Seepage Pressure Research Articles

Shale Gas Pseudo Two-Dimensional Unsteady Seepage Pressure Simulation Analysis in Capillary Model

Shale gas is rapidly growing as a source of natural gas in China. Compared with the conventional gas reservoir, the shale gas reservoir is characterized by low porosity, low permeability, and adsorbed gas, making the flow mechanism of shale gas reservoir more complex. In this study, we investigated six factors influencing the gas flow: the Darcy flow, the slippage effect, the Knudsen diffusion effect, the desorption of gas on pore walls, the diffusion effect of gas in organic matter, and the matrix deformation effect. We simplified gas flow in the development process to only include gas flow in the capillaries and then considered the six influence factors. This study establishes a shale gas pseudo two-dimensional unsteady capillary seepage mathematical model based on the continuity equation, using the implicit difference method to solve the mathematical model. Certain capillary parameters were added to the calculation, and the study analyzed the effect of the different factors on both the pressure distribution and the cumulative gas production. Results show that the Knudsen diffusion effect and the desorption of gas from pore walls have lower impact on the pressure than the others factors. The diffusion effect of gas in organic matter, the slippage effect, and the matrix deformation effect have a stronger impact on the pressure. The gas in organic matter continuously diffuses into the capillary with the increasing of the production time, and the pressure drop becomes slow because of the gas diffusion.

Seismic response of fluid–structure interaction of undersea tunnel during bidirectional earthquake

In this study, the seismic response of the fluid–structure interaction (FSI) of an undersea tunnel in a broken fault zone during a bidirectional earthquake is examined. An undersea tunnel FSI model that accounts for the effects of the viscoelastic artificial boundary, seepage, and dynamic liquid pressure, and considers the rock mass as a saturated porous medium, is created through finite element analysis software ADINA. The seismic response of the undersea tunnel is determined by considering both horizontal and vertical ground motion and analyzing the time history curve of the displacement, acceleration, and principal stress of the lining key point. Numerical results show that (1) the maximum displacement, acceleration, and tensile stress of the lining structure are all present in the vault area; (2) the time history curves of the displacement, acceleration, and principal stress of the key points follow a similar variation law; (3) the vertical displacement of the lining structure is greater than its horizontal displacement; and (4) tensile areas generally appear in the vault and inverted arch, but the hance is in the compression state.

Numerical analysis of THM coupling of a deeply buried roadway passing through composite strata and dense faults in a coal mine

Because of the reduction in shallow-buried coal resources, increasingly coal mines in China extend to deep resources. The coupling of thermal-hydro–mechanical (THM) fields is much more complicated in deep strata, especially when the roadway passes through composite strata and dense faults. High ground pressures, high ground temperature and high seepage pressure are most important features of deep strata. In order to investigate the THM coupling mechanism of deeply buried roadways, this article presents the geological features of deep strata and analyzes the interactions among thermal, hydraulic and mechanical fields considering the water-weakening effect of the surrounding rock. Finally, the THM coupling process of a deeply buried roadway passing through composite strata and dense faults is simulated. The deformation characteristics and distribution of the stress field are described in the results.

Performance of the Inducing Joints in <i>Xiaowan</i> Arch Dam with Reservoir Impounded to Normal Water Level

To reduce the tensile stress at dam heel, inducing joints have been set in Xiaowan arch dam; they were designed to work without water pressure. After the reservoir was impounded to the normal water level of E.L.1240m, monitoring data showed that almost half of the inducing joints were working with water pressure, but leakage remained small. It also indicated the opening and shear deformation of all the inducing joints were small, and the joint surface remained in compression although the compressive stress was decreased by 2.03MPa~9.29MPa. So it can be concluded that the inducing joints are generally working at closing and compressive state. However, some abnormalities were detected: large seepage pressure and increasing crack width in block No.16 which is at the right end of the inducing joints; 5 small cracks appeared with leakage water at the downstream inner surface of the inspection gallery of the inducing joint in block No.22. Therefore, close attention has to be paid to the crack propagation around the inducing joints for the safety monitoring in future.

