Using FMS Log to Aid in Structural Interpretation, Point Arguello, Offshore California

Michael Ponek

Formation Microscanner (FMS) images computed by Schlumberger from dual dipmeter's microresistivity curves have been used as an aid in mapping complex thrust structures at Platform Harvest, Point Arguello field, offshore California. The FMS images were analyzed and compared to the tadpole plots from seven deviated wells drilled into the fractured Monterey Formation. Intervals where the dipmeter data was highly scattered or unresolved on the tadpole plots were resolved by examining the FMS images. Tight folds where the bedding was too steep for resolution by a dipmeter could be identified through the examination of the FMS images. Additional structural details such as fold geometry, hinge area characteristics, and fault induced breccia zones could be identified, allowing detailed correlation and mapping of the Monterey Formation structure. Detailed structural interpretations in these complex areas of the structure resulted in a better understanding of drilling tendencies and re uced directional drilling costs.

The use of the FMS tool to identify fractures was also examined. Core observations and core photographs were compared to the FMS log to compare the FMS images to areas of known fracturing. Large well-defined fractures and brecciated zones could typically be identified from the FMS images. However, some limitations do exist with using the FMS images to determine fracture characteristics of the formation. Details such as the degree of mineralization within the fractures and distinguishing a fracture from a stylolite are not easily derived from the FMS images. In addition, small scale fractures are not detectable on the images.

AAPG Search and Discovery Article #91024©1989 AAPG Pacific Section, May 10-12, 1989, Palm Springs, California.