Summary
Downhole water sink (DWS) technology controls bottomwater coning by draining
water with a second completion placed under the oil-water contact. The
technology has been studied theoretically with analytical, numerical and
physical models, showing an increased rate of oil production and recovery.
Also, improved wells? productivity with DWS has also been demonstrated in
several field implementations. However, downhole drainage in DWS wells requires
independent lifting of considerable volumes of water that necessitates using
either two tubing strings (for water and for oil) or one tubing and the
tubing/casing annulus--for water and oil, respectively. Also, extensive water
drainage in the systems with weak bottomwater drive may cause a reservoir
pressure drop and the need to return the produced water from the surface to the
aquifer for pressure maintenance using designated injection wells. DWS well
completion with the downhole water loop (DWL) offers the benefit of
re-injecting the drainage water back to the same aquifer in the same well
without lifting the water to the surface. This could be achieved by designing a
DWS well with three completions: the top (oil) completion, the middle
completion for water drainage and the bottom completion for water injection.
Despite mechanical complexity of the triple well completion, there are two
limitations of the DWL system--the drained-and-injected water must be free from
oil and the pressure interference between the two water completions must be
minimized.
In this work, a well performance (nodal) analysis model has been developed
for a DWL well completed in an oil reservoir underlain by water layer of known
thickness. In the model, the positions (depths) of the three well completions
and the rates of production and drainage/injection are design parameters, while
all other properties are reservoir system properties. The model has been used
to find the operational range of DWL for a given reservoir system and to
compare DWL wells with conventional wells, single-completed at the top of the
oil layer.
The results show that for each DWL system, there is such a combination of
the top production rate, bottom drainage-injection rate and drainage-injection
distance (D/I spacing) that would result in water-free oil production. There is
a minimum value of D/I spacing above which the detrimental effect of pressure
interference between the two water completions is practically eliminated and
the beneficial effect of water drainage on well performance is strong ? a
two-fold increase of water drainage rate would increase the critical oil rate
by 80%. Also, because the minimum D/I spacing is relatively small, DWL wells
may be installed in reservoirs with thin layers of bottomwater.
© 2010. Society of Petroleum Engineers
View full textPDF
(
2,454 KB
)
History
- Original manuscript received:
12 June 2008
- Meeting paper published:
18 June 2008
- Revised manuscript received:
2 April 2010
- Manuscript approved:
8 April 2010
- Published online:
21 June 2010
- Version of record:
1 June 2010
View Cart