The Seepage Pressure Distribution and the Capacity of Low-Permeability Reservoirs Gas

Low-permeability gas reservoirs are influenced by slippage effect (Klinkenberg effect) , which leads to the different of gas in low-permeability and conventional reservoirs. According to the mechanism and mathematical model of slippage effect, the pressure distribution and flow state of flow in low-permeability gas reservoirs, and the capacity of low-permeability gas well are simulated by using the actual production datum.

Experimental Study on Three Dimensional Coupled Stress-Seepage Law of Single Fracture

Equation of three dimensional stress, seepage pressure and permeability coefficient was obtained by theoretical analysis. Applying the true triaxial rock testing system of coupled stress-seepage, seepage test of granite sample with prefabricated single fracture was made under three dimensional coupled stress-seepage. The results show that three dimensional stress have the inhibition effect on single fracture seepage, and the normal main stress, having the leading role, obviously influences the permeability coefficient; seepage pressure has the promote effect on single fracture seepage, resisting the normal main stress. Fitting formula of granite permeability coefficient was gained under coupled stress-seepage which indicated the exponential relationship between permeability coefficient and three dimensional stress and seepage pressure.

Researches of the Differential Fiber Bragg Grating Seepage Pressure Sensor

Seepage pressure is the pressure of pore fluid inside soil, which directly influences the stability state of engineering structure. A differential fiber Bragg grating seepage pressure sensor is developed, in which two fiber Bragg gratings are respectively pasted on the top and bottom surfaces of the uniform intensity cantilever. Acted as the seepage pressure measurement cavity, the free end of metal bellows is connected to the cantilever girder free end. Under the pressure of pore fluid function, the engender axial displacement of metal bellows is converted to the deflection change of cantilever girder free end, which generates the wavelength shifts of two pasted fiber Bragg gratings. The experiment results of pressure loading and unloading show that the sensitivity of the sensor is 1.96 nm/ MPa, the repeatability error is 2.27% FS, and the nonlinear error is 1.7% FS.

Online Monitoring System of Tailing Dam Seepage Line in Abominable Weather

Tailings pond is a high potential energy artificial debris flow dangerous source. Once break, it will bring great harmless. Plant the seepage pressure meter in tailing dam thin section and use lightning protection and intelligence power supply unit which can adapt to extreme weather conditions. The people in site duty room can obtain the real time data, which is acquired by data acquisition unit (MCU) and transmitted by GPRS wireless. The government administration departments and enterprise leaders can also very quickly and easily watch it through the Internet. It will provide a reliable guarantee for the normal operation of the mining enterprises. This project has a innovation point of high reliability distributed intelligent power device, which can adapt to extreme weather conditions.

Elastoplastic Analysis of Surrounding Rocks of Submarine Tunnel with Consideration of Seepage

AbstractBased on the twin shear unified strength theory, the analytical equations for calculating stress, displacement, radius of plastic zone, and characteristic curve equation of surrounding rock in circular submarine tunnels were proposed under the condition of fluid-solid coupling. As the tunnel is usually located under high water pressure, the effective stress of surrounding rock will be reduced for high pore water pressure and seepage pressure according to the calculation results. This may bring about the arch formation and lower stability of strata. Moreover, intermediate principal stress has a certain influence on the stress, displacement, and radius of the plastic zone of surrounding rock. Hence, it is necessary that seepage and intermediate principal stress are rationally considered in the surrounding rock stability analysis and the lining structure design of submarine tunnels because this is beneficial for maximizing the strength of the surrounding rock. Selecting reasonable strength criterion ...

