Interpretation of Cleat from Image Logs

Resistivity and acoustic scanner image logs, in both the Coal Seam Gas (CSG) and coal-mining industries, are the predominant means of determining azimuths of joints/cleat in coal. This paper indicates the need for care if interpreting cleat azimuths from image logs. The value of cleat and joint azimuth information, and horizontal stress azimuths, is in planning the optimal orientation of deviated in-seam (lateral) production wells (CSG) and in-seam gas drainage holes. Image logs of the bore wall often exhibit large fractures (joints) that intersect the entirety of the bore wall. They are visible as sinusoidal traces. Those fractures that have low height (“cleat”) and intersect one or both sides of the bore wall are represented by vertical to sub-vertical linear traces. Acoustic image logs often only record joints. An image log of a cleat lineation records the bore-wall intersection azimuth (BIAZ), that is an apparent azimuth, as well as the apparent dip (or plunge) of the lineation. The best way to determine true cleat azimuths from lineations on an image log is from a statistical weighted mean of numerous apparent azimuths (BIAZ).