Passively induced forced vibration rock drilling system

A bottomhole assembly (BHA), comprising:

• a drill bit operable to vibrate when engaged with a formation and rotated;
• and
• a suspension sub comprising:
• a stator barrel for connection to a pipe string;
• a traveler barrel for connection to the drill bit;
• a slip joint longitudinally coupling the traveler barrel to the stator barrel while allowing movement of the traveler barrel between an extended position and a retracted position;
• a torsional joint connecting the traveler barrel to the stator barrel at and between the positions;
• and
• one or more springs disposed between the stator barrel and the traveler barrel,
• wherein the suspension sub is tuned relative to the drill bit to:
• dampen the vibration of the drill bit when the BHA is rotated at a first angular velocity;
• and
• resonate the vibration of the drill bit when the BHA is rotated at a second angular velocity, thereby imparting percussive energy to the drill bit,
• wherein:
• the suspension sub further comprises a variable damper operable to dampen the vibration of the drill bit,
• the one or more springs are disposed in a spring chamber formed between the stator barrel and the traveler barrel,
• the suspension sub further comprises:
• hydraulic fluid disposed in the spring chamber;
• a hydraulic reservoir;
• and
• a hydraulic passage extending between the spring chamber and the hydraulic reservoir,
• the variable damper comprises a dashpot disposed in the hydraulic passage,
• the suspension sub further comprises a second hydraulic passage extending between the spring chamber and the hydraulic reservoir, and
• the variable damper further comprises a bypass valve disposed in the second hydraulic passage.

A bottomhole assembly (BHA), comprising:

• a drill bit operable to vibrate when engaged with a formation and rotated;
• and
• a suspension sub comprising:
• a stator barrel for connection to a pipe string;
• a traveler barrel for connection to the drill bit;
• a slip joint longitudinally coupling the traveler barrel to the stator barrel while allowing movement of the traveler barrel between an extended position and a retracted position;
• a torsional joint connecting the traveler barrel to the stator barrel at and between the positions;
• and
• one or more springs disposed between the stator barrel and the traveler barrel,
• wherein the suspension sub is tuned relative to the drill bit to:
• dampen the vibration of the drill bit when the BHA is rotated at a first angular velocity;
• and
• resonate the vibration of the drill bit when the BHA is rotated at a second angular velocity, thereby imparting percussive energy to the drill bit,
• wherein:
• the suspension sub further comprises a variable damper operable to dampen the vibration of the drill bit,
• the one or more springs are disposed in a spring chamber formed between the stator barrel and the traveler barrel,
• the suspension sub further comprises:
• hydraulic fluid disposed in the spring chamber;
• a hydraulic reservoir;
• and
• a hydraulic passage extending between the spring chamber and the hydraulic reservoir,
• the variable damper comprises a dashpot disposed in the hydraulic passage, and
• the dashpot is either a fixed choke or a variable choke valve.