Unconventional low-permeability (tight) light oil reservoirs have emerged as a significant source of oil supply in North America. As with unconventional gas reservoirs, these low-permeability oil plays exhibit a wide variety of reservoir characteristics, and consequently well-performance profiles. Further, different drilling and completion strategies are used to exploit them. In this work, we suggest that a categorization analogous to that used for unconventional gas reservoirs (i.e. based on reservoir/fluid properties) be used for unconventional light oil reservoirs because of the significant difference in reservoir and production characteristics observed to date in Western Canada. We propose the term "Unconventional Light Oil" (ULO) to capture the spectrum of play types and to distinguish them from unconventional heavy (high viscosity) oil plays. We further propose the following categories of ULO, which can be used as a practical guide for exploration and development:
"Halo Oil" – light oil plays where the source ≠ the reservoir, and matrix permeability is relatively high (> 0.1 md) compared to the other categories. These plays represent portions of conventional light oil pools that do not meet traditional petrophysical cutoffs and pay criteria, and may be clastics or carbonates.
"Tight Oil" – light oil plays where the source ≠ the reservoir, and matrix permeability is low (< 0.1 md). These plays are analogous to tight gas plays and may be clastics or carbonates.
"Shale Oil" – light oil plays where the source = the reservoir, matrix permeability is very low, and organic matter content may be high. These plays are analogous to shale gas plays.
We note that for all three categories, modern completion (ex. horizontal wells) and stimulation methods (hydraulic fracturing) are required to commercially produce oil. We further note that the differences between these play types and their gas counterparts are not strictly related to fluid PVT differences.
In this work, we examine, using modern rate-transient analysis methods, differences in production characteristics of three ULO play types in Western Canada, and infer the primary controls on production performance in each. As expected, there are significant differences related to reservoir type and completion strategy.