The Physical Response of Dip-Measuring Logging Devices to Clastic Sedimentary Structures: A Case Study
KACZMAREK, EDWARD L., and MARK W. ALBERTY, BP Exploration, Houston, TX
An understanding of the physical response of dip-measuring devices to sedimentary structures within sandstones can provide important constraints on reservoir character and geometry. To address this issue, BP Exploration cored a shallow well in the Gypsy Sandstone (Pennsylvanian) near Tulsa, Oklahoma. The core was fully analyzed to describe and orient the sedimentary structures within the sandstone. The hole was logged with four dip-measuring devices: the six-arm resistivity dipmeter, six-arm acoustic dipmeter, Circumferential Acoustic Scanning Tool (CAST), and Formation MicroScanner (FMS). Full-scale playbacks of the logs were prepared for correlation with the sedimentary features.
Detection of sedimentary features is a function of tool resolution, scale of the structure being sampled, and presence of contrasting physical properties associated with the structures. Large-scale (> 4 in.) bedding structures were detected by both of the resistivity devices; small-scale (4 in.) structures were detected only by the FMS because of its relatively dense radial sampling. The acoustic devices were effective for detecting large-scale interbedding. On a small scale, the acoustic six-arm dipmeter could only detect borehole-crossing features. The CAST detected small-scale interbedding and other structures but was unable to resolve features smaller than 3 in. due to limited impedance contrasts.
Current logging-tool technology and processing allow for identification and orientation of small-scale sedimentary features. The CAST and especially FMS are best suited for sedimentological studies due to their superior borehole coverage and resolution.
AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)