the repeated mining with hard roof are studied combined with microseismic monitoring on site. The results show that the energy of W1123 working face released by the overburden damage under B4-1 solid coal is higher than that of the gob, and the peak value of the AE energy appears near the W1145 open-off cut. Through the statistics of the AE data, the large energy rate of AE event is defined, and the AE events with large energy rate appear in the scale of 82.4–231.2 cm within the model. This area is shown as a stress superposition area according to the numerical simulation. On the basis of comparing with the characteristics of energy distribution in the field, it is considered that the main control factors of rock burst in this area are hard roof of the working face and the stress concentration caused by the repeated mining. It provides a scientific guidance for the prevention and control measures of rock burst in this type of mining condition.

Roof Deformation Associated with Mining of Two Panels in Steeply Dipping Coal Seam Using Subsurface Subsidence Prediction Model and Physical Simulation Experiment

This research investigates roof deformation and failure characteristics, as well as mechanical interaction between the panels of the roof strata above two adjacent working faces in a steeply inclined coal seam. Physical modeling with photogrammetry measurement method has been employed in this investigation. The movement of roof strata and section pillar, as well as the stratum morphological characteristics, was quantitatively analyzed. Results show that the roof movement direction above the two panels has zoning characteristics, especially in the lower panel. Roof migration in the lower panel of the working face is larger than that in the upper panel. The roof to floor closure perpendicular to the seam direction is larger than the sliding along the seam. The maximum roof concave and convex bending occurred at the middle and upper parts of both panels; the roof bending in the upper panel mining area indicates a larger mining disturbance induced by lower panel mining. The void ratio contour of the lower panel is an asymmetrically arched shape, which is different from that of the upper panel area. The higher roof strata above the upper panel exhibit separation and breaking, whereas the lower roof exhibits compression due to mining in lower panel. The section pillar is compressed and slides slightly, which aggravates the mechanical interaction between the panels and increases the caving height of the roof over the lower panel and the periodic weighting intensity.

Study on the Evolution Law of Overburden Breaking Angle under Repeated Mining and the Application of Roof Pressure Relief

Aiming at the serious problems caused by coal mine mining activities causing the rock burst accidents, this paper is based on rock mechanics and material mechanics to establish the key layer breaking by the double-key layer beam breaking structural mechanics model of a single working face and double working face under repeated mining. The theoretical calculation formula of the angle was used as the theoretical basis for the elevation angle of the pre-reloading hole of the hard roof. The rationality and reliability of the formula were verified by the physical similarity simulation experiment and the 3 Dimension Distinct Element Code numerical simulation experiment, revealing the rock formation under the influence of repeated mining. The results show that the derived key layer breaking angle formula is suitable for the theoretical calculation of the breaking angle of the key layer of a single coal seam when the repeated disturbance coefficient is λ = 1; when it is λ = 2, it is suitable for the repeated mining of the short-distance double-coal mining. The rationality and reliability of the theoretical formula of the breaking angle of the double key layer of single coal seam and double coal seam were verified by the physical similarity simulation experiment. Through the 3DEC numerical simulation results and theoretical calculation results, the W1123 working face hard top pre-cracking pressure relief drilling elevation angle was 78°. The drilling peeping method was used to verify the results. The results show that the theoretical formula of the critical layer breaking angle is well applied in engineering practice.

Laboratory and field-scale parameter optimization of CO2 huff–n–puff with the staged-fracturing horizontal well in tight oil reservoirs

With the help of large-scale physical simulation experiment technology, the physical simulation experiments of the CO2 huff–n-puff with the staged-fracturing horizontal well could be acheived. We studied the production process of CO2 huff–n–puff and influence of different parameters affect oil recovery during the CO2 huff-n-puff procedure, ultimately, the operation parameters were optimized by numerical simulation. The results show that CO2 can quickly enter the deep formation through the horizontal well and the fracture during the huff period and staged-fracturing horizontal well can greatly increase the contact area between CO2 and crude oil, which improves the efficiency of extraction, dissolution, reduction of viscosity between CO2 and crude oil. During the puff period, the horizontal well and fractures can reduce the flow resistance effectively, so as to improve the flow capacity of crude oil. After 3 cycles of CO2 huff and puff, the oil recovery can be enhanced by 11.13%~21.39% compared with that obtained by elastic flooding, which indicates that the exploitation method of CO2 huff–n–puff can improve the development effects of tight oil reservoirs. CO2 huff-n-puff injection parameters are optimized, the results show that the optimum time of injection is 1 year, the optimum soaking time is 30d, and the optimal injection pore volume is 0.18HCPV. This research can provide a certain technical support for effective development of tight oil reservoirs.