Stability analysis of the slope around flood discharge tunnel under inner water exosmosis at Yangqu hydropower station

The stability of the slope around a flood discharge tunnel is influenced by the space topography, the geological structure, the seepage of the flood discharge tunnel, the rainfall and so on, which introduce complexity and uncertainty to the problem of slope engineering. For slope stability analysis at the outlet of a flood discharge tunnel affected by high interior hydraulic pressure, the inner water exosmosis (IWE) phenomenon will become obvious, the rock’s mechanical properties will be changed, and the seepage effects of the flood discharge tunnel should be focused on. In this paper, a complicated three-dimensional (3D) numerical simulation and safety assessment of the slope around the flood discharge tunnel at Yangqu hydropower station is implemented in FLAC3D, and 3D slide arcs of good shape are obtained. When calculating the safety coefficient of slopes, the Shear Strength Reduction Technique (SSRT) is adopted, and a factor of safety (FOS) is then found. It is found that the FOS of the natural slope is 1.43 in its original condition, and in this case, the slope is in a stable state. The safety factor of the slope is 1.30 after the slope excavation without considering IWE. Under the condition of normal seepage from inside the tunnel to the outside, the safety factor is 1.29. For investigating the influence of IWE on the slope stability, we design three types of scenarios – minimal seepage, normal seepage and serious seepage – for the fluid–solid coupling calculation. Under the serious seepage condition, the safety factor of the slope is 1.26, and it is in a critical failure state. It should be pointed out that uncertainties in input parameters are not researched in this paper. There is not big difference among safety factors under different scenarios mainly because the maximum of inner water head of the flood discharge tunnel is only about 80m. It still can be found that seepage action has an effect on the stability of the whole slope from calculation results. The stress concentrated region (SCR) near the surrounding rock grows from inside to outside as the seepage intensity increases. The surrounding rock will experience more water pressure and seepage pressure, and, at the same time, the area of the plastic zone grows. Suitable treatments and suggestions are discussed to eliminate the adverse effects of IWE. The research results in this paper can provide a reference for construction, reinforcement and drainage design of the slope in similar hydropower slope engineering scenarios.

Shale Gas Seepage Mechanism and Pressure Dynamic Characteristics Research

The shale gas reserves could bring huge economic benefits. Therefore, many domestic and international scholars had researched it in all aspects. The research of seepage mechanism is mostly based on double seepage medium, they think gas spread directly into the fracture system when gas instantaneous desorbing from adsorption medium surface. However, the processing method is not very appropriate, because a certain amount of free gas present in rock matrixes pores. In order to describe the flow process accurately, this paper proposed a new concept of triple porous media, established a new model of shale gas seepage and solved the mathematical model by using Laplace transform and Stehfest numerical inversion. Finally figured out pressure dynamic response curves and analyzed the influence of all parameters on these curves.

Predicting piezometric water level in dams via artificial neural networks

The safety control of dams is based on measurements of parameters of interest such as seepage flows, seepage water clarity, piezometric levels, water levels, pressures, deformations or movements, temperature variations, loading conditions, etc. Interpretation of these large sets of available data is very important for dam health monitoring and it is based on mathematical models. Modelling seepage through geological formations located near the dam site or dam bodies is a challenging task in dam engineering. The objective of this study is to develop a feedforward neural network (FNN) model to predict the piezometric water level in dams. An improved resilient propagation algorithm has been used to train the FNN. The measured data have been compared with the results of FNN models and multiple linear regression (MLR) models that have been widely used in analysis of the structural dam behaviour. The FNN and MLR models have been developed and tested using experimental data collected during 9 years. The results of this study show that FNN models can be a powerful and important tool which can be used to assess dams.

