Mechanical Specific Energy (MSE) is a term used by the oilfield drilling industry to describe several formulae quantifying the energy input within a drilling system. MSE mainly describes the Mechanical (WOB and Torque), for a given unit (Length, area or mass), and the energy required to do the work (i.e. force, time, distance).

Although several different formulae have been developed in an attempt to quantify this value, the accepted industry standard is as below:

$Es=WAX+120πNTAXR$

Where:

Es = Specific Energy (psi) N = Rotary Speed (rpm)

W = Weight on Bit (Ibf) T = Drilling Torque (ft-lbf)

Ax = Borehole x-sectional area (inA2) R = Rate of Penetration (ft/hr)

When using surface parameters such as RPM and Weight, the drill string and BHA frictional losses are the primary source of energy loss in typical drilling systems. As such, introduction of solutions to reducing these frictional losses would have a significant impact on reducing the MSE of the system. This would lead to improved drilling efficiency, thus lower drilling time and reduced costs.

The effect of having an axial oscillation tool (AOT) in the drill string has been previously demonstrated to be effective, particularly in applications where sliding with steerable motors has been problematic. Axial oscillation in the drill string is generated through a series of pressure pulses coming from one part of the AOT. The pressure pulses act on the pump open area of a shock tool, generating the axial motion required to reduce friction, improve the weight transfer to the bit, reduce reactive (and thus overall) downhole torque. The hydraulic vibration also enhances the performance through reducing friction.

The AOT's influence on reducing friction in a constant axial oscillation helps reduce the total friction significantly. Friction reduction enables the entire suite of drilling parameters to be optimized through proper weight transfer, which in return, reduces the chance of buckling, reduced torque, increases ROP, and increase bit life; all are a source of energy improvement.