Drilling system and methods of drilling lateral boreholes

A method of drilling a lateral borehole from a main borehole, comprising:

• positioning a drilling system in the main borehole, the drilling system comprising:
• a drilling machine including anchors;
• a drill string connected at one end to the drilling machine so as to be driveable in an axial direction;
• and
• a guide connected to the drilling machine such that when the drill string is driven axially by the drilling machine, the drill string interacts with the guide so as to be directed in a predetermined radial direction;
• the guide being rotatable by the drilling string and fixed relative to the drilling machine in the axial direction;
• and
• wherein the guide comprises anchor arms mounted thereon and movable between a first position close to the guide and a second position in which they engage the main borehole wall to anchor the guide in place whereby the drilling machine can push the drill string forward while the guide stays anchored at a fixed position;
• the anchor arms being different from the anchors of the drilling machine;
• anchoring the drilling system with the anchors in the main borehole;
• orienting an exit of a guide path in the guide in the predetermined radial direction;
• anchoring the guide with the anchor arms in the main borehole adjacent the location at which the lateral borehole is to be drilled;
• operating the drilling machine to drive the drill string in the axial direction;
• and
• deflecting the drill string, by means of the guide, in the predetermined radial direction into the wall of the main borehole to drill the lateral borehole.