Simulation of Matrix/Fracture Interaction in Low-Permeability Fractured Unconventional Reservoirs

SPE Journal ◽  
2018 ◽  
Vol 23 (04) ◽  
pp. 1389-1411 ◽  
Author(s):  
D. Y. Ding ◽  
N.. Farah ◽  
B.. Bourbiaux ◽  
Y.-S.. -S. Wu ◽  
I.. Mestiri
Keyword(s):  
Transient Flow ◽  
Unconventional Reservoirs ◽  
Hydraulic Fractures ◽  
Low Permeability ◽  
State Matrix ◽  
Discrete Fracture Model ◽  
Matrix Fracture ◽  
Discrete Fracture ◽  
The Matrix ◽  
Fracture Interaction

Summary Unconventional reservoirs, such as shale-gas or tight oil reservoirs, are generally highly fractured (including hydraulic fractures and stimulated and nonstimulated natural fractures of various sizes) and embedded in low-permeability formations. One of the main production mechanisms in unconventional reservoirs is the flow exchange between matrix and fracture media. However, because of extremely low matrix permeability, the matrix/fracture exchange is very slow and the transient flow may last several years to tens of years, or almost the entire production life. The commonly used dual-porosity (DP) modeling approach involves a computation of pseudosteady-state matrix/fracture transfers with homogenized fluid and flow properties within the matrix medium. This kind of model clearly fails to handle the long-lasting matrix/fracture interaction in very-low-permeability reservoirs, especially for multiphase flow with phase-change problems. Moreover, a DP model is not adapted for the simulation of matrix/fracture exchange when fractures are described by a discrete-fracture network (DFN). This paper presents an embedded discrete-fracture model (EDFM) dependent on the multiple-interacting-continua (MINC) proximity function to overcome this insufficiency of the conventional DP model.

scholarly journals An Integrally Embedded Discrete Fracture Model for Flow Simulation in Anisotropic Formations

Energies ◽  
2020 ◽  
Vol 13 (12) ◽  
pp. 3070
Author(s):  
Renjie Shao ◽  
Yuan Di ◽  
Dawei Wu ◽  
Yu-Shu Wu
Keyword(s):  
Flow Simulation ◽  
Fracture Model ◽  
Fluid Exchange ◽  
Two Phase ◽  
Fine Grid ◽  
Discrete Fracture Model ◽  
Matrix Fracture ◽  
Discrete Fracture ◽  
The Matrix ◽  
Anisotropic Formation

The embedded discrete fracture model (EDFM), among different flow simulation models, achieves a good balance between efficiency and accuracy. In the EDFM, micro-scale fractures that cannot be characterized individually need to be homogenized into the matrix, which may bring anisotropy into the matrix. However, the simplified matrix–fracture fluid exchange assumption makes it difficult for EDFM to address the anisotropic flow. In this paper, an integrally embedded discrete fracture model (iEDFM) suitable for anisotropic formations is proposed. Structured mesh is employed for the anisotropic matrix, and the fracture element, which consists of a group of connected fractures, is integrally embedded in the matrix grid. An analytic pressure distribution is derived for the point source in anisotropic formation expressed by permeability tensor, and applied to the matrix–fracture transmissibility calculation. Two case studies were conducted and compared with the analytic solution or fine grid result to demonstrate the advantage and applicability of iEDFM to address anisotropic formation. In addition, a two-phase flow example with a reported dataset was studied to analyze the effect of the matrix anisotropy on the simulation result, which also showed the feasibility of iEDFM to address anisotropic formation with complex fracture networks.

