Fractured Vuggy Porous Media Research Articles

An efficient adaptive implicit scheme with equivalent continuum approach for two-phase flow in fractured vuggy porous media

This work investigates numerical method and equivalent continuum approach (ECA) of fluid flow in fractured porous media. The commonly used discrete fracture model (DFM) without upscaling needs full discretization of all fractures. It enjoys the merit of capturing each fracture accurately but will get in trouble with mesh partition and low computational efficiency, especially when a complex geometry is involved. In this study, we develop an efficient implicit scheme with adaptive iteration, in which an improved ECA is devised and then integrated in this scheme. Numerical studies show that the proposed numerical scheme improves the convergence condition and computational efficiency. Then, a test is conducted to demonstrate the feasibility of using superposition principle of permeability tensor in upscaling. Based on these, different strategies are applied to simulate fluid flow in fracture networks with a complex geometry. It is demonstrated that the proposed ECA is able to reproduce the results computed by DFM. The accuracy depends on resolution of background grids. The presented method enjoys a low computational cost and desirable convergence performance compared with the standard DFM in which equivalent continuum is not considered.

Predict the mud loss in natural fractured vuggy reservoir using discrete fracture and discrete vug network model

In carbonate reservoirs, the leakage path is complex and the law of mud loss is not clear, which brings difficulties to the implementation of plugging measures. Carbonate reservoir is a naturally fractured vuggy media. One of the key scientific problems is that the fluid mass transfer among matrix pores, natural fractures and vugs is not well understood. In this paper, a discrete fracture and discrete vug model is presented to study the law of mud loss in the naturally fractured reservoir wherein natural fractures and vugs developed. The model solved the fluid flow in the discrete fracture and vug network, consisting of 1) Darcy flow in lowly permeable rock matrix and highly permeable natural fractures; 2) free flow in macro vugs. A physically-based boundary is applied to ensure the mass continuity on interfaces between vugs and matrix pores, vugs and natural fractures. A good agreement with analytical results for Poiseuille flow in a porous/free connected media is achieved. Two numerical examples using the commercial software COMSOL provide validation of the new model. When simulating the mud loss process, we find that as soon as vugs are connected to wellbore through natural fractures, total loss is observed. The size and number of vugs play prominent roles in increasing mud loss rate and accumulated mud loss. The numerical results show that the discrete fracture and discrete vug model provides a reliable way to model realistic fluid flow in fractured vuggy porous media. The model in this paper can not only simulate the mud loss process, but also the production process of carbonate reservoirs.

Numerical simulation of hydro-mechanical coupling in fractured vuggy porous media using the equivalent continuum model and embedded discrete fracture model

In this study, an efficient numerical model is proposed to simulate the hydro-mechanical coupling in the fractured vuggy porous media containing multi-scale fractures and vugs. Specifically, an improved Equivalent Continuum Model (ECM), which is obtained through the asymptotic homogenization method, is applied to model micro fractures and vugs, while macro fractures are modeled explicitly by using the Embedded Discrete Fracture Model (EDFM) and non-matching grids. As an important feature of the explicit representment, the effects of fillings and fluid pressure on preventing macro fractures from closing can be considered. After that, the new mixed space discretization (i.e., Mimetic Finite Difference (MFD) method for flow and stabilized eXtended Finite Element Method (XFEM) for geomechanics) and fully coupled methods are applied to solve the proposed model. The mixed space discretization can deal with complex heterogeneous properties (e.g., full tensor permeability), and yields the benefits of local mass conservation and numerical stability in space. Finally, we demonstrate the accuracy and application of the proposed model to capture the coupled hydro-mechanical impacts of multiscale fractures and vugs on fluid flow in fractured porous media.

