Reduction of Gross Rock Volume Uncertainty in a Salt Flank Structure Using Dipmeter and Image Log Data

Abstract

Poor seismic imaging in the vicinity of salt domes is a well-known problem in major hydrocarbon basins such as the Gulf of Mexico and the North Sea. The consequence of poor imaging is volumetric and well targeting uncertainty. Structural interpretation of dipmeter and image logs is an essential technique to locally calibrate seismic maps and capture gross rock volume uncertainty. Dipmeter and image log interpretation is based on the assumption that some beds, commonly low-energy deposits, were deposited horizontally. However, salt domes commonly develop at structural discontinuities, such as above basement faults or at breaks in depositional slope, so this assumption should be applied with caution. Core calibration and an appreciation of the structural history of the salt play are essential to arrive at meaningful interpretations. The workflow described in this chapter is used to derive structural dips from dipmeter and logging-while-drilling (LWD) image logs for a typical salt flank play. This interpretation, complementary to seismic, is an additional calibration for local structure in poorly imaged areas. We show how structural scenarios were derived and reconciled with actual drilling results. This example demonstrates the usefulness of commonly run dipmeter, image log, and LWD data in calibrating seismic interpretations where seismic resolution is poor.