Development of an Embedded Discrete Fracture Model for Multi-Phase Flow in Fractured Reservoir

2014 ◽  
Vol 668-669 ◽  
pp. 1488-1492
Author(s):  
Fang Qi Zhou
Keyword(s):  
Neumann Boundary ◽  
Fracture Model ◽  
Fractured Reservoir ◽  
Discrete Fracture Model ◽  
Matrix Fracture ◽  
Discrete Fracture ◽  
The Matrix ◽  
Multi Phase Flow ◽  
Multi Phase ◽  
Fracture Interface

Considering the discontinuities of the phase saturations and pressure gradients at the matrix-fracture interface, a modified algorithm for the embedded discrete fracture model is proposed. In this algorithm, the exchange rate between fracture and matrix on two sides of the interface are calculated separately. To avoid the problem for defining the physical variables on the matrix grid blocks overlaid by fracture, the Neumann boundary conditions are instead in the calculations of other matrix grid blocks. The numerical examples show that the simulation results of the proposed algorithm agree very well with those of the discrete fracture model. In reservoir with high matrix capillary pressure, the grids must be enough refined in the neighborhood of the matrix-fracture interface to achieve high numerical accuracy.

Three-Dimensional Projection-Based Embedded Discrete-Fracture Model for Compositional Simulation of Fractured Reservoirs

SPE Journal ◽  
2020 ◽  
Vol 25 (04) ◽  
pp. 2143-2161 ◽  
Author(s):  
Olufemi Olorode ◽  
Bin Wang ◽  
Harun Ur Rashid
Keyword(s):  
Fractured Reservoirs ◽  
Unconventional Reservoirs ◽  
Fracture Model ◽  
Hydraulic Fractures ◽  
Natural Fractures ◽  
Compositional Simulation ◽  
Discrete Fracture Model ◽  
Fracture Surfaces ◽  
Discrete Fracture ◽  
Simulation Results

Summary Most unconventional oil and gas reservoirs are known to have several natural fractures in different orientations, which are consistent with the prevailing stresses when they were created. The accurate and efficient modeling of natural and hydraulic fractures presents a significant computational challenge. In this work, we show the limitations of the embedded discrete-fracture model (EDFM) and present the first 3D projection-based EDFM (pEDFM) algorithm and compositional simulation studies with realistic fracture networks in a fully 3D space. The simulation results from this work indicate that the pEDFM presented can model realistic fractured unconventional reservoirs accurately and efficiently. To validate the model, we present some simplistic fracture cases that can be meshed and modeled easily using explicit-fracture modeling in commercial-reservoir simulators. From the cases studied, we observe that using progressively finer grids near the hydraulic-fracture surfaces helps to improve model accuracy because this allows us to capture the sharp pressure drops expected near these fracture surfaces. The simulation results show that, unlike EDFM, the robust pEDFM algorithm presented here is accurate even at the low fracture-conductivity values expected in many of these ubiquitous natural fractures. In this paper, we present the first full 3D compositional modeling with pEDFM. We demonstrate that our model can accurately and efficiently model multiply fractured horizontal wells in unconventional reservoirs, which have complex networks of thousands of fractures at various orientations.

Efficient Localized Nonlinear Solution Strategies for Unconventional-Reservoir Simulation with Complex Fractures

2021 ◽  
Author(s):  
Jiamin Jiang
Keyword(s):  
Transient Flow ◽  
A Priori ◽  
Time Discretization ◽  
Unconventional Reservoirs ◽  
Hydraulic Fractures ◽  
Nonlinear Solution ◽  
Compositional Model ◽  
Simulation Speed ◽  
Flow Mechanisms ◽  
Solution Accuracy

Abstract It is very challenging to simulate unconventional reservoirs efficiently and accurately. Transient flow can last for a long time and sharp solution (pressure, saturation, compositions) gradients are induced because of the severe permeability contrast between fracture and matrix. Although high-resolution models for well and fracture are required to achieve adequate resolution, they are computationally too demanding for practical field models with many stages of hydraulic fracture. The paper aims to innovate localization strategies that take advantage of locality on timestep and Newton iteration levels. The strategies readily accommodate to complicated flow mechanisms and multiscale fracture networks in unconventional reservoirs. Large simulation speed-up can be obtained if performing localized computations only for the solution regions that will change. We develop an a-priori method to exploit the locality, based on the diffusive character of the Newton updates of pressure. The method makes adequate estimate of the active computational gridblock for the next iterate. The active gridblock set marks the ones need to be solved, and then the solution to local linear system is accordingly computed. Fully Implicit Scheme is used for time discretization. We study several challenging multi-phase and compositional model cases with explicit fractures. The test results demonstrate that significant solution locality of variables exist on timestep and iteration levels. A nonlinear solution update usually has sparsity, and the nonlinear convergence is restricted by a limited fraction of the simulation model. Through aggressive localization, the proposed methods can prevent overly conservative estimate, and thus achieve significant computational speedup. In comparison to a standard Newton method, the novel solver techniques achieve greatly improved solving efficiency. Furthermore, the Newton convergence exhibits no degradation, and there is no impact on the solution accuracy. Previous works in the literature largely relate to the meshing aspect that accommodates to horizontal wells and hydraulic fractures. We instead develop new nonlinear strategies to perform localization. In particular, the adaptive DD method produces proper domain partitions according to the fluid flow and nonlinear updates. This results in an effective strategy that maintains solution accuracy and convergence behavior.

