Summary
This paper presents the results of a comprehensive study to improve our
understanding of high-mobility-ratio waterflood (HMRWF) and to improve
performance prediction. Published data on heavy-oil water-injection field
projects are limited. Several successful HMRWF projects have been reported, and
they show significant oil recovery at high watercut. However, the range of
reported recovery is large—waterflood recoveries of approximately 1 or 2% to
20% of original oil in place (OOIP) have been reported for similar reservoirs.
Higher viscosities result in lower recovery.
Mechanistic studies using fine-scale simulations show that the viscosity (or
mobility) ratio primarily controls oil recovery response, and that the recovery
is lower at higher viscosity ratios. Further, viscous fingers dominate
high-viscosity-ratio floods, and mobile water can significantly reduce
recovery. Field-scale simulation results indicate that heterogeneity plays a
more important role for a HMRWF than conventional waterfloods. The amount of
primary production before the start of the waterflood has a larger effect on
incremental oil recovery for high-mobility-ratio floods. Further,
highly-correlated, thin, thief zones reduce recovery of HMRWF more severely,
and rock wettability (relative permeabilties) strongly influences oil recovery.
These results indicate that, in addition to reservoir geology, accurate
viscosity and relative permeability measurements are essential for a reliable
performance prediction.
Introduction
Waterflood has been conducted in many high viscosity reservoirs in the past,
and several water injection projects in high viscosity reservoirs are ongoing
and planned around the world (Oefelein and Walker 1964; Jennings 1966; Roark
1960; Nelson 1976; Woodling et al. 1993; Jenkins et al. 2004; Adams 1982;
Edgson and Czyzewski 1985; Kasraie et al. 1993; Smith 1992; Lim et al. 1993; Ko
et al. 1995; Etebar 1995; Pallant et al. 1995; Foerster et al. 1997; Yang et
al. 1998; Forth et al. 1996; Yao 1999; Hanafy 1999; Cook et al. 2000;
Jayasekera and Goodyear 2000; Capeleiro Pinto et al. 2001). However, published
data on HMRWF performance is limited and results are sometimes conflicting.
Further, it has been postulated that some of the recovery mechanisms might be
different (Cook et al. 2000). It is apparent from the literature that our
understanding of HMRWF performance is inadequate.
This paper presents the results of a comprehensive study to provide improved
insight into mechanisms governing HMRWF and to help to improve performance
prediction. The specific objectives were to: (1) evaluate published field data,
(2) determine key parameters that govern the process using analytical methods
and fine-scale mechanistic numerical models, and (3) quantify the effects of
reservoir heterogeneity on HMRWF field performance. Accordingly, the paper is
divided into four parts. The first presents a review of published field data.
Next, definitions of mobility ratio are examined and a preferred definition is
proposed. This is followed by a fine-scaled mechanistic modeling of HMRWF to
identify key parameters. Finally, field-scale simulations are conducted to
delineate key differences between HMRWF and conventional waterflood.
© 2008. Society of Petroleum Engineers
View full textPDF
(
3,729 KB
)
History
- Original manuscript received:
1 September 2005
- Meeting paper published:
5 December 2005
- Revised manuscript received:
4 April 2007
- Manuscript approved:
10 May 2007
- Version of record:
25 February 2008
View Cart
