Numerical simulation of migration–accumulation of oil resources

Numerical simulation of oil migration and accumulation is to describe the history of oil migration and accumulation in basin evolution. It is of great value to the evaluation of oil resources and to the determination of the location and amount of oil deposits. This thesis discusses the characteristics of petroleum geology and permeation fluid mechanics. For the three-dimensional problems of Dongying hollow of Shengli Petroleum Oil Field, it puts forward a new model and a kind of modified method of upwind finite difference fractional steps implicit interactive scheme. For the famous hydraulic experiment of secondary migration–accumulation, the numerical simulation test has been done, and both the computational and experimental results are basically identical. For the actual problem of Dongying hollow, the numerical simulation test and the actual conditions are basically coincident. Thus, the well-known problem has been solved.     

A hybrid discrete–finite element model for numerical simulation of geomaterials

A hybrid discrete–finite element model is introduced for simulation of mechanical behavior of geomaterials. The soil or rock is modeled as a system of discrete balls that interact through normal and shear springs. The balls can be bonded at the contact points to withstand the applied deviatoric stresses. The important feature of this model is that the confining walls that can be imagined for example as the surrounding membrane or the mold in a physical test are modeled by deformable finite elements. This allows simulation of laboratory test features more realistically compared to the situations where the surrounding walls are rigid. The relationships between micro- and macro-properties are investigated in this paper as well. These relationships and the corresponding curves are helpful tools in calibration of the numerical model for the macroscopic elastic properties.     

Numerical simulation of carbon dioxide migration in a sandstone aquifer considering the fluid–solid coupling

Very limited investigations have been done on the numerical simulation of carbon dioxide (CO₂) migration in sandstone aquifers taking consideration of the interactions between fluid flow and rock stress. Based on the poroelasticity theory and multiphase flow theory, this study establishes a mathematical model to describe CO₂ migration, coupling the flow and stress fields. Both finite difference method (FDM) and finite element method (FEM) were used to discretize the mathematical model and generate a numerical model. A case study was carried out using the numerical model on the Jiangling sandstone aquifer in the Jianghan basin, China. The rock mechanics parameters of reservoir and overlying strata of Jiangling depression were obtained by triaxial tests. A two-dimensional model was then built to simulate carbon dioxide migration in the sandstone aquifer. The numerical simulation analyzes the carbon dioxide migration distribution rule with and without considering capillary pressure. Time-dependent migration of CO₂ in the sandstone aquifer was analyzed, and the result from the coupled model was compared with that from a traditional non-coupled model. The calculation result indicates a good consistency between the coupled model and the non-coupled model. At the injection point, the CO₂ saturation given by the coupled model is 15.39 % higher than that given by the non-coupled model; while the pore pressure given by the coupled model is 4.8 % lower than that given by the non-coupled model. Therefore, it is necessary to consider the coupling of flow and stress fields while simulating CO₂ migration for CO₂ disposal in sandstone aquifers. The result from the coupled model was also sensitized to several parameters including reservoir permeability, porosity, and CO₂ injection rate. Sensitivity analyses show that CO₂ saturation is increased non-linearly with CO₂ injection rate and decreased non-linearly with reservoir porosity. Pore pressure is decreased non-linearly with reservoir porosity and permeability, and increased non-linearly with CO₂ injection rate. When the capillary pressure was considered, the computed gas saturation of carbon dioxide was increased by 10.75 % and the pore pressure was reduced by 0.615 %.     

Numerical simulation of air–soil two-phase flow based on turbulence modeling

Soil flow and induced air blasts are of great harm to humanity, and historically they have caused a lot of damage to infrastructure. However, these phenomena cannot be described by traditional analog modeling methods that limit their use in disaster prevention efforts. Computational fluid dynamics (CFD) is an applied technique commonly used in a range of fields including the chemical industry, and aircraft and automobile manufacturing, but little is reported on the use of this method to simulate flowing soil in geotechnical engineering applications. The CFD method can effectively make up for the deficiency of normal calculation methods in the analysis of soil flow and air blasts. This paper uses the FLUENT (version 6.3) CFD calculation software to simulate the processes of soil flow and induced air blast changes during soil flow with an Eulerian air–soil two-phase model included in a standard k-ε turbulence model. Velocity vectors of air blasts at different times during soil flow are obtained, and the characteristics of turbulent flow can be found based on the velocity vectors. The numerical simulation techniques adopted in this paper captured precise configurations of soil flow. The results show that the CFD method is especially suitable for simulating the process of soil flow; hazard assessments can be implemented, and the performance of structures involved with disaster prevention can be improved based on the numerical simulation of changing air blasts.     

