Improving Recovery from Partially Depleted Reservoirs after Cyclic Steam Stimulation (CSS) Operations

摘要

High Pressure Cyclic Steam Stimulation (HP CSS) with both horizontal and vertical wells has been applied successfully to produce bitumen from the Clearwater Formation at CNRL's Primrose and Wolf Lake fields in the Cold Lake area of east central Alberta, Canada. The ultimate bitumen recovery from only the CSS process is relatively low (<30% of OBIP) in the Primrose and Wolf Lake areas. Various follow-up processes after CSS have been tested in the field in an attempt to achieve additional bitumen recovery. Field results indicated that gravity drainage would be one of the dominate mechanisms in any follow-up process. However, gravity drainage as the initial recovery process presents a greater challenge in the Clearwater Formation due to the presence of inter- bedded mud layers. HP CSS (above the fracturing pressure) improved the vertical flow in the reservoir due to its dilation and can be used as a conditioning phase prior to converting to a gravity drainage process. In this paper, the performance and related recovery mechanisms for some of the earlier field tests are reviewed and the challenges associated with the geology and field operations are also discussed Some of the key factors affecting the performance such as operating pressures, geomechanical effects, placement of wellbores and reservoir quality were analyzed based on the field evidence and the reservoir modeling. These learnings helped to advance the understanding of the field data and influenced the design of the future follow-up processes to CSS.