Achieving water shut-off in gravel packed wells is challenging, particularly being able to place a mechanical barrier to flow into a gravel packed annulus. Gravel packed wells, often in deepwater environments, are often high rate wells and interventions can be costly, therefore only techniques with a high probability of success are typically sanctioned.

Many gravel pack wells are completed in multiple sands. If there are barriers between the sands that are believed to be laterally extensive, and if water is entering the lower sand, then isolating the lower sand can be a cost-effective intervention. Deepwater wells in Angola were reviewed as to whether a chemical solution or a mechanical solution would be preferred.

Providing a suitable mechanical methodology could be developed, it was felt this would provide a preferred solution. Further criteria for applying a mechanical solution were developed, to increase the chances of success. Extensive well modelling was also conducted to identify an optimum set of plugs to be placed in the well.

The operator identified a company that had an emerging technology that could offer such a solution. They then worked together to mature the technology through a series of proof-of-concept tests, through trials in Alaska, an early application in a deepwater well in the Gulf of Mexico, followed by a series of qualification tests to be ready for application in Angola. The qualification tests considered not only the mechanical configuration of the wells, but temperature, pressure and wellbore deviation. The application would require placement using a tractor, therefore testing with connecting to the relevant equipment was also incorporated in the plans for the wells.

Using a deepwater rig, several plugs were run in each well, including a meltable alloy plug. The latter plug provided a barrier to flow in both the annulus and inside the sand screens. Although not providing a barrier to shunt tubes, extensive modelling work at Cambridge university showed that it was possible to influence gravel movement in the annulus and shunt tubes, so as to maximise the pressure loss.

Two wells have had plugging systems run. The first well has reduced water cut from 100% to ca. 40% and shown a significant oil rate benefit. The second well has also shown a reduced water cut (from 70% to 40%).

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