A core gamma log will also be included in a core analysis report. The gamma-ray response is measured along the length of the core in the laboratory. It is used to match up the core depths to the depths on the wireline gamma-ray log run over the cored interval in the reservoir. These can differ from about half a meter to sometimes more than 6 m (18 ft). This is because over a distance of 2000 or 3000 m (6500 or 10,000 ft) within the borehole, the drill string to which the core barrel is attached will stretch under tension a few meters more or less than the wireline to which the log is attached. Also, incomplete recovery of core, particularly unconsolidated core, can lead to discrepancies in the core log. Comparison of the core gamma with the wireline gamma log allows the core-to-log shift to be determined. This is important for matching features in the core to the equivalent log response. | A core gamma log will also be included in a core analysis report. The gamma-ray response is measured along the length of the core in the laboratory. It is used to match up the core depths to the depths on the wireline gamma-ray log run over the cored interval in the reservoir. These can differ from about half a meter to sometimes more than 6 m (18 ft). This is because over a distance of 2000 or 3000 m (6500 or 10,000 ft) within the borehole, the drill string to which the core barrel is attached will stretch under tension a few meters more or less than the wireline to which the log is attached. Also, incomplete recovery of core, particularly unconsolidated core, can lead to discrepancies in the core log. Comparison of the core gamma with the wireline gamma log allows the core-to-log shift to be determined. This is important for matching features in the core to the equivalent log response. |