Automated sidewall coring

1. A method, comprising:

positioning a downhole tool in a wellbore extending into a subterranean formation;

commencing coring operations by rotating a coring bit of the downhole tool and extending the rotating coring bit into a sidewall of the wellbore;

measuring a rotating speed of the coring bit using a bit rotating speed sensor;

measuring a rotating speed of a bit rotation motor using a bit rotation motor speed sensor;

computing via a controller a ratio of the measured rotating speed of the coring to the measured rotating speed of the bit rotation motor;

comparing via the controller the computed ratio to a target ratio of the measured rotating speed of the coring to the measured rotating speed of the bit rotation motor; and

automatically adjusting via the controller a rotating speed of a weight on bit (WOB) motor based on the comparison of the computed ratio to the target ratio.

2. The method of claim 1 further comprising determining a compressive strength of the formation based on the measured rotating speed of the coring bit, and wherein adjusting the rotating speed of the WOB motor is further based on the determined compressive strength of the formation.

3. The method of claim 1 , wherein the controller is disposed in the downhole tool in the wellbore.

4. The method of claim 1 , comprising:

measuring a WOB of the coring bit using a WOB sensor;

computing via the controller a target WOB based on the comparison of the computed ratio to the target ratio;

comparing via the controller the measured WOB to the target WOB; and

automatically adjusting via the controller the rotating speed of the WOB motor based on the comparison of the measured WOB to the target WOB.

5. The method of claim 1 , comprising:

measuring a rate of penetration (ROP) of the coring bit using a ROP sensor;

computing via the controller a target ROP based on the comparison of the computed ratio to the target ratio;

comparing via the controller the measured ROP to the target ROP; and

automatically adjusting via the controller the rotating speed of the WOB motor based on the comparison of the measured ROP to the target ROP.

6. A method, comprising:

positioning a downhole tool in a wellbore extending into a subterranean formation;

commencing coring operations by rotating a coring bit of the downhole tool and extending the rotating coring bit into a sidewall of the wellbore;

measuring a weight on bit (WOB) of the coring bit using a WOB sensor;

measuring a rate of penetration (ROP) of the coring bit using a ROP sensor;

measuring a rotating speed of the coring bit using a bit rotating speed sensor;

measuring a torque at bit (TAB) using a TAB sensor;

computing via the controller a rock characteristic based on the measured WOB, measured ROP, measured rotating speed, and measured TAB;

computing via the controller a target rotating speed of the coring bit based on the computed rock characteristic;

comparing via the controller the computed target rotating speed to the measured rotating speed;

automatically adjusting via the controller a rotating speed of a bit rotation speed motor based on the comparison of the computed target rotating speed to the measured rotating speed;

computing via the controller a target ROP based on the computed rock characteristic;

comparing via the controller the computed target ROP to the measured ROP;

automatically adjusting via the controller a rotating speed of a WOB motor based on the comparison of the computed target ROP to the measured ROP.