Systems and methods for improving drilling efficiency

A method for maintaining non-steady state conditions in a borehole being drilled in an earthen formation, comprising:

• (a) providing a drilling system including a drillstring having a longitudinal axis, a bottom-hole assembly coupled to a lower end of the drillstring, and a drill bit coupled to a lower end of the bottom-hole assembly;
• (b) applying torque to the drill bit to rotate the drill bit, wherein the drill bit has a rotational speed and a rotational acceleration;
• (c) applying weight-on-bit to the drill bit to advance the drill bit through the formation to form the borehole, wherein the drill bit has an axial speed and an axial acceleration;
• (d) pumping a drilling fluid down the drillstring to the drill bit, wherein the drilling fluid has a flow rate down the drillstring and a pressure at an inlet of the drillstring;
• (e) selecting a first set point value for the rotational speed of the drill bit, a second set point value for the axial speed of the drill bit, and a third set point value for the flow rate of the drilling fluid down the drillstring;
• (f) controllably oscillating rotational speed of the drill bit, the axial speed of the drill bit, and the flow rate of the drilling fluid down the drillstring about the first set point value, the second set point value, and the third set point value, respectively, during (c)
• wherein the oscillations in (f) of the rotational speed of the drill bit, the axial speed of the drill bit, and the flow rate of the drilling fluid down the drillstring each have a random period less than 10 seconds and
• wherein the rotational speed of the drill bit, the axial speed of the drill bit, and the flow rate of the drilling fluid down the drillstring are each randomly oscillated in (f) between a predetermined maximum value and a predetermined minimum value.

A computer-readable storage medium comprising software that, when executed by a processor, causes the processor to:

• (a) receive a predetermined maximum rotational speed for a drill bit, a predetermined minimum rotational speed for the drill bit, and a predetermined set point value for the rotational speed of the drill bit;
• (b) monitor the rotational speed of the drill bit;
• (c) control the rotational speed of the drill bit;
• and
• (d) oscillate the rotational speed of the drill bit asymmetrically and non-uniformly about the predetermined set point value, the oscillations of the rotational speed of the drill bit having a random period or a random amplitude between the predetermined maximum rotational speed and the predetermined minimum rotational speed.