Technique for damping oscillations in a drill string

A shock sub for connection in a drill string, comprising:

• a barrel having means at one end for connection to the drill string;
• a mandrel mounted in the barrel for telescoping movement along a longitudinal axis and having means at one end for connection to the drill string;
• means for transmitting torque between the mandrel and barrel;
• a ring spring assembly for damping relative movement between the mandrel and barrel, the assembly comprising:
• a multiplicity of inner and outer annular ring springs residing in planes transverse to the axis;
• the inner ring springs comprising radially outer surfaces inclined to the axis;
• the outer ring springs comprising radially inner surfaces inclined to the axis and engaging the radially outer surfaces of the inner ring springs;
• means carried by the mandrel and barrel for expanding the outer ring springs and compressing the inner ring springs upon collapsing movement of the mandrel and barrel;
• the ring springs reaching the yield point of the material thereof at a predetermined amount of collapsing movement of the barrel and mandrel;
• and
• means carried by the barrel and mandrel for limiting the amount of collapsing movement therebetween to less than the predetermined amount.

A shock sub for connection in a drill string, comprising:

• a barrel having means for connection to the drill string;
• a mandrel mounted in the barrel for relative telescoping movement along a longitudinal axis and having means at one end for connection to the drill string;
• means for transmitting torque between the mandrel and barrel;
• a ring spring assembly for damping relative movement between the mandrel and barrel, the assembly comprising:
• a multiplicity of inner and outer annular ring springs residing in planes transverse to the axis;
• the inner ring springs comprising radially outer surfaces inclined to the axis;
• the outer ring springs comprising radially inner surfaces inclined to the axis and engaging the radially outer surfaces of the inner ring springs;
• means mounting the springs in a unit handled body;
• and
• means carried by the mandrel and barrel for expanding the outer ring springs and compressing the inner ring springs upon collapsing movement of the mandrel and barrel.

A method of drilling a hole in the earth using a drill string comprising a bit, a shock sub, a plurality of drill collars and a string of drill pipe, the shock sub including a barrel;

• a mandrel mounted in the barrel for telescoping movement along a longitudinal axis;
• a ring spring assembly for damping relative movement of the mandrel and barrel, the assembly comprising a multiplicity of inner and outer annular ring springs residing in planes transverse to the axis, the inner ring springs comprising radially outer surfaces inclined to the axis, the outer ring springs comprising radially inner surfaces inclined to the axis and engaging the radially outer surfaces of the inner ring springs, the assembly exhibiting a spring rate of less than 25,000 pounds per inch of deflection and a load capacity of between 10,000-125,000 pounds;
• and means carried by the mandrel and barrel for expanding the outer ring springs and compressing the inner ring springs upon collapsing movement of the mandrel and barrel, the method comprising:
• applying a load to the bit in the range of 10,000-125,000 pounds;
• maintaining the neutral point of the drill string substantially above the shock sub;
• causing the mandrel and barrel to telescope relative to one another in both inward and outward telescoping directions during load application and bit rotation;
• and
• damping oscillations induced in the drill string in both inward and outward telescoping directions by changing the stresses induced in the ring spring assembly.

A method of using a shock sub of the type comprising a barrel having a passage therein, a mandrel mounted in the barrel for telescoping movement along a longitudinal axis and having a passage communicating with the barrel passage providing a flow path through the shock sub;

• means for transmitting torque between the mandrel and barrel;
• a spring assembly positioned relative to the barrel and mandrel for damping relative movement therebetween;
• and means responsive to the application of fluid pressure along the flow path creating a pump open force biasing the mandrel and barrel in an untelescoping direction for stressing the spring assembly;
• the method comprising:
• drilling a hole in the earth with a drill string including a bit having nozzles therein, the shock sub, a plurality of drill collars and drill pipe wherein the shock sub is oriented with the mandrel end facing toward the drill collars and passing drilling fluid through the flow path to generate the pump open force and passing the drilling fluid through the bit nozzles to generate a bit thrust, the directions of the bit thrust and the pump open force being in a first relationship;
• and
• drilling a hole in the earth with a drill string including a bit having nozzles therein, the shock sub, a plurality of drill collars and drill pipe wherein the shock sub is oriented with the mandrel end facing toward the bit and passing drilling fluid through the flow path to generate the pump open force and passing the drilling fluid through the bit nozzles to generate a bit thrust, the direction of the bit thrust and the pump open force being in a second relationship.

A drill string for drilling a hole in the earth, comprising in an interconnected torque transmitting string:

• a rotatable bit;
• a multiplicity of drill collars;
• a multiplicity of joints of drill pipe;
• and
• a shock sub, located in the string substantially below the neutral point thereof, including:
• a barrel and a mandrel mounted in the barrel for telescoping movement along a longitudinal axis;
• means for transmitting torque between the barrel and mandrel;
• a ring spring assembly for damping oscillations in the drill string, the assembly including:
• a multiplicity of inner and outer annular ring springs residing in planes transverse to the axis;
• the inner ring springs comprising radially outer surfaces inclined to the axis;
• the outer ring springs comprising radially inner surfaces inclined to the axis and engaging the radially outer surfaces of the inner ring springs;
• the assembly exhibiting a substantially constant spring rate of less than 25,000 pounds per inch of deflection and a load capacity of between 10,000-125,000 pounds;
• and
• means carried by the mandrel and barrel for expanding the outer ring springs and compressing the inner ring springs upon collapsing movement of the barrel and mandrel.