Federal University of Santa Catarina
Centro Tecnológico
Departamento de Engenharia Mecânica
Coordenadoria de Estágio do Curso de
Engenharia Mecânica
CEP 88040-970 - Florianópolis - SC - BRASIL
www.emc.ufsc.br/estagiomecanica
estagio@emc.ufsc.br
INTERNSHIP REPORT – 1/3
Período: de 09/01/2010 a 10/20/2010
The University of Texas at Austin –
Center for Petroleum and Geosystems Engineering
Intern: Bruno Terêncio do Vale
Supervisor: Prof. Kamy Sepehrnoori, Ph.D.
Advisor: Prof. Clovis Raimundo Maliska, Ph.D.
Austin, TX, 10/20/2010.
Institution, work areas and products
The University of Texas at Austin (also referred to as UT or UTAustin) is a public research university located in Austin, Texas, USA.
Founded in 1883, the university has the fifth largest single-campus
enrollment in the nation as of fall 2009 (and had the largest enrollment in
the country from 1997–2003), with over 50,000 students, 2,900 faculty,
and 21,000 staff members.
The Center for Petroleum and Geosystems Engineering Research
(CPGE), located on the main campus, is where this internship takes place.
CPGE has, as missions, the objectives to encourage and develop
interdisciplinary research in petroleum and geosystems engineering as
well as other areas related to energy and the environment, to provide
educational
opportunities
for
graduate
students,
to
provide
an
organizational structure for funding new areas of research and conduct
meetings, symposia, and workshops on research topics, and to provide a
mechanism for technology transfer.
The center works with a large range of projects, including
environmental engineering, drilling, well completions, rock mechanics, and
production engineering. Prof. Kamy Sepehrnoori, supervising this work,
oversees research projects and teaches courses primarily focusing on
computational methods in the area of reservoir engineering, natural gas
engineering, and integrated reservoir characterization.
In the area of reservoir simulation, research activities include
reservoir modeling and simulation as well as model developments, such as
wettability alteration, geomechanics, unstructured grid, naturally fractured
reservoirs,
and
compositional
models.
With
this
knowledge,
the
development and the maintenance of simulators for enhanced oil recovery
(EOR) processes, such as GPAS (General Purpose Adaptive Simulator - a
fully implicit parallel compositional simulator) and the UTCHEM (IMPEC –
implicit pressure, explicit concentration - compositional chemical flooding
simulator) can be performed.
Introduction
This is the first report written to detail my activities at CPGE. The
internship concerns the last semester of the undergraduate course of
mechanical engineering at the Federal University of Santa Catarina
(UFSC), standing as a requirement for the completion of the course. The
internship has an initial duration of six months – from September 1, 2010,
until February 28, 2011 – and takes place at The University of Texas at
Austin, in the Center for Petroleum and Geosystems Engineering, in the
area of numerical simulation of multiphase flow in fractured-porous media.
There is a growing interest in naturally fractured hydrocarbon
reservoirs, since the behavior presented by a multiphase flow in such
reservoirs cannot be modeled as a single-phase flow in a porous media. As
Monteagudo and Firoozabadi (2004) explain, “fractured-porous media are
composed of rock matrix and fractures […] Often the rock matrix provides
the storage, and in single-phase flow, fractures provide the fluid flow
path. In two-phase flow, fractures may provide the flow path of one phase
and the less permeable matrix can provide the flow path of the other
phase […] The flow path of a phase in multiphase flow is affected by
capillary, gravity, diffusion/dispersion, and viscous forces”.
There are many situations in which multiphase flow in fracturedporous media occurs, which has raised economic interest. Multiphase flow
in subsurface fractured-hydrocarbon formations is of high interest in
hydrocarbon production (Monteagudo and Firoozabadi, 2004). Another
example of multiphase flow in fractured-porous media is the analysis of
water and non-aqueous-phase liquids flow in fractured media. However,
the main reason for the need of this study comes from the fact that
naturally fractured formations comprise to 20% of the world’s petroleum
and natural gas reserves. It is worth mentioning that it is common to
generate fractures in the reservoir during the drilling of a well to improve
the permeability in the proximity of the wellbore.
