To reduce the surveying error in a wellbore, the creation of several
reference points within a borehole is carried out by physically placing
borehole markers in the borehole casing, the borehole wall or in the
formation itself, and providing an accurate reference of the marker
locations by either storing information specific to the borehole markers
inside or on the marker itself, or assigning an identification number to
the marker and storing the information relating to that identification
number remotely in a database. The borehole markers may contain an
electronic module which includes a microcircuit, a transponder dedicated
to the transmission and reception of data to/from a detector placed on a
wireline tool, a drill string or a coiled tubing. The detectors may have
an additional role of interrogating the electronic modules.