Abstract: The aim of drilling exploratory well TZ406 is to ascertain the oil bearing structures and develop the thin oil reservoirs economically.A pilot hole was drilled to verify the oil and gas reserves and locate their exact positions,and the hole was then backfilled;after backfilling,a double-stage horizontal well was drilled to develop the two thin oil reservoirs at different depths using one hole.During the whole drilling process,only 502m long of surface casing was run in hole without intermediate casing run in,and the open hole was as long as 3628.83m.MWD tools were used,and by using of reversed BHA and optimizing of drilling parameters,precise target hitting was achieved.The horizontal well was successfully drilled,with a measured depth of 4131m,a TVD of 3686.83m,well inclination of 89.98°,orientation of 48.72° and horizontal displacement of 538.26m.An initial production rate of 86t per day was obtained after the well was put into production.