| Authors |
L. Nuryaningsih, H. Jiang, SPE, H. Adidharma, SPE, University of Wyoming
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| Source |
SPE International Conference on CO2 Capture, Storage, and Utilization,
10-12 November 2010,
New Orleans, Louisiana, USA
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| Preview |
Abstract
The effect of half cycle slug size (HCSS) on Water Alternating Gas (WAG)
performance in tertiary miscible carbon dioxide (CO2) flooding is
experimentally investigated. Different half cycle slug size influences the
fluids mobility and the contact time between the injected fluids and oil, and
hence to achieve the best possible displacement efficiency, an optimum
water/gas half cycle slug size could exist and deserves investigation.
Coreflood experiments are performed in Berea sandstone core, from which the WAG
performance, such as percent oil recovery, tertiary recovery factor, and CO2
utilization factor are determined. The core flooding experiments are conducted
at 60 and at miscible condition, i.e., at a pressure 20% above the minimum
miscible pressure (MMP) of the oil sample. The experiments utilize Cottonwood
Creek crude oil and artificial brines. The injection and connate brine contain
33.33 wt% CaCl2 and 66.67 wt% NaCl with salinities of 16000 ppm (mg/L) and
30000 ppm, respectively. In every core flood test, alternate cycles of brine
and CO2 with a WAG ratio of 1:1 are injected with half cycle slug size ranging
from 0.05 to 0.75 PV.
The results show that for the system of interest, the optimum HCSS is 0.1 PV,
in which the CO2 usage is only 0.6 PV to reach a high tertiary oil recovery of
40.63%. An HCSS higher or lower than 0.1 PV gives lower oil recovery. When HCSS
is lower than 0.1 PV, the system gives lower oil recovery because some of the
gas is trapped by water and keeps staying in the core instead of displacing
oil. Meanwhile, an HCSS higher than 0.1 PV results in larger clusters of CO2
and water, thus water inefficiently controls CO2 mobility, which makes the
CO2-oil contact time and interfacial area for mass transfer decrease and gas
breakthrough occurs prematurely.
This experimental study is an essential effort to obtain better understanding
the effect of half cycle slug size on WAG performance, which has never been
experimentally investigated before. The understanding is critical for
optimizing the WAG performance.
Keywords: WAG, half cycle slug size, mobility control, tertiary mode, miscible
flooding, CO2 flooding, CO2 usage
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