There are few ways to reduce the stick slip while drilling, the pdc/rock interaction has a critical role in this issue. I've seen the performane of a specific type of hybrid bits which significantly reduces the stick-slip and torque spikes while tracking the planned trajectory with minimal sliding. They've achieved up to 12 deg BUR in very hard and abbrasive formaions with lots of chert in Northern Alberta. If anyone is interested you can drop me a note and I can share their information. Reviewing but dull grading can easily identify how sever the situation is if you are not running vibration tools. Running these tool can help to optimize drilling parameters to reduce the stick slip issues.
In addition to the bit, utilizing downhole motor and roller reamers instead of stabs may help reducing stick slips.
Personnaly haven't used any agitators but have heard a lot about Tomax tool.
I personnaly reviwed the same situation in a 6 1/8" hole in Middle East and the operator had issues with drilling exteremly hard chert rich carbonates and were suffering from bit durability issues. No vibration tools and motor is used and they drill rotary BHA at the depth of 4100m to 4700m. The dull gradings revealed that using a pendulum BHA along with not fit for purpose PDC and same drilling parameters along the entire interval cause the bits to fail prematurely specially in the shoulder and gauge.
I hope it helps.[email protected]