Borehole logging system and method

Abstract

A borehole logging method comprises processing density measurements taken by at least one probe at intervals along a borehole to determine the gravitational effects of geologic formations intersected by the borehole; and removing the determined gravitational effects from gravity measurements taken by at least one probe at intervals along the borehole to determine the gravitational efforts of geologic formations from the borehole.

What is claimed is: 
     
         1 . A borehole logging method comprising:
 processing density measurements taken by at least one probe at intervals along a borehole to determine the gravitational effects of geologic formations intersected by the borehole; and   removing the determined gravitational effects from gravity measurements taken by at least one probe at intervals along the borehole to determine the gravitational efforts of geologic formations from the borehole.   
     
     
         2 . The method of  claim 1 , wherein the density and gravity measurements are taken independently, at different times 
     
     
         3 . The method of  claim 1 , wherein the density and gravity measurements are taken simultaneously. 
     
     
         4 . The method of  claim 1 , comprising, prior to said processing, taking density measurements at first vertical intervals along the borehole and taking gravity measurements at second longer vertical intervals along the borehole. 
     
     
         5 . The method of  claim 4  further comprising pre-processing the gravity measurements prior to said processing. 
     
     
         6 . The method of  claim 6  wherein said pre-processing comprises correcting the gravity measurements to compensate for the effects of at least one of instrumental drift, effects of the Earth's tides and the normal variation with depth of the Earth's gravitational attraction. 
     
     
         7 . A borehole logging system comprising:
 a density probe taking density measurements within a borehole;   a gravity probe taking gravity measurements within the borehole; and   processing structure receiving the density and gravity measurements from the probes and processing the measurements to determine the gravitational effort of geologic formations remote from the borehole.   
     
     
         8 . The borehole logging system of  claim 7  wherein said processing structure processes the density measurements to calculate gravitational effects of geologic formations in the vicinity of the borehole and removes the calculated gravitation effects from the gravitational measurements thereby to determine density variations remote from the borehole. 
     
     
         9 . The borehole logging system of  claim 8  wherein the density and gravity probes take the density measurements and gravity measurements at vertical intervals along the borehole. 
     
     
         10 . The borehole logging system of  claim 9  wherein the density probe takes the density measurements at first vertical intervals and wherein the gravity probe takes the gravity measurements at second vertical intervals, the first vertical intervals being smaller than the second vertical intervals. 
     
     
         11 . The borehole logging system of  claim 10  wherein said processing structure pre-processes the gravity measurements prior to removing the calculated gravitational effects therefrom. 
     
     
         12 . The borehole logging system of  claim 11  wherein during pre-processing, said processing structure corrects the gravity measurements to compensate for the effects of at least one of instrumental drift, effects of the Earth's tides and the normal variation with depth of the Earth's gravitational attraction. 
     
     
         13 . The borehole logging system of  claim 11  wherein during pre-processing, said processing structure corrects the gravity measurements to compensate for the effects of instrumental drift, effects of the Earth's tides and the normal variation with depth of the Earth's gravitational attraction 
     
     
         14 . The borehole logging system of  claim 7 , wherein the density probe is one of a gamma-gamma density probe and a neutron gamma density probe. 
     
     
         15 . The borehole logging system of  claim 10 , wherein the density probe is one of a gamma-gamma density probe and a neutron gamma density probe. 
     
     
         16 . The borehole logging system of  claim 13 , wherein the density probe is one of a gamma-gamma density probe and a neutron gamma density probe. 
     
     
         17 . The borehole logging system of  claim 7 , wherein the density probe and the gravity probe are combined in a single sonde. 
     
     
         18 . The borehole logging system of  claim 10 , wherein the density probe and the gravity probe are combined in a single sonde. 
     
     
         19 . The borehole logging system of  claim 13 , wherein the density probe and the gravity probe are combined in a single sonde. 
     
     
         20 . The borehole logging system of  claim 7  wherein said density probe and gravity probe are separate sondes. 
     
     
         21 . The borehole logging system of  claim 10  wherein said density probe and gravity probe are separate sondes. 
     
     
         22 . The borehole logging system of  claim 13  wherein said density probe and gravity probe are separate sondes.