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CO2-triggered gelation for mobility control and channeling blocking during CO2 flooding processes
CO2-triggered gelation for mobility control and channeling blocking during CO2 flooding processes
De-Xiang Li 0 1
Liang Zhang 0 1
Yan-Min Liu 0 1
Wan-Li Kang 0 1
Shao-Ran Ren 0 1
0 Edited by Yan-Hua Sun
1 School of Petroleum Engineering, China University of Petroleum , Qingdao 266580, Shandong , China
CO2 flooding is regarded as an important method for enhanced oil recovery (EOR) and greenhouse gas control. However, the heterogeneity prevalently distributed in reservoirs inhibits the performance of this technology. The sweep efficiency can be significantly reduced especially in the presence of ''thief zones''. Hence, gas channeling blocking and mobility control are important technical issues for the success of CO2 injection. Normally, crosslinked gels have the potential to block gas channels, but the gelation time control poses challenges to this method. In this study, a new method for selectively blocking CO2 channeling is proposed, which is based on a type of CO2-sensitive gel system (modified polyacrylamide-methenamine-resorcinol gel system) to form gel in situ. A CO2-sensitive gel system is when gelation or solidification will be triggered by CO2 in the reservoir to block gas channels. The CO2-sensitivity of the gel system was demonstrated in parallel bottle tests of gel in N2 and CO2 atmospheres. Sand pack flow experiments were conducted to investigate the shutoff capacity of the gel system under different conditions. The injectivity of the gel system was studied via viscosity measurements. The results indicate that this gel system was sensitive to CO2 and had good performance of channeling blocking in porous media. Advantageous viscosity-temperature characteristics were achieved in this work. The effectiveness for EOR in heterogeneous formations based on this gel system was demonstrated using displacement tests conducted in double sand packs. The experimental results can provide guidelines for the deployment of the CO2-sensitive gel system for field applications.
CO2 flooding sensitivity; Sweep efficiency; Mobility control; Gas channeling; CO2; Enhanced oil recovery
1 Introduction
In recent years, sequestration and utilization of CO2 is
becoming an important research topic
(Ren et al. 2010;
Zhang et al. 2010)
. With the promotion of CO2 capture and
storage technology, the problem of CO2 gas source can be
solved and an increasing number of oil reservoirs will be
candidates for CO2 EOR projects
(Ren et al. 2014)
.
Injection of CO2 into oil and gas reservoirs may have both
economic and environmental benefits
(Elsharkawy et al.
1996; Sweatman et al. 2009; Talebian et al. 2014)
. Targets
for reducing greenhouse gas emission were also
emphasized during the 21st session of the conference of the
parties (COP21) which was held in 2015. Carbon dioxide
capture and storage (CCS) is a promising way of making
low-carbon energy solutions sustainable. However, CCS
has made limited progress. An important route to making
CCS a more sustainable option is via CO2 EOR as
part of carbon capture, utilization and storage (CCUS)
systems
(http://www.bbc.co.uk/news/science-environment35086346). In the southern states of the United States, CO2
flooding has been one of the main techniques for EOR due
to their abundant natural CO2 sources (Zhu et al. 2011). It
has been demonstrated that CO2 flooding can be one of the
most effective EOR technologies proven in field tests and
indoor experiments. There is a large-scale CO2 EOR
project in the Weyburn Oilfield of Canada to deal with the
industrial carbon emissions. Since 2000, about 1.8 million
tons of CO2 per year captured from a coal gasification plant
in the North Dakota have been transported to the Weyburn
Oilfield through pipelines for injection to meet the
requirements of storage and enhancing oil recovery. The
potential of CO2 storage in the field is over 50 million tons
and the incremental oil recovery can be achieved is
approximately 9.8 % OOIP
(Preston et al. 2005)
. Also a
large-scale CO2 EOR project has been under way in China
since 2006 in the Jinlin Oilfield (Northeast China)
(Li and
Fang 2007)
, in which CO2 produced and separated from
natural gas reservoirs nearby is utilized, and about 0.3–0.5
million tons of CO2 per year have been injected into oil
reservoirs since then. Meanwhile, in the Shengli Oilfield
CO2 is captured from a coal-fired electricity plant for EOR
and the capacity of CO2 injection will be over 0.5 million
tons per year.
For the oil and gas industry, CO2 EOR has been
demonstrated as a feasible technology to improve oil
recovery. The EOR mechanisms include interfacial tension
(IFT) reduction, CO2 dissolution into oil to reduce its
viscosity and swell oil, permeability improvements as the
reaction of carbonic acid (due to CO2 dissolution in water)
with the limestone/dolomite, and wettability alteration due
to asphaltene precipitation. It is notable that CO2 and oil
may become miscible when the reservoir pressure exceeds
the minimum misci (...truncated)