TABLE OF CONTENTS The preceding chapters discussed the physical and chemical properties of crude oil and natural gas and the behavior of fluids in the subsurface. The object of this chapter is to discuss the genesis, migration, and maturation of petroleum. We now have a good understanding of what oil and gas are made of and plenty of empirically derived data that show how they occur. Thus we know how to find and use oil and gas. However, the precise details of petroleum generation and migration are still debatable. Recent advances in geochemistry, especially in analytical techniques, have resulted in rapid progress on this front, but many problems remain to be solved. Any theory of petroleum generation must explain two sets of observations: geological and chemical.
A theory of petroleum genesis must explain the following geological facts:
Major accumulations of hydrocarbons characteristically occur in sedimentary rocks (Table 5.1). In the words of Pratt (1942): I believe that oil in the earth is far more abundant and far more widely distributed than is generally realized. Oil is characteristic of unmetamorphosed marine rocks of shallow water origin. In its native habitat in the veneer of marine sediments that came with time to be incorporated into the earth s crust, oil is a normal constituent of that crust; a creature of the direct reaction of common earth forces on common earth materials. Half a century later few geologists would disagree with this statement, except perhaps to note in passing that continental and deep marine sediments...
