Water and Polymer Flooding in Heavy Oil ReservoirsImproved results seen in Alberta
Normally the idea of waterflooding heavy oil reservoirs is impractical. One issue that stands out immediately is the highly unfavorable mobility ratio. While heavy oils have viscosities of 100 cp to 1000 cp and higher, water has a viscosity of just 1 cp; this large mobility ratio may cause some to immediately disregard the idea of waterflooding. There are several cases throughout Alberta that show very favorable results from water flooding with recovery factors in some pools reaching above 30%.
A search of the public database resulted in a large number of waterflood projects in heavy oil reservoirs throughout Alberta (See Table 1). The oil viscosity ranges from 152 cp to 1020 cp. The performance of each reservoir is most easily compared through the use of a dimensionless plot of recovery factor (RF) versus hydrocarbon pore volume injected (HCPVI). This plot can be thought of as cumulative oil produced versus cumulative water injected, scaled to the reservoir volume. The range of recovery factors is between 24% and 34%.
The objective of this study was to determine the expected range of oil recovery from fields defined as heavy oil producers. With this goal in mind, the Pelican Lake field was chosen for further examination. The Wabiskaw-McMurray formation is exploited, first through primary depletion and then through waterflooding. Recently, polymer flooding has also been tested and has been found to yield incremental recovery. The Pelican Lake production history includes water injection starting in 2003 and a subsequent increase in oil production.
The oil has a density of 14 o API and a viscosity ranging from 900 cp to 3000 cp. Due to this particularly high oil viscosity a polymer flood pilot was introduced; it was found to yield significant incremental oil recovery.
The use of waterfloods in heavy oil reservoirs have shown to yield promising results in many cases throughout Alberta. Recovery factors range from 24% to 34% and with the use of polymer flooding can reach even higher values.
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