Numerical simulation of flow processes in liquefied soils using a soil–water-coupled smoothed particle hydrodynamics method

Liquefaction can result in the damage or collapse of structures during an earthquake and can therefore be a great threat to life and property. Many site investigations of liquefaction disasters are needed to study the large-scale deformation and flow mechanisms of liquefied soils that can be used for performance assessments and infrastructure improvement. To overcome the disadvantages of traditional flow analysis methods for liquefied soils, a soil–water-coupled smoothed particle hydrodynamics (SPH) modeling method was developed to analyze flow in liquefied soils. In the proposed SPH method, water and soil were simulated as different layers, while permeability, porosity, and interaction forces could be combined to model water-saturated porous media. A simple shear test was simulated using the SPH method with an elastic model to verify its application to solid phase materials. Subsequently, the applicability of the proposed SPH modeling method to the simulation of interaction forces between water and soil was verified by a falling-head permeability test. The coupled SPH method produced good simulations for both the simple shear and falling-head permeability tests. Using a fit-for-purpose experimental apparatus, a physical flow model test of liquefied sand has been designed and conducted. To complement the physical test, a numerical simulation has been undertaken based on the soil–water-coupled SPH method. The numerical results correspond well with the physical model test results in observed configurations and velocity vectors. An embankment failure in northern Sweden was selected so that the application of the soil–water-coupled SPH method could be extended to an actual example of liquefaction. The coupled SPH method simulated the embankment failure with the site investigation well. They have also estimated horizontal displacements and velocities, which can be used to greatly improve the seismic safety of structures.     

Numerical analysis of seepage–deformation in unsaturated soils

A coupled elastic–plastic finite element analysis based on simplified consolidation theory for unsaturated soils is used to investigate the coupling processes of water infiltration and deformation. By introducing a reduced suction and an elastic–plastic constitutive equation for the soil skeleton, the simplified consolidation theory for unsaturated soils is incorporated into an in-house finite element code. Using the proposed numerical method, the generation of pore water pressure and development of deformation can be simulated under evaporation or rainfall infiltration conditions. Through a parametric study and comparison with the test results, the proposed method is found to describe well the characteristics during water evaporation/infiltration into unsaturated soils. Finally, an unsaturated soil slope with water infiltration is analyzed in detail to investigate the development of the displacement and generation of pore water pressure.     

Numerical simulation of the effect of heavy groundwater abstraction on groundwater–surface water interaction in Langat Basin, Selangor, Malaysia

The paper aims at evaluating the interaction between ground and surface water along the Langat River in Malaysia through the development of a numerical simulation. Malaysia has been experiencing a rapid economic growth since the last few decades, driven by many factors such as agriculture, industry, and the like. The demand for water in these sectors has increased so tremendously that surface water has been utilized in conjunction to groundwater. Approximately 18,184 m³ of water per day is obtained from the aquifer to supply to the steel factory. There are also workshops, petroleum stations, and houses in the area thus causing the water quantity and quality to degrade. In terms of quantity, the pumping activity has altered the interaction between the groundwater and surface water. Therefore, a numerical model was proposed and two aquifer layers were simulated, with the first layer being approximately >20 m in depth and the second layer >100 m. The recharge estimated from the tank model was input into the groundwater modeling. The effects of the surface water to the aquifer were included in the simulation by defining the river conductance, river bed, and river level. The calibrated model (error about 0.9 m) was achieved and applied to predict the flow pattern in its natural state without the pumping and with the pumping states. As a result, in the first scenario, the stream was in an effluent condition influenced by the groundwater from the northeast to the west. A hyporheic flow occurred and was observed from the contour map. The flow system was changed in the second scenario when the pumping activity was included in the simulation. The groundwater lost its original function but received leakage from the stream near the pumping sites. The findings of this study will help the local authorities and other researchers to understand the aquifer system in the area and assist in the preparation of a sustainable groundwater management.     

