Single Porosity Model Research Articles

The Analysis of Permeability Influence on CO2 Plume based on Reservoir Simulation

Abstract Permeability is critical in site characterization and geoscience studies for carbon capture and storage projects. There is significant uncertainty of CO2 movement in the subsurface caused by permeability. This study aims to analyze the influence of permeability on the movement of CO2 plumes using a synthetic single-porosity model based on reservoir simulation. By simplifying geomechanics, employing tornado experimental design, as well as utilizing Pearson and Spearman correlations from 30,000 neural network proxy models based on Latin Hypercube and Monte Carlo experimental design, this research successfully explains the impact of permeability on CO2 movement. The reservoir can withstand pressures up to 6500 psi without rock failure. The total CO2 injection with a 90% probability is ∼1.3 TSCF equivalent, with an injection rate of 30 MMSCFD, optimized for a duration of 120 years. Initially, the CO2 movement tends to be upward during injection due to gravitational effects, but over time, it tends to move laterally. Vertical permeability exhibits a negative correlation with total CO2 injection, lateral distribution of CO2 plumes, and CO2 solubility in water. On the other hand, horizontal permeability shows a positive correlation with total CO2 injection. Factors such as perforation location and layer thickness also influence the extent of permeability’s role. However, the lateral and vertical movement of CO2 in this study has not been fully identified, and more complex quantification formulas are needed in commercial simulators. Despite the limitations in data and computational resources, this research successfully explains the movement of CO2 plumes and highlights the importance of other factors such as porosity, perforation location, layer thickness, among others. The recommendations of this study include the use of more complex quantification formulas to model the movement of CO2 plumes, along with increasing the complexity of the model.

Single porosity model: Exploring the spatial resolution limits in complex urban patterns

When modeling large-scale urban floods, the Porosity Nonlinear Shallow Water Equations (PNSWE) emerge as an interesting and consistent subgrid approach to reduce computational time while preserving the solution structure, allowing for computational efficiency at the cost of some loss in the accuracy of the results. Porosity accounts for changes in storage and exchanges due to obstacles in urban areas, and it introduces an extra source term proportional to the porosity gradient into the momentum equations. However, no systematic analyses on the effects of grid size have been performed in real domains, when this model is used to represent fine-scale topographic information at a coarser scale. In this study, we analyze how accuracy is affected by gradually increasing grid resolution in a generalized porosity approach computed at the cell-level. The Single Porosity model (SP) in Cartesian coordinates is employed to simulate a real-world urban flooding event, with resolution transitioning from fine- to macro-scale. At an intermediate scale, the meso-scale, where cell size approximates street width and computational time is significantly reduced, the model captures main preferential flow paths by means of the porosity gradient within the urban area. Good agreement with refined classical model solutions is observed at this scale for flood extension and hazard maps, providing valuable information for early-warning systems. Numerical results underscore the importance of porosity models in rapidly assessing flow properties during an event, enhancing real-time decision-making with reliable information.

Can effective porosity be used to estimate near-well protection zones in fractured chalk?

Protection of fractured carbonate aquifers is often based on a single-porosity description of a dual-porosity system. However, it is difficult to assess a trustworthy value of the effective porosity based on scientific principles; thus, a range of estimates is often suggested. The complexity of the problem is compounded by the fact that the effective porosity may be scale-dependent. This paper investigates whether it is possible to describe solute transport in fractured carbonate rocks with an equivalent porous medium model using a constant value of effective porosity. It is assumed that the dual-porosity model provides an acceptable description of transport mechanisms in fractured porous rock and that it is possible to estimate the parameters needed in the single-porosity models from results generated by the dual-porosity model. The effective porosity is estimated from the dual-porosity results that are used as targets. For Danish chalk, an effective porosity of 13% (11–17%) is estimated. However, it is demonstrated that the estimated effective porosity is only valid at the specific transport time (1 year) from which simulation results of the dual-porosity model were extracted. The effective porosity is shown to increase with travel time until equilibrium conditions are realised between the fractures and matrix, following which, the effective porosity equals the matrix porosity and will maintain this value at larger transport times. Assuming that the dual-porosity model provides a trustworthy description of solute transport in fractured chalk and limestone, a method to estimate the effective porosity of an equivalent porous medium model is presented.

