The standard method involves percussion drilling in which a drill is alternatively raised and dropped in the descending borehole. It is suited to the drilling of wells in any material from soft clay to the hardest rock.
[pdf] “Blue Whale 1,” the world’s largest and most advanced ultra-deep-water semi-submersible drilling rig was built by Yantai CIMC Raffles Offshore Limited in east China's Shandong Province. The 42000-ton oil platform has cost $700 mil. more
[pdf] The answer ranges from just a few thousand dollars for a manual rig to several hundred thousand for a high-capacity commercial unit. The right rig for you depends on your drilling needs, budget, and long-term goals. Choosing the right rig is about more than price.
[pdf] 
