A Heuristic Production Model for Cyclic Steam Stimulation in a Fractured Heavy Oil Carbonate Reservoir

Abstract

The Upper Devonian Grosmont formation is considered to be Canada's next largest unconventional oil resource play, with an estimated 406 billion barrels of heavy oil in place. A number of production pilots targeting the Grosmont formation have tested various thermal enhanced oil recovery techniques, which include steam flood, combustion, and cyclic steam stimulation (CSS). To date, the CSS process has demonstrated considerable promise based on performance from the Unocal Buffalo Creek Phase 2 pilot and through the application of C-SAGD, a CSS variant designed for the Grosmont, at the Laricina-Osum joint-venture pilot in Saleski. While the methodologies for forecasting CSS production profiles are well understood for clastic oil sands reservoirs, no direct analogue exists for carbonate reservoirs such as the Grosmont. The current profiling model for clastics appears to be suitable for matching and forecasting the production characteristics of CSS and the early cycles of C-SAGD in the Grosmont. However, a few extensions to the current profiling models are required to address differences in cycle length, bitumen ramp up, and oil cut characteristics. For instance, oil cuts are typically low initially and increase with time for the majority of cycles in clastic oil sands, whereas in the Grosmont, there is observed cycle-to-cycle variability. The first few cycles typically show high initial oil cuts, decreasing with time; in subsequent cycles, the oil cuts behave similarly to clastic reservoirs. These differences can be attributed to the presence of secondary porosity and permeability systems in the carbonate formation, such as vugs and fracture networks, and their interactions with the matrix. This paper will describe the modification to existing models for profiling production, based on field observations from the aforementioned pilots.

Thermal Recovery of Bitumen From the Grosmont Carbonate Formation—Part 2: Pilot Interpretation and Development Strategy

“…The bitumen drains downward in the matrix until it encounters a flow barrier, where it diverges into the fracture. The drained bitumen accumulates at the bottom of the fracture system and is produced (Shahin et al 2006).…”

Modelling Fluid Flow in Grosmont C Carbonates Using Fractals - A Concept

“…In addition to the stochastic nature, these highly connected fracture/vugs systems with fractal geometry in Grosmont C may also be more than likely oil wet. This phenomenon is evidently less pronounced in the later cycles of CSS and similar thermal processes in Grosmont C [Qin et al 2013] as less oil is available near the producer at the beginning of the production period. In particular, steam/condenste can break through a higher permeable zone, filled with significant oil volume with relative ease.…”

Type Curves for Cyclic Steam Operations in the Grosmont Saleski Pilot and Their Implications for Recovery Mechanisms

“…Using conventional CSS as an analogue, Qin and MacDonald (2013) developed a heuristic production model that is based on pressure driven processes. We present a method assuming heat and gravity drainage are the key to production.…”