Evolution Procedure of Multiple Rock Cracks under Seepage Pressure

In practical geotechnical engineering, most of rock masses with multiple cracks exist in water environment. Under such circumstance, these adjacent cracks could interact with each other. Moreover, the seepage pressure, produced by the high water pressure, can change cracks’ status and have an impact on the stress state of fragile rocks. According to the theory of fracture mechanics, this paper discusses the law of crack initiation and the evolution law of stress intensity factor at the tip of a wing crack caused by compression-shear stress and seepage pressure. Subsequently, considering the interaction of the wing cracks and the additional stress caused by rock bridge damage, this paper proposes the intensity factor evolution equation under the combined action of compression-shear stress and seepage pressure. In addition, this paper analyzes the propagation of cracks under different seepage pressure which reveals that the existence of seepage pressure facilitates the wing crack’s growth. The result indicates that the high seepage pressure converts wing crack growth from stable form to unstable form. Meanwhile, based on the criterion and mechanism for crack initiation and propagation, this paper puts forward the mechanical model for different fracture transfixion failure modes of the crag bridge under the combined action of seepage pressure and compression-shear stress. At the last part, this paper, through investigating the flexibility tensor of the rock mass’s initial damage and its damage evolution in terms of jointed rock mass's damage mechanics, deduces the damage evolution equation for the rock mass with multiple cracks under the combined action of compression-shear stress and seepage pressure. The achievement of this investigation provides a reliable theoretical principle for quantitative research of the fractured rock mass failure under seepage pressure.

A New Apparatus for Evaluation of Contact Erosion at the Soil–Structure Interface

Abstract The interface between clay core-wall and concrete cut-off wall is one of the weakest parts of high earth and rockfill dams. An unsuitable design can cause contact erosion at the interface or shear failure surfaces, and eventually this will harm the safety of the dam. A new soil–structure contact erosion apparatus was developed for the evaluation of contact erosion at the interface under high stress, high hydraulic head, and large shear deformation. It consists of a soil–structure model base, a seepage pressure system, a confining pressure system, an axial pressure system, and a data acquisition system. The seepage pressure system simulates the seepage erosion effect at the interface, and the maximum seepage pressure is 2.0 MPa. The confining and axial pressure systems simulate the triaxial stress state of the interface and the large shear deformation of the soil structure; the maximum confining and axial pressures are 2.0 MPa and 4.0 MPa, respectively. The data acquisition system can monitor pore pressure dissipation and settlement. Two repeatable experiments on the interface between a kind of highly plastic clay and a concrete cut-off wall were conducted to verify the scientific utility of the new apparatus. The new apparatus was found to be capable of yielding fairly consistent results in repeatable experiments. The new apparatus will prove an effective tool for studying a reasonable connection form of concrete cut-off wall and core wall in high earth and rockfill dams.

Effect Evaluation of Foam System with Dripping Injection Foaming Agent in CO2 Flooding Reservoir

In order to research the effects of the concentration of foaming agent and gas-liquid ratio on the steady seepage pressure of the foam, surfactants of HY-3 and HABS are used as foaming agents in this paper. And compared with the steady seepage pressure of the process of injecting CO2 individually and injecting CO2 accompany with dripping water, the results shows that these two kinds of foaming agents both can solve the problem of injecting gas breakthrough and injecting water difficultly, and the effect of HY-3 is better than that of HABS. By the evaluation experiment of the effect of the foam system which was applied in the ultra low permeability reservoirs with crack, it can be seen that these two kinds of foaming agents both can play the role of adjusting gas injection profile. The plugging ability and shunting effect of HY-3 is superior to that of HABS.

Multiplexed FBG Monitoring System for Forecasting Coalmine Water Inrush Disaster

This paper presents a novel fiber-Bragg-grating- (FBG-) based system which can monitor and analyze multiple parameters such as temperature, strain, displacement, and seepage pressure simultaneously for forecasting coalmine water inrush disaster. The sensors have minimum perturbation on the strain field. And the seepage pressure sensors adopt a drawbar structure and employ a corrugated diaphragm to transmit seepage pressure to the axial strain of FBG. The pressure sensitivity is 20.20 pm/KPa, which is 6E3 times higher than that of ordinary bare FBG. The FBG sensors are all preembedded on the roof of mining area in coalmine water inrush model test. Then FBG sensing network is set up applying wavelength-division multiplexing (WDM) technology. The experiment is carried out by twelve steps, while the system acquires temperature, strain, displacement, and seepage pressure signals in real time. The results show that strain, displacement, and seepage pressure monitored by the system change significantly before water inrush occurs, and the strain changes firstly. Through signal fusion analyzed it can be concluded that the system provides a novel way to forecast water inrush disaster successfully.

