An improved method of determining and reducing the impact of borehole size and standoff on the measurement of formation density and neutron porosity has been developed. The use of standoff based binning in the density tool provides the first simultaneous measurement of density and compensation at several different standoffs.
In addition to providing standoff binning for the density, the three axis caliper provides a robust measure of the borehole size. This borehole size is used to calculate both the borehole size correction and standoff correction for the neutron tool. Techniques for accurately making these corrections while rotating and while sliding will be given.
The advantages of this technique are observed in both laboratory and downhole formations. The laboratory work will include the techniques used to make the standoff measurement. They will also include comparisons of measurements made with and without standoff based binning. Once the response in the lab is established, field test logs will be considered. Densities obtained at different standoffs as well as the optimized density will be presented to provide a quantitative measure of the effects of standoff, as well as to demonstrate the accuracy of the optimized density measurement. The comparison of MWD neutron logs with wireline neutron logs provides a measure of the accuracy of corrections while sliding and while rotating. In this manner we will see several independent measures of the improvement in the accuracy of the density and neutron measurements afforded by the use of standoff based binning and the three axis acoustic caliper.