Oil & Natural Gas Projects
Exploration and Production Technologies
Wettability and Oil Recovery by Imbibition and Viscous Displacement from
Fractured and Heterogeneous Carbonates
This project was selected in response to DOE's Oil Exploration and Production
solicitation DE-PS26-01NT41048, Focus Area No. 13, Critical Upstream Advanced
Diagnostics and Imaging Technologies.
The project goals are to:
- Relate wettability alteration of carbonate surfaces to methods of wettability
control of carbonate rocks by adsorption from selected crude oils.
- Measure oil recovery and characterize wettability by spontaneous imbibition
measurements for strongly water-wet carbonate rocks and for the same rocks after
systematic changes in wettability induced by adsorption from crude oil.
- Investigate the sensitivity of oil recovery to displacement rate for carbonate
University of Wyoming
New Mexico Institute of Mining and Technology
Researchers measured wettability alteration at carbonate surfaces for more
than 16 crude oils. Correlations were reported for imbibition into carbonate
rocks for very strongly water-wet and crude oil-induced wettability variations.
The project also demonstrated the sensitivity of oil recovery to flow rate
for heterogeneous outcrop limestone for very strongly water-wet conditions
and for mixed-wettability states established by adsorption from crude oil.
Researchers identified sources of outcrop carbonate rock and made unique
comparisons for oil recovery by spontaneous imbibition and waterflooding for
very strongly water-wet conditions versus a range of mixed-wettability states
for different rock types and crude oils. They also demonstrated the rate sensitivity
of waterflood residual oil originally observed for reservoir carbonate rocks.
Major advances have been made in methods of wettability control in carbonates
that serve as model rocks. The completed parametric studies of oil recovery
by spontaneous imbibition and viscous displacement will find many other applications
in improved oil recovery and reservoir diagnostics. These results confirm
and explain the unexpected but repeatedly observed sensitivity of oil recovery
to injection rate reported by industry for reservoir carbonate cores. Companies
(mainly independents) operating in states such as Wyoming-in which a substantial
fraction of oil-in-place is held in heterogeneous and fractured carbonates-have
a direct economic interest in this project.
About half of U.S. oil reserves is held in carbonate formations. The remaining
oil in low-permeability fractured carbonate reservoirs is a major domestic
target for improved oil recovery. This study addresses the quantification
of crude oil/brine/rock interactions and the impact of heterogeneity on oil
recovery by spontaneous imbibition and viscous displacement.
The problem of wettability and oil recovery from carbonate reservoirs was
recognized throughout the oil industry as being largely unexplored. Both laboratory
and field evidence of the sensitivity of waterflood recovery to flow rate-even
down to field rates-revealed phenomena that could be turned to advantage with
respect to improved recovery. For example, increased injection pressure, increased
injectivity, decreased well spacing, or lowering of interfacial tension would
lead to additional oil recovery.
In this project, researchers have:
- Identified sources of outcrop carbonate rock.
- Identified crude oils for oil recovery studies from contact angle measurements.
- Made unique comparisons for oil recovery by spontaneous imbibition and waterflooding
for very strongly water-wet conditions versus a range of mixed wettability states.
- Demonstrated the rate sensitivity of waterflood residual oil at below and
above field flow rates for heterogeneous outcrop carbonate rock.
Wettability-alteration characteristics of crude oils measured at carbonate
surfaces were related to the properties of the crude oils. The effect of wettability
on oil recovery was investigated for limestones that cover more than three
orders of magnitude in permeability and a factor of four variations in porosity.
The rate sensitivity of oil recovery to waterflooding has been demonstrated
for very strongly water-wet and mixed-wet heterogeneous carbonate rocks. Homogeneous
samples did not exhibit rate sensitivity at any wetting condition. These results
are consistent with reservoir condition tests reported by industry researchers.
Nearly all aspects of the project are now complete. A 6-month, no-cost extension
has been requested, mainly to allow completion of tracer test work that will
utilize equipment at the University of Bergen's Department of Physics. (Two
PhD students from the University of Wyoming are currently at Norway's University
of Bergen with Prof. Arne Graue.)
Industry has shown strong interest in this project. Operators continue to
observe the rate sensitivity of oil recovery to waterflooding for many carbonate
reservoirs and are likely to provide matching support for further work on
rate effects and relative permeabilities for carbonate rocks. The advances
made in wettability control for a variety of rock types (including sandstones)
provide the opportunity for the study of variation in relative permeabilities
resulting from systematic change in wettability.
Tie, H.G., Tong, Z.X., and Morrow, N.R., The Effect of Different Crude
Oil/Brine/Rock Combinations on Wettability through Spontaneous Imbibition,
Proceedings of the International Society of Core Analysts Annual Meeting,
Pau, France, September 2003.
Fischer, H., Morrow, N.R., and Mason, G., Application of water desorption/adsorption
isotherms data to characterization of micro- and meso-porosity in sandstone
and carbonate rocks, presented at the 7th International Symposium on the Characterization
of Porous Solids, COPS VII, Aix-en-Provence, France, May 26-28, 2005.
Tie, H., and Morrow, N.R., Oil Recovery by Spontaneous Imbibition Before
and After Wettability Alteration of Three Carbonate Rocks by a Moderately
Asphaltic Crude Oil, to be presented at the International Society of Core
Analysts Annual Meeting, Toronto, Canada, August 21-34, 2005.
Tie, H., and Morrow, N.R., Low Flood Rate Residual Saturations in Carbonate
Rocks, to be presented at the International Technology Conference, Doha, Qatar,
November 21-23, 2005.
Project Start: July 18, 2002
Project End: July 17, 2006
Anticipated DOE Contribution: $749,522
Performer Contribution: $333,315 (30% of total)
NETL - Chandra Nautiyal (firstname.lastname@example.org or 918 699-2021)
U. of Wyoming - Norman Morrow (email@example.com or 307-766-2838)
Wyoming Cottonwood carbonate.