Clearwater oil production continues to accelerate with an increase of over 23,000 bopd in the last few years. Production comes from three main areas—Marten Hills, Nipisi and Jarvie—along with smaller fields such as Gift, Canal and Cadotte (figure1). The Clearwater is complex, and understanding the variations and interplay of oil and reservoir quality oil is important to ensure strong productivity as the play progresses.
The key productivity factors include reservoir quality, oil quality and well design. Clearwater well design does not vary significantly, so the emphasis is placed on the interaction between reservoir and oil quality.The Clearwater has a range of oil qualities from 10° API and 17,000 cP at Gift to over 20° API and 20 cP at Marten Hills (CDL, 2020). The observed variation in oil quality is complex and likely related to formation temperature, potential biodegradation and the initial source of the oil.
Viscosity at formation temperature (figure 2) demonstrates a general relationship of increasing temperature and decreasing viscosity within different Clearwater zones. Biodegradation is another factor to consider. Sulphur increases in concentration as oils become heavier and can be used as a proxy for biodegradation (CDL, 2020). Biodegradation is often related to the influx of inorganic nutrients through the mechanism of fluid flow. Higher permeability reservoirs may have a higher degree of water invasion leading to more hydrocarbon degradation. Figure 3 demonstrates the relationship between viscosity and the reservoir quality (permeability times reservoir thickness). Higher permeability areas tend to have higher viscosity oils, demonstrating an inverse relationship between reservoir and oil quality.
The Clearwater oil play has been a shining light in recent years. Through a deeper understanding of important productivity factors, the Clearwater will hopefully continue to be a highlight in a time that is anything but clear.
Canadian Discovery Ltd. 2020. Clearwater Regional Hydrodynamics and Reservoir Study (CWHD). Calgary.