Print this pageLacustrine Petroleum Source Rock Systems- Evolving Concepts
KATZ, BARRY J.
A significant amount of the world's remaining undiscovered petroleum reserves are derived from lacustrine source rock systems. This has resulted in an increased interest in the depositional and early diagenetic controls on their development. To a large extent the same processes that constrain the formation of marine hydrocarbon source rocks are active in lacustrine settings, with the addition of those factors controlling the development of large, long-lived lakes. There are, however, significant differences in scale and sensitivity of the depositional system to extremal forcing factors. The variability typical of marine systems appears compressed both areally and stratigraphically (i.e., there is greater facies and geochemical variability in lacustrine systems). This increased complexity can be observed in source rock precursor settings (e.g., Lake Malawi) as well as in documented effective source rocks (e.g., Pematang Formation, Central Sumatra basin; Green River Formation, Unita basin) and is manifested in both bulk source rock properties as well as at the molecular and isotopic levels. Data from these lacustrine systems and others reveal that the anoxic, deep-water lacustrine source rock model based on Lake Tanganyika and the "bulls-eye" facies pattern of the Songliao basin are oversimplifications. Lacustrine source rock development may occur over a much broader suite of conditions than previously thought resulting in the complex facies distributions observed. There are, however, specific depositional settings that preclude the development of oil-prone sources (e.g., oxic, oligotrophic lakes such as Lake Baikal).