Precise well positioning is crucial to the success of drilling advance
d horizontal and extended-reach wells. To overcome problems related to
incorrect positioning of the well path because of uncertainties attac
hed to directional surveys and seismic data, a new measurement-while-d
rilling (MWD) concept fdr geological positioning has been developed. B
y applying borehole acoustic reflection techniques, a direct measure o
f the well position with respect to critical fluid contacts and strati
graphic interfaces parallel to the well can be obtained. The radial de
tection range has been extended from a few meters with current geostee
ring tools to about 20 m. Theoretical analysis and tests with a full-s
cale research prototype have demonstrated the feasibility of this tech
nology.