Study on Deformation and Energy Release Characteristics of Overlying Strata under Different Mining Sequence in Close Coal Seam Group Based on Similar Material Simulation

For the characteristics of overburden deformation and energy release under different mining sequences of close-distance coal seam groups, physical material similar simulation experiments were carried out, and comprehensive monitoring methods such as dial gauge, total station, micro-seismic monitor, and pressure sensor were used to test the Guangou Coal Mine. The comparative analysis of the initial mining and the upward recovery of the B4-1 coal seam is carried out to study the migration law, mine pressure distribution, and energy release characteristics of the overlying strata during W1145 mining face mining and residual coal mining. The results show that the maximum subsidence of surface and rock formation caused by re-mining of B4-1 residual coal is 0.96 m and 2.57 m respectively, which is 0.42 m and 0.47 m lower than that of W1145 working face. The boundary angle, moving angle, and rock stratum formed by the upward recovery of the remaining coal seam are 79.3°, 81.1°, and 67.5° respectively, which are smaller than the 80.9°, 82.3°, and 75.8° formed by the first mining. The cumulative development height of the fracture zone caused by upward mining is 115.7 m, which is 8.0% smaller than the cumulative development height of the downstream fracture zone of 125.8 m. When the up-level mining is carried out, the fragmentation effect of the rock layer below the key layer is strong, which makes the loosely broken rock block have a better supporting effect. Therefore, the residual coal mining time is longer than that of the first mining. The initial pressure step of the residual coal recovery is 139.2 m, and the average step of the cycle is 34.2 m, which is significantly larger than the 128.0 m and 26.0 m of the first mining. The loose rock strata that are disturbed by the upward recovery are more likely to be broken. Therefore, there are more micro-seismic events during the re-mining of the remaining coal. The B4-1 residual coals have a total of 945 incidents of re-seismic micro-seismic events, which is 292 more than the W1145 working face. After the B2 coal seam mining disturbance, the energy of some rock layers above the B4-1 coal seam is released, so that the micro-seismic energy caused by re-mining of the remaining coal seam is small. Through microseismic monitoring, it can be concluded that the accumulated energy in the process of upward re-mining of remaining coal seam is less than that in the process of downward mining of W1145 working face. Upward recovery is more likely to cause damage in the disturbed loose rock formation. Therefore, the frequency of micro-seismic events during the upward recovery is higher, and the partial energy release of the rock after the disturbance is caused, so that the source energy generated in the unit length of the upward recovery is smaller than the initial one.

Research and Application of Radial Borehole Fracturing Based on Numerical Simulation

The radial borehole fracturing technology has been applied in a certain number of oilfields with good results being achieved. However, the morphology and variation of fracture still require further study. In this paper, the reservoir model based on formation fluid-solid coupling equation is established with the extended finite element method (XFEM) in ABAQUS, and the fracture morphologies in the single-radial borehole, vertical multiradial borehole, and horizontal multiradial borehole are simulated and analyzed with criteria of maximum principal stress and maximum energy release rate as the damage mechanism. Moreover, the accuracy of numerical simulation results is verified with the large-scale true 3D physical simulation experiment. The results show that the induced stress field along the radial borehole during fracturing is the root cause of fracture directional propagation along the radial borehole whose effective guidance distance reaches 40 m. The vertical multiradial borehole can effectively enhance fracture directional propagation and is capable of reducing fracture initiation pressure. In the horizontal multiradial borehole, the major fracture propagating along each radial borehole is formed in the remote-borehole area, and the secondary fracture connecting the neighboring radial boreholes is formed in the near-borehole zone. Coordination of major and secondary fractures can effectively increase the drainage area and reduce the flow resistance in the near-borehole zone. Based on the research on fracture morphology of multiradial borehole fracturing, the scheme of radial borehole arrangement is optimized and verified through numerical simulation of deliverability. The final optimum borehole arrangement scheme is the intersectional angle of 45° between four orthogonal radial boreholes and horizontal maximum principal stress.

