Borehole gravity meter survey in drill hole USW G-4, Yucca Mountain Area, Nye County, Nevada

Abstract

Drill hole USW G-4 was logged with the US Geological Survey borehole gravity meter (BHGM) BH-6 as part of a detailed study of the lithostratigraphic units penetrated by this hole. Because the BHGM measures a larger volume of rock than the conventional gamma-gamma density tool, it provides an independent and more accurate measurement of the in situ average bulk density of thick lithologic units. USW G-4 is an especially important hole because of its proximity to the proposed exploratory shaft at Yucca Mountain. The BHGM data were reduced to interval densities using a free-air gradient (F) of 0.3083 mGal./m (0.09397 mGal/ft) measured at the drill site. The interval densities were further improved by employing an instrument correction factor of 1.00226. This factor was determined from measurements obtained by taking gravity meter BH-6 over the Charleston Peak calibration loop. The interval density data reported herein, should be helpful for planning the construction of the proposed shaft.