Seepage Flow Characteristics Research Articles

Pore-fracture structures and seepage flow characteristics during spontaneous coal combustion based on CT 3D reconstruction

To study the evolution characteristics of the pore-fracture structures and seepage properties of coal in the process of spontaneous combustion, a high-temperature tube furnace was used to heat the coal samples. The coal samples were scanned using Xray-CT scanning technology, and the CT 3D reconstruction technology was used to extract the 3D pore structure and equivalent pore network model of each group of coal samples. Firstly, the specific surface area and volume of pore cleavage is statistically characterized; the change rules of Ep, Et, Lc, and Cn are quantitatively analyzed. At 200 °C, the coal body produces a large number of pore fractures, the development of coal samples is more significant, and the pore-specific surface area and the number of pore throats reached their maximum value. In addition, the changes of fractal dimension, porosity, connectivity, and permeability of coal with temperature were discussed, and the best permeability of the coal was achieved at 200 °C. The connectivity and permeability were weakened with the further increase of temperature, and the structural changes had a close influence on the gas seepage pressure and seepage flow rate. The results of the study provide important engineering guidance for deepening fire prevention in coalfields.

Experimental study on seepage flow characteristics of leaked molten salt in foundation fillers in concentrating solar power plants

AbstractThe leakage of molten salt storage tanks in concentrating solar power plants has attracted much attention. This paper focused on seepage and migration characteristics of molten salt in the thermal‐steady foundation fillers with different configurations after leakage occurs through a self‐built experimental system modeling the actual leaking process. The results show that the thermal insulation of light expanded clay aggregate (LECA) as foundation fillers is better than that of sand and gravel. When the operating temperature is 565°C, the average temperatures of each layer of LECA, sand, and gravel are 131.73°C, 141.91°C, and 149.27°C, respectively. And the seepage depths in light expanded clay aggregate, sand, and gravel are 482 mm, 223 mm, and 270 mm, respectively. It is found that the seepage depth of molten salt distinctly increases with higher operating temperature in all kinds of fillers. Nevertheless, the seepage depth of molten salt in the multi‐layer fillers diminishes with the increase of the thickness of the sand or gravel layer. The results obtained from this research would be helpful for the engineering design of storage tank foundations and reduce economic losses and the complexity of accident handling.

Study on the microscopic pore structures of the four different kinds of lithological reservoirs in the basin of Western China

In the basin of western China, four different kinds of lithological reservoirs are developed, including low-permeability sandstone, sedimentary tuff, shale and volcanic rock. There is generally a large difference in the micropore structure characteristics and distribution laws due to different reservoirs. The reserving capacity as well as the porous flowability, mechanism and laws are determined by the micropore structure characteristics and distribution laws of hydrocarbon reservoirs. Low-temperature nitrogen adsorption and desorption technology, high-pressure mercury injection experiment and nuclear magnetic resonance (NMR) testing technology are applied to study the micropore size, quantity, structure and distribution laws of four different kinds of lithological reservoirs as well as their similarities and differences of corresponding relation with macroporosity–permeability physical parameters. This paper also studies the movable fluid and nonlinear seepage flow characteristics of four different kinds of lithological reservoirs.

Experimental investigation on macro-mesoscopic characteristics of seepage flow in transparent porous media

Aiming to investigate the macro-mesoscopic characteristics of seepage flow in porous media, flume experiments have been conducted with the visualization technology. As comparisons, a series of numerical simulations were performed. The results show that the local flow regime of seepage in porous media can be different from the global flow regime. It is found that the seepage velocity in the middle region is lower than that near the wall of flume. This phenomenon is more obvious in the upper part of the porous media. It is proved by both numerical simulations and experiments that the small deviations in the size and position of internal pores are the reason for different flow characteristics between the local and global seepage fields.

