Crisman Annual Report 2009 - Harold Vance Department of ...

Modeling of Discrete Fracture Network using Voronoi Grid System
Objectives
Dual-porosity (DP) is the most common model to
simulate fluid flow through fractured media. This
model comprises several limitations (i.e., it is not
well suited to accurately model fracture networks
with multiple orientations). On the other hand, a
single-porosity model with conventional gridding
techniques requires an excessive number of grids to
model fractures explicitly.
The objectives of this work are to develop a
reservoir simulator (DFNSIM) along with a novel
gridding technique based on Voronoi algorithm to
allow fracture networks represented explicitly into
reservoir model.
Approach
It requires two different domains to represent
fractures explicitly in a simulation model: geometrical
and computational (Fig. 1). In the geometrical
domain, the fracture is represented as a line. The
volume and permeability of each fracture segment
are calculated based on a given fracture aperture
distribution (i.e. log-normal distribution from X-Ray
CT Scan) in the computational domain.
(a) Geometrical domain
(b) Computational domain
(a) Unfractured
(b) Fractured
Fig. 2. Grid generation for unfractured and fractured systems.
by Chong et al. However, the governing equation of
the simulator was similar to DFNSIM (CVFD).
Prior to using DFNSIM in modeling reservoirs with
fractures including their apertures distribution,
the simulator was validated against commercial
simulators. The simulator provides results in close
agreement with those of reference finite-difference
simulators (SPE-1 comparative solutions; after Aziz
& Odeh, SPEJ, 1981).
CRISMAN INSTITUTE
Project Information
3.1.19 Modeling of Discrete Fracture Network using Voronoi
Grid System
Related Publications
Chong, E., Syihab, Z., Putra, E., Hidayati, D.T., Schechter,
D. A New Grid Block System for Reducing Grid Orientation
Effect, Journal of Petroleum Science and Technology.
(November 2007) London, UK.
Fig. 1. Fracture representation (geometrical and computational domains).
Accomplishments
Two major accomplishments were achieved from
this work: (1) fracture network gridding and (2)
development of a control volume finite-difference
numerical simulatior (CVFD), which can be used for
both fractured and unfractured systems (Fig. 2).
The unstructured grid (without fracture) was initially
tested to reduce the grid orientation effect. The
grid model was constructed by a combination of
rectangular, hexagonal, and triangle shapes. The
test was run using a separate simulator developed
Tae, H. K. and Schechter, D.S. Estimation of Fracture
Porosity of Naturally Fractured Reservoirs with No Matrix
Porosity Using Fractal Discrete Fracture Networks. Paper
SPE presented at the 2007 SPE Annual Technical Conference
and Exhibition, Anaheim, California, 11–14 November.
Syihab, Zuher.: 2009. Simulation of Discrete Fracture
Network Using Flexible Voronoi Gridding. PhD dissertation.
Texas A&M U., College Station, Texas.
Contacts
David Schechter
979.845.2275
david.schechter@pe.tamu.edu
Zuher Syihab
68
Crisman Annual Report 2009