Estimating the impact of vadose zone heterogeneity on agricultural managed aquifer recharge: A combined experimental and modeling study

Agricultural managed aquifer recharge (Ag-MAR) is a promising approach to replenish groundwater resources using flood water and cropland as spreading grounds. However, site selection, particularly the layering of sediment deposits in the subsurface, can greatly influence Ag-MAR efficacy as it controls water flow and solute transport in the vadose zone. In this study, we use the HYDRUS-1D software to simulate water flow and solute transport from the land surface to the groundwater table in three vadose zone profiles (LS, MS, HS) characterized by differing fractions of sand (44 %, 47 %, and 64 %). For each profile, the single- and dual-porosity models (i.e., considering or not nonequilibrium water flow and solute transport) were calibrated using observed surface ponding, soil water content, and KBr breakthrough data. Water flow and bromide transport in the profile with the lowest sand fraction (LS) were best captured using the model that considered both preferential flow and nonequilibrium bromide transport. Water flow and bromide transport in the profile with the highest sand fraction (HS) was best simulated with the model that considered preferential flow and equilibrium bromide transport. Uniform water flow and nonequilibrium bromide transport provided the best fit for the third profile (MS). The degree of preferential flow was highest in the profile with the largest sand fraction (HS), which also showed the largest flow velocities compared to the profiles with lower sand amounts (LS and MS). Preferential flow did not significantly impact the overall water balance (within 3 %), but caused a significant decrease in vadose zone travel times (bromide) by up to 38 %, relative to a single-porosity model fit. Recharge efficiency varied between 88 % and 90 %, while the average travel times from the soil surface to groundwater varied up to 119 % (from 3.6 to 7.9 days) between the three sites. This study demonstrates that similar recharge efficiency can be achieved at sites with differing soil texture profiles, but subsurface heterogeneity can substantially affect contaminant transport processes and their travel times.

Coping with geometric discontinuities in porosity-based shallow water models

The use of classic two-dimensional (2D) shallow water equations (SWE) for flooding simulation in complex urban environments is computationally expensive, due to the need of refined meshes for the representation of obstacles and building. Aiming to reduce the computational burden, a class of sub-grid SWE models, where small-scale building features are preserved on relatively coarse meshes by means of macroscale porosity parameters, has been recently introduced in the literature. Among the other porosity-based models, the single porosity (SP) model is relevant because the corresponding one-dimensional (1D) Riemann problem is the building block for the construction of many porosity-based numerical schemes. Like the Riemann problem connected to mathematical models such as the SWE with variable bed elevation and the 1D Euler equations in contracting pipes, the SP Riemann problem may exhibit multiple solutions for certain initial conditions. This ambiguity can be solved by restoring the microscale information of the 2D SWE model that is lost at the SP macroscale. In the present paper, we disambiguate the solutions' multiplicity by systematically comparing the solution of the SP Riemann problem at local porosity discontinuities with the corresponding 2D SWE numerical solutions in contracting channels. An additional result of this comparison is that the SP Riemann problem should incorporate an adequate amount of head loss when strongly supercritical flows past sudden porosity reductions occur. An approximate Riemann solver, able to pick the physically congruent solution among the alternatives and equipped with the required head loss amount, shows promising results when implemented in a 1D single porosity finite volume scheme.

A computational workflow to study CO2 transport in porous media with irregular grains: Coupling a Fourier series-based approach and CFD