Pore characteristics analysis and numerical seepage simulation of antifreeze permeable concrete

The study of pore structure and seepage flow characteristics can help to reveal the structural and functional performance of permeable concrete from the macroscopic pores. This research aims to investigate the pore structure features and seepage characteristics of fiber-reinforced permeable concrete called antifreeze permeable concrete (AFPC) based on the images obtained by computer tomography (CT) and computed fluid dynamics method (CFD). The results show that the CT scanning and digital image processing technology is an efficient way to analyze the 2D and 3D pore structure of AFPC. 2D planar porosity and 3D connected porosity can generally represent the actual total porosity and connected porosity, respectively. The distribution of 2D Feret diameter and 3D equivalent diameter is in accordance with the normal distribution. The pore structure of AFPC shows fractal features of self-similarity and scale invariance. The fractal dimension shows a linear relationship with 2D planar porosity. CFD method can be applied on the generated 3D connected pore models to reveal the distribution of pressure and velocity in the pores of AFPC during seepage process. The relationship between seepage velocity and pressure gradient is described by Darcy’s law and Forchheimer’s law and the critical Reynolds numbers for AFPC with different pore structure are obtained.

The seepage flow characteristics of hydrophobically associated polymers with different aggregation behaviours in porous media.

The polymer solution for oil displacement is subjected to strong shear action in practical application, and this action will affect its percolation characteristics in porous media. The effects of mechanical shearing on the solution properties and seepage characteristics of modified hydrophobically associated polymers and dendrimers with two different aggregation behaviours were studied. The results showed that mechanical shearing did not affect hydrophobic microzones. Polymers can re-associate to restore part of the network structure, thereby improving shear resistance (dendritic hydrophobically associating polymers > hydrophobically modified partially hydrolysed polyacrylamide). Polymers with ‘cluster’ aggregation behaviour enhanced solution performance, enabling them to establish higher resistance coefficient (RF) and residual resistance factor (RRF) in porous media but also bringing about injection difficulties. Increasing the injection rate would increase the injection pressure, but the established RF and RRF showed a downward trend. Mechanical shear pretreatment effectively improved the injectability of the polymer. To achieve polymer injection and flow control, pre-shearing polymer solution and low-speed injection can be used in field applications.

Effects of boundary layer and stress sensitivity on the performance of low-velocity and one-phase flow in a shale oil reservoir: Experimental and numerical modeling approaches

Seepage flow is important because it is useful for production optimization and well spacing decisions. In this study, an enclosed high-precision seepage flow apparatus is used to determine the seepage flow characteristics of the Qianjiang shale reservoir in China under various pressures from 3 MPa to 24 MPa. The results revealed that the seepage flow curve has an inverse-spoon shape, which is completely different from the results for low-permeability and tight sandstone reservoirs, as reported in the literature. In addition, according to the full-scale pore size distribution technique, the modular automated processing system (MAPS), and the nuclear magnetic resonance (NMR) T2 spectrum before and after the seepage flow experiments, the seepage flow characteristics of the Qianjiang shale oil reservoir were not only caused by the boundary effect, but also dependent upon the stress sensitivity. It was also found that micro-fractures or macro-pore were compressed as the effective stress increased in the experiment. Moreover, a new non-Darcy model for a shale reservoir was derived, and the model was verified using experimental data. This model demonstrated it would be a good candidate for quantitative evaluation of affecting factors. It can also be applied to determine the main controlling factor. The calculated results showed that the shape of the nonlinear flow portion of the seepage flow curve for the Qianjiang shale oil reservoir was primarily dependent upon the effect of stress sensitivity. However, the linear flow portion of the seepage flow curve was dependent upon the combined effects of stress sensitivity and the boundary layer. Therefore, from the enhanced individual-well production point of view, the control of production pressure drops and selection of rational well spacing is important for the effective development of shale oil reservoirs.

On Ground Water Flow to an Imperfect Gallery: Case of Evaporation from a Free Surface

The plane steady-state filtration in a phreatimetric formation to an imperfect gallery in the presence of evaporation from the free surface of groundwater is considered. In order to study the evaporation effect, a multiparameter mixed boundary-value problem of the theory of analytic functions is posed and solved by the Polubarinova-Kochina method. Based on the proposed model, we develop an algorithm to compute the seepage flow characteristics and provide the hydrodynamic analysis of the impact of the dependences of all the physical parameters of the scheme on the flow rate of the gallery and the ordinate of the exit point of the depression curve on an impermeable screen.

