Chapter from:
AAPG Memoir 67: Seals, Traps, and the Petroleum System, Edited
by R. C. Surdam
(Publication Subject: Oil Methodology, Concepts)
AAPG Memoir 67: Seals, Traps, and the Petroleum System. Chapter 6: Evaluating Seal Potential: Example from the Talang Akar Formation,
Offshore Northwest Java, Indonesia, by J.G. Kaldi and C.D. Atkinson, p. 85-101
Copyright © 1997 by The American Association of Petroleum Geologists. All rights
reserved.
Chapter 6
Evaluating Seal Potential: Example from the
Talang Akar Formation, Offshore Northwest Java, Indonesia
by
J.G. Kaldi
ARCO Indonesia Jakarta, Indonesia
C.D. Atkinson
ARCO British Ltd. Guildford, United Kingdom
ABSTRACT
The seal potential of various lithologies in the Upper
Oligocene Talang Akar Formation (TAF) is evaluated in the BZZ area of offshore northwest
Java. Seal potential comprises (1) seal capacity (the calculated amount of hydrocarbon
column height a lithology can support); (2) seal geometry (the structural position,
thickness, and areal extent of the lithology); and (3) seal integrity (rock mechanical
properties such as ductility, compressibility, and propensity for fracturing). Seal
capacity is determined by mercury injection capillary pressure (MICP) analyses. Seal
geometry is derived by integrating seismic data, core, detailed well correlations,
regional sedimentological/stratigraphic relationships, and comparisons to known
depositional analogs. Seal integrity is evaluated qualitatively by core examination,
borehole imaging, and petrographic studies. These three variables were integrated and the
totals were "ranked." In the BZZ area, deltaic distributary channel sandstones
and delta-front/mouth bar heterolithic sandstones comprise the main reservoirs. Possible
seals include prodelta, delta-front, and delta-plain shales; channel abandonment silts;
and transgressive shelf carbonates in both the upper and lower TAF. Seal potential is best
in the delta-front shales, which have high seal capacity and are thick, laterally
continuous, and very ductile. Seal potential is moderate in the thicker (upper TAF)
transgressive carbonates. These rocks have high seal capacity and excellent lateral
continuity, but are brittle and, hence, prone to fracturing. Delta-plain shales and
prodelta shales are poor seals due to their limited seal capacity (delta-plain) or because
they are too thin (prodelta shales). Channel abandonment siltstones have even poorer seal
potential because of small lateral extent and limited seal capacity. The least favorable
seal potential occurs within the thin (lower TAF) carbonates. These rocks are relatively
thin, as well as being prone to fractures.