Summary
The need for additional underground gas storage (UGS) in Europe and in
France is increasing. TOTAL has therefore undertaken feasibility studies to
convert the depleted Pécorade oil field, situated in South West France, into an
UGS.
The Pécorade field offers a number of positive characteristics which make it
a good candidate for UGS, but it is also deep at 2500 m and contains hydrogen
sulphide.
This paper describes some of the challenges faced by the project,
including:
- The sizing of the working volume (volume of gas which can be stored and
cycled each year), which required the acquisition and processing of a new 3D
seismic program, and the construction of specific geological and reservoir
models.
- The safety and environmental issues related to caprock integrity and
sour-gas production.
- The conversion of existing oil and gas wells into gas injection and
production wells.
- The processing of cycled gas (including sour-gas treatment).
- The cost of the project compared to more conventional UGSs.
The main benefits expected from the project are:
- The development of a sizeable working volume, in the order of one billion
cubic meters, in an ideal location to serve the French and possibly Spanish
market.
- An improved oil recovery, as the annual cycling of the gas would induce
production of an additional 20 to 30% over current projections.
These studies also confirmed that the development of a sizeable UGS is a
lengthy, difficult, and complex project.
The decision to launch the project is mainly dependent on the results of the
future preproject studies, regulations, and market conditions.
Introduction
While Europe’s gas consumption is increasing, domestic gas production is
declining, and gas imports are on the rise. Therefore Europe is eager to secure
additional gas imports, cater for seasonal gas demand, and prevent supply
shortages. One of the means to achieve these targets is the development of new
underground gas storage (UGS), and it is estimated that Europe UGS capacity
must at least double in the next 25 years (Plan Indicatif 2006).
France has not been endowed with a proliferation of oil- and gas-bearing
reservoirs, and as a result the vast majority of existing UGS are of the
aquifer type. However, the development of this type of UGS is now facing more
stringent environmental regulations, and therefore TOTAL has undertaken studies
to convert the depleted Pécorade oil field into a UGS.
The Pécorade field is situated in South West France, 150 km from Bordeaux,
and has produced oil since 1978 (Fig. 1). The field was selected as a
possible UGS after a screening study of the oil and gas fields situated in the
area. Pécorade presents the following advantages:
- It is situated near an existing gas pipeline network.
- It has a proven gas capacity, as it contained an initial gas cap.
- It is depleted, with reservoir pressure having declined from an initial
pressure of 26.5 MPa to today’s 10 MPa.
- It has proven caprock integrity.
However, the reservoir is deep by UGS standards at 2500 m and contains
hydrogen sulphide. These are major disadvantages and drive the development cost
of UGS up. Therefore, a feasibility study was launched and completed to assess
the possibility of economically converting this oil field into a UGS. This
paper describes the feasibility studies performed and the particular challenges
overcome during the project evaluation.
© 2008. Society of Petroleum Engineers
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History
- Original manuscript received:
11 July 2007
- Meeting paper published:
4 December 2007
- Revised manuscript received:
8 October 2007
- Manuscript approved:
19 October 2007
- Version of record:
15 March 2008
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