Oil & Natural Gas Projects
Exploration and Production Technologies
Development and Optimization of Gas-Assisted Gravity Drainage (GAGD) Process
for Improved Light Oil Recovery
The main objective of this project was to develop a new gas-injection enhanced
oil recovery process, called Gas-Assisted Gravity Drainage (GAGD), to recover
large amounts of oil trapped in reservoirs subsequent to primary recovery and
secondary waterflood techniques. This new process being developed consists of
placing a horizontal producer near the bottom of the pay zone and injecting
gas through the existing vertical wells used in the prior waterfloods.
Louisiana State University
Baton Rouge, LA
The important dimensionless groups operating in gravity-stable field projects
were identified using the dimensional analysis approach. These dimensionless
numbers were successfully utilized to capture and characterize the operational
forces from field-gas injection projects for the laboratory physical model experiments.
The gas-oil interfacial tension measurements were conducted at elevated pressures
and temperatures using the standard gas-oil systems of known miscibility conditions.
The miscibilities determined from the vanishing interfacial tension (VIT) technique
agreed well with the reported miscibilities for all the standard fluid systems
used. This indicates the sound conceptual basis of the VIT technique for accurate,
quick, and cost-effective determination of miscibility conditions for miscible
gas injection improved oil recovery applications.
Laboratory corefloods of relevant reservoir rock and fluids showed the performance
of the GAGD process to be superior to almost all presently practiced commercial
modes of gas injection. This study has identified important multiphase mechanisms
and fluid dynamics operational in the GAGD process. The GAGD process has been
found to be largely immune to the deteriorating effects of reservoir heterogeneity,
and the results indicate that the presence of vertical fractures possibly aids
the GAGD performance.
The oil recoveries from currently practiced water-alternating-gas (WAG) horizontal gas injection processes are low, about 5-10% of original-oil-in-place (OOIP). The newly developed GAGD process can improve the overall efficiency of gas injection projects and hence will be of immediate interest to the US oil industry. Gas-oil miscibility conditions can be determined using the VIT technique in an easy and cost-effective manner. There is also the possibility of developing new miscibility correlations and computational models and the potential benefit of sequestering large quantities of CO2 in oil reservoirs.
After the application of primary and secondary oil recovery technologies, more
than 60% of the OOIP remains unrecovered in America's oilfields. This remaining
oil amounts to a staggering 377 billion barrels in the known oilfields of the
In spite of several ongoing WAG floods in the US, their incremental oil recoveries
have been disappointing. By comparison, oil recoveries were much better-15-40%
of OOIP-in the gravity-stable vertical gas floods conducted in pinnacle reefs
and dipping reservoirs. These field results indicate the benefits of working
with nature by making use of the buoyancy rise of injected gas to displace oil
downwards. This led to the conceptual basis of this project: injecting the
gas in a gravity-stable mode at the top of the pay zone in order to drain the
oil downwards to a horizontal producer.
The project consisted of three main tasks:
- Task 1 involved the design and development of a scaled physical model to identify
the optimum parameters for GAGD process performance.
- Task 2 called for further development of the VIT technique to determine miscibility
between the injected gas and crude oil for GAGD process optimization.
- Task 3 entailed corefloods using reservoir rocks and fluids to investigate
the effects of various multiphase mechanisms and fluid dynamics operational
in the GAGD process.
Researchers accomplished the following:
- Construction and experimentation with physical models to visualize the drainage
and displacement phenomena in the GAGD process.
- Design and assembly of a high-pressure, high temperature VIT experimental
system for gas-oil interfacial tension measurements at reservoir conditions.
- Completion of VIT experiments with model fluid systems of known phase behavior
conditions to determine gas-oil miscibility conditions.
- Completion of GAGD corefloods and comparative evaluation against horizontal
WAG and CGI using the high-pressure, high-temperature 6-foot coreflood assembly.
- Correlation of laboratory results against field performance characteristics
using a dimensionless gravity number (ratio of Bond to capillary number).
Current Status (July 2007)
This project is in close-out. All technical reports have been accepted as of February 2007.
Project Start: October 1, 2002
Project End: September 30, 2006
Anticipated DOE Contribution: $622,287
Performer Contribution: $242,238 (28% of total)
NETL - Betty Felber (firstname.lastname@example.org or 918-699-2031)
Louisiana State University - Dandina N. Rao (email@example.com or 225-578-6037)
Ayirala, S.C., Rao, D.N., and Casteel, J., Comparison of Minimum Miscibility Pressures Determined from Gas/Oil Interfacial Tension Measurements with Equations of State Calculations, SPE 84187 presented at the 2003 SPE Annual Technical Conference and Exhibition, Denver, CO, October 5-8, 2003.
Rao, D.N., Ayirala, S.C., Kulkarni, M.M., and Sharma, A.P., Development of Gas Assisted Gravity Drainage (GAGD) Process for Improved Light Oil Recovery, SPE 89357, presented at the 14th SPE/DOE Improved Oil Recovery Symposium, Tulsa, OK, April 17-21, 2004.
Kulkarni, M.M., and Rao, D.N., Experimental Investigation of Various Methods of Tertiary Gas Injection, SPE 90589 presented at the 80th SPE Annual Technical Conference and Exhibition, Houston, TX, September 26-29, 2004.
Ayirala, S.C. and Rao, D.N., Solubility, Miscibility and their Relation to Interfacial Tension for Application in Reservoir Gas-Oil Systems, SPE 91918 presented at the SPE International Petroleum Conference, Puebla, Mexico, November 7-9, 2004.
Ayirala, S.C. and Rao, D.N., Application of a New Mechanistic Parachor Model to Predict Dynamic Gas-Oil Miscibility in Reservoir Crude Oil-Solvent Systems, SPE 91920 presented at the SPE International Petroleum Conference, Puebla, Mexico, November 7-9, 2004.
Kulkarni, M.M., and Rao, D.N., Is Gravity Drainage an Effective Alternative to WAG?, paper presented at the American Institute of Chemical Engineers 2004 Annual Meeting, Austin, TX, November 7-12, 2004.
Ayirala, S. C., and Rao, D. N., Comparative Evaluation of a New MMP Determination Technique, SPE/DOE 99606 presented at the 15th SPE/DOE Improved Oil Recovery Symposium, April 2006.
Rao, D. N. Gas-Assisted (CO2) Gravity Drainage IOR: The Process and a Louisiana Field Project, presented at 15th SPE/DOE Improved Oil Recovery Symposium Independents Day Workshop, April 2006.
Schematic of GAGD physical model experimental apparatus.
Apparatus used for gas-oil interfacial tension measurements at elevated pressures