Water Injection Optimization for a Complex Fluvial Heavy-Oil Reservoir by Integrating Geological, Seismic, and Production Data

Abstract

AbstractBZ25-1s field in Bohai Bay, China is characterized as a complex fluvial channelized reservoir where small meandering channels (100-300m wide and 500 - >1000m long) were deposited at different geological times cross-cutting each other. There are many isolated small reservoir systems following channel distributions. Early production showed steep pressure and production decline. Quick implementation of water injection is needed to arrest the fast production decline and to stabilize reservoir pressure.While designing the water injection plan, we faced a number of challenges, such as high mobility ratio (oil viscosity of ~200 cp), strong heterogeneity, poor reservoir connectivity, complex channel geometry, and irregular well patterns. A workflow integrating geological, well log, seismic and dynamic production data was developed to optimize water injection plan for this field.Following the workflow, the optimal water injection design for platforms D and E areas was developed and quickly implemented within the first year of production. We started with a relatively small water injection rate and gradually increased the injection rate to avoid the fast water breakthrough and yet to limit the pressure decline rate. The responses from the water injection were very positive resulting in stable reservoir pressure and increase of oil production. Before water injection, the production decline rates were 30% and 50% for the wells in platforms D and E. After 1 year of water injection, oil production decline rates were reduced to 19% and 14%, respectively.The responses of water injection for different well groups were analyzed in a timely fashion and adjustments to injection/production strategies were implemented accordingly. New information from the water injection response analysis was used to update the geological model to reduce the model uncertainty, as well as to adjust the water injection strategies for better sweep efficiency. Our experiences showed that such dynamic adjustment of injection and production schedule is very important to achieve better water injection efficiency for this heavy oil reservoir with complex channel geometry.