Understanding CO2 transport in porous media is important for enhanced oil recovery and CO2 sequestration. In this study, we aimed to develop a computational workflow to automatically simulate CO2 transport in porous media, including generating digital porous media from a grain morphological perspective, a pipeline, and pore-scale modeling. A method for generating porous media using a Fourier series-based approach was proposed for this workflow. Contact detection introduced the Floyd-Warshall algorithm to improve the computational efficiency and application scope of the method. Furthermore, the simultaneous application of parametric equations and grid mapping makes the output results diverse. A pipeline was built to link the proposed method with pore-scale modeling to automate the workflow. Drawing on the developed computational workflow, we simulated CO2 transport in porous media and discussed the effects of varying the different pore structures, capillary numbers and wettabilities. In different pore structures, the dual-porosity model is easily broken through by CO2 causing a small swept area making its oil recovery lower than the single-porosity model. In the capillary number, the CO2-free oil recovery period decreased with an increasing capillary number in the media. The concomitant imbibition in the low capillary number increased swept area and oil recovery but can lead to economic and time losses. At the wettabilities, the maximum recovery was achieved with weak CO2 wetting. This computational workflow can be used as an effective tool to investigate CO2 transport within porous media, contributing to the design and application of innovative enhanced CO2 sequestration and oil recovery method.

Self-similar solutions of shallow water equations with porosity

Simulated free surface transients in periodic urban layouts have been reported to be self-similar in the space-time domain when averaged on the scale of the building period. Such self-similarity is incompatible with the head loss model formulae used in most porosity-based shallow water models. Verifying it experimentally is thus of salient importance. New dam-break flow laboratory experiments are reported, where two different configurations of idealized periodic buildings layouts are explored. A space-time analysis of the experimental water level fields validates the self-similar character of the flow. Simulating the experiment using the two-dimensional shallow water model also yields self-similar period-averaged flow solutions. Then, the Single Porosity (SP), Integral Porosity (IP) and Dual Integral Porosity (DIP) models are applied. Although all three models behave in a similar fashion when the storage and connectivity porosities are close to each other, the DIP model is the one that upscales best the refined 2D solution.

A Review of Simulation Models of Heat Extraction for a Geothermal Reservoir in an Enhanced Geothermal System

This paper reviews the heat transfer model for geothermal reservoirs, the fracture network in reservoirs, and the numerical model of hydraulic fracturing. The first section reviews the heat transfer models, which contain the single-porosity model, the dual-porosity model, and the multi-porosity model; meanwhile the mathematical equations of the porosity model are summarized. Then, this paper introduces the fracture network model in reservoirs and the numerical method of computational heat transfer. In the second section, on the basis of the conventional fracture theory, the PKN (Perkins–Kern–Nordgren) model and KGD (Khristianovic–Geertsma–De Klerk) model are reviewed. Meanwhile, the DFN (discrete fracture network) model, P3D (pseudo-3D) model, and PL3D (planar 3D) model are reviewed. The results show that the stimulated reservoir volume method has advantages in describing the fracture network. However, stimulated reservoir volume methods need more computational resources than conventional fracture methods. The third section reviews the numerical models of hydraulic fracturing, which contains the finite element method (FEM), the discrete element method (DEM), and the boundary element method (BEM). The comparison of these methods shows that the FEM can reduce the computational resources when calculating the fluid flow, heat transfer and fracture propagations in a reservoir. Thus, a mature model for geothermal reservoirs can be developed by coupling the processes of heat transfer, fluid flow and fracture propagation.

Modeling Fracture Propagation in a Dual-Porosity System: Pseudo-3D-Carter-Dual-Porosity Model

Despite the significant advancements in geomodelling techniques over the past few decades, it is still quite challenging to obtain accurate assessments of hydraulic fracture propagation. This work investigates the effect of fluid leak-off in a dual-porosity system on the hydraulic fracture propagation geometry, which, in turn, affects hydrocarbon recovery from tight and unconventional reservoirs. Fracture propagation within tight reservoirs was analyzed using the Pseudo Three-Dimensional-Carter II model for single- (P3D-C) and dual-porosity systems (P3D-C-DP). Previous studies have accounted for leak-off in single-porosity models; however, studies within dual-porosity systems are still quite limited. We present a novel approach to coupling fluid leak-off in a dual-porosity system along with a fracture-height growth mechanism. Our findings provide important insights into the complexities within hydraulic fracturing treatment design using our new and pragmatic modeling approach. The simulation results illustrate that fluid leak-off in dual-porosity systems contributes to a confined fracture half-length (xf), that is 31% smaller using the P3D-C-DP model as opposed to the single-porosity model (P3D-C). As for the fracture height growth (hf), the P3D-C-DP model resulted in a 40% shorter fracture height compared to the single-porosity model.

