Causes of Seal Failure and Breached Reservoirs
Selim Simon Shaker
Geopressure Analysis Services
A viable prospect with a good potential for hydrocarbon reserves requires four amalgamated components. Hydrocarbon source and the presence of reservoir that receives, contains and delivers the hydrocarbon to the well-head. Top seal is essential to keep the hydrocarbon trapped in the reservoir. Last but not least is the drillable feasibility. The absence of any of the aforementioned criteria can lead to the abandonment of the whole prospect. However, the common known cause is seal failure that leads to reservoir breaching. Some of the reasons for seal failure are as follows:
- The lack of seismic velocity reversal vs. depth (top seal)
- Subsurface structural failure such as faults
- Intrusive salt-sediment interface
- Shallow faults that reach the mud line in deep water
- Prospect closes against a salt weld
- Rocking basin
- High sand – shale ratio at the objective
- Narrow drilling tolerance window (DTW) where the pore and fracture pressure are in proximity
- Drilling mechanical failure and challenges
- The presence of large hydrocarbon column. It is a double edged sword.
These issues need to be examined methodically during the process of generating a prospect. Geopressure coupled with sequence stratigraphy and basin modeling can help establish a winning endeavor.
AAPG Search and Discovery Article #90205 © AAPG Geoscience Technology Workshop, Permian and Midland Basin New Technologies, September 4-5, 2014, Houston, Texas