Orbital Forcing of Glacioeustasy and Its Implications for Petroleum Exploration and Production

R. K. Matthews, Cliff Frohlich

For many years, geologists have pointed to perturbations of the earth's orbit as a plausible qualitative explanation for glacioeustasy and thereby cyclicity in marginal marine sediments. Recent advances make it possible to quantify these relationships. Comparison of high resolution model calculations to low resolution geologic data serves as a guide for the establishment of a glacioeustatic signature for various time intervals.

The most robust outcome of these calculations is the tendency for intervals of maximum glaciation approximately every 2.4 million years when eccentricity approaches a prolonged near-zero state. The glacioeustatic signature between these major regressive events is best estimated by calculations of glacioeustasy at five thousand year time steps which are made to converge with sparse deep sea planktic oxygen isotope proxy data for glacioeustasy. These calculations suggest each sequence has characteristics distinctive to itself. These result from both the ever changing nature of the orbital forcing time series and ever changing boundary conditions.

High resolution calculations of glacioeustasy may have large predictive value when used in conjunction with stratigraphic forward modeling. Within coastal clastic sand/shale sequences, the models predict reservoir separation which could lead to step-out field extension plays and solution of complex production problems. With regards deep water sands, the models predict number and volume of sands. With regards shallow water carbonate reservoirs, the models predict number and geometry of thin permeability barriers which commonly disrupt otherwise permeable reservoir facies.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995