Today, oil companies produce an average of three barrels of water for each barrel of oil from their depleting reservoirs. Every year more than $40 billion is spent dealing with unwanted water. In many cases, innovative water-control technology can lead to significant cost reduction and improved oil production.
Managing the cycle of water production, separation down-hole or at the surface, and disposal involves a wide range of oilfield services. These include data acquisition and diagnostics using downhole sensors; production logging and water analysis for detecting water problems; reservoir modeling to characterize flow; and various technologies to eliminate water problems such as conformance control and chemical shutoff technique.
Vertical conformance problems quite often result from high-permeability strata residing within matrix-rock reservoirs. However, this is not always the case. For example, high-permeability-anomaly horizontal fractures can be present in relatively shallow oil reservoirs or high-permeability-anomaly horizontally-layered solution channels; or, interconnected vugular porosity can occur in carbonate reservoirs.
The mitigation and treatment of vertical conformance problems have been, at times, referred to as profile modification treatments. Vertical conformance problems occurring in matrix-rock reservoirs normally involve the radial flow of fluids into, or out of, the wellbore for vertical wells when the wells are not hydraulically fractured. Areal conformance problems often result from high-permeability-anomaly vertical fractures. But, this is not always the case. For example, areal conformance problems in matrix-rock reservoirs can be caused by large-scale high-permeability areal directional trends.
Front figure depicts a water flooding operation being conducted in a heterogeneous matrix- rock reservoir in a five-spot well pattern, where the water flood is experiencing both poor vertical and areal sweep. Thus, the water flood in this well pattern is experiencing both vertical and areal conformance problems.
Types of Conformance Problems
Typical oil field conformance problems are briefly presented. After identifying the problem, the best solution could be selected wisely. The most common conformance issues are illustrated in figures below:
- Mobility-Induced Viscous Fingering
- High-Permeability Matrix-Rock Directional Trends
- High-Permeability Matrix-Rock Strata with Crossflow
- High-Permeability Matrix-Rock Strata without Crossflow
- Water Coning Through Matrix Rock
- Water Coning Through Fractures
- Fracture Channeling
- Solution Channels and Interconnected Vuggy Porosity
- Water Channeling behind Pipe
- Casing Leaks
- Reservoir Compartmentalization
Water treatment methodologies can be summarized in following table: