Importance

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Abstract

A borehole (2) serves to produce e.g. hydrocarbons in a preferably soft or relatively soft underground formation (1), such as chalk or sandstone. The borehole (2) is surrounded by a substantially tubular reinforcement shell (9), which consists of formation material so compressed that the solid components of the material are substantially crushed to particles, and these are bonded together by the fluid or viscous components of the material and/or drilling mud. The borehole (2) if formed by first predrilling a small hole and then rolling said hole up to final borehole diameter by compressing the formation so that a reinforcement shell (9) of the desired thickness is formed. A self-propelling drive assembly (5) with a plurality of driven, elastic rollers (6) is used for this process, said rollers successively rolling down the borehole wall (7) and transferring the pressure force and moment from the drill bit (3) to the wall (7). Hereby horizontal boreholes can be formed far deeper into shallow hydrocarbon-bearing strata of the type which are found e.g. in the underground below the North Sea, so that these can be exploited profitably.

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First Claim