Increased Production Through Cyclic Steaming
Steaming the reservoir serves two purposes:
- Fracturing to increase permeability: Certain types of formations (including diatomite) have very low permeabilities because their geological characteristics prevent the flow of oil between pore spaces. The use of high pressure steam creates small fractures in the resource - essentially breaking its resistance to flow - and enables flow into the well bore for production,
- Reducing Viscosity: adding pressure and heat to the resource enables the heavy oil to flow more easily by increasing the temperature of the oil (reducing viscosity), and adding reservoir drive (pressure) to move the oil to producing wells.
The method commonly used to steam deposits is known as Cyclic Steaming. Cyclic steaming involves three cycles including: steaming, soaking and producing intervals. The sketch below indicates the application of cyclic steaming in horizontal inclined wells drilled from a tunnel into a resource. The first interval (~200' long) is isolated by means of a packer in the well bore and steamed, soaked and produced in cycles. Once the first interval has been successfully produced (and the
production rate falls below the desired minimum level), the next interval is
produced. Interval 2 goes through the same cycle: steam, soak and produce. The cylindrical zones surrounding the well bore represent the volume that can be effectively steamed and fractured in a particular interval. The radius of this zone has been determined empirically in similar formations. For diatomite deposits, experience has shown the effective radius from the well bore for steam intrusion into the formation to be approximately 30 feet.
As represented in the sketch below, well spacing equivalent to the steaming or fracturing radius combined with a systematic cyclic steaming process enables a high percentage of resource recovery. Adequate cover below the surface contains the steam in the resource. The wells in these sketches are "inverted" permitting gravity drainage back to the tunnel during the productive phase of the cyclic steaming cycles.
|
