Summary
Weyburn oil field, located in southeast Saskatchewan, has been the site of
one of the largest carbon dioxide (CO2) flooding projects in the
world since September 2000.
In this paper, data of the past performance of waterflooding in the Weyburn
field was used to develop empirical correlations to predict the performance of
CO2 flooding. Two different correlations were developed based on
CO2-injection schemes in Weyburn. The first correlation is based on
a water-alternating-gas (WAG) process through vertical wells, and the second
correlation is based on the cases in which CO2 is injected through
horizontal wells and water is injected separately through vertical wells. The
first step was to collect and analyze production data from 1958 to 2004.
Oil-production rates for both waterflooding and CO2 flooding
periods, water-injection rates, and CO2-injection rates were used in
developing the correlations. The empirical model for injecting CO2
and water through vertical wells was verified using the Kinder Morgan
CO2 flood-scoping model (this is not a trademark product) and actual
field production data. The comparative analysis showed 12% error between our
simple correlation and the Kinder Morgan model. For injecting CO2 in
horizontal wells, the correlation could not be verified against the Kinder
Morgan model, but the correlation followed the actual oil production in the
field very closely.
This new model can be used effectively as a screening tool for predicting
the performance of CO2 flooding in various locations in the Weyburn
reservoir based on the data obtained from past waterflooding performance and
the rate of CO2 injection. Therefore, it can contribute significant
savings in time and expense to the operating oil company. Also, this approach
can be used for other potential CO2-flooding processes in reservoirs
with histories and properties similar to those of the Weyburn field.
Introduction
The Weyburn oil field was developed in 1954 while undergoing primary
production of medium oil with a American Petroleum Institute (API) degree
ranging from 25 to 34 (Fig. 1). Waterflooding started in 1964, and reached its
peak production of 7 500 m3/d (47,175 STB/D) in 1966. To
maintain production, drilling of vertical infill wells followed by horizontal
drilling began in 1986. Initial investigations indicated that CO2
flooding might be a viable option for enhancing oil recovery from this field.
Therefore, CO2 flooding was commenced in the Weyburn field in
September 2000. It is estimated that implementation of a CO2 flood
would extend the economic life of this field more than 25 years, with an
incremental recovery prediction of 13 to 19%.
The field has two carbonate layers that are CO2-flooded: the
marly dolomite (upper) and the vuggy limestone (lower). Relative to the
vuggy zone, the marly zone has a tighter formation with an average porosity of
26% and an average permeability of 10 md. The Marly zone has low flow
capacity and sweep efficiency. The vuggy zone has an average porosity of
15% and an average permeability of 30 md.
Natural vertical fractures are present in the Weyburn-Midale
formations. Three major fracture trends exist in the northeast.southwest,
northwest/southeast, and north/south directions. Analysis of logs indicates
that the dominant fracture orientation is parallel to the current
southwest/northeaste orientation (Monea and Wilson 2004).
© 2007. Society of Petroleum Engineers
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History
- Original manuscript received:
4 October 2005
- Revised manuscript received:
21 June 2006
- Manuscript approved:
26 June 2006
- Version of record:
20 May 2007
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