Those effects of hydrodynamics which result in tilted oil pools have been known for some time, but the problem has been whether or not a practical application of these effects could be used in exploration. What is not commonly realized is that hydrodynamics plays a very important part in stratigraphic, fault, and unconformity oil accumulations which do not exhibit a noticeably tilted oil/water contact.

In tilted oil pools the tilt of the oil/water contact for a potentiometric surface increases as the gravity of the oil decreases. This tilt is accomplished, not by rapid movement of water through the aquifer past the oil/water interface, but rather by the pressure drop across the area of the oil accumulation due to extremely slow movement of the water through the pores of the aquifer.

Under static conditions, the size of an oil accumulation below a pinch-out or against a fault is dependent solely on the entry pressure of the barrier. If hydrodynamic conditions exist, however--and this appears to be almost universal--the size of the accumulation is increased or decreased from what would normally be expected, according to the direction of hydrodynamic force. This can result in very large oil accumulations or barren "traps" under what appear to be the same structural and stratigraphic conditions.

The practical application of hydrodynamics begins with the mapping of the potentiometric surface of the various reservoirs of interest. The map is then used in conjunction with the geology of the prospects to be evaluated and the gravity of the oil expected in the trap.

The application of hydrodynamics is developing into a very important exploration tool.

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