Effect of Fluid Pressure and Pore Structure on Tight Sand Gas Saturation—Evidence from Micro-CT Simulation Experiment

Summary Numerous technical papers have been published on the reservoir evaluation of tight sand gas in recent decades. It is believed that tight sand gas is characterized by low permeability, complex pore structure, abnormal pressure, and low gas saturation. Researchers have characterized tight gas in terms of, for example, statistics; and some of them are increasingly interested in the effect of fluid pressure and pore structure on gas saturation. However, there is still a lack of effective experimental and mechanism analysis. The focus of this paper is to investigate the effect of two factors on controlling the tight gas saturation. A method was proposed for determining the in-situ injection pressure of the DB 2 gas reservoir in the Kuqa area during the gas-accumulation period, and the result was 1.2 MPa. A polyetheretherketone carbon-fiber core holder (maximum temperature 180 °C, maximum confining pressure 30 MPa) was designed for the microcomputed-tomography (CT) simulation experiment. After that, four physical simulation experiments of different fluid pressures (0.1, 0.5, 1.5, and 5.0 MPa) were implemented using X-ray CT and the new core holder to study the effect of fluid pressure and pore structure on gas saturation. The results show that the fluid pressure and micropore connectivity are important factors for gas-saturation increase; the number of gas clusters (connected pores containing gas) increases with the increase of fluid pressure and the maximum volume of gas clusters increases with the increase of pore connectivity. The connected pores with the largest volume are an important source of gas-saturation contribution. The three types of modes (the blowing balloon mode, stitching mode, and composite mode) of microscopic gas-cluster formation are discussed. The blowing balloon mode is key to gas-saturation growth in the period of low fluid pressure or the early stage of the injection process. The stitching mode is key to gas-saturation growth in the period of high fluid pressure or the late stage of the injection process. The above research system investigates the quantitative control of fluid parameters (pressure) and reservoir parameters (pore structure) on gas saturation, which might change the situation where previous research was too focused on the pore-structure and fluid-pressure characterization, with a lack of quantitative control analysis of reservoir gas saturation. It provides a valuable reference and framework for the reader to conduct further quantitative research on tight gas saturation.

Orthogonal Testing on Ratio of Physical Simulation Material Similar to Sandstone

In this paper, the ratio of physical simulation material similar to sandstone was studied through orthogonal testing, which was made up of five levels and four factors (sand-cement ratio, cement ratio, molding loading rate and molding pressure). Physical and mechanical parameters including density, uniaxial compressive strength, elastic modulus and tensile strength of the physical simulation material were obtained by the testing. The key influencing factors and variation rules of physical and mechanical properties of the material were analyzed by range analysis method. The results show that the factors affecting density from large to small are: molding pressure, sand-cement ratio, cement ratio and molding loading rate. The density increases with the increment of both molding pressure and sand-cement ratio. However, the density value decreases slowly with the increment of loading rate, and it does not change significantly with the increment of cement ratio. Uniaxial compressive strength (UCS) is influenced by factors including sand-cement ratio, molding pressure, cement ratio and loading rate. The UCS decreases with the increment of both sand-cement ratio and loading rate, and increase with the increment of cement ratio and molding pressure. Both elastic modulus and tensile strength are influenced by sand-cement ratio, cement ratio, molding pressure and loading rate, too. The elastic modulus and tensile strength decrease with the increment of sand-cement ratio and loading rate, and increase with the increment of cement ratio. Meanwhile, they increase slowly with the increment of molding pressure. The linear regression equations between all considering factors are obtained through the testing, which provide scientific basis for the reasonable selection of the material ratio in the physical simulation experiment.

Non-Linear Regression Method for Instability Problems in Haptic Rendering System

This paper addresses instability problems in 6-DoFs haptic rendering system due do the virtual stiffness technology in haptic device by using non-linear polynomial regression analysis method for haptic feedback value. The method is based on the locally optimized generalized penetration computation algorithm which computes the minimum translational and rotational motion to separate two overlapping objects. The essence of penalty-based haptic rendering method is the stability problem which is the prospect in virtual manipulation and physical experiment simulation. The algorithm which employs the virtual coupling method in order to optimize the haptic feedback value in haptic rendering system. Combining with the non-linear regression method, we get a well-distributed output and stable force feedback. The constructed rendering algorithm can process the complexity polygon-soup models and make no assumption about the underlying geometry topology. The experiment result shows the non-linear regression analysis method can make the haptic system stable and get realistic force feedback.