A dual-porosity model for coupled rainwater and landfill gas transport through capillary barrier covers

A two-dimensional dual-porosity model for coupled rainwater and landfill gas transport through capillary barrier covers (CBCs) was established. The proposed model was partially verified using published data from a laboratory loess column test. By fitting the field-measured data using the proposed model, the optimal dual-porosity parameters of the in-situ loess of a loess/gravel CBC in Northwest China were determined to be wf = 0.1 (volume fraction of macropore system), Kf/Km = 150 (intrinsic permeability ratio of macropore to micropore system) and Re = 1 (reduction factor of mass exchange at the interface between macropore and micropore systems). This model was used to predict the performance of the CBC experiencing a 15-day rainfall period followed by a 30-day no-rainfall period. Results showed that the presence of macropores induced an earlier occurrence of percolation accompanied with a higher percolation rate. The cumulative percolation and CH4 emission rate derived from the dual-porosity model were about 50 % and one order of magnitude higher than those predicted by the single-porosity model, respectively. In addition, the existence of gravel layer had remarkable influence on minimizing water percolation and CH4 emission, but these were practically independent of its thickness. The results of this study can provide an effective method, crucial parameters and guidelines for the design of CBCs.

Analytical Time-Dependent Shape Factor for Counter-Current Imbibition in Fractal Fractured Reservoirs

Summary The fluid exchange behavior for counter-current imbibition in fractured reservoirs can be quantitatively characterized by the transfer function in numerical simulation. The time-dependent shape factor (TDSF) in the transfer function is one of the main factors controlling fluid transport, which directly affects the result of ultimate oil recovery prediction. In practice, fractured reservoirs with different microscopic pore structures often have varied flow laws under the same flow conditions. However, the current TDSFs proposed for counter-current imbibition assume that the microscopic pore structure has no impact on the fluid inter-porosity flow behavior, which is inconsistent with the actual situation. In this work, the fractal theory is used to establish the TDSF of counter-current imbibition, which is related to the microscopic pore structure. First, the analytical solutions of average water saturation and imbibition rate are obtained under different conditions related to the maximum pore diameter and tortuosity fractal dimension of the matrix. The validity of the new analytical solution for strong water-wet and moderate water-wet reservoirs is ascertained by a single-porosity model and experimental data. Subsequently, the proposed analytical solution is applied to the two-phase transfer function to develop the new TDSF for counter-current imbibition, and the sensitivity analysis is carried out. The results demonstrate that the unsteady-state duration of the TDSF is proportional to the characteristic length and tortuosity fractal dimension of the matrix, and it is negatively proportional to the maximum pore diameter of the matrix. The influence of the characteristic length, tortuosity fractal dimension, and maximum pore diameter of the matrix on a constant shape factor (SF) under quasi-steady-state is exactly the opposite. This work provides an enhanced clarification of the fluid exchange behavior of counter-current imbibition in strong water-wet and moderate water-wet fractured reservoirs.

A COMSOL Multiphysics study on block-to-block interactions in naturally fractured reservoirs