Proposed work
The objective of this work relates to The University of Texas
chemical
compositional
simulator
(UTCHEM)
simulator,
an
IMPEC
simulator, particularly to the part of the code that uses the Element-based
Finite Volume Method (EbFVM). Since this method enables the use of
unstructured meshes in two- and three-dimensions, ensuring flexibility in
representing the complex geometries in reservoirs, the implementation of
a discrete fracture model is the main objective of this work.
Overview
UTCHEM is a 3D, multi-component, multiphase, compositional, nonisothermal simulator used for modeling chemical flooding processes. This
simulator accounts for complex phase behavior and the transport of
chemicals and hydrocarbons in heterogeneous porous media that can be
used both for groundwater analysis and for oilfield applications.
The mass conservation equation for each species, the energy
balance, and the aqueous phase pressure equations are used in this
program. For the first set of equations, the boundary conditions are no
flow or dispersive flow on the impermeable boundaries. The boundary
condition for the energy balance equation is that the energy is only a
function of the temperature and the energy flux in the media occurs just
by advection and diffusion. The boundary condition for the pressure
equation is obtained by an overall mass balance on volume-occupying
components (water, oil, surfactant, co-solvent, and gas), substituting
Darcy’s law for the phase flux terms and noting that the sum of the
concentration of all components is equal to one. The other phase
pressures are computed by adding the capillary pressure between phases.
As result of its initial implementation, the UTCHEM simulator
originally used the finite difference method, requiring a structured mesh
(Cartesian, radial, or curvilinear). However, the use of that kind of mesh,
in the case of complex geometries or in the local refinement of wells and
faults, common in real situations, shows restrictions. Based on this
evidence, a new line of research was started, resulting in a new version of
the UTCHEM simulator working with EbFVM. That method was, and is,
widely studied in the SINMEC – Computational Fluid Dynamics Laboratory,
at the Federal University of Santa Catarina, providing the intern some
familiarity with the method.
Figure 1 – Control volume assembling in EbFVM
The
EbFVM
methodology
was
implemented
in
the
UTCHEM
simulator. As this method uses more flexibility in mesh generation,
additional features are being developed for the software. The objective of
this work will be carried out with the implementation of a discrete fracture
model in the code. A similar implementation was performed for GPAS, the
fully implicit simulator aforementioned. Therefore, that software will be
used as a reference for this internship.
For the implementation of the naturally fracture model, one can use
the dual porosity and the dual permeability models. Both methods,
however, have some drawbacks in the representation of complex fracture
configurations. These methods do not use mesh flexibility gained by the
EbFVM method, which is the main motivation for this research. An
alternative for these models is the discrete-fracture model. Moreover,
when compared with the dual-porosity/dual-permeability models, the
discrete-fracture model offers several advantages (Monteagudo and
Firoozabadi, 2004):
 It can account explicitly for the effect of individual fractures on
fluid flow.
 There is no need to compute the exchange term between the
matrix and the fracture.
 The performance of the method is not affected by very thin
fractures.
The discrete fracture modeling takes much more computational time
than the dual porosity models; however, the discrete fracture model is
more accurate.
Work Plan
A plan for this work is shown below. The chart shows the tasks for
this work and the duration of each task. The work plan will be revised as
the work continues based on the time needed to complete the tasks.
September
October
November December
January
February
Overview
Implementation
Validation
Approach
In the process to include the discrete fracture model in the UTCHEM
simulator, some steps have to be performed:
 Identify the fractures in the mesh file (the fractures, in the
mesh, should always go through the edges of the elements;
the user can simply indicate the nodes in which the fracture is
present).
Figure 2 – Representation of the fracture (thick line) in an unstructured mesh
 Provide the data needed to fully characterize the problem (like
the thickness and the porosity of the fracture).
