Deltaic reservoir prediction from rotational dipmeter patterns

Abstract

Summary The dipmeter is a useful logging tool for predicting the distribution of petroleum reservoirs in deltaic sediments, particularly in the Tertiary deltas of the Gulf Coast petroleum province of the USA. Conventionally upward-coarsening genetic increments are defined on gamma or sonic potential logs. Then progradational dip motifs are back-plotted to define the apex of the delta lobe and hence the highest sand-to-shale ratio of the reservoir. This method can also be applied to lobate deposits of alluvial and submarine fan origin. The dipmeter technique can be extended by noting how depositional dips rotate as a fan lobe progrades. When viewed down-fan the depositional dip slope rotates clockwise on the right flank and anticlockwise on the left flank. These rotational dips may be detectable on the dipmeter log. Rotating dips are poorly displayed on the conventional tadpole plot but are readily apparent on graphic vector plots. Thus it may be possible to determine which side of a fan lobe is well penetrated. Dip data from two wells may define the origin and termination of the fan axis and hence locate the parent distributary channel that may contain the best reservoir sand development.