ABSTRACT: Application of an MWD Propagation Resistivity and Neutron Tool
Today, measurement-while-drilling (MWD) has become a successful drilling and formation evaluation tool for geologists and drilling engineers. However, in several situations and field examples, anomalous MWD formation responses have left many unanswered questions for formation log analysts.
Many of us assumed that MWD measurements should have easily recognizable patterns that are able to be compared to the standards of wireline measurements. In many cases this is true; however, we look at MWD formation measurements with caution. We are impressed when these measurements agree with the standard wireline measurements and suspicious of MWD tool responses when they do not agree with these standards.
MWD has the advantage of measuring the formation within minutes after the formation has been drilled and exposed to drilling fluids. This time of measurement is a dynamic period when invasion is taking place, mud cake is being built, borehole diameter is changing, etc. The time since drilled factor allows us to take advantage of good hole conditions and provide additional drilling and formation information. Also, the ability to transmit real-time data (mud pulsing) for surface monitoring allows us to make timely rig-site decisions and to provide downhole memory data for detail formation analysis. These advantages have made the resistivity and neutron combination a valuable MWD tool today.
Log examples show various formation examples and interpretations. Also useful are examples of well-site quick-look interpretations using the drilling parameters and MWD measurements for hydrocarbon identification, pore pressure analysis, formation identification, and correlation and log analyses.
AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990