 Include the contribution of the flow of the fracture in the
balance equations in each volume that contains a stretch of
the fracture.
The last step is interesting in the discrete fracture model since there
is no need to create two separate systems of equations, which decreases
the computational time. There is just one system of equations, in which
both the matrix and fractures are considered. This occurs through the
integration of the equations of both systems using the superposition
principle.
Figure 3 – Control volume cell: (a) unfractured and (b) fractured media.
To create the meshes that will be used in the validation cases, a
program called GID most likely will be used. For the post-processing of
data, the software that will be used is called Kraken, developed and
licensed by ESSS - Engineering Simulation and Scientific Software Ltd., a
simulation company based in Florianopolis with a long list of works in
conjunction with SINMEC. With Kraken, the simulations results of the
UTCHEM
simulator
can
be
visualized
and
analyzed,
allowing
the
comparison of its results with the results of other commercial simulators
such as ECLIPSE, IMEX, and Stars.
Results
During the first month of research, an extensive review was carried
out, including topics such the FORTRAN 90, in which the code of UTCHEM
is written, the model formulation of the UTCHEM simulator (studied
through the UTCHEM user guide and the UTCHEM Technical Manual), the
discrete fracture model, the IMPEC method, the UTCHEM simulator
(specifically, the EbFVM implementation part of the code), and the GPAS
simulator (particularly, the discrete fracture model part of the code).
Future Work
For the next month, the objective is to begin working on the code
and become familiar with the mesh generator program. With regard to the
code, the necessary data will be inserted in the mesh file (geometry) and
the UTCHEM input file (properties). With that information, the next step
will be changing the conservation equations, so that it considers the
effects of fractures.
References
1. Karpinski, L., Maliska, C. R., Marcondes, F., Delshad, M.,
Sepehrnoori, K. “An Element Based Conservative Approach Using
Unstructured
Grids
in
Conjunction
with
a
Chemical
Flooding
Compositional Reservoir Simulator”, XX International Congress of
Mechanical Engineering - COBEM, Gramado, RS, Brazil, 2009.
2. Marcondes, F., Varavei, A., Sepehrnoori, K. “An Element-Based
Finite-Volume
Method
Approach
for
Naturally
Fractured
Compositional Reservoir Simulation”, 13th Brazilian Congress of
Thermal Sciences and Engineering – ENCIT, Uberlândia, MG, Brazil,
2010.
3. Monteagudo, J. E. P., Firoozabadi, A. “Control-Volume Method
for Numerical Simulation of Two-Phase Immiscible Flow in Two- and
Three-Dimensional
Discrete-Fractured
Media”,
Water
Resources
Research, Vol. 40, 2004.
4. Monteagudo, J. E. P., Firoozabadi, A. “Comparison of Fully
Implicit and IMPES Formulations for Simulation of Water Injection in
Fractured
and
Unfractured
Media”,
International
Journal
for
Numerical Methods in Engineering, vol. 69, p. 698-728, 2007.
5. Karpinski, L. “UTCHEM – EbFVM User’s GUIDE (Based on UTCHEM
9.9
User’s
GUIDE)”,
Center
for
Petroleum
and
Geosystems
Engineering – CPGE, The University of Texas at Austin, Austin, TX,
2009.
6. UTCHEM-9.0. User’s Guide for UTCHEM-9.0: A Three-Dimensional
Chemical Flood Simulator, Volume I, Reservoir Engineering Research
Program, Center for Petroleum and Geosystems Engineering –
CPGE, The University of Texas at Austin, Austin, TX, 2008.
7. UTCHEM-9.0. Technical Documentation for UTCHEM-9.0 - A ThreeDimensional
Chemical
Engineering
Research
Flood
Simulator,
Program,
Center
Volume
for
II,
Reservoir
Petroleum
and
Geosystems Engineering – CPGE, The University of Texas at Austin,
Austin, TX, 2000.