Pendulum Assembly
The principles behind a Pendulum Assembly is that the unsupported weight of drill collars will force the bit against the low side of the hole. The resulting decrease or drop off in angle depends on WOB, RPM, stabilization and the distance between the bit and the first reamer (Figure 13b). The basic drop off assembly is: Bit — Monel DC — reamer — DC — stab — DC — stab — 90′ DC — stab
To increase the tendency to drop angle :
• Apply less WOB (lower penetration rate)
• Apply more RPM and pump pressure in soft formations where jetting and
• Reaming down is possible
• Use bigger size Monel DC below the reamer, small DCs above.
The principles behind a Fulcrum Assembly is to place a reamer near the bit (Figure 13c) and apply a high WOB. When WOB is applied, the DCs above the reamer will tend to bend against the low side of hole, making the reamer act as a fulcrum forcing the bit upwards. The rate of build up depends on WOB, size of collars, position of reamer and stabilization above the reamer. The basic build-up assembly is: Bit — sub — reamer — Monel DC — DC — stab — DC — stab — 90’DC — stab
To increase the build:
• Add more WOB
• Use smaller size monel (increase buckling effect)
• Reduce RPM and pump rates in soft formations
The whipstock is a steel wedge, which is run in the hole and set at the KOP. This equipment is generally used in cased hole when performing a sidetracking operation for recompletion of an existing well. The purpose of the wedge is to apply a sideforce and deflect the bit in the required direction. The whipstock is run in hole to the point at which the sidetrack is to be initiated and then a series of mills (used to cut through the casing) are used to make a hole in the casing and initiate the sidetrack. When the hole in the casing has been created a drilling string is run in hole and the deviated portion of the well is commenced.