Modeling of Matrix/Fracture Transfer with Nonuniform-Block Distributions in Low-Permeability Fractured Reservoirs

SPE Journal ◽  
2019 ◽  
Vol 24 (06) ◽  
pp. 2653-2670 ◽  
Author(s):  
Didier–Yu Ding
Keyword(s):  
Shale Gas ◽  
Shape Factor ◽  
Oil Reservoirs ◽  
Dual Porosity ◽  
Tight Oil ◽  
Fracture Networks ◽  
Matrix Block ◽  
Matrix Fracture ◽  
Discrete Fracture ◽  
The Matrix

Summary Unconventional shale–gas and tight oil reservoirs are commonly naturally fractured, and developing these kinds of reservoirs requires stimulation by means of hydraulic fracturing to create conductive fluid–flow paths through open–fracture networks for practical exploitation. The presence of the multiscale–fracture network, including hydraulic fractures, stimulated and nonstimulated natural fractures, and microfractures, increases the complexity of the reservoir simulation. The matrix–block sizes are not uniform and can vary in a very wide range, from several tens of centimeters to meters. In such a reservoir, the matrix provides most of the pore volume for storage but makes only a small contribution to the global flow; the fracture supplies the flow, but with negligible contributions to reservoir porosity. The hydrocarbon is mainly produced from matrix/fracture interaction. So, it is essential to accurately model the matrix/fracture transfers with a reservoir simulator. For the fluid–flow simulation in shale–gas and tight oil reservoirs, dual–porosity models are widely used. In a commonly used dual–porosity–reservoir simulator, fractures are homogenized from a discrete–fracture network, and a shape factor based on the homogenized–matrix–block size is applied to model the matrix/fracture transfer. Even for the embedded discrete–fracture model (EDFM), the matrix/fracture interaction is also commonly modeled using the dual–porosity concept with a constant shape factor (or matrix/fracture transmissibility). However, in real cases, the discrete–fracture networks are very complex and nonuniformly distributed. It is difficult to determine an equivalent shape factor to compute matrix/fracture transfer in a multiple–block system. So, a dual–porosity approach might not be accurate for the simulation of shale-gas and tight oil reservoirs because of the presence of complex multiscale–fracture networks. In this paper, we study the multiple–interacting–continua (MINC) method for flow modeling in fractured reservoirs. MINC is commonly considered as an improvement of the dual–porosity model. However, a standard MINC approach, using transmissibilities derived from the MINC proximity function, cannot always correctly handle the matrix/fracture transfers when the matrix–block sizes are not uniformly distributed. To overcome this insufficiency, some new approaches for the MINC subdivision and the transmissibility computations are presented in this paper. Several examples are presented to show that using the new approaches significantly improves the dual–porosity model and the standard MINC method for nonuniform–block–size distributions.

A Dynamic Discrete Fracture Model for Simulation of Tight Low-Permeability Reservoirs

2014 ◽  
Author(s):  
Zhengdong Lei ◽  
Changbing Tian ◽  
Fang Wang ◽  
Wenhuan Wang ◽  
Huanhuan Peng ◽  
...  
Keyword(s):  
Fracture Model ◽  
Low Permeability ◽  
Discrete Fracture Model ◽  
Discrete Fracture ◽  
Low Permeability Reservoirs
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