Simulating the dynamic response of a drilling tool assembly and its application to drilling tool assembly design optimization and drilling performance optimization

1. A method for simulating a drilling tool assembly having a drill string and a drill bit, comprising:

simulating a dynamic response of the drill string;

simulating a dynamic response of the drill bit; and

resolving the dynamic response of the drill string and the dynamic response of the drill bit into a dynamic response of the drilling tool assembly.

2. The method of claim 1 , wherein the simulating comprises,

solving for the dynamic response of the drill string to an incremental rotation using a first part of a two-part mechanics analysis model of the drilling tool assembly that represents the drill string; and

repeating said solving for a select number of successive incremental rotations.

3. The method of claim 1 , wherein the simulating comprises,

solving for the dynamic response of the drill string to an incremental rotation using a second part of a two-part mechanics analysis model of the drilling tool assembly that represents the drill bit; and

repeating said solving for a select number of successive incremental rotations.

4. The method of claims 2 or 3 , wherein said solving comprises,

constructing the two-part mechanics analysis model of the drilling tool assembly using selected drilling tool assembly design parameters;

determining well bore constraints from well bore trajectory parameters, a specified bottom hole geometry, and a specified hook load,

determining loads on the drilling tool assembly for a position of the drilling tool assembly in the well bore using at least the two-part mechanics analysis model and the well bore constraints; and

calculating the dynamic response of the drilling tool assembly under the loads to the incremental rotation using the two-part mechanics analysis model.

5. The method of claim 1 , wherein said resolving comprises,

applying a convergence algorithm to said simulating the dynamic response of the drill string and said simulating the dynamic response of the drill bit.

6. A new method of claim 1 , further comprising:

converting the dynamic response of the drilling tool assembly into a visual presentation of drilling characteristics of the drilling tool assembly.

7. A method for designing a drill string of a drilling tool assembly, comprising:

defining initial drilling tool assembly design parameters;

simulating a dynamic response of the drill string of the drilling tool assembly;

simulating a dynamic response of a drill bit of the drilling tool assembly;

resolving the dynamic response of the drill string and the dynamic response of the drill bit into a dynamic response of the drilling tool assembly;

adjusting a value of at least one of the drill string design parameters;

repeating the simulating and the adjusting a selected number of times;

evaluating the dynamic responses of the drilling tool assembly; and

based on the evaluating, selecting desired drill string design parameters.

8. A method for designing a drill string of a drilling tool assembly, comprising:

defining initial drilling tool assembly design parameters;

simulating a dynamic response of the drill bit of the drilling tool assembly;

simulating a dynamic response of a drill string of the drilling tool assembly;

resolving the dynamic response of the drill string and the dynamic response of the drill bit into a dynamic response of the drilling tool assembly;

adjusting a value of at least one of the drill bit design parameters;

repeating the simulating and the adjusting a selected number of times;

evaluating the dynamic responses of the drilling tool assembly; and

based on the evaluating, selecting desired drill bit design parameters.