Gravimetric determination of anomalies lateral to boreholes

Abstract

Abstract A portable gravimeter is traversed over a selected interval in an exploratory borehole. Formation density data is obtained for the same selected interval. This gravity and density information is then combined with the gravity value at the surface of the borehole when no anomaly is present, the ''''free air'''' correction and the Bouguer correction to obtain a measured perturbation effect. The measured perturbation effect represents the net perturbation in the gravity values measured within the borehole due to the presence of a gravimetric anomaly lying lateral to the borehole. The measured perturbation effect is subjected to high pass filtering to render it solely a function of the lateral distance from the borehole to the adjacent flank of the gravimetric anomaly. A trend is subtracted from the filtered measured perturbation effect. Anomaly models are then employed to simulate the gravimetric anomaly which produces the measured perturbation effect. A calculated perturbation effect is generated for the anomaly model. This calculated perturbation effect is high pass filtered and is subjected to trend subtraction. Finally, the filtered measured perturbation effect is compared with the filtered calculated perturbation effect and differences are noted. The parameters of the anomaly model are varied to reduce these differences and further comparisons are made. The process of varying parameters and making comparisons is repeated with the aid of iterative computer programs employing regression techniques such as the method of least squares. When the differences between the filtered measured perturbation effect and the filtered calculated perturbation effect are smaller than some preassigned arbitrary number the anomaly model represents the actual anomaly. The distances between the anomaly model and the simulated borehole are the actual distances between the gravimetric anomaly and the exploratory borehole.

Inventors

• 👤 S Yungul

Bibliographic Details