Since their origin in 1912, wireline-conveyed logging tools have firmly established themselves as the industry preferred tools and often the only accepted formation evaluation method. Since its inception over 25 years ago, Logging While Drilling (LWD) formation evaluation measurements have been often viewed as correlation only. This "correlation stigma" is caused by a number of factors including a lack of accounting for environmental effects, formation changes, and evolving tool capabilities. These issues are compounded by low resolution and sparse real-time data resulting from transmission rates that have been as low as 1/2 bit per second (bps).
This paper will review the fundamental differences in LWD and wireline conveyed measurements. It addresses the environmental corrections being applied to LWD measurements by the industry today; the positive effects that new drilling technology can have on the logging environment; the changes to the formation that occur between drilling with LWD tools and wireline evaluation; the advancements in real-time capabilities; the evolution of LWD tools that enable real-time formation evaluation; and the need to develop physical measurements in LWD.
Better understanding of these areas will allow direct well-to-well comparisons regardless of the method of conveyance of the formation evaluation measurements and will enable operators to make more informed decisions as to which technology applies best for each well environment.