Abstract
CO2 flooding in naturally fractured reservoirs is becoming
increasingly more popular. The Midale Field is a good example of this
phenomenon and has gained a great deal of interest, not only from enhanced oil
recovery, but also from a CO2 sequestration point of view. To
consider future opportunities for greenhouse sequestration in these types of
reservoirs while improving oil recovery specifically in the Midale field, a
series of experiments were performed.
The goal of this work was to study the effect of miscibility (miscible,
immiscible and near-miscible regions) and injection rate on incremental oil
recovery and sequestration during continuous injection in fractured porous
media. Another important aspect considered was to analyze the effect of
pressure drawdown or depletion on additional recovery with sequestration
optimization. First, artificially fractured Berea sandstone samples were used.
CO2 was injected at constant, slow rates into the fracture, while
maintaining the high-pressure into the core and the system. At the end of the
production life, the pressure into the system was released to different
pressure steps and kept for a longer period of time at each of the reduced
steps of pressure. In between two pressure steps, the system was shut down for
enough time to observe the effect of CO2 and oil diffusion/back
diffusion. After a series of Berea sandstone experiments, a few tests were
conducted on the Midale cores, which were obtained from a good quality matrix
part of the field. Injection and production data were collected using a
continuous data logging system, an analysis of the produced liquids and
measuring the gas production using a continuous flowmeter, which led to the
understanding of the mechanism. The results showed that the pressure blowdown,
followed by shut in after continuous injection, can increase oil recovery
significantly until a certain critical pressure. Storage capacity of the rock
with change in pressure and amount of oil recovered during blowdown period will
lead to the critical understanding of abandonment pressure during the project
life to achieve the goal of sequestration and recovery optimization.
© 2010. Society of Petroleum Engineers
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History
- Original manuscript received:
24 June 2008
- Meeting paper published:
17 June 2008
- Revised manuscript received:
14 January 2010
- Manuscript approved:
14 January 2010
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