In fractured reservoirs, block-to-block interactions (re-infiltration and capillary continuity) significantly affect gravity drainage performance. Re-infiltration controls the drainage rate. This process may significantly delay oil production. Despite the numerous attempts to study the re-infiltration process, there is still much controversy about the factors that affect this phenomenon. This work focused on designing two sets of 2D models aimed at improving the simulation and visualization of multiphase flow in fractured porous media while providing a more realistic understanding of the pore-scale phenomena and flow communication between matrix-fracture and matrix-matrix. The simulation was performed in COMSOL Multiphysics in the single-porosity model. Moreover, the impact of different parameters such as rock type, physical properties of the fluids, tilt angle, matrix block height and area, fracture opening, and matrix blocks porosity-permeability on gravity drainage performance, especially block-to-block interactions, has been examined. Besides investigating the effect of each parameter, combined effects of those parameters have likewise been investigated. To rank the most critical observed parameters on the re-infiltration process, the grey relational analysis was applied. The results of this analysis showed the physical properties of the fluids have the most influence on re-infiltration. In addition, it was demonstrated that tilt angle reduces the degree of re-infiltration in deviated blocks. Also, a combination of oil-wet rocks and high irreducible water saturation results in a decrease in oil recovery, a delay in production, and a decrease in the degree of re-infiltration. Additionally, fractures with small openings and taller blocks promote greater re-infiltration; however, their impact on ultimate recovery is not significant. The findings of this study can help for a better understanding of the relative influence of different reservoir parameters on gravity drainage performance and block-to-block interactions. • Visualization and simulation of block-to-block interaction in fractured porous media using COMSOL multiphysics. • Providing a new insight on the relative importance of different reservoir parameters in block-to-block interaction. • Using grey relational analysis (GRA) to rank the influence of parameters on the re-infiltration process.

Multiple porosity model of a heterogeneous layered gas hydrate deposit in Ulleung Basin, East Sea, Korea: A study on depressurization strategies, reservoir geomechanical response, and wellbore stability

Precise simulation of the geomechanical response is crucial for the gas hydrate production such as from the deposits in Ulleung Basin, East Sea, Korea, which exhibit severe vertical heterogeneity of the hydrate-bearing sand and mud layers. Physically, depressurization causing hydrate dissociation can induce critical subsidence. Meanwhile, it is numerically cumbersome to apply the fine-scale single porosity model to the heterogeneous layered system particularly for geomechanics. In this study, to investigate geomechanical responses of the intercalated layer system based on various depressurization scenarios, we employ a multiple porosity (MP) model with upscaled geomechanical properties while flow variables kept in the fine-scale. For the rigorous two-way coupling between the fluid flow and geomechanics, the fixed-stress sequential method is employed with two individual simulators, the TOUGH+HYDRATE for the flow and an in-house code (called the ROCMECH) for the geomechanics. Specifically for the ROCMECH, we applied axisymmetric geomechanics for more precise calculation of deformation near the wellbore. Numerical experiments of field-wide simulations are about two different comparison studies for depressurization: a constant bottom hole pressure (BHP) and several different BHPs cases. For a constant BHP case, gas production periods, i.e., 14- and 100-days productions representing short- and long-term, respectively, are compared, while several different BHPs case including continuous and periodic depressurizations is focused on the comparison of the productivity and geomechanical stability. From the case of constant BHP, we confirm significant vertical displacement due to the weaker stiffness of the formation after hydrate dissociation, which can aggravate as the production continues. Among the cases with varying BHP, the periodic depressurization scenario exhibits superiority with significantly small subsidence despite similar productivity. The MP model employed in this study can help devise depressurization strategies for gas hydrate reservoirs, especially for the precise and efficient calculation of the geomechanical responses of the intercalated layer system.

Modeling of the Hydrological Processes in Caatinga and Pasture Areas in the Brazilian Semi-Arid

The semi-arid regions of northeastern Brazil have historically suffered from water shortage. In this context, monitoring and modeling the soil moisture’s dynamics with hydrological models in natural (Caatinga) and degraded (Pasture) regions is of fundamental importance to understand the dynamics of hydrological processes. Therefore, this work aims to evaluate the hydraulic parameters in Caatinga and Pasture areas using the Hydrus-1D inverse method. Thus, five soil hydraulic models present in Hydrus-1D were used, allowing the comparison of the single-porosity model with more complex models, which consider the dual porosity and the hysteresis of the porous medium. The hydraulic models showed better adjustments in the Caatinga area (RMSE = 0.01–0.02, R2 = 0.61–0.97) than in the Pasture area (RMSE = 0.01–0.03, R2 = 0.61–0.90). Regarding the hydraulic parameters, for all models, the Pasture showed smaller saturated hydraulic conductivity and water content values of the mobile region than the Caatinga. This fact demonstrates the negative impact of compaction and change in natural vegetation in the Brazilian semi-arid. The dual-porosity model presented the best fit to the data measured in the Pasture area. However, a single-porosity model could be considered representative of the Caatinga area. The results showed that Caatinga areas contribute to maintaining soil moisture and increasing the water storage in semi-arid regions.

