Summary
The technical success of an enhanced oil recovery (EOR) project depends on
two main factors: first, the reservoir remaining oil saturation (ROS) after
primary and secondary operations, and second, the recovery efficiency of the
EOR process in mobilizing the ROS. These two interrelated parameters must be
estimated before embarking on a time-consuming and costly process for designing
and implementing an EOR process. The oil saturation can vary areally and
vertically within the reservoir, and the distribution of the ROS will determine
the success of the EOR injectants in mobilizing the remaining oil. There are
many methods for determining the oil saturation (Chang et al. 1988; Pathak et
al. 1989), and these include core analysis, well-log analysis, log/inject/log
(LIL) procedures (Richardson et al. 1973; Reedy 1984), and single-well chemical
tracer tests (SWCTT) (Deans and Carlisle 1986). These methods have different
depths of investigation and different accuracies, and they all provide valuable
information about the distribution of ROS. No single method achieves the best
estimate of ROS, and a combination of all these methods is essential in
developing a holistic picture of oil saturation and in assessing whether the
oil in place (OIP) is large enough to justify the application of an EOR
process. As Teletzke et al. (2010) have shown, EOR implementation is a complex
process, and a staged, disciplined approach to identifying the key
uncertainties and acquiring data for alleviating the uncertainties is
essential. The largest uncertainty in some cases is the ROS in the reservoir.
This paper presents the results from a fieldwide data acquisition program
conducted in a west Texas carbonate reservoir to estimate ROS as part of an EOR
project assessment. The Means field in west Texas has been producing for more
than the past 75 years, and the producing mechanisms have included primary
recovery, secondary waterflooding, and the application of a CO2 EOR process.
The Means field is an excellent example of how the productive life and oil
recovery can be increased by the application of new technology. The Means story
is one of judicious application of appropriate EOR technology to the sustained
development of a mature asset. The Means field is currently being evaluated for
further expansion of the EOR process, and it was imperative to evaluate the oil
saturation in the lower, previously undeveloped zones. This paper briefly
outlines the production history, reservoir description, and reservoir
management of the Means field, but this paper concentrates on the residual oil
zone (ROZ) that underlies the main producing zone (MPZ) and describes a recent
data acquisition program to evaluate the oil saturation in the ROZ. We discuss
three major methods for evaluating the ROS: core analysis, LIL tests, and SWCTT
tests.
© 2012. Society of Petroleum Engineers
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History
- Original manuscript received:
2 September 2011
- Meeting paper published:
20 July 2011
- Revised manuscript received:
10 February 2012
- Manuscript approved:
10 August 2012
- Published online:
11 October 2012
- Version of record:
30 October 2012
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