Gyda is a mature oil development in the Norwegian sector of the North Sea. The first production wells were drilled more than twenty years ago. This study focuses on wells drilled in the porer reservoir quality areas of the Gyda reservoir. Some recent production wells have significantly underperformed relative to equivalent initial wells. In particular, a sidetrack to an early successful well, had very poor performance on initial start-up.

The geometry of the original well and the sidetrack were simulated, together with various assumptions and sensitivities to formation damage. In the original well an attempted hydraulic fracture had been assumed to have failed. This assumption was challenged in the model.

The model demonstrated that the original well must have included a successful hydraulic fracture in order to flow at the historical rates recorded. In addition for the sidetrack, that contained no fracture, there were indications that the perforation tunnels may not have fully cleaned up and that whilst the well performance may recover somewhat with time, a significant change in completion would be required in order to match the performance of the original well.

The model constructed included the completion geometry and formation damage and has enabled evaluation of old wells and more importantly, design of new wells in this mature reservoir development.

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