Abstract

Borehole gravimetry measurements are affected by the presence of the borehole at the top and the bottom of the borehole. Less frequently recognized is a borehole effect in the vicinity of the formation bed boundaries across which density varies. The borehole effect is usually insignificant. In typical oil well conditions with 1-m station spacing, the borehole effect is on the order of 1 μgal, just below the sensitivity of the traditional gravimeters. However, the borehole effect can be significant when the station spacing is not much larger than the borehole radius and also in applications with small tolerance to error. For example, determination of oil saturation accurate to 10 percent requires on the order of 0.3 μgal/meter sensitivity. New gravimeter technologies (Prothero and Goodkind, 1968) and developments in gradiometers (Chan, Moody, and Paik, 1987) promise higher sensitivity and resolution, which call for more detailed environmental corrections. The purpose of this note is to examine the size of the borehole effect in this context.

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