A Study on the Seepage Flow Characteristics and Disaster‐Causing Mechanism of Collapse Column

Factors such as the hydrogeological conditions, the lithological characteristics of the columns’ components, and the lithological characteristics and stress conditions of the coal seam roof and floor are interrelated and jointly affect column collapse. In this study, the disaster‐causing mechanism of column collapse was studied. Based on the system theory, a collapsed column is divided into the column and the surrounding fissure zone as two subsystems for analysis. And, the permeability coefficient of the broken rock under different conditions was measured by a self‐designed equipment. The variations of the permeability coefficient for rock samples with different particle diameters, different axial pressures Pa, and different seepage velocities were further studied. Through phenomena analysis and experimental data processing, it was concluded that, under the same pressure state, smaller particle diameter meant smaller permeability coefficient; with the increase of axial pressure, the permeability coefficient decreased; and the larger the water flow velocity was, the smaller the permeability coefficient became. For particle diameter Φ = 2.5–5 mm or larger, the tiny particles formed by randomly washing and breaking in the water flow blocked some of the channels. For particle diameters smaller than Φ = 2.5–5 mm, the smaller permeability coefficient was attributed to the turbulence resulting from non‐Darcy flow. The study on the permeability of the fractured rock mass clarified the mechanism of water inrush from the fissure zone of the collapsed column: the collapsed column itself was impermeable, and the permeability of the fissure zone around the collapsed column was related to the lithological characteristics of the rock within the fissure zone and the sequencing of rock strata. When mining coal in areas with collapsed columns, experiments on collapsed columns and fissure zones are prerequisites. This study has a certain referential value for coal mining in this region.

Seepage flow characteristics and ability for enhanced oil recovery based on ultra high molecular weight partially hydrolysed polyacrylamide

Seepage flow characteristics and ability for enhanced oil recovery based on ultra high molecular weight partially hydrolysed polyacrylamide

Seepage flow characteristics and ability for enhanced oil recovery based on ultra high molecular weight partially hydrolysed polyacrylamide

The ultra high molecular weight partially hydrolysed polyacrylamide (UHMW-HPAM) has captured much attention because of its good thickening property and rheological behaviour. In this paper, the seepage property, dynamic retention capacity and effective viscosity of UHMW-HPAM are studied and compared with traditional partially hydrolysed polyacrylamide (HPAM). The results indicate that the UHMW-HPAM can build stronger flow resistance in porous medium than HAPM, but the effective viscosities of UHMW-HPAM and HPAM have few discrepancies. It is because the retention capacity of UHMW-HPAM is generally higher than that of HPAM under the same conditions. The result also confirms that the molecular weight has no significant influence on effective viscosity. The abilities to improve oil recovery of chemical flooding based on UHMW-HPAM and HPAM were also investigated. When the permeability ratio is approximately 5.0, the ability of alkaline-surfactant-polymer (ASP) flooding based on UHMW-HPAM to increase oil recovery is far better than that of ASP system based on ordinary HPAM. [Received March 5, 2015; Accepted November 23, 2015]

Experimental and modeling study of CO2 - Improved gas recovery in gas condensate reservoir

Abstract This paper presents the effectiveness of the CO 2 injection process at different periods during gas-condensate reservoir development. Taking a real gas-condensate reservoir located in China's east region as an example, first, we conducted experiments of constant composition expansion (CCE), constant volume depletion (CVD), saturation pressure determination, and single flash. Next, a series of water/CO 2 flooding experiments were been investigated, including water flooding at present pressure 15 MPa, CO 2 flooding at 25.53 MPa, 15 MPa, which repents initial pressure and present pressure respectively. Finally, the core flooding numerical model was constructed using a generalized equation-of-state model reservoir simulator (GEM) to reveal miscible flooding mechanism and the seepage flow characteristics in the condensate gas reservoir with CO 2 injection. A desirable agreement achieved in experimental results and predicted pressure volume temperature (PVT) properties by the modified equation of state (EOS) in the CVD and CCE tests indicated that the proposed recombination method can successfully produce a fluid with the same phase behavior of initial reservoir fluid with an acceptable accuracy. The modeling results confirm the experimental results, and both methods indicate that significant productivity loss can occur in retrograde gas condensate reservoirs when the flowing bottom-hole pressure falls below dew point pressure. Moreover, the results show that CO 2 treatment can improve gas productivity by a factor of about 1.39 compared with the water flooding mode. These results may help reservoir engineers and specialists to restore the lost productivity of gas condensate.

