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Priority to NL6806780ApriorityCriticalpatent/NL6806780A/xx
Priority to BE732629Dprioritypatent/BE732629A/fr
Publication of NL6806780ApublicationCriticalpatent/NL6806780A/xx
E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
E21B7/00—Special methods or apparatus for drilling
E21B7/20—Driving or forcing casings or pipes into boreholes, e.g. sinking; Simultaneously drilling and casing boreholes
E21B7/201—Driving or forcing casings or pipes into boreholes, e.g. sinking; Simultaneously drilling and casing boreholes with helical conveying means
E21B7/203—Driving or forcing casings or pipes into boreholes, e.g. sinking; Simultaneously drilling and casing boreholes with helical conveying means using down-hole drives