Abstract: Processing and Interpretation of Structural and Stratigraphic Information from Dipmeter and FMS Data at Auger Field

Deborah S. Pfeiffer

Dipmeter (Schlumberger's SHDT) and/or FMS (Schlumberger's Formation Microscanner log) tools were run in ten wells at Auger (Garden Banks 426), a large, turbidite field located in approximately 915 meters of water. The tools were run to (1) determine structural dip and azimuth for comparison to seismic structure maps and calculation of true vertical thickness, (2) determine laminated vs. massive beds, and (3) help calculate net pay. The objectives of this study were to make further use of the data by defining uncertainties and obtain more stratigraphic information.

These data were processed by Schlumberger, but Z & S's Incline II was also used to process raw dipmeter data from several wells to see how "tadpole" data are affected by varying computation methods (e.g. merged correlation vs. side-by-side), correlation lengths, steps, and search angles. The processing showed that (1) different computation methods can give vastly different "tadpole" data over the same interval, (2) correlation length must be chosen carefully to get the best structural or stratigraphic information, (3) step distances of less than 50% of the correlation interval often cause dip repetitions to occur and thus produce spurious "tadpole" patterns, and (4) search angeles of 60-70° are needed to account for high angle dips.

Dipmeter and FMS structural dips and azimuths generally agree with seismic structure maps. Stratigraphic dips within the turbidite sheet sands are sometimes higher than expected after structural dip and azimuth are removed. These higher dips may be due to an additional structural component such as slumping that has not been taken into account. Accurate structural dips and azimuths are critical for restoration to true stratigraphic information. In several instances, structural dip changes of more than 2° moved the stratigraphic azimuths more than 90°. Structural azimuth changes of greater than 10° were needed to get the same effect.

Other observations from dipmeter and FMS data include the following:

1. Depositional environment from "tadpole" patterns have not proven to be unique in identifying channel sands vs. sheet sands in Auger turbidite reservoirs. However, tadpole patterns and FMS images are useful in distinguishing laminated vs. massive sands.

2. SE-S-SW depositional flow directions generally agree with seismic and well control.

3. Core to FMS ties are poor at Auger. Therefore, sedimentary structures, debris flows, and slumps are difficult to identify with certainty on FMS.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994