Numerical simulation of fractured-vuggy porous media based on gamblets

Numerical simulation of a fractured-vuggy porous medium is a challenging problem. One reason is the coexistence of matrix, fractures and vugs on multiple scales that need to be coupled, and the other reason is that the high-resolution fractured-vuggy model may contain up to several millions of gridcells in applications, which brings severe computational challenges into the numerical methods. Therefore, the requirement for accurate and efficient technique is widely increasing. Fractured-vuggy porous medium is generally represented by triple-continuum model in which the matrix system, fracture system and vug system each are treated as a parallel continuous system. Although triple-continuum model is widely used because of its easy-implementation and high efficiency, it fails to capture the detailed flow patterns of reservoir with disconnected long fractures. Discrete fracture-vug network (DFVN) model can precisely model the fluid flow in fractures and vugs. However, the simulation of this model is deemed intractable even with the advent of supercomputers because of the large amount of calculation. In view of the fact that the multigrid method is now well known as one of the fastest method of solving elliptic problems, in this paper we introduce a nearly linear complexity multiresolution decomposition method for fluid flow in a fractured-vuggy reservoir. The detailed flow patterns are described by combing the advantages of continuum model and discrete model. That is, the homogenization theory is used to construct an equivalent permeability in each coarse grid block in which the vugs and small-scale fractures are represented by discrete fracture-vug network model. We decompose the solution space into several subspaces and then we compute the corresponding solutions of heterogeneous discrete fracture network model in each subspace. Gamblets are constructed and they are elementary solutions of hierarchical information games associated with the process of computing with partial information and limited resources. These gamblets have a natural Bayesian interpretation under the mixed strategy emerging from the game theoretic formulation. This method could realize its fast simulation by decomposing the solution space into a direct sum of linear subspaces that are orthogonal to each other. Finally, the pressure difference distribution of fractured-vuggy porous medium is obtained by combing the DFVN solutions of all subspaces. Numerical results are presented to demonstrate the accuracy and efficiency of the proposed multiresolution decomposition method. The results show that this method is a promising method of numerically simulating the fractured-vuggy porous medium.

Multiscale mixed finite element, discrete fracture–vug model for fluid flow in fractured vuggy porous media

Numerical simulation in naturally fractured-vuggy media is challenging because of the coexistence of porous media, fractures and vugs on multiple scales that need to be coupled. We present a new approach to reservoir simulation, based on the discrete fracture–vug network (DFVN) model, which gives accurate resolution of both large-scale and fine-scale flow patterns.In this work, we use a multiscale mixed finite element method (MsMFEM) for fluid flow in fractured-vuggy media using the discrete fracture–vug model. By combining MsMFEM with the discrete fracture–vug model, we aim towards a numerical scheme that facilitates fractured vuggy reservoir simulation without upscaling. MsMFEM uses a standard Darcy model to approximate the pressure and velocity on a coarse grid, whereas fine scale effects are captured through basis functions constructed by solving local flow problems using the discrete fracture–vug model. The accuracy and the robustness of MsMFEM are shown through several examples. In the first example, we consider Beavers–Joseph model and then compare the analytic solution. We use the MsMFEM in more complex models. The results indicate that the MsMFEM is a promising path toward direct simulation of highly resolution geomodels.

Effects of Fractured-Vuggy Porous Media Geometrical Configuration on Oil and Gas Reservoir Pressure Force Field

According to the Darcy - Stokes equations of fractured-vuggy porous medium, using COMSOL Multiphysics software, we calculated several typical conceptual model pressure field distribution, analyzed the influence of fractured-vuggy porous medium internal vug and fractured geometric configuration on the pressure field in the model.

Numerical Simulation of Pollutant Transport in Fractured Vuggy Porous Karstic Aquifers

This paper begins with presenting a mathematical model for contaminant transport in the fractured vuggy porous media of a species of contaminant (PCP). Two phases are numerically simulated for a process of contaminant and clean water infiltrated in the fractured vuggy porous media by coupling mixed finite element (MFE) method and finite volume method (FVM), both of which are locally conservative, to approximate the model. A hybrid mixed finite element (HMFE) method is applied to approximate the velocity field for the model. The convection and diffusion terms are approached by FVM and the standard MFE, respectively. The pressure distribution and temporary evolution of the concentration profiles are obtained for two phases. The average effluent concentration on the outflow boundary is obtained at different time and shows some different features from the matrix porous media. The temporal multiscale phenomena of the effluent concentration on the outlet are observed. The results show how the different distribution of the vugs and the fractures impacts on the contaminant transport and the effluent concentration on the outlet. This paper sheds light on certain features of karstic groundwater are obtained.