Simplified approximation for seepage effect on penetration resistance of suction caissons in sand

ABSTRACTDuring the installation process of suction caisson in sandy seabed, the applied suction not only produces a downward driving force, but also decreases the penetration resistance to the caisson. In this paper, numerical studies were performed to investigate the characteristics of seepage flow around the caisson as well as its effects on the wall friction and the caisson tip resistance. A simplified approximation method was proposed to predict the reduction of penetration resistance. In particular, for the case of sandy seabed interbedded by a layer of low-permeability soil, the seepage flow will be suppressed with the caisson tip getting closer to the low-permeability layer. The seepage flow around the caisson was first studied, and then a new approximation for the seepage-induced resistance reduction, considering the effect of low-permeability layer, was proposed for the engineering practice.

Study on Physical Simulation of Polymer Flooding System in the Block of Liaohe Oilfield

Through the method of physical simulation, the seepage flow characteristics of polymer solution with different mass concentrations were studied, which polymer is from Daqing Refining & Chemical Company with molecular weights of 9.7 million, 19 million, 25 million. In the condition of same slug combinations, the displacement effect of polymer solution with different mass concentrations and molecular weights were studied. The results show that the polymer solution (molecular weight is 1.9×107, concentration is 1500mg/L) has a good match with the artificial core of this tract; and with the increase of polymer molecular weight, oil recovery of chemical flooding and total recovery raise up; in the condition of the same molecular weight, the oil recovery of chemical flooding will increase with the polymer mass concentration.

Numerical analysis of seepage flow characteristic of collapse column under the influence of mining

Based on the importance of fractured rock mass seepage research, in order to analyze seepage flow characteristics of collapse column under the influence of mining, a method by embedding fractured rock mass flow solid coupling relationship into FLAC3D internal flow models is presented according to fluid–solid coupling theory and strength criterion. A calculation model of numerical analysis was established, and the influences of mining pressure and plastic damage to pore water pressure and seepage vector change rule were studied. The results show that collapse column is the main channel of confined water seepage upward. The impact is not big when the workface is away from the collapse column. But when the workface is nearing a collapse column, there will be a seepage channel on a side near the workface, in which seepage vector and head are comparatively large. With workface pushing through collapse column, the seepage channel transfers to the other side of the column. In addition, when the plastic damage area within the collapse column breaks through, a “pipeline flow” will be formed within the column, and seepage field will change remarkably and the possibility of water bursting will be greater.

Stability of two consecutive floors with intermediate filters

A subsidiary weir is proposed to be constructed downstream of each of the existing barrages on the Nile river in Egypt to secure its stability, which might have been affected after the construction of the Aswan High Dam. The present paper is intended to investigate the characteristics of seepage flow beneath two structures with an intermediate filter. The downstream structure (the proposed weir) has a slopping middle apron and two flat aprons in the upstream and downstream sides and is also provided with upstream and downstream cutoffs. The upstream structure (the existing barrage) has upstream and downstream cutoffs. A conformai mapping technique is used to solve the problem. Equations to calculate the uplift pressure distribution acting on both the existing barrage and the suggested weir are obtained; also equations to calculate the values of exit gradient along the intermediate filter and the downstream bed are derived. The seepage flows which seep into and/or drained f r om the intermediate filter are estimated. The analytical results are verified using experimental measurements performed on electrical analogue model and a very good agreement is noticed. A computer program is designed to compute the seepage flow, the uplift pressure and the exit gradients.