Oil & Natural Gas Projects
Exploration and Production Technologies
Investigation of Efficiency Improvement During CO2 Injection in Hydraulically
and Naturally Fractured Reservoirs
This project was in response to DOE's solicitation DE- PS26-01NT41048, Reservoir
Efficiency Processes. The goal of this solicitation was to reduce the amount
of oil bypassed due to the poor sweep of carbon dioxide and to increase oil
predictability and improve oil extraction using new technologies.
The project goal was to perform unique laboratory experiments with artificial
fractured cores (AFCs) and X-ray computer tomography (CT) to examine the physical
mechanisms of bypassing in hydraulically and naturally fractured reservoirs
that eventually result in less efficient CO2 flooding in heterogeneous or fracture-dominated
Texas Engineering Experiment Station (TEES)
Texas A&M University
College Station, TX
The project used an X-ray CT scanner to image saturation profiles of flow patterns
for direct measurement of bypassing mechanisms and to measure bypassed oil in
order to optimize CO2 flooding efficiency. With this equipment, researchers
have established the relationship between fracture aperture distribution and
overburden pressures. They found that CO2 gravity drainage still plays an important
role in oil recovery, even in a short-matrix block. CO2 sweep efficiency was
improved significantly by controlling the CO2 mobility in the fracture with
viscosified water and placing a cross-linked gel in the fracture.
In the United States, oil that is potentially producible by advanced recovery
methods amounts to 200 billion barrels. Of the available advanced oil recovery
methods, gas injection has the greatest potential for additional oil recovery
from domestic light oil reservoirs. CO2 flooding is the most promising gas injection
technique for widespread use among enhanced oil recovery (EOR) technologies.
New CO2 projects are commencing in the U.S. and internationally each year.
CO2 suppliers are drilling new CO2 production wells to increase available CO2
for delivery, and plans are under way to increase current pipeline capacities
in areas where there are a lot of CO2 floods, such as the Permian Basin of New
Mexico and Texas. Also, other areas in North America, such as the Wyoming-to-Canada
corridor, California, and the Mississippi River region, continue development
or consideration of extending the current CO2 pipeline networks to more-distant
reservoirs. However, there are many reservoirs that are not being considered
for CO2 flooding or any type of EOR methods because of extreme heterogeneity,
or natural fractures. Because of CO2 flooding's huge potential, efforts to overcome
this challenge offer potential to bolster the Nation's economic and energy security.
The primary goal of this research is to maximize the potential of CO2 flooding
in the United States. As more technical knowledge accumulates, it becomes clear
that natural and hydraulically induced fractures often dominate pattern or reservoir
sweep efficiency. As the level of sophistication grows, low permeability reservoirs
become more amenable to EOR via CO2. Low-permeability reservoirs are usually
characterized by brittle matrix rock, which cracks under natural or induced
Many of the issues involved in saturation distribution during CO2 injection
have been tested in Berea cores above and below miscibility pressure. However,
the level of heterogeneity rarely, if ever, includes the presence of natural
fractures. This is not coincidental, since the level of experimentation required
is high in order to develop useful interpretations. The fact remains that reservoir
heterogeneity dominates the performance of gas injection. Hydraulic or natural
fractures can exert a major influence on the economics of CO2 injection projects.
But the fundamental mechanisms of transfer in fracture systems are virtually
unexplored. The transfer of injected gas from hydraulically induced or natural
fractures determines the ultimate displacement and sweep efficiency. It is the
intent of this proposed work to advance the understanding of this dynamic process
and determine the implications on the ultimate performance of bypassing reserves
during CO2 injection.
Among the project highlights:
- Advanced imaging technology has been employed to 1) characterize matrix
and fracture systems, 2) image saturation profile, and 3) investigate transfer
and bypassing mechanisms in order to optimize CO2 flooding efficiency.
- The new laboratory experiments have been developed to 1) demonstrate the
effect of different overburden pressures and injection rates on fracture aperture
and matrix and fracture productivities, and 2) mitigate bypassing mechanisms
that will result in less bypassing and more efficient CO2 flooding in fracture-dominated
- Different CO2 injection rates and WAG (water-alternating-gas) injection
ratios, along with increasing water viscosity in the WAG process and placing
a gel-polymer in the fracture system were conducted as the laboratory scale
to improve CO2 flooding efficiency.
- The laboratory techniques have been used to reduce CO2 bypassing and optimize
CO2 flood design in the Wasson Field of west Texas.
- Analytical and numerical modeling have been performed to 1) investigate
the effect of fracture aperture at variable overburden pressure, 2) study
the effect of different rock heterogeneity on flow path contributors, 3) validate
the use of cubic law equation, 4) examine the transfer mechanism during core
flooding in fractured cores, and 5) assess the effect of grid orientation
in different mobility ratios.
- A new discrete fracture simulator with flexible and unstructured gridding
techniques was developed to accurately model the fluid flow through fracture
networks with multiple orientations.
Current Status (August 2005)
All the proposed tasks have been completed on time. The final report is being
X-ray images of a CO2 front movement through a fractured core, showing the influence
of gravity segregation.
Pressure distribution map with unique gridding technique.
Publications (partial list)
Schechter, D.S., et al. Investigation of Efficiency Improvement during CO2 Injection
in Hydraulically and Naturally Fractured Reservoirs, Semi-Annual Progress Report
(DOE Contract No.: DE-FC26-01BC15361), Oct 2001-March 2002, April 2002-October
2002, October 2002-March 2002, April 2003-October 2003, November 2003-March
2004, April 2004-October 2004, and October 2004-April 2005.
Kaul, S.P., Putra, E., and Schechter, D.S., Spontaneous Imbibition Simulation
with Rayleigh-Ritz Finite Element Method, paper SPE 90053, presented at the
SPE International Petroleum Conference, Puebla, Mexico, November 8-9, 2004.
Muralidharan, V., Chakravarthy, D., Putra, E., and Schechter, D.S.,:Simulation
of Fluid Flow through Rough Fractures, paper SPE 89941, presented at the SPE
International Petroleum Conference, Puebla, Mexico, November 8-9, 2004.
Chong, E., Syihab, Z., Putra, E., and Schechter, D.S., A Unique Grid-Block
System for Improved Grid Orientation, paper SPE 88617 presented at Asia Pacific
Oil and Gas Conference and Exhibition (APOGCE), Perth, Australia, October 18-20,
Muralidharan, V., Chakravarthy, D., Putra, E., and Schechter, D.S., Simulation
and Imaging Experiments for Flow through a Fracture Surface: A New Perspective,
SPE paper presented at the International Student Paper Contest, Houston, TX,
September 26-29, 2004.
Muralidharan, V., Putra, E., and Schechter, D.S., Experimental and Simulation
Analysis of Fractured Reservoir Experiencing Different Stress Conditions, paper
CIPC 2004-229 presented at the Annual Technical Meeting of the Petroleum Society,
Calgary, Canada, June 8-10, 2004
Project Start: September 28, 2001
Project End: September 27, 2005
Anticipated DOE Contribution: $937,000
Performer Contribution: $235,000 (20% of total)
NETL - Daniel J. Ferguson (firstname.lastname@example.org 918-699-2047)
TAMU- David Schechter (email@example.com or 979-845-2275)