Numerical Analysis of Infiltration in One-Dimensional Unsaturated Soil–Geotextile Column

Geotechnical and Geological Engineering - Numerical modelling development for capillary barrier investigation considering unsaturated soil–geotextile interface has been studied and evaluated...     

Formulation of non-coaxial plastic dissipation and stress–dilatancy relations for geomaterials

Acta Geotechnica - Stress–dilatancy theories play a central role in the modeling of the plastic dissipation of geomaterials. There exist several mathematical frameworks for describing the...     

Numerical Analysis of Pile–Soil–Pile Interaction in Pile Groups with Batter Piles

Battered piles are usually used to counteract lateral forces in a pile group. As there is little spacing between piles, they are affected by one another, and there is interaction between them. In this study, pile–soil–pile interaction in a group of battered piles was numerically simulated using finite element analysis. Double and frictional pile groups under static lateral and axial loadings were analyzed separately. The effects of batter angle, slenderness ratio, spacing between piles, pile–soil stiffness ratio, and soil plasticity on interaction factors were computed and presented in curves.     

DEM–SPH simulation of rock blasting

A numerical model is proposed for the simulation of rock blasting. A bonded particle system is utilized to mimic the behavior of rock. The particles interact at the contact points through normal and shear springs to simulate rock elasticity. To withstand the deviatoric stresses, the particles are glued to each other. If the applied force exceeds the contact strength, local failure occurs and microcracks are developed in the synthetic rock. For simulation of gas flow, the smooth particle hydrodynamic method is implemented. The interaction of gas particles with the rock grains is assumed to follow a perfect plastic collision model in which the initial momentum of the colliding particles is preserved. A detailed examination of the interaction of gas with blast hole is investigated. It is shown that the proposed hybrid model is capable of simulating the induced shock waves in the gas together with wave propagation in the rock material. The model successfully mimics crack propagation in rock. In particular, the crushed zone around the borehole, radial cracks, and surface spalling are all captured successfully. The results of numerical analysis suggest that gas–rock interaction can, in fact, generate a few successive compressive waves in the rock specimen, causing further extension of radial cracks with time as the weaker secondary and tertiary waves interact with the crack tips.     

Identifying the Representative Elementary Volume for Permeability in Heterolithic Deposits Using Numerical Rock Models

Using a range of realistic 3D numerical lithofacies (dm-scale) models of ripple laminated sandstone intercalated with mudstone we evaluate how single-phase permeability varies as a function of sample support. The models represent a range of mudstone content which is typical for tidal deposits. Furthermore, the spatial distribution of flow barriers (i.e. mudstone) is not random, but governed by sedimentological rules giving a variable anisotropy ratio as a function of mudstone content. Both vertical and horizontal permeability are found to vary at small sample volumes, but these fluctuations reduce as the sample volume increases. The vertical permeability increases while the horizontal permeability is nearly constant as a function of sample support for small mudstone contents. For higher mudstone content, the horizontal permeability decreases while the vertical permeability is nearly constant as a function of sample support. We propose a criterion, based on a normalised standard deviation, to determine the Representative Elementary Volume (REV). The size of the REV is dependent on both the property measured (vertical and horizontal permeability) and the correlation lengths of the lithological elements (i.e. lithofacies). Based on this we identify three flow upscaling regimes that each require a different method for upscaling: (1) layered systems where the arithmetic and harmonic averages are appropriate, (2) systems close to the percolation threshold where a percolation model should be used, and (3) discontinuous systems where an effective medium method provides the best estimate of permeability. The work gives, by using numerical experiments on a range of heterogeneous systems, a new insight in determination of the REV for permeability at the lithofacies scale and its relation to sedimentological parameters.     

Numerical analysis of a pile–slab-supported railway embankment

This paper presents a numerical analysis of a well-monitored pile–slab-supported embankment for the Beijing–Tianjin high-speed railway in China. Cement–fly ash–gravel piles were used in this project. A coupled two-dimensional mechanical and hydraulic numerical model was used for this analysis and the results are compared with the field measurements including settlement, load distribution between soil and pile, and excess pore pressure. The numerical model calculated the settlement profile close to that measured in the field. The proportion of the load carried by the soil was small thus significantly reducing the settlement. The stress transfer from the soil to the piles reduced the excess pore pressure effectively. A parametric study was conducted to investigate the influence of three key factors on the performance of the embankment. The parametric study indicated that the existence of a cushion reduced the shear force in the slab. The increase in slab thickness and pile stiffness increased the shear force and bending moment in the slab. An increase in pile stiffness reduced the settlement and lateral displacement of the embankment.     

