ABSTRACT: Formation Microscanner Image* Logs for Evaluating Stratigraphic Features and Key Surfaces in Thin-Bedded Turbidite Sequences

SPANG, R. J., R. M. SLATT, G. H. BROWNE, N. F. HURLEY, E. T. WILLIAMS, R. J. DAVIS, R. KEAR, and L. S. FOULK

Two 50-100m deep holes were drilled 150m apart, continuously cored, and logged behind a coastal outcrop of Miocene slope fan (channel-levee) strata in New Zealand. Characteristics of thinly-interbedded sands (Bouma Tb/Tc) and silt which comprise the cores and outcrops were calibrated to FMI^* and Platform Express^* logs of both holes. Cumulative dip and modified Fischer plot techniques were applied to improve correlations.

Well logs exhibit a low resistivity-low contrast appearance. Sedimentary facies exhibit subtle, but distinct, FMI^* characteristics. FMI^* and core characteristics and correlations suggest that one well penetrated a mud-filled channel and the other well penetrated levee strata. A regional unconformity that occurs in outcrop is also evident on FMI^* logs and in cores. Depositional dip orientations from the FMI^* logs were projected to the outcrop to provide some 3D correlation of strata and the unconformity. This projection also provided a means of tying the wells and outcrop to a high resolution seismic line that was shot at the base of the outcrop to determine the seismic response of the slope fan strata.

Correlation and calibration of well logs and cores with outcrops have provided a means of better visualizing and understanding features of thin-bedded, slope fan reservoirs that are commonly observed in Gulf of Mexico FMS^*/FMI^* logs and cores. These features include: low resistivity-low contrast log response of thin-bedded strata; channel-fill and levee successions; Bouma facies; scour surfaces; and unconformities. Comparison of the logs and core with outcrop provides insight into lateral aspects of slope fan strata when such features are identified on subsurface data.

AAPG Search and Discovery Article #90941©1997 GCAGS 47th Annual Meeting, New Orleans, Louisiana