Slips: Rotary-Table Drillstring Suspension, Tapered Wedge Gripping, and WCSB Tripping Operations

Slips are the toothed, wedge-shaped gripping device that suspends a drillstring in the wellbore whenever the rig is not actively lifting it with the hook. Functionally, slips are a set of three or more hardened steel segments hinged together to form a near-circle around the drill pipe. The outer faces of the segments are tapered to match the bowl of the master bushing seated in the rotary table, and the inner faces carry replaceable hardened tool-steel teeth, called dies, that bite slightly into the pipe body. The mechanism is elegantly simple and entirely mechanical. When the rig crew sets the slips around the pipe and the driller slowly lowers the string, the teeth grip the pipe and the downward pull drags the slips deeper into the tapered bowl. That taper converts the vertical load of the hanging string into a powerful inward radial squeeze, so the heavier the suspended weight, the tighter the grip becomes. With the string locked in the table, the crew can break out the kelly, a saver sub, or the top joint or stand and add or remove pipe without the string falling into the hole. Slips are therefore central to every trip, the operation of running pipe in or pulling it out, which on a deep WCSB well can mean handling thousands of metres of drillstring one stand at a time. The term covers a family of tools. Drill-pipe slips grip the relatively thin-walled pipe body; drill-collar slips are sized for the thick, slick collars in the bottom-hole assembly, where extra contact area is needed because collars have no tool-joint upset to help; and casing slips handle large-diameter casing during running operations. The same self-gripping principle is applied well beyond the rotary table: as the SLB Oilfield Glossary notes, any self-gripping toothed device that functions this way is loosely called slips even when it grips something other than drillstring, such as wireline, metal sinker bars, or drill collars in a slip-type elevator or a power-slip system. Modern rigs increasingly use power slips, hydraulic or pneumatic units that set and release at the driller's command and remove the crew from the most pinch-point-prone task on the rig floor. Manual slips, by contrast, are physically set and pulled by the floorhands and remain common on smaller WCSB service and drilling rigs. Slips are safety-critical tooling: worn or wrong-size dies can slip under load and drop a string, while improperly set slips can crush or notch the pipe and create a fatigue failure point. They are manufactured and inspected to API Spec 7K for drilling and well-servicing equipment, and die condition, hinge-pin wear, and bowl taper match are routine items on a rig's pre-tour inspection. In short, slips are the small, unglamorous tool on which the entire weight of a WCSB drillstring repeatedly rests, and their correct selection and condition is a daily determinant of both efficiency and safety on the rig floor.

Drill-Collar and Casing Slips Versus Drill-Pipe Slips

Not all slips are interchangeable, and matching the slip to the tubular is a core competency on the rig floor. Drill-pipe slips rely partly on the tool-joint upset and the relatively short gripped length to hold thin-walled pipe. Drill collars, by contrast, are thick, smooth, and very heavy, so drill-collar slips use a longer body and more die contact area to spread the load and avoid notching the collar. Casing slips are larger again, sized to the specific casing outside diameter, and are used while running casing before cementing. On a WCSB intermediate string, using a drill-pipe slip on a collar can score the collar and seed a washout, while an undersized casing slip can crush casing and ruin a CAD 400,000 casing run.

Power Slips and Rig-Floor Safety

The rotary slip-setting task has historically been one of the highest-injury jobs on a drilling rig, exposing floorhands to crushing, pinch, and back-strain hazards every connection. Power slips, integrated into the rotary table or mounted as a stand-alone unit, set and release hydraulically or pneumatically at the driller's control, keeping hands clear of the slip area. On modern WCSB pad-drilling rigs running long horizontal Montney wells with thousands of connections per well, power slips also shave seconds off every stand, which compounds into hours of saved rig time over a multi-well pad at day rates that can exceed CAD 30,000.

Related Terms

Slips work hand in glove with the rotary table, whose master bushing provides the tapered bowl the slips seat into and which also transmits rotary torque to the string. They share the load-handling role with the elevator, the hinged clamp that latches the tool joint so the hook can lift a stand, while slips hold the string stationary in the table. All three are part of handling the drillstring, the full assembly of pipe, collars, and bottom-hole tools that slips repeatedly support during tripping on every WCSB well.

Real-World WCSB Scenario: A Slip Die Failure on a Grande Prairie Montney Rig

On a triple drilling rig near Grande Prairie, Alberta, a crew was tripping out of a 5,200 m Montney horizontal when a floorhand noticed the drill-pipe slips chattering and the pipe creeping under load. Inspection showed two of the slip dies were worn smooth past their wear line and a third hinge pin was loose, reducing effective grip. The driller stopped operations and the crew changed the full die set, a CAD 1,200 part, before resuming.

The half-hour stop cost roughly CAD 18,000 in rig time at the contract day rate, but a dropped string in that hole would have meant a fishing job and possible sidetrack costing well over CAD 1 million, plus a serious safety incident. The catch on routine pre-tour slip inspection, mandated by the contractor's API 7K maintenance program, turned a potential disaster into a routine die change.