Integration of discrete fracture reconstruction and dual porosity/dual permeability models for gas production analysis in a deformable fractured shale reservoir

Permeability of gas shale in Changning region is exceptionally low and ranges from 0.76 × 10−4 to 1.56 × 10−4 mD, and fracturing stimulation measures can produce high diversion channels. Therefore, the technology of multi-stage fractured horizontal wells (MFHWs) is essential for commercial exploitations. Microseismic hydraulic fracture mapping (MSM) can effectively provide visual information (spatial position, hydraulic fracture geometry, and distribution complexity) and has now been currently used to evaluate and optimize the fracturing operations and well completions.The shale gas pressure changes with production time after injection and stimulation treatments, which can result in the dynamic evolution and redistribution for in-situ stresses. This study established a poroelastic porosity and permeability model for triple-continuum incorporating desorption-induced deformation, Knudsen diffusion, and viscous flow. The discrete fracture network (DFN) was interpreted by the robust occurrence calculation method based on the Random Sample Consensus (RANSAC) algorithm. This dual porosity/dual permeability (DPDP) model was more accurate than the other four classical models that were based on the single porosity and permeability model. The porosity and permeability for matrix and natural fractures decreased exponentially with production time, and the reduction ranges were less than 1% in the whole production, and the variation ranges for hydraulic fractures can reach nearly 5%. Meanwhile, the induced deformations under the same in situ stresses were maximum for the hydraulic fractures, and minimum for the inorganic pores, while intermediate for the natural fractures. Furthermore, this study compared the equilibrium desorption mechanism (EDM) with the non-equilibrium desorption/adsorption mechanism (NEDAM) on cumulative production. It was discovered that NEDAM exposed the delayed effect for the shale gas, and the calculated production for NEDAM was smaller and more reasonable than EDM. This study provided a workflow from fracture interpretation to reservoir evaluation by an effective geophysical method.

The method of fundamental solutions for the elastic wave scattering in a double-porosity dual-permeability medium

For materials that have a matrix porosity at the microscopic scale, and an interconnecting fracture system at the mesoscopic scale, the double-porosity dual-permeability model provides a better prediction of seismic wave attenuation than the single porosity model, due to the flow exchange mechanism between these different size pores. The current work offers for the first time a numerical solution tool based on the method of fundamental solutions for problems of 3-D wave scattering and dynamic stress concentration around scatterers, such as cavities and embedded inhomogeneous inclusions, in an infinite double-porosity dual-permeability medium. The method of fundamental solutions is based on the spherical wave potentials representing three compressional waves and one shear wave. The accuracy and stability of the method are tested against other available results, and are demonstrated to be excellent. Wave scattering and dynamic stress concentration problems due to spherical cavity and poroelastic inclusion are then investigated for incident plane P1 and SV waves in the frequency domain. The research shows that the seismic responses are sensitive to the incident frequency, the boundary drainage condition, and material properties such as porosity.

Analytical analysis of the leachate flow to a horizontal well in dual-porosity media

Horizontal wells are gradually used for dewatering at municipal solid waste (MSW) landfills in recent years. A theoretical model of leachate flow to horizontal well is required to better evaluate its dewatering performance. In this study, a dual-porosity model of the leachate flow to a horizontal well in MSW landfills is established. The proposed model divides waste into fracture and matrix domains. Leachate in these two domains flows horizontally and vertically into a horizontal well together with leachate exchange occurring between them. An analytical solution of leachate level drawdown under horizontal well draining is obtained through Laplace integral transformation and Separation of variables. The analytical solution is verified with the numerical solution obtained by finite element method in COMSOL Multiphysics software. A sensitivity analysis is performed to investigate the effect of model key parameters, including anisotropy of hydraulic conductivity kr/kz, hydraulic conductivity ratio of fracture domain to matrix domain kfr/kmr, and proportion of fracture domain in total domain wf, on leachate level drawdown. A case study of the horizontal well draining test at the Tianziling landfill indicated that the dual-porosity model performed better than the single-porosity model in leachate level drawdown estimation, especially near the horizontal well. The average value of hydraulic conductivity ratio of fracture domain to matrix domain kfr/kmr is fitted to be 419 for typical MSW with high kitchen waste content in China.

