TerraTek, A Schlumberger Company. Smaller Footprint Drilling System for Deep and Hard Rock Environments; Feasibility of Ultra-High-Speed Diamond Drilling, report, December 31, 2008; (https://digital.library.unt.edu/ark:/67531/metadc833694/m1/1/: accessed October 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .