Abstract
The idea of gasifying (reforming) a fraction of a light crude oil in the
reservoir, was conceived originally by Davidson and Yule(1). This involved
“stringing” a series of downhole gasification (DHG) units along either a
horizontal producer well or vertical producer well, or along some other
suitable well arrangement.
Although catalytic steam reforming of naphtha practiced on a large scale has
been extensively researched, such understanding is largely restricted to much
lower pressures than those investigated in the present study. We present
results obtained using a small, “pilot-scale” DHG unit, or reforming reactor,
operated at up to 100 bar pressure. The feed to this unit was a light naphtha
fraction cut from Statfjord crude oil. The effect of pressure, catalyst
loading, steam to hydrocarbon ratio and gasifier temperature were
investigated.
Essentially, the conversion to inert gases, principally hydrogen and carbon
dioxide, at high pressure was sufficiently high to make the process technically
feasible in depleted light oil reservoirs. Furthermore, the economics of this
novel enhanced oil recovery process, which also produces (and stores) hydrogen,
appear to be very favourable. However, the experiments, which were conducted
under pilot-scale conditions using a single–tube reactor unit, were not of
sufficient duration time to test the long-term effects on catalyst activity
owing to carbon fouling and sulphur poisoning. These factors (at least carbon
deposition) can be controlled as demonstrated in the experiments by adjusting
the steam-to-hydrocarbon ratio and the depth of naphtha-cut taken from the
crude oil. These aspects of the process are to be further investigated in a
Phase 2 project.
Introduction
Davidson and Yule(1) originally conceived the idea of a self-contained,
downhole gasification (DHG) unit as a safer, “greener” method for transporting
oil out of environmentally sensitive areas, such as the Everglades, as gas.
Subsequently, the focus was directed towards applying DHG in depleted light oil
reservoirs. The inert gases generated by a downhole DHG unit(s) are directed
into a gas cap, or used to create a gas cap (Figure 1). This would then allow
gravity stabilized displacement (GSGI), WAG, or another assisted gas injection
technique, to be implemented for the purpose of improved oil recovery. This is
still a high priority, especially in such areas as the North Sea, and the many
hundreds of depleted light oil fields in the US, where output continues to
fall. The main IOR problem is the availability of a suitable gas to inject into
the reservoir, especially offshore. Although the displacement dynamics are
likely to be complex because of the hydrogen in the generated gas, it is
estimated that valuable incremental oil can be gained using the DHG
process.
© 2010. Society of Petroleum Engineers
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History
- Original manuscript received:
20 March 2008
- Meeting paper published:
17 June 2008
- Revised manuscript received:
20 January 2010
- Manuscript approved:
31 January 2010
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