Abstract: A method for determining along-hole well depth of a wellbore. A value for a calibrated drill string length is calculated, by determining length of drill pipe sections which form a drill string, prior to insertion of the drill pipe sections in the wellbore as part of the drill string. A correction which is calculated based upon one or more physical characteristics of the drill string. At least one of the physical characteristics is derived from measurements made at defined locations in the wellbore when the drill string is under tension whilst being pulled out of the wellbore. The correction to the calibrated drill string length is applied to obtain a value for a corrected drill string length as a measure of along hole depth. Advantageously, by calculating the correction based upon physical characteristics of the drill string associated with the process of pulling the drill string out of the well, the present invention reduces the number of physical characteristics which affect the correction.

Abstract: A method for determining along-hole well depth of a wellbore. A value for a calibrated drill string length is calculated, by determining length of drill pipe sections which form a drill string, prior to insertion of the drill pipe sections in the wellbore as part of the drill string. A correction which is calculated based upon one or more physical characteristics of the drill string. At least one of the physical characteristics is derived from measurements made at defined locations in the wellbore when the drill string is under tension whilst being pulled out of the wellbore. The correction to the calibrated drill string length is applied to obtain a value for a corrected drill string length as a measure of along hole depth. Advantageously, by calculating the correction based upon physical characteristics of the drill string associated with the process of pulling the drill string out of the well, the present invention reduces the number of physical characteristics which affect the correction.