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Your advanced compact under reamer


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Drillstar  Z-Reamer is a « block-type » PDC hydraulic operated underreamer capable of enlarging up to one bit size from the pilot bit.

Designed with simplicity and reliability in mind, the Drillstar Z-Reamer is a compact block-type underreamer featuring advanced reaming capabilities. Its long blades provide unique cutter density and optimized stability, while its compact size opens up new reaming applications. Z reamer is available in two versions; the “near bit” reamer (“H” suffix) with box  down connection and the “String” reamer (“S” suffix), with box-up connection and drop ball activation capability.


As the Z-Reamer can be located immediately above the bit, long ratholes are no longer required, saving rig time and reducing drilling risks. The Z-Reamer is compact enough to be run below a mud motor or a point-the-bit RSS in directional applications.

Unlike a bicenter bit, the Z-reamer is a fully centered tool, reducing drilling vibrations and improving stability.

The Z-Reamer can be activated by ball drop in the “S”  ( string ) version ..

Both “S” ( String) and “H” ( near bit ) versions can be activated  by hydraulic pressure using specially designed shear pins or rupture discs.

This allows activation possible below BHA components such as mud motor, RSS, etc.

Activation pressure can be adjusted on site by selection of shear pins

The Z-reamer is a sturdy tool, tested to perform in harsh drilling environments while remaining simple enough to be maintained in the field with few spare parts and hand tools, reducing turnaround time and improving reliability.

The Z-reamer does not rely on any mechanical lock to remain open while drilling. The reaming blades are kept open by WOB and hydraulics, and retract once the pumps are stopped and the BHA is picked up from bottom.
The blades shape prevents them from being pulled away from the body, strongly reducing the risk of losing any component downhole.

Reaming blades design can be optimized for your formation and desired well trajectory. Matching Z-Reamer blades & drilling bits can be delivered. Advanced computer analysis for directional behaviour, modal analysis and hydraulics can be conducted to select the best BHA components and drilling parameters.

Standard dimensions

 Nominal Pilot Bit SizeMax Body ODOpening RangeMax Flow Rate (GPM)Standard Connections
Z3503⅝”- 3 3½”3¾” - 5”1502⅜” REG / IF
Z4504½”4⅜”4¾’’ – 6⅜’’2502⅞” REG / IF
Z6005⅞” - 6”5¾”6¼” - 8½”4503½” REG / IF
Z8508½”8¼”8¾” - 12¼”9004½” REG / IF
Z100010⅜”10”10¼” - 14”18006⅝” REG
Z122512¼”11¾”12¼” - 17 ½”18006⅝” REG