2.1.3 Operating Envelope
The Flow Loop Analysis provides the critical flow rates for each specific tool and enables the DD to
adjust these rates depending on mud weight as the run progresses. The operating envelop contained
in the OST package is specific to that particular tool and is based on the torque measurements taken
while flowing that tool in the shop. The DD must be careful to use only the Operating Envelop that
matches the exact tool being run since all tools have slightly different ranges.
PowerDrive’s steering performance is based upon a balance of frictions. Internal frictions exist within
the tool’s many bearings and assemblies which the tool must be able to overcome in order hold a
steady toolface. This is determined by the Torque output from the flow kit. As mud weight increases,
the flow kit generates more torque. Therefore, the tools minimum flow rates will decrease with
increasing mud weight.
Before picking up tools, the DD must refer to the specific tool’s Operating Envelop and adjust
the minimum flows accordingly. This is especially important if a tool was transferred from a
different job with different mud weight. If the mud weight is less than what the tool was
originally planned for, its minimum flows will be higher. If the flow rates are not adjusted for
mud weight, there is a high probability of tool failure due to insufficient torque.
1. Telemetry, Not Drilling Zone: This region can only be used for downlinking (Telemetry) off-bottom. The tool
cannot generate enough torque to hold a steady toolface in this range and therefore drilling cannot be done
at flow rates below the “Min Drilling Flowrate”.
2. Drilling and Telemetry Zone: This region can be used for both downlinking (Telemetry) and Drilling.
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