An operator in the Middle East planned to drill and perform a hole-enlargement-while-drilling (HEWD) operation in hard carbonate formations with an unconfined compressive strength (UCS) between 20,000 and 35,000 psi [138 to 241 MPa]. The main concern from the operator was ensuring that the hydraulic reamer was fully activated while drilling ahead.

Downhole logging-while-drilling (LWD) tools that provide real-time caliper data cannot be run above the reamer because of the operational requirements of both the reamer and the LWD caliper tools. The reamer requires a small plastic ball to be dropped through the inside of the drillpipe to activate the reamer and, consequently, placing a real-time caliper tool above the reamer would prevent the ball from reaching the reamer. Additionally, such a configuration would prevent electrical signal communication between the LWD tool and the real-time data transmission available at the measurements-while-drilling (MWD) tool. Hence, it was not possible to use real-time LWD data to confirm the reamer activation, and an alternate method had to be developed.

A new process was developed to monitor and confirm the full pad activation of the reamer. When the reamer is not activated, then 100% of the flow passes through the reamer, MWD tool, and drill bit. However, when the reamer is activated, then 20% to 30% of the flow is diverted through the HEWD tool to open the pads and cool and lubricate the cutters. The process ensures activation of the underreamer using the relation between MWD turbine RPM and flow. Alarms built into the monitoring software are triggered under certain conditions to alert the system operator to the expanded or retracted state of the underreamer. The operator can quickly check flow conditions and make adjustments to change the state of the underreamer. The process was used to perform a successful HEWD run with a BHA that included a rotary steerable system (RSS), MWD tool, an underreamer, and a 14.5-in. drill bit. The BHA delivered a high-quality in-gauge borehole and met all directional objectives, holding tangent at 19° inclination and 94° azimuth.

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