A water retention model accounting for void ratio changes in double porosity clays

This paper presents a constitutive model that predicts the water retention behaviour of compacted clays with evolving bimodal pore size distributions. In line with previous research, the model differentiates between the water present inside the saturated pores of the clay aggregates (the microstructure) and the water present inside the pores between clay aggregates (the macrostructure). A new formulation is then introduced to account for the effect of the macrostructural porosity changes on the retention behaviour of the soil, which results in a consistent evolution of the air-entry value of suction with volumetric deformations. Data from wetting tests on three different active clays (i.e. MX-80 bentonite, FEBEX bentonite, and Boom clay), subjected to distinct mechanical restraints, were used to formulate, calibrate, and validate the proposed model. Results from free swelling tests were also modelled by using both the proposed double porosity model and a published single porosity model, which confirmed the improvement in the predictions of degree of saturation by the present approach. The proposed retention model might be applied, for example, to the simulation of the hydromechanical behaviour of engineered bentonite barriers in underground nuclear waste repositories, where compacted active clays are subjected to changes of both suction and porosity structure under restrained volume conditions.

Transient shape factors for dual-porosity simulation of tight rocks

The shape-factor concept provides an elegant and powerful upscaling method for fractured reservoir simulation. Many different shape-factors, among which the well-known Warren and Root, and Kazemi shape-factors have been proposed in the past. Since different shape-factors can lead to totally different reservoir behavior, selection of the appropriate shape-factor value is critical for accurate fractured reservoir modeling. Constant shape factor is commonly used for simulation of fractured reservoirs by assuming that pressure transient reaches to center of the matrix block within very small time. On the contrary, tight rocks exhibit longer duration of unsteady-state flow such that matrix – fracture transfer is not constant, but rather varies with time until reaching to a constant value. In this regard, dual-porosity simulation of tight rocks using constant shape factor does not capture actual physics of matrix to fracture flow and yields inaccurate performance prediction. In this study, analytical solutions of pressure diffusion and corresponding shape factors are presented for various matrix shapes. The results are compared to those obtained with simple empirical functions. Proposed functions significantly improve accuracy over existing approaches in the prediction of both mean matrix pressure and transfer function. Results of fine grid single-porosity model are compared with two different dual porosity models, one with constant shape factor and one with time dependent shape factor, to verify proposed approach.

Nanoemulsion flooding for enhanced oil recovery: Theoretical concepts, numerical simulation and history match

In current scenario of depleting oil reserves, chemical flooding is a vital enhanced oil recovery (EOR) technique. Present study discusses laboratory flooding experiments of surfactant/nanoparticle nanoemulsions on sand-pack system, with bulk approach to model and simulate the flooding strategies portraying the potential of nanoemulsion assisted EOR. Physicochemical properties of nanoemulsions were characterized in terms of droplets size, interfacial tension, wetting behavior, viscosity improvement and crude oil displacement. A numerical methodological simulation is performed on porous media through CMG-STARS simulator. Cartesian single porosity model equipped with well pattern, injection fluid flow-rate and rock-fluid properties was developed via simulation tool during compositional investigation. Tuning of relative permeability values to successfully fit with cumulative oil production and water cut was extremely challenging role during model development. Oil saturation profiles and relative permeability curves displayed the alteration in wetting behavior of sand-pack system to strongly water-wet from oil/intermediate-wet condition. 23–28% tertiary recoveries were achieved, contingent to composition of surfactant/nanoparticle in injected nanoemulsion. History match (HM) of production data via CMOST for experimental and simulation outcomes exhibited a good match with global HM error < 6%. Numerical simulation investigation facilitates a holistic approach to predict the performance and practicability of nanoemulsions as chemical EOR fluid.