Oil & Natural Gas Projects
Exploration and Production Technologies
Time-Lapse Seismic Modeling and Inversion of CO2 Saturation for Sequestration
and Enhanced Oil Recovery
This project seeks to improve current methods of time-lapse seismic reflection
modeling for carbon dioxide sequestration and miscible CO2 floods in oil and
gas reservoirs and to develop new strategies to invert such data to estimate
changes in pressure and CO2 saturation over time.
4th Wave Imaging Corp.
Aliso Viejo, CA
This project has resulted in new algorithms to model accurately time-lapse seismic
changes during CO2 injection, and to invert these data to estimate changes in
reservoir properties, such as pressure and CO2 saturation, that cause the seismic
anomalies. Both modeling and inversion algorithms rely on rock physics relations
to estimate seismic parameters, such as velocities and densities, as a function
of CO2 saturation and pressure.
The major achievements of this project include:
- Investigations of new ways to compute fluid properties of oil-water-CO2
- Development of a 1-D time-lapse well-log modeling program.
- An algorithm to generate time-lapse seismic attribute changes as a function
of changes in CO2 saturation and pressure.
- New tools to invert time-lapse seismic anomalies to yield estimates of CO2
saturation and pressure changes and the calibration of these tools on a synthetic
- Quantification of time-lapse seismic anomalies from different vintages of
a 3-D data set from Sleipner gas field in the Norwegian North Sea.
Miscible CO2 flooding has become an increasingly important enhanced oil recovery
(EOR) technique in the U.S. for recovering residual or bypassed oil. For example,
roughly half the CO2 floods in the world are located in the Permian Basin, producing
more than 20% of the area's total oil production. A broad application of CO2
EOR methods to thousands of U.S. reservoirs may contribute an additional 43
billion bbl of reserves, which would provide significant revenues to state treasuries,
provide thousands of additional domestic jobs, and improve the U.S. trade balance
by reducing imports. By developing an accurate approach for tracking CO2 fronts
during EOR operations, this project is expected to help improve recovery rates,
optimize well patterns, locate bypassed oil, and minimize the cost of injected
CO2. Project results also will benefit the public by addressing the potential
contribution of CO2 to postulated manmade climate change. By improving current
methods for monitoring reservoir leaks and verifying the location and quantity
of sequestered CO2, this project will help minimize the impact of CO2 on the
Time-lapse seismic monitoring during CO2 injection is still in its infancy.
Seismic monitoring requires knowledge of the rock and fluid properties of the
oil reservoir to track changes in CO2 saturation and pressure over time. Despite
the growing importance of CO2 for EOR projects and geologic storage and sequestration,
very little is understood about its physical properties in oil-water/porous
rock systems. Further understanding is needed to remotely monitor the injected
CO2 and to estimate injected CO2 saturation distributions in subsurface aquifers
The three major objectives of this DOE/NETL research project are to:
- Research and develop improved methods to quantitatively model the rock physics
effects of CO2 injection in porous reservoir/aquifer rock systems.
- Develop a means to quantitatively model the seismic response to CO2 injection
from well logs (1-D) and from digital earth model volumes (3-D and 4-D).
- Research and develop new technology to perform quantitative inversions of
time-lapse 4-D seismic data to estimate injected CO2 distributions and pore
pressure changes within subsurface reservoirs and aquifers.
In Phase I of the project, researchers investigated new ways to calculate fluid properties of oil-water CO2mixtures under varying reservoir conditions using both EOS (equation of state) methods and molecular dynamics modeling. An EOS formulation has been developed that can calculate bulk fluid properties from multiple liquid and gas phases for supercritical CO2 mixtures. In Phase II this EOS has been used to perform 1-D time-lapse seismic modeling to predict changes in seismic data during CO2 injection by calculating how well-log velocities and densities change under varying CO2 saturations and pressures. In addition, progress has been made in building a 3-D seismic modeling tool that can be used to predict time-lapse seismic anomalies in 3-D field data. In Phase III, a method was developed to invert time-lapse seismic anomalies to yield maps of CO2 saturation and pressure changes over time. This method, which was applied successfully to a synthetic dataset, is based on the generation of seismic attribute changes as a function of CO2 saturation and pressure, including changes in both miscible and free CO2 levels. Many of these seismic attributes have been extracted from the Sleipner 3-D time-lapse seismic dataset for use later in the inversion algorithm.
The work has resulted an improved and efficient ability to remotely monitor injected CO2 for safe storage and enhanced hydrocarbon recovery.
Current Status (June 2006)
The project is complete. All the tasks of Phase 1, 2, and 3 are completed. The final report is submitted to DOE.
Project Start: September 30, 2003
Project End: December 31, 2005
Anticipated DOE Contribution: $624,000
Performer Contribution: $156,000 (20% of total)
NETL-Purna Halder (firstname.lastname@example.org or 918-699-2083)
4th Wave-Mark Allan Meadows (email@example.com or 949-916-9787)
The image on the top shows a seismic travel-time difference map produced from
two vintages of the Sleipner CO2 seismic dataset. The image at right depicts
the plot of time-lapse seismic travel-time differences (in seconds) through
a reservoir model generated by modeling travel times across a range of CO2 pressures
(in megapascals) and saturation changes.
Time-lapse CO2 seismic data set showing a clear amplitude anomaly caused by
increasing CO2 saturation at this level.
Seismic stacked sections from the Sleipner time-lapse CO2 project. Sleipner is a giant natural gas/condensate field in the Norwegian North Sea. Vertical sections are taken from the 1994 (left), 2002 (middle), and 2002-1994 difference (right) cubes. Clear evidence of a time-lapse anomaly is visible in the difference section starting at around 900 milliseconds. CO2 injection started in 1996.
3-D perspective view of seismic reflection amplitudes from the 2002 Sleipner North Sea data set. Clouds of high-amplitude values delineate the location and extent of the CO2-saturated zones within the Utsira sand.