Abstract
With the advent of Measurement-While-Drilling (MWD) density tools in 1987, a new alternative to wireline for obtaining formation bulk density was introduced. As with any such introduction and evolution, comparative evaluations were made in order to assess the quality and quantitative nature of the MWD density data.
Analysis of MWD and comparable wireline density data show that the two can have different responses for several reasons. These include differing instrument designs, different logging environments, and evolving reservoir conditions. MWD and wireline density responses may also differ due to standoff, mudcake, mud density, hole rugosity, drilling dynamics, formation exposure time, and time dependent invasion profiles. Comparative evaluations show that without careful analysis, mis-interpretation of the data can frequently occur.
The ability to obtain and understand quantitative MWD density data greatly enhances the value of Formation-Evaluation-While-Drilling (FEWD) with resulting well cost savings and increased operational efficiency. While a case may be made for wireline replacement applications, it is often true that obtaining data in the MWD and wireline time domains may provide complementary views of changing reservoir conditions thereby enhancing the characterization of the reservoir.
