Summary
The Schönkirchen Tief reservoir is located in the Vienna basin. The
reservoir contained 19 MSm3 oil originally in place. The current
recovery factor after 45 years of production is 59%. The field was produced by
water injection. The wells, located at the crest of the high relief structure
are exhibiting a high water cut. In 2006–07, a comprehensive study was
performed to optimize the future development of the field.
The field is made up of different types of dolostones. The lower part of the
field consists of fractured dolomite, the upper part of weathered dolomite and
dolomite debris. A dual-permeability model was used to simulate the flow in the
dolomite and the weathered zone, whereas a single-permeability model was
sufficient for the debris.
The main recovery mechanisms for this reservoir are imbibition and water/oil
gravity drainage. Laboratory experiments indicated that the dolomite is
water-wet to mixed-wet at reservoir conditions of 100°C.
The results of the study show that an economically attractive option for the
field development is establishing an underground gas storage (UGS) and using
the injected gas to increase the oil recovery. Because of the fact that the
current reservoir pressure is below initial pressure, within half a year,
approximately 1 GSm3 can be injected. Only approximately one-third
of this gas has to remain as cushion gas during the first cycle. To further
increase the amount of gas that can be used for UGS, fluids have to be
withdrawn from the reservoir. Drilling horizontal wells close to the original
oil/water contact enables injection of an additional 2 GSm3 gas.
The gas injection leads to gas/oil gravity drainage of the oil and water
present in the matrix of the fractured reservoir. The oil is collected by the
horizontal wells, resulting in incremental oil recovery of up to 5% of oil
originally in place.
Introduction
In 2006, approximately 60% of the gas consumed in the European Union was
imported. Russia supplied 25% of the gas, Norway supplied 16.7%, and Algeria
supplied 10.5%. Because of declining production from The Netherlands and the
United Kingdom, the percentage of gas imports into the European Union is
forecasted to increase to more than 70% in 2030.
One of the main gas-import pipelines in which gas is transported from Russia
to the European Union crosses Austria. This pipeline passes the Vienna basin, a
pull-apart basin in which Austria’s largest oil and gas fields are located.
The demand for more UGS capacity and the shortfall in gas supply from Russia
in winter 2006 and 2009 triggered the investigation of conversion of oil or gas
fields in the Vienna basin into UGS.
The Schönkirchen Tief field, which is located approximately 20 km northeast
of Vienna in the Vienna basin, was identified as a suitable candidate field for
high performance UGS. The field consists of dolomites and shows
dual-permeability behavior. It exhibits high permeabilities, has a large enough
size, and is at the end of the oil-production lifetime.
In 2006–2007, an integrated study eas performed to determine the suitability
of using this field for UGS. Initially, the field contained oil, and it has
been waterflooded from the bottom upward for the last 46 years. The current
reservoir pressure is approximately 40 bar lower than the initial reservoir
pressure. The questions that should be answered by the study were: How much gas
can be injected until the initial pressure is reached? Is there a risk that the
gas/oil contact in the fracture system is pushed lower than the spill point of
the field during the gas injection phase? How much additional gas can be
injected by producing water from the reservoir? What ratio of working volume to
cushion gas can be achieved? How much oil reserves would be lost if the field
is converted into UGS, or does gas injection lead to an improvement of the oil
recovery?
To address these questions, a detailed geological study and laboratory
experiments have been performed. A static and dynamic numerical model was
created, history matched, and used for prediction of the UGS behavior. These
simulations were complemented by simulations using a fine grid to investigate
reservoir processes in more detail.
The geological study included various data sources such as outcrop analysis,
core analysis, formation microimage (FMI), log data analysis, and geomechanical
analysis. A brief overview of the geological setting and parameters derived
from this study is given in the following section. Also, production data were
used for constraining the geological model. The overall production history of
the field is given in the Production History section. This section is followed
by showing the history match, which was achieved in close cooperation of the
various disciplines. After a satisfactory history match including uncertainties
was achieved, injection of gas for UGS was simulated (see Transforming
Schönkirchen Tief Into UGS section). In the section Increased Oil Recovery
Because of Injection of Gas for UGS, the optimization of the field-development
plan for incremental oil recovery is described.
© 2009. Society of Petroleum Engineers
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History
- Original manuscript received:
17 July 2008
- Meeting paper published:
3 December 2008
- Revised manuscript received:
6 May 2009
- Manuscript approved:
16 May 2009
- Published online:
17 November 2009
- Version of record:
31 December 2009
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