In liner drilling operations the annular velocity of the drilling fluid drops significantly when it transits from the narrow cross section of the openhole-liner annulus into the increased annular volume between the casing and the drillpipe above the liner. The reduced annular velocity might cause critical hole-cleaning problems that can jeopardize the entire drilling operation and therefore needs to be managed.

To effectively mitigate this problem Statoil (operator) and Baker Hughes (service company) have jointly developed and tested a smart flow diverter (FLD) that can be positioned in the drillstring directly above the liner running tool.

The FLD is designed as a standalone tool that can be placed anywhere in the drillstring and can be used in different applications where enhanced hole cleaning is required, independently of the measurement-while-drilling (MWD) supplier. The tool ultimately must deliver a continuous flow split during the drilling operation, so the main considerations of required features and specifications were carefully reviewed in the early phase of the project:

  • Unlimited activation/de-activation on demand

  • Failsafe closed

  • No compromising of and interference with normal well-control procedures

  • Direction of flow exit to annulus

  • Adjustable flow split

  • No interference with mud pulse telemetry

The tool is activated either by drillstring rotation and a differential pressure threshold or by a flow pattern signal if string rotation is not possible. Both activations can be incorporated in standard connection procedures, thereby eliminating non-productive time (NPT). This paper highlights and discusses the background for the development, specifications, features and method of activation.

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