Effects of temperature and pressure differences on water seepage in breccia

Effects of temperature and pressure differences on water seepage in breccia were investigated by using the physicochemical seepage instrument. The results show that the relationship of flow and pressure differences can be expressed by a linear equation, and the seepage coefficient is linearly correlated with temperature. The relationship between seepage flow and temperature could be described with the linear equation. The constant and temperature seepage coefficient showed a linear relation with pressure. Binary quantitative equation for the seepage flow, temperature and pressure was obtained, and explained with experimental data and theoretical analysis.

Deformation Characteristics of a Preexisting Landslide in Reservoir Area during Reservoir Filling and Operation

A monitoring system was implemented to monitor the hydrodynamic and deformation response of a preexisting landslide in the Three Gorges Reservoir area. The monitoring results indicate that the deformation is mainly caused by reservoir impounding and is mainly composed of the deformation of the slip band. The effect of reservoir level fluctuation on landslide stability mainly depend on two aspects, one is the change of shear stress and shear strength on the slip surface due to the change of slide body weight and pore water pressure, the other is seepage pressure.

Analysis on Strength of Fractured Rock Mass under Seepage Pressure

According to the rapture mechanics, model of fractured rock mass under crevice water pressure is established to deduce the formula of stress intensity factor at the cracks tip under mutual effect of remote stress and seepage pressure by superposition principle based on which the mutual effect of adjacent cracks is further studied. The result shows that, the mutual effect of cracks have large effect on the stress field of crack tip if the intervals of cracks are small. There are two effect zones after different superposition of stress fields, that is, reinforcing zone and receding zone of stress intensity. When adjacent cracks’ tips are located in reinforcing zone, the stress intensity factor of the crack will grow or reduce if opposite. The mutual effect of cracks is concerned with the interval between, as the interval grows, the intensity factor tents to a constant which is considered as intensity factor of single crack without mutual effect of cracks. Therefore, when the interval is larger than the length of cracks, mutual effect of adjacent cracks can be ignored. Meanwhile, the seepage pressure effect the stress field at the tip of cracks obviously. The KI of each crack tip grow while the seepage pressure grows (-KI reduce), this demonstrates that seepage pressure counterbalanced part of the normal stress at the crack surface, which provides theoretical basis of establishing Rupture instability mechanism of fractured rock mess under seepage pressure.

Creep properties and permeability evolution in triaxial rheological tests of hard rock in dam foundation

Triaxial creep tests were carried out under seepage pressure by using rock servo-controlled triaxial rheology testing equipment. Based on experimental results, rock rheological properties influenced by seepage−stress coupling were studied, and variations of seepage rate with time in complete creep processes of rock were analyzed. It is shown that, when the applied stress is less than failure stress level, the creep deformation is not obvious, and its main form is steady-state creep. When applied stress level is greater than or less than but close to fracture stress, it is easier to see the increase of creep deformation and the more obvious accelerative creep characteristics. The circumferential creep deformation is obviously higher than the axial creep deformation. At the stage of steady-state creep, the average of seepage flow rate is about 4.7×10^(−9) m/s at confining pressure (σ3) of 2 MPa, and is about 3.9×10^(−9) m/s at σ3 of 6 MPa. It is seen that the seepage flow rate at σ3 of 2 MPa in this case is obviously larger than that at σ3 of 6 MPa. At the stage of creep acceleration, the seepage flow rate is markedly increased with the increase of time. The variation of rock permeability is directly connected to the growth and evolution of creep crack. It is suggested that the permeability coefficient in complete creep processes of rock is not a constant, but is a function of rock creep strain, confining pressure, damage variable and pore water pressure. The results can be considered to provide a reliable reference for the establishment of rock rheological model and parameter identification.