The Impacts of Nano-Micrometer Pore Structure on the Gas Migration and Accumulation in Tight Sandstone Gas Reservoirs

The uncertainties between reservoir quality and gas migration and accumulation in tight sandstone gas reservoirs are intrinsically attributed to complex microscopic pore structures. Integrated analysis including the physical simulation experiment of gas migration and accumulation, X-ray computed tomography (X-CT), and casting thin section (CTS) were conducted on core plug samples collected from the Upper Paleozoic Permian Lower Shihezi and Shanxi tight sandstone of the Daniudi area in the Ordos Basin to investigate the impacts of pore structure on the gas migration and accumulation. Physical simulation suggested that the gas flows in migration in tight sandstone reservoirs were characterized by deviated-Darcy linear flow and non-linear flow regimes. Minimum and stable migration pressure square gradients determined by application of apparent permeability were employed as key parameters to describe gas flow. Pore structure characterization revealed that the tight sandstone reservoir was characterized by wide pore and throat size distributions and poor pore-throat connectivity. The pore–throat combinations could be divided into three types, including the macropore and coarse throat dominant reservoir, full-pore and full-throat form, and meso-small pore and fine throat dominant form. Comparative analyses indicated that pore and throat radii determined the gas flow regimes by controlling the minimum and stable migration pressure gradients. Gas accumulation capacity was dominated by the connected effective porosity, and the gas accumulation process was controlled by the cumulative effective porosity contribution from macropores to micropores. Variations in pore structures resulted in differences in gas migration and accumulation of tight sandstone reservoirs. The macropore and coarse throat-dominant and the full-pore and full-throat reservoirs exhibited greater gas migration and accumulation potentials than the small pore and fine throat dominate form.

Experimental investigation on the diffusion of carbon fibre composite grouts in rough fractures with flowing water

Although grouting has been widely used in tunnels to seal groundwater inrush and reinforce rock masses, dynamic water grouting in fractured rock remains challenging. Carbon fibre and an additive were added to a traditional cement grout to enhance the sealing efficiency and dynamic water resistance in dynamic water grouting. A series of orthogonal tests and contrast tests were conducted to investigate the effect of the additive and carbon fibre on the solidification time and dynamic water resistance of carbon fibre composite grouts. The results demonstrate that the grout solidification time is shortest when the additive comprises 60% sodium aluminate, 20% sodium silicate, 14% calcium chloride, and 6% cellulose, which is favourable to enhancing the efficiency of dynamic water grouting in tunnels. The dynamic water resistance rapidly increases with the carbon fibre concentration when the carbon fibre concentration is less than 0.4%. Barton Curves were introduced to highlight the effect of fracture surface roughness on the grouting and improve the reliability of the simulation experiment. Physical simulation experiments were conducted to investigate the effects of the initial water flow speed, aperture width (roughness), cement water ratio, and additive concentration on the grout diffusion in rough rock fractures in tunnels using a self-designed simulation device. The results indicate that the diffusion distance of the carbon fibre composite grout increases with the initial water flow speed and decreases with an increase in aperture width, cement water ratio, and additive concentration. The most influential factor is the initial water flow speed. A fitting equation for grout diffusion is obtained to provide references for practical grouting operations in tunnels. The distribution of residual grout suggests that the cement-water ratio and additive concentration should be reduced to promote the diffusion of grout in rock fractures in tunnels when the water flow speed is low.

Experimental research on leaf vein geometric characteristics of multibranch horizontal well for coalbed methane recovery

AbstractThe similarity in the structure and function between leaf veins and multibranch wells provided the inspiration for a novel design of multibranch coalbed methane (CBM) well. The leaf vein structure of leaves was analyzed by leaf specimen scanning and microstructure measurements. Fluorescence labeling experiments were used to study the influence of leaf vein structure on moisture transport, and the geometric characteristics were obtained. A CBM extraction physical simulation experiment was carried out in a custom‐made experimental system. The temporal and spatial evolution of seepage‐temperature fields in reservoir during CBM recovery were studied, and the influence of leaf vein geometric characteristics and how they affected was analyzed. The results indicated that in experimental gas extraction, asymmetrically distributed branch wells improved the CBM recovery 4.02% higher than symmetric structure after 1000 seconds. The reduction in branch well angle leads to the decrease in gas pressure relief. If the branch well angle is reduced by 20°, it reduced by 11.34% after 4000 seconds. When the branch well length increased by 50%, it increased by 28.37%. Coalbed methane recovery effect can be improved by 6.81%, when the distance between branch wells increased by 50%. In the early extraction stage, the reduction in methane pressure and reservoir temperature was positively correlated with the initial methane pressure, but they were less affected in the later stage.