Hydrates contain vast store of world gas resources

A comparison of approaches for rapidly drilling small-diameter (25-50 mm) and near-surface holes along a short-radius (30 m) arc, in a variety of hard rock types, is described. Four approaches are considered: (1) Rotary diamond drilling with a downhole motor; (2) Ultra-high pressure (UHP) water jet drilling; (3) Mechanically assisted UHP water jet drilling; and (4) Abrasive jet drilling -- abrasive water jet and abrasive slurry jet. Data relating mechanical and hydraulic drilling parameters for each approach were compiled from literature and drilling tests for all four techniques. The drilling data are summarized in a common format to provide direct drilling efficiency comparisons for: Jet pressure and hydraulic power, and thrust and torque requirements and abrasive feed.