Abstract: Locating the Remaining Oil in Mature Fields with 3D-Sedimentological Models

WEBER, K.J.

The difference between the original oil-in-place and the cumulative production after 25 years tells us something about the volume of remaining moveable oil but very little about its whereabouts. The quantity is related to the irreducible residual oil saturations in each rock type and to the sweep efficiency throughout the reservoir. Recent improvements in measuring techniques have shown that residual oil saturations have often been overestimated in the past. Thus sweep efficiencies were also overestimated. The conclusion can be that there must be much more moveable oil remaining in mature fields than assumed hitherto.

Indeed, modern through-casing logging methods for evaluating remaining oil saturations frequently show zones with moveable oil in between swept intervals. A study has been made to identify the typical sites of high remaining oil saturations in clastic reservoirs via 3D-modeling of common configurations.

A systematic overview has been compiled of sedimentary configurations that can lead to uneven sweep efficiency and bypassing of oil. It can be shown that specific combinations of structural dip orientation and sedimentary trend significantly enhance or reduce the sweep efficiency in a waterdrive. This is particularly true for low net-to-gross labyrinthine reservoirs. In deltaic reservoirs bypassed oil can be predicted with the aid of detailed sequence stratigraphic analysis. The objective of the overview is to provide guidelines for systematic data acquisition programs in mature fields aiming at identifying worthwhile redevelopment targets.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria