Application of Paleogeomorphology to Exploration for Oil and Gas: ABSTRACT

Abstract

Hydrocarbon traps are customarily subdivided into two main classes: structural and stratigraphic. A third important class, hitherto not considered separately, includes hydrocarbons trapped in buried hills, ancient sandstone-filled valleys, fossil reefs, and other primarily geomorphological phenomena. These are termed as paleogeomorphic traps. The analysis of and prospecting for this type of trap must proceed along purely geomorphological lines of reasoning. These include both form and process: the form creates the trap, but the process shapes the form. Trapping may be below or above the paleogeomorphological surface, and be either direct or indirect. Paleogeomorphology includes all geomorphic phenomena recognized in subsurface geology, i.e., all buried-relief features, whether formed on land or under water. Geomorphic processes may be divided into constructive and destructive. Constructive forms of interest to petroleum geologists are dunes, barrier beaches, organic reefs, etc. Destructive processes create hills and valleys, underground drainage in carbonates, submarine canyons, etc., and create or destroy porosity by weathering. End_Page 1567------------------------------ Fossil organic reefs have a multitude of morphological characteristics which may be explained in terms of hydraulics, rate of subsidence, influence of deep-seated faulting, and other factors not of a strictly stratigraphical nature. The interpretation of buried landscapes presents many problems still unresolved among geomorphologists and also high lights several lesser-known geomorphological phenomena. Subsurface data reveal that many landscapes exposed for millions of years, although technically peneplains, still have sufficient relief for the accumulation of sizable hydrocarbon reserves. The solution of paleogeomorphological problems is aided greatly by applying quantitative geomorphological principles. The geological aspects of paleogeomorphology concern primarily the identification of erosion-resistant and less resistant horizons and the influence of structure (folding and faulting) on ancient drainage systems. Sandstone bodies filling buried valleys commonly are dissected by river meanders and thus exhibit shapes that are different from the shape of the valley. The analysis of a drainage system from headwaters to delta can help to relate sandstone reservoirs to source areas. End_of_Article - Last_Page 1568------------