Patent ID: 7700910

Claim:
A method for determining formation density in a region in the vicinity of a borehole wall by producing a compensated density log by logging a borehole using a density logging device, the method including irradiating the region using a source of gamma radiation and detecting using near-spaced and far-spaced radiation detectors for obtaining a density derived from near and far density values obtained from the outputs of the near-spaced and far-spaced detectors, the method comprising the steps of: (i) compensating the far density values using a programmable computer by adding a correction at a given point in a density log wherein: (a) the correction comprises a first correction function and a second correction function; (b) the method includes the step of relating the first correction function at a given point in the density log to the difference between the far and near density values multiplied by a first function of penetration ratio and the first correction is defined by the expression: (k−1)*(far density−near density) in which k is said first function of penetration ratio; and (c) the method includes the step of relating the second correction at a given point in the log to the difference between the far density difference and the near density difference multiplied by a second function of penetration ratio and defining the second correction by the expression: (k′−1)*(far density difference−near density difference) in which k′ is said second function of penetration ratio, “far density difference” at a given point in the density log is the difference between the far density filtered by a long filter, and the logged far density; and “near density difference” at a given point in the density log is the difference between the near density filtered by the long filter, and the logged near density; wherein the value of the second correction is not zero; and (ii) producing the compensated density log derived from said previous steps.