Abstract

Lacustrine source rocks account for over 80% of Indonesia's known petroleum reserves. This large amount of lacustrine source rocks is very significant when the global resource base is examined, with only China and Brazil displaying comparable proportions. Although these nonmarine source systems dominate the reserve base, they are not universally distributed across the archipelago in either time or space. An understanding of the factors which control the deposition of these rocks is a key element in predicting exploratory success and reducing risk.

Within Indonesia the factors which favored lacustrine source rock development include: the tectonic development of narrow depositional basins, thermal or tectonic subsidence rates in excess of sedimentation rates, rainfall rates in excess of evaporation but insufficient to support the growth of rain forests, the lack of winter storms, and limited seasonality of surface temperatures. Although some of these factors exhibit only slight temporal and spatial variability (e.g., temperature, the lack of winter storms, etc.) across the island chain during the Tertiary, the period of economic interest, other factors appear to be limiting (e.g., precipitation rate, subsidence versus sedimentation rate, etc.). It is these limiting factors which this paper will examine using both the rock record and the results of a series of numeric simulations.