Abstract
Productivity Index (PI) decline is caused by different mechanisms in both the wellbore region and the far field. The damages in the wellbore region can be simulated by detailed wellbore modeling. To incorporate field pressure evolution and impact on well productivity, a newly developed full-field and near-wellbore poromechanics coupling scheme is used to model PI degradation against time. Near wellbore damages, field and well interactions are identified when applying the coupling scheme for a deep water well. History matching, production forecast and safe drawdown limits are derived for operation decisions.
The coupling scheme is applied in a deep water well for history matching and drawdown strategy evaluation. The field model containing reservoir properties and operation conditions is coupled to multiple near-wellbore models which have completion and detailed wellbore geometry. During history matching, the field model is explicitly coupled with near-wellbore models. Field pressure is dynamically mapped into near-wellbore models and the PI multiplier in the field model for the given well(s) is updated based on near wellbore flow paths simulated in the near-wellbore models. Well productivity changes are accurately represented in the reservoir model for history matching and the production forecast.
Using the coupling scheme, we successfully history matched well production and the PI trend. PI decline damage mechanisms, such as perforation efficiency, fines migration, fracture connectivity, fracture conductivity, compaction, are modeled in the coupling scheme. At each coupling step, well productivity calculated in near-wellbore model(s) is updated as a PI multiplier for the well(s) in the field model. History matching results showed the dominant PI decline factors are perforation efficiency, fines migration, and fracture conductivity. Near wellbore perforation collapse reduces flowing area and changes flow path. Fines migration is observed at the high velocity region. It damages the permeability around high velocity flow path and the damage accumulates with time. Maintaining perforation efficiency and conducting a stimulation job to remove fines damage could mitigate PI decline.
Production forecast is performed with different drawdown rates. Results showed that there is no further PI decline with low drawdown. For high drawdown rate, PI could continue to decline and PI decline slope is related with drawdown pressure.
