Many auxiliary pieces of equipment required for the drilling process are maintained on the rig floor and should be provided by the drilling contractor. The equipment must be selected for the drillpipe to be used, the loads to be expected, and the rig's basic equipment. An additional design consideration in some cases is the actual placement of the equipment on the rig floor to facilitate access during normal and emergency use.
Bit Breakers. The drill bit is an awkward-shaped tool that cannot be connected easily with conventional tools to the drillstring. Its initial connection must be tight for the trip into the hole. Removing the bit is difficult due to its shape and the inherent tightening of the connection during drilling,
The bit breaker plate, or bit box, is designed to help when making up and breaking out the bit (Fig, 16—53). It is sized according to the bit that is run into the hole. The breaker plate sits in the rotary table and is held sccurc by the rotary lock. The plates are purchased from the bit manufacturer. In many cases, a single size plate, such as 97/s in., will work with all 97/s-in. bits, regardless of the manufacturer.
Lift Nipples. Slim-bole drillpipe and drill collars do not have large tool joints that can be latched easily with the elevators when tripping or making connections. Many operators use a short sub with a large latch head to provide additional safety when connecting with the elevators. Although elevators can be used with some pipe and collars, the lift nipples are more often used. The nipple must have the same threads as the pin end of the pipe or collars.
Weight Indicator. A common piece of equipment found on every drilling rig is the weight indicator (Fig. 16-54). Its sensor is connected to the dead line and measures the strain of the line under certain loads. The indicator has reversible face plates when a different number of drill lines arc used with the crown sheave and traveling block. In addition, most weight indicators have an adjustable calibrated outer face plate that can be rotated to any off-bottom hook load to make it easier for the driller to determine weight-on-bit loads when drilling.
Standpipe Pressure Gauge. Pump pressure is measured at the rig floor with a pressure gauge installed in the standpipe leading to the rotary kelly hose. The cameron gauge, as it is often called after a manufacturer, is durable but may be reasonably accurate only to within 100-200 psi for an uncalibrated gauge. (Fig. 16-55). In addition, pump pressure surges on each stroke cause an oscillation on the gauge that increases the difficulty in reading it. The drilling engineer should use the pressure gauge on the choke panel if accurate readings are required.
Mud Bucket. Pulling wet strings out of the hole necessitates the use of a mud bucket. A wet string has mud in the stand above the rotary table that flows onto the rig floor when the pipe is unscrewed. The mud sometimes will flow quite violently and spray the crew and floor equipment. A mud bucket wraps around the connection and catches the mud spray, returning it by hose to
tbe pits via the Mow line. In addition to preveniing a significant loss of mud on each trip, it decreases the handling time for each wet connection. Slugging the pipe with heavy mud prevents most wet strings but is not always feasible.
Elevators. The elevator is the latching device that connects the driilstring to the traveling block during tripping (Fig. 16-56). The bail, which is an ex-
Cameron stand pipe gauge (Courtesy Cameron Iron Works)
Fig. 16-56 Elevators (Courtesy Hughes Drilling Equipment)
tension dcvice that connects the elevators to the hook on the traveling block, allows space for other tools connected to the top of the drillstring. The elevators must conform to specifications in API Spec. 8A, "Drilling and Production Hoisting Equipment."
Slips. The slips secure the drillstring in the rotary table during each connection. The outer diameter of the slips has a taper of 9° 27' 45". The inner diameter has a set of jaws for "biting" into the pipe. The slips should never be set while the drillstring is being lowered because the jaws will bite deeply into the pipe and the inertia of the pipe may cause pipe stretching or "bottlenecking" at the point where the slips were set.
Safety Clamps. Drill collar slips are not as effective at holding the string since the collars usually do not have upsets. As a safety measure, clamps arc secured around the collars above the slips to prevent the collars from sliding through the slips. The clamps require a small amount of additional effort from the rig crew during each trip.
Tongs. The pipe or collar is made up or broken out with the tongs (Fig. 16-57). Backup tongs grip the pipe, while lead tongs apply torque to the pipe. The tongs should be installed on the rig so that the tong body is perpendicular to the pulling line at the optimum torque point. If the perpendicular pull docs not occur, the torque gauges on the tongs do not provide an accurate estimate of torque being applied to the pipe.
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