A major operator has initiated the data-acquisition campaign in the southern
North Sea for a future storage facility capable of holding 5 billion m3 of gas.
It is estimated this venture will double the existing gas supplies stored in
the UK and represent more than 5% of its annual gas demand. As North Sea gas
production decreases and the UK becomes more dependent on imports, the ability
to store gas has become an important part of the UK energy policy.
Drilling into depleted reservoirs for gas storage produces several major
technical problems and issues that must be addressed. This field is a
pressure-depleted reservoir with a differential pressure equivalent to 7.3
lbm/gal between the drilling fluid's hydrostatic pressure and the reservoir
pressure. This differential must be controlled to eliminate the risk of
differential sticking, downhole losses, and hole collapse.
Because of the reservoir depletion, it would be impossible to backflow and
clean up the near-wellbore region without a post-drill-in treatment fluid to
remove the fluid filter cake and water-wet all the surfaces for gas injection.
To ensure project success and usable fluid designs, reservoir conditions were
simulated in the laboratory and fluid parameters were altered to provide the
optimum properties to minimize the future risks.
The paper discusses in full the laboratory design process, the verification
of the drill-in and treatment fluids as being fit-for-purpose, and their
successful application in the field. Initial well testing suggested that the
expected injection rates of 500 scf/min at 300 psi were exceeded, with rates of
750 scf/min at 280 psi reported.
© 2012. Society of Petroleum Engineers
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- Original manuscript received:
11 July 2011
- Meeting paper published:
7 June 2011
- Revised manuscript received:
7 December 2011
- Manuscript approved:
26 December 2011
- Published online:
9 March 2012
- Version of record:
15 March 2012