Hybrid continuum–discrete simulation of granular impact dynamics

Acta Geotechnica - Granular impact—the dynamic intrusion of solid objects into granular media—is widespread across scientific and engineering applications including geotechnics....     

Integration of local–global upscaling and grid adaptivity for simulation of subsurface flow in heterogeneous formations

We propose a methodology, called multilevel local–global (MLLG) upscaling, for generating accurate upscaled models of permeabilities or transmissibilities for flow simulation on adapted grids in heterogeneous subsurface formations. The method generates an initial adapted grid based on the given fine-scale reservoir heterogeneity and potential flow paths. It then applies local–global (LG) upscaling for permeability or transmissibility [7], along with adaptivity, in an iterative manner. In each iteration of MLLG, the grid can be adapted where needed to reduce flow solver and upscaling errors. The adaptivity is controlled with a flow-based indicator. The iterative process is continued until consistency between the global solve on the adapted grid and the local solves is obtained. While each application of LG upscaling is also an iterative process, this inner iteration generally takes only one or two iterations to converge. Furthermore, the number of outer iterations is bounded above, and hence, the computational costs of this approach are low. We design a new flow-based weighting of transmissibility values in LG upscaling that significantly improves the accuracy of LG and MLLG over traditional local transmissibility calculations. For highly heterogeneous (e.g., channelized) systems, the integration of grid adaptivity and LG upscaling is shown to consistently provide more accurate coarse-scale models for global flow, relative to reference fine-scale results, than do existing upscaling techniques applied to uniform grids of similar densities. Another attractive property of the integration of upscaling and adaptivity is that process dependency is strongly reduced, that is, the approach computes accurate global flow results also for flows driven by boundary conditions different from the generic boundary conditions used to compute the upscaled parameters. The method is demonstrated on Cartesian cell-based anisotropic refinement (CCAR) grids, but it can be applied to other adaptation strategies for structured grids and extended to unstructured grids.     

Permeability and P-wave velocity change in granitic rocks under freeze–thaw cycles

An extensive experimental investigation of microstructural changes in granites under freeze–thaw cycles using permeability and P-wave velocity measurements is described. Two types of natural granite rocks are considered and tested under dry and saturated conditions. The specimens were subjected to 200 heating–cooling cycles (??20°C/?+?20°C); each cycle had a duration of 24 h. The results indicate that the ageing process decreases the permeability and the P-wave velocity. The reduction in P-wave velocity is likely to be due to microcrack development (material damage). In dry samples, the microcracks result from the repeated differential contraction–dilatation of the mineral components. In water-saturated samples, there is an additional effect of freezing and thawing of water in the porous network. The decrease in permeability in the dry samples is due to partial closure of existing microcracks. In water-saturated samples, there was no increase in the permeability. A physically acceptable explanation is that new microcracks are not necessarily connected with those that already exist. Therefore the physicochemical process resulting from water–rock interactions also affects the permeability. This phenomenon reduces fluid flow in the material.     

Numerical modeling of soil–structure interface of a concrete-faced rockfill dam

Concrete-faced rockfill dams (CFRD) are widely used in large-scale hydraulic projects. The face slab, the key seepage-proof structure of great concern, has a strong interaction with the neighboring gravel cushion layer due to a significant difference in their stiffness. An elasto-plasticity damage interface element, a numerical format of the EPDI model, is described for numerical analysis of a CFRD that can trace the separation and re-contact between the face slab and the cushion layer at the interface. As verified by simulating slide block and direct shear interface tests, this element was confirmed to capture effectively the primary monotonic and cyclic behaviors of the interface. This element can easily be extended to the finite element method (FEM) programs that involve the Goodman interface element. The analysis of a typical CFRD showed that the interface model describes a significant effect on the stress response of the face slab under different conditions, including dam construction, water storage, and earthquake. Treatments of the cushion layer, such as an asphalt layer, changed the behavior of the interface between it and the face slab, which resulted in a significant effect on the stress response of the face slab. The top of the face slab exhibited a significant separation from the cushion layer during construction, induced mainly by construction of the neighboring dam body.