Abstract: More and more mature oil/gas fields were developed by horizontal wells, the complications and challenges of geological features of reservoir which pushed the LWD technical progress from the initial shallow non-directional DOI measurements though deep directional DOI measurements today. The deeper DOI and significant boundary responses of Azimuthal propagation resistivity (APR) were very useful for early detection of boundaries whatever the formation or OWC/OGC, the most valuable output of tools is the distance to boundary (D2B). Currently three different kind of boundary detection tools were developed by world major oilfield service companies, AziTrak^TM LWD tool was one of those outstanding tools which was developed by Baker Hughes and extensively used in fields for geo-steering decision making. Boundary detection technology combining of the other LWD data and related struc-ture/reservoir data which achieved significant positive horizontal drilling results in South China Sea, some cases have been discussed in this paper.