Assembly and process for drilling and completing multiple wells

A process for drilling and completing multiple subterranean wells from a common well bore (9) and an assembly for guiding a drill string during drilling and casing during completion of such multiple wells. The assembly comprises a wellhead (6) located at or near the surface of the earth and positioned over the common well bore (9), at least two tubulars (30, 34) positioned within the common well bore, and means positioned at said wellhead (6) for segregating and supporting the tubulars. In accordance with the process, at least one subterranean well bore is drilled through one of the tubulars (30, 34) and into a subterranean formation and hydrocarbons can be produced from the subterranean formation to the surface via production casing and/or production tubing positioned within the subterranean well bore (9). Other subterranean well bores can be drilled in a similar manner through other tubulars of the assembly.