Borehole Gravity (BHGM) measurements are passive observations of the gravity field beneath the surface. The BHGM responds to the bulk density of a large rock volume surrounding the borehole, which is orders of magnitude larger than the volume sampled by nuclear logs or cores.
A summary of the corrections applied to BHGM measurements during processing as well as simplistic rules-of-thumb for interpreting BHGM data in a uniform host rock are presented. However, processing and interpretation of BHGM data are complicated by changes in the density of formations intersected by the borehole, and modeling and inversion yield more sophisticated solutions.
The first generation borehole gravity instrument was introduced in the 1960s and was suitable for large diameter petroleum wells. A second generation BHGM probe for mining and geotechnical applications was introduced in 2011. Using this recently developed probe several examples of BHGM data acquired in Canada and USA